ANXIOLYTIC EFFECT OF NITRIC-OXIDE SYNTHASE INHIBITORS MICROINJECTED INTO THE DORSAL CENTRAL GREY

NITRIC oxide synthase (NOS) accounts for most of the NADPH-diaphorase neuronal activity in the brain. NADPH-diaphorase-positive neurones have been localized at the dorso-lateral part of the periaqueductal grey (FAG), a region related to anxiety. Microinjections of the NOS inhibitors L-NAME (10-200 nmol 0.5 mu l(-1)) and L-NOARG (10-100 nmol) at this site induced anxiolytic-like effects in the elevated plus maze. These effects, however, occurred only at a limited range of doses and the dose-effect curve had a bell shape, higher doses of both compounds tending to be anxiogenic. The anxiolytic effect of L-NAME was antagonized by a previous microinjection of L-arginine (50 nmol 0.5 mu l(-1)). These results suggest that NO may play a role in FAG neurotransmission involved in anxiety.