GaAlAs (830 nm) low-level laser enhances peripheral endogenous opioid analgesia in rats

Low-level laser therapy (LLLT) has been reported to relieve pain with minimal side effects. Recent studies have demonstrated that opioid-containing immune cells migrate to inflamed sites and release beta-endorphins to inhibit pain as a mode of peripheral endogenous opioid analgesia. The present study investigates whether LLLT may enhance peripheral endogenous opioid analgesia.

The effect of LLLT on opioid analgesia and production was evaluated in vivo in a rat model of inflammation as well as in vitro in Jurkat cells, a human T-cell leukemia cell line. mRNA expression of the beta-endorphin precursors proopiomelanocortin and corticotrophin releasing factor was assessed by reverse transcription polymerase chain reaction.

LLLT produced an analgesic effect in inflamed peripheral tissue which was transiently antagonized by naloxone. Beta-endorphin precursor mRNA expression increased with LLLT, both in vivo and in vitro.

This study demonstrates that LLLT produces analgesic effects in a rat model of peripheral inflammation. We further revealed an additional mechanism of LLLT-mediated analgesia via enhancement of peripheral endogenous opioids. These findings suggest that LLLT induces analgesia in rats by enhancing peripheral endogenous opioid production in addition to previously reported mechanisms.