Paraventricular nucleus controls 5-HT2C receptor-mediated corticosterone and prolactin but not oxytocin and penile erection responses.

There is evidence that administration of the 5-HT2C receptor agonist, m-chlorophenylpiperazine (m-CPP), increases plasma concentrations of oxytocin, prolactin, corticosterone, induces penile erections and excessive grooming in male rats. To test the hypothesis that the hypothalamic paraventricular nucleus mediates these neuroendocrine and behavioural responses, we measured the effects of m-CPP (0.6 mg/kg i.v.) on these parameters in chronically cannulated, freely moving male rats after surgical lesion of the paraventricular nucleus or sham operation. Paraventricular nucleus lesion markedly attenuated prolactin, corticosterone and excessive grooming, but not oxytocin and penile erection responses to m-CPP. In contrast, both oxytocin and corticosterone responses to the dopamine receptor agonist, apomorphine (0.05 mg/kg i.v.), were attenuated in lesioned rats. The present studies suggest that the paraventricular nucleus mediates m-CPP-induced prolactin, corticosterone and probably also excessive grooming responses, and the mechanisms of apomorphine and m-CPP action on oxytocin secretion and penile erection responses differ.