Evidence for an involvement of nitric oxide in memory of shock avoidance task in rats.

Nitric oxide (NO), which occurs as a gaseous chemical messenger in the brain, is synthesized from L-arginine by nitric oxide synthase (NOS) as a coproduct of L-citrulline (1). NO has been well documented to have a neurotransmitter/neuromodulator role in the brain (2). Studies carried out on passive avoidance response of rats treated with Larginine and N-nitro-L-arginine methyl ester (L-NAME), and inhibitor of NOS (3), have suggested that NO has a significant role in learning and memory processes. In these studies, memory has been found to be faciLitated following an increased synthesis of NO in animals treated with L-arginine (4). Conversely, administration of a NO decreasing dose of L-NAME has impaired memory of rats to radial arm maze task (5). However, the effect of L-arginine and LNAME have not been tested on memory of rats to previously learnt active avoidance task. Thus, the present study has been designed to assess the effects of these compounds on shock avoidance task of rats using a traditional pole-climbing apparatus (6). The effect of L-arginine was tested in LNAME-pretreated animals also.