Rat sex and strain differences in responses to stress.

Sensitivity to stress has been linked to the development of a variety of physical and psychological disorders. Studies to-date have focused on extreme stress phenotypes, have studied mostly male responses, have used limited dependent variables, and have included a limited number of measurement time points. The present experiment was designed to address these limitations. Feeding, body weight, open-field activity, acoustic startle reflex (ASR), and prepulse inhibition (PPI) responses of adult male and female Sprague-Dawley and Long-Evans rats to daily immobilization stress (20 min/day) were evaluated for 3 weeks. Stress significantly decreased feeding and body weight of males but generally not of females. Effects were greatest in Long-Evans males. Stress decreased 15-min activity levels for males on Stress Day 1, but not on other days. Stress did not affect 15-min activity levels of Long-Evans females but decreased 15-min activity levels of Sprague-Dawley females on every measurement day. ASR responses to stress differed based on rat strain; percent PPI responses differed based on rat strain and sex. Stress increased startle responses of Sprague-Dawley males and females but not of Long-Evans males and females. Stress reduced PPI of Long-Evans females on every measurement day but not of other groups. These findings indicate that strain and sex of rat is important to consider in evaluating behavioral and physiological responses to stress.