Extrafusal and intrafusal muscle effects in experimental botulinum toxin-A injection

TLDR

Both extrafusal and intrafusal muscle fibers are cholinergically innervated and are progressively affected by botulinum toxin, with potential differences in degree, and the toxin may also alter spindle afferent discharge in dystonia. The effects of botulinum toxin‑A were compared on both extrafusal and intrafusal muscle fibers in the biceps femoris of Wistar rats. Four days post‑injection, no action potentials were elicited and extrafusal fibers began to atrophy, while by day 14 jitter increased, both extrafusal and intrafusal fibers showed progressive atrophy, and there were increased terminal innervation ratios, end‑plate spread of cholinesterase, and a higher density of very small myelinated fibers in large intramuscular nerves. © 1996 John Wiley & Sons, Inc.

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. © 1996 John Wiley & Sons, Inc.