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Volume 26 , Issue 2
Spring 2012

Pages 132-141

Participation of Microglial p38 MAPK in Formalin-Induced Temporomandibular Joint Nociception in Rats

Kyoung A. Won, MSD/Young M. Kang, DDS, PhD/Min K. Lee, MSD, PhD/Min Kyoung Park, MSD/Jin S. Ju, MSD/Yong C. Bae, DDS, PhD/Dong K. Ahn, DDS, PhD

PMID: 22558613

Aims: To investigate nociceptive behavior and the immunoreactivity of microglia and phosphorylated-p38 (p-p38) mitogen-activated protein kinase (MAPK) following intracisternal administration of SB203580, a p38 MAPK inhibitor, or minocycline, a microglia -inhibitor, in rats with temporomandibular joint (TMJ) inflammation. Methods: The number of nociceptive behavioral responses was recorded for nine successive 5-minute intervals following formalin injections into the left TMJ. SB203580 or minocycline was administered intracisternally 2 hours prior to the formalin injection. Statistical analysis used one-way analysis of variance followed by least significant difference post-hoc analysis. Results: The intra-articular injection of formalin increased the expression of p-p38 MAPK in the ipsilateral medullary dorsal horn. Most of the p-p38 MAPK co-localized with OX42, a microglial marker, but not with GFAP, an astrocyte marker. Intracisternal injections of SB203580 (0.5, 1, or 5 g) attenuated the number of nociceptive behavioral responses and the expression of p-p38 MAPK in the medullary dorsal horn. Intracisternal injections of minocycline (25 or 50 g) also attenuated the responses and the expression of OX42 and p-p38 MAPK in the medullary dorsal horn. Conclusion: These findings suggest that p38 MAPK in microglia plays an important role in the central processing of inflammatory TMJ nociception in rats. The data further indicate that a targeted blockade of the microglial p38 MAPK pathway is a potentially important new treatment strategy for inflammatory TMJ nociception. J OROFAC PAIN 2012;26:132141

Key words: formalin, microglia, p38 MAPK, pain, TMJ

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