The Effect of Resistance Training and Androgen Administration on Neuromuscular Junction Morphology and Neurotrophin Expression

Purpose This study examined the effect of resistance training (RT) and nandrolone decanoate (ND) administration on neuromuscular junction (NMJ) morphology and neurotrophin expression. Methods Forty 3-month-old male C57Bl/6 J mice were randomized to a RT or sedentary (SED) group. Each group of animals were further divided into sham (S) or ND (35 mg/kg/week) groups. All interventions were seven weeks in duration. Brain-derived neurotrophic factor (BDNF), tropomyosin receptor kinase B (TrkB), p75 and androgen receptor expression (AR) in the plantaris and soleus muscles were examined via western blot, while NMJ morphology was examined via immunofluorescence. Results Significant interactions for BDNF expression was noted in the plantaris (p = 0.009) and soleus (p = 0.010). In the plantaris BDNF expression for RT-ND was greater than RT-S (p = 0.019) and SED-ND (p = 0.016), while BDNF expression in RT-S was greater than all other groups (p's < 0.05) in the soleus. A significant interaction for TrkB expression was observed in the plantaris. TrkB in RT-ND was significantly greater (p = 0.031) than SED-ND. Analysis of the postsynaptic membrane within the plantaris revealed that RT increased the acetylcholine (ACh) receptor-stained area (p = 0.036), ACh-stained perimeter (p = 0.006), and total area (p = 0.044) compared to SED. In addition, ND administration increased (p = 0.050) ACh total area. In the presynaptic membrane both RT and ND increased ACh vesicle-stained area (p < 0.001 and p = 0.006, respectively), ACh vesicle-stained perimeter (p < 0.001 and p = 0.02, respectively), and ACh vesicle total area (p < 0.001 and p = 0.01, respectively), while RT only was noted to increase presynaptic ACh vesicles total perimeter (p < 0.001). In the soleus, ND increased ACh receptor-stained (p = 0.002) and total area (p = 0.035) at the post-synaptic membrane. Conclusions RT and ND administration stimulate increases in neurotrophin expression and NMJ morphology in plantaris and soleus muscles.