Studies investigating the abundance of GABAA-R subtypes using subunit-specific antibodies, confirmed that receptors composed of α1β2βγ2 subunits are the most abundant GABAA-R in the brain. Similarly, α2βγ2, α3βγ2, α4βγ2, α5βγ2, α6βγ2, α4βδ and α6βδ seem to be abundant, but to a lower extent (for review see Sieghart and Sperk, 2002). Given the promiscuity of subunits discussed above, and the receptor subtypes so far identified, it was estimated that more than 800 distinct GABAA-R subtypes might exist in the brain (Barnard et al., 1998). Most of these receptors are not very abundant, but due to the widespread distribution and quantitative importance of the GABAergic system, even minor GABAA-R subtypes probably exhibit an abundance comparable with that of major norepinephrine, dopamine, serotonin or peptide receptors.
