title: Light-Emitting Diode Phototherapy Reduces Nocifensive Behavior Induced by Thermal and Chemical Noxious Stimuli in Mice: Evidence for the Involvement of Capsaicin-Sensitive Central Afferent Fibers.
abstract: Low-intensity phototherapy using light fonts, like light-emitting diode (LED), in the red to infrared spectrum is a promising alternative for the treatment of pain. However, the underlying mechanisms by which LED phototherapy reduces acute pain are not yet well understood. This study investigated the analgesic effect of multisource LED phototherapy on the acute nocifensive behavior of mice induced by thermal and chemical noxious stimuli. The involvement of central afferent C fibers sensitive to capsaicin in this effect was also investigated. Mice exposed to multisource LED (output power 234, 390, or 780 mW and power density 10.4, 17.3, and 34.6 mW/cm2, respectively, from 10 to 30 min of stimulation with a wavelength of 890 nm) showed rapid and significant reductions in formalin- and acetic acid-induced nocifensive behavior. This effect gradually reduced but remained significant for up to 7 h after LED treatment in the last model used. Moreover, LED (390 mW, 17.3 mW/cm2/20 min) irradiation also reduced nocifensive behavior in mice due to chemical [endogenous (i.e., glutamate, prostaglandins, and bradykinin) or exogenous (i.e., formalin, acetic acid, TRPs and ASIC agonist, and protein kinase A and C activators)] and thermal (hot plate test) stimuli. Finally, ablating central afferent C fibers abolished LED analgesia. These experimental results indicate that LED phototherapy reduces the acute painful behavior of animals caused by chemical and thermal stimuli and that LED analgesia depends on the integrity of central afferent C fibers sensitive to capsaicin. These findings provide new information regarding the underlying mechanism by which LED phototherapy reduces acute pain. Thus, LED phototherapy may be an important tool for the management of acute pain.
authors.affiliation: Graduate Program in Pharmacology, Center of Health Sciences, Federal University of Santa Maria, Camobi, Santa Maria, RS, 97105-900, Brazil.|Laboratory of Neurobiology of Pain and Inflammation, Department of Physiological Sciences, Center of Biological Sciences, Federal University of Santa Catarina, Trindade, Florianópolis, SC, 88040-900, Brazil.
authors.forename: Glauce Regina
authors.initials: GR
authors.lastname: Pigatto
authors.affiliation: Laboratory of Neurobiology of Pain and Inflammation, Department of Physiological Sciences, Center of Biological Sciences, Federal University of Santa Catarina, Trindade, Florianópolis, SC, 88040-900, Brazil.
authors.forename: Igor Santos
authors.initials: IS
authors.lastname: Coelho
authors.affiliation: Laboratory of Neurobiology of Pain and Inflammation, Department of Physiological Sciences, Center of Biological Sciences, Federal University of Santa Catarina, Trindade, Florianópolis, SC, 88040-900, Brazil.
authors.forename: Rosane Schenkel
authors.initials: RS
authors.lastname: Aquino
authors.affiliation: Graduate Program in Pharmacology, Center of Health Sciences, Federal University of Santa Maria, Camobi, Santa Maria, RS, 97105-900, Brazil.|Department of Physiology and Pharmacology, Center of Health Sciences, Federal University of Santa Maria, Camobi, Santa Maria, RS, 97105-900, Brazil.
authors.forename: Liliane Freitas
authors.initials: LF
authors.lastname: Bauermann
authors.affiliation: Graduate Program in Pharmacology, Center of Health Sciences, Federal University of Santa Maria, Camobi, Santa Maria, RS, 97105-900, Brazil. adair.santos@ufsc.br.|Laboratory of Neurobiology of Pain and Inflammation, Department of Physiological Sciences, Center of Biological Sciences, Federal University of Santa Catarina, Trindade, Florianópolis, SC, 88040-900, Brazil. adair.santos@ufsc.br.
authors.forename: Adair Roberto Soares
authors.initials: ARS
authors.lastname: Santos
mesh_terms: D019342:Acetic Acid; D062565:Acid Sensing Ion Channels / Q000378:metabolism; D000262:Adenylyl Cyclases / Q000378:metabolism; D000344:Afferent Pathways / Q000187:drug effects / Q000502:physiology*; D000698:Analgesia; D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects*; D002211:Capsaicin / Q000494:pharmacology*; D004487:Edema / Q000473:pathology; D005260:Female; D005557:Formaldehyde; D006358:Hot Temperature; D008027:Light; D051379:Mice; D010789:Phototherapy; D011493:Protein Kinase C / Q000378:metabolism; D012018:Reflex; D050051:Transient Receptor Potential Channels / Q000378:metabolism
chemical_list: D062565:Acid Sensing Ion Channels; D050051:Transient Receptor Potential Channels; D005557:Formaldehyde; D011493:Protein Kinase C; D000262:Adenylyl Cyclases; D019342:Acetic Acid; D002211:Capsaicin
keywords: Acute pain; Analgesia; Chemical and thermal stimuli; Light-emitting diode; Phototherapy