COMT and major depressive disorder: Because of (1) the well-documented status of Comt as a most important enzyme engaged in the degradation process of catecholamines (adrenaline, noradrenaline, and dopamine) [65], (2) positive correlation between depression and COMT gene (for review see [63]), and (3) evidence showing that chronic (21-day) treatment with fluoxetine causes down-regulation of Comt mRNA level in rat frontal cortex [66], the expression of Comt in the prefrontal cortex in mice was evaluated.