GDNF and brain disorder: HDACis may be beneficial in the treatment of various brain disorders through three potential mechanisms: (1) anti-inflammatory effect via down-regulation of pro-inflammatory factors such as Fas-L and IL-6; (2) anti-neurotoxic effects through down-regulation of neurotoxic proteins such as α-synuclein and β-amyloid; and (3) neuroprotective effect via up-regulation of neuroprotective proteins such as brain-derived neurotrophic factor (BDNF) and the glial cell-derived neurotrophic factor (GDNF) [3,4,5].