PHYSIOLOGICAL ASSESSMENT OF BOTULINUM TOXIN EFFECTS IN THE RAT LARYNX

Objective: Botulinum toxin (BT) is a currently used treatment for spas modic dysphonia (SD) and other related focal dystonias. The goal of th is study is to provide a basis for using the rat larynx to objectively assess physiological and histological effects of BT. Study Design: Do sages and volumes of BT injection were varied and three physiological parameters were measured. These measures included: optical density of PAS-stained laryngeal muscle after electrical stimulation, which is an indirect measure of denervation, spontaneous laryngeal muscle activit y, and laryngeal movement. Methods: A new microlaryngoscopic technique was developed, which made it possible to observe and manipulate the r at larynx endoscopically. Laryngeal movement and electromyographic (EM G) measures were made prior to injection and 3 days following BT injec tions of various dosages and volumes. Optical density measures were ma de 3 days after injection. Results: Significant reductions in vocal fo ld motion and spontaneous laryngeal muscle activity as a function of i ncreased BT dosage were observed. In addition, the optical density of PAS stained laryngeal muscle after electrical stimulation was increase d following BT injection. Significant volume effects in optical densit y were observed in the lateral thyroarytenoid and lateral cricoaryteno id muscles on the contralateral side. Conclusions: The rat laryngeal m odel is suitable for assessing BT effects. In addition, the three phys iological variables provided useful and reliable measures of laryngeal function. It is the authors' intention to use the rat laryngeal model to further examine the physiological and histological effects of BT w ith the goal of developing new methods for the treatment of patients w ith SD and other focal dystonias.