Cellular basis of tolerance in neonatally induced mouse chimeras.

In mice, thymectomized as young adults, neonatally induced tolerance persists in the putative absence of cell chimerism. The finding provides evidence that a selective deficiency of specific clones of lymphocytes exists in transplantation tolerance when induced under the conditions of these experiments.

The development of a male pseudohermaphroditic rat using an inhibitor of the enzyme 5 alpha-reductase.

Incomplete masculinization of the external genitalia occurred in male Sprague-Dawley rats treated with a potent inhibitor of enzyme 5 alpha-reductase at the critical period of sexual differentiation in utero. The studies were performed using the 5 alpha-reductase inhibitor, 4-methyl-4-aza-5-pregnan-3-one-20[s] carboxylate, one of a series of aza steroids known to competitively inhibit the enzyme 5 alpha-reductase. The degree of inhibition of male external genital development was dependent upon the dose of the inhibitor, and at a dose of 36 mg/kg X day, there was complete feminization of the external genitalia of the male animal with a urogenital sinus and a pseudovagina. These studies provide conclusive evidence for the hypothesis that 5 alpha-reductase activity and dihydrotestosterone (17 beta-hydroxy-5 alpha-androstan-3-one) formation are essential for normal differentiation of male external genitalia. Epididymidis, vasa deferentia, and seminal vesicles were present at all doses of the inhibitor, suggesting testosterone dependency. However, confirmation of the testosterone dependency of Wolffian ductal differentiation awaits further studies, particularly comparison studies with the rabbit and dog, since Wolffian ductal differentiation in the rat, unlike the rabbit and dog, is not abolished with the antiandrogen, cyproterone acetate. The presence of prostatic buds, despite complete external genital feminization, was unexpected and suggests that these structures may have different thresholds of response for dihydrotestosterone. Prostatic differentiation may have a much lower threshold, requiring less dihydrotestosterone for differentiation.

Tissue renin and prorenin increase in female cats during the reproductive cycle without commensurate changes in plasma, amniotic or ovarian follicular fluid.

The renin gene is expressed, primarily as prorenin, in the ovary, uterus and placenta. High concentrations of prorenin are present in human ovarian follicular and amniotic fluids and ovarian secretion causes increases in plasma prorenin at mid-menstrual cycle and during pregnancy. Plasma prorenin is low but detectable in nephrectomized human subjects. Comparative studies in female cats revealed several differences. Cat plasma prorenin became undetectable after bilateral nephrectomy. Neither plasma prorenin nor renin increased during pregnancy. Renin and prorenin were undetectable in ovarian follicular, amniotic and allantoic fluids. Human chorionic gonadotropin-induced ovulation caused only small increases in plasma prorenin. In contrast, renin and prorenin were clearly present in extracts of reproductive tissues. Ovarian total renin was lowest during anestrus (169 +/- 27 ng/g per h) and estrus (258 +/- 58 ng/g per h) and increased with ovulation (385 +/- 31 ng/g per h). Higher ovarian levels were found during pseudopregnancy (1370-2030 ng/g per h) and early pregnancy (1312-2700 ng/g per h) and in the placental chorion disc of early pregnancy (1755-1184 ng/g per h). In the uterus, the level was 98-183 ng/g per h during gestation. These results demonstrate that, in marked contrast to humans, only the cat kidney secretes prorenin into body fluids. Nonetheless, total renin increases in cat ovaries during follicle maturation, ovulation, pregnancy and pseudopregnancy, in the uterus during gestation and in the placental chorion disc. These results are consistent with an autocrine or paracrine role for the tissue renin system in cat reproductive tissues.

Effects of concanavalin A, phytohemagglutinin, pokeweed mitogen, and lipopolysaccharide on the replication and immunoglobulin synthesis by canine peripheral blood lymphocytes in vitro.

Canine peripheral blood lymphocytes (cPBLs) were used to investigate the mitogenic effects of Con A (concanavalin A), LPS (lipopolysaccharide), PHA (phytohemagglutinin), and PWM (pokeweed mitogen) in vitro by measuring tritium-labeled thymidine [( 3H]thymidine) incorporation and immunoglobulin (Ig) secretion. An ELISA specific for canine IgG and IgM showed that cPBLs secreted significantly more IgG than IgM in response to mitogen concentrations from 30,000 to 0.03 ng/10(5) cells. The optimal stimulating dose of mitogen for lymphocyte response measured by IgG secretion was over a much narrower range of concentration than was the [3H]thymidine incorporation measured response. At a concanavalin A dose where there was increased [3H]thymidine incorporation with a decrease in IgG secretion, it appeared that an active suppression of the IgG response was induced.

