GUINEA PIGS:MODELS AND USES IN RESEARCH Advantages of Animal Models: 1. Short life span - react faster. age faster. 2. Can be sacrificed - entire disease process studied. 3. Sufficient numbers available - statistics. 4. Infectious agents used without moral constraints. 5. Interactions of various factors studied - physiology, anatomy known. Types of Models: 1. Experimental - This type is surgically induced, should mimic the disease being studied, and be easily manipulated and readily reproducible. If this model does not reproduce the disease exactly. the correlation between animal and man must be significant. verifiable. and predictable. 2. Negative - This type of model does not develop the disease and is usually avoided. Can be helpful in determining why some species are resistant. eg. Herpes saimirii does not affect the squirrel monkey. wood rat resistant to snake bite. and opossum resistant to rabies. 3. Orphan - This type of model includes diseases of animals which do not have human counterparts or disease similar to those in man with dissimilar etiologies or pathogenesis. For example, Rous sarcoma in the chicken was discovered in 1910 and has been used extensive!y since in immunology and cancer research. but does not have a known human counterpart. 4. Spontaneous - These naturally occurring diseases of animals which mimic those occurring in man. Over 890 types have been reported. Factors to be Considered When Selecting an Animal for Research: 1. Species Availability - Select a species which is either readily available or can be ready to supply the animals yourself so that your work can be confirmed and/or expanded upon. 2. Pathogenesis - Understand the process you are going to be studying. 3. Life Span of the Species and the Segment Best Suited. Each phase of life may respond differently than the other. 4. Anatomic Characteristics - Unique anatomical features; size of animal; conformation. especially where long-term restraint is involved. 5. Nutritional Requirements and Habits - May vary with age. sex. gestation. lactation. pregnancy. disease. season of the year, temperature, relative humidity, ventilation, some internal physiological mechanism. or the stress of experimentation. 6. Genetics - Size of gene pool compared to man. 7. Polymorphism - Each stock and strain have certain unique characteristics which separate them from others. Polymorphism can be controlled to some degree by inbreeding. 8. Reproduction - Reproductive characteristics include such things as the animal's sex its endocrine status, its gestation period, type of placentation, litter size. and in utero growth rate. 9. Indigenous Factors Peculiar to a Species; Strain or Supplier - May need to define normal flora whether it be viral, fungal, or bacterial. 10. Type of Agent - Should be defined along with its possible metabolic pathways and products. its effect on an end organ and its mode of excretion. These may call for special care and handling. 11. Schedule of Administration - Dose frequency. quantity and route given. 12. State of Health - Animals should be as healthy as the experimental design calls for. Within monetary constraints. 13. Environmental Requirements - Temperature, humidity. light, cleanliness, noise. as well as other numerous factors must be considered. 14. Caging - Selection of model often based on space and/or caging availability. Overcrowding and adequate ability for normal behavioral patterns do have marked effects of the animal's response to research. 15. Past Experience of Investigator Characteristics of Guinea Pigs Which Enhance Their Use in Research: 1. Long Gestation Period With Mature Central Nervous System at Birth - Important for toxicology and teratology studies. 2. Sensitivity of Respiratory System - Important for asthma and environmental pollution studies. 3. Quiet. Calm Disposition - Important for entomology studies. Can be used to test repellents and insecticides, and as feeding source for biting insects. 4. Anatomy of the Guinea Pig Ear and Associated Structures Important for inner ear studies because it is easily dissected and exposed. 5. Vitamin C Requirement - Important for wound healing. bone, tooth and atherosclerosis studies. 6. Guinea Pig serum - Possesses hemolytic complement with higher activity levels than other lab animals. Widely used as a source of complement for complement fixation test. 7. Susceptibility to Infectious Diseases - Can be used as sentinel animals because of their acute susceptibility to Coxiella burnetii. Mycobacterium sp. Listeriosis. 8. Similar lmmune System to Man - Guinea Pig immune system possesses a similar antigen-macrophage interaction to man and delayed cutaneous hypersensitivity reaction. 9. High Dietary Requirements - For folic acid. thiamine. arginine and potassium make guinea pigs useful in nutrition studies. 10. Precocious Young - Good for germ free raising. Specific Techniques and Use of Guinea Pigs in Research 1. Schultz-Dale technique - Sensitized guinea Pig uterus exposed to foreign protein releases histamine and smooth muscle contraction is measured. 2. Preyer reflex - To check for deafness. observe a cocking of ear pinnae in response to Galton Whistle. 3. Anaphylaxis - Sensitized guinea pig develops acute shock. respiratory collapse and death within 2-5 minutes upon later re-exposure to the antigen. 4. Antihistamine effects of drugs can be evaluated in guinea pigs because of their high susceptibility to histamineinduced gastric ulcers and histamine-induced bronchospasm. 5. Evaluation of analgesics can be done by the use of radiant heat to produce flinching of the skin in the guinea pig. The threshold of pain is determined by the time of exposure and it is compared with the threshold in the presence of the analgesic in question. 6. Evaluation of antitussive agents using guinea pigs involves inhalation of coughing agents such as ammonia, sulfur dioxide. and citric acid. MODELS BY SYSTEMS Gastrointestinal Ulcerative Colitis (Model "113 in Fascicles) Human Disease: Clinical signs - Remitting and relapsing attacks of colitis. Lesions - Ulcerative colitis with occasional extension to the ileum. crypt abscesses. craterous ulcers. infarction, secondary development of carcinoma. pseudopolyps which are residual islands of inflamed mucosa adjacent to ulcerated areas. Pathogenesis - May involve an autoimmune disease in which circulating antibodies cross-react with antigens extracted from the colon. Vascular lesions could be due to hypersensitivity. Emotional stress and virus infection may play a role. Animal disease: Experimental Model - In guinea pigs. induced with degraded carrageenan derived from red seaweed. Lesions - Crypt abscesses in the cecum and colon. craterous ulcers, mucosal and submucosal granulation tissue. Amebic Dysentery (Model #171 in Fascicles) Human Disease: Transmitted through ingestion of cysts excreted by infected individuals. Lesions - Pinhead mucosal ulcerations to large confluent ulcers filled with necrotic material and covered with exudate and has massive acute inflammation and capillary thrombosis around the ulceration. Animal Disease: Experimental Model - Using the germ free guinea pig inoculated intracecally with E. histolytica and associated human intestinal flora. The germ free status of the experimental host insures there will be no interference with ameba metabolism by extraneous intestinal flora or by other species of commensal ameba such as the E. caviae. Lesions - Same as human disease. Inflammatory Bowel Disease (IBD) (Ulcerative colitis and Crohn's Disease) (Model #205 in Fascicles) Human Disease: Lesion - crypt abscesses. superficial mucosal ulcerations depletion of mucus in cells lining the crypts, edema of mucosa and submucosa with infiltration of the lamina propria with plasma cells, lymphocytes. and polymorphonuclear leukocytes. Pathogenesis - Passage to animals with cell free extracts suggest infectious agent. lmmune response to infectious agent and impaired neutrophil function have also been suggested. Animal Disease: Experimental Model - Dinitrochlorobenzene (DNCB) acts as a hapten when bound to tissue protein elicits a cell mediated (T-cell dependant) response. Animal initially sensitized on skin then later challenged by placing DNCB in the colon. Cell mediated immunity in colon induces lesions compatible with IBD. Liver and Gallbladder: Cholelithiasis (Gallstones) Human Disease: Pathogenesis - Abnormal bile composition. bile stasis and/or infection are involved. Formation o! stones is physiochemical. Bile is a supersaturated solution in which the ratio of cholesterol to bile salt maintains the fluidity of the bile. Bile salts are kept in solution by bile acid. Animal Disease: Models - Dogs. cats, squirrel monkeys, prairie dogs and guinea pigs have been used. Experimental Model - guinea pigs form cholesterol gallstones when given 1% cholestyramine while on a weight-loosing pellet diet. Cholestyramine is an ion-exchange resin that binds bile salts and prevents their absorbtion in the ileum. resulting in a decrease in the bile salt pool size. an increase in cholesterol. and a decrease in the bile salt concentrations in the bile. ln humans with disease or resection of the ileum. a decrease in bile salt pool size and increased frequency of gallstone formation is found. Thus. the guinea pig model mimics the malabsorption of bile salts seen in the human disease. III. Respiratory A. Giant Cell Pneumonia 1. Human Disease: Cytomegalic Inclusion Disease - is a rare, viral infection of very young or debilitated individuals, especially kidney trans- plant patients. Lesions - pneumonitis with giantism and intranuclear and intra- cytoplasmic inclusions in the septal cells. Inclusions also seen in salivary gland, kidney and pancreas. 2. Animal Disease: Many Species Affected by Cytomegaloviruses - but pneumonia is not a common sequela of infection. Guinea Pig Cytomegalovirus - crosses the placenta to produce infection in multiple organs of the fetus. No acute placental or fetal pathology has been noted, thus the guinea pig infection is similar to most cases of human intra-uterine cytomegalovirus infection. Intratracheal Inoculation of Guinea Pigs - with large doses of infected salivary gland material produced interstitial pneumonia with intranuclear inclusions. Neuropathological Features - observed after intracerebral inoc- ulation in guinea pigs resembled findings in congenital human cytomegalovirus infection and in infected patients with renal transplants. These changes include focal inflammation with microgliosis, and intranuclear inclusions in the gray matter of the cerebrum, pons and the molecular layer of the cerebellum. B. Pulmonary Tuberculosis (Model #142 in Fascicles) 1. Human Disease: Pathogenesis - inhalation of droplet nuclei containing one to three tubercle bacilli. Cavitary tuberculosis-develops at sites in the apical and sub- apical areas of the lung, and is thought to be the result of bacillemia after primary infection. 2. Animal Disease: Guinea Pigs Can Be Infected - by the respiratory route with small numbers of virulent tubercle bacilli, and a bacillemia ensues with development of cavitary lesions. IV. Cardiovascular A. Experimental Cobalt Cardiomyopathy An animal model for cobalt-induced cardiac disease is reported. Cardiac lesions involving the pericardium, the myocardium, and the endocardium were produced in guinea pigs by oral administration of 20 mg. per kilogram per day of cobalt. Light and electron-microscopic features and electrocardiographic findings of experimentally produced cobalt lesions were strikingly similar to those observed in Quebec beer drinkers' cardiomyopathy. Addition of 2 Gm. of ethyl alcohol to the cobalt regimen failed to modify the incidence or the severity of the disease. Authors' summary. 1 B. Coronary Lipophyalinosis Male guinea pigs were fed for 9 to 16 weeks an atherogenic diet containing 1% cholesterol with either 10% butter or 10% corn oil. The intramyocardial arteries of 25 of 31 experimental guinea pigs had a stenotic to occlusive, acellular to hypocellular intimal lesion appearing similar to hyalin and rich in lipid. Histochemically the lipohyalin contained cholesterol, neutral lipids and fibrinoid. The apparent acellular character of lipohyalin, its location in small intramyocardial arteries and renal arterioles and its possible thrombogenic origin are unique characteriestics which suggest that the guinea pig would be a useful model to study.morphologically and histochemically similar lesions in man. 2 1Mohiuddin, S. M. (Institut de Cardiologie de Quebec, Laval University, Quebec, Canada), P. K. Taskar, M. Rheault, p. E. Roy, J. Chenard, and Y. Morin. 