A possible neural source of nitric oxide in the rat penis.

NADPH diaphorase staining was used to indicate the presence of nitric oxide synthase (NOS) in whole mounts of rat major pelvic ganglion (MPG) and sections of rat penis. Many stained neurons were observed in the MPG and were distributed in a manner identical to that of retrogradely labelled penile neurons described previously. Staining was also observed within many axons of the penile (cavernous) nerve and in varicose terminals associated with various tissues of the penis. The results suggest that many, if not all, penile neurons of the MPG contain NOS and that a neural source of NO within the penis is likely.