ABSTRACT
In vertebrate brains, inhibition is provided mainly by -aminobutyric acid (GABA) acting on type A (GABAA) receptors. These receptors are anion-permeable channels (Cl/HCO3
) formed as pentameric assemblies of subunits. A gene family encodes different GABAA receptor subunits (1-6, 1-3, 1-3, , , , and 1-3). The genes are differentially transcribed (Persohn et al., 1992; Wisden et al., 1992; Fritschy and Möhler, 1995; Hedblom and Kirkness, 1997; Whiting et al., 1997; Bonnert et al., 1999) and the subunits assembled into different combinations depending on the celltype. Most GABAA receptors are likely to be or forms. Within the class the subunit ratio is probably 2/2/1 (Tretter et al., 1997; Farrar et al., 1999). The large family of subunit genes results in considerable receptor diversity. These GABAA receptors differ in properties such as their affinity for neurotransmitter, activation rate, desensitization rate, and channel conductance (Barnard et al., 1998). Important questions are: ‘How many receptor subtypes are there?’, ‘What receptor subtypes are used by which types of neuron and where are they located on the cell?’, ‘What are the functions of these different receptor subtypes?’, and ‘How are the expression patterns of the receptor subunit genes controlled?’