1970. Experimental cobalt cardiomyopathy. Amer. Heart J. 80:532-543. 2Manning, P. J. (Sinclair Comparative Medicine Research Farm, Columbia, Mo. 65201), S. S. Lee, and W. K. Yamanaka. 1974. Coronary lipophyalinosis. Dietary induction in guinea pigs. Atherosclerosis 20:437-445. C. Pulmonary Arterial Granulomatous Inflammation: An experimental method to investigate pulmonary granuloma formation in the guinea pig was established. Animals sensitized to human serum albumin (HSA) and challenged intravenously with HSA covalently linked to Sepharose 2B beads developed a specific granulomatous response. This intense pulmonary arterial, focally necrotizing, but mainly granulomatous inflammatory reaction developed 5 to 7 days after the administration of the HSA-bead conjugate. Unsensitized animals did not show such extensive inflammation, but rather exhibited a typical foreign body reaction to the bead. In both the experimental and control groups, the inflammatory response was indistinguishable at 14 and 21 days. Thus the initial acute inflammatory reaction was seen only in specifically sensitized animals. On the other hand, HSA alone produced no demonstrable inflammatory lesion. These observations suggest that locally retained antigen may trigger antigen-specific T (thymus-dependent) lymphocytes to release mediators which contribute to granuloma formation. 1 V. Hematopoietic and Reticuloendothelial A. Experimental Porphyria A number of chemical agents, including certain drugs and steroids, can produce biochemical disorders in various animal species (mice, rats, rabbits, guinea pigs, dogs) which resemble different types of hepatic porphyria in man. The main agents used to produce experimental porphyria are allylisopropylactamide, dicarbethoxy- dihydrocollidine, griseofulvin, and hexa chlorobenzene. The porpyrias produced by these agents are discussed in this paper. The experimental porphyrias also provide excellent systems for study of a complex control mechanism in mammalian liver. Thus, it has been shown that drugs, diet, hormones, and iron all affect the induction of the mitochondrial enzyme #-amino-levulinic acid synthetase (ALA synthetase) which plays a major role in the control of heme biosynthesis. In addition, clinical observations provided the basis for the development of experimental porphyria which in turn has provided information that has had significant clinical applica- tion. A close interrelationship between clinical observations and basic research is seen in the history of the development and use of the experimental porphyrias. - Authors' abstract. 1 1Kasdon, E. J. (Department of Pathology, Beth Israel Hospital, 330 Brookline Ave., Boston, Mass. 02215), and S. F. Schlossman. 1973. An experimental model of pulmonary arterial granulomatous inflammation. Am. J. Pathol. 71:365-374. VI. Immunologic and Connective Tissue A. Lymphoblastic Leukemia (Model #180 in Fascicles) 1. Human Disease: Clinical Signs - acute in young children; high white blood cell count, containing high number of lymphoblasts; infiltration into major organs. 2. Animal Disease: Spontaneous Leukemia - in strain 2 guinea pig is a unique transmissible disease similar to human acute lymphoblastic leukemia. The fulminant course, blood picture, organ in- volvement, immunologic features and the response to therapy, closely resemble the human counterpart. B. Acute-Tubular-Basement-Membrane-Antibody Tubulointerstitial Nephritis (Model #197 in Fascicles) 1. Human Disease: Clinical Instances - in which Anti-TBM disease occurs in man include immune-complex type glomerulonephritis, methicillin- induced tubular necrosis, and in patients with renal homografts who develop antibodies to their own kidney and the graft, or to the graft alone. 2. Animal Disease: Experimentally Induced - in Lewis/Brown Norway and Brown Norway rats, and in guinea pigs. 1Tschudy, D. P. (Metabolism Branch, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20814), and H. L. Bonkowsky. 1972. Experimental porphyria. Fed. Proc. 31:147-159. Guinea Pigs - injected with heterologous renal tubular basement membrane and complete Freund's adjuvant develop tubulointerstitial nephritis and autoantibodies which react with the guinea pig's own tubular basement membrane and form the characteristic, linear continuous deposit of IgG, as seen by immunofluorescence along the basement membrane of cortical proximal and distal tubules. C. Complement Deficiency - C4 1. Human Disease: Autosomal Recessive (Codominant) Trait - associated with systemic lupus erythematosis-like syndrome. 2. Animal Disease: Autosomal Recessive Trait - with reduced levels of C: and Cz in addition to C# deficiency. Intrinsic coagulation is slower with decreased factor VIII activity. Animals appear healthy and do not have symptoms of lupus. D. Cobra Venom Factor-Induced Complement Deficiency 1. Human Disease: Spontaneous Complement Deficiency states. 2. Animal Model: Experimental - in which cobra venom factor depletes Cs in vivo and significantly affects platelet function and coagulation in guinea pigs. VII. Endocrine A. Diabetes Mellitus 1. Human Disease: A Genetically and Clinically Heterogeneic Group - of disorders characterized by varying degrees of carbohydrate intolerance. Types - (1) juvenile or insulin dependent - usually have total destruction of islet cells resulting in need for insulin, tend to be prone to ketosis. (2) Maturity onset milder and can usually be controlled by diet, not ketosis prone, and does not require insulin. 2. Animal Disease: Wide Variety - of spontaneous and induced models. Contagious Disease - characterized by diminished response to exogenous insulin, early onset of hyperglycemia and glucosuria, abnormal glucose tolerance tests, rare ketosis, and degranulated, hyperplastic B-cells. In chronic cases, micro angiopathy is often present and fertility is reduced. This is a unique model for insulin independent diabetes mellitus with peripheral insulin resistance. B. Congenital Athymia 1. Human Disease: Di George Syndrome: Congenital Thymic Hypoplasia - hypoplasia or aplasia of thymus in children and marked depletion of paracortical areas of lymph nodes. Lymphopenia - absence of significant number of T cells, reduced response to Con A and PHA, and reduced response to thymic dependent agents. 2. Animal Disease: Athymic Hairless Guinea Pig. Primary Thymic Aplasia or Hypoplasia - with germinal follicles in lymph nodes and Peyer's patches reduced or absent, and para- cortical lymphoid depletion. Animals are also agammaglob- ulinemic. VIII. Urogenital A. Pregnancy Toxemia (Preeclampsia) 1. Human Disease: Characterized By - hypertension, proteinuria and edema. Develops in 6% of pregnancies. 2. Animal Disease: Experimental In - sheep, rabbits, dogs, non-human primates and guinea pigs. C. Osteoarthritis 1. Human Disease: Mechanical Erosion - of articular surfaces of moveable joints. 2. Animal Disease: Guinea Pigs - naturally occurring articular eburnation in femorotibial joints and scapulo-humeral joints. Experimental Induction - of arthritic-like disease in guinea pigs by injection of histamine; chronic changes resembled human arthritis. X. Nervous A. Demyelinating Optic Neuritis (Model 1 #166 in Fascicles) 1. Human Disease: Seen In - multiple sclerosis; chronic, with remissions and relapses. Pathogenesis - focal primary demyelination, glial plaques, per#vasculitis with lipid-laden macrophages. 2. Animal Disease: Experimental - in juvenile Strain 13 guinea pigs by intradermal injection of guinea pig spinal cord suspensions with Freund's adjuvant. Similar Lesion - to man except no lipid-laden macrophages present. B. Anopthalmia Anophthalmos is prevalent as an inherited trait in an actively reproducing stock of guinea pigs. Forty-three matings of bilaterally anophthalmic boars and sows.produced 113 offspring, 93 (82.3%) of which were bilaterally anophthalmic. Nervous tissue changes included absence of the optic nerves and optic tracts, as well as hypoplasia of related oculovisual structures (lateral geniculate bodies and superior colliculi) within the brain. The optic canals and orbits of the bony skull were small. Anophthalmic guinea pigs demonstrated In Guinea Pigs - uterine arteries are banded and the ovarian arteries are transected prior to conception. Animals Manifest - hypertension, proteinuria, and elevated creatinine levels without edema. IX. Musculoskeletal A. Polydactyly - Supernumerary Digits on Hands or Feet 1. Human Disease: Most forms inherited as a dominant trait. 2. 2. Animal Disease: Normal Guinea Pig - four toes on front feet; three toes on the hind feet. Px/+ heterozygote - have missing digits restored so feet are pentadactylous. Px/Px homozygote - polydactylism is extreme - ten toes per foot, also skeletal and visceral anomalies with high mortality at an early age. B. Achondroplasia 1. Human Disease: Dominantly Inherited - short-limbed dwarfism characterized by a disproportionately large head with a depressed nasal bridge and frontal bossing, and short and stubby hands and feet. 2. Animal Disease: Numerous Animal Models - in many species of inherited achon- droplasia. In Guinea Pigs - disproportionate dwarfism occurs as a sublethal recessive trait characterized by a very short skull base, a short jaw and very short and thick long bones, with reduced growth rate postnatally. Normal breeding behavior and reproduced satisfactorily. Birth weights and growth curves were comparable to normal values, and longevity was unaffected. It is anticipated that this stock of guinea pigs will provide the scientific community with a new laboratory animal model. 1 C. Sporadic Deaf-Mutism 1. Human Disease: Autosomal Recessive Trait - associated with defects such as retinitis pigmentosa, imbecility, and skeletal anomalies. Two Types - primary degeneration of cochleal duct, or primary degeneration of spiral ganglion. 2. Animal Disease: Two Independent Mutants - causing "waltzing'' or circling behavior in guinea pigs. (wz and wtz) wz Mutation - autosomal dominant with full penetrance and lethal in the homozygote; normal at birth followed by atrophy of the cellular elements of the organ of Corti, with subsequent cochlar neuronal atrophy. wtz - autosomal recessive characterized by progressive de- generation of organ of corti, cochlear nerve and spiral ganglia cells, and manifested by circling deafness and head tremors becoming more pronounced with age. XI. Integumentary A. Acute Contact Dermatitis 1. Human Disease: Contact irritants such as synthetic resins, turpentine, acids, alkalies, cosmetics and cleaning agents. 1 Komich, R. J. (3741 High Point Road, Greensboro, North Carolina 27407). 1971.Anophthalmos: An inherited trait in a new stock of guinea pigs. Am. J.Vet. Res. 32:2099-2105. A Delayed Hypersensitivity Reaction - characterized by erythema edema and induration. Histo - infiltration of mononuclear cells in the dermis. 2. Animal Disease: Models - include dogs, guinea pigs and pigs. Guinea Pigs Are Used Extensively - because they are easily sensitized, and the lesions are readily observed. 0.05 0.1% conc. of the allergen in a topical closed patch technique and then challenge with .05 - 5% conc. with patch on for 24 hours. Read at 24, 48 and 72 hours after applications. XII. Metabolic A. Vitamin C Deficiency 1. Human Disease: Scurvy - anorexia, depressed growth, anemia, lassitude, swollen and inflamed gums and joints, loose teeth, petechial hemorrhages, depressed wound healing, increased susceptibility- to infections, and long bone abnormalities. 