Nociceptive scores and endorphin-containing cells reduced by low-level laser therapy (LLLT) in inflamed paws of Wistar rat.
OBJECTIVE
This study aimed to investigate how local pain relief is mediated by laser therapy and how dose affects the relationship.


METHODS
Inflammation was induced in the hind-paws of Wistar rats. Two groups of rats received 780-nm laser therapy (Spectra-Medics Pty Ltd.) at one of two doses (2.5 and 1 J/cm(2)). One group acted as a control. Scores of nociceptive threshold were recorded using paw pressure and paw thermal threshold measures.


RESULTS
A dose of 1 J/cm(2) had no statistically significant effect on antinociceptive responses. A dose of 2.5 J/cm(2) demonstrated a statistically significant effect on paw pressure threshold ( p < 0.029) compared to controls. There was no difference in paw thermal threshold responses and paw volumes at either dose. Immunohistochemistry in control animals demonstrated normal beta-endorphin containing lymphocytes in control inflamed paws but no beta-endorphin containing lymphocytes in rats that received laser at 2.5 J/cm(2).


CONCLUSIONS
The results confirm previous findings that the effect of laser therapy is dose-related. The mechanism of effect may occur via a differentiated pressure-sensitive neural pathway rather than a thermal-sensitive neural pathway. The significance of the immunohistochemistry findings remains unknown.
Laakso
E-Liisa
EL
School of Physiotherapy and Exercise Science, Griffith University, Gold Coast Campus, PMB50 Gold Coast Mail Centre, Queensland 9726, Australia. l.laakso@griffith.edu.au
Cabot
Peter J
PJ
D000818:Animals; D006614:Hindlimb / Q000378:metabolism* / Q000528:radiation effects; D007249:Inflammation / Q000532:radiotherapy*; D028022:Low-Level Light Therapy; D008214:Lymphocytes / Q000378:metabolism*; D008297:Male; D010146:Pain / Q000532:radiotherapy; D017288:Pain Threshold; D011879:Radiotherapy Dosage; D051381:Rats; D017208:Rats, Wistar; D001615:beta-Endorphin / Q000378:metabolism*
D001615:beta-Endorphin