Role of central neurons system in hypothalamus on regulation of copulatory behavior in male rats.

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We measured the extracellular concentrations of dopamine (DA) and acethylcholine (Ach) in the medial preoptic area (MPOA) of rats during male sexual activity. During copulation, the concentration of DA and Ach in the MPOA was significantly increased. Elevation of DA due to the drug administration facilitated male copulatory behavior in rats. These findings were consistent with the assertion that DA neuron activity in the MPOA facilitates male copulatory behavior.We investigated the effects of long-term psychological stress on sexual behavior and brain catecholamines in rats. The results showed that long-term psychological stress impaired the sexual behavior of male rats. Long-term psychological stress decreased the concentrations of catecholamine and its metabolites in the brain, especially in the medial preoptic area (MPOA). Thus, we hypothesized thet low catecholamine neurotransmission in the brain results in impairment of male rat sexual behavior.We then tried to restore the impaired sexual behavior by administration of a cerebral-activating drug, indeloxazine hydrochloride. The administration of indeloxazine hydrochloride for a 3-week period restored the sexual behavior that had been impaired by long-term psychological stress.Furthermore, we investigated the effects of testosterone replacements on copulatory behavior of aged male rats. Testosterone replacement restored the copulatory behavior and DA neuron activity of aged male rats.These present results suggest that impairment of cause of sexual dysfunction, and activation of neurotransmission may result in restoration of impaired male sexual behavior.