Synaptic organization of lobula plate tangential cells in Drosophila: γ-aminobutyric acid receptors and chemical release sites

In flies, the large tangential cells of the lobula plate represent an important processing center for visual navigation based on optic flow. Although the visual response properties of these cells have been well studied in blowflies, information on their synaptic organization is mostly lacking. Here we study the distribution of presynaptic release and postsynaptic inhibitory sites in the same set of cells in Drosophila melanogaster. By making use of transgenic tools and immunohistochemistry, our results suggest that HS and VS cells of Drosophila express γ-aminobutyric acid (GABA) receptors in their dendritic region within the lobula plate, thus being postsynaptic to inhibitory input there. At their axon terminals in the protocerebrum, both cell types express synaptobrevin, suggesting the presence of presynaptic specializations there. HS- and VS-cell terminals additionally show evidence for postsynaptic GABAergic input, superimposed on this synaptic polarity. Our findings are in line with the general circuit for visual motion detection and receptive field properties as postulated from electrophysiological and optical recordings in blowflies, suggesting a similar functional organization of lobula plate tangential cells in the two species.