SIRT1 and major depressive disorder: The lack of a correlation between SIRT1 levels and performance in the FST in mice that experienced similar isolation stress in adulthood (ASI) or those with a naturally high level of depression-like phenotype (C57) strengthens the hypothesis that only stress at an early age interferes with SIRT1 function and confirms that in mice, similar to what happens in humans, distinct etiological pathways characterize the early stress-induced depression-like phenotype.