title: Novel method to assess axonal excitability using channelrhodopsin-based photoactivation.
abstract: Measuring the excitability of individual axons is complicated by the prohibitive difficulty in obtaining intracellular recordings. Here, we present an innovative methodology that enables local excitability to be measured anywhere in a channelrhodopsin (ChR2)-expressing neuron. The approach hinges on activating ChR2 in a spatially and temporally precise manner while recording the resulting spike train from a remote site. We validated this approach in primary afferent neurons (PANs). Initial encoding of somatosensory stimuli relies on transduction of the physical stimulus into a receptor potential and transformation of the receptor potential into a spike train; the transformation process depends on the excitability of the most distal PAN endings but, as explained above, is extraordinarily difficult to study in situ using traditional methods. Using ChR2-based photoactivation, we show 1) that excitability differs between the distal endings and more proximal portions of PAN axons, 2) that the transformation process differs between PANs, and 3) that the transformation process is directly affected by inflammation. Beyond presenting an innovative method by which to study axonal excitability, this study has validated its utility in helping to decipher the earliest stages of somatosensory encoding.
authors.affiliation: Center for Pain Research, Department of Anesthesiology, University of Pittsburgh, Pittsburgh, Pennsylvania;
authors.forename: Yi
authors.initials: Y
authors.lastname: Zhu
authors.affiliation: Center for Pain Research, Department of Anesthesiology, University of Pittsburgh, Pittsburgh, Pennsylvania;
authors.forename: Bin
authors.initials: B
authors.lastname: Feng
authors.affiliation: Center for Pain Research, Department of Anesthesiology, University of Pittsburgh, Pittsburgh, Pennsylvania;
authors.forename: Erica S
authors.initials: ES
authors.lastname: Schwartz
authors.affiliation: Center for Pain Research, Department of Anesthesiology, University of Pittsburgh, Pittsburgh, Pennsylvania;
authors.forename: G F
authors.initials: GF
authors.lastname: Gebhart
authors.affiliation: Center for Pain Research, Department of Anesthesiology, University of Pittsburgh, Pittsburgh, Pennsylvania; Neurosciences and Mental Health, The Hospital for Sick Children, Toronto, Ontario, Canada; and Department of Physiology and the Institute for Biomaterials and Biomedical Engineering, University of Toronto, Toronto, Ontario, Canada steve.prescott@sickkids.ca.
authors.forename: Steven A
authors.initials: SA
authors.lastname: Prescott
mesh_terms: D000200:Action Potentials / Q000502:physiology*; D000818:Animals; D001369:Axons / Q000502:physiology*; D002478:Cells, Cultured; D000075402:Channelrhodopsins; D008027:Light; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008815:Mice, Inbred Strains; D009431:Neural Conduction / Q000502:physiology*; D062308:Optogenetics / Q000379:methods*; D010775:Photic Stimulation / Q000379:methods*
chemical_list: D000075402:Channelrhodopsins
keywords: axon; channelrhodopsin; excitability; optogenetics; somatosensory