title: Long-lasting antinociceptive effects of green light in acute and chronic pain in rats.
abstract: Treatments for chronic pain are inadequate, and new options are needed. Nonpharmaceutical approaches are especially attractive with many potential advantages including safety. Light therapy has been suggested to be beneficial in certain medical conditions such as depression, but this approach remains to be explored for modulation of pain. We investigated the effects of light-emitting diodes (LEDs), in the visible spectrum, on acute sensory thresholds in naive rats as well as in experimental neuropathic pain. Rats receiving green LED light (wavelength 525 nm, 8 h/d) showed significantly increased paw withdrawal latency to a noxious thermal stimulus; this antinociceptive effect persisted for 4 days after termination of last exposure without development of tolerance. No apparent side effects were noted and motor performance was not impaired. Despite LED exposure, opaque contact lenses prevented antinociception. Rats fitted with green contact lenses exposed to room light exhibited antinociception arguing for a role of the visual system. Antinociception was not due to stress/anxiety but likely due to increased enkephalins expression in the spinal cord. Naloxone reversed the antinociception, suggesting involvement of central opioid circuits. Rostral ventromedial medulla inactivation prevented expression of light-induced antinociception suggesting engagement of descending inhibition. Green LED exposure also reversed thermal and mechanical hyperalgesia in rats with spinal nerve ligation. Pharmacological and proteomic profiling of dorsal root ganglion neurons from green LED-exposed rats identified changes in calcium channel activity, including a decrease in the N-type (CaV2.2) channel, a primary analgesic target. Thus, green LED therapy may represent a novel, nonpharmacological approach for managing pain.
authors.affiliation: Departments of Anesthesiology and.|Pharmacology, College of Medicine, University of Arizona, Tucson, AZ, USA.
authors.forename: Mohab M
authors.initials: MM
authors.lastname: Ibrahim
authors.affiliation: Departments of Anesthesiology and.|Pharmacology, College of Medicine, University of Arizona, Tucson, AZ, USA.
authors.forename: Amol
authors.initials: A
authors.lastname: Patwardhan
authors.affiliation: Departments of Anesthesiology and.
authors.forename: Kerry B
authors.initials: KB
authors.lastname: Gilbraith
authors.affiliation: Pharmacology, College of Medicine, University of Arizona, Tucson, AZ, USA.
authors.forename: Aubin
authors.initials: A
authors.lastname: Moutal
authors.affiliation: Pharmacology, College of Medicine, University of Arizona, Tucson, AZ, USA.
authors.forename: Xiaofang
authors.initials: X
authors.lastname: Yang
authors.affiliation: Pharmacology, College of Medicine, University of Arizona, Tucson, AZ, USA.
authors.forename: Lindsey A
authors.initials: LA
authors.lastname: Chew
authors.affiliation: Pharmacology, College of Medicine, University of Arizona, Tucson, AZ, USA.
authors.forename: Tally
authors.initials: T
authors.lastname: Largent-Milnes
authors.affiliation: Departments of Anesthesiology and.|Pharmacology, College of Medicine, University of Arizona, Tucson, AZ, USA.
authors.forename: T Philip
authors.initials: TP
authors.lastname: Malan
authors.affiliation: Departments of Anesthesiology and.|Pharmacology, College of Medicine, University of Arizona, Tucson, AZ, USA.
authors.forename: Todd W
authors.initials: TW
authors.lastname: Vanderah
authors.affiliation: Departments of Anesthesiology and.|Pharmacology, College of Medicine, University of Arizona, Tucson, AZ, USA.
authors.forename: Frank
authors.initials: F
authors.lastname: Porreca
authors.affiliation: Pharmacology, College of Medicine, University of Arizona, Tucson, AZ, USA.
authors.forename: Rajesh
authors.initials: R
authors.lastname: Khanna
mesh_terms: D000700:Analgesics / Q000627:therapeutic use*; D000818:Animals; D020864:Calcium Channels, N-Type / Q000235:genetics / Q000378:metabolism; D059350:Chronic Pain / Q000628:therapy*; D003116:Color; D004195:Disease Models, Animal; D004307:Dose-Response Relationship, Radiation; D005260:Female; D005727:Ganglia, Spinal / Q000166:cytology / Q000187:drug effects; D008297:Male; D008526:Medulla Oblongata; D009270:Naloxone / Q000494:pharmacology; D009292:Narcotic Antagonists / Q000494:pharmacology; D017288:Pain Threshold / Q000528:radiation effects; D010789:Phototherapy / Q000379:methods*; D010812:Physical Stimulation / Q000009:adverse effects; D020671:Posterior Horn Cells / Q000187:drug effects / Q000528:radiation effects; D051381:Rats; D020318:Rats, Long-Evans; D017207:Rats, Sprague-Dawley; D011930:Reaction Time / Q000528:radiation effects
chemical_list: D000700:Analgesics; C503279:Cacna1b protein, rat; D020864:Calcium Channels, N-Type; D009292:Narcotic Antagonists; D009270:Naloxone