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Effects of hindlimb unloading on neuromuscular development of neonatal ratsWe hypothesized that hindlimb suspension unloading of 8-day-old neonatal rats would disrupt the normal development of muscle fiber types and the motor innervation of the antigravity (weightbearing) soleus muscles but not extensor digitorum longus (EDL) muscles. Five rats were suspended 4.5 h and returned 1.5 h to the dam for nursing on a 24 h cycle for 9 days. To control for isolation from the dam, the remaining five littermates were removed on the same schedule but not suspended. Another litter of 10 rats housed in the same room provided a vivarium control. Fibers were typed by myofibrillar ATPase histochemistry and immunostaining for embryonic, slow, fast IIA and fast IIB isomyosins. The percentage of multiple innervation and the complexity of singly-innervated motor terminal endings were assessed in silver/cholinesterase stained sections. Unique to the soleus, unloading accelerated production of fast IIA myosin, delayed expression of slow myosin and retarded increases in standardized muscle weight and fiber size. Loss of multiple innervation was not delayed. However, fewer than normal motor nerve endings achieved complexity. Suspended rats continued unloaded hindlimb movements. These findings suggest that motor neurons resolve multiple innervation through nerve impulse activity, whereas the postsynaptic element (muscle fiber) controls endplate size, which regulates motor terminal arborization. Unexpectedly, in the EDL of unloaded rats, transition from embryonic to fast myosin expression was retarded. Suspension-related foot drop, which stretches and chronically loads EDL, may have prevented fast fiber differentiation. These results demonstrate that neuromuscular development of both weightbearing and non-weightbearing muscles in rats is dependent upon and modulated by hindlimb loading.
Document ID
20040141667
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
Authors
Huckstorf, B. L.
(Medical College of Wisconsin 8701 Watertown Plank Road, Milwaukee, WI 53226, United States)
Slocum, G. R.
Bain, J. L.
Reiser, P. M.
Sedlak, F. R.
Wong-Riley, M. T.
Riley, D. A.
Date Acquired
August 22, 2013
Publication Date
February 7, 2000
Publication Information
Publication: Brain research. Developmental brain research
Volume: 119
Issue: 2
ISSN: 0165-3806
Subject Category
Aerospace Medicine
Funding Number(s)
CONTRACT_GRANT: UO1NS33472
Distribution Limits
Public
Copyright
Other
Keywords
Non-NASA Center
NASA Discipline Musculoskeletal
NASA Program Fundamental Space Biology

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