Sexual motivation: involvement of endogenous opioids in the ventral tegmental area.

The sexual motivation and performance of male rats were observed in a bilevel testing chamber after bilateral infusion of 40 pmol beta-endorphin, 2.75 nmol naloxone or saline into the ventral tegmental area for four succeeding, weekly tests. In the 5 min prior to introduction of the female rat, the male rat explores the bilevel testing chamber. It was previously shown that the increase over tests of these anticipatory level changes is sexually motivated and a response to olfactory stimuli. Naloxone infusion into the VTA prevented the increase of anticipatory level changes. beta-Endorphin failed to affect the anticipatory level-changing behavior. The sexual performance was unaffected by naloxone or beta-endorphin treatment, but the number of ejaculating rats decreased with repeated testing after naloxone treatment. It is concluded that endogenous opioid systems in the ventral tegmental area contribute to the stimulation of sexual motivation and/or reward, presumably by stimulating the mesolimbic dopamine system in response to sex-related olfactory stimuli.