MODULATION OF AMERICAN GINSENG ON BRAIN-STEM GABAERGIC EFFECTS IN RATS

Single neurons in the region of the medial nucleus tractus solitarius (NTS), responding or not responding to gastric vagal branch stimulatio n, were recorded in an in vitro neonatal rat brainstem-gastric prepara tion. The spontaneous activity of the majority of these two types of N TS units was inhibited by GABA, receptor agonist, muscimol (30 mu M), and this inhibition (approximately 52% compared to 100% of the control level) could be antagonized by selective GABA, receptor antagonist, b icuculline (10 mu M). Application of Panax quinquefolium L. extracts ( 3.0 mu g/ml) into the brainstem compartment of the preparation also si gnificantly reduced the discharge rate of these NTS neurons (approxima tely 27% compared to the control level), but this reduction could not be reversed by bicuculline (10 CIM). Pretreatment with Panax quinquefo lium L. (3.0 mu g/ml) significantly decreased the NTS inhibitory effec ts induced by muscimol (30 mu M), approximately from 51 to 33%. Our re sults demonstrated the interactions of Panax quinquefolium L. with lig and-bindings of GABA(A) receptors, and the modulation of the brainstem GABAergic mechanism by Panax quinquefolium L. Our data suggest that t he regulation of GABAergic neurotransmission may be an important actio n of Panax quinquefolium L. (C) 1998 Published by Elsevier Science Ire land Ltd. All rights reserved.