Int J Oral Biol.  2010 Sep;35(3):83-89.

A Blockade of the Central MAPK Pathway Attenuates Referred Pain in Rats with Complete Freund's Adjuvant-Induced Inflammation of the Temporomandibular Joint

• Won KA
• Lim NH
• Lee MK
• Park MK
• Yang GY
• Park YY
• Ahn DK
• Bae YC

Abstract

We investigated the role of the central MAPK pathways in extra-territorial (referred) pain resulting from inflammation of the temporomandibular joint (TMJ). Experiments were carried out on male Sprague-Dawley rats weighing 220-280 g. Under anesthesia, these animals were injected with 50 microL of complete Freund's adjuvant (CFA) into the TMJ using a Hamilton syringe. In the control group, saline was injected into the TMJ. To identify the extent of inflammation of the TMJ, Evans blue dye (0.1%, 5 mg/kg) was injected intravenously at 1, 3, 6, 9, 12 and 15 days after CFA injection. The concentration of Evans blue dye in the extracted TMJ tissue was found to be significantly higher in the CFA-treated animals than in the saline-treated group. Air-puff thresholds in the vibrissa pad area were evaluated 3 days before and at 3, 6, 9, 12, 15 and 18 days after CFA injection into the TMJ. Referred mechanical allodynia was established at 3 days, remained until 12 days, and recovered to preoperative levels at 18 days after CFA injection. This referred mechanical allodynia was observed in contralateral side area. To investigate the role of central MAPK pathways, MAPK inhibitors (10 microg) were administrated intracisternally 9 days after CFA injection. SB203580, a p38 MAPK inhibitor, significantly attenuated referred mechanical allodynia, as compared with the vehicle group. PD98059, a MEK inhibitor, also reduced CFA-induced referred mechanical allodynia. These results suggest that TMJ inflammation produces extra-territorial mechanical allodynia, and that this is mediated by central MAPK pathways.

Keyword

temporomandibular joint; referred pain; p38 MAPK; ERK; complete Freund's adjuvant

MeSH Terms

Anesthesia
Animals
Evans Blue
Flavonoids
Freund's Adjuvant
Humans
Hyperalgesia
Imidazoles
Inflammation
Male
p38 Mitogen-Activated Protein Kinases
Pain, Referred
Pyridines
Rats
Rats, Sprague-Dawley
Syringes
Temporomandibular Joint
Evans Blue
Flavonoids
Freund's Adjuvant
Imidazoles
Pyridines
p38 Mitogen-Activated Protein Kinases