Background: Hippocampus is well known to be involved in learning and memory. It is proved that antioxidants improve learning and memory. Origanum vulgare L. ssp. Viridis (ORG) is a rich source of antioxidants. The aim of this study was to investigate the effect of intra-hippocampal injection of aqueous extract of ORG on spatial learning and memory.

Materials and Methods: Twenty-eight adult male Wistar rats (275-300gr) were used in this study. The animals were bilaterally canulated in dorsolateral hippocampus. One week after recovery the animals were trained (4 trails for four consecutive days) in Morris water maze (MWM). Then, the retention of spatial training was evaluated in the fifth day. Twenty minutes before the training or retrieval test, different concentrations of ORG (0.003, 0.03 and 0.3 µl/rat) or saline were injected into the hippocampus.

Results: Repeated-measure ANOVA showd that intra-hippocampal injection of ORG significantly decreased the distance and time of reaching to hidden platform in MWM, Intra-hippocampal injection of ORG in the retrieval day did not show any significant difference in the duration of target zone and the platform proximity compared to the saline group.

Conclusion: The intra-hippocampal injection of Origanum aqueous extract improves the rat working memory in MWM however it doesn't affect on the consolidation of memory.