Effects of paced coital stimulation on termination of estrus and brain indoleamine levels in female rats.

Serotonin (5-HT) and 5-hydroxy-indoleacetic acid (5-HIAA) levels were measured in brain regions of ovariectomized, steroid-primed rats at the end of behavioral estrus. At the onset of behavioral estrus three groups of rats received coital stimulation which included (1) mounts without penile intromission only, (2) temporally-controlled (paced) mounts with intromission, and (3) non-paced mounts with intromission. Within 12 hr after the initial treatment, sexual receptivity was significantly lower in females given paced intromissions than in the other two groups. Brain stem 5-HT and 5-HIAA concentrations were significantly higher in females which received intromissions, regardless of whether or not they were paced than in females given mounts only. Hypothalamic and cortical concentrations of 5-HT and 5-HIAA were equivalent in the two groups. These results suggest that the termination of behavioral estrus is not associated with increased metabolic activity in central serotonergic neurons.