5-hydroxytryptamine(2C) receptors on spinal neurons controlling penile erection in the rat

The localization of 5-hydroxytryptamine(2C) receptors in the lumbosacral spinal cord of the rat was investigated using selective antibodies raised against the carboxyl-terminal part of the rat receptor. The distribution of immunoperoxidase labelling at the light microscope level revealed numerous labelled neurons in the gray matter, with a higher intensity in the sacral parasympathetic nucleus, the dorsal gray commissure and particularly the motoneurons of the ventral horn. Confocal microscope analysis showed that immunostaining was mainly intracellular (moroneurons), but could also be associated with the membrane of cell bodies and dendrites. Actually, electron microscope immunogold experiments demonstrated an exclusive staining of the cis-Golgi apparatus. Following pseudo-rabies virus transsynaptic retrograde labelling from the corpus cavernosum, labelled neurons were found in the sacral parasympathetic nucleus and the dorsal gray commissure of the L6-S1 segments. All virus-labelled neurons exhibited 5-hydroxytryptamine(2C) receptor immunoreactivity. These results indicate that all parasympathetic preganglionic neurons and their related interneurons which contribute to the innervation of cavernosal tissue bear 5-hydroxytryptamine(2C) receptors. In the sacral parasympathetic nucleus, most neurons which were retrogradely- labelled from the pelvic ganglion with Fast Blue also showed 5- hydroxytryptamine(2C) receptor immunoreactivity. In the ventral horn, motoneurons retrogradely labelled from the ischiocavernosus muscle and the bulbospongiosus muscle, both of which are involved in erection and ejaculation, were also 5-hydroxytryptamine(2C) receptor-immunopositive. The supraspinal serotoninergic control of erection at the lumbosacral level therefore appears to be strongly associated with the activation of 5- hydroxytryptamine(2C) receptors, consistent with the proerectile properties of 5-hydroxytryptamine(2C) agonists.