Responses of acutely isolated neurons from the rostral nucleus of the solitary tract (rNST) to GABA receptor agonists and antagonists were investigated using whole-cell recording in current clamp mode. The isolated neurons retain their morphology and can be divided into multipolar, elongate and ovoid cell types. Most rNST neurons (97%), including all three cell types, respond to GABA with membrane hyperpolarization and a reduction in input resistance. The GABA(A) receptor agonist muscimol reduces neuronal input resistance in a concentration-dependent manner, whereas the GABA(B) receptor agonist baclofen had no effect on any of the neurons tested. The GABA and muscimol reversal potentials were both found to be -75 mV Both the GABA competitive antagonist picrotoxin and the GABA(A) receptor antagonist bicuculline block the effect of GABA in a concentration-dependent manner. These results suggest that GABA activates all neurons in the rNST and that inhibitory synaptic activity is important in brainstem processing of gustatory and somatosensory information.