Serotonergic neurotoxic lesions facilitate male sexual reflexes.

The effects of the neurotoxin 5,7 dihydroxytryptamine (5,7 DHT) on the urethrogenital reflex was examined in anesthetized male rats. Both ICV and intrathecal administration of 5,7 DHT produced a marked depletion (92%) of spinal 5-hydroxytryptamine (5-HT) and 5-hydroxyindole acetic acid (5-HT IAA) levels. ICV but not intrathecal administration of 5,7 DHT also caused a moderate reduction in 5-HT and 5-HT IAA levels in the medulla and hypothalamus (40-48%). No reduction in adrenergic levels were observed. In spinally intact, vehicle-treated rats the urethrogenital reflex could not be evoked. However, the urethrogenital reflex could be evoked in rats pretreated with either ICV or intrathecal 5,7 DHT prior to section of the spinal cord. These data support the hypothesis that 5-HT mediates the descending inhibition of male sexual reflexes.