Tracer Coupling Patterns of the Ganglion Cell Subtypes in the Mouse Retina

It is now clear that electrical coupling via gap junctions is prevalent across the retina, expressed by each of the five main neuronal types. With the introduction of mutants in which selective gap junction connexins are deleted, the mouse has recently become an important model for studying the function of coupling between retinal neurons. In this study we examined the tracer-coupling pattern of ganglion cells by injecting them with the gap junction-permanent tracer Neurobiotin to provide, for the first time, a comprehensive survey of ganglion cell coupling in the wildtype mouse retina. Murine ganglion cells were differentiated into 22 morphologically distinct subtypes based on soma-dendritic parameters. Most (16/22) ganglion cell subtypes were tracer-coupled to neighboring ganglion and/or amacrine cells. The amacrine cells coupled to ganglion cells displayed either polyaxonal or wide-field morphologies with extensive arbors. We found that different subtypes of ganglion cells were never coupled to one another, indicating that they subserved independent electrical networks. Finally, we found that the tracer-coupling patterns of the 22 ganglion cell populations were largely stereotypic across the 71 retinas studied. Our results indicate that electrical coupling is extensive in the inner retina of the mouse, suggesting that gap junctions play essential roles in visual information processing. J. Comp. Neurol. 512:664-687, 2009. (C) 2008 Wiley-Liss, Inc.