NPPA and mood disorder: This drop can be largely explained by 1) the overactivation of IDO-1 shunts the available TRYP into KP, increasing KP metabolites, depleting serotonin, and causing mood disorders and other related neurological symptoms; 2) QUIN, at pathophysiological concentrations can trigger oxidative stress and apoptosis viaexcitotoxicity in different cells including neurons and astrocytes.