GDNF and amyotrophic lateral sclerosis: The delivery of growth factors such as BDNF, insulin-like growth factor-1 (IGF-I), vascular endothelial growth factor (VEGF) and glial derived neurotrophic factor (GDNF) into ALS experimental models has been very promising since these factors were shown to be neuroprotective, improved motor function and prolonged motor neuron survival [112].