title: S100 and p65 expression are increased in the masseter muscle after botulinum toxin-A injection.
abstract: BACKGROUND
  The purpose of this study was to compare the expression levels of p65 and S100 in the rat masseter muscle after the injection of different concentrations of botulinum toxin-A (BTX-A).
  
  
  METHODS
  We injected either 5 or 10 U of BTX-A into both masseter muscle of rats. As a control group, the same volume of saline was injected. After 14 days, the animals were sacrificed. Subsequently, a biopsy and immunohistochemical staining of the samples were performed using a p65 or S100 antibody.
  
  
  RESULTS
  The cross-sectional area of each myofibril was significantly reduced by BTX-A injection (P< 0.001). The expression of p65 and S100 increased significantly with increasing concentrations of BTX-A (P< 0.001).
  
  
  CONCLUSIONS
  The injection of BTX-A into the masseter muscle induced muscle atrophy. Subsequently, p65 and S100 expression in myoblasts were increased for the protection of muscle cells.
authors.affiliation: Department of Oral and Maxillofacial Surgery, College of Dentistry, Gangneung-Wonju National University, 7 Jukhyun-gil, Gangneung, 210-702 South Korea.
authors.forename: Young-Wook
authors.initials: YW
authors.lastname: Park
authors.affiliation: Department of Oral and Maxillofacial Surgery, College of Dentistry, Gangneung-Wonju National University, 7 Jukhyun-gil, Gangneung, 210-702 South Korea.
authors.forename: Seong-Gon
authors.identifier: 0000-0001-5088-2732
authors.initials: SG
authors.lastname: Kim
authors.affiliation: Sericultural and Apicultural Materials Division, National Academy of Agricultural Science, Suwon, South Korea.
authors.forename: You-Young
authors.initials: YY
authors.lastname: Jo
keywords: Apoptosis; Botulinum toxin-A; Masseter muscle; S100; p65