2. Animal Disease: Non-Human Primates - guinea pigs, the red vented bulbul bird, and some species of fruit-eating bats of India depend on food sources for ascorbic acid requirement; lack L-gulonolactone oxidase and can't synthesize Vitamin C. Deficiency Signs in the Guinea Pig - include weakness, lassitude, anorexia, anemia.and widespread hemorrhages. Growth and maintenance of connective tissue in the skin depends on ascorbic acid in the guinea pig. Hemorrhages in the subcutaneous tissues, joints, muscle and intestine in scorbutic guinea pigs, are partly the result of defective connective tissue maintenance, and are also due to impaired clotting mechanism. Also Rainbow Trout and Flying Fox Addendum I. Respiratory A. Legionnaire's Disease (Baskerville, et al; 1981) 1. Human Disease is an acute fibrinopurulent pneumonia caused by aerosol infection of the lungs with Legionella pneumophila. 2. Animal Disease - pyrexia and pneumonia develop in guinea pigs and rhesus monkeys after aerosol exposure. B. Fatal Arenavirus Infection (Model #301 in Fascicles) 1. Human Disease: Lassa Fever 2. Animal Model: Adapted Pichinde Virus Infection in Strain 13 guinea pigs. Disease is remarkably similar to Lassa fever in humans in histologic appearance and distribution of viral antigens. Outbred Hartley Strain guinea pigs are more resistant than Strain 13 guinea pigs. II. Urogenital A. Genital Herpes Simplex Infection (Hsiung, et al, 1984) 1. Human Disease: Infection may take several forms and can be inapparent. After primary infection, which can be clinical or subclinical, an individual can become latently infected. Cannot be prevented or cured. 2. Animal Disease: Guinea pigs, mice, and cebus monkeys have been used for experimental infections. Clinical and pathological features of acute and recurrent genital disease of guinea pigs innoculated with low does of Herpes Simplex Virus are similar to those seen in human infections. The appearance and evolution of the genital lesions, the characteristic histologic changes in the genital epithelium and nerve tissues, the establishment of latent virus infection in the dorsal root ganglion with the potential for reactivation, and the transmission of virus from mother to newborn through an infected birth canal, all mimic the human disease. III. Nervous A. Creutzfeldt-Jacob Disease (Kim, et. al, 1983) 1. Human Disease: A subacute spongiform encephalopathy occurring in man charaterized by clear, swollen and/or vacuolar changes in the neurons and astrocytes in the brain. Cause is thought to be a slow virus. 2. Animal Models: Chimpanzees, other primates, guinea pigs. cats, hamsters, mice, and rats have been successfully infected with human biopsy material. Changes in the central nervous system are similar in guinea pigs to those seen in man and involve vacuolization in the neurons and astrocytes. B. Mannosidosis (Model #253 in Fascicles) 1. Human Disease: A genetic enzymopathy present from conception in which lysosomal-D-mannosidase activity is deficient in all tissues. Mannose-rich oligosaccharides accumulate in lysosomes in many tissues. Affected children suffer from mental retardation, psychomotor deterioration along with immunologic and connective tissue abnormalities. 2. Animal Models: Disease can be induced by feeding swainsonine, a potent inhibitor of lysosomal#-D- mannosidase in sheep, cattle, horses, and guinea pigs. Guinea pigs given drinking water containing lOmg/dl swainsonine develop marked neurovisceral mannoside storage within 4 weeks with extensive involvement of neurons on the central nervous system and peripheral ganglia. ALLERGY Title: An animal model for nonimmunologic contact urticaria. The suitability o: the guinea pig for studies on nonimmunologic contact urticaria ( NlCU) was investigated. Hartley guinea pigs were challenged with various concentrations of human NICU agents. The thickness of the ear was measured with a string micrometer before application and at 5 to 30 min intervals. Maximal increase in ear thickness was produced within 30 to 40 min. All responses were dose dependent. The histology of the maximal reaction showed dermal edema. and intra and perivascular infiltrate of heterophils (neutrophils in man). eosinophils. and some lymphocytes. The guinea pig ear-swelling test provides a quantitative animal model to screen human NlCU agents. Source: Toxicol Appl Pharmacol 1984 Nov:76 (2):219-24 Title: Experimental asthma in guinea pigs revisited. The relation between guinea pig asthma and human bronchial asthma is established. The underlying mechanism in both processes is the misdirected (aberrant) formation of anaphylactic or reaginic (IgE) antibody against innocuous antigens, leading at renewed exposure to the antigen to release of mast cell mediators (such as histamine. SRS-A. eosinotactic peptides. PAF. bronchoconstriction. vasodilation and eosinophilic inflammation at the sites of antigen-antibody reactions in the tissues of the respiratory organs. Source: Int Arch Allergy Appl lmmunol 1984; 73 (1):77-85 NEUROIMMUNOLOGY Title: An immune-mediated guinea pig model for lower motor neuron disease. Guinea pigs were immunized with motor neurons from swine spinal. one month after the last of five serial immunizations. the recipients showed progressive weight loss. By seven months of age, five of the six immunized animals had died. Pathological examination showed destruction of motor neurons in the spinal cords without demyelination. but with atrophy of the related skeletal muscle groups. This may serve as a model for the human motor neuron diseases. Source: J Neuroimmunol l986 Oct:12(4):27#-90 RESPIRATORY Title: A technique for monitoring respiratory responses in guinea pigs. A piezoelectric crystal was used to detect respiration rates and pulmonary retractions of guinea pigs in response to intratracheal! administration of histamine. Voltage output from the crystal was displayed on a recorder for visual processing and interfaced to a microcomputer for automatic data processing. Using intratracheal instillation of histamine. this system accurately reproduces the visual observation of respiratory responses in guinea pigs. Source: Lab anim Sci 1984 Oct;34 (5): 475-9 Cardiology Title: Experimental autoimmune myocarditis in the guinea pig. Guinea pigs underwent immunization with heterologous heart protein (rat heart). complete Freund's adjuvant and pertussis vaccine (immunized) or normal saline (control) at weekly intervals for 6 weeks, and were subsequently studied. It was concluded that inflammatory.probably immune-mediated. chronic myocarditis can be produced in the guinea pig. Source: Cariovasc Res 1085 Oct; 19 (10) :613-22 Title: A simple method for the production of ventricular tachycardia in the rat and guinea pig. A simple method for the production of ventricular tachycardia in the rat and guinea pig was developed. The animals were made to inhale benzene vapors for 2 min. An intravenous injection of adrenaline was given during the last 30 sec of benzene administration. Ventricular tachycardia developed in 95% of the animals used. Development of ventricular tachycardia in guinea pigs was earlier than in rats. but the duration of the tachycardia was almost equal in both species of animals. The arrhythmia by this method is of short duration. reliable. and reproducible. This method can be utilized for the rapid screening of antiarrhythmic agents. Source: J Pharmacol Methods l986 Jun;15 (3) :279-82 MUSCULOSKELETAL Title: lntroduction of osteoarthrosis in the guinea pig knee by papain. Guinea pigs were given papain intra-articularly. Microscopic surface irregularities could be observed in the animals after 6 hours. The first osteoarthritic changes were observed macroscopically after B months. Radiographic changes in the experimental joint could be observed in all animals killed after 10 months. lt was concluded that osteoarthrosis similar to that occurring in humans can be induced by this method. Source: Oral Surg Oral Med Oral Path 1983 Mar: 55 (3) :259-66 IMMUNOLOGY Title: Reappraisal of the guinea pig as an experimental host for studies of schistosomiasis mansoni. The guinea pig is a potential laboratory host for Schistosoma mansoni. Twenty-six percent of an infective cercarial population survive to maturity in this rodent. Schistosome eggs are never detected in the feces of infected guinea pig, but they can be observed in the pulmonary. hepatic and intestinal tissues. only 55% of the eggs that can be recovered from the intestinal tract are viable. and some of these can be hatched to release miracidia that penetrate the snail host. Source: Parasitology Authors: Pearce EJ; McLaren DJ INFECTIOUS DISEASES Title: Experimental syphilis: guinea pig model Outbred Hartley male guinea pigs were infected intradermally with various concentrations of Treponema pallidum Nichols strain in the pubic region. Though less susceptible to T pallidum infection than the rabbit when infected with a sufficient number of organisms. the guinea pig may be a useful model in experimental syphilis. Source: Br J Vener Dis 1983 Jun:59(3):157-68 Title: Pathogenicity of Campylobacter jejuni and Campylobacter coli strains in the pregnant guinea pig model. Pathogenicity of 17 Campylobacter isolates for pregnant guinea pigs was investigated. Of 14 isolates. 12 produced rates of abortion ranging from 13%-87%. Two isolates did not produce abortion. Inoculated organisms were recovered from uterus. blood. liver, kidney. spleen.and gallbladder of the guinea pigs at a rate as high as 83% for 2 ovine strains and as low as 13% for 2 bovine isolates. Most isolations were from the uterus. The guinea pig was a suitable and practical model for evaluating the pathogenicity of Campylobacter organism. regardless of their host of origin. Source: Am J Vet Res l983 Nov;44(11):2175-8 Title: Plasmid content and pathogenicity of Campylobacter jejuni and Campylobacter coli strains in the pregnant guinea pig model. Plasmid carriage was not. found to correlate with pathogenicity as determined by ability of the strains to produce abortions in the pregnant guinea pig model. Source: Am J Vet Res 1984 Oct;45(10):2201-2 Title: The guinea pig model for Argentine hemorrhagic fever. Guinea pigs infected by the peripheral rout with the XJ pathogenic strain of Junin virus showed viscerotropism mainly in reticulo-phagocytic rich organs. There was an absence of neurotropism. The results show that infection of guinea pigs by the peripheral route is an adequate model for human Argentine hemorrhagic fever with the exception of central nervous system involvement. Comparisons are made with infections produced in guinea pigs by attenuated strains. as well as with the disease in primates and humans. Source: Am J Trop Med Hyg 1984 Nov:33 (6) :1251-7 REFERENCES A Handbook: Animal Models of Human Disease, The Registry of Comparative Pathology, Armed Forces Institute of Pathology, Washington, D.C., 1979. Andrews, E.J., Ward, B.C., Altman, N.H., Spontaneous Animal Models of Models ofHuman Disease, Vol. I and II, Academic Press New York, NY, 1979. Alspaugh, M.A., Van Hoosier, G.L., Jr., "Naturally-Occurring and Experimentally-Induced Arthritides in Rodents: A Review of the Literature.", Laboratory Animal Science, 23:724-736. 1973. Baskerville, A., Fitzgeorge, R.B., Broster, M., Hambleton. P., and Dennis, P.J., "Experimental Transmission of Legionnaires' Disease by Exposure to aerosols of Legionella pneumophila". Lancet,2(8260-61):1389-90, 1981 Dec 19-26. Dodds, W.J., "Second International Registry of Animal Models of Thromboses and Hemorrhagic Diseases", ILAR News, 24:11-50, 1981. Hsiung, G.D., Mayo, D.R., Lucia, H.L., and Landry, M.L., "Genital Herpes: Pathogenesis and Chemotherapy in the Guinea Pig Model.", Rev. Inf. Dis., 6:33- 50, 1984. Melby, E.C., Jr., Altman, N.H., Handbook of Laboratory Animal Science, Vol. I, II and III, CRC Press, Cleveland, Ohio, 1974. Mitruka, B.M., Rawnsley, H.M., and Vadehra, D.V., Animals for Medical Research: Models for the Study of Human Disease, John Wiley & Sons, Inc., 1976 Wagner, J.E., Manning, P.J., The Biology of the Guinea Pig, Academic Press, New York. NY, 1976. GUINEA PIGS:MODELS AND USES IN RESEARCH BERNARD M FLYNN DVM NAVAL MEDICAL RESEARCH INSTITUTE 3 APRIL 1987 Advantages of Animal Models: 1. Short life span - react faster. age faster. 2. Can be sacrificed - entire disease process studied. 3. Sufficient numbers available - statistics. 4. Infectious agents used without moral constraints. 