Converging evidence indicates that electrical synaptic transmission via gap junctions plays a crucial role in signal processing in the retina. In particular, amacrine and
ganglion cells express numerous gap junctions, resulting in extensive electrical networks in the proximal retina. Both connexin36 (Cx36) and connexin45 (Cx45) subunits are widely distributed in the inner plexiform layer (IPL) and therefore are likely contribute to gap junctions formed by a number of
ganglion cell subtypes. In the present study, we used the gap junction-permeant tracer
Neurobiotin to compare the coupling pattern of different
ganglion cell subtypes in wild-type (WT) and Cx36 knockout (KO) mouse retinas. We found that homologous
ganglion-to-
ganglion cell coupling was lost for two subtypes after deletion of Cx36, whereas two other
ganglion cell subtypes retained homologous coupling in the KO mouse. In contrast, deletion of Cx36 resulted in a partial or complete loss of
ganglion-to-amacrine cell heterologous coupling in 9 of 10
ganglion cell populations studied. Overall, our results indicate that Cx36 is the predominant subunit of gap junctions in the proximal mouse retina, expressed by most
ganglion cell subtypes, and thereby likely plays a major role in the concerted activity generated by electrical synapses.