Monoclonal antibodies directed at human T lymphocyte activation antigens cross react with concanavalin A-stimulated canine and baboon peripheral blood lymphocytes.

A panel of 10 monoclonal antibodies directed at activation antigens on human T lymphocytes were tested for cross reactivity with canine and baboon resting and ConA stimulated peripheral blood lymphocytes. Monoclonal antibodies anti-OKT19, anti-OKT-21, and anti-OKT22 labeled a high percentage of both resting and stimulated canine and baboon cells. Anti-OKT24 labeled activated but not resting baboon lymphocytes and did not label canine lymphocytes. Anti-HLA-DR labeled a small percentage of resting baboon lymphocytes (presumably B cells) and a high percentage of activated baboon and resting and activated canine lymphocytes. Anti-OKT14, anti-OKT20, and anti-OKT23 did not label canine or baboon lymphocytes. Anti-OKT9 did not label baboon lymphocytes, but labeled a low percentage of lymphocytes in one dog. Anti-TAC labeled activated but not resting canine and baboon cells.

The pathogenesis of experimental toxic shock syndrome: the role of interleukin-2 in the induction of hypotension and release of cytokines.

Toxic shock syndrome (TSS) is a multisystem disorder characterized by fever, hypotension, and involvement of three other organ systems. The etiologic agent is a toxigenic strain of Staphylococcus aureus which secretes the exotoxin, TSST-1. The toxin is a superantigen which stimulates the immune system to produce interleukin-1 (IL-1), interleukin-2, and tumor necrosis factor (TNF). We hypothesized that TSST-1 induces the release of IL-2 which in turn is either directly involved or acts via an additional mediator to produce hypotension. We submitted four pairs of normal anesthetized adult female baboons to intravenous boluses of TSST-1. One baboon in each pair received anti-IL-2 intravenously and anti-IL-2 receptor intrathyroidally 15 min prior to TSST-1. The other baboon received the same dose and placement of anti-sheep red blood cell antibody. Systolic and diastolic blood pressure was recorded continuously and mean arterial pressure was calculated and plotted. IL-1, IL-2, IL-6, and TNF were measured in serum at varying times before and after toxin administration. Systolic, diastolic, and mean arterial pressure were significantly lower in the sham-treated group versus the experimental (anti-IL-2/IL-2R) group (p < .05 for all variables). In addition no differences were seen in any of the measurements between experimentally treated baboons and those receiving no TSST-1.(ABSTRACT TRUNCATED AT 250 WORDS)

Induction of hepatic cytochromes P450 in dogs exposed to a chronic low dose of polychlorinated biphenyls.

Induction of cytochrome P450 isoforms, specifically CYP1A1, and their catalytic activities are potential biomarkers of environmental contamination by polychlorinated biphenyls (PCBs). In this study, dogs were exposed to 25 ppm or 5 ppm Aroclor 1248 (PCB mixture) daily in their diet for 10 or 20 weeks, respectively. Relative to controls, hepatic microsomes from dogs dosed with PCBs had higher levels of CYP1A1 detected in immunoblots and higher levels of EROD activity, but low levels of induction for CYP2B and PROD activity. Concentrations of 96 PCB congeners in serum and liver were evaluated using capillary chromatography. Results showed that all dogs exposed to PCB mixtures had higher levels of PCB in serum and liver. Dogs preferentially sequestered highly chlorinated PCB congeners in liver relative to serum. With these experiments, we demonstrated that EROD activity was a potentially sensitive marker of PCB exposure at 5 and 25 ppm. Furthermore, CYP1A1 and EROD activity were maximally induced in dogs consuming dietary concentrations only 2.5 times the maximal permissible level for human food (FDA). The value of CYP1A1 induction as a biomarker of PCB exposure was tenuous because neither CYP1A1 levels nor EROD activity correlated with total PCB body burden. However, a small subset of congeners were identified in liver that may strongly influence EROD and PROD induction. Finally, two dogs in the 25 ppm dose group were fasted for 48 h. After 24 h of fasting, several new congeners appeared in the serum and remained in the serum for the remainder of the fast. The fast caused a 293% increase in PCB concentration in serum. This increase has strong implications regarding mobilization of toxic PCBs in wildlife during fasting (e.g., migration, hibernation).

