Fos activation and upregulation of nicotinamide adenine dinucleotide phosphate diaphorase in the rat pituitary by acute capsaicin injection

In this study, we examined the effect of acute capsaicin injection on nicot inamide adenine dinucleotide phosphate diaphorase (NADPH-d, a histochemical index of nitric oxide, NO, synthase) and Fos expression in the rat pituita ry gland. Compared with vehicle, capsaicin significantly activated Fos expr ession in the anterior and intermediate robes. In addition, capsaicin-treat ed rats showed a significant upregulation of NADPH-d in the anterior and ne ural lobes. Pretreatment of the animals with a specific NO synthase inhibit or, N-omega-nitro-L-arginine methyl ester (L-NAME), significantly attenuate d the capsaicin-induced Fos expression in the anterior and intermediate lob es. These observations suggest that NO is a key regulator of the acute effe ct of capsaicin on the pituitary gland. (C) 2000 Published by Elsevier Scie nce Ireland Ltd.