Effect of intrahippocampal L-NAME injection on passive avoidance memory in adult male rats exposed to restraint stress

Introduction: Nitric oxide is an important messenger in hippocampal region which is affected in learning and memory processes and hippocampal responses to stress. In this study, we investigated the effect of L-NAME on passive avoidance memory in adult male rats exposed to restraint-stress. Methods: For this purpose, male Wistar rats were bilaterally implanted with cannulas aimed at the CA1 region of the hippocampus. Thirty min after intrahippocampl injections of saline (alone) or L-NAME (20, 40 and 80μg/0.5μl/side) animals were immobilized in restrainer for 2 h/day for 7 days (7 days after surgery), and then were tested for step-through latency and the time-spent in dark chamber in inhibitory avoidance task. Results: Our findings showed that intrahippocampal injection of L-NAME (80 μg/0.5 μl/side) significantly increased the step-through latency and decreased the time spent in the dark chamber in comparison with the control group. Conclusion: Since the inhibition of NO synthesis resulted in memory and learning improvements in rats exposed to restraint-stress, NO might be involved in stress related learning and memory deficits.