Oxytocin and the Gastrin-Releasing Peptide System in the Spinal Cord: Implications for Male Sexual Problems

Neural circuits underlying male sexual function comprise several nuclei located in the brain and spinal cord. We have previously demonstrated in rats that the gastrin-releasing peptide (GRP) system influences spinal centers promoting penile reflexes. Moreover, a group of oxytocin (OXT) neurons, situated in the parvocellular part of the paraventricular nucleus of the hypothalamus, project into the spinal cord and control penile reflexes. Therefore, it has been hypothesized that OXT is transported by long descending paraventriculospinal pathways and activates proerectile spinal centers. Consequently, we have shown that in rats, axonal distribution of OXT in the lumbar spinal cord exhibits a male-dominant sexual dimorphism. Furthermore, OXT binding is observed in the spinal GRP neurons. Thus, OXT axons may secrete OXT from spinal axonal terminals and regulate male sexual function via an OXT receptor-mediated mechanism in spinal GRP neurons. Future studies should address the relationship between the hypothalamic OXT and spinal GRP systems. Identification of the male-specific brain-spinal cord neural circuit that regulates male sexual behavior may provide new avenues for therapeutic approaches to masculine reproductive dysfunction, including erectile dysfunction and/or ejaculation disorder.