Figure 6. Exogenous GABA reduces excitability of isolated petrosal neurones.

A, under current clamp, a long depolarizing current pulse (50 pA; 50 ms) triggered multiple action potentials in a petrosal neurone. B, bath application of 20 μm GABA depolarized the membrane potential by 5 mV and only a single action potential could be elicited by the same depolarizing stimulus. C, on washing out GABA, the control response and initial membrane potential recovered. D, the magnitude of the GABA-induced depolarization was mimicked by artificially injecting a continuous current to depolarize the cell by ∼5 mV. However, this artificial depolarization did not mimic the inhibitory effect of GABA, as the depolarizing current pulse still triggered multiple action potentials similar to A. These data suggest that the effects of GABA were not simply due to secondary effects of depolarization on membrane excitability. Data are representative of 8/10 cells that behaved in this way.