GDNF Content and NMJ Plasticity in Slow and Fast Twitch Myofibers Follows Recruitment in Exercise

Glial cell line-derived neurotrophic factor (GDNF)supports and maintains the neuromuscular system duringdevelopment and through adulthood by promoting neuro-plasticity. The aim of this study was to determine if differentmodes of exercise can promote changes in GDNF expres-sion and neuromuscular junction (NMJ) morphology inslowand fast-twitch muscles. Rats were randomlyassigned to a run training (run group), swim training (swimgroup), or sedentary control group. GDNF protein contentwas determined by enzyme-linked immunosorbant assay.GDNF protein content increased significantly in soleus(SOL) following both training protocols (P< 0.05). Althoughnot significant, an increase of 60% in the extensor digitorumlongus (EDL) followed swim-training (NS; P< 0.06). NMJmorphology was analyzed by measuring a-bungarotoxinlabeled post-synaptic end plates. GDNF content and totalend plate area were positively correlated. End plate areadecreased in EDL of the run group and increased in SOLof the swim group. The results indicate that GDNF expres-sion and NMJ morphological changes are activity depen-dent and that different changes may be observed byvarying the exercise intensity in slowand fast-twitch fibers.2013 IBRO. Published by Elsevier Ltd. All rights reserved.