GABAA receptors mediate fast inhibitory neurotransmission and are assembled as heteropentameric chloride channels from 19 subunits, typically consisting of 2α, 2β, and 1γ subunits (Olsen and Sieghart, 2008) (Figure 4G–H). The vast majority of possible subunit combinations remain tentative as previous studies do not achieve cellular resolution of subunit co-expression. Whereas γ2 is regarded as the ubiquitous obligatory subunit of most if not all synaptic GABAaRs that mediate phasic inhibition, γ3 is sparsely expressed in cortical neurons of unknown identity and can assemble with α and β to form synaptic receptors with slowly decaying IPSCs (Kerti-Szigeti et al., 2014). We found that, surprisingly, γ3 is not only prevalent but also transcribed at much higher levels than γ2 subunits in all 6 PCPs (Figure 4H). This suggests that γ3 might contribute to the assembly of a class of slower decaying, longer duration synaptic GABAARs in GABAergic neurons. Different PCPs show specific subunit profiles and levels (Figure 4G, H). PVBCs express the largest variety (all except α2, α6, γ1) and overall highest levels of subunits, and uniquely high level of the GABAAR
