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Protein Inhibitor of Nitric Oxide Synthase (NOS) and the N-Methyl-D-Aspartate Receptor Are Expressed in the Rat and Mouse Penile Nerves and Colocalize with Penile Neuronal NOS¹

^a Department of Urology, UCLA School of Medicine, Los Angeles, California 90095 ^b Research and Education Institute, Harbor-UCLA Medical Center, Torrance, California 90502 ^c Johns Hopkins University, Department of Urology, Baltimore, Maryland 21287

Nitrergic neurotransmission triggering penile erection is mediated by nitric oxide (NO) synthesized in the cavernosal nerves of the penis by penile neuronal NO synthase (PnNOS). In the central nervous system, nNOS is activated by the N-methyl-D-aspartate receptor (NMDAR) and, presumably, is inhibited by the protein inhibitor of NOS (PIN). The PnNOS and NMDAR are expressed in the penis, and PnNOS has been localized in penile nerves. Both proteins colocalize with PIN in the hypothalamus and the spinal cord involved in the control of erection. The present study aimed to elucidate the relationship between PnNOS, PIN, and NMDAR in the penis. It was found that in the rat, PIN was expressed in the pelvic ganglion and the cavernosal nerve, and penile PIN cDNA was cloned, sequenced, and expressed. Immunohistochemistry localized PIN to the cavernosal and dorsal nerve of the penis, whereas NMDAR was not detected in the latter. Dual-fluorescence labeling showed that PnNOS colocalized with PIN in both nerves but with NMDAR only in the cavernosal nerve. Aging did not affect the mRNA levels of PnNOS, nNOS, NMDAR, and PIN. Both PIN and NMDAR were detected in penile nerves of the wild-type and nNOS^-/- mouse. The PIN protein did not inhibit or bind NOS in penile extracts, and in vivo, PIN cDNA reduced the erectile response to electrical field stimulation. In conclusion, PIN and NMDAR colocalize with PnNOS in penile nerves, but the functional significance of these protein interactions for penile erection remains to be elucidated.

¹ Funded by NIH grant R01DK-53069 to N.G.C. and in part by NIH Program grant G12RR-03026.

² Correspondence: Nestor F. Gonzalez-Cadavid, Harbor-UCLA Research and Education Institute, Urology, Bldg. F-6, 1124 West Carson Street, Torrance, CA 90502. FAX: 310 222 1914; ncadavid{at}ucla.edu

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