Ginkgo biloba extract enhances noncontact erection in rats: The role of dopamine in the paraventricular nucleus and the mesolimbic system

Penile erection is essential for successful copulation in males. Dopaminergic projections from the paraventricular nucleus (PVN) to the ventral tegmental area (VTA) and from the VTA to the nucleus accumbens (NAc) are thought to exert a facilitatory effect on penile erection. Our previous study showed that treatment with an extract of Ginkgo biloba leaves (EGb 761) enhances noncontact erection (NCE) in male rats. However, the relationship between NCE and dopaminergic activity in the PVN, VTA, and NAc remains unknown. The present study examined the relationship between NCE and central dopaminergic activity following EGb 761 treatment. We report here that, in comparison with the controls, there was a significant increase in the number of NCEs in rats after treatment with 50 mg/kg of EGb 761 for 14 days. EGb 761-treated rats also showed more NCEs than the same group before EGb 761 treatment. A significant increase in the expression of catecholaminergic neurons in the PVN and the VTA was seen by means of tyrosine hydroxylase immunohistochemistry, and tissue levels of dopamine and 3,4-dihydroxyphenylacetic acid in the NAc were also markedly increased in the EGb 761-treated animals. However, the norepinephrine tissue levels in the PVN and the NAc in the EGb 761-treated group were not significantly different from those in the controls. Together, these results suggest that administration of EGb 761 increases dopaminergic activity in the PVN and the mesolimbic system to facilitate NCE in male rats.