PubMed · 8480321
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V L Voith. 1993. Behaviour problems in cats.. https://pubmed.ncbi.nlm.nih.gov/8480321/
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Unpredictable and uncontrollable stressful events have been shown to affect cognitive processes. Interestingly, only hippocampus-mediated memory processes are thought to be sensitive to the effects of chronic stress. In contrast, the hippocampus-independent memory processes have been shown to be resistant to chronic stressful experiences. A central feature of the stress response is the activation of the hypothalamus-pituitary-adrenocortical (HPA)-axis, resulting in increased plasma levels of glucocorticoids, and several studies suggested that the performance of hippocampus-mediated memory processes might be directly modulated by these adrenal steroids. We investigated the impact of chronic psychosocial stress on hippocampus-mediated and hippocampus-independent memory processes in male tree shrews. By using a modified holeboard we followed memory performance during 23 weeks of alternating stress-free and stressful conditions. This schedule was designed to mimic a more realistic situation with stress-free conditions being sequentially interrupted by challenging events. The results indicate that chronic stress differentially affects hippocampus-mediated and hippocampus-independent memory processes in tree shrews. While hippocampus-independent memory processes remained unimpaired throughout the study, hippocampus-mediated memory was persistently impaired, not only during stress periods but also during recovery periods. This persistent impairment seems not to be exclusively triggered by glucocorticoids because urinary free cortisol concentration returned to normal during recovery periods. The present study is the first to evaluate the consequences of sequential stress exposure on memory performance in animals. Apparently, the mechanisms modulating cognitive processes are far from being understood and need a very systematic analysis in animal models with a high face and predictive validity to human stress-related memory disorders.
The development of laboratory rodent models for elicitation and measurement of a range of defensive behaviors raises the question of the relationship between defense in these animals and those of their wild congeners. To evaluate this relationship for mice, defensive responses to an anesthetized rat were compared for fourth-generation laboratory-bred wild mice and Swiss CD-1 (Swiss-Webster derived) laboratory mice in a Mouse Defense Test Battery. Wild mice showed enhanced levels of both freezing and flight, fleeing from distant approach of the predator in several situations and fleeing more quickly than the Swiss mice. However, Swiss mice did flee upon contact with the rat and also showed levels of several other defensive behaviors (risk assessment, defensive threat, and attack) that were often reliably higher than those of the wild mice. However, when wild mice were prevented from fleeing, their levels of defensive threat and attack were as high as, or at very short prey-predator distances higher than, those of the Swiss mice. These findings suggest that flight and freezing are the major defensive behaviors reduced in Swiss mice and that these reductions allow the appearance of higher levels of additional defensive behaviors in the laboratory animals. However, although Swiss mice do show lower levels of flight and freezing, their patterns of defensive behavior are sufficiently similar to those of wild mice that they provide adequate subjects for research on the biologic bases of defensive behavior. A final experiment indicated that when wild mice are familiarized with a chamber providing a place of concealment, they flee directly to this chamber on presentation of a rat, indicating that flight is a targeted response and not simply an abrupt increase in forward locomotion. Over 10 rat presentation trials with a blocked chamber entrance, however, this response declines.
Social status in randomly constituted groups of male CFLP mice was predictable from early suckling behaviour and rate of weight gain in natal litters. High-ranking males were those that had suckled on more anterior teats and gained weight more quickly. Rank was not predicted by any measures of sibling interaction or hormone (testosterone, corticosterone) concentration. Aggressiveness in eventual high-rankers was associated negatively with the proportion of males in the litter at birth and the amount of maternal attention received. Aggressive social relationships within natal litters did not predict polarized rank relationships in randomized groups. Nevertheless, while still in their natal litters, and in the absence of aggressive rank relationships, eventual rank categories showed the same difference in modulation of testosterone concentration in relation to current immunocompetence (low-rankers modulating, high-rankers not), as has repeatedly been found in randomized groups by earlier studies. The role of maternal condition in determining rank-related life-history development in male mice is discussed.