Type grouping in skeletal muscles after experimental reinnervation: another expl

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Eur J Neurosci. 2005 Mar;21(5):1249-56.

Type grouping in skeletal muscles after experimental reinnervation:

another explanation.

Vleggeert-Lankamp CL, de Ruiter GC, Wolfs JF, Pego AP, Feirabend HK,

Lakke EA, Malessy MJ.

Neuroregulation group, Department of Neurosurgery, Leiden University

Medical Centre, PO Box 9600, NL-2300 RC Leiden, The Netherlands.

Type grouping signifies clustering of muscle fibres of the same

metabolic type, and is a frequent finding in reinnervated muscles. To

elucidate the mechanism behind it, the rat sciatic nerve was either

autografted or grafted with hollow synthetic nerve grafts. Twelve

weeks later the number and fibre area of the type I and type II

muscle fibres in the gastrocnemic and anterior tibial muscles were

determined after ATP-ase staining.

The number and diameter of peroneal nerve fibres distal to the grafts

were measured, and the number of Aalpha-nerve fibres was derived.

Nearly all nerve and muscle morphometrical parameters changed equally

in both experimental groups. However, type grouping occurred

frequently only after autografting, whereas the number of nerve

fibres and the number of Aalpha-nerve fibres increased in this group.

Hence type grouping cannot be explained by increased intramuscular

sprouting subsequent to a decrease in the number of innervating nerve

fibres, as previously presumed.

Regenerating axons branch along their course through the peripheral

nerve. We propose that the probability of the occurrence of type

grouping is related to the dispersion of sibling branches in the

nerve. In the autograft, emerging branches are kept together by

Schwann cell basal lamina scaffolds, in contrast to the hollow

synthetic nerve grafts where the emerging branches become dispersed.

Thus, in muscles reinnervated after autografting, the probability

that nerve branches that arrive at a specific muscle territory are

sibling branches is greater than after hollow tube grafting.

Consequently, the probability that type grouping will occur is

greater.