Electrical coupling of lobula plate tangential cells to a heterolateral motion-sensitive neuron in the fly.

Many motion-sensitive tangential cells of the lobula plate in blowflies are well described with respect to their visual response properties and the connectivity among them. In addition to extensive connections between tangential cells within the lobula plate of one brain hemisphere, there exist many connections between the two hemispheres. Most of these connections have been found for neurons sensitive to horizontal motion. For neurons sensitive to vertical motion, however, only the connection of vertical sensitive cells (VS cells) and a cell (V1 cell) projecting to the other hemisphere has been demonstrated thus far. The ability to identify the presynaptic and postsynaptic cells as well as the good accessibility has made this specific synapse a model for graded transmission of synapses. However, the exact type of synapse, electrical or chemical, is not known. Investigating the connectivity between VS cells 1-3 and the V1 cell by means of dual recordings, we find that the VS cells are coupled via electrical synapses to the V1 cell. The results were confirmed by visualizing dye coupling between VS cells and V1.