Differential effects of imipramine and phenelzine on corticosteroid receptor gene expression in mouse brain: Potential relevance to antidepressant response

Although glucocorticoid feedback sensitivity of the hypothalamic-pituitary-adrenal (HPA) axis is frequently impaired in depression, atypical depression may exhibit increased feedback sensitivity. Because monoamine oxidase inhibitors (MAOI) are often more effective than tricyclic antidepressants (TCA) for atypical depression, we hypothesized that to normalize HPA function in atypical depression, MAOI would differ from TCA in decreasing rather than increasing feedback sensitivity. Consistent with this hypothesis and prior evidence for opposing effects on HPA feedback in mice, we report contrasting effects of chronic MAOI (phenelzine) and TCA (imipramine) treatment on neural corticosteroid receptor gene expression in adrenalectomized male C57BL/6 mice with fixed glucocorticoid levels. Our findings corroborate prior reports of antidepressant-induced increases in hippocampal mineralocorticoid (MR) and glucocorticoid receptor (GR) expression. However, hippocampal effects were neither sustained nor representative of effects in other brain regions. Imipramine typically increased and phenelzine decreased GR expression in other feedback-related brain regions such as the paraventricular hypothalamus and prefrontal cortex. Imipramine effects were limited to feedback-related regions, whereas phenelzine had additional effects to decrease accumbens GR and central amygdala MR expression. Our results suggest an expansion of the corticosteroid receptor hypothesis of depression to include drug- and brain region-specific actions of antidepressants to decrease as well as increase corticosteroid receptor expression and feedback sensitivity. Our findings further suggest how antidepressants could improve glucocorticoid regulation of HPA activity without also facilitating the adverse effects of glucocorticoids on mood.