Reproductive experience and the response of female Sprague-Dawley rats to fear and stress.

The present work examines the relationship between reproductive experience (comprising breeding, parturition, and lactation) and the behavioral and hormonal processes of fear and stress in the female laboratory rat. Previous research has indicated that reproductive experience functions to decrease the female's stress response in potentially harmful environments, thereby providing her with numerous survival benefits, including decreased fearfulness, increased aggression, and refined hunting skills. This study was designed to determine how nulliparous (no reproductive experience), primiparous (1 reproductive experience) and multiparous (at least 2 reproductive experiences) rats respond to a Pavlovian paradigm of learned fear, involving the pairing of a neutral stimulus (conditioned stimulus) with an aversive stimulus (unconditioned stimulus). We report evidence that reproductive experience is linked with fear-response and anxiety-like behaviors. Our findings indicate that reproductive experience has an additive effect: primiparous mothers showed a different response to the paradigm of conditioned fear not only compared with those of nulliparous rats as well as multiparous mothers. Assessing the complex interconnections among the behavioral and physiologic measures recorded in this study, multidimensional scaling confirmed a clear separation among the 3 groups of rats in terms of the behavioral and physiologic responses to the experimental paradigm, supporting the conclusion that reproductive experience influences the maternal mind.