Dual modulation of male sexual behavior in rats by central prolactin: relationship with in vivo striatal dopaminergic activity.

Prolactin (PRL) appears to be localized in several brain structures. Central, behaviorally meaningful, neural actions of this protein have been demonstrated in a large number of studies. The present report describes sexual behavioral and in vivo neurochemical data obtained from adult male rats injected intracerebroventricularly acutely (10 micrograms) or chronically (5 days; 10 micrograms/day) with ovine prolactin (oPRL). The extracellular striatal concentrations of dopamine and serotonin metabolites were estimated by HPLC measurements in microdialysis perfusates. A single (10 micrograms) administration of oPRL facilitated sexual activity and increased extracellular striatal DOPAC, HVA and 5HIAA levels, whereas five daily intracerebroventricular injections of oPRL, decreased the sexual behavior and reduced DOPAC and HVA striatal extracellular concentrations in response to a central oPRL injection. These results show that acute and chronic central oPRL treatments have stimulatory and inhibitory effects on male sexual behavior, respectively. In addition, the results suggest that striatal dopaminergic activity is increased and decreased by acute and 5-day central oPRL treatments. These data suggest that behavioral effects of PRL occur simultaneously with changes in striatal dopaminergic activity.