Effects of GABA on neurons of the gustatory and visceral zones of the parabrachial nucleus in rats

Response characteristics of neurons in the gustatory and visceral zone of the parabrachial nucleus (PBN) to γ-aminobutyric acid (GABA) were examined using whole cell recordings in brain slices of the rat. Based on the recording site, neurons were divided into three groups: neurons in the dorsolateral quadrant of the PBN (DL-neurons), neurons in the dorsomedial quadrant of the PBN (DM-neurons) and neurons in the ventromedial quadrant of the PBN (VM-neurons). Recordings were made from 44 DL-, 43 DM-, 39 VM-neurons. Superfusion of GABA resulted in a concentration-dependent reduction in input resistance in 67.5% of the neurons in the PBN (73.1% of the DL-, 62.5% of the DM-, 66.7% of the VM-neurons). No obvious difference of the concentration–response curve was found among three groups. The mean reversal potential of the GABA effect was about −74 mV and no significant differences were observed among three groups of neurons. The GABA response was partly or completely blocked by the GABA_A antagonist bicuculline in all neurons tested. Superfusion of the GABA_A agonist muscimol resulted in a decrease of the input resistance in all neurons tested. It was concluded that GABA functions as an inhibitory neurotransmitter in both gustatory and visceral part of the PBN, mediated in part, by GABA_A receptors.