THE PHARMACOLOGY OF THE GABA-INDUCED BIPHASIC RESPONSE IN GUINEA-PIG CELIAC GANGLION NEURONS IN VITRO

In guinea-pig celiac ganglion neurons, GABA induced a biphasic response,i.e.a depolarizing response associated with a resistance decrease followed by.a hyperpolarizing response associated with a resistance increase. Such response Persisted in low Ca2+high Mg2+medium. The GABA-induced biphasic response was mimicked by muscimoland inhibited by bicuculline methiodide (100 μmol/L) and picrotoxin (100-300μmol/L). At doses producing almost equal depolarizing responses, muscimol wasweaker in producing hyperpolarizing responses than GABA. Baclofen had no effect onmembrane potentials of the ganglion cells. These results suggest that the depolarizingphase of the GABA-induced biphasic response is mediated by GABA./Cl-ionophorereceptor complex and the hyperpolarizing phase may be mediated by a novel type ofGABA receptor possessing similar pharmacological properties as the classical GABAAreceptor.