title: Increase in the number of intrafusal muscle fibres in rat muscles after neonatal motor denervation.
abstract: Rat muscle spindles disintegrate after total neonatal muscle denervation in which both sensory and motor axons are cut, but develop almost normally during the first three weeks after neonatal de-efferentation, attaining the usual complement of four intrafusal fibres, two bag and two chain fibres. Thereafter additional intrafusal fibres differentiate in most of the de-efferented spindles. We have examined the development of supernumerary fibres in muscle spindles of the rat hind limb muscles one to four months after neonatal de-efferentation using transmission electron microscopy. Additional intrafusal fibres originate both from activated intrafusal myosatellites and by different forms of fibre division. In a sample of 27 muscle spindles examined along the A zone five weeks after de-efferentation, the mean number of intrafusal fibre profiles increased almost two-fold to 7.9 +/- 3.3 (S.D.). Up to 20 intrafusal fibre profiles per spindle cross-section were found in muscles de-efferented for four months. The supernumerary fibres were apparently derived from all three intrafusal fibre types, but predominantly from the chain fibres. It is noteworthy that de-efferentation which causes wasting of extrafusal muscle initiates myogenesis and maintains additional intrafusal fibres within the spindle capsules.
authors.affiliation: Institute of Physiology, Czechoslovak Academy of Sciences, Prague.
authors.forename: J
authors.initials: J
authors.lastname: Zelená
authors.forename: T
authors.initials: T
authors.lastname: Soukup
mesh_terms: D000818:Animals; D000831:Animals, Newborn / Q000502:physiology*; D008854:Microscopy, Electron; D009046:Motor Neurons / Q000502:physiology*; D009121:Muscle Denervation; D009132:Muscles / Q000294:innervation* / Q000648:ultrastructure; D009412:Nerve Fibers / Q000502:physiology* / Q000648:ultrastructure; D009475:Neurons, Afferent / Q000502:physiology; D051381:Rats; D017208:Rats, Wistar