5. Interactions of various factors studied - physiology, anatomy known. Types of Models: 1. Experimental - This type is surgically induced, should mimic the disease being studied, and be easily manipulated and readily reproducible. If this model does not reproduce the disease exactly. the correlation between animal and man must be significant. verifiable. and predictable. 2. Negative - This type of model does not develop the disease and is usually avoided. Can be helpful in determining why some species are resistant. eg. Herpes saimirii does not affect the squirrel monkey. wood rat resistant to snake bite. and opossum resistant to rabies. 3. Orphan - This type of model includes diseases of animals which do not have human counterparts or disease similar to those in man with dissimilar etiologies or pathogenesis. For example, Rous sarcoma in the chicken was discovered in 1910 and has been used extensive!y since in immunology and cancer research. but does not have a known human counterpart. 4. Spontaneous - These naturally occurring diseases of animals which mimic those occurring in man. Over 890 types have been reported. Factors to be Considered When Selecting an Animal for Research: 1. Species Availability - Select a species which is either readily available or can be ready to supply the animals yourself so that your work can be confirmed and/or expanded upon. 2. Pathogenesis - Understand the process you are going to be studying. 3. Life Span of the Species and the Segment Best Suited Each phase of life may respond differently than the other. 4. Anatomic Characteristics - Unique anatomical features; size of animal; conformation. especially where long-term restraint is involved. 5. Nutritional Requirements and Habits - May vary with age. sex. gestation. lactation. pregnancy. disease. season of the year, temperature, relative humidity, ventilation, some internal physiological mechanism. or the stress of experimentation. 6. Genetics - Size of gene pool compared to man. 7. Polymorphism - Each stock and strain have certain unique characteristics which separate them from others. Polymorphism can be controlled to some degree by inbreeding. 8. Reproduction - Reproductive characteristics include such things as the animal's sex its endocrine status. its gestation period, type o! placentation, litter size. and in utero growth rate. 9. Indigenous Factors Peculiar to a Species; Strain or Supplier - May need to define normal flora whether it be viral, fungal, or bacterial. 10. Type of Agent - Should be defined along with its possible metabolic pathways and products. its effect on an end organ and its mode of excretion. These may call for special care and handling. 11. Schedule of Administration - Dose frequency. quantity and route given. 12. State of Health - Animals should be as healthy as the experimental design calls for. Within monetary constraints. 13. Environmental Requirements - Temperature, humidity. light, cleanliness, noise. as well as other numerous factors must be considered. 14. Caging - Selection of model often based on space and/or caging availability. Overcrowding and adequate ability for normal behavioral patterns do have marked effects of the animal's response to research. 15. Past Experience of Investigator Characteristics of Guinea Pigs Which Enhance Their Use in Research: 1. Long Gestation Period With Mature Central Nervous System at Birth - Important for toxicology and teratology studies. 2. Sensitivity of Respiratory System - Important for asthma and environmental pollution studies. 3. Quiet. Calm Disposition - Important for entomology studies. Can be used to test repellents and insecticides, and as feeding source for biting insects. 4. Anatomy of the Guinea Pig Ear and Associated Structures Important for inner ear studies because it is easily dissected and exposed. 5. Vitamin C Requirement - Important for wound healing. bone, tooth and atherosclerosis studies. 6. Guinea Pig serum - Possesses hemolytic complement with higher activity levels than other lab animals. Widely used as a source of complement for complement fixation test. 7. Susceptibility to Infectious Diseases - Can be used as sentinel animals because of their acute susceptibility to Coxiella burnetii. Mycobacterium sp. Listeriosis. 8. Similar lmmune System to Man - Guinea Pig immune system possesses a similar antigen-macrophage interaction to man and delayed cutaneous hypersensitivity reaction. 9. High Dietary Requirements - For folic acid. thiamine. arginine and potassium make guinea pigs useful in nutrition studies. 10. Precocious Young - Good for germ free raising. Specific Techniques and Use of Guinea Pigs in Research 1. Schultz-Dale technique - Sensitized guinea Pig uterus exposed to foreign protein releases histamine and smooth muscle contraction is measured. 2. Preyer reflex - To check for deafness. observe a cocking of ear pinnae in response to Galton Whistle. 3. Anaphylaxis - Sensitized guinea pig develops acute shock. respiratory collapse and death within 2-5 minutes upon later re-exposure to the antigen. 4. Antihistamine effects of drugs can be evaluated in guinea pigs because of their high susceptibility to histamineinduced gastric ulcers and histamine-induced bronchospasm. 5. Evaluation of analgesics can be done by the use of radiant heat to produce flinching of the skin in the guinea pig. The threshold of pain is determined by the time of exposure and it is compared with the threshold in the presence of the analgesic in question. 6. Evaluation of antitussive agents using guinea pigs involves inhalation of coughing agents such as ammonia, sulfur dioxide. and citric acid. MODELS BY SYSTEMS Gastrointestinal Ulcerative Colitis (Model "113 in Fascicles) Human Disease: Clinical signs - Remitting and relapsing attacks of colitis. Lesions - Ulcerative colitis with occasional extension to the ileum. crypt abscesses. craterous ulcers. infarction, secondary development of carcinoma. pseudopolyps which are residual islands of inflamed mucosa adjacent to ulcerated areas. Pathogenesis - May involve an autoimmune disease in which circulating antibodies cross-react with antigens extracted from the colon. Vascular lesions could be due to hypersensitivity. Emotional stress and virus infection may play a role. Animal disease: Experimental Model - In guinea pigs. induced with degraded carrageenan derived from red seaweed. Lesions - Crypt abscesses in the cecum and colon. craterous ulcers, mucosal and submucosal granulation tissue. Amebic Dysentery (Model #171 in Fascicles) Human Disease: Transmitted _ Through ingestion of cysts excreted by infected individuals. Lesions - Pinhead mucosal ulcerations to large confluent ulcers filled with necrotic material and covered with exudate and has massive acute inflammation and capillary thrombosis around the ulceration. Animal Disease: Experimental Model - Using the germ free guinea pig inoculated intracecally with E. histolytica and associated human intestinal flora. The germ free status of the experimental host insures there will be no interference with ameba metabolism by extraneous intestinal flora or by other species of commensal ameba such as the E. caviae. Lesions - Same as human disease. Inflammatory Bowel Disease (IBD) (Ulcerative colitis and Crohn's Disease) (Model #205 in Fascicles) Human Disease: Lesion - crypt abscesses. superficial mucosal ulcerations depletion of mucus in cells lining the crypts, edema of mucosa and submucosa with infiltration of the lamina propria with plasma cells, lymphocytes. and polymorphonuclear leukocytes. Pathogenesis - Passage to animals with cell free extracts suggest infectious agent. lmmune response to infectious agent and impaired neutrophil function have also been suggested. Animal Disease: Experimental Model - Dinitrochlorobenzene (DNCB) acts as a hapten when bound to tissue protein elicits a cell mediated (T-cell dependant) response. Animal initially sensitized on skin then later challenged by placing DNCB in the colon. Cell mediated immunity in colon induces lesions compatible with IBD. Liver and Gallbladder: Cholelithiasis (Gallstones) Human Disease: Pathogenesis - Abnormal bile composition. bile stasis and/or infection are involved. Formation o! stones is physiochemical. Bile is a supersaturated solution in which the ratio of cholesterol to bile salt maintains the fluidity of the bile. Bile salts are kept in solution by bile acid. Animal Disease: Models - Dogs. cats, squirrel monkeys, prairie dogs and guinea pigs have been used. Experimental Model - guinea pigs form cholesterol gallstones when given 1% cholestyramine while on a weight-loosing pellet diet. Cholestyramine is an ion-exchange resin that binds bile salts and prevents their absorbtion in the ileum. resulting in a decrease in the bile salt pool size. an increase in cholesterol. and a decrease in the bile salt concentrations in the bile. ln humans with disease or resection of the ileum. a decrease in bile salt pool size and increased frequency of gallstone formation is found. Thus. the guinea pig model mimics the malabsorption of bile salts seen in the human disease. III. Respiratory A. Giant Cell Pneumonia 1. Human Disease: Cytomegalic Inclusion Disease - is a rare, viral infection of very young or debilitated individuals, especially kidney trans- plant patients. Lesions - pneumonitis with giantism and intranuclear and intra- cytoplasmic inclusions in the septal cells. Inclusions also seen in salivary gland, kidney and pancreas. 2. Animal Disease: Many Species Affected by Cytomegaloviruses - but pneumonia is not a common sequela of infection. Guinea Pig Cytomegalovirus - crosses the placenta to produce infection in multiple organs of the fetus. No acute placental or fetal pathology has been noted, thus the guinea pig infection is similar to most cases of human intra-uterine cytomegalovirus infection. . Intratracheal Inoculation of Guinea Pigs - with large doses of infected salivary gland material produced interstitial pneumonia with intranuclear inclusions. Neuropathological Features - observed after intracerebral inoc- ulation in guinea pigs resembled findings in congenital human cytomegalovirus infection and in infected patients with renal transplants. These changes include focal inflammation with microgliosis, and intranuclear inclusions in the gray matter of the cerebrum, pons and the molecular layer of the cerebellum. B. Pulmonary Tuberculosis (Model #142 in Fascicles) 1. Human Disease: Pathogenesis - inhalation of droplet nuclei containing one to three tubercle bacilli. Cavitary tuberculosis-develops at sites in the apical and sub- apical areas of the lung, and is thought to be the result of bacillemia after primary infection. 2. Animal Disease: Guinea Pigs Can Be Infected - by the respiratory route with small numbers of virulent tubercle bacilli, and a bacillemia ensues with development of cavitary lesions. IV. Cardiovascular A. Experimental Cobalt Cardiomyopathy An animal model for cobalt-induced cardiac disease is reported. Cardiac lesions involving the pericardium, the myocardium, and the endocardium were produced in guinea pigs by oral administration of 20 mg. per kilogram per day of cobalt. Light and electron-microscopic features and electrocardiographic findings of experimentally produced cobalt lesions were strikingly similar to those observed in Quebec beer drinkers' cardiomyopathy. Addition of 2 Gm. of ethyl alcohol to the cobalt regimen failed to modify the incidence or the severity of the disease. Authors' summary. 1 B. Coronary Lipophyalinosis Male guinea pigs were fed for 9 to 16 weeks an atherogenic diet containing 1% cholesterol with either 10% butter or 10% corn oil. The intramyocardial arteries of 25 of 31 experimental guinea pigs had a stenotic to occlusive, acellular to hypocellular intimal lesion appearing similar to hyalin and rich in lipid. Histochemically the lipohyalin contained cholesterol, neutral lipids and fibrinoid. The apparent acellular character of lipohyalin, its location in small intramyocardial arteries and renal arterioles and its possible thrombogenic origin are unique characteriestics which suggest that the guinea pig would be a useful model to study.morphologically and histochemically similar lesions in man. 2 1Mohiuddin, S. M. (Institut de Cardiologie de Quebec, Laval University, Quebec, Canada), P. K. Taskar, M. Rheault, p. E. Roy, J. Chenard, and Y. Morin. 