title: Type grouping in skeletal muscles after experimental reinnervation: another explanation.
abstract: 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.
authors.affiliation: Neuroregulation group, Department of Neurosurgery, Leiden University Medical Centre, PO Box 9600, NL-2300 RC Leiden, The Netherlands. cvleggeert@lumc.nl
authors.forename: C L A M
authors.initials: CL
authors.lastname: Vleggeert-Lankamp
authors.forename: G C W
authors.initials: GC
authors.lastname: de Ruiter
authors.forename: J F C
authors.initials: JF
authors.lastname: Wolfs
authors.forename: A P
authors.initials: AP
authors.lastname: Pêgo
authors.forename: H K P
authors.initials: HK
authors.lastname: Feirabend
authors.forename: E A J F
authors.initials: EA
authors.lastname: Lakke
authors.forename: M J A
authors.initials: MJ
authors.lastname: Malessy
mesh_terms: D000251:Adenosine Triphosphatases / Q000378:metabolism; D000818:Animals; D004146:Dioxanes / Q000600:supply & distribution; D005260:Female; D023421:Models, Animal; D009121:Muscle Denervation / Q000379:methods; D018485:Muscle Fibers, Skeletal / Q000145:classification / Q000166:cytology / Q000473:pathology / Q000502:physiology*; D018482:Muscle, Skeletal / Q000294:innervation* / Q000503:physiopathology; D009413:Nerve Fibers, Myelinated / Q000502:physiology / Q000637:transplantation; D009416:Nerve Regeneration / Q000502:physiology*; D010543:Peroneal Nerve / Q000293:injuries* / Q000473:pathology / Q000601:surgery / Q000648:ultrastructure; D019736:Prostheses and Implants; D011897:Random Allocation; D051381:Rats; D017208:Rats, Wistar; D012584:Sciatic Nerve / Q000637:transplantation; D013194:Staining and Labeling / Q000379:methods; D014182:Transplantation, Autologous / Q000379:methods
chemical_list: D004146:Dioxanes; C443643:trimethylene carbonate; D000251:Adenosine Triphosphatases