Repeated administration of the nitric oxide synthase inhibitor L-NAME differentially affects rats' recognition memory

Nitric oxide (NO) is sought to be an intracellular messenger in the central nervous system and its implication in learning and memory is well documented. Compounds that inhibit nitric oxide synthase (NOS), the key synthesizing enzyme, block cognition, though discrepant findings, in this context, have also been reported. The present study was designed to investigate in the rat (a) the effects of repeated treatment with the NOS inhibitor L-NAME (1, 3 and 10 mg/kg, i.p., for 5 consecutive days) on rats' recognition memory and (b) whether or not at this treatment condition, L-NAME (1,3 and 10 mg/kg, i.p., for 5 consecutive days), was able to counteract delay-dependent recognition memory deficits. For this aim, the novel object recognition task was selected. L-NAME (3, but not 1 or 10 mg/kg) disrupted rats' performance in this recognition memory paradigm as compared to that expressed by their vehicle-treated cohorts. Subsequently, L-NAME (1 and 10, but not 3 mg/kg)-treated rats were capable to antagonize delay-dependent deficits, which instead were present in the vehicle-treated animals. These results indicate that repeated administration of this NOS inhibitor exerts a dual effect on rats' recognition memory abilities suggesting a complex involvement of L-NAME in cognition. (C) 2011 Elsevier B.V. All rights reserved.