The effect of apomorphine on genital reflexes in male rats deprived of paradoxical sleep

Drugs that stimulate dopamine (DA) systems can stimulate sexual arousal in male rats and humans, and previous work has shown that cocaine enhances genital reflexes [penile erection (PE) and ejaculation (EJ)] in rats deprived of paradoxical sleep (PS). The present study sought to expand the latter finding by assessing the effects of DA receptor agonist apomorphine in sleep-deprived rats. Apomorphine in doses ranging from 10 to 240 mug/kg was administered intraperitoneally to rats that had been deprived of sleep for 4 days and to normal controls, and the incidence of PEs and Us was measured for 60 min. Sleep deprivation alone induced PE and this effect was potentiated by apomorphine, with maximal effects occurring with the 120 mug/kg dose; results for this dose group differed from those of PSD groups treated with 0, 10, 20, 40, 80, and 240 mug/kg of apomorphine. Sleep deprivation alone also induced spontaneous EJ, but this response was not potentiated by apomorphine in the dose range tested. We suggest that the potentiating effects of apomorphine on PE are likely due to PSD-induced DA receptor supersensitivity. (C) 2003 Elsevier Inc. All rights reserved.