TRICHLOROETHANOL POTENTIATES SYNAPTIC TRANSMISSION MEDIATED BY GAMMA-AMINOBUTYRIC ACIDA RECEPTORS IN HIPPOCAMPAL-NEURONS

We have examined the actions of trichloroethanol (TCEt), the active metabolite of the general anesthetic chloral hydrate, on responses mediated by gamma-aminobutyric acid (GABA)A receptors in response to application of exogenous GABA and activation of endogenous GABAergic transmission, by using hippocampal neurons in cell culture and in brain slices. In the presence of TCEt, Cl- current activated by exogenous GABA was both enhanced in amplitude and prolonged, leading to a net increase in total charge passing through GABA(A) receptor channels. Prolongation of GABA-activated current increased in magnitude in a concentration-dependent manner from 0.2 to 10 mM TCEt. inhibitory postsynaptic currents produced at synapses between pairs of cultured GABAergic neurons or by activation of interneurons in hippocampal slices were also prolonged by TCEt, at concentrations from 0.5 to 10 mM. Application of TCEt at concentrations of 1 mM and above produced a small amplitude current which was directed outwardly at -40 mV in neurons in which methylsulfate or gluconate was the major intracellular anion and directed inwardly in neurons filled with Cl-. Our observations indicate that TCEt potentiates GABAergic transmission; presumably by potentiating the function of GABA(A) receptors in a manner similar to barbiturate or steroid anesthetics. This action is likely to contribute to the general anesthetic effect of TCEt which occurs after chloral hydrate administration.