Alteration of intrafusal bundle composition by nerve crush in neonatal rats.
We examined the expression of myosin heavy-chain isoforms in intrafusal muscle fibers of spindles formed in gastrocnemius muscles reinnervated in the presence of exogenous nerve growth factor after nerve crush in neonatal rats. Only 50% of the experimental spindles contained intrafusal fibers that expressed a slow-tonic myosin normally expressed by at least one fiber in every rat spindle. In addition, spindles containing only bag1 and/or chain fibers, but no bag2 fibers, were observed in reinnervated muscles whereas all normal spindles contain a bag2 fiber. These data suggest that afferents retain the capacity to induce the expression of a spindle-specific myosin in a period other than during normal development of intrafusal fibers. However, a scarcity of precursor cells available to become intrafusal fibers when contacted by afferents might have resulted in the alteration of intrafusal bundle composition in some spindles of reinnervated muscles.
Kucera
J
J
Department of Neurology, School of Medicine, Boston University, MA 02118.
Walro
J
J
D000251:Adenosine Triphosphatases / Q000032:analysis; D000818:Animals; D000831:Animals, Newborn / Q000502:physiology*; D009132:Muscles / Q000166:cytology / Q000294:innervation*; D009409:Nerve Crush; D009475:Neurons, Afferent / Q000648:ultrastructure; D051381:Rats; D011919:Rats, Inbred Strains; D013194:Staining and Labeling
D000251:Adenosine Triphosphatases