1970. Experimental cobalt cardiomyopathy. Amer. Heart J. 80:532-543. 2Manning, P. J. (Sinclair Comparative Medicine Research Farm, Columbia, Mo. 65201), S. S. Lee, and W. K. Yamanaka. 1974. Coronary lipophyalinosis. Dietary induction in guinea pigs. Atherosclerosis 20:437-445. C. Pulmonary Arterial Granulomatous Inflammation An experimental method to investigate pulmonary granuloma formation in the guinea pig was established. Animals sensi tized to human serum albumin (HSA) and challenged intravenously with HSA covalently linked to Sepharose 2B beads developed a specific granulomatous response. This intense pulmonary arterial, focally necrotizing, but mainly granulomatous inflammatory reaction developed 5 to 7 days after the administration of the HSA-bead conjugate. Unsensitized animals did not show such extensive inflammation, but rather exhibited a typical foreign body reaction to the bead. In both the experimental and control groups, the inflammatory response was indistinguishable at 14 and 21 days. Thus the initial acute inflammatory reaction was seen only in specifically sensitized animals. On the other hand, HSA alone produced no demonstrable inflammatory lesion. These observations suggest that locally retained antigen may trigger antigen-specific T (thymus-dependent) lymphocytes to release mediators which contribute to granuloma formation. 1 V. Hematopoietic and Reticuloendothelial A. Experimental Porphyria A number of chemical agents, including certain drugs and steroids, can produce biochemical disorders in various animal species (mice, rats, rabbits, guinea pigs, dogs) which resemble different types of hepatic porphyria in man. The main agents used to produce experimental porphyria are allylisopropylactamide, dicarbethoxydihydrocollidine, griseofulvin, and hexa chlorobenzene. The porpyrias produced by these agents are discussed in this paper. The experimental porphyrias also provide excellent systems for study of a complex control mechanism in mammalian liver. Thus, it has been shown that drugs, diet, hormones, and iron all affect the induction of the mitochondrial enzyme #-amino- levulinic acid synthetase (ALA synthetase) which plays a major role in the control of heme biosynthe- sis. In addition, clinical observations provided the basis for 1Kasdon, E. J. (Department of Pathology, Beth Israel Hospital, 330 Brookline Ave., Boston, Mass. 02215), and S. F. Schlossman. 1973. An experimental model of pulmonary arterial granulomatous inflammation. Am. J. Pathol. 71:365-374. the development of experimental porphyria which in turn has provided information that has had significant clinical application. A close interrelationship between clinical observations and basic research is seen in the history of the development and use of the experimental porphyrias. - Authors' abstract. 1 VI. Immunologic and Connective Tissue A. Lymphoblastic Leukemia (Model #180 in Fascicles) 1. Human Disease: Clinical Signs - acute in young children; high white blood cell count, containing high number of lymphoblasts; infiltration into major organs. 2. Animal Disease: Spontaneous Leukemia - in strain 2 guinea pig is a unique transmissible disease similar to human acute lymphoblastic leukemia. The fulminant course, blood picture, organ in- volvement, immunologic features and the response to therapy, closely resemble the human counterpart. B. Acute-Tubular-Basement-Membrane-Antibody Tubulointerstitial Nephritis (Model #197 in Fascicles) 1. Human Disease: Clinical Instances - in which Anti-TBM disease occurs in man include immune-complex type glomerulonephritis, methicillin- induced tubular necrosis, and in patients with renal homografts who develop antibodies to their own kidney and the graft, or to the graft alone. 2. Animal Disease: Experimentally Induced - in Lewis/Brown Norway and Brown Norway rats, and in guinea pigs. 1Tschudy, D. P. (Metabolism Branch, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20814), and H. L. Bonkowsky. 1972. Experimental porphyria. Fed. Proc. 31:147-159. Guinea Pigs - injected with heterologous renal tubular basement membrane and complete Freund's adjuvant develop tubulointerstitial nephritis and autoantibodies which react with the guinea pig's own tubular basement membrane and form the characteristic, linear continuous deposit of IgG, as seen by immunofluorescence along the basement membrane of cortical proximal and distal tubules. C. Complement Deficiency - C4 1. Human Disease: Autosomal Recessive (Codominant) Trait - associated with systemic lupus erythematosis-like syndrome. 2. Animal Disease: Autosomal Recessive Trait - with reduced levels of C: and Cz in addition to C# deficiency. Intrinsic coagulation is slower with decreased factor VIII activity. Animals appear healthy and do not have symptoms of lupus. D. Cobra Venom Factor-Induced Complement Deficiency 1. Human Disease: Spontaneous Complement Deficiency states. 2. Animal Model: Experimental - in which cobra venom factor depletes Cs in vivo and significantly affects platelet function and coagulation in guinea pigs. VII. Endocrine A. Diabetes Mellitus 1. Human Disease: A Genetically and Clinically Heterogeneic Group - of disorders characterized by varying degrees of carbohydrate intolerance. Types - (1) juvenile or insulin dependent - usually have total destruction of islet cells resulting in need for insulin, tend to be prone to ketosis. (2) Maturity onset milder and can usually be controlled by diet, not ketosis prone, and does not require insulin. 2. Animal Disease: Wide Variety - of spontaneous and induced models. Contagious Disease - characterized by diminished response to exogenous insulin, early onset of hyperglycemia and glucosuria, abnormal glucose tolerance tests, rare ketosis, and degranulated, hyperplastic B-cells. In chronic cases, micro angiopathy is often present and fertility is reduced. This is a unique model for insulin independent diabetes mellitus with peripheral insulin resistance. B. Congenital Athymia 1. Human Disease: Di George Syndrome: Congenital Thymic Hypoplasia - hypoplasia or aplasia of thymus in children and marked depletion of paracortical areas of lymph nodes. Lymphopenia - absence of significant number of T cells, reduced response to Con A and PHA, and reduced response to thymic dependent agents. 2. Animal Disease: Athymic Hairless Guinea Pig. Primary Thymic Aplasia or Hypoplasia - with germinal follicles in lymph nodes and Peyer's patches reduced or absent, and para- cortical lymphoid depletion. Animals are also agammaglob- ulinemic. VIII. Urogenital A. Pregnancy Toxemia (Preeclampsia) 1. Human Disease: Characterized By - hypertension, proteinuria and edema. Develops in 6% of pregnancies. 2. Animal Disease: Experimental In - sheep, rabbits, dogs, non-human primates and guinea pigs. C. Osteoarthritis 1. Human Disease: Mechanical Erosion - of articular surfaces of moveable joints. 2. Animal Disease: Guinea Pigs - naturally occurring articular eburnation in femorotibial joints and scapulo- humeral joints. Experimental Induction - of arthritic-like disease in guinea pigs by injection of histamine; chronic changes resembled human arthritis. X. Nervous A. Demyelinating Optic Neuritis (Model 1 #166 in Fascicles) 1. Human Disease: Seen In - multiple sclerosis; chronic, with remissions and relapses. Pathogenesis - focal primary demyelination, glial plaques, per#vasculitis with lipid-laden macrophages. 2. Animal Disease: Experimental - in juvenile Strain 13 guinea pigs by intra- dermal injection of guinea pig spinal cord suspensions with Freund's adjuvant. Similar Lesion - to man except no lipid-laden macrophages present. B. Anopthalmia Anophthalmos is prevalent as an inherited trait in an actively reproducing stock of guinea pigs. Forty-three matings of bilaterally anophthalmic boars and sows.produced 113 offspring, 93 (82.3%) of which were bilaterally anophthalmic. Nervous tissue changes included absence of the optic nerves and optic tracts, as well as hypoplasia of related oculovisual structures (lateral geniculate bodies and superior colliculi) within the brain. The optic canals and orbits of the bony skull were small. Anophthalmic guinea pigs demonstrated In Guinea Pigs - uterine arteries are banded and the ovarian arteries are transected prior to conception. Animals Manifest - hypertension, proteinuria, and elevated creatinine levels without edema. IX. Musculoskeletal A. Polydactyly - Supernumerary Digits on Hands or Feet 1. Human Disease: Most forms inherited as a dominant trait. 2. 2. Animal Disease: Normal Guinea Pig - four toes on front feet; three toes on the hind feet. Px/+ heterozygote - have missing digits .restored so feet are pentadactylous. Px/Px homozygote - polydactylism is extreme - ten toes per foot, also skeletal and visceral anomalies with high mortality at an early age. B. Achondroplasia 1. Human Disease: Dominantly Inherited - short-limbed dwarfism characterized by a disproportionately large head with a depressed nasal bridge and frontal bossing, and short and stubby hands and feet. 2. Animal Disease: Numerous Animal Models - in many species of inherited achon- droplasia. In Guinea Pigs - disproportionate dwarfism occurs as a sublethal recessive trait characterized by a very short skull base, a short jaw and very short and thick long bones, with reduced growth rate postnatally. normal breeding behavior and reproduced satisfactorily. Birth weights and growth curves were comparable to normal values, and longevity was unaffected. It is anticipated that this stock of guinea pigs will provide the scientific community with a new laboratory animal model. 1 C. Sporadic Deaf-Mutism 1. Human Disease: Autosomal Recessive Trait - associated with defects such as retinitis pigmentosa, imbecility, and skeletal anomalies. Two Types - primary degeneration of cochleal duct, or primary degeneration of spiral ganglion. 2. Animal Disease: Two Independent Mutants - causing "waltzing'' or circling behavior in guinea pigs. (wz and wtz) wz Mutation - autosomal dominant with full penetrance and lethal in the homozygote; normal at birth followed by atrophy of the cellular elements of the organ of Corti, with subsequent cochlar neuronal atrophy. wtz - autosomal recessive characterized by progressive de- generation of organ of corti, cochlear nerve and spiral ganglia cells, and manifested by circling deafness and head tremors becoming more pronounced with age. XI. Integumentary A. Acute Contact Dermatitis 1. Human Disease: Contact irritants such as synthetic resins, turpentine, acids, alkalies, cosmetics and cleaning agents. 1 Komich, R. J. (3741 High Point Road, Greensboro, North Carolina 27407). 1971.Anophthalmos: An inherited trait in a new stock of guinea pigs. Am. J.Vet. Res. 32:2099-2105. A Delayed Hypersensitivity Reaction - characterized by erythema edema and induration. Histo - infiltration of mononuclear cells in the dermis. 2. Animal Disease: Models - include dogs, guinea pigs and pigs. Guinea Pigs Are Used Extensively - because they are easily sensitized, and the lesions are readily observed. 0.05 0.1% conc. of the allergen in a topical closed patch technique and then challenge with .05 - 5% conc. with patch on for 24 hours. Read at 24, 48 and 72 hours after applications. XII. Metabolic A. Vitamin C Deficiency 1. Human Disease: Scurvy - anorexia, depressed growth, anemia, lassitude, swollen and inflamed gums and joints, loose teeth, petechial hemorrhages, depressed wound healing, increased susceptibility- to infections, and long bone abnormalities. 2. Animal Disease: Non-Human Primates - guinea pigs, the red vented bulbul bird, and some species of fruit-eating bats of India depend on food sources for ascorbic acid requirement; lack L-gulonolactone oxidase and can't synthesize Vitamin C. Deficiency Signs in the Guinea Pig - include weakness, lassitude, anorexia, anemia.and widespread hemorrhages. Growth and maintenance of connective tissue in the skin depends on ascorbic acid in the guinea pig. Hemorrhages in the subcutaneous tissues, joints, muscle and intestine in scorbutic guinea pigs, are partly the result of defective connective tissue maintenance, and are also due to impaired clotting mechanism. Also Rainbow Trout and Flying Fox Addendum I. Respiratory A. Legionnaire's Disease (Baskerville, et al; 1981) 1. Human Disease is an acute fibrinopurulent pneumonia caused by aerosol infection of the lungs with Legionella pneumophila. 