Evaluation of Origanum Vulgare L. ssp. Viridis Leaves Extract Effect on Discrimination Learning and LTP Induction in the CA۱ 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 CA۱ region of the rat hippocampus. Materials and Methods A group of adult male Wistar rats weighing ۲۷۵±۲۵ g received aqueous extract of ORG (۱۵۰, ۳۰۰, ۴۵۰ mg/kg/day) by intraperitoneal injection for one week, and the other group received saline (n= ۶). 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 CA۱ hippocampus area was determined. LTP was evaluated in CA۱ region after high-frequency stimulation (۲۰۰ Hz) of the Schaffer collaterals. Also, serum antioxidant levels were analyzed in the two groups (n= ۴). Results Statistical analysis showed significant decreases in the number of total (significantly at the dose of ۳۰۰ and ۴۵۰ mg/kg) and wrong (significantly at the dose of ۳۰۰ mg/kg) entrance into opposite box of T-maze procedure in ORG-treated animals (P< ۰.۰۵). In electrophysiological study, the rats which had received ORG (۱۵۰, ۳۰۰, and ۴۵۰ mg/kg) showed an increase in both population spike amplitude (۵۹.۷±۱۴.۱%, ۸۵±۱۴.۷% and ۴۹.۳±۸.۷% respectively, compared to ۳۹±۹.۲% increase in saline group) and maintenance of LTP in hippocampus CA۱ after high frequency stimulation in Schaffer collateral pathway. In serum antioxidant assay, level of antioxidants in ORG groups (۳۰۰ and ۴۵۰ mg/kg) remarkably increased in comparison to saline group (P< ۰.۰۵ and P< ۰.۰۰۱, in turn). Conclusion Our results suggest that Origanum aqueous extract can improve the learning criteria in rats.

Keywords:

Antioxidant assay , Long term potentiation , Medicinal plant , Origanum vulgare , Spatial learning , T-maze