Role of Sex and Strain in Behavioral and Biologic Stress Responses of Rats

摘要

Stress has been implicated in the etiology of many behavioral disorders (i.e., drug abuse, feeding disorders) and disease states (i.e., hypertension, diabetes, depression). Individuals differ, however, in vulnerability to stress- related disease. The goal of this doctoral research was to identify potential behavioral and possibly biochemical markers of stress vulnerability vs. resilience in male and female rats of two strains (Sprague- Dawley and Long-Evans) that might predict eventual development of specific stress-related behavioral disorders or diseases in certain subgroups of humans. The experiment assessed the effects of mild, repeated daily stress on multiple behaviors and biochemical indices within the same subjects to construct a detailed model of potential markers of stress vulnerability vs. resilience. Specifically, subjects were exposed to no stress or to 20 min/day immobilization stress for three weeks. During this period, behaviors were measured in two domains: (1) body weight, feeding, and locomotion; and (2) acoustic startle reflex and pre-pulse inhibition, passive avoidance, and Morris water maze performance (three measures of cognitive performance). Hormones of the hypothalamo-pituitary- adrenocortical (HPA) axis were measured at the end of the experiment. The major findings were: (1) the four subgroups (i.e., two strains of male and female rats) manifested behavioral stress responses that varied with the domain assessed (i.e., feeding, body weight, and activity vs. cognitive performance) and imply different stress vulnerabilities; (2) the four subgroups manifested consistent stress responses within each behavioral domain, suggesting that stress vulnerability may be domain-specific; and (3) stressed animals within each of the four subgroups manifested changes in HPA axis hormones consistent with a stress response.