2. Animal Disease - pyrexia and pneumonia develop in guinea pigs and rhesus monkeys after aerosol exposure. B. Fatal Arenavirus Infection (Model #301 in Fascicles) 1. Human Disease: Lassa Fever 2. Animal Model: Adapted Pichinde Virus Infection in Strain 13 guinea pigs. Disease is remarkably similar to Lassa fever in humans in histologic appearance and distribution of viral antigens. Outbred Hartley Strain guinea pigs are more resistant than Strain 13 guinea pigs. II. Urogenital A. Genital Herpes Simplex Infection (Hsiung, et al, 1984) 1. Human Disease: Infection may take several forms and can be inapparent. After primary infection, which can be clinical or subclinical, an individual can become latently infected. Cannot be prevented or cured. 2. Animal Disease: Guinea pigs, mice, and cebus monkeys have been used for experimental infections. Clinical and pathological features of acute and recurrent genital disease of guinea pigs innoculated with low does of Herpes Simplex Virus are similar to those seen in human infections. The appearance and evolution of the genital lesions, the characteristic histologic changes in the genital epithelium and nerve tissues, the establishment of latent virus infection in the dorsal root ganglion with the potential for reactivation, and the transmission of virus from mother to newborn through an infected birth canal, all mimic the human disease. III. Nervous A. Creutzfeldt-Jacob Disease (Kim, et. al, 1983) 1. Human Disease: A subacute spongiform encephalopathy occurring in man charaterized by clear, swollen and/or vacuolar changes in the neurons and astrocytes in the brain. Cause is thought to be a slow virus. 2. Animal Models: Chimpanzees, other primates, guinea pigs. cats, hamsters, mice, and rats have been successfully infected with human biopsy material. Changes in the central nervous system are similar in guinea pigs to those seen in man and involve vacuolization in the neurons and astrocytes. B. Mannosidosis (Model #253 in Fascicles) 1. Human Disease: A genetic enzymopathy present from conception in which lysosomal-D-mannosidase activity is deficient in all tissues.Mannose-rich oligosaccharides accumulate in lysosomes in many tissues. Affected children suffer from mental retardation, psychomotor deterioration along with immunologic and connective tissue abnormalities. 2. Animal Models: Disease can be induced by feeding swainsonine, a potent inhibitor of lysosomal#-D- mannosidase in sheep, cattle, horses, and guinea pigs. Guinea pigs given drinking water containing lOmg/dl swainsonine develop marked neurovisceral mannoside storage within 4 weeks with extensive involvement of neurons on the central nervous system and peripheral ganglia. ALLERGY Title: An animal model for nonimmunologic contact urticaria. The suitability o: the guinea pig for studies on nonimmunologic contact urticaria ( NlCU) was investigated. Hartley guinea pigs were challenged with various concentrations of human NICU agents. The thickness of the ear was measured with a string micrometer before application and at 5 to 30 min intervals. Maximal increase in ear thickness was produced within 30 to 40 min. All responses were dose dependent. The histology of the maximal reaction showed dermal edema. and intra and perivascular infiltrate of heterophils (neutrophils in man). eosinophils. and some lymphocytes. The guinea pig ear-swelling test provides a quantitative animal model to screen human NlCU agents. Source: Toxicol Appl Pharmacol 1984 Nov:76 (2):219-24 Title: Experimental asthma in guinea pigs revisited. The relation between guinea pig asthma and human bronchial asthma is established. The underlying mechanism in both processes is the misdirected (aberrant) formation of anaphylactic or reaginic (IgE) antibody against innocuous antigens, leading at renewed exposure to the antigen to release of mast cell mediators (such as histamine. SRS-A. eosinotactic peptides. PAF. bronchoconstriction. vasodilation and eosinophilic inflammation at the sites of antigen-antibody reactions in the tissues of the respiratory organs. Source: Int Arch Allergy Appl lmmunol 1984; 73 (1):77-85 NEUROIMMUNOLOGY Title: An immune-mediated guinea pig model for lower motor neuron disease. Guinea pigs were immunized with motor neurons from swine spinal. one month after the last of five serial immunizations. the recipients showed progressive weight loss. By seven months of age, five of the six immunized animals had died. Pathological examination showed destruction of motor neurons in the spinal cords without demyelination. but with atrophy of the related skeletal muscle groups. This may serve as a model for the human motor neuron diseases. Source: J Neuroimmunol l986 Oct:12(4):27#-90 RESPIRATORY Title: A technique for monitoring respiratory responses in guinea pigs. A piezoelectric crystal was used to detect respiration rates and pulmonary retractions of guinea pigs in response to intratracheal! administration of histamine. Voltage output from the crystal was displayed on a recorder for visual processing and interfaced to a microcomputer for automatic data processing. Using intratracheal instillation of histamine. this system accurately reproduces the visual observation of respiratory responses in guinea pigs. Source: Lab anim Sci 1984 Oct;34 (5): 475-9 Cardiology Title: Experimental autoimmune myocarditis in the guinea pig. Guinea pigs underwent immunization with heterologous heart protein (rat heart). complete Freund's adjuvant and pertussis vaccine (immunized) or normal saline (control) at weekly intervals for 6 weeks, and were subsequently studied. It was concluded that inflammatory.probably immune-mediated. chronic myocarditis can be produced in the guinea pig. Source: Cariovasc Res 1085 Oct; 19 (10) :613-22 Title: A simple method for the production of ventricular tachycardia in the rat and guinea pig. A simple method for the production of ventricular tachycardia in the rat and guinea pig was developed. The animals were made to inhale benzene vapors for 2 min. An intravenous injection of adrenaline was given during the last 30 sec of benzene administration. Ventricular tachycardia developed in 95% of the animals used. Development of ventricular tachycardia in guinea pigs was earlier than in rats. but the duration of the tachycardia was almost equal in both species of animals. The arrhythmia by this method is of short duration. reliable. and reproducible. This method can be utilized for the rapid screening of antiarrhythmic agents. Source: J Pharmacol Methods l986 Jun;15 (3) :279-82 MUSCULOSKELETAL Title: lntroduction of osteoarthrosis in the guinea pig knee by papain. Guinea pigs were given papain intra-articularly. Microscopic surface irregularities could be observed in the animals after 6 hours. The first osteoarthritic changes were observed macroscopically after B months. Radiographic changes in the experimental joint could be observed in all animals killed after 10 months. lt was concluded that osteoarthrosis similar to that occurring in humans can be induced by this method. Source: Oral Surg Oral Med Oral Path 1983 Mar: 55 (3) :259-66 IMMUNOLOGY Title: Reappraisal of the guinea pig as an experimental host for studies of schistosomiasis mansoni. The guinea pig is a potential laboratory host for Schistosoma mansoni. Twenty-six percent of an infective cercarial population survive to maturity in this rodent. Schistosome eggs are never detected in the feces of infected guinea pig, but they can be observed in the pulmonary. hepatic and intestinal tissues. only 55% of the eggs that can be recovered from the intestinal tract are viable. and some of these can be hatched to release miracidia that penetrate the snail host. Source: Parasitology Authors: Pearce EJ; McLaren DJ INFECTIOUS DISEASES Title: Experimental syphilis: guinea pig model Outbred Hartley male guinea pigs were infected intradermally with various concentrations of Treponema pallidum Nichols strain in the pubic region. Though less susceptible to T pallidum infection than the rabbit when infected with a sufficient number of organisms. the guinea pig may be a useful model in experimental syphilis. Source: Br J Vener Dis 1983 Jun:59(3):157-68 Title: Pathogenicity of Campylobacter jejuni and Campylobacter coli strains in the pregnant guinea pig model. Pathogenicity of 17 Campylobacter isolates for pregnant guinea pigs was investigated. Of 14 isolates. 12 produced rates of abortion ranging from 13%-87%. Two isolates did not produce abortion. Inoculated organisms were recovered from uterus. blood. liver, kidney. spleen.and gallbladder of the guinea pigs at a rate as high as 83% for 2 ovine strains and as low as 13% for 2 bovine isolates. Most isolations were from the uterus. The guinea pig was a suitable and practical model for evaluating the pathogenicity of Campylobacter organism. regardless of their host of origin. Source: Am J Vet Res l983 Nov;44(11):2175-8 Title: Plasmid content and pathogenicity of Campylobacter jejuni and Campylobacter coli strains in the pregnant guinea pig model. Plasmid carriage was not. found to correlate with pathogenicity as determined by ability of the strains to produce abortions in the pregnant guinea pig model. Source: Am J Vet Res 1984 Oct;45(10):2201-2 Title: The guinea pig model for Argentine hemorrhagic fever. Guinea pigs infected by the peripheral rout with the XJ pathogenic strain of Junin virus showed viscerotropism mainly in reticulo-phagocytic rich organs. There was an absence of neurotropism. The results show that infection of guinea pigs by the peripheral route is an adequate model for human Argentine hemorrhagic fever with the exception of central nervous system involvement. Comparisons are made with infections produced in guinea pigs by attenuated strains. as well as with the disease in primates and humans. Source: Am J Trop Med Hyg 1984 Nov:33 (6) :1251-7 REFERENCES A Handbook: Animal Models of Human Disease, The Registry of Comparative Pathology, Armed Forces Institute of Pathology, Washington, D.C., 1979. Andrews, E.J., Ward, B.C., Altman, N.H., Spontaneous Animal Models of Models ofHuman Disease, Vol. I and II, Academic Press New York, NY, 1979. Alspaugh, M.A., Van Hoosier, G.L., Jr., "Naturally-Occurring and Experimentally-Induced Arthritides in Rodents: A Review of the Literature.", Laboratory Animal Science, 23:724-736. 