PROGESTERONE-INDEPENDENT ACTIVATION OF RAT-BRAIN PROGESTIN RECEPTORS BY REPRODUCTIVE STIMULI

Activation of steroid hormone receptors by steroid hormones alters bot h the physiology and behavior of animals. Steroid hormone receptors (e .g., progestin receptors) can also be activated in the absence of ster oid hormones by pharmacological treatment with neurotransmitters or ne uropeptides. However, it is not known if progesterone-independent acti vation of brain progestin receptors occurs under natural, physiologica l, conditions. We report that increases in reproductive behavior and b rain immediate early gene expression in female rats induced by mating stimuli can be blocked by prior treatment with progesterone antagonist s in the absence of circulating progesterone. This suggests that proge stin receptors are activated in a progesterone-independent manner by a physiologically relevant stimulus in female rats, thus implicating a novel pathway by which mating stimuli and other environmental influenc es could activate steroid receptors to influence neuronal response and behavior.