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B. Volgyi, C. Davies–Venn, Y. Kruman, S. Bloomfield; Connexin36 Is Localized at Heterologous Ganglion Cell Gap Junctions in Mammalian Retina . Invest. Ophthalmol. Vis. Sci. 2006;47(13):3105.
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© ARVO (1962-2015); The Authors (2016-present)
To determine whether connexin36 (Cx36) comprises homologous and/or heterologous gap junctions formed by ganglion cells (GCs) in the rabbit and mouse retinas.
GC somata in flattened eye–cup preparations of the rabbit and mouse retinas were targeted under infrared illumination. Cells were injected with the gap junction–permeant tracer Neurobiotin and then visualized by streptavidine conjugated fluorophores (Cy3 or FITC). Subsequently, retinas were processed for Cx36 immunocytochemistry with expression by injected and tracer–coupled cells determined with confocal microscopy.
The coupling pattern of several GC subtypes were studied, including that of ON direction selective (DS) GCs, ON alpha GCs and OFF alpha GCs. In the rabbit, Cx36–immunolabeled puncta were often found on dendrites of ON DS GCs and OFF alpha GCs, which show heterologous coupling to amacrine cells (ACs) and mixed heterologous and homologous coupling to ACs and nearby GCs, respectively. However, dendrites of ON alpha GCs of the rabbit retina, which do not show tracer coupling, showed little or no expression of Cx36 puncta. In the mouse retina, Cx36–immunolabeled puncta were often found on dendrites of both ON and OFF alpha GCs, which are tracer coupled to ACs and a mixture of ACs and GCs, respectively. To localize Cx36–positive puncta more precisely, we closely examined dendritic crossings of tracer–coupled GC/GC pairs as well as GC/AC neighbors. As expected, Cx36 immunolabels were not detected at dendritic crossings of neighboring ON alpha cells in the rabbit retina. Likewise, we found no evidence of Cx36 at the dendritic crossings of neighboring OFF alpha cells in either rabbit or mouse retinas. In contrast, Cx36–immunolabeled puncta were evident at ganglion/amacrine cell dendritic crossings seen at ON DS and OFF alpha GC arrays in the rabbit retina. Cx36 was also found at ganglion/amacrine cell dendritic crossings at both ON and OFF alpha GC arrays in the mouse retina.
Our results indicate that Cx36 is expressed at ON DS and alpha GC gap junctions formed with nearby ACs, but not at those formed with GC neighbors. Although limited to 3 GC subtypes, these data suggest a general organization whereby Cx36 comprises heterotypic GC/AC gap junctions, but not homotypic GC/GC junctions in the mammalian retina.
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