Evidence for an involvement of peripheral serotonin in p-chloroamphetamine-induced ejaculation of rats

The purpose of the present study was to determine the mechanism of the ejaculatory response induced by the 5-HT-releasing compound p-chloroamphetamine (PCA) in rats. The ejaculatory response was assessed by weighing the coagulated seminal materials accumulated over 1 h. Intraperitoneal injection of PCA (0.5-5.0 mg/kg) produced a dose-related increase in both the incidence of ejaculation and the weight of the accumulated seminal materials. The ejaculatory response induced by PCA (5.0 mg/kg) was abolished by pretreatment with the 5-HT synthesis inhibitor p-chlorophenylalanine, the 5-HT receptor antagonists methysergide and MDL72222, or by the selective 5-HT reuptake inhibitor citalopram, suggesting that the 5-HT-releasing property of PCA mainly involved the expression of ejaculation. Neither the section of the spinal cord at thoracic (T8-9) level nor the lumbosacral spinal 5-HT denervation by intrathecal (i.t.) injection of 5,7-dihydroxytryptamine affected the ejaculatory response induced by PCA. The i.t. injection of PCA (20-160 μg/rat) at lumbosacral spinal level did not exert the systemic PCA-like prominent effect on ejaculation, whereas i.t. injection of lidocain at the same site completely abolished the response to systemic PCA. Additionally, the peripherally administered 5-HT (0.1 and 0.25 mg/kg, i.p.) enhanced the proejaculatory effect at a threshold dose (1.0 mg/kg, i.p.) of PCA. From these observations, it is concluded that the ejaculatory response induced by PCA is mainly a spinally mediated reflex response that is triggered by the release of 5-HT in the peripheral sites.