A rat model of the post-polio motor unit.
We examined the long-term effects of muscle usage on a rat model of the post-polio motor unit. Isometric tensions, type I and type II muscle fiber areas, the incidence of collateral sprouting, and motor endplate morphology were examined following 1, 3, 6, and 9 months of partial denervation in rat plantaris muscle. Full morphologic and functional stability of the expanded motor units occurred at 6 months post-partial denervation. Fiber hypertrophy was observed, possibly the result of compensatory work hypertrophy due to muscle overuse. Following 9 months of partial denervation and muscle overuse, the twitch and tetanic tensions and type I and type II muscle fiber areas were significantly reduced as compared to sham controls; angulated myofibers and group atrophy also were seen. The percent collateral sprouting, the number of terminal branches per endplate, and the endplate area were all increased, possibly a compensatory response to a decreased synthesis of neurotrophic factor(s) and/or transmitter-related components. These aging-like changes seem to occur earlier in chronically stressed, overenlarged, and overworked motor units.
Pachter
B R
BR
Department of Rehabilitation Medicine, New York University Medical Center, NY 10016.
Eberstein
A
A
D000818:Animals; D004195:Disease Models, Animal; D005260:Female; D007537:Isometric Contraction; D009045:Motor Endplate / Q000648:ultrastructure*; D009121:Muscle Denervation; D009132:Muscles / Q000294:innervation* / Q000473:pathology / Q000503:physiopathology; D009210:Myofibrils / Q000648:ultrastructure; D009416:Nerve Regeneration; D016262:Postpoliomyelitis Syndrome / Q000473:pathology* / Q000503:physiopathology; D051381:Rats; D011919:Rats, Inbred Strains