title: Feedback network controls photoreceptor output at the layer of first visual synapses in Drosophila.
abstract: At the layer of first visual synapses, information from photoreceptors is processed and transmitted towards the brain. In fly compound eye, output from photoreceptors (R1-R6) that share the same visual field is pooled and transmitted via histaminergic synapses to two classes of interneuron, large monopolar cells (LMCs) and amacrine cells (ACs). The interneurons also feed back to photoreceptor terminals via numerous ligand-gated synapses, yet the significance of these connections has remained a mystery. We investigated the role of feedback synapses by comparing intracellular responses of photoreceptors and LMCs in wild-type Drosophila and in synaptic mutants, to light and current pulses and to naturalistic light stimuli. The recordings were further subjected to rigorous statistical and information-theoretical analysis. We show that the feedback synapses form a negative feedback loop that controls the speed and amplitude of photoreceptor responses and hence the quality of the transmitted signals. These results highlight the benefits of feedback synapses for neural information processing, and suggest that similar coding strategies could be used in other nervous systems.
authors.affiliation: Department of Biomedical Science, University of Sheffield, UK.
authors.forename: Lei
authors.initials: L
authors.lastname: Zheng
authors.forename: Gonzalo G
authors.initials: GG
authors.lastname: de Polavieja
authors.forename: Verena
authors.initials: V
authors.lastname: Wolfram
authors.forename: Musa H
authors.initials: MH
authors.lastname: Asyali
authors.forename: Roger C
authors.initials: RC
authors.lastname: Hardie
authors.forename: Mikko
authors.initials: M
authors.lastname: Juusola
mesh_terms: D000818:Animals; D004331:Drosophila melanogaster / Q000502:physiology*; D004594:Electrophysiology; D005074:Evoked Potentials, Visual / Q000502:physiology; D005246:Feedback / Q000502:physiology*; D007395:Interneurons / Q000502:physiology; D008027:Light; D008839:Microelectrodes; D008954:Models, Biological; D018408:Patch-Clamp Techniques; D017956:Photoreceptor Cells, Invertebrate / Q000502:physiology*; D015398:Signal Transduction / Q000502:physiology; D009435:Synaptic Transmission / Q000502:physiology*; D013696:Temperature