Background & Objectives: I ntra-hippocampal adminestration of origanum (ORG) improves spatial learning of rats. T he aim of the present study was to investigate the possible mechanism for origanum extract on spatial learning and memory in the hippocampus.

  Methods : In this study 42 adult male Wistar rats were used . Animals were cannulated bilaterally in the posterior laterl of hippocampus. After the recovery period, the spatial learning and memory were assessed using Morris Water Maze (MWM). Saline, ORG (0.03μg/site) glutamate receptor antagonist MK801 (0.08, 0.2 and 0.4 μmol/site) and co-injected of MK + ORG was injected into the posterior lateral of hippocampus 20 minutes before the training and retrival sesions (for 5 consecutive days) (n=7).

  Results: The results showed that the intra-hippocampal injection of MK 801 significantly blocked the decreased distance and time of reaching (due to ORG injection) to find hidden platform of MWM (p<0.05). On the retrival tests, the average of time spent in the target area is reduced in the co-injected of MK801 + ORG group.

  Conclusion: The intra-hippocampal injection of aqueous extract of�origanum may improve working memory in rats through glutamate-dependent NMDA receptors.