Distribution of the receptor-anchoring protein gephyrin in the rat dentategyrus and changes following entorhinal cortex lesion

We analyzed the distribution of the receptor-anchoring protein gephyrin in the normal and deafferented rat dentate gyrus to investigate whether the ex pression of this postsynaptic protein is altered in response to the formati on of new synaptic contacts. Confocal microscopy and digital image analysis revealed that in normal dentate gyrus immunolabeling was most prominent in the outer molecular layer and decreased successively in the direction of t he granule cell layer. Simultaneous immunolabeling for gephyrin and cell-sp ecific markers showed that granule cells and parvalbumin positive interneur ons express gephyrin. Large, intensely stained, gephyrin-positive clusters were distributed along distinct dendrites, and most of them were positive f or parvalbumin. Calbindin-immunostained dendrites were associated with smal ler, gephyrin-positive clusters. Lesion of the medial entorhinal cortex lea ds to deafferentiation of the middle molecular layer which resulted in an i ncreased gephyrin immunoreactivity. These changes were due to a significant ly increased concentration of the very small gephyrin-positive clusters. Pa rvalbumin-positive dendrites did not display any increase in co-localizing gephyrin-positive structures. The altered immunolabeling pattern persisted until 12 weeks after lesion, a time when the process of synaptic reorganiza tion is complete. Our findings suggest that synaptogenesis following deaffe rentiation results in a cell-specific redistribution of gephyrin immunoreac tivity at specific inhibitory synapses.