Expression of mRNAs encoding seven GABA(A) receptor subunits (alpha1, alpha2, alpha3, alpha5, beta2, beta3, gamma2) in the nucleus tractus solitarii (NTS) of rat medulla oblongata was examined by reverse transcription-polymerase chain reaction (RT-PCR). All subunit mRNAs, except alpha5, were clearly detected. Band densities produced by alpha1, alpha3, beta3, and gamma2 subunits were greater than those corresponding to beta2 and alpha2 transcripts. The localization of these subunits in tissue sections through NTS was examined by immunohistochemistry. The differential patterns of immunoreactivity in neuronal somata and dendrites of NTS neurons were generally in agreement with the PCR results, confirming that mRNA expression is correlated with receptor protein synthesis. At ultrastructural level, alpha1, alpha3, beta2/3, and gamma2 subunits were localized in both cytoplasmic and subsynaptic sites, the latter often apposed to GABA immunoreactive synapses. These results suggest that ionotropic receptors comprising the alpha1, alpha3, beta2/3, and gamma2 may mediate inhibitory GABA responses in the NTS.