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B. Volgyi, D. L. Paul, S. A. Bloomfield; Deletion of Connexin36 Reduces Coupling of Most Ganglion Cell Subtypes in the Mouse Retina. Invest. Ophthalmol. Vis. Sci. 2008;49(13):3050.
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© ARVO (1962-2015); The Authors (2016-present)
To determine whether connexin36 (Cx36) subunits are obligatory elements in the electrical synapses that ganglion cells form with their ganglion and/or amacrine cell neighbors in the mouse retina.
Somata of the different ganglion cell subtypes in both wild-type (WT) and constituitive Cx36 knockout (KO) mouse littermates were targeted for intracellular impalement under infrared guidance. The gap junction-permeable tracer Neurobiotin was iontophoresed into ganglion cells using a sinusoidal current for 10-15 minutes. The soma/dendritic morphology and tracer coupling pattern of injected cells were revealed by peroxidase histochemistry. Ganglion cells were classified morphologically and then the coupling patterns of corresponding ganglion cell subtypes in WT and KO mouse retinas were compared.
We differentiated mouse ganglion cells in both WT and KO retinas into 17 distinct populations based on classic morphological criteria including the size and shape of their somata and dendritic arbors as well as dendritic stratification in the IPL. We found that 13 of the 17 ganglion cell subtypes were coupled to nearby ganglion cells and/or amacrine cells in WT retinas. However, the coupling pattern of most of these ganglion cell subtypes was dramatically altered by the deletion of Cx36 protein in the KO mouse retinas. In KO retinas, ganglion-to-ganglion cell (homologous) coupling was disrupted in 3 of 6 ganglion cell subtypes that showed homologous coupling in the WT animals. Deletion of Cx36 had an even greater effect on ganglion-to-amacrine cell (heterologous) coupling. In WT retinas, 11 of the 17 ganglion cell subtypes displayed coupling to neighboring amacrine cells of usually more than one subtype. With only one exception, this heterologous coupling was altered in Cx36 KO retinas. For 9 of these subtypes, ganglion-to-amacrine cell coupling was completely disrupted in the KO, with the remaining ganglion cell subtype retaining coupling, but to only a subset of the amacrine cells to which it was coupled in the WT.
Our data indicate that Cx36 is a crucial component of gap junctional coupling involving most, but not all subtypes of ganglion cells in the mouse retina. Our finding that deletion of Cx36 did not alter all coupling further indicates that other connexin subunits subserve ganglion-to-ganglion cell coupling and to a lesser extent ganglion-to-amacrine cell coupling in the mouse retina.
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