Use of cage space by guineapigs.

Cage space requirements for laboratory animals have been established by Government Regulation and Recommendations. In order to test the adequacy of these space allocations, the use of cage floor area by breeding groups of guineapigs was studied. A computer-coupled video tracking system capable of imaging in low light intensity as well as total darkness was used to determine the average per cent occupancy by guineapigs in all portions of a cage over 12-h light and dark cycles. Simultaneous time synchronized slow motion video recordings permitted an analysis of activity to be coordinated with cage use data. Results of the study revealed that breeding groups of guineapigs utilize the periphery of the cage almost to the total exclusion of the centre of the cage. Approximately 75-85% of all occupancy in both the day and evening hours occurred in 47% of the cage floor area located along the periphery. Analysis of video recordings revealed that the animals remained active throughout the day and night with no prolonged period of quiescence that could be associated with sleep. Results of this study suggest that while guidelines for housing guineapigs based on area allocation per animal can be formulated and are easy to administer, they cannot be supported by the behavioural characteristics of these animals or careful quantitation of their pattern of cage space utilization.

Emerging models in the U.S.A.: swine, woodchucks, and the hairless guinea pig.

Swine have been used in biomedical research for many years, but have generally been limited to those locations with personnel familiar with this species and with specially designed facilities and equipment. There is currently a growing trend in the United States for more swine, both miniature and domestic to be used as research models. Commercial availability, education through workshops and symposia, and specific research applicability in the areas such as: organ transplantation, cardiovascular surgery, nutrition, diabetes, dermatology, and renal physiology have all contributed to the increased usage of swine. Additionally, increasing costs and public concern about the use of random source dogs and cats have also resulted in a refocus on swine as a laboratory animal model. The woodchuck (Marmota monax) has recently gained a role as a laboratory animal model when it was discovered that woodchuck hepatitis virus (WHV) is closely related to hepatitis B virus in humans (HBV). Chronic infections in woodchucks with WHV have shown protein particles in their blood which are similar to the Australian antigen found on the surface of HBV. There is also immunologic response similarities by the respective host to these viruses. These findings have resulted in a number of laboratories using the woodchuck in infectious disease comparative research studies. A euthymic hairless guinea pig has been described in Canada and recently been produced on a limited basis commercially in the United States. For dermatologic studies requiring an immunocompetent animal model the hairless guinea pig may prove useful. time to have the ability to add

Spontaneous corneal opacities in laboratory mice.

Corneal opacities were observed in numerous strains and stocks of laboratory mice (Mus musculus) from different microbiological environments. The opacities were characterized as acute and chronic inflammatory lesions of the corneal epithelium and anterior corneal stroma, including corneal ulcers and erosions, acute keratitis, stromal neovascularization and mineralization of the basement membrane zone. Some strains and stocks of mice from barrier-reared colonies had a high incidence of corneal opacities [DBA/2 (29.1%), C3H (16.2%), CF1 (16.2%) and BALB/c (10.0%)] while others had a lower incidence [CD-1 (4.3%) and C57BL/6 (4.1%)]. Axenic and gnotobiotic mice had a very low incidence of corneal opacities (1.6%). An experimental study demonstrated that twice weekly cage cleaning would reduce the incidence of corneal opacities to a very low level. A bacterial product, such as ammonia, is proposed as a significant factor in the pathogenesis of spontaneous corneal opacities in laboratory mice.

Immunochemical cross-reactions between type III group B Streptococcus and type 14 Streptococcus pneumoniae.

Serological cross-reactions between certain streptococci and some serotypes of Streptococcus pneumoniae have been reported. These studies detail the serological cross-reactivity observed between hot HCl-extracted group b streptococcus type III (GBS III) antigens and S. pneumoniae type 14 (Pn 14) polysaccharide. Similar electrophoretic migration patterns of GBS III and Pn 14 were observed when either type-specific BGS III antisera or pneumococcal omniserum was utilized to precipitate these antigens. Both the GBS III antigen and the Pn 14 polysaccharide migrated toward the cathode, whereas all other pneumococcal polysaccharides migrated toward the anode. No cross-reactions were observed between GBS III antisera and the 11 other types of pneumococcal polysaccharides. Lines of identity were observed between type-specific GBS III antisera and monospecific Pn 14 antiserum with either GBS III antigens or purified Pn 14 polysaccharide. The cross-reacting antigens of GBS III and Pn 14 appear to be identical by immunodiffusion and immunoelectrophoresis.

Intrafollicular pressure within preovulatory follicles of the pig.

