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J Neurosci Res. 2014 Jul;92(7):904-14. doi: 10.1002/jnr.23370. Epub 2014 Feb 25.

Mechano- and metabosensitive alterations after injection of botulinum toxin into gastrocnemius muscle.

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Aix-Marseille Université (AMU) and Centre National de la Recherche Scientifique (CNRS), UMR 7287, Institut des Sciences du Mouvement: Etienne-Jules MAREY (ISM-EJM) Equipe Plasticité des Systèmes Nerveux et Musculaire, Parc Scientifique et Technologique de Luminy Faculté des Sciences du Sport de Marseille, Marseille, France.


This study was designed to investigate effects of motor denervation by Clostridium botulinum toxin serotype A (BoNT/A) on the afferent activity of fibers originating from the gastrocnemius muscle of rats. Animals were randomized in two groups, 1) untreated animals acting as control and 2) treated animals in which the toxin was injected in the left muscle. Locomotor activity was evaluated once per day during 12 days with a test based on footprint measurements of walking rats (sciatic functional index). At the end of the functional assessment period, electrophysiological tests were used to measure muscle properties, metabosensitive afferent fiber responses to chemical (KCl and lactic acid) injections, electrically induced fatigue (EIF), and mechanosensitive responses to tendon vibrations. Additionally, ventilatory response was recorded during repetitive muscle contractions. Then, rats were sacrificed, and the BoNT/A-injected muscles were weighed. Twelve days postinjection we observed a complete motor denervation associated with a significant muscle atrophy and loss of force to direct muscle stimulation. In the BoNT/A group, the metabosensitive responses to KCl injections were unaltered. However, we observed alterations in responses to EIF and to 1 mM of lactic acid (which induces the greatest activation). The ventilatory adjustments during repetitive muscle activation were abolished, and the mechanosensitive fiber responses to tendon vibrations were reduced. These results indicate that BoNT/A alters the sensorimotor loop and may induce insufficient motor and physiological adjustments in patients in whom a motor denervation with BoNT/A was performed.


Clostridium botulinum; electrophysiology; muscular afferents; neurotoxin; rat

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