Genetic and behavioral differences among five inbred mouse strains commonly used in the production of transgenic and knockout mice.

Five strains of mice commonly used in transgenic and knockout production were compared with regard to genetic background and behavior. These strains were: C57BL/6J, C57BL/6NTac, 129P3/J (formerly 129/J), 129S6/SvEvTac (formerly 129/SvEvTac) and FVB/NTac. Genotypes for 342 microsatellite markers and performance in three behavioral tests (rotorod, open field activity and habituation, and contextual and cued fear conditioning) were determined. C57BL/6J and C57BL/6NTac were found to be true substrains; there were only 12 microsatellite differences between them. Given the data on the genetic background, one might predict that the two C57BL/6 substrains should be very similar behaviorally. Indeed, there were no significant behavioral differences between C57BL/6J and C57BL/6NTac. Contrary to literature reports on other 129 strains, 129S6/SvEvTac often performed similarly to C57BL/6 strains, except that it was less active. FVB/NTac showed impaired rotorod learning and cued fear conditioning. Therefore, both 129S6/SvEvTac and C57BL/6 are recommended as background strains for targeted mutations when researchers want to evaluate their mice in any of these three behavior tests. However, any transgene on the FVB/NTac background should be transferred to B6. Habituation to the open field was analyzed using the parameters: total distance, center distance, velocity and vertical activity. Contrary to earlier studies, we found that all strains habituated to the open field in at least two of these parameters (center distance and velocity).

Exclusion of mouse hepatitis virus from a filtered, plastic rodent shipping container during an in transit field challenge.

Although leading suppliers of laboratory mice and rats continue to use filtered shipping boxes to protect their animals from contamination during transport to the end user, no information had been available in the literature to demonstrate that any of these boxes actually accomplish this task. To test this hypothesis, 12 plastic shipping boxes with filters and tight-fitting lids and six cardboard shipping boxes without filters (controls) were each stocked with adult, adventitious disease-free mice. All 18 shipping boxes were transported to a facility housing a breeding colony of mice enzootically infected with four murine viruses, including mouse hepatitis virus (MHV), and were placed inside the colony for 15 h. The boxes were then transported to a commercial testing laboratory, at which the animals were aseptically removed and were held in microisolation cages for 28 days, after which their sera tested for antibody to all four murine viruses. All serum samples from mice held in the control boxes were positive for antibody to MHV, whereas sera from all mice held in filtered boxes were negative for antibody to any of the four viruses. This study demonstrates that at least one type of filtered shipping container protects mice from a field challenge of MHV. To the best of our knowledge, this is the first documentation of any microbial efficacy testing conducted on filtered shipping containers for laboratory animals.

Latent Pneumocystis carinii infection in commercial rat colonies: comparison of inductive immunosuppressants plus histopathology, PCR, and serology as detection methods.

Histopathologic evaluation combined with a period of immunosuppression has been the standard procedure for detection of Pneumocystis carinii in commercial rat colonies. Variation in induction regimens and in the sensitivity of detection methods may result in underreporting of the presence of P. carinii in breeding colonies or delay its detection. In the present study, methylprednisolone and cyclophosphamide were evaluated for the ability to induce P. carinii infection in rats from an enzootically infected commercial barrier colony. The presence of P. carinii was detected by histopathologic methods and by amplification of a targeted region of the P. carinii thymidylate synthase gene by PCR over the 8-week study period. Sera taken from rats prior to either induction regimen were evaluated for the presence of P. carinii-specific antibodies by the immunoblotting technique. Few significant differences in ability to induce organism burden or in histopathology were observed between the two immunosuppressive regimens. However, a dramatic loss of weight over the study period was observed in rats treated with methylprednisolone but not in rats treated with cyclophosphamide. Although histopathologic changes attributable to P. carinii did not appear before 2 weeks with either immunosuppressant, the presence of the organism in these animals was detected by immunoblotting and PCR. Cyst scores and the intensities of the histopathologic lesions increased during the study period, but the number of rats exhibiting evidence of P. carinii infection did not change after week 3. These results suggest that use of the PCR method on postmortem lung tissue of rats without prior induction regimens or identification of anti-P. carinii antibodies in antemortem serum samples is a sufficiently sensitive method for detection of the presence of a P. carinii carrier state in rodent breeding colonies.

Epizootic of group B Streptococcus agalactiae serotype V in DBA/2 mice.

Beta-hemolytic Streptococcus agalactiae serotype V was identified as the cause of an infection in laboratory mice. Principally, the organism induced fatal septicemia in DBA/2 breeding-age mice. The syndrome appeared to originate as an ascending pyelonephritis, which progressed to septicemia. Microscopic lesions were found in the heart, kidneys, spleen, and liver, and less commonly in the uterus, thoracic cavity, lymph nodes, and lungs. The epizootic was controlled by eradication of the breeding colonies, disinfection of the barrier, and autoclaving of all equipment. The new replacement colonies have remained free of the organism.

Mucinous gastric hyperplasia in a colony of rhesus monkeys (Macaca mulatta) induced by polychlorinated biphenyl (Aroclor 1254).

Since 1971, 45 of 259 male rhesus monkeys housed in a primate building have died of a chronic and progressive disease characterized by diarrhea, dehydration, weakness, gingivitis, emaciation, and alopecia. The principal necropsy finding in these monkeys, and in eight others killed for experimental purposes, was hypertrophic and hyperplastic mucinous gastropathy involving both the mucosa and submucosa. The toxic agent involved was identified as the polychlorinated biphenyl (PCB), Aroclor 1254. The suspected source of the toxic agent was a concrete sealer used during building construction.

A record-keeping system for a pigeon breeding and research colony.

Seven different records were used to monitor a 2,000-bird pigeon colony. A nest card was placed on each nest box to record current production. This information was collected monthly and transferred to a breeding pair record which was used to evaluate yearly reproductive performance as well as to maintain a record of the number of offspring produced. An individual record was maintained on each bird to record it life history and pedigree. Weekly, when new offspring were banded, a squab data sheet was taken into the pen to record the offspring's permanent leg band number, hatch date, strain, pen number, and parents' band numbers. An individual pen record was used to record the leg band numbers of each bird occupying each pen. A monthly death record and a health record were maintained to monitor the colony's health status. From examination of the death record, one could determine if the mortality was excessive and if any specific pens were involved. On the health record were recorded diet, monthly morbidity and mortality, results of monitoring programs, and any treatments rendered. The system provided ready accessibility do detailed records of production, pedigrees, pen locations of birds, colony health status, and the number, strain, and age of birds available for research.

Leptospirosis in zoo workers associated with bears.

Leptospirosis due to Leptospira interrogans serovar icterohaemorrhagiae was diagnosed in two zoo animal keepers. The implicated source of infection was bear cubs that had microscopic agglutination antibody titers to leptospires of the Icterohaemorrhagiae serogroup.