title: Early effect of Botox-A injection into the masseter muscle of rats: functional and histological evaluation.
abstract: BACKGROUND
  The purpose of this study was to evaluate the change of food intake after different dosages of botulinum toxin A (BTX) injection in the animal model. Additionally, the dimensional and histological change at 14 days after BTX injection was also evaluated.
  
  
  METHODS
  The comparative study was performed using the BTX injection model in rats (n= 5 for each group). Group 1 was the saline-injected group. Group 2 was the 5-unit BTX-injection group to each masseter muscle. Group 3 was the 10-unit BTX-injection group to each masseter muscle. Food intake rates and body weight were checked daily before and after BTX injection until 10 days. All animals were sacrificed at 14 days after BTX injection, and the specimens underwent hematoxylin and eosin stain and immunohistochemical staining for myosin type II (MYH2).
  
  
  RESULTS
  The recovery of food intake in groups 2 and 3 decreased significantly compared with group 1 from day 2 to day 7 and day 9 after injection (p< 0.05). The BTX-treated masseter muscles were significantly smaller than those in group 1 (p= 0.015). The immunohistochemical findings demonstrated that the expression of MYH2 was significantly higher in group 3 compared to groups 1 and 2 (p< 0.001).
  
  
  CONCLUSIONS
  BTX injection to the masseter muscle in rats demonstrated short food-intake-rate reduction with recovery until 10 days after injection. The thickness of the masseter muscle and MYH2 expression were significantly changed according to the injected dose of BTX.
authors.affiliation: Department of Orthodontics, School of Dentistry, Dental Research Institute, Seoul National University, Seoul, South Korea.
authors.forename: Young-Min
authors.initials: YM
authors.lastname: Moon
authors.affiliation: Department of Oral Medicine and Diagnosis, College of Dentistry, Research Institute of Oral Science, Gangneung-Wonju National University, Gangneung, South Korea.
authors.forename: Young-Jun
authors.initials: YJ
authors.lastname: Kim
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: Min-Keun
authors.initials: MK
authors.lastname: Kim
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.initials: SG
authors.lastname: Kim
authors.affiliation: Sericultural and Apicultural Materials Division, National Academy of Agricultural Science, Suwon, South Korea.
authors.forename: HaeYong
authors.initials: H
authors.lastname: Kweon
authors.affiliation: Department of Orthodontics, School of Dentistry, Dental Research Institute, Seoul National University, Seoul, South Korea.
authors.forename: Tae-Woo
authors.initials: TW
authors.lastname: Kim
keywords: Botulinum toxin A; Food intake; Masseter muscle; Myosin type II