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This Article Full Text Full Text (PDF) All Versions of this Article: 543/2/655    most recent 2001.012982v1 Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Tam, S. L. Articles by Gordon, T. Search for Related Content PubMed PubMed Citation Articles by Tam, S. L. Articles by Gordon, T.

Tetrodotoxin prevents motor unit enlargement after partial denervation in rat hindlimb muscles

S. L. Tam, V. Archibald, N. Tyreman and T. Gordon

Findings that increased neuromuscular activity significantly reduced sprouting in partially denervated muscles prompted this present study to determine if the converse is true, namely that reduced activity promotes sprouting and motor unit (MU) enlargement. Partial denervation of rat hindlimb muscles by either the L4 or L5 spinal root avulsion resulted in extensive denervation (> 80 %) in tibialis anterior (TA) and medial gastrocnemius (MG) muscles, and moderate denervation (~50 %) in soleus (SOL) and plantaris (PL) muscles. The partially denervated muscles were then subjected to a 4 week programme of normal caged activity or TTX-induced neuromuscular inactivity. At 1 month, measurement of MU enlargement and quantification of sprouting were evaluated, respectively, by electrophysiological and histochemical means. Analysis of electrophysiological data showed that MU forces were significantly increased in both extensively and moderately denervated muscles 1 month after partial denervation and normal cage activity and that neuromuscular activity blockade by TTX completely abolished the MU enlargement in these partially denervated muscles. Histochemical analysis of sprouting revealed that the number of sprouts was significantly increased after partial denervation and normal cage activity, particularly after extensive denervation. TTX-induced neuromuscular inactivity dramatically reduced the number of sprouts and increased the number of free endplates in the extensively but not the moderately denervated muscles. These data demonstrate that a reduction in neuromuscular activity mediated by presynaptic blockade of neural action potentials reduces MU enlargement in partially denervated muscles by reducing axonal sprouting.