Oxytocinergic innervation of autonomic nuclei controlling penile erection in the rat.

In the rat, spinal autonomic neurons controlling penile erection receive descending pathways that modulate their activity. The paraventricular nucleus of the hypothalamus contributes oxytocinergic fibers to the dorsal horn and preganglionic sympathetic and parasympathetic cell columns. We used retrograde tracing techniques with pseudorabies virus combined with immunohistochemistry against oxytocin and radioligand binding detection of oxytocinergic receptors to evidence the oxytocinergic innervation of thoracolumbar and lumbosacral spinal neurons controlling penile erection. Spinal neurons labelled with pseudo-rabies 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 close appositions between oxytocinergic varicosities and pseudorabies virus-infected neurons, suggesting strongly the presence of synaptic contacts. Electron microscopy confirmed this hypothesis. Oxytocin binding sites were present in the superficial layers of the dorsal horn, the dorsal gray commissure and the intermediolateral cell column in both the thoracolumbar and lumbosacral 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 paraventriculo-spinal pathways, activates proerectile spinal neurons.

Expression of alpha 1 adrenoceptor subtypes in rat corpus cavernosum.

Norepinephrine mediates the antierectile role of the sympathetic nervous system. It binds to postsynaptic alpha 1 adrenoceptors present on smooth muscle fibers of the corpus cavernosum. Receptor cloning studies have evidenced three alpha 1 adrenoceptor subtypes: alpha 1A, alpha 1B and alpha 1D. We searched for the presence of these three alpha 1 adrenoceptor subtypes in the rat corpus cavernosum using in situ hybridization with specific oligonucleotide probes. Brain tissue was used as the reference of probes specificity. Autoradiographic films were studied with light illumination and computer-assisted densitometry using an image analyser. We provide evidence that the three alpha 1 adrenoceptor subtypes are expressed in the rat corpus cavernosum. These three subtypes appear to be more expressed in the trabecular smooth muscle fibers than in vascular smooth muscle fibers. Further experiments are needed to determine whether the proportion of alpha 1 adrenoceptor subtypes changes according to the etiology of erectile dysfunction. This morphological approach provides a basis for future pharmacological research of specific alpha 1 adrenoceptor subtypes blocking agents designed to treat erectile dysfunction.