title: Optogenetic analysis of a nociceptor neuron and network reveals ion channels acting downstream of primary sensors.
abstract: BACKGROUND
  Nociception generally evokes rapid withdrawal behavior in order to protect the tissue from harmful insults. Most nociceptive neurons responding to mechanical insults display highly branched dendrites, an anatomy shared by Caenorhabditis elegans FLP and PVD neurons, which mediate harsh touch responses. Although several primary molecular nociceptive sensors have been characterized, less is known about modulation and amplification of noxious signals within nociceptor neurons. First, we analyzed the FLP/PVD network by optogenetics and studied integration of signals from these cells in downstream interneurons. Second, we investigated which genes modulate PVD function, based on prior single-neuron mRNA profiling of PVD.
  
  
  RESULTS
  Selectively photoactivating PVD, FLP, and downstream interneurons via Channelrhodopsin-2 (ChR2) enabled the functional dissection of this nociceptive network, without interfering signals by other mechanoreceptors. Forward or reverse escape behaviors were determined by PVD and FLP, via integration by command interneurons. To identify mediators of PVD function, acting downstream of primary nocisensor molecules, we knocked down PVD-specific transcripts by RNAi and quantified light-evoked PVD-dependent behavior. Cell-specific disruption of synaptobrevin or voltage-gated Ca(2+) channels (VGCCs) showed that PVD signals chemically to command interneurons. Knocking down the DEG/ENaC channel ASIC-1 and the TRPM channel GTL-1 indicated that ASIC-1 may extend PVD's dynamic range and that GTL-1 may amplify its signals. These channels act cell autonomously in PVD, downstream of primary mechanosensory molecules.
  
  
  CONCLUSIONS
  Our work implicates TRPM channels in modifying excitability of and DEG/ENaCs in potentiating signal output from a mechano-nociceptor neuron. ASIC-1 and GTL-1 homologs, if functionally conserved, may denote valid targets for novel analgesics.
authors.affiliation: Buchmann Institute for Molecular Life Sciences, Goethe-University Frankfurt, Max von Laue Str. 15, 60438 Frankfurt, Germany.
authors.forename: Steven J
authors.initials: SJ
authors.lastname: Husson
authors.forename: Wagner Steuer
authors.initials: WS
authors.lastname: Costa
authors.forename: Sebastian
authors.initials: S
authors.lastname: Wabnig
authors.forename: Jeffrey N
authors.initials: JN
authors.lastname: Stirman
authors.forename: Joseph D
authors.initials: JD
authors.lastname: Watson
authors.forename: W Clay
authors.initials: WC
authors.lastname: Spencer
authors.forename: Jasper
authors.initials: J
authors.lastname: Akerboom
authors.forename: Loren L
authors.initials: LL
authors.lastname: Looger
authors.forename: Millet
authors.initials: M
authors.lastname: Treinin
authors.forename: David M
authors.initials: DM
authors.lastname: Miller
authors.forename: Hang
authors.initials: H
authors.lastname: Lu
authors.forename: Alexander
authors.initials: A
authors.lastname: Gottschalk
mesh_terms: D007473:Ion Channels / Q000378:metabolism*; D009474:Neurons / Q000166:cytology* / Q000378:metabolism
chemical_list: D007473:Ion Channels