BigFly Project
The circuitry of tangential cells in the lobula plate of the blow fly
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Figure 1: Connectivity between tangential cells.
Within the past decade, our picture of the lobula plate has changed dramatically. Whereas before, the various tangential cells of the lobula plate have been assumed to process their dendritic signal more or less in parallel, independent from each other, a series of double recording studies revealed a pronounced intra- and inter-hemispheric connectivity between almost all tangential cells investigated so far. A summary of the emerging lobula plate circuitry is depicted in Fig.1. There are several things noteworthy: First of all, many of the connections found between different tangential cells turned out to be electrical in nature. The existence of gap junctions has been confirmed not only by double recordings but in addition by Neurobiotin dye coupling. Second, while some of the connections are located between the axon terminals of the neurons, others are located between the dendrites of neighboring cells. Third, most of the connections are between horizontal sensitive cells or vertical sensitive cells. However, additional connections have been found which link the horizontal and the vertical system.
A well investigated network within the lobula-plate circuitry is the VS-cell network (Figure 2). It turned out that all VS-cells are connected to their direct neighbors in a chain-like fashion via axo-axonal gap-junctions. This electrical coupling of the VS-cells leads to a broadening of the receptive field of single VS-cells along the azimuth. This consequence of the coupling has been demonstrated by laser ablation experiments and in network simulations by detailed, biophysically realistic compartmental models.
