Abstract
Dopamine in the medial preoptic area (mPOA) stimulates sexual activity in males. This is evidenced by microdialysis and microinjection experiments revealing that dopamine receptor antagonists in the mPOA inhibit sexual activity, whereas agonists facilitate behavior. Microdialysis experiments similarly show a facilitative role for dopamine, as levels of dopamine in the mPOA increase with mating. While the majority of evidence suggests an important role for dopamine receptors in the mPOA in the regulation of male sexual behaviors, whether sexual activity or sexual experience influence dopamine receptor function in the mPOA has not been previously shown. Here we used immunohistochemical assays to determine whether varying levels of sexual activity or experience influence the number of cells containing Fos or D2 receptor immunoreactivity. Results show that sexual experience facilitated subsequent behavior, namely experience decreased latencies. Moreover, the number of cells with immunoreactivity for Fos or D2 correlated with levels of sexual experience and sexual activity. Sexual activity increased Fos immunoreactivity. Sexually experienced animals also had significantly more D2-positive cells. Sexually inexperienced animals copulating for the first time had a larger percentage of D2-positive cells containing Fos, when compared to sexually experienced animals. Finally, regardless of experience, animals that had sex prior to sacrifice had significantly more D2-positive cells that contained Fos, vs. animals that did not copulate. These findings are noteworthy because sexually experienced animals display increased sexual efficiency. The differences in activation of D2 and changes in receptor density may play a role in this efficiency and other behavioral changes across sexual experience.
Highlights
Dopamine plays an important role in the regulation of male sexual behavior (Hull and Dominguez, 2015)
Studies show that dopamine agonists microinjected into the medial preoptic area (mPOA) facilitate sexual behavior, whereas microinjections of dopamine antagonists impair copulation, genital reflexes, and sexual motivation (Hull and Dominguez, 2015)
Dopamine levels increase in the mPOA during precopulatory exposure to an estrous female and during copulation (Hull and Dominguez, 2015)
Summary
Dopamine plays an important role in the regulation of male sexual behavior (Hull and Dominguez, 2015). Administration of dopamine antagonists inhibit anticipatory sexual behavior, as sexually experienced male rats receiving drugs display fewer anticipatory level changes, before the introduction of a sexually receptive female (Pfaus and Phillips, 1991) in a bilevel chamber that is used as an assay of sexual motivation (Mendelson and Pfaus, 1989) It appears that central, not peripheral, dopamine receptors facilitate erectile response, since erections elicited by systemically administered apomorphine were blocked by haloperidol (a centrally active dopamine antagonist) but not domperidone (a peripherally active dopamine antagonist) in mice (Rampin et al, 2003) and in rats (Pehek et al, 1988a)
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