Friendliness to humans and defensive aggression in cats: the influence of handling and paternity.

This study was undertaken to examine and reduce the stress and aggressiveness associated with fear of handling in laboratory cats (Felis sylvestris catus). Thirteen litters of kittens from a specific pathogen-free breeding colony were divided into three treatment groups: two were early weaned, removed from the colony and caged individually with or without handling up to 8 weeks of age, and the third served as a control group, removed from the colony just before testing. Behavior tests measuring degree of friendliness to humans and response to physical restraint were performed at ages 8, 12, 16, and 20 weeks. Serum cortisol concentrations were measured after each test. Results indicate that litter and sire influenced tractability but that handling or individual caging of kittens did not. Posttest serum cortisol concentrations were below normal adult levels in most kittens, including those reacting fearfully during testing and aggressively during restraint, and, therefore, are not a reliable indicator of stress in juvenile cats.

A radiolabeled staphylococcal protein A assay for detection of anti-erythrocyte IgG in warm agglutinin autoimmune hemolytic anemia of dogs and man.

A cell wall protein from Staphylococcus aureus, Protein A, (SpA) has been shown to have the ability to bind the Fc region of most mammalian IgG molecules. This study uses this unusual property as the basis for a quantitative assay for erythrocyte (RBC) bound antibodies. Test serum is incubated in a suspension of normal RBC's. The cells are then washed and incubated with 125Iodine-labeled SpA (125I-SpA). After incubation cells are pelleted and bound radiolabeled SpA counted. This procedure has been performed using canine anti-goat RBC (DagRBC) serum and human anti-D serum (positive controls) to establish the kinetics of the SpA reaction in the above system. The results indicate that SpA binds to red blood cells as a function of membrane bound antibody. RBC's incubated with indirect Coombs positive sera bound 42.6% and 43.3% of the 125I-SpA, as compared to 19.2%, the upper limit of the 95% confidence interval (n = 9) for normal sera. Furthermore, significant binding was observed for certain indirect Coombs negative (direct Coombs positive) sera indicating that the SpA assay is more sensitive than the indirect Coombs test. The SpA system should provide the clinician with an inexpensive, sensitive, quantitative assay for the diagnosis of warm agglutinin autoimmune hemolytic anemia, as well as other autoimmune disorders involving membrane bound IgG.

Functional and phenotypic analysis of in vitro stimulated canine peripheral blood mononuclear cells.

The inter-species cross-reactivity of cytokine bioassays for interleukin-2 (IL2) and interleukin-6 (IL6) was investigated in the canine species. The kinetics of normal canine peripheral blood mononuclear cells (PBMC) stimulated with pokeweed mitogen (PWM), were analyzed in terms of cytokine release and responsiveness to cytokine stimulation, in conjunction with determination of cell proliferation, de novo antibody synthesis and cell surface phenotype. PBMC were stimulated with PWM at the beginning of the culture and human recombinant IL2 (rIL2) was added 3-4 days post stimulation (d.p.s.). Mitogenically stimulated cells proliferated and synthesized antibody in a linear fashion up to 6 d.p.s. Resting PBMC had a mean CD4+/CD8+ ratio of 1.7:1; whereas cells stimulated with PWM were predominantly of CD8 phenotype at 7 d.p.s.. Three days after addition of IL2, stimulated cells were predominantly of the Thy+, sIg-, CD4+, CD8- phenotype, with an increase in the CD4+/CD8+ ratio. The magnitude of de novo antibody synthesis was lower in rIL2-supplemented cultures than in cultures stimulated only with PWM, and suggested a negative relationship between de novo antibody synthesis and proliferative responses of the same cultures. Supernatants from mitogen-stimulated cultures induced proliferation of mouse IL2- and IL6-dependent cell lines. Antibodies reactive with human IL2 or IL6 inhibited these responses. IL2-like activity in PWM-stimulated culture peaked by 2 d.p.s. and decreased thereafter. IL6-like activity peaked later (4-6 d.p.s.).

