Nitric oxide in the dorsal hippocampal area is involved on muscimol state-dependent memory in the step-down passive avoidance test

In the present study, the effects of intra-dorsal hippocampal (intra-CA1) injections of nitric oxide (NO) agents on muscimol state-dependent memory were examined in mice. A single-trial step-down passive avoidance task was used for the assessment of memory retrieval in adult male NMRI mice. Post-training intra-CA1 administration of a GABA(A) receptor agonist, muscimol (0.05 and 0.1 mu g/mouse) dose dependently induced impairment of memory retention. Pre-test injection of muscimol (0.05 and 0.1 mu g/mouse) induced state-dependent retrieval of the memory acquired under post-training muscimol (0.1 mu g/mouse, intraCA1) influence. Pre-test injection of a NO precursor, L-arginine (1 and 2 mu g/mouse, intra-CAI) improved memory retention, although the low dose of the drug (0.5 mu g/mouse) did not affect memory retention. Pre-test injection of an inhibitor of NO-synthase, L-NAME (0.5 and 1 mu g/mouse, intra-CAI) impaired memory retention, although the low dose of the drug (0.25 mu g/mouse) did not affect memory retention. In other series of experiments, pre-test intra-CAI injection of L-arginine (0.25 and 0.5 mu g/mouse) 5 min before the administration of muscimol (0.1 mu g/mouse, intra-CAI) dose dependently inhibited muscimol statedependent memory. Pre-test intra-CAI administration of L-arginine (0.125, 0.25 and 0.5 mu g/mouse) by itself cannot affect memory retention. Pre-test intra-CA1 injection of L-NAME (0.25 mu g/mouse, intra-CA1) reversed the memory impairment induced by post-training administration of muscimol (0.1 mu g/mouse, intra-CA1). Moreover, pre-test administration ofi.NAME (0.125 and 0.25 mu g/mouse, intra-CAI) with an ineffective dose of muscimol (0.025 mu g/mouse, intra-CA1) significantly restored the retrieval and induced muscimol state-dependent memory. Pre-test intra-CAI administration of L-NAME (0.0625, 0.125 and 0.25 mu g/mouse) by itself cannot affect memory retention. It may be suggested that the nitric oxide in the dorsal hippocampal area play an important role in muscimol statedependent memory. (C) 2013 Elsevier Inc. All rights reserved.