GABAergic synaptic transmission. Regulation by drugs.

Beside the gamma-aminobutyric acid (GABA)-transporter and the GABAB-autoreceptor, the subsynaptic GABAA-receptor is therapeutically the most relevant target for drug actions influencing GABAergic synaptic transmission. New strategies in drug development focus on partial agonists acting at the benzodiazepine receptor. Since these compounds display less of the undesirable effects associated with the presently used full agonists, a major therapeutic advance is to be expected in the treatment of anxiety disorders and epilepsy. In addition, the extensive structural heterogeneity of GABAA-receptors, derived from a family of more than 15 subunits, may point to an unexpected functional heterogeneity of the receptor which may be exploited pharmacologically. The potential diversity of GABAA-receptor function is presently being analyzed using recombinant GABAA-receptors, which consist of various subunit combinations. These studies point not only to variations in the affinity of GABA, depending on the type of subunit combination, but also to differences in the affinities and intrinsic efficacies of benzodiazepine receptor ligands. Provided these distinctions can be confirmed at GABAA-receptors in situ, a new picture of the physiological and pharmacological regulation of the subsynaptic actions of GABA will emerge.