Involvement of medullary dorsal horn glial cell activation in mediation of masseter mechanical allodynia induced by experimental tooth movement.
OBJECTIVE
To investigate the involvement of microglial and astrocytic activation in the medullary dorsal horn (MDH) during the mediation of masseter area allodynia induced by experimental tooth movement (ETM).


METHODS
Five groups of adult Sprague-Dawley rats (n=60) were divided into control (CON), minocycline (MIN), ETM, and 10mg/kg or 30mg/kg MIN plus ETM (METM) groups. The upper-first-molar was moved mesially for rats in ETM and METM groups. Rats were pre-injected with minocycline in the MIN (30mg/kg) and METM (10mg/kg or 30mg/kg) groups. Pressure pain threshold (PPT) in masseter area was tested from day 0 to 14 for all 5 groups. Immunohistochemistry against OX42 (microglial marker) or GFAP (astrocytic maker) in the MDH was examined at days 1, 3, 7 and 14 for CON, MIN and 30mg/kg METM groups.


RESULTS
Baseline PPT was expectedly seen in either CON or MIN groups, masseter mechanical allodynia was detected in the ETM group from day 4 to 13 (P<0.05). OX42 expression level at days 1, 3 and 7, and GFAP expression level at days 3, 7 and 14 were higher in ETM (P<0.05), but not in 30mg/kg METM, than in CON group. Minocycline reduced activation of microglia and astrocytes, and significantly attenuated the development of masseter mechanical allodynia in this model.


CONCLUSIONS
These results indicate that mechanical allodynia in the masseter area induced by ETM can be attenuated by minocycline. Activation of microglia, possibly together with subsequent activation of astrocytes, seems to contribute to masseter mechanical allodynia.
Liu
Xiao-Dong
XD
Department of Oral Anatomy & Physiology and TMD, The Fourth Military Medical University, Xi'an, Shaanxi, PR China.
Wang
Jing-Jie
JJ
Sun
Lei
L
Chen
Liang-Wei
LW
Rao
Zhi-Ren
ZR
Duan
Li
L
Cao
Rong
R
Wang
Mei-Qing
MQ
D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology / Q000627:therapeutic use; D001253:Astrocytes / Q000187:drug effects / Q000378:metabolism; D005157:Facial Pain / Q000209:etiology / Q000503:physiopathology* / Q000517:prevention & control; D008297:Male; D008406:Masseter Muscle / Q000502:physiology*; D017628:Microglia / Q000187:drug effects / Q000378:metabolism; D008911:Minocycline / Q000494:pharmacology / Q000627:therapeutic use; D009419:Nerve Tissue Proteins / Q000096:biosynthesis; D017288:Pain Threshold; D020671:Posterior Horn Cells / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D018013:Receptors, Neuropeptide / Q000096:biosynthesis; D014087:Tooth Movement Techniques / Q000009:adverse effects
D000900:Anti-Bacterial Agents; D009419:Nerve Tissue Proteins; D018013:Receptors, Neuropeptide; D008911:Minocycline