Development and Characterization of An Injury-free Model of Functional Pain in Rats by Exposure to Red Light.

TitleDevelopment and Characterization of An Injury-free Model of Functional Pain in Rats by Exposure to Red Light.
Publication TypeJournal Article
Year of Publication2019
AuthorsKhanna R, Patwardhan A, Yang X, Li W, Cai S, Ji Y, Chew LA, Dorame A, Bellampalli SS, Schmoll RW, Gordon J, Moutal A, Vanderah TW, Porreca F, Ibrahim MM
JournalJ Pain
Volume20
Issue11
Pagination1293-1306
Date Published2019 11
ISSN1528-8447
KeywordsAnimals, Disease Models, Animal, Female, Hyperalgesia, Light, Male, Pain, Rats, Rats, Sprague-Dawley
Abstract

We report the development and characterization of a novel, injury-free rat model in which nociceptive sensitization after red light is observed in multiple body areas reminiscent of widespread pain in functional pain syndromes. Rats were exposed to red light-emitting diodes (RLED) (LEDs, 660 nm) at an intensity of 50 Lux for 8 hours daily for 5 days resulting in time- and dose-dependent thermal hyperalgesia and mechanical allodynia in both male and female rats. Females showed an earlier onset of mechanical allodynia than males. The pronociceptive effects of RLED were mediated through the visual system. RLED-induced thermal hyperalgesia and mechanical allodynia were reversed with medications commonly used for widespread pain, including gabapentin, tricyclic antidepressants, serotonin/norepinephrine reuptake inhibitors, and nonsteroidal anti-inflammatory drugs. Acetaminophen failed to reverse the RLED induced hypersensitivity. The hyperalgesic effects of RLED were blocked when bicuculline, a gamma-aminobutyric acid-A receptor antagonist, was administered into the rostral ventromedial medulla, suggesting a role for increased descending facilitation in the pain pathway. Key experiments were subjected to a replication study with randomization, investigator blinding, inclusion of all data, and high levels of statistical rigor. RLED-induced thermal hyperalgesia and mechanical allodynia without injury offers a novel injury-free rodent model useful for the study of functional pain syndromes with widespread pain. RLED exposure also emphasizes the different biological effects of different colors of light exposure. PERSPECTIVE: This study demonstrates the effect of light exposure on nociceptive thresholds. These biological effects of red LED add evidence to the emerging understanding of the biological effects of light of different colors in animals and humans. Understanding the underlying biology of red light-induced widespread pain may offer insights into functional pain states.

DOI10.1016/j.jpain.2019.04.008
Alternate JournalJ Pain
PubMed ID31054915
PubMed Central IDPMC6824986
Grant ListK08 NS104272 / NS / NINDS NIH HHS / United States
R01 AT009716 / AT / NCCIH NIH HHS / United States
R01 DA042852 / DA / NIDA NIH HHS / United States
R01 NS098772 / NS / NINDS NIH HHS / United States
Faculty Member Reference: 
Mohab M. Ibrahim, PhD, MD
Rajesh Khanna
Aubin Moutal
Amol Patwardhan, M.D., Ph.D.
Frank Porreca, PhD
Todd Vanderah, PhD