Phasic and tonic type A γ-Aminobutryic acid receptor mediated effect of Withania somnifera on mice hippocampal CA1 pyramidal Neurons

Background: In Nepali and Indian system of traditional medicine, Withania somnifera (WS) is considered as a rejuvenative medicine to maintain physical and mental health and has also been shown to improve memory consolidation. Objective: In this study, a methanolic extract of WS (mWS) was applied on mice hippocampal CA1 neurons to identify the receptors activated by the WS. Materials and Methods: The whole cell patch clamp recordings were performed on CA1 pyramidal neurons from immature mice (7-20 postnatal days). The cells were voltage clamped at -60 mV. Extract of WS root were applied to identify the effect of mWS. Results: The application of mWS (400 ng/μl) induced remarkable inward currents (-158.1 ± 28.08 pA, n = 26) on the CA1 pyramidal neurons. These inward currents were not only reproducible but also concentration dependent. mWS-induced inward currents remained persistent in the presence of amino acid receptor blocking cocktail (AARBC) containing blockers for the ionotropic glutamate receptors, glycine receptors and voltage-gated Na ⁺ channel (Control: -200.3 ± 55.42 pA, AARBC: -151.5 ± 40.58 pA, P > 0.05) suggesting that most of the responses by mWS are postsynaptic events. Interestingly, these inward currents were almost completely blocked by broad GABA _A receptor antagonist, bicuculline- 20 μM (BIC) (BIC: -1.46 ± 1.4 pA, P < 0.001), but only partially by synaptic GABA _A receptor blocker gabazine (1 μM) (GBZ: -18.26 ± 4.70 pA, P < 0.01). Conclusion: These results suggest that WS acts on synaptic/extrasynaptic GABA _A receptors and may play an important role in the process of memory and neuroprotection via activation of synaptic and extrasynaptic GABA _A receptors.