Interactions with males promote rapid changes in gonadotropin-releasing hormone immunoreactive cells

It is well known that hormones can regulate behaviors. However, the reciprocal interaction, the effects of behavior on hormones, has received 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 accelerate production of pulsatile release of gonadotropins and steroid hormones which, in turn, initiate estrous cycles, ovulation, and sexual behavior in females. Ultimately all of these actions are controlled by changes in production and secretion of gonadotropin-releasing hormone (GnRH). Little is known about how behavior affects GnRH-producing neurons. 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 soon as 1 h after interactions with males there is a significant increase in the numbers of GnRH-immunoreactive (GnRH-ir) neurons in specific brain regions. In the present study, we examined changes in GnRH-ir cell number during the initial mating bout. We found dynamic changes in the numbers of GnRH-containing cells, correlated with changes in behavior. Interactions with males for less than 30 minutes induced a significant increase in GnRH-ir neurons in specific olfactory-related forebrain nuclei. At the end of a mating bout, numbers of GnRH-ir neurons declined. Because behavioral interactions have rapid and pronounced effects on the neurons that produce GnRH, this model can be used to examine the behavioral regulation of neuronal plasticity.