GDNF heterozygous knock-out (KO) mice with about 50% reduction in GDNF display increase in extracellular DA levels in the striatum likely reflecting compensatory response [52], earlier age-dependent loss in motor function and TH expression at least in some strains of mice [53], anxiety [54], spatial memory defect [55], and altered striatal response to morphine [56]. Here, TH is linked to Anxiety.