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B. Volgyi, J. Abrams, D. Paul, S. Bloomfield; Connexin36 Comprises Heterologous but Not Homologous Gap Junctions Formed by Alpha Ganglion Cells in Mouse Retina . Invest. Ophthalmol. Vis. Sci. 2005;46(13):2231.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To describe the tracer–coupling pattern of alpha ganglion cells in the mouse retina and any contribution of connexin36 (Cx36) to their gap junctions. Methods: We carried out intracellular Neurobiotin injections into visually–targeted cells in the ganglion cell layer (GCL) in a flattened eyecup preparation of wild type (WT) and Cx36 knock–out (KO) mice. Morphology of injected and tracer–coupled cells was revealed by either the use of streptavidine conjugated fluorescent probes or DAB histology. Results: Both fluorescent and DAB histology revealed Neurobiotin tracer coupling of both On– and Off–center alpha ganglion cells with other inner retinal neurons. On–center alpha cells in the WT retina showed heterologous tracer coupling to at least two morphological types of amacrine cell with somata in the GCL. One population of these amacrine cells had faintly–labeled small somata, whereas cell bodies of the other population were large and darkly labeled. The dendrites of this second group of amacrine cell were often dark and easily visualized. Homologous coupling of neighboring On–center cells was never observed. Neurobiotin injections of On–center alpha cells in the Cx36 KO retina revealed a relatively smaller number of tracer–coupled amacrine cells. Whereas the faintly–labeled cells seen in WT retinas were also present in the KO, the darkly–labeled amacrine cells were missing. In contrast, Off–center alpha ganglion cells in the WT retina showed homologous tracer coupling to 3–8 neighboring alpha cells and heterologous tracer coupling to 2–3 types of amacrine cells with cell bodies locating mainly in the inner nuclear layer (INL). One population of these tracer–coupled amacrine cells showed characteristics of wide–field amacrine cells with dendrites spanning several hundred microns. Injections of Off–center alpha cells in Cx36 KO animals revealed the same pattern of homologously–coupled alpha ganglion cells seen in WT retinas, but tracer coupling to amacrine cells was completely absent. Conclusions: Our data indicate a clear difference in the tracer coupling pattern of On– and Off–center alpha cells in the mouse retina. Further, we find that the gap junctions connecting amacrine cells to either On– or Off–center alpha ganglion cells are comprised, at least in part, by Cx36. However, our results suggest that homologous gap junctions formed between neighboring Off–center alpha cells are composed by other connexins.
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