Oxytocinergic innervation of autonomic nuclei controlling penile erection in the rat

In the rat, spinal autonomic neurons controlling penile erection receive de scending pathways that modulate their activity. The paraventricular nucleus of the hypothalamus contributes oxytocinergic fibers to the dorsal horn an d preganglionic sympathetic and parasympathetic cell columns. We used retro grade tracing techniques with pseudorabies virus combined with immunohistoc hemistry against oxytocin and radioligand binding detection of oxytocinergi c receptors to evidence the oxytocinergic innervation of thoracolumbar and lumbosacral spinal neurons controlling penile erection. Spinal neurons labe lled with pseudorabies virus transsynaptically transported from the corpus cavernosum were present in the intermediolateral cell column and the dorsal gray commissure of the thoracolumbar and lumbosacral spinal cord. Confocal laser scanning microscopic observation of the same preparations revealed c lose appositions between oxytocinergic varicosities and pseudorabies virus- infected neurons, suggesting strongly the presence of synaptic contacts. El ectron microscopy confirmed this hypothesis. Oxytocin binding sites were pr esent in the superficial layers of the dorsal horn, the dorsal gray commiss ure and the intermediolateral cell column in both the thoracolumbar and lum bosacral segments. In rats, stimulation of the paraventricular nucleus induces penile erection , but the link between the nucleus and penile innervation remains unknown. Our findings support the hypothesis that oxytocin, released by descending p araventriculo-spinal pathways, activates proerectile spinal neurons. (C) 19 99 IBRO. Published by Elsevier Science Ltd.