Direct nitric oxide-containing innervation from the rat spinal cord to the penis.

Nitric oxide synthase (NOS)-immunoreactive pathways to the rat penis were studied by combining retrograde tracing by Fluorogold with NOS immunohistochemistry. Injection of the tracer into the penile shaft resulted in Fluorogold labelling in a vast number of NOS-immunoreactive neurons in the major pelvic ganglion. In addition, some neurons in the spinal cord intermediolateral column consistently contained Fluorogold label in the upper lumbar levels. Most of these neurons were also NOS-immunoreactive. These findings suggest that the sympathetic preganglionic, NOS-containing neurons project to the penis, and they may participate in nitric oxide-mediated penile erection.