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KMID : 0355820140350010089
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Korean Journal of Oral Anatomy
2014 Volume.35 No. 1 p.89 ~ p.103
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Evaluation of MAPK pathway activation in brainstem induced by the masseter muscle inflammation
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Nakatsuka Michiko
Kumabe Shunji
Gamoh Shoko
Akiyama Hironori
Jue Seong-Suk
Kim Ji-Youn
Ueda Katsura
Matsuda Yoshifumi
Shimizutani Kimishige
Shin Je-Won
Iwai Yasutomo
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Abstract
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To evaluate the inflammatory hyperalgesia induced by noxious stimulation of the masticatory muscles, we performed an immunohistochemical study on the expressions of phosphorylated-p38 (p-p38) mitogen activated-protein kinase (MAPK) and the distribution of activated microglia in the trigeminal subnucleus caudalis (Vc). The left masseter muscle (LMM) of Sprague Dawley rats (male, 250 g, n=60) was stimulated in the following methods: 1) L-L group (control); the LMM was injected with lipopolysaccharide (LPS, 2 μg/kg, 100μl) on the 1st day of the experiment. On day 2, the same site was injected with the LPS again. 2) L-S6 group (experimental); the LMM was injected with LPS (2 μg/kg, 100μl) on the 1st day of the experiment. On day 2, the same site was injected with 6 % sodium chloride solution (S6, 100 μl, 5 times per 90 min). Rats were allowed to survive for 1 day, 7 days or 14 days after the last injection. The brainstems were dissected and cut
with a cryostat (at 30 μm thickness). These specimens were investigated with anti-TNFα (masseter muscle), the bradykinin receptor B2 (BKRB2, masseter muscle), anti-p-p38 MAPK (brainstem) and anti-Iba1 (ionized calcium-binding adapter molecule 1: Iba1, a marker for microglial activity; brainstem) enzyme-labeled antibody method. The specimens were observed and evaluated using a light microscope (LM) mounted with an Olympus FX380 3CCD digital camera system connected with a FLvFs software (Flovel Image Filling System, Tokyo, Japan). In both groups, the TNF-α and the BKRB2-immunoreactive (IR) cells were observed until 7 days after stimulation. In the experimental group, the LM histology indicates that p-p38 MAPK and Iba1-IR cells were particularly localized in the left Vc until 14 days after stimulation. In the experimental group, 7 days or 14 days after nociception, the p-p38 MAPK-IR cells were recognized in the contralateral and ipsilateral in the Vc. The results suggest that the prolonged MAPK activity in the Vc is related to central sensitization in chronic pain of the masseter muscle.
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KEYWORD
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masseter muscle, chronic pai
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