title: Extrafusal and intrafusal muscle effects in experimental botulinum toxin-A injection.
abstract: The effects of botulinum toxin-A was compared on both extrafusal and intrafusal muscle fibers in the biceps femoris of Wistar rats. Four days after injection no action potentials were elicited with stimulation single-fiber electromyography on the injected side. Fourteen days after injection, jitter became measurable and these values were increased on the injected side. Extrafusal muscle fibers began to atrophy on the 4th day and this continued to the 14th day postinjection. Atrophy was also evident and progressive in intrafusal muscle fibers. Increased terminal innervation ratios, end-plate spread of cholinesterase, and increased density of very small myelinated fibers in large intramuscular nerves were observed 14 days postinjection. Both extrafusal and intrafusal fibers are cholinergically innervated, and both were progressively affected by botulinum toxin, perhaps varying in degree only. In addition to partial denervation, Botulinum toxin effects in dystonia may also be related to modified spindle afferent discharge.
authors.affiliation: Third Department of Internal Medicine, Kagoshima University School of Medicine, Kagoshima, Japan.
authors.forename: R L
authors.initials: RL
authors.lastname: Rosales
authors.forename: K
authors.initials: K
authors.lastname: Arimura
authors.forename: S
authors.initials: S
authors.lastname: Takenaga
authors.forename: M
authors.initials: M
authors.lastname: Osame
mesh_terms: D000251:Adenosine Triphosphatases / Q000378:metabolism; D000818:Animals; D001905:Botulinum Toxins / Q000494:pharmacology*; D004576:Electromyography; D004594:Electrophysiology; D007279:Injections, Subcutaneous; D018485:Muscle Fibers, Skeletal / Q000187:drug effects / Q000378:metabolism / Q000648:ultrastructure; D009470:Muscle Spindles / Q000187:drug effects / Q000378:metabolism; D009132:Muscles / Q000187:drug effects* / Q000294:innervation / Q000502:physiology; D009420:Nervous System / Q000187:drug effects / Q000473:pathology; D051381:Rats; D017208:Rats, Wistar
chemical_list: D001905:Botulinum Toxins; D000251:Adenosine Triphosphatases