Movie S2.

This movie illustrates the Cx35 immuno-labeling of gap junctions in the zebrafish Mauthner cell. This analysis suggests electrical synapses in the input pathway to the axon initial segment. The movie shows the GFP-labeled two Mauthner neurons (green) and labeling (red) of the connexin homolog Cx35. To show the adequacy of our staining protocol, the movie first sweeps towards the lateral dendrite of the intact cell to the site (asterisk) where the so-called club endings of the M cells are located. These are mixed synapses that are known to contain Cx35. The movie then proceeds to focus on the axon initial segment (AIS, arrowheads) that strongly expresses Cx35. This suggests, that electrical synapses are employed both in the inputs to the lateral dendrite and to the AIS.