Effects of masticatory muscle treatment with Botulinum neurotoxin type A on cell division in the mandibular condyle in rabbits

Abstract

The purpose of this thesis was to gain a better insight into proliferative activity of cells in the mandibular condylar cartilage in the condition of paralysis of the masseter using BTX-A. Fifty adult five-month-old female New Zealand rabbits had been used, thirty-one animals received an injection of 10U BTX (Botox, Allergan Inc., Irvine, CA) while the other nineteen received an equivalent volume of 0.9% saline (sham animals) into one randomly chosen superficial masseter muscle. Each animal had been injected i.v. with BrdU (40 mg/kg as a 10 mg/ml solution in phosphate-buffered saline) seven days prior to sacrifice. The animals were terminated at two endpoints: 4 weeks and 12 weeks. From the widest part of each sectioned condyle, slides were were reacted for BrdU. Counts of replicating cells in the condylar cartilage were performed in each third in the 3 defined zones: fibrous, proliferative, and mature plus hypertrophic. Our findings showed that BTX-A therapy affected mitotic activity of cells at the mandibular condyle. BTX caused a high frequency of local thickening of the fibrous zone associated with high proliferation. Overall levels of proliferation were comparable to or higher than those of controls. The effect was especially prominent on the uninjected contralateral side 12 weeks after BTX administration.