Functional evidence for nitrergic neurotransmission in a human clitoral corpus cavernosum: a case study.

Although the presence of neuronal nitric oxide synthase (nNOS) has been demonstrated in human clitoral corpus cavernosum, functional evidence for the nitrergic neurotransmission as a nonadrenergic noncholinergic (NANC) transmitter has been limited to animal studies. Here we show that electrical field stimulation elicited reproducible NANC relaxation responses in a clitoral corpus cavernosum, obtained from a 38-y-old woman undergoing clitoral reduction surgery. These relaxation responses were abolished by an inhibitor of NO synthase or tetrodotoxin proving that they were nitrergic in nature and neuronal in origin. Large and small calibre nitrergic nerves were demonstrated with immunohistochemistry using nNOS antibody, which were also immunostained with cholinergic nerve markers. nNOS expression was confirmed using Western blotting. This is the first report to show that NO produced by nNOS within the cholinergic-nitrergic nerves is responsible for the NANC relaxation responses in a human clitoral corpus cavernosum.