Antral pressure was measured within the follicles of unstimulated ovaries in prepubertal pigs and following an ovulatory stimulus with exogenous gonadotropins. No increase in intrafollicular pressure (IFP) was observed as the time of ovulation approached. A wide range of IFP was noted within follicles of the unstimulated ovary. In many follicles IFP was greater than 30 cm H2O, suggesting that the antral fluid was not in hydrostatic equilibrium with the surrounding thecal capillaries. IFP of unstimulated follicles could be increased to more than 400 cm H2O by antral injection of mineral oil without follicular rupture--a demonstration of the need for stigma formation in the release of the ovum from the follicle. Stimulated follicles were found to be more distensible than unstimulated follicles. The follicles also fell into two groups--those in which sustained versus transient elevation in IFP occurred following oil injection. It is postulated that the follicle wall develops the ability to undergo stress relaxation during follicular maturation and that this process plays a role in regulating IFP.

Experimental subcapsular hematoma of the spleen: natural history and radioisotope scan correlation.

An experimental model was developed in dogs to correlate radioisotope scan findings of iatrogenic, in vivo, splenic injury with the natural history of the injury as determined by the clinical course and both gross and microscopic observations. It was found that small subcapsular injuries do not appear as discrete focal defects on scanning as do larger injuries; however, both small and large injuries cause an increased uptake of the radioactive colloid and increased clearing from the blood. In no dog did the subcapsular injury lead to delayed rupture, bleeding, or cyst formation, and all injuries healed by scarring and thickening of the overlying capsule. This study suggests that the entity of delayed rupture of the spleen in humans is, in fact, delayed diagnosis and not delayed bleeding.

Evaluation of miconazole therapy in experimental disseminated candidiasis in laboratory rats.

Miconazole, a broad-spectrum antimycotic agent with some antibacterial activity, has recently become available for experimental parenteral use in the United States. Its efficacy as an anticandidal drug was tested in adult Wistar rats. A previously established infectious dose of 5 x 10(6)Candida albicans was intravenously injected into 250- to 300-g animals. This dose was fatal to 95% (20/21) of placebo-treated control animals within the 2-week postinfection observation period. Only 4% (2/53) of rats receiving intramuscular miconazole treatment died. Miconazole therapy in Candida-infected rats at a dosage of 50 mg/kg per day resulted in 85% survival, and, although 100 mg/kg per day was 100% efficacious, it was a relatively large volume to give intramuscularly to a rat. Therefore, 75 mg/kg per day was used as a therapeutic dose, and it gave favorable results in this study. Histological examination of all placebo-treated animals revealed C. albicans and a marked inflammatory response in the kidney, brain, and heart. C. albicans organisms were observed to be very prominent in these tissues by using the Gomori methenamine silver stain, and were cultured from these organs. Miconazole-treated rats that were killed after surviving the 2-week observation period had minimal histopathological changes, and the organisms present did not exhibit the same staining characteristics, nor were they isolated like those in the placebo-treated group. Miconazole appears to be an efficacious drug for parenteral therapy, as demonstrated in this reproducible model of disseminated candidiasis in laboratory rats, and more extensive experimental studies are indicated.

Immunopotentiation and antiviral chemotherapy in a suckling rat model of herpesvirus encephalitis.

Encephalitis was induced in 10-day-old Wistar rats by intraperitoneal injection of approximately 100 50% tissue culture infective doses of herpes simplex virus type 2. Treatment regimens included immunopotentiation with levamisole and combined therapy with levamisole and an antiviral agent, adenine arabinoside. Rats treated with levamisole alone had significantly higher rates of survival than placebo-treated controls 14 days after injection of virus. Combination therapy with levamisole and adenine arabinoside prolonged survival, but there was no significant difference between treated animals and controls given placebo. Because adenine arabinoside inhibits the beneficial effect of levamisole in this model, antiviral chemotherapy in conjunction with immunopotentiation should be used with caution in humans. Further studies will be necessary to determine the value of immunopotentiation therapy in the treatment of life-threatening viral infections.

Exocrine pancreatic dysfunction in guinea pigs with diabetes mellitus.

In this study, 37 guinea pigs were classified, on the basis of histologic examination of the pancreas, into three categories: nondiabetic, latent diabetic, and overt diabetic. In order to compare the exocrine pancreatic function in these three groups of animals, pancreatic secretion was collected from each animal following an intravenous infusion of secretin and pancreozymin. Pancreatic enzyme activity, bicarbonate concentration, and the total volume of pancreatic secretion were all significantly decreased in guinea pigs with overt diabetes, but not in those with latent diabetes mellitus. Pancreatic histologic changes characteristic of both latent and overt diabetes were beta-cell hyperplasia and generalized fatty degeneration of the acini. Only the animals with overt diabetes showed total degranulation and severe vacuolation of theta-cells. The same type of exocrine pancreatic dysfunction observed in guinea pigs with spontaneous overt diabetes mellitus is found in human diabetics, and is particularly common in the juvenile type. The guinea pig, therefore, appears to be a suitable animal model for the study of human juvenile diabetes mellitus.