Differentiating the role of γ-aminobutyric acid type A (GABAA) receptor subtypes

The inhibitory tone maintained throughout the central nervous system relies predominantly on the activity of neuronal GABA_A (γ-aminobutyric acid type A) receptors. This receptor family comprises various subtypes that have unique regional distributions, but little is known about the role played by each subtype. The majority of the receptors contain a γ₂ subunit and are sensitive to modulation by BZs (benzodiazepines), but differ with regard to α and β subunits. Mutagenesis studies combined with molecular modelling have enabled a greater understanding of receptor structure and dynamics. This can now be extended to in vivo activity through translation to genetically modified mice containing these mutations. Ideally, the mutation should leave normal receptor function intact, and this is the case with mutations affecting the BZ-binding site of the GABA_A receptor. We have generated mutations, which affect the BZ site of different α subunits, to enable discrimination of the various behavioural consequences of BZ drug action. This has aided our understanding of the roles played by individual GABA_A receptor subtypes in particular behaviours. We have also used this technique to explore the role of different β subunits in conferring the anaesthetic activity of etomidate. This technique together with the development of subtype-selective compounds facilitates our understanding of the roles played by each receptor subtype.