GABA(A) receptors: structure and function in the basal ganglia.

gamma-Aminobutyric acid type A (GABA(A)) receptors, the major inhibitory neurotransmitter receptors responsible for fast inhibition in the basal ganglia, belong to the superfamily of "cys-cys loop" ligand-gated ion channels. GABA(A) receptors form as pentameric assemblies of subunits, with a central Cl(-) permeable pore. On binding of two GABA molecules to the extracellular receptor domain, a conformational change is induced in the oligomer and Cl(-), in most adult neurons, moves into the cell leading to an inhibitory hyperpolarization. Nineteen mammalian subunit genes have been identified, each showing distinct regional and cell-type-specific expression. The combinatorial assembly of the subunits generates considerable functional diversity. Here we place the focus on GABA(A) receptor expression in the basal ganglia: striatum, globus pallidus, substantia nigra and subthalamic nucleus, where, in addition to the standard alpha1beta2/3gamma2 receptor subtype, significant levels of other subunits (alpha2, alpha3, alpha4, gamma1, gamma3 and delta) are expressed in some nuclei.