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Glial cell-line derived neurotrophic factor (GDNF) supports and maintains the neuromuscular system during development and through adulthood by promoting neuroplasticity. The aim of this study was to determine if different intensities of exercise can promote changes in GDNF expression and neuromuscular junction (NMJ) morphology in slow- and fast-twitch muscles. Rats were randomly assigned to a low intensity run-training (run group), higher intensity swim-training (swim group), or control group. GDNF protein content increased in both soleus (SOL) and extensor digitorum longus (EDL) following run-training and in EDL following swim-training determined by enzyme-linked immunosorbent assay. NMJ morphology was analyzed by measuring α-bungarotoxin labeled post-synaptic end plates. GDNF and total end plate area were positively correlated. End plate area decreased in EDL of run group and increased in SOL of swim group. Run group was able to alter plasticity by significantly increasing the number of end plates in EDL. The higher intensity swim-training elicited more dispersed synapses in SOL and less dispersion in EDL. The results indicate that GDNF expression may be altered depending on exercise intensity and fiber phenotype potentially inducing NMJ plasticity.

This work was supported by NIH grant 1 R15 AG022908-01A2, NSF grant DBI 0552517 and Western Michigan University

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