title: In vivo optogenetic activation of Nav1.8+cutaneous nociceptors and their responses to natural stimuli.
abstract: Optogenetic methods that utilize expression of the light-sensitive protein channelrhodopsin-2 (ChR2) in neurons have enabled selective activation of specific subtypes or groups of neurons to determine their functions. Using a transgenic mouse model in which neurons natively expressing Nav1.8 (a tetrodotoxin-resistant voltage-gated sodium channel) also express the light-gated channel ChR2, we have been able to determine the functional properties of Nav1.8-expressing cutaneous nociceptors of the glabrous skin in vivo. Most (44 of 53) of the C-fiber nociceptors isolated fromNav1.8-ChR2+mice were found to be responsive to blue (470 nm) light. Response characteristics, including conduction velocity and responses to mechanical stimuli, were comparable between nociceptors isolated fromNav1.8-ChR2+and control mice. Interestingly, while none of the non-light-responsive C-fibers were sensitive to heat or cold, nearly all (77%) light-sensitive fibers were excited by mechanical and thermal stimuli, suggesting that Nav1.8 is predominantly expressed by C-fiber nociceptors that are responsive to multiple stimulus modalities. The ability to activate peripheral nociceptors with light provides a method of stimulation that is noninvasive, does not require mechanical interruption of the skin, and accesses receptive fields that might be difficult or impossible to stimulate with standard stimuli while allowing repeated stimulation without injuring the skin.NEW & NOTEWORTHYTransgenic mice that express the blue light-sensitive protein channelrhodopsin2 (ChR2) in nociceptive nerve fibers that contain voltage-gated sodium channel Nav1.8 were used to determine functional properties of these afferent fibers. Electrophysiological recordings in vivo revealed that most nociceptive fibers that possess Nav1.8 are C-fiber nociceptors that respond to multiple stimulus modalities. Furthermore, responses evoked by blue light stimulation were comparable to those elicited by noxious mechanical, heat, and cold stimuli.
authors.affiliation: Department of Diagnostic & Biological Sciences, School of Dentistry, University of Minnesota, Minneapolis, Minnesota.
authors.forename: Megan L
authors.initials: ML
authors.lastname: Uhelski
authors.affiliation: Department of Pharmacology, University of Minnesota, Minneapolis, Minnesota.
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Bruce
authors.affiliation: Montreal Neurological Institute, Department of Neurology and Neurosurgery, McGill University, Montreal, Quebec, Canada.
authors.forename: Philippe
authors.initials: P
authors.lastname: Séguéla
authors.affiliation: Department of Pharmacology, University of Minnesota, Minneapolis, Minnesota.|Department of Neuroscience, University of Minnesota, Minneapolis, Minnesota; and.|Department of Dermatology, University of Minnesota, Minneapolis, Minnesota.
authors.forename: George L
authors.initials: GL
authors.lastname: Wilcox
authors.affiliation: Department of Diagnostic & Biological Sciences, School of Dentistry, University of Minnesota, Minneapolis, Minnesota; simon003@umn.edu.
authors.forename: Donald A
authors.initials: DA
authors.lastname: Simone
mesh_terms: D000200:Action Potentials; D000818:Animals; D000075402:Channelrhodopsins / Q000235:genetics / Q000378:metabolism; D005260:Female; D006614:Hindlimb; D008297:Male; D008822:Mice, Transgenic; D062559:NAV1.8 Voltage-Gated Sodium Channel / Q000235:genetics / Q000378:metabolism*; D036421:Nerve Fibers, Unmyelinated / Q000378:metabolism*; D059225:Nociception / Q000502:physiology; D009619:Nociceptors / Q000378:metabolism*; D062308:Optogenetics; D010812:Physical Stimulation; D012867:Skin / Q000294:innervation* / Q000378:metabolism
chemical_list: D000075402:Channelrhodopsins; D062559:NAV1.8 Voltage-Gated Sodium Channel
keywords: C-fiber; channelrhodopsin2; electrophysiology; peripheral neuron; tibial nerve