State-dependent impairment in object recognition after hippocampal NOS inhibition

IN the present study we investigated the consequences of hippocampal nitric oxide synthase (NOS) inhibition on the performance in an object recognition task in rats. In a first study we injected N-omega-nitro-L-arginine (LNA) into the hippocampus directly after the first trial. One hour later the discrimination performance of the animals was assessed. It was found that 10 mu g and 30 mu g, but not 3 mu g, L-NA impaired the performance of the rats. In a second study in which we injected L-NA 45 min before the first trial no effects of treatment (10 mu g and 30 mu g) were observed. Since treatment with 30 mu g has been found to inhibit hippocampal NOS almost completely and lasts longer than 2 h, it was concluded that hippocampal NOS inhibition induced a state-dependent performance deficit. Consequently, studies that examine the effects of NOS inhibition on cognitive functions should take this confounding effect into account. (C) 1998 Lippincott Williams & Wilkins.