title: Changes of masseter muscle activity following injection of botulinum toxin type A in adult rats.
abstract: OBJECTIVE
  To investigate changes in masseter muscle function following intramuscular injection of different dose-dependent botulinum toxin type A (BTXA).
  
  
  METHODS
  Department of Orthodontics at Taipei Medical University. Fifty-two, 70-day-old male Wistar rats were randomly divided into four groups. Group I received 7.5 U of BTXA (0.3 ml), Group II received 5.0 U, and Group III received 2.5 U in the right masseter muscle, respectively. Group IV is the control and received no BTXA injection.
  
  
  METHODS
  A wire electrode device was implanted to record muscle activity. One week after implantation, the rats were fed every 2 h and EMG signals were recorded during the first hour. All signals were recorded for 12 weeks. Thereafter, EMG data were analyzed for statistical calculation and weights of masseter muscles were measured.
  
  
  RESULTS
  Masseter muscle activity decreased 99% during the first week after BTXA injection and gradually recovered from the 3rd week on in Groups I-III. By the 12th week, muscle activity recovered to 41% in Groups I and II and 56.26% in Group III. No significant changes of muscle activity were observed in Group IV.
  
  
  CONCLUSIONS
  BTXA induced a reduction in masseter muscle activity and an increased toxin dose resulted in greater depression of muscle activity.
authors.affiliation: School of Dentistry, College of Oral Medicine, Taipei Medical University, Taipei, Taiwan.|Division of Orthodontics, Department of Dentistry, Taipei Medical University Hospital, Taipei, Taiwan.
authors.forename: C Y
authors.initials: CY
authors.lastname: Tsai
authors.affiliation: School of Dentistry, College of Oral Medicine, Taipei Medical University, Taipei, Taiwan.
authors.forename: Y Y
authors.initials: YY
authors.lastname: Lei
authors.affiliation: Department of Physiology, College of Medicine, Taipei Medical University, Taipei, Taiwan.
authors.forename: L Y
authors.initials: LY
authors.lastname: Yang
authors.affiliation: School of Dentistry, College of Oral Medicine, Taipei Medical University, Taipei, Taiwan.|Department of Orthodontics, Cardinal Tien Hospital Yung Ho Branch, Yungho, New Taipei City, Taiwan.
authors.forename: W C
authors.initials: WC
authors.lastname: Chiu
mesh_terms: D000703:Analog-Digital Conversion; D000818:Animals; D019274:Botulinum Toxins, Type A / Q000008:administration & dosage*; D004305:Dose-Response Relationship, Drug; D004576:Electromyography / Q000187:drug effects; D008297:Male; D008406:Masseter Muscle / Q000033:anatomy & histology / Q000187:drug effects*; D008409:Mastication / Q000502:physiology; D009465:Neuromuscular Agents / Q000008:administration & dosage*; D009929:Organ Size / Q000187:drug effects; D011897:Random Allocation; D051381:Rats; D017208:Rats, Wistar; D013997:Time Factors
chemical_list: D009465:Neuromuscular Agents; D019274:Botulinum Toxins, Type A
keywords: EMG; botulinum toxin type A; masseter muscle