Reactive astrocytes surround degenerating MNs in patients and transgenic animal models of ALS, and in particular those localized in the ventral SC of SOD1G93A mice, are a source of nerve growth factor (NGF) and NO, which are both required for MN apoptosis (Table 2) (Pehar et al., 2004). Here, NGF is linked to amyotrophic lateral sclerosis.