Influence of environmental enrichment and sex on predator stress response in rats.

Based on sex, rats were randomly assigned to either an enriched or standard environment for 30 days prior to behavioral testing. The predator stress testing consisted of placing the rat in a cat avoidance apparatus so that the rat's behavioral response to a natural stressor, the cat, could be assessed. The rats were subsequently exposed to a partial predator stimulus (cat urine) that was placed in the home cages for 7 days. Each animal was then sacrificed and the stomach, adrenal glands, and thymus gland were removed and assessed. Results indicated that 1) the enriched rats engaged in less defensive behavior than the standard rats during behavioral testing, 2) female rats demonstrated more defensive behavioral patterns compared to male rats, and 3) the enriched environment affected females more than males, as evidenced by the interaction effects on various recorded behaviors.