Localization of the clustering protein gephyrin at GABAergic synapses in the main olfactory bulb of the rat

The tubulin‐binding protein gephyrin is essential for the formation of postsynaptic glycine‐receptor clusters in cultured spinal neurons. In addition, there is increasing evidence that gephyrin can also be present at nonglycinergic synapses. Here we analyzed immunocytochemically the subcellular localization of gephyrin in the main olfactory bulb of the rat and compared its distribution with that of γ‐aminobutyric acid (GABA) and of two major GABAA‐receptor subunits. Gephyrin was selectively localized to the postsynaptic side of symmetric synaptic junctions, where the presynaptic terminals contained GABA. Moreover, gephyrin colocalized extensively with the α1 and γ2 subunits of the GABAA receptor. In contrast, gephyrin was not detected at presumed glutamatergic synapses. These results indicate that gephyrin is not uniquely associated with glycine receptors, but can also be found at distinct GABAergic synapses. Thus, they raise the possibility that gephyrin is involved in anchoring certain GABAA‐receptor subtypes in the postsynaptic membrane. J. Comp. Neurol. 395:231–244, 1998. © 1998 Wiley‐Liss, Inc.