Morphological Diversity of Gap Junctions in the Central Nervous System
Abstract: Gap junctions are channel structures between cells and act as electrical synapses between neurons. Gap junctions are composed of “connexin” proteins. Connexins assemble as a hexameric transmembrane channel, connexon. We found morphological diversities of neuronal gap junctions in rodent retina by SDS-digested freeze-fracture replica immunogold labeling. They often showed string-, ribbon-, reticular- arrangements of connexons as well as typical plaque forms especially in the OFF sublamina of the inner plexiform layer. We also found that small gap junctions (<100 connexons) were abundant in the central nervous system, which were technically difficult to be detected by light microscopy or thin-sectioning electron microscopy. Double-replica labeling for Cx36 and Cx45 revealed that these two connexins made bi-homotypic gap junctions. The labeling for Cx36 and Cx45 were segregated in gap junction hemiplaques, and the segregation pattern was kept as same in the complementary side of hemiplaques.
Key words: Freeze-fracture replica immunogold labeling, gap junction, central nerve system, retina, double-replica