Opioid modulation and sensitization of dopamine release elicited by sexually relevant stimuli: a high speed chronoamperometric study in freely behaving rats.

High speed chronoamperometry was used to measure oxidation and reduction currents associated with monoamine release in the caudate putamen and nucleus accumbens of freely moving rats exposed to bedding from cages that housed other male, ovariectomized female, or estradiol-progesterone-primed female rats. Estrus female, but not male or ovariectomized female bedding potently increased the electrochemical signal from electrodes implanted within the nucleus accumbens, and less effectively from more dorsal sites. Naloxone pretreatment attenuated the increase in the electrochemical signal. Repeated exposure to estrus female bedding led to an increased, or sensitized, response within the nucleus accumbens that was also sensitive to naloxone pretreatment. The ratios of the reduction to oxidation currents indicated that dopamine was the principal contributor to the increase in the electrochemical signal, suggesting that activation of the mesolimbic dopamine system accompanies exposure to sexually relevant stimuli. These results suggest that the facilitation of sexual behaviors by dopamine may be due, at least in part, to the processing of incentive motivational cues, and not necessarily to effects on copulation, itself. The results of the present study also suggest that opioid peptides contribute to the activation of mesolimbic dopamine by sexually relevant olfactory stimuli.