Effects of prior housing on endocrine responses to differential caging in male TO-strain mice

The Impact of Social and Behavioral Factors on Reproducibility in Terrestrial Vertebrate Models

The use of animal models remains critical in preclinical and translational research. The reliability of the animal models and aspects of their validity is likely key to effective translation of findings to medicine. However, despite considerable uniformity in animal models brought about by control of genetics, there remain a number of social as well as innate and acquired behavioral characteristics of laboratory animals that may impact on research outcomes. These include the effects of strain and genetics, age and development, sex, personality and affective states, and social factors largely brought about by housing and husbandry. In addition, aspects of the testing environment may also influence research findings. A number of considerations resulting from the animals' innate and acquired behavioral characteristics as well as their social structures are described. Suggestions for minimizing the impact of these factors on research are provided.

D1 dopamine receptors and the reversal of isolation-induced behaviors in mice

In a previous study, it was demonstrated that the high rates of social reactivity exhibited by isolated male mice in a dyadic encounter were mediated, at least in part, by an increased sensitivity of the D1 dopamine receptors. The present research was guided by the hypothesis that the behavioral effects of isolation are reversible, and that changes in dopaminergic function support this reversibility. To this end, mice selectively bred for high and low levels of aggression were reared in isolation from weaning (21 days) to puberty (45 days), at which point they were either assigned to groups or left in isolation until day 69. By comparison to the continuous isolation condition, mice that eventually formed groups exhibited significantly less reactivity in a dyadic test conducted on day 69, showed a reduced response to dihydrexidine (DHX), and a decreased density of D1 dopamine receptors. This experiment provided evidence for the plasticity of the neurobiological system supporting reactive responses, and confirmed the view that its functional organization is open to experientially-induced changes.

Structural changes in nuclear chromatin in rat pituitary after chronic stress of low intensity

Acute, intense sources of "psychogenic" stress clearly modify the structure and function of the hypophysis, and there are concomitant changes in many peripheral physiological systems. Less dramatic sources of stress yield more equivocal results. An experiment is reported in which nuclear morphology of adenohypophyseal cells from 49 male rats exposed to a chronic, low-intensity stressor was examined both by conventional histological and computer-assisted-image-processing methods. The hypothesis tested was that an unequivocal pattern of morphological changes in the nucleus and nuclear chromatin would be revealed by image processing. Rats were killed after living for a year in a relatively low-stress environment, "crowded" in groups of five animals per cage. The control condition was a minimal stress environment of two rats per cage. Results suggested few signs of pathology from peripheral measures of hypophyseal activity, and direct light microscopic examination of the gland revealed no differences between the two groups. Analysis of computer-enhanced images of the pars distalis nuclei from the adenohypophysis, on the other hand, generated findings that were statistically and biologically significant. Nuclear size increased in the stress condition, the number of chromatin and area occupied by the particles increased, and the position of chromatin shifted toward the periphery of the nucleus. Perhaps more important, optical density analysis indicated that chromatin was less tightly packed in the experimental animals. Implications are that chronic, low-intensity stress modulates nuclear structural changes from a dormant to an active state that portend changes in the peripheral systems influenced by the hypophysis.

Hypothalamic levels of LHRF in male mice of differing social status and from individual housing

Swiss male mice were individually-housed or maintained in groups of 8 from weaning until 80 days of age. At this time, the grouped mice were allocated to new groups of 5-6 previously unfamiliar individuals. Identified dominants were then caged with two clearly submissive males for 1 week. At this time hypothalamic samples were taken from the dominant and one subordinate and from a number of long-term individually-housed males. A radio- immunoassay for LHRF was carried out. The levels of this hypothalamic releasing factor were significantly higher in both dominant and subordinate grouped mice than in 'isolates'. Mice of differing social status showed comparable titres of this hormone. The results suggest that social conflict and/or disturbance augments this factor in mice irrespective of the social status achieved by individual animals.

The influence of the parental environment on sexual maturation in male mice

Experiments were designed to examine the influence of either one or both parents on the sexual maturation of male mice. A pregnant female and an adult vasectomized male were housed together and, at delivery, the litter was reduced to 6 pups, 3 of each sex. After weaning, mother, foster-father or both, stayed in cohabitation with their pups until sacrifice. The results showed that: (1) the permanent presence of one or both parents did not affect either testicular growth or the age at first fertile matings. (2) in maturing males (30-40 days), seminal vesicle growth was accelerated by the presence of the mother, inhibited by the presence of the foster-father. (3) in maturing males, the presence of one or both parents lowered plasma testosterone levels. On the opposite, in 90-day-old males, the same conditions increased testosterone levels. These results indicate that only the endocrine function of the testis is affected by the parental environment. The effects are age-dependent.