Evaluation the role of hippocampal Kappa opioid receptors in retrieval of spatial memory in rats

Previous studies indicated that hippocampal opioid receptors have an important role in memory retrieval, but the underyling subtypes of opioid receptors are not known. The aim of the present study was investigate to examine the role of hippocampal kappa opioid receptors on spatial memory retrieval in a water maze. 80 young rats (250-300 gr) in Wistar strain, carrying bilateral cannulae aimed at the hippocampus were trained in a WM task with six trials per day for six consecutive days. Retention of the spatial training was assessed 24h after the last training session with a 60-s probe trial. Animals were received inta-hippocampal injections of U111 (0.8, 2, 5 μg/0.5 μl per site), a selective kappa opioid receptor agonist or N-BNI (0.75, 1.5 and 3 μg/0.5 μl per site), a selective kappa opioid receptor antagonist 60 min before retention testing. Control animals received same volume of saline. The results showed that both U111 (0.8, 5 μg) and N-BNI in all tested doses induced an impairment of spatial memory retrieval as compared with control animals (P<0.05). Findings above indicated that hippocampal kappa opioid receptors have an important role in regulating of spatial memory retrieval.