Date of Defense

4-18-2013

Date of Graduation

4-2013

Department

Biological Sciences

First Advisor

John Spitsbergen

Second Advisor

Cindy Linn

Keywords

GDNF, Aging, Neuromuscular Junctions, Skeletal Muscle

Abstract

Neurotrophic factors are an important class of extracellular signaling proteins involved in the maintenance and survival of neurons. Glial cell line-derived neurotrophic factor (GDNF) is the most potent neurotrophic factor for promoting the development, maintenance and survival of peripheral motor neurons. Progressive loss of motor neurons occurs with age, and over time this degeneration elicits devastating consequences on the physical performance and quality of life of elderly individuals. One possible explanation for age-induced motor neuron degeneration is a reduction in neurotrophic factor support. The primary objective of this study is to evaluate the age-related changes in the location and content of GDNF in skeletal muscle of sedentary Sprague-Dawley rats. Acquiring a better understanding of how GDNF expression in skeletal muscle changes with age will provide insight into the role of GDNF in the process of ageinduced motor neuron degeneration. An inverted confocal scanning microscope was used to view GDNF protein localization in the extensor hallucis longus (EHL) skeletal muscle from rats aged 3 weeks to 24 months. The muscles were fixed with paraformaldehyde, and the size and shape of neuromuscular junctions were measured using alpha-bungarotoxin to detect acetylcholine receptors, antibodies against synaptic vesicle protein 2 (SV2) to detect nerve terminal and antibodies against GDNF to determine where and how much GDNF is present in the muscle. The results of the study demonstrate that neuromuscular junctions (NMJ) are immature, with GDNF at and around the acetylcholine receptors in rats aged 3 and 5 weeks. The endplates are fully developed and GDNF is primarily localized to endplate regions in 8-week-old rats. A significant reduction in GDNF and dispersing endplates are observable in tissues from 6-month-old rats, while some of the endplates appear intact and complex with GDNF distinct at and around the NMJs in 24-month-old rats. These results suggest that GDNF expression is distinct at and around the NMJ during motor neuron development, is primarily localized to fully developed endplates to maintain the NMJ, and the reduction in GDNF support may contribute to NMJ deterioration. An increase in GDNF expression and intact, complex endplates following NMJ deterioration may be attributable to muscle-type conversion. This work was supported by NIH grant 1 R15 AG022908-0 1 A2, NSF grant DBI 0552517, the Lee Honors College, the Office of Vice President for Research (OVPR) Undergraduate Research Excellence Award, and the College of Arts and Sciences Research and Creative Activities Award at Western Michigan University.

Access Setting

Honors Thesis-Restricted

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