Spontaneous mammary tumors: decrease of incidence in mice infected with an enzyme-elevating virus

1 Management of Immunocompromised and Infected Animals

This chapter discusses the management of immunocompromized and infected animals. The microbiological quality of laboratory animals is a direct result of colony management practices, and monitoring provides an after-the-fact assessment of the adequacy of those practices. In the case of immunocompromised animals or in infection experiments, however, monitoring for a comprehensive list of micro-organisms is reasonable. The testing of animals usually starts with necropsy and blood sampling for serology, followed by microscopic examination for parasites and sampling of organs for bacteriology, pathology, and, in rare cases, virological examinations. Biological materials represent a high risk, if they originate from or have been propagated in animals. In particular, tumors, viruses, or parasites that are serially passaged in animals often pick up pathogens, and therefore a high percentage of these are contaminated. It has been shown in mice and rats that all preimplantational stages can be revitalized successfully upon freezethaw procedures. For long-term storage, eight-cell stages have been recommended in the chapter, while two-cell stages were considered to be less suitable. One embryo batch (inbred strain) derived from a single pedigree donor pair may be regarded as a prospective breeding nucleus, if one fertile breeding pair is obtained upon revitalization. Assuming an average revitalization rate of 20% (fertile breeders), one embryo batch should contain a minimum number of 10 embryos to obtain at least one breeding pair with a 50% chance of revitalization.

Management of immunocompromised and infected animals

This chapter discusses the management of immunocompromised and infected animals. The microbiological quality of laboratory animals is a direct result of colony management practices and monitoring provides an after-the-fact assessment of the adequacy of those practices. Monitoring is, therefore, of greatest value in connection with the maintenance of animals in isolation systems where vigorous microbiological control is applied. In addition to constructive measures, an appropriate management system is necessary for the prevention of infections, as well as for their detection and control. It is a major task for the management of an animal facility to understand the way micro-organisms might be introduced or spread under the specific conditions given. The management of all animal facilities in an institution is best centralized. This warrants that all information dealing with the purchase of animals, the use of experimental materials and equipment and the performance of animal experiments flows through one office. This reduces the opportunity for the failures of communication. Centralized management can best establish comprehensive monitoring programs to evaluate important risk factors, such as animals and biological materials, before they are introduced into a facility.

Physiological relationships among stress, viruses, and cancer in experimental animals

Anxiety-induced psychoneural stimulation, via the hypothalamic-pituitary axis, activates the adrenal cortex to release corticosteroids, which elicit various alterations of corticoid-sensitive cell-mediated immunologic processes. Stress sensitive murine tumor-host experimental models have been utilized to demonstrate various effects of stress upon aspects of tumor development. Although many of the observed anxiety-induced alterations of tumor-related parameters can be interpreted in terms of corticoid-induced modifications of immune functions, other observations are more difficult to interpret, and may be caused in part by corticosteroid-independent modulation of lymphocyte functions. In the case of tumors induced by oncogenic viruses, anxiety-induced plasma corticoid elevations may also act independently of the immune system to stimulate tumor development via hormone binding sites on proviral DNA. Rigorously controlled environmental and experimental conditions are fundamental for the demonstration and interpretation of stress-related phenomena. Technical prerequisites include protective animal facilities, special handling procedures, the use of nontraumatic stressors, and the recognition of vital psychosocial, coping and timing factors. Various biologic factors, such as sex, genetic substrain differences and common interfering viral infections, must also be controlled or taken into consideration.

Potential detrimental effects of rodent viral infections on long-term experiments

Healthy animals are of paramount importance in obtaining meaningful, reliable scientific results. Viral infections of rodents often have a significant impact on various types of biomedical research. Laboratory animal specialists and researchers must be aware of the possible consequences associated with the use of infected animals. The objective of the paper is a discussion of the frequently encountered viral infections that can complicate or invalidate the interpretation of results by altering the host's response.

Spinal leptomeningeal epidermoid cysts in inbred mouse strains

The anatomic location and histological appearance of spinal cord epidermoid cysts in a variety of inbred mouse strains was examined. A variable incidence of cysts was found in mice of the C57BR/cdJ, C57BL/6J, B10.BR/SgSnJ, C58/J, AKR/J, C57L/J, and RF/J strains. Cysts were largely found in the leptomeninges, adjacent to the posterior horn and the lateral or anterior columns. The cysts consisted of a central whorled mass of keratinized cells surrounded by polygonal epithelial cells; some of these cells contained keratohyaline granules. Basal cells were absent. The presence of cysts did not correlate with the H-2k or H-2b haplotypes of the mouse.

Mouse mammary tumors: alteration of incidence as apparent function of stress

Eighty to 100 percent of female mice of the C3H/He strain carrying the Bittner oncogenic virus usually develop mammary tumors within 8 to 18 months after birth when studied under the usual housing and experimental conditions. By subjecting various groups of such mice to environmental circumstances providing different degrees of chronic stress, mammary tumor incidence at 400 days was modified, with incidences ranging from 92 percent under stress to 7 percent in a protected environment. The data suggest that moderate chronic or intermittent stress may predispose such mice to an increased risk of mammary carcinoma, possibly through a resultant compromise of their immunological competence or tumor surveillance system, and that adequate protection from physiological stress may reduce mammary tumor occurrence in mice.