Disruption of postsynaptic GABAA receptor clusters leads to decreased GABAergic innervation of pyramidal neurons

We have used RNA interference (RNAi) to knock down the expression of the γ2 subunit of the GABAA receptors (GABAARs) in pyramidal neurons in culture and in the intact brain. Two hairpin small interference RNAs (shRNAs) for the γ2 subunit, one targeting the coding region and the other one the 3′‐untranslated region (UTR) of the γ2 mRNA, when introduced into cultured rat hippocampal pyramidal neurons, efficiently inhibited the synthesis of the GABAA receptor γ2 subunit and the clustering of other GABAAR subunits and gephyrin in these cells. More significantly, this effect was accompanied by a reduction of the GABAergic innervation that these neurons received. In contrast, the γ2 shRNAs had no effect on the clustering of postsynaptic α‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazolepropionic acid (AMPA) receptors, postsynaptic density protein 95 (PSD‐95) or presynaptic glutamatergic innervation. A γ2‐enhanced green fluorescent protein (EGFP) subunit construct, whose mRNA did not contain the 3′‐UTR targeted by γ2 RNAi, rescued both the postsynaptic clustering of GABAARs and the GABAergic innervation. Decreased GABAAR clustering and GABAergic innervation of pyramidal neurons in the post‐natal rat cerebral cortex was also observed after in utero transfection of these neurons with the γ2 shRNAs. The results indicate that the postsynaptic clustering of GABAARs in pyramidal neurons is involved in the stabilization of the presynaptic GABAergic contacts.