Endocrine Abstracts

Central dopamine and oxytocin have been shown in many studies to facilitate aspects of male sexual function. However, it is poorly understood how these two neuromodulators interact to mediate sexual behaviour or which receptors are involved. Much evidence has recently implicated a role for the dopamine D2 receptor in the paraventricular nucleus (PVN) and supraoptic nucleus (SON) in regulating aspects of male sexual behaviour. Using Sprague-Dawley male rats (225–250 g), we investigated the hypothesis that Quinelorane, a non-selective D2-like agonist, increases penile erection frequency and activates oxytocin neurones within the hypothalamic nuclei, using Fos as a marker of neuronal activation. Either Quinelorane (0.5 μg/μl, n=7) or vehicle (2 μl, n=5) was given via a previously implanted intracerebroventricular cannula and the effect on penile erection observed. Brains were collected and processed by double immunocytochemistry for Fos and oxytocin. Quinelorane significantly increased the number of penile erections per rat compared to vehicle (P<0.05). It also significantly increased the number of Fos-positive oxytocin neurons in the parvocellular PVN compared to vehicle (P<0.05), particularly within the medial parvocellular region (P<0.05). In contrast there were no significant differences found in the magnocellular PVN or the SON. Additionally, brains from other male rats (225–250 g) were processed by double fluorescence immunocytochemistry for the dopamine D2 receptor and oxytocin in the PVN and SON. Co-localisation of the D2 receptor and oxytocin in neurones of the PVN and SON provided anatomical evidence that oxytocin neurones express D2 receptor. The data show that Quinelorane has a clear proerectile effect and suggest that it activates parvocellular oxytocin neurones in the PVN but not magnocellular neurones in the PVN or SON during penile erection.

Supported by Pfizer Pharmaceuticals.