Investigation of cross-reactivity between commercially available antibodies directed against human, mouse, and rat lymphocyte surface antigens and surface markers on canine cells.

Using automated flow cytometry, 23 commercially available antibodies (all but one of them monoclonal) raised against surface antigens of specific populations of human, rat, and mouse lymphocytes were tested for cross-reactivity to peripheral blood lymphocytes from five clinically healthy adult dogs. Of all the antibodies tested, only the polyclonal anti-asialo GM1 directed against mouse NK cells, and the monoclonal antibodies anti-HLA-DR directed against the human class II antigen and anti-B1, a human pan B cell marker, consistently labeled subpopulations of canine lymphocytes.

Longitudinal evaluation of bovine mammary gland health status by somatic cell counting, flow cytometry, and cytology.

Bovine mastitis phases induced by Staphylococcus aureus were assessed in 6 lactating cows before challenge and at 1, 4-8, and 9-14 days postinoculation (dpi). Milk lymphocytes, macrophages, and polymorphonuclear cells (PMN) were counted by conventional (manual) cytology, identified by CD3+ and CD11b+ immunofluorescence and counted by flow cytometry (based on leukocyte forward and side light scatter values). Somatic cell counts (SCC) and recovery of bacteria were recorded at the same times. Preinoculation samples showed a lymphocyte-dominated composition. At 1 dpi, the percentage of PMN increased and that of lymphocytes decreased. At 4-8 dpi, PMN were predominant, but the percentage of mononuclear cells increased above that at 1 dpi and further increased by 9-14 dpi (when lymphocytes approached prechallenge values). Based on leukocyte percentages, 3 indices were created from the data: 1) the PMN/lymphocyte percentage ratio (PMN/L), 2) the PMN/macrophage percentage ratio (PMN/M), and 3) the phagocyte (PMN and macrophage)/lymphocyte percentage ratio (Phago/L). Significant correlations were found between cytologic and flow cytometric data in all of these indicators (all with P < or = 0.01). These indices identified nonmastitic, early inflammatory (1-8 dpi), and late inflammatory (9-14 dpi) animals. In contrast, SCC and bacteriology did not. Although sensitivity of the SCC was similar to that of Phago/L, the specificity of SCC was almost half that of the Phago/L index. Based on flow cytometry indicators, an algorithm for presumptive diagnosis of bovine mastitis was developed. Flow cytometry provides results as valid as those obtained by conventional (manual) cytology, shows greater ability to identify mastitic cases than does SCC, and may identify 3 mammary gland health-related conditions.

Adrenal function in the cat: comparison of the effects of cosyntropin (synthetic ACTH) and corticotropin gel stimulation.

The serum cortisol responses of 10 normal cats to natural adrenocorticotrophic hormone (ACTH) gel and synthetic ACTH (cosyntropin) were evaluated and compared. Following administration of either ACTH gel or cosyntropin, mean serum cortisol concentrations increased significantly (P less than 0.05) within 30 minutes and reached a maximal response (2.5 to 10 times basal values) at 90 minutes. The time to reach peak serum cortisol concentrations was variable, however, and occurred sooner after cosyntropin (30 to 60 minutes) than after ACTH gel administration (90 to 180 minutes). While ACTH gel tended to produce a prolonged cortisol response, the effects of cosyntropin were more transient, with serum cortisol concentrations returning to normal range within three hours after injection. Results of this study indicate that the administration of either ACTH gel or cosyntropin consistently produces an adequate adrenocortical response in the cat. Based on the time response studies, post ACTH cortisol samples should be collected 60 to 90 minutes after cosyntropin or 90 to 120 minutes after ACTH gel injection to ensure detection of peak adrenocortical response with either ACTH preparation.

Blood and milk cellular immune responses of mastitic non-periparturient cows inoculated with Staphylococcus aureus.

