ACUTE INHIBITION OF NITRIC-OXIDE SYNTHESIS INDUCES ANXIOLYSIS IN THE PLUS-MAZE TEST

The involvement of nitric oxide (NO) in anxiety was investigated in ra ts, using the elevated plus maze test. Acute, but not chronic, systemi c treatment with N omega-nitro-L-arginine methyl ester(L-NAME, 10 and 60 mg.kg(-1)), an inhibitor of NO synthase, increased the time spent b y the rats in the open arms. Both the acute and chronic treatments wit h L-NAME inhibited NO synthase in endothelial cells and in the central nervous system, as shown by the increase in mean arterial pressure an d decreased NO synthase activity in brain tissue. Chronic treatment wi th L-NAME also decreased the serum nitrate levels. The anxiolysis indu ced by acute L-NAME treatment is unlikely to be due to hypertension, s ince two-kidney one-clip hypertension in non-L-NAME-treated rats faile d to significantly change exploratory behaviour in the elevated plus m aze. These results indicate that acute inhibition of NO synthesis decr eases anxiety in rats. (C) 1997 Elsevier Science B.V.