Loss of postsynaptic GABA(A) receptor clustering in gephyrin-deficient mice

The tubulin-binding protein gephyrin, which anchors the inhibitory glycine receptor (GlyR) at postsynaptic sites, decorates GABAergic postsynaptic mem branes in various brain regions, and postsynaptic gephyrin clusters are abs ent from cortical cultures of mice deficient for the GABA(A) receptor gamma 2 subunit. Here, we investigated the postsynaptic clustering of GABA(A) re ceptors in gephyrin knock-out (geph -/-) mice. Both in brain sections and c ultured hippocampal neurons derived from geph -/- mice, synaptic GABA(A) re ceptor clusters containing either the gamma 2 or the alpha 2 subunit were a bsent, whereas glutamate receptor subunits were normally localized at posts ynaptic sites. Western blot analysis and electrophysiological recording rev ealed that normal levels of functional GABA(A) receptors are expressed in g eph -/- neurons, however the pool size of intracellular GABA(A) receptors a ppeared increased in the mutant cells. Thus, gephyrin is required for the s ynaptic localization of GlyRs and GABA(A) receptors containing the gamma 2 and/or alpha 2 subunits but not for the targeting of these receptors to the neuronal plasma membrane. In addition, gephyrin may be important for effic ient membrane insertion and/or metabolic stabilization of inhibitory recept ors at developing postsynaptic sites.