GEPHYRIN ACCUMULATES AT SPECIFIC PLASMALEMMA LOCI DURING NEURONAL MATURATION IN-VITRO

The distribution of glycine receptor (GlyR)-associated gephyrin has be en investigated in rat spinal cord neurons maintained in vitro by mean s of immunocytochemical techniques. Gephyrin, which is crucial for the stabilization of postsynaptic GlyR microdomains, is present in mature neurons at postsynaptic differentiations. With immunofluorescence, di scontinous patches of gephyrin were detected within the neuronal soma of spinal cord neurons on the Ist day after plating. Subsequently, gep hyrin was present at membrane areas that correspond to points of conta ct between cells or with the culture dish. By the 5th day, gephyrin wa s mostly associated with the MAP2-positive somatodendritic compartment . With immunoelectron microscopy, gephyrin blobs detected at the earli est stages (1-3 days after plating) were found within the cytoplasm or associated with the plasma membrane. Asymmetrically immunostained int ercellular contacts were only detected after 5 days, and gephyrin was found in association with clearly differentiated postsynaptic membrane s at 7 days. At later stages, we observed gephyrin immunoreactivity on ly at some synapses. Our results suggest that gephyrin accumulates ini tially at the locus of cell-to-cell contacts involved in adhesion proc esses. These localizations may define hot spots for later accumulation of the GlyR and possibly other receptors. (C) 1996 Wiley-Liss, Inc.