The goal of this study is to understand the influence of microgravity on the development, maturation, and maintenance of the neuromuscular system of terrestrial mammals, including humans. The proposed studies will use rats as a model and will explore the broad hypothesis stating that gravity-associated weightbearing is required postnatally for normal neuromuscular development of motoneurons, neuromuscular junctions, and muscle fiber types of the antigravity soleus muscle, but not for that of the extensor digitorum longus, a nonweightbearing muscle. Rat pups (3-5 days old) will be exposed to microgravity for 14-21 days. One group of flight animals will be killed inflight near the end of the mission, and another group will be returned to terrestrial gravity for 1 month before tissues are processed. Parallel groups of ground controls will be conducted on normal and hindlimb suspended unloaded (HSU) rats. Three predictions will be tested in these studies. Firstly, that the neuromuscular system of the soleus will not develop normally in the rat pups exposed to microgravity whereas the EDL development will proceed uncompromised. This analysis will establish whether microgravity disrupts maturation of motoneurons, whether there will be normal elimination of multiple innervation of muscle fibers, and whether normal differentiation of muscle fiber types in the soleus and EDL will occur. Secondly, that the effects on neuromuscular development of unloading by hindlimb suspension (in ground-based study) and microgravity may be similar. But they may not be identical since there are added variables in the hindlimb suspension study that should not be a problem in space flight (isolation from mother and disruption of suckling, body temperature changes, etc). Thirdly, the aberrant soleus neuromuscular system of rat pups raised in microgravity will not be restored to normality by late exposure to weight bearing whereas the EDL will continue normal maturation. Animals returned to earth and processed 1 month after gravity exposure will be analyzed. Overall analysis in these studies will involve processing of the lumbar spinal cords and soleus and EDL muscles using histochemistry, immuno-cytochemistry, in situ hybridization, gel electrophoresis, and electron microscopy. Retrograde labelling will be employed to identify soleus and EDL motoneurons. Analysis of the neuromuscular system development will include assessing maturation of the motoneurons of the two muscle groups (using somal size, cytochrome oxidase (CO) activity, CO mRNA levels, and choline acetyltransferase (CHAT) activity), elimination of polyneuronal innervation of motor endplates, and differentiation of muscle fiber types (using myosin protein isoforms, and messages, myofibrillar ATPase activity, and CO activity and message). It is predicted that microgravity will cause persistence of neonatal attributes and/or the development of anomalies in the soleus but not the EDL, and returning animals to terrestrial gravity is not predicted to reverse induced abnormalities. It is anticipated that these results will raise important implications for rearing normal animals (including humans) in the microgravity environment of space, but additionally will further our understanding of the importance of weightbearing activity for motor system development of individuals on Earth.

Agency
National Institute of Health (NIH)
Institute
National Institute of Neurological Disorders and Stroke (NINDS)
Type
Research Project--Cooperative Agreements (U01)
Project #
1U01NS033472-01
Application #
2272296
Study Section
Special Emphasis Panel (SSS (S1))
Project Start
1995-09-30
Project End
1999-06-30
Budget Start
1995-09-30
Budget End
1996-06-30
Support Year
1
Fiscal Year
1995
Total Cost
Indirect Cost
Name
Medical College of Wisconsin
Department
Anatomy/Cell Biology
Type
Schools of Medicine
DUNS #
073134603
City
Milwaukee
State
WI
Country
United States
Zip Code
53226
Riley, Danny A; Bain, James L W; Thompson, Joyce L et al. (2002) Thin filament diversity and physiological properties of fast and slow fiber types in astronaut leg muscles. J Appl Physiol 92:817-25
Vijayan, K; Thompson, J L; Norenberg, K M et al. (2001) Fiber-type susceptibility to eccentric contraction-induced damage of hindlimb-unloaded rat AL muscles. J Appl Physiol 90:770-6
Riley, D A; Bain, J L; Thompson, J L et al. (2000) Decreased thin filament density and length in human atrophic soleus muscle fibers after spaceflight. J Appl Physiol 88:567-72
Thompson, J L; Vijayan, K; Riley, D A (2000) Immunohistochemical myofiber typing and high-resolution myofibrillar lesion detection in LR white embedded muscle. Microsc Res Tech 49:589-95
Huckstorf, B L; Slocum, G R; Bain, J L et al. (2000) Effects of hindlimb unloading on neuromuscular development of neonatal rats. Brain Res Dev Brain Res 119:169-78
Thompson, J L; Balog, E M; Fitts, R H et al. (1999) Five myofibrillar lesion types in eccentrically challenged, unloaded rat adductor longus muscle--a test model. Anat Rec 254:39-52
Riley, D A (1999) Is skeletal muscle ready for long-term spaceflight and return to gravity? Adv Space Biol Med 7:31-48
Macias, M Y; Lehman, C T; Sanger, J R et al. (1998) Myelinated sensory and alpha motor axon regeneration in peripheral nerve neuromas. Muscle Nerve 21:1748-58
Riley, D A; Bain, J L; Thompson, J L et al. (1998) Disproportionate loss of thin filaments in human soleus muscle after 17-day bed rest. Muscle Nerve 21:1280-9
Vijayan, K; Thompson, J L; Riley, D A (1998) Sarcomere lesion damage occurs mainly in slow fibers of reloaded rat adductor longus muscles. J Appl Physiol 85:1017-23