Neuromuscular adaptations to cross-reinnervation in 12- and 29-mo-old Fischer 344 rats.
The aim was to test hypotheses regarding the adaptive response of the extensor digitorum longus (EDL) muscle of 12- and 29-mo rats following denervation and cross-reinnervation by the soleus nerve. The mass of cross-reinnervated EDL muscle was 87 and 86% of self-reinnervated control values in 12-mo (99 +/- 3 mg) and 29-mo (74 +/- 3 mg) rats, respectively. Cross-reinnervated EDL fiber area was 56 and 67% of self-reinnervated values in 12-mo (1,733 +/- 253 microns 2) and 29-mo (1,264 +/- 71 microns 2) rats, respectively. Cross-reinnervation increased the density of neural contact 26% in 12-mo rats and decreased density by 50% in 29-mo animals. In 12-mo rats 17% of motor end plates (MEP) were void of terminal nerves following cross-reinnervation compared with 48% in 29-mo rats. In cross-reinnervated muscles, slow myosin heavy chain (MHC) was 65 +/- 9 and 25 +/- 3% of total MHC in 12- and 29-mo rats, respectively. The percentage of type I fibers derived histochemically was 65 +/- 8% in 12-mo rats and 18 +/- 1% in 29-mo rats. In conclusion, there is an age-associated decrease in the ability of neurons to reinnervate the MEP area after nerve section. The conversion of fiber type in innervated fibers in response to cross-reinnervation may not differ due to age.
Clark
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KI
Department of Kinesiology, University of Michigan, Ann Arbor 48109-2214.
White
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TP
D000375:Aging; D000818:Animals; D008297:Male; D009045:Motor Endplate / Q000502:physiology*; D009121:Muscle Denervation; D024510:Muscle Development; D009132:Muscles / Q000294:innervation*; D009218:Myosins / Q000378:metabolism; D009411:Nerve Endings / Q000502:physiology; D051381:Rats; D011916:Rats, Inbred F344; D012016:Reference Values; D012038:Regeneration
D009218:Myosins