A LARGE PROPORTION OF PELVIC NEURONS INNERVATING THE CORPORA CAVERNOSA OF THE RAT PENIS EXHIBIT NADPH-DIAPHORASE ACTIVITY

Nicotinamide adenine dinucleotide phosphate (NADPH)-diaphorase histoch emistry, which indicates the presence of neural nitric oxide synthase, the enzyme responsible for the generation of nitric oxide, was used i n combination with retrograde labelling methods to determine, in whole -mounts and sections of rat major pelvic ganglia, whether neurons dest ined for the penile corpora cavernosa were able to produce nitric oxid e. In wholemount preparations of pelvic ganglia, among the 607 +/- 106 retrogradely labelled neurons innervating the penile corpora cavernos a, 84 +/- 7% were NADPH-diaphorase-positive, 30 +/- 7% of which were i ntensely histochemically stained. In serial sections of pelvic ganglia , out of a mean count of 451 retrogradely labelled neurons, 65% staine d positively for NADPH-diaphorase. An average of 1879 +/- 363 NADPH-di aphorase positive cell bodies was counted in the pelvic ganglion. In t he major pelvic ganglion, neurons both fluorescent for Fluorogold or F ast Blue and intensely stained for NADPH-diaphorase were consistently observed in the dorso-caudal part of the ganglia in the area close to the exit of the cavernous nerve and within this nerve. This co-existen ce was much less constant in other parts of the ganglion. In the rat p enis, many NADPH-diaphorase-positive fibres and varicose terminals wer e observed surrounding the penile arteries and running within the wall of the cavernous spaces. This distribution of NADPH-diaphorasepositiv e nerve cells and terminals is consistent with the idea that the relax ation of the smooth muscles of the corpora cavernosa and the dilation of the penile arterial bed mediated by postganglionic parasympathetic neurons is attributable to the release of nitric oxide and that nitric oxide plays a crucial role in penile erection. Moreover, the existenc e in the pelvic ganglion of a large number of NADPH-diaphorase-positiv e neurons that are not destined for the corpora cavernosa suggests tha t nitric oxide is probably also involved in the function of other pelv ic tissues.