Document Type : Original Article
Learning and Memory Lab, Physiology Research Center, Semnan University of Medical Sciences
Objective: Strong evidence indicate that activity of glucocorticoid receptors is necessary for emotional memory processess and these effects probably are mediated by hipppocampal opioid receptors. The aim of this study was to test whether there were any interaction between glucocorticoid and hippocampal opiate receptors on consolidtaion and retrieval of spatial memory.
Materials and Methods: In this experimental study, 120 male Wistar rats (250 – 300 gr) were used. At first, the animals underwent surgery implant canulae in bilateraly of dorsal hippocampus (DH). Then one week later they were trained in a Water Maze task with eight trials for one day for consolidation and six trials per day for six consecutive days for retrieval processes. The retention of the spatial training was assessed 24h after the last training session with a 60-s probe trial. Corticosterone (1 mg/kg the best dose) was injected IP immediately after training or 30 min before retrieval. Also Nalthroxone (10 and 20 μg/ul/ per side) was injected bilaterally into hippocmapus immediately after training or 60 min before retrieval test.
Results: The results indicated that injection of corticostrone immediatly after training or 30 min before retention significantly enhanced or impaired consolidation and retrieval memory respectively (p<0.01) and these effects were blocked by injection of naltroxone in to DH (p<0.05) in either cases.
Conclusion: The findings suggest that the opioid receptors in hippocampus play an important role in mediating the enhancing or impairing effects of systemic corticosterone on memory consolidation and retrieval.