Apomorphine and L-DOPA lower ejaculation threshold in the male rat

Pharmacological analysis of male rat sexual behavior

“…In vigorous copulators, I-DOPA significantly decreased both ejaculation latency and the number of intromissions preceding ejaculation [176,213]. I-DOPA is the precursor molecule for both DA and NE.…”

“…In accord with the facilitative effects of increased DA synthesis, systemic injections of apomorphine, a DA receptor agonist, dramatically reduced the number of intromissions preceding ejaculation [54,61,85,176,213]. The reduction in ejaculatory threshold induced by apomorphine was blocked by the DA receptor antagonists halopendol, pimozide, and sulplride [85,176,213].…”

“…The reduction in ejaculatory threshold induced by apomorphine was blocked by the DA receptor antagonists halopendol, pimozide, and sulplride [85,176,213]. Apomorphlne's effects on male copulatory behavior appear to be mediated by central, rather than peripheral DA receptors, since systemic administration of domperidone, a DA antagomst that does not cross the blood-brain barrier, was ineffective in blocking apomorphlne-lnduced facilitation of sexual behavior [85].…”

“…Some investigators [22,61,64,65,85,96,169,176] have proposed that the reduction m ejaculatory threshold by DA agomsts results from the selectwe activation of presynaptic autoreceptors, which decrease the release of endogenous DA, thereby reducing postsynaptic actlvlty This hypothesis was based largely on the observation that the doses of DA agonists that reduced e, laculatory threshold were lower than those that usually result in hyperactivity, a commonly accepted indication of postsynaptlc activation. Thus, inhibition of dopaminerglc neurotransmission was hypothesized to facilitate an ejaculatory mechanism.…”

Dopamine, the medial preoptic area, and male sexual behavior

“…Earlier studies showed that systemic administration of l-dopa resulted in more rats displaying sexual behaviors, compared with controls [9,10]. Administration of apomorphine also resulted in decreased ejaculation threshold, with rats requiring less time to reach an ejaculation and a larger percentage of them achieving ejaculations [10].…”