INCREASED ACUTE AND CHRONIC MITOTIC-ACTIVITY IN RAT LARYNGEAL MUSCLESAFTER BOTULINUM TOXIN INJECTION

Objectives: To characterize the acute and chronic cellular effects of botulinum toxin (BT) injection into rat laryngeal muscles. A complete characterization of these effects is important because patients with f ocal dystonias of the head and neck are commonly treated with BT injec tion. Further, potential muscular changes in the larynx must be carefu lly delineated owing to the critical phonatory and airway protective f unctions of these muscles. Study Design: The acute and chronic cellula r effects of BT injection were studied using 5'-bromo 2'-deoxyuridine (BrdU) following single and repeated BT injection into rat laryngeal m uscles. BrdU is incorporated into mitotically active nuclei such that changes in cell proliferative behavior following BT injection can be m onitored. Results: Increased mitotic activity was detected in the tiss ue samples studied following ET injection, Differences in the times of the peak distribution of BrdU-labeled cells in each laryngeal muscle were observed, This may be related to the diffusion effects of BT. Pro longed muscle fiber changes, including splitting, were also observed a s the result of repeated BT injection. Conclusions: The results of thi s study suggest that BT may induce a proliferative response in muscle tissue.