Expression of neuronal connexin36 in AII amacrine cells of the mammalian retina

We have studied the expression pattern of neuronal connexin36 (Cx36) in the mouse and rat retina. In vertical sections of both retinas, a polyclonal a ntibody directed against Cx36 produced punctate labeling in the inner plexi form layer (IPL). Intense immunoreactivity was localized to the entire OFF sublamina of the IPL, and much weaker staining could be observed in the ON sublamina. Double-labeling experiments in the rat retina with antibodies di rected against parvalbumin indicate that Cx36 is expressed on dendrites of AII amacrine cells. Cx36-like immunoreactivity in sublamina a of the IPL di d not overlap with lobular appendages or cell bodies of AII amacrine cells. In a mouse retinal slice preparation, AII amacrine and ON cone bipolar cel ls were intracellularly injected with Neurobiotin and counterstained with a ntibody against Cx36. Punctate labeling appeared to be in register with den dritic arborization of AII amacrines and cone bipolar cells in the ON subla mina of the IPL. Whereas AII amacrine cells isolated from the rat retina cl early displayed Cx36-like immunoreactivity, isolated ON cone bipolar cells were negative for Cx36. Axon terminals of rod bipolar cells were decorated with Cx36-positive contacts but did not express Cx36 themselves. These results indicate that Cx36 is expressed by AII amacrine cells in homo logous and heterologous gap junctions made with AII amacrines and cone bipo lar cells, respectively. The heterologous gap junctions appear to be hetero typic, because ON cone bipolar cells do not express Cx36.