GABAergic effects on nucleus tractus solitarius neurons receiving gastric vagal inputs

Single units in the region of the medial nucleus tractus solitarius (NTS), responding to electrical stimulation of gastric vagal fi-bers, were recorded in an in vitro neonatal rat brainstem-gastric preparation. g-Aminobutyric acid (GABA) subreceptor agonists and antagonists were applied to the gastric and brainstem compartments of the bath chamber to evaluate the peripheral gastric and central brainstem GABAergic effects on NTS neu-ronal activity. The gastric effects of the GABAA receptor agonist muscimol and GABAB receptor agonist baclofen were evalu-ated on 55 tonic units that received the gastric vagal inputs. For;58 % (32 of 55) and 38 % (21 of 55) of the units observed, muscimol (30 mM; IC50 5 2.0 mM) and baclofen (30 mM; IC50 5 1.5 mM) in the gastric compartment induced a concentration-dependent inhibition of 36.2 6 3.1 % (mean 6 S.E.) and 31.0 6 2.9 % of the control level of the NTS neuronal activity, respec