LOCALIZATION OF GAP-JUNCTIONS AND TRACER COUPLING IN RETINAL MULLER CELLS

Physiological studies have demonstrated the existence of direct interc ellular communication, presumably mediated by gap junctions, both betw een neurons and between glial cells in the vertebrate retina. We local ized gap junctions in the retinas of rat, goldfish, and mudpuppy by us ing antisera directed against proteins that make up the connexon chann els in two tissues from which connexins have been isolated: liver (con nexin 32; CX32) and heart (connexin 43; CX43). Although the antiserum against CX32 stained liver gap junctions, it did not reveal any staini ng in rat or goldfish retina. The antiserum against CX43 stained gap j unctions associated with the intercalated disk in rat heart and also s tained gap junctions between pigment epithelium cells in rat, goldfish , and mudpuppy retina. Anti-CX43 also stained gap junctions between Mu ller cells in goldfish and mudpuppy retina but not in rat retina. Intr acellular injections of the tracer Neurobiotin into Muller cells in th e mudpuppy retina revealed that these glial cells are extensively trac er coupled. Staining with the tracer formed a syncytium of thin proces ses surrounding every neuron from the outer limiting membrane to the i nner limiting membrane. Confocal microscopy demonstrated that the Mull er cells were in close apposition with one another at every level of t he retina. However, CX43 immunoreactivity was heaviest at the outer li miting membrane, where the apical processes of Muller cells are locate d. Some anti-CX43 staining was observed at the level of the outer nucl ear layer and the inner plexiform layer but not in the ganglion cell l ayer or at the Muller cell end feet forming the inner limiting membran e. J. Comp. Neurol. 393:48-57, 1998. (C) 1998 Wiley-Liss, Inc.