Dual action of neuro-estrogens in the regulation of male sexual behavior.

Estrogens derived from brain testosterone aromatization (neuro-estrogens) are critical for the activation of male sexual behavior. Their effects on this behavior are typically associated with long-term changes in circulating levels of testosterone and the transcriptional activity of their liganded nuclear receptors. According to this view, neuro-estrogens would prime the neural circuits controlling the long-term expression of behavior, which would then be acutely regulated by neurotransmitter systems conveying information from the social environment. In parallel, neuro-estrogens are also able to produce much faster effects than previously anticipated. Our recent investigations in Japanese quail revealed an interesting dichotomy in the regulation of male sexual behavior by membrane- and nuclear-initiated estrogen signaling providing respectively an acute modulation of sexual motivation and a long-term control of the capacity to display the copulatory sequence. In parallel, a similar dichotomy applies to the regulation of brain aromatase whose expression depends on the transcriptional activity of testosterone metabolites while its enzymatic activity is rapidly regulated in a region- and context-dependent manner. Recent evidences suggest that rapid changes in sexual motivation result from rapid changes in local estrogen production. Together, these data support the idea that the acute regulation of some aspects of male sexual behavior depends not only on classical neurotransmitter systems, but also on rapid and spatially restricted changes in local estrogen availability. The existing literature suggests that this acute regulation by neuro-estrogens of the motivational aspects of behavior could be generalized to other systems such as singing behavior in songbirds.