Hormone-neurotransmitter interactions in the control of sexual behavior

The stimuli from st receptive female and/or copulation itself leads to the release of dopamine (DA) in at least three integrative hubs. The nigrostria tal system promotes somatomotor activity; the mesolimbic system subserves n umerous types of motivation; and the medial preoptic area (MPOA) focuses th e motivation onto specifically sexual targets, increases copulatory rate an d efficiency, and coordinates genital reflexes. The previous (but not neces sarily concurrent) presence of testosterone is permissive for DA release in the MPOA, both during basal conditions and in response to a female. One me ans by which testosterone may increase DA release is by upregulating nitric oxide synthase, which produces nitric oxide, which in turn increases DA re lease. Hormonal priming in females may also increase DA release in the MPOA , and copulatory activity may further increase DA levels in females. One of the intracellular effects of stimulation of DA D-1 receptors in the MPOA o f male rats may be increased expression of the immediate-early gene c-fos, which may mediate longer term responses to copulation. Furthermore, increas ed sexual experience led to increased immunoreactivity to Fos, the protein product of c-fos, following copulation to one ejaculation. Another intracel lular mediator of DA's effects, particularly in castrates, may be the phosp horylation of steroid receptors. Finally, while DA is facilitative to copul ation, 5-HT is generally inhibitory. 5-HT is released in the LHA, but not i n the MPOA, at the time of ejaculation. Increasing 5-HT in the LHA by micro injection of a selective serotonin reuptake inhibitor (SSRI) increased the latency to begin copulating and also the latency to the first ejaculation, measured from the time the male first intromitted. These data may at least partially explain the decrease in libido and the anorgasmia of people takin g SSRI antidepressants. One means by which LHA 5-HT decreases sexual motiva tion (i.e. increases the latency to begin copulating) may be by decreasing DA release in the NAcc, a major terminal of the mesolimbic system. Thus, re ciprocal changes in DA and 5-HT release in different areas of the brain may promote copulation and sexual satiety, respectively. (C) 1999 Elsevier Sci ence B.V. All rights reserved.