ABSTRACT
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. A group of adult male Wistar rats weighing 275 +/- 25 g received aqueous extract of ORG [150, 300, 450 mg/kg/day] by intraperitoenal 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 effects of ORG leaves extract on induction and maintenance 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]. 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]. Our result suggest that Origanum aqueous extract can improve the learning criteria in rats