RXRA and major depressive disorder: Alterations in markers that determine the effect of thyroid hormones in the frontal cortex clearly indicated that in the studied model of depression, their function could be weakened (as shown by the decreases in T3, TRα1, and DIO2), while in the hippocampus, only a downward trend in the T3 level was observed, while the changes in TRβ1, RXRα, and DIO3 suggested the induction of compensatory mechanisms for enhancing T3 action.