NGF and amyotrophic lateral sclerosis: In ALS, astrocytic function is compromised in several ways that impair neuronal survival and includes: (1) deficient release of neurotrophic factors [87]; (2) release of nerve growth factor (NGF) or extracellular mutant superoxide dismutase 1 (SOD1) [88,89]; and (3) insufficient clearance of glutamate from the synaptic cleft, due to reduced density and loss of EAAT2 [90].