[Responses mediated by GABAA and GABAB receptors on the somatic membrane of toad dorsal root ganglion neurones].

Intracellular recordings were made from neurons in toad dorsal root ganglion in vitro. Bath application of GABA (10(-4)-10(-3) mol/L) elicited either depolarization or depolarization followed by hyperpolarization respectively in 79% and 10% of the neurons. The remaining 11% did not show any response. The GABA-induced depolarization, which was accompanied by an increase of membrane conductance and usually a shortening of action potential duration (ApD), could be blocked by bicuculline. The GABA-depolarization was enhanced by low Cl- Ringer or reduced by high Cl- Ringer The membrane potential was not affected by 10(-4) mol/L baclofen. On the other hand, shortening of ApD could be produced by baclofen, but not blocked by bicuculline. Our results suggested that GABAA and GABAB receptors coexist on the somatic membrane of toad dorsal root ganglion neurons and mediate the changes respectively in membrane potential and shortening of ApD. The mechanism underlying presynaptic inhibition in the terminals of the primary afferents was discussed.