INTERACTIONS WITH MALES PROMOTE RAPID CHANGES IN GONADOTROPIN-RELEASING-HORMONE IMMUNOREACTIVE CELLS

It is well known that hormones can regulate behaviors. However, the re ciprocal interaction, the effects of behavior on hormones, has receive d less direct experimental attention. Dramatic changes in hormones and behaviors occur at puberty and some of these changes can be triggered by modification of the social environment. Interactions with males ac celerate production of pulsatile release of gonadotropins and steroid hormones which, in turn, initiate estrous cycles, ovulation, and sexua l behavior in females. Ultimately all of these actions are controlled by changes in production and secretion of gonadotropin-releasing hormo ne (GnRH). Little is known about how behavior affects GnRH-producing n eurons. In female musk shrews, the first mating initiates the onset of puberty. Musk shrews lack a behavioral estrous cycle and they become receptive within minutes after their first contact with a male. As soo n as 1 h after interactions with males there is a significant increase in the numbers of GnRH-immunoreactive (GnRH-ir) neurons in specific b rain regions. In the present study, we examined changes in GnRH-ir cel l number during the initial mating bout. We found dynamic changes in t he numbers of GnRH-containing cells, correlated with changes in behavi or. Interactions with males for less than 30 minutes induced a signifi cant increase in GnRH-ir neurons in specific olfactory-related forebra in nuclei. At the end of a mating bout, numbers of GnRH-ir neurons dec lined. Because behavioral interactions have rapid and pronounced effec ts on the neurons that produce GnRH, this model can be used to examine the behavioral regulation of neuronal plasticity.