Evaluation of Origanum Vulgare L. ssp. Viridis Leaves Extract Effect on Discrimination Learning and LTP Induction in the CA1 Region of the Rat Hippocampus

Objective(s) The objective of this study was to determine the effect of aqueous extract of Origanum vulgare L. ssp. Viridis (ORG) on discrimination learning and long term potentiation (LTP) in CA1 region of the rat hippocampus. Materials and Methods A group of adult male Wistar rats weighing 275±25 g received aqueous extract of ORG (150, 300, 450 mg/kg/day) by intraperitoneal injection for one week, and the other group received saline (n= 6). A wooden T-maze was used to evaluate the discrimination learning. In electrophysiological experiments, the effect of ORG leaves extract on induction and maintenance of long term potentiation (LTP) in CA1 hippocampus area was determined. LTP was evaluated in CA1 region after high-frequency stimulation (200 Hz) of the Schaffer collaterals. Also, serum antioxidant levels were analyzed in the two groups (n= 4). Results Statistical analysis showed significant decreases in the number of total (significantly at the dose of 300 and 450 mg/kg) and wrong (significantly at the dose of 300 mg/kg) entrance into opposite box of T-maze procedure in ORG-treated animals (P< 0.05). In electrophysiological study, the rats which had received ORG (150, 300, and 450 mg/kg) showed an increase in both population spike amplitude (59.7±14.1%, 85±14.7% and 49.3±8.7% respectively, compared to 39±9.2% increase in saline group) and maintenance of LTP in hippocampus CA1 after high frequency stimulation in Schaffer collateral pathway. In serum antioxidant assay, level of antioxidants in ORG groups (300 and 450 mg/kg) remarkably increased in comparison to saline group (P< 0.05 and P< 0.001, in turn). Conclusion Our results suggest that Origanum aqueous extract can improve the learning criteria in rats.