UC San Diego

The effects of Botulinum neurotoxin A on the passive mechanical properties of skeletal muscle have not been researched but may have significant clinical effects in the treatment of neuromuscular disorders including spasticity. Single fiber and fiber bundle passive mechanical testing was performed on muscles treated with Botulinum neurotoxin A. Myosin heavy chain and titin composition of single fibers was determined by gel electrophoresis. Muscle collagen content was determined using a hydroxyproline assay. Botulinum neurotoxin treated single fiber passive elastic modulus, stiffness, and slack sarcomere length was reduced from the contralateral side. Single fiber myosin heavy chain composition shifted from faster to slower isoforms after treatment. The average titin molecular weight in a fiber also increased after treatment. Fiber bundle passive elastic modulus and stiffness increased while collagen content per mass of muscle tissue increased 48 percent. The passive mechanical properties of muscle change after injection with Botulinum neurotoxin and may be clinically beneficial to patients with spastic muscle