1973. Baskerville, A., Fitzgeorge, R.B., Broster, M., Hambleton. P., and Dennis, P.J., "Experimental Transmission of Legionnaires' Disease by Exposure to aerosols of Legionella pneumophila". Lancet,2(8260-61):1389-90, 1981 Dec 19-26. Dodds, W.J., "Second International Registry of Animal Models of Thromboses and Hemorrhagic Diseases", ILAR News, 24:11-50, 1981. Hsiung, G.D., Mayo, D.R., Lucia, H.L., and Landry, M.L., "Genital Herpes: Pathogenesis and Chemotherapy in the Guinea Pig Model.", Rev. Inf. Dis., 6:33- 50, 1984. Melby, E.C., Jr., Altman, N.H., Handbook of Laboratory Animal Science, Vol. I, II and III, CRC Press, Cleveland, Ohio, 1974. Mitruka, B.M., Rawnsley, H.M., and Vadehra, D.V., Animals for Medical Research: Models for the Study of Human Disease, John Wiley & Sons, Inc., 1976 Wagner, J.E., Manning, P.J., The Biology of the Guinea Pig, Academic Press, New York. NY, 1976. THE GUINEA PIG OR CAVY Taxonomic Relations The most recent revision of the family Caviidae concludes that the domestic guinea pig is a derivative of Cavia aperea and designates all other forms. including C. porcellus. C. rufescens. C. cobaya, and C. cutleri, as invalid synonyms or subspecies of C. aperea. The Latin name most frequently used today for the domestic guinea pig is C. porcellus, but papers prior to 1940 frequently used C. cobaya. The confusion is due to several factors including the total lack of records from the first domestication and conflicting reports of genetic and zoological studies of the large and widely distributed genus. It can be said with reasonable certainty, thought, that a wild progenitor of the domestic cavy is still available. The four genera making up the family Caviidae are all found in South America. The genus Cavia is widely distributed in almost all areas except the Amazon rain forest. Southern Argentina is the home of the Patagonian cavy, a hare=like animal frequently seen in zoos in this country. A closely related family, Hydrochoeridae, contains the largest living rodent the capybara. which may weigh up to 50 kg. This animal is also frequently seen in zoos. History The Spanish conquistadors brought guinea pigs back to Europe with .them 400 years ago. The Incas of Peru had been breeding them in complete domesticity for an unrecorded length of time. There has never yet been any conclusive evidence of the exact geographic origin of their stocks. The animal was kept as a table delicacy and both the wild and domestic forms are eaten today in South America. The name "guinea pig'' is of unknown origin: the only excuse for it is the squeal that the animal emits when excited. Fanciers and the pet trade prefer the name "cavy" and their disdain for "guinea pig" is absolute. A veterinarian uses the two names for the -ame animal according to the owner's sensitivity. The German name is meerschwein, which translates "sea pig). Utilization Guinea pigs, along with rats, mice, and rabbits, have been used as experimental animals from the earliest time. Lavoisier used guinea pigs in his early experiments in heat production in 1780. Because of its very high requirement for exogenous ascorbic acid it has been used since 1907 in the study of this vitamin. Many other lines of nurrirional work have been developed in the guinea pig following its early introduction in this field. The sensivitivy of the guinea pig to tuberculosis has made it a very important animal in the study of the disease. Other diseases studied in the guinea pig include brucellosis, diphtheria, and anthrax. The dramatic immunological phenomenon called anaphylaxis was studied extensively in guinea pigs who display this type of reaction more strongly than most other species. Guinea pig serum complement is widely used as the standard . . Hucklinghaus. F., 1962. Untersuchungen uber die Formenmannig-feltigkeit der Unterfamilie Caviinae.Z. Wiss. Zool.. 166:1-98. Reference: Anatomy of the Guinea Pig. Cooper. G. and Alan L. Schiller, 1975. Harvard University Press: Cambridge, MA. reagent in serology, although in recent# times o#her species have found increasing importance. In 1969 there were 869,000 guinea pigs used in research and thousands more sold as pet. Strains. Guinea pigs are grouped into three 'breeds" by fanciers on the basis of pelage. The English type has short, straight, coarse hair that follows the body contours. The Abyssinian type has similar hair, but the coat is arranged in rosettes or swirls over the body, giving the animal a somewhat appearance. Crosses are as common as the pure types, so total confusion reigns. A third type is called Peruvian; this type has hair (very much like the angora type in rabbits) that is long and silky and totally unsuited to a laboratory animal. The range of colors available is the same as for mice and rabbit. Albino, English-type animals are often referred to as Dunkin-Hartley guinea pigs. Dunkin and-Hartley were geneticists who developed a strain for their own work that proved to be very productive, relatively docile, and bred true to color. Genetics in guinea pigs has been very thoroughly and systematically in- vestigated by the famous geneticist Sewall Wright. His inbred lines, some of which were begun in 1906, are the most completely inbred strains. In 1958 two of Wright's original 23 lines were still being maintained and were then tested by skin grafting for homozygosity. At that time both strains (numbers 2 and 13 of the original series) were found to be isologous. They had been continuously bred B x S for over fifty generations. Coat color Zenes have not been selected for, so that these strains remain heterozygous for several color types, yet are apparently homozygous for the histocompatability genes. 1, 2 These two strains, therefore, provide the largest mammals available for tissue transplant work that display complete histocompatability. The domestic cavy will hybridize easily with C. aperea and several of its subspecies, although in some crosses there is F1 male sterility. See J. P. Rood and B. J. Weir, 1970, "Reproduction in female wild guinea pigs", J. Reprod. Fertility, 23:393-409, for a full discussion. The Special Anatomy of the Guinea Pig General Description A medium sized rodent of stocky, square profile with the appearance of being laterally compressed. The face is blunt and the head about the same width as the shoulders. The tail is externally absent; only a coccyx remains. The feet show a reduction of toes with four in front and three on the hind feet. All-toes have strong, straight claws. The soles of the feet are naked. Although the wild coat color is agouti, most domestic cavies are white or white- spotted. The body weights of adult animals average 850 gms and 1000: gms for females and males, respectively. Bauer, J.A., Jr., 1958. Histocompatability in inbred strains of guinea pigs. Ann. N.Y. Acad. Sci., 73:663-672. 8 Bauer, J.A.,Jr., 1960. Genetics of skin transplantation and an estimate of the number of histocompatable genes in inbred guinea pigs. Ann. X.Y. Acad. Sci., 87:78=92. The sexes are commonly referred to as sows and board and several other terms from swine husbandry are transferred to guinea pigs. The animals are docile, they very seldom bite but are always excitable, nervous, and constantly chuckle, squeal, and chatter amongst themselves in colonies. They are commonly maintained in harems for breeding purposes with one male for as many as 12 females. The young are born fully furred, their eyes open, and dentition ready for solid food. Their need for exogenous vitamin C is unique among rodents and must be provided for in their husbandry. External Features The pelage is coarse and somewhat rough. Depending upon breed, their growth patterns will vary from the normal smooth contours to a series of large rosettes or whorls over the body. Color is variable in most strains although the dark-pointed strains with white skin and fur generally breed true. The short, fleshy ear is naked. Its veins are nor large enough for routine injections although blood may conveniently be obtained from a nick in the ear. The blunt nose is different enough from the more pointed nose of rats that slotted feeder designed for rat should not be used in guinea pig cages. The lips close behind the incisors as in other rodents. There are no cheek pouches. Posture is like that in many other rodents; the anus is pressed to the ground in the normal standing position. A large scent gland field in the perineum is thus brought into contact and marks the surface where the animal rests. These perineal glands open into deep clefts between the anus and genital papilla of both sexes. A single pair of inguinal nipples is seen in BOTH SEXES although mammary gland development normally occurs only in females. Skeleton The vertebral formula ia 7 cervical, 13 thoracic. 6 lumbar. 2 sacral, and 6 coccygeal. The clavicle is vestigial. The symphysis of the mandibular rami is ossified. The pelvic symphysis of females is destroyed at time of parturition. This process begins more than two weeks prior to parturition and results in a gap of 22 mm at the time of birth. A practiced technician can estimate the stage of pregnancy by palpating this developing gap. There are no differences in the times of closure of epiphyses in the sexes. Guinea pigs have a similar growth pattern to rats and other rodents in that sexual maturity fails to appreciably slow the rate of skeletal growth. Dentition Dental formula: I 1/1, C 0/0, P 1/1, M 3/3 = 20. The incisors are open rooted chisel-shaped teeth. The molars are also rootless. in contrast to the case in myomorphs. The molariform teeth are arranged in convergent rows so that the premolars are closer to each other than the last molars. There is also a tendency for the teeth to wear at an acute angle rather than squarely. The lateral movements are restricted; grinding is accomplished by fore and aft movement. The angular process of the dentary is very long to provide insertion for the horizontal component of the masseter which drives the forward thrust of the lower jaw in both gnawing and food grinding movements. The pterygoid fossa of the guinea pig skull is open to the orbit allowing the internal pterygoid muscle to spread its origin over the orbital wall. The infraorbital canal is much enlarged for the pulley-like passage of a long head to the masseter that has its origin on the maxilla. Digestive System The stomach is not divided into glandular and non-glandular regions as described for all the other rodents studied in this sequence. The small intes- tine of a guinea pig of 22 cm body length measures 120 cm (vs 100 cm for a rat of the same body length. The cecum is relatively larger in the guinea pig. measuring 14 cm (vs 5 cm in the rat). The colon of the guinea pig is roughly 60 percent the length of the small intestine: whereas that of the rat is only about 16 percent. The guinea pig would appear to be more highly specialized as a strict herbivore. The guinea pig cecum is a source of volatile fatty acids derived from bacterial degradation of cellulose and presumably also of several vitamins. The cecum enlarges enormously in so=called germ-free animals, shortening their life in many cases. The enlargement is not understood. The organ returns to normal size if the animal is carefully infected with a normal flora of enteric microorganisms. The "normal" anatomy would seem to be in reality as much a function of the animals' internal ecology as of its genes. The long colon is doubled and coiled on itself before reaching the direct transverse and descending branches. The liver is about 3:7 percent of the body weight in a 1 kg animal. It has eight lobes. The bile duct and gallbladder are rather loosely attached to the liver and therefore easily observed, cannulated, or tied. The formation of an ampullary swelling in the common bile duct just at its entry to the duodenum is presumably unique. This chamber fills, is cut off by sphincter action, then empties itself into the gut. The pancreas is not so diffuse as that of murid rodents, although well defined head and tail regions can be identified. Spleen and Thymus The spleen of the guinea pig is somewhat broader in its proportions than seen in rabbits and murid rodents. Its vascular pattern shows some variation from other species also. There are no sheaths (of Schweigger-Seidel) and the arterioles ramify in the red pulp as a well=defined system of capillaries before entering the venous sinuses. The red pulp does not store large quantities of red blood cells in its RE cells, the storage capacity of this spleen is largely a function of the venous sinuses. According to T. Snook (Anat. Rec. 89:413- 428, 1944) the guinea pig spleen is thus more like the human than either the cat or mouse. Myeloid elements are absent from the normal guinea pig spleen. The red pulp harbors large numbers of plasma cells amongst its RE cells. The thymus differs in two important aspects from that of all other mammals commonly used in the laboratory: (1) It is located entirely in the neck where it occurs as a pair of distinctly separate, ovoid masses. Spleen and Thymus (cont.) (2) It has a well developed system of efferent lymphatic that serve to distribute the small lymphocytes (thymocytes) to other lymphoid organs. Diapedesis is not observed in its blood vessels. See Harris and Templeton, Acta Anat., 69:366-377, 1968, for details of this lymphatic drainage and further discussions of comparative functional morphology. Although: most species of mammals may be thymectomized experimentally, no species offers the ready access to this organ that you will see in the guinea pig where the organ can be exposed with relatively little trauma and observed during experimental procedures. Endocrine Organs Pituitary: This gland is not encased by the sella