We have analyzed the effects of 14 days of chronic fluoxetine treatment on middle-aged (8 month old) rat brains, studying the expression of PSA-NCAM and that of different presynaptic proteins in regions known to be specially affected in patients and in animal models of major depression, as well as by antidepressant treatment, such as the mPFC, the amygdala, and the hippocampus [38-42]. This evidence concerns the gene NCAM1 and major depressive disorder.