Lymphocyte function and phenotype of peripheral blood and mammary gland cells were evaluated in non-periparturient cows before and at 1, 4 to 8 and 9 to 14 d after inoculation with Staphylococcus aureus, as expressed by percentage of CD3+, CD2+, and CD45R+ cells, antigen density of these markers per lymphocyte, and mitogen-induced blastogenesis. Milk bacterial counts and somatic cell counts (SCC) were also assessed. Mitogen-induced blastogenic responses were strong in blood and weak in mammary gland cells in all observations and positively correlated with the percent of CD45R+ cells. Significantly greater percentages of milk CD3+ lymphocytes and increased CD3, CD2, and CD45R antigen density per cell were observed after challenge. The blood CD3 and CD2 antigen density per lymphocyte and the milk CD2+ lymphocyte percent were negatively correlated with SCC (P < or = 0.01). No mastitis (SCC < or = 500 000 cells/mL) was observed in cows showing blood lymphocyte CD2 and CD3 antigen density indices < or = 2.5 and 6, respectively. Forty-one percent of SCC values were predicted by the combined blood CD2 and milk CD3 antigen density (P < or = 0.01). These findings support the hypotheses that mitogen-induced lymphocyte blastogenesis is not a valid test to assess mammary gland immunocompetence and that CD2 expression may facilitate immune responses by decreasing the number of T cell receptors required to achieve full activation.

Identification of subpopulations of bovine mammary-gland phagocytes and evaluation of sensitivity and specificity of morphologic and functional indicators of bovine mastitis.

The number and function of bovine mammary-gland phagocytes were assessed in 8 lactating cows, each tested at least twice within an 8-mo period (total number of observations, 20). Macrophages and polymorphonuclear (PMN) cells were evaluated by conventional cytology, flow cytometry, fluorescent microscopy, and somatic-cell count (SCC). Phagocytosis was evaluated from the uptake of fluorescent beads and expressed as median fluorescence intensity (MFI). Two major subpopulations of phagocytes, of low or high MFI (LFI or HFI), were observed, and there were up to 4 sub-subpopulations within the HFI subpopulation of both macrophages and PMN cells. Fluorescent microscopy identified phagocytes containing up to 4 beads per cell. Cows showing < or = 72.3% phagocytes by cytology were regarded as non-mastitic (11 observations), and those showing > or = 80.7% phagocytes were considered to be mastitic (8 observations). Phagocyte MFI was negatively associated with mastitis; that is, the higher the MFI, the lower the SCC. The percentage of HFI PMN cells was the only indicator of mastitis with 100% sensitivity and specificity. Thus, bovine mammary-gland phagocytes consist of several subpopulations of different phagocytic ability, whose assessment more adequately predicts bovine mastitis than do morphologic indicators.

Longitudinal evaluation of CD4+ and CD8+ peripheral blood and mammary gland lymphocytes in cows experimentally inoculated with Staphylococcus aureus.

Staphylococcus aureus is a major pathogen associated with mastitis, a disease affecting both women and dairy cows. The longitudinal profiles of bovine peripheral blood and mammary gland lymphocyte phenotypes in response to S. aureus-induced mastitis were investigated in dairy cows. Increased percentage of CD4 lymphocytes in the mammary gland between 1 and 8 days post-inoculation, increased milk CD4 protein density per cell between 1-8 days post-inoculation, and a statistically significant negative correlation between post-inoculation bacterial counts in milk and blood lymphocyte CD4 protein density were found. Together with blood and milk leukocyte counts, the milk lymphocyte CD4/CD8 ratio and the milk lymphocyte CD4 protein density were more informative indicators than milk somatic cell counts and bacteriology for identification of early vs. late inflammatory phases. These findings suggest that CD4+ lymphocytes play a protective role in the early stages of S. aureus-induced mastitis.

Efficacy of immunoserodiagnostic procedures in the recognition of canine immunologic diseases.

Six immunologic tests were conducted on a large population of dogs with a variety of diseases. The test results were analyzed retrospectively and correlated to the clinical and final pathologic diagnoses. The results indicated that rheumatoid factor and the direct antiglobulin (Coombs) test were both sensitive and specific for the diagnoses of canine rheumatoid arthritis and autoimmune hemolytic anemia. The antinuclear antibody test was useful in supporting the diagnosis of systemic lupus erythematosus (SLE) only when both antibody titer and the staining pattern were taken into consideration. The lupus erythematosus cell test was specific but not sensitive when used to confirm a diagnosis of canine SLE. Cellulose acetate serum electrophoresis and immunoelectrophoretic techniques were each useful in supporting the diagnosis of multiple myeloma. Epizootiologic data collected in this study indicated that dogs with primary immunologic disease had a poor prognosis. A female predisposition was observed in cases of canine autoimmune hemolytic anemia and SLE. Ovariectomy seemed to prevent the development of canine SLE.

