GABA-mimetic actions of Withania somnifera on substantia gelatinosa neurons of the trigeminal subnucleus caudalis in mice

The plant Withania somnifera (WS), also known as Ashwagandha, has been used widely in traditional medicine systems in India and Nepal (Ayurveda), and has been accepted to cure various ailments. In this study, the whole-cell patch clamp technique was performed to examine the mechanism of action of WS on the SG neurons of the Vc from mouse brainstem slices. In whole-cell patch clamp mode, methanol extract of Withania somnifera (mWS) induced short-lived and repeatable inward currents in all SG neurons tested (31.3±8.51 pA, n = 7) using a high chloride pipette solution. The mWS-induced inward currents were concentration dependent and maintained in the presence of tetrodotoxin (TTX), a voltage gated Na⁺ channel blocker, CNQX, a non-NMDA glutamate receptor antagonist, AP5, an NMDA receptor antagonist and strychnine, a glycine receptor antagonist. The mWS induced currents were blocked by picrotoxin, a GABA_A receptor antagonist. These results show that mWS has an inhibitory effects on SG neurons of the Vc through GABA_A receptor-mediated activation of chloride ion channels, indicating that mWS contains compounds with sedative effects on the central nervous system. These results also suggest that mWS may be a potential target for modulating orofacial pain processing.