turcica in this species. Average weight for adult animals is 50 mg Per kg body weight. Adrenals: Relatively very large with most of the unusual size due to hypertrophy of the zona reticularis of the cortex. The functional significance of this excessive development remains obscure (as is true for this region of the cortex in all mammals). Thyroid: Size and location conforms to-that of mammals generally. Parathyroids: Found four sites embedded in the thyroid lobes. Reproductive Systems Male. The testis of the guinea pig matures rapidly. There are spermatozoa in the ejaculate at about 50 days of age (average body weight of 611 gms). The testes weigh between five and six gms. There is no seasonal variation in testis weight or fertility. Males are retained in breeding colonies as long as three years. The testes are found in shallow scrotal sacs on either side of the penis. The typical rodent pattern with broadly open inguinal canal and large epididymal fat pad is present. The deferent duct unites with the vesicular gland duct before entering the prostatic urethra. These is no separate ampullary gland. The vesicular glands are very long (up to 10 cm), slender, tubular structures; the coagulating glands are short and not so clearly differentiated from the prostatic tissue as in myomorphs. There are separate dorsal and lateral lobes to the prostate. Bulbourethral glands are present. There are small preputial glands. The prepuce and glans penis are adorned with rows of cornified papillae forming a corona-like structure. An os penis is present. Female. The ovary is not so completely encased by its bursa as was the case for the myomorph rodents. The uterine tube is also less coiled, though tortuous in its path. These structures are nearly always embedded in fat which develops in the mesotubarium and mesovarium. The guinea pig ovary products functional corpora lutea at each 16- to 17-day cycle; they are grossly visible as pink structures in the cut ovary, the color fading as the cycle passes the 13th day. Graafian follicles are also visible to the naked eye. The uterine horns are joined at the cervices and a single os cervicis opens to the vagina. The vagina is a long structure passing the entire length of the long pelvis. The mammalian cycle of vaginal cornification, sloughing, and repair which follows the development of follicles; their rupture and leuteinization were first studied in this animal (Papanicolaou, 1917). The urethral meatus is sub-terminal to the clitoris. Perineal glands are conspicuously present in both sexes on the walls of the cleft-like vestibule which encloses anus, vaginal opening, and urethral meatus. The vagina is closed by a membrane which ruptures just before estrus, stays open for about four days, then reseals. If the animal is bred and conceives, there will be a period of opening around the end of the fourth week of pregnancy that coincides with the transition from ovarian (luteal) control of pregnancy to placental control. After this time a pregnant female may be ovariectomized without aborting. The membrane opens again at term and a postpartum estrus is the normal time for rebreeding. Lactation does not interfere with the subsequent implantation. The young are weaned at about three weeks and the gestation period is about 68 days. Growth Guinea Pigs are born fully furred, with their eyes and ears open and are able to begin taking solid food within two days. Birth weight is a function of litter size and may range from 45 to 100 gms. The young are usually weaned at 160 gms rather than according to an age criterion; the age for this weight may range from 14 to 28 days. Sexual maturity, as judged by rupture of the vaginal membrane and willingness to copulate, may occur as early as 33 days of age, which will mean that some females may be bred by their sires before weaning. Such breedings are always unsuccessful, however, and the normal practice is to keep the sexes separated until the females reach three and a half to four and a half months of age or about 500 gms. There is a danger in not breeding them at this age in that the pubic symphysis may ossify so completely as to prevent its proper dissolution at parturition. Earlier breedings result in a high percentage of abortions. The males are normally not used as breeders until six months of age or about 700 gms although spermatozoa are present after ten weeks and fertility is high. The reason for the practice of using older males is that the usual ratio of females per male in breeding harems is 12 to 1. The adage is "don't send a boy out to do a man's job." 1 Ford, et al., Anat. Rec., 109:707-714, 1951. . Growth of Guinea Pigs. Weights in grams. Age in Weeks Males Females Birth 45 - 104 45 - 98 2 134 131 4 189 186 6 258 259 8 296 314 10 386 380 12 411 400 14 507 483 18 596 564 22 676 609 26 722 655 30 723 687 36 750 825 42 765 873 52 780 825 100 1100 900 Reference: H.H. Kibler, S. Brody, and D. Worstell, 1947. J. Nutrition 33:33. GUINEA PIG (CAVIA PORCELLUS) Age of puberty 45 to70 days Minimum breeding age 12 weeks (female averages 450 grants and male 500 grams) Breeding season Any time of year Estrus cycle Polyestrous; all year Duration of estrus cycle 16 to 19 days Deration of period of heat (cstrus) 6 to 15 hours (for acceptance of the male) Gestation period 58 to 75 days (average is 68) Litter size 1 to 8 (average is 3) Ovulation time 10 hours from onset of estrus; type spontaneous Number of ova 2 to 4, both avaries involved Copulation time At estrus Sperm transit, vagina to tube 15 minutes Ovum transit, tube to uterus 3-1/2 days Fertilization time A few hours after ovulation Cleavage of ovum to formation 5 to 6 days of blastocoele Implantation or attachment of ova 6 days Return to estrus, postpartum 6 to 8 hours Sperm deposition site Uterus Fertilization site Fallopian tube Chromosome number, diploid 64 in somatic cells Birth weight 75 to 100 grams Weaned 14 to 21 days Eats solid food 5 days Breeding life of female 3 years Breeding life of male 4 years Breeding habits 1 male to 10 or 12 females Conception interval Variable (6 to 8 hours is usually satisfactory) Sex ratio at birth 50 to 54% males average is 52 Lactation period 21 days Fertilizable longevity of 22 hours sperm in female tract Fertilizable longevity 20 hours after ovulation of egg in oviduct LABORATORY GUIDE The dissection of the guinea pig and the hamster are scheduled together so that certain comparisons may be facilitated. Both species are to some degree burrowing rodent, but, as we have discussed already, there are numerous differences in the adaptations. Wild cavies tend to live in rocky areas where their 'burrows" take advantage of the natural crevices and broken structure of the substrate. Their feet,are not digging feet, but their body form is typical of burrowing animals. Guinea pigs are quite safe to handle even though they are not previously gentled. The animals may squeal and attempt in every way to avoid capture, but they will not bite unless injured or severely mistreated. Examine the live animal on a surface where its movements can be observed. When capturing the animals, place the hand over the shoulders and grasp.it around the body: Do not try to pick up the animal by the skin alone. The hide is not as loose as you might expect from experience with the other species studied. Heavy-bodied animals should be supported with a second hand scooped under the hindquarters. Both sexes are quite accurate at urine spraying, so keep them aimed away from yourself until they have voided completely. ( A good habit with all small mammals.) Determine the sex of several animals. Palpate the females gently to see if you can detect pregnancy. This is possible as early as the tenth day with experience. It is unlikely that any of the animals provided in this lab will be pregnant, but the exercise is worth doing anyway. Attempt also to determine where the heart is most strongly felt and verify your observations during dissection. Guinea pigs are used so widely in immunological work that you are very likely to be required to assist or instruct in their bleeding and injection. The following comments are taken from "Methods in Immunology", by D. H. Campbell, J. S. Garvey, N. E. Cremer, and D. H. Sussdorf; W. A. Benjamin. Inc., N.Y., 1963. 263 pp. "Injections of antigens are done either in the foot pads or in the skin of the shoulder region, both intradermally and subcutaneously. Intravenous injections are done in the very small ear veins, the dorsal vein of the penis, or in the saphenous vein above the tarsus. The latter vein is entered after clipping a small fold of skin away to expose the vein on the lateral aspect of the leg about 1 cm above the ankle. This procedure must be done under light anesthesia." Euthanize the animal under chloroform. Examine by palpation again, noting any differences due to loss of muscle tone. Find the saphenous vein as noted above. Evert the phallus and compare the two sexes. Examine the mouth and eyes. Compare jaw movements and articulations in hamster and guinea pigs. Skin the specimen using a different method than used for the rat, i.e., by dorsal incision if you used a ventral approach for the rat, etc. Identify the salivary glands, exorbital lacrimal gland, and (after removing the eye) the Harderian gland. Compare the jaw muscles of hamster and guinea pig. Refer to the prepared skeletal material during examination. Find the thymus and thyroid glands and then open the rib cage to examine the position of the heart. Determine the proper external landmarks for ventricular heart puncture. Open the abdominal cavity and sketch the position of the major viscera. Consider the problem of minimizing the risk-of puncturing the cecum or stomach or urinary bladder intraperitoneal injections. Spread the viscera and identify all structures discussed under Special Anatomy. Familiarize yourself with the characteristic forms and relationships so that you could identify these organs as to species. After removing the gastrointestinal tract wash and examine its mucosal surfaces. Compare the partitioning of the cecae of the two species. Look for the aggregated lymphoid patches along the tract. Examine the reproductive systems of both sexes as outlined for previously dissected species. In the male be sure to open the urethra and see the elaborate structure of the prepuce, glans, and fossa. By collecting the secretions of the coagulating glands and the vesicular glands, you should be able to obtain a gel similar to the copulation plug. If any of the specimens show a patent vaginal introitus, evaluate the status by checking the cut surface of the ovary. Correlate your findings with the information provided in the Special Anatomy section. Anatomical and Biological Date for the Mouse, Mus musculus, and Rat, Rattus norvegicus Mouse Rat Weight 20-40 grams 300-4-- grams Adult male 25-90 grams 250-300 grams female Birth 1.5 grams 5-6 grams Life span 2 years - max. 2-3 years - Max 4 years Breeding age 3 yr. 2 mo. and weight male 60 days - 20-35 100 days - 300 grams grams female 50-60 days - 100 days - 200 grams Avg. 19 Estrus cycle 4-5 days 5 days Gestation 17-21 days - 20-23 days - Avg. 21 Avy. 19 with lactation Add 3-5 days Add 5-7 days Litter size 1-23 - Avg. 10-12 8-17 - Avg. 10 Number of 6-10 8-12 litters Weaning age and weight 16-20 days - 21 days - 40-50 grams 10-12 grams Postpartum yes yes heart Breeding life male 18 months 12-14 months female 10-12 months, 6-10 1 year - 4-5 litters litters Mating pair yes yes colony 1 male to 3 females 1 male to 3-4 females Water 1.5 cc/10 G. body wt. 1 cc/10 G.body wt. Ad libitum Ad libitum Feed usage 4-5 grams/day 12-15 grams/day Dry food consumption by young begins 10 days Approx. 12 days Hair growth 2-3 days 3-5 days apparent Recommended 72 F 70-80 F temperature Humidity 45-55 45-55 Light Minimal 14 2 hours Noise Minimal Minimal Heart beat adult 600 (328-780)min 328(261-600)min newborn ----- 161(81-241)min Breathing rate 163(84-230)min 94(75-115)min Body 97.5 F.(36.5C.) 99.1F.(37.3C) temperature Hematology RBC/mm 9 x 10 6 7-10x106 Avg.9.35x106 WBC/mm 8 - 16 x 103 6 - 18x103 Avg.9x103 Differential Lymphocytes 70# 78# Neutrophils 20# 20# Monocytes 10# <1% Ecsinophils <1% 2# pressure