Expression of CD3 and CD11b antigens on blood and mammary gland leukocytes and bacterial survival in milk of cows with experimentally induced Staphylococcus aureus mastitis.

OBJECTIVES: To differentiate early (1 to 8 days) from late (9 to 14 days) inflammatory phases and assess relationships between leukocyte phenotype and bacterial recovery in cows with Staphylococcus aureus-induced mastitis. ANIMALS: 10 first-lactation Holstein cows. PROCEDURE: Blood and milk samples were collected from 4 or 6 cows before and after intramammary infusion of sterile broth or S. aureus, respectively. Flow cytometric expression of CD3 and CD11b antigens on blood and milk leukocytes, leukocyte differential counts, bacterial counts in milk, and somatic cell counts were determined longitudinally. RESULTS: Density of CD3 molecules decreased on blood lymphocytes and increased on milk lymphocytes after infusion of bacteria. Density of CD11b molecules on lymphocytes and phagocytes and percentage of CD11b+ lymphocytes in milk increased significantly after infusion; maximum values were achieved during the early inflammatory phase. Density of CD3 and CD11b molecules on milk lymphocytes and macrophages, respectively, 1 day after inoculation were negatively correlated with bacterial recovery on day 1 and days 9 to 14, respectively. Density of CD11b molecules on milk macrophages and the ratios of phagocyte to lymphocyte percentages and polymorphonuclear cell to macrophage percentages in milk differentiated the early from the late inflammatory phase. CONCLUSIONS AND CLINICAL RELEVANCE: Activation of bovine mammary gland macrophages and T cells in response to intramammary infusion of S. aureus was associated with an inability to culture this bacterium from milk. Identification of specific inflammatory phases of S. aureus-induced mastitis in cows may allow for the design of more efficacious treatment and control programs.

Molecular epidemiologic features and antimicrobial susceptibility profiles of various ribotypes of Pseudomonas aeruginosa isolated from humans and ruminants.

OBJECTIVES: To assess automated ribotyping for characterization of Pseudomonas aeruginosa isolates and to identify their type prevalence and geographic distribution. SAMPLE POPULATION: 39 human and 56 ruminant P aeruginosa isolates. PROCEDURES: Isolates were identified by use of bacteriologic techniques and automated Pvull-based ribotyping. Susceptibility to antimicrobials was tested in vitro. Data were analyzed for index of discrimination; prevalence ratio; geographic distribution of ribotypes found only in humans, only in cows, or only in goats (single-host ribotypes); and geographic distribution of ribotypes found in humans and ruminants (multihost ribotypes). RESULTS: All isolates were typeable (45 ribotypes, 35 single-host ribotypes). Ribotyping index of discrimination was 0.976. More isolates (45.3%) than expected yielded multihost ribotypes (22% of all ribotypes). Although 8.6% of single-host ribotypes were found in 4 or more isolates, 60% of multihost ribotypes were found in 4 or more isolates. Ninety percent of multihost ribotypes were isolated from different geographic areas, whereas 3.0% of single-host ribotypes were isolated from different geographic areas. All ruminant isolates were susceptible to gentamicin and polymyxin B. In contrast, antibiogram profiles differed for human isolates from different geographic areas. Susceptibility to antimicrobials differentiated 6 isolates not distinguished by ribotyping. CONCLUSIONS AND CLINICAL RELEVANCE: Automated ribotyping with Pvull discriminated more isolates than in vitro antimicrobial susceptibility. In combination, both tests provided more information than either test alone. Given the greater prevalence and geographic distribution of multihost ribotypes, immunocompromised humans and lactating ruminants may have a greater risk for disease if exposed to multihost P aeruginosa ribotypes, compared with single-host ribotypes.

Twenty-five years of progress in laboratory animal science.

During the past 25 years tremendous improvements have been made in the field of laboratory animal science. Refinements in genetic and microbial quality assurance and animal housing coupled with the development of professional expertise has contributed to enhanced animal well-being and a reduction in the variability of data collected from research animals. These advances occurred concomitant with an increased public awareness of research animal use. In 1967 Laboratory Animals Ltd. published the first issue of Laboratory Animals. In celebration of its Silver Jubilee, I will briefly highlight some of the changes which occurred in the field of laboratory animal science since 1967 and some of the medical advances which depended on animal-based research.