Experimental myalgia induced by repeated infusion of acidic saline into the human masseter muscle does not cause the release of algesic substances
Version of Record online: 7 NOV 2012
© 2012 European Federation of International Association for the Study of Pain Chapters
European Journal of Pain
Volume 17, Issue 4, pages 539–550, April 2013
How to Cite
Ernberg, M., Castrillon, E.E., Ghafouri, B., Larsson, B., Gerdle, B., List, T. and Svensson, P. (2013), Experimental myalgia induced by repeated infusion of acidic saline into the human masseter muscle does not cause the release of algesic substances. European Journal of Pain, 17: 539–550. doi: 10.1002/j.1532-2149.2012.00216.x
This work was funded by an IASP grant from Scan|design Foundation by INGER & JENS BRUUN, the Swedish Research Council, the Swedish Rheumatism Association, the Swedish Dental Association and Karolinska Institutet.
Conflicts of interest
The authors declare that they have no conflict of interests.
- Issue online: 14 MAR 2013
- Version of Record online: 7 NOV 2012
- Manuscript Accepted: 25 JUL 2012
- INGER & JENS BRUUN
- Swedish Research Council
- Swedish Rheumatism Association
- Swedish Dental Association
- Karolinska Institutet
Animal studies have shown that two repeated intramuscular injections of acidic saline induce mechanical allodynia that lasts for 4 weeks with spread to the contralateral side. In this study, we tested the hypothesis that two repeated intramuscular infusions of acidic saline into the human masseter muscle is associated with pain, mechanical allodynia and release of algesic substances. Eighteen healthy volunteers participated. On day 1, 2.5 mL of acidic saline (pH 3.3) was infused into one of the masseter muscles and isotonic saline (pH 6.0) into the other (randomized and single-blind). Two days later, intramuscular microdialysis was performed to sample serotonin, glutamate, pyruvate, lactate and glucose, during which the saline infusions were repeated. Pain and pressure pain thresholds (PPTs) were recorded before and after infusions on both days.
Pain intensity induced by the infusions was higher after acidic than that after isotonic saline (p < 0.05). PPTs were decreased on both sides after microdialysis compared with baseline day 1 (p's < 0.05), but there were no differences in PPTs between sides at any time point. The levels of serotonin, glutamate, pyruvate, lactate or glucose did not change significantly during microdialysis.
Infusion of acidic saline caused low levels of muscle pain, but no mechanical allodynia and no increased release of algesic substances. The value of this model appears modest, but future studies could be performed with larger sample size and higher flow rate before definite conclusions about the validity of the model for craniofacial myalgia can be drawn.