Abstract
Abstract: :
Purpose: To identify direct gap junction connections between retinal ganglion cells (RGCs). Neuronal gap junction subunit connexin36 (Cx36) is a molecular candidate for gap junctions in RGCs. Methods: Anatomically identifiable gap junctions were examined in contact sites between Neurobiotin-coupled mature rat alpha RGCs by high voltage (at 1,000 kV, HITACHI 1250M, Okazaki NIPS; #02-405) as well as conventional electron microscopy. We further studied localization of Cx36 in their gap junctions, using a newly generated antiserum against Cx36 (Hidaka et al., JIN 1(1): 3-22, 2002; URL, http://ejournals.wspc.com.sg/jin/jin.shtml). Double labeling immunofluorescence with the anti-Cx36 antibody was analyzed in Lucifer Yellow labeled pairs of neighboring alpha RGCs. Results: We ultrastructurally found the presence of numerous gap junctions in Neurobiotin-labeled dendrites of alpha RGCs of inner- (ON-) and outer type (OFF-cells). Gap junctions were also identified in contact sites between the dendrites of tracer-coupled RGCs following light-microscopical documentation of the interconnected sites. Anti-Cx36 antibody labeled discrete puncta on labeled dendrites and somata of alpha RGCs as well as parvalbumin-immunopositive AII amacrine cells. Immunopuncta were found also in the dendrodendritic contacts between the labeled RGCs both of ON- and OFF-types, apart from the localization in AII cells. Conclusion: Rat alpha RGCs of the same type are directly interconnected with gap junctions involving Cx36. Dendrodendritic gap junctions between mature RGCs provide the occurrence of electrical coupling in the interconnected population. Cx36 is possibly essential in cell-to-cell communication between RGCs, in addition to interneurons in the rod pathway.
Keywords: ganglion cells • gap junctions/coupling • retina: proximal(bipolar, amacrine, and gangli