Which GABAA-receptor subtypes really occur in the brain?

GABAA receptors are a heterogeneous family of ligand-gated ion channels responsible for mediating inhibitory neurotransmission in the CNS. Since the identification of mammalian cDNAs encoding 13 GABAA-receptor subunits, the composition of native receptor molecules and their localization in the brain has been an area of intense study. We conclude that the number of major subtypes is probably less than ten but their physiological roles have yet to be clearly defined and this represents the next step in GABAA-receptor research.