Figure 2: A novel hypothesis in terms of the oxytocin (OXT)-GRP system, which controls male sexual functions in the lumbar spinal cord. Hypothalamic OXT-ergic efferents may trigger ejaculation via an OXT receptor-mediated mechanism in the spinal GRP system during male sexual behaviour. Abbrev: pPVN, parvocellular part of the hypothalamic paraventricular nucleus.