A role for nitric oxide in the median eminence and arcuate nucleus response to capsaicin treatment in rats

THIS study examined a possible functional involvement of nitric oxide (NO) in the median eminence (ME) :ind arcuate nucleus (ARC) after capsaicin trea tment in rats. Subcutaneous injection of capsaicin increased nicotinamide a denine dinucleotide phosphate diaphorase (NADPH-d) activity in the ARC-ME c ompared with vehicle treatment. Fos expression was increased in the ARC aft er capsaicin injection compared with vehicle-treated rats. Pretreatment wit h the NO synthase (NOS) inhibitor, NW-nitro-L-arginine methyl ester (L-NAME ) attenuated the effect of capsaicin on Fos expression and NADPH-d reactivi ty in the ARC-ME in comparison with rats injected with D-NAME, the inactive stereoisomer of L-NAME. These observations suggest that NO makes a major c ontribution to the response of the ARC-ME to a stressor such as capsaicin. (C) 1999 Lippincott Williams & Wilkins.