title: Evidence for Dynamic Network Regulation of Drosophila Photoreceptor Function from Mutants Lacking the Neurotransmitter Histamine.
abstract: Synaptic feedback from interneurons to photoreceptors can help to optimize visual information flow by balancing its allocation on retinal pathways under changing light conditions. But little is known about how this critical network operation is regulated dynamically. Here, we investigate this question by comparing signaling properties and performance of wild-type Drosophila R1-R6 photoreceptors to those of the hdc (JK910) mutant, which lacks the neurotransmitter histamine and therefore cannot transmit information to interneurons. Recordings show that hdc (JK910) photoreceptors sample similar amounts of information from naturalistic stimulation to wild-type photoreceptors, but this information is packaged in smaller responses, especially under bright illumination. Analyses reveal how these altered dynamics primarily resulted from network overload that affected hdc (JK910) photoreceptors in two ways. First, the missing inhibitory histamine input to interneurons almost certainly depolarized them irrevocably, which in turn increased their excitatory feedback to hdc (JK910) R1-R6s. This tonic excitation depolarized the photoreceptors to artificially high potentials, reducing their operational range. Second, rescuing histamine input to interneurons in hdc (JK910) mutant also restored their normal phasic feedback modulation to R1-R6s, causing photoreceptor output to accentuate dynamic intensity differences at bright illumination, similar to the wild-type. These results provide mechanistic explanations of how synaptic feedback connections optimize information packaging in photoreceptor output and novel insight into the operation and design of dynamic network regulation of sensory neurons.
authors.affiliation: Department of Biomedical Science, University of Sheffield Sheffield, UK.
authors.forename: An
authors.initials: A
authors.lastname: Dau
authors.affiliation: Department of Biomedical Science, University of Sheffield Sheffield, UK.
authors.forename: Uwe
authors.initials: U
authors.lastname: Friederich
authors.affiliation: Department of Biomedical Science, University of Sheffield Sheffield, UK.
authors.forename: Sidhartha
authors.initials: S
authors.lastname: Dongre
authors.affiliation: Department of Biomedical Science, University of Sheffield Sheffield, UK.
authors.forename: Xiaofeng
authors.initials: X
authors.lastname: Li
authors.affiliation: Department of Physiology Development and Neuroscience, Cambridge University Cambridge, UK.
authors.forename: Murali K
authors.initials: MK
authors.lastname: Bollepalli
authors.affiliation: Department of Physiology Development and Neuroscience, Cambridge University Cambridge, UK.
authors.forename: Roger C
authors.initials: RC
authors.lastname: Hardie
authors.affiliation: Department of Biomedical Science, University of SheffieldSheffield, UK; National Key Laboratory of Cognitive Neuroscience and Learning, Beijing Normal UniversityBeijing, China.
authors.forename: Mikko
authors.initials: M
authors.lastname: Juusola
mesh_terms: D000818:Animals; D030801:Animals, Genetically Modified; D001766:Blindness / Q000235:genetics / Q000473:pathology; D003623:Dark Adaptation / Q000235:genetics; D004195:Disease Models, Animal; D004330:Drosophila; D029721:Drosophila Proteins / Q000235:genetics*; D004558:Electric Stimulation; D004596:Electroretinography; D005260:Female; D005583:Fourier Analysis; D006632:Histamine / Q000172:deficiency*; D008564:Membrane Potentials; D046529:Microscopy, Electron, Transmission; D009154:Mutation / Q000235:genetics*; D018408:Patch-Clamp Techniques; D010775:Photic Stimulation; D017956:Photoreceptor Cells, Invertebrate / Q000502:physiology* / Q000648:ultrastructure; D014795:Visual Pathways / Q000502:physiology*
chemical_list: D029721:Drosophila Proteins; C098014:Hdc protein, Drosophila; D006632:Histamine
keywords: feedback synapses; histamine; information theory and signal processing; photoreceptor cells; visual perception