Long-term treatment with antidepressants increases glucocorticoid receptor binding and gene expression in cultured rat hippocampal neurones

Since the glucocorticoid receptor (GR) and/or mineralocorticoid receptor (MR) in the hippocampus have been implicated in cortisol feedback of the hypothalamus-pituitary-adrenal (HPA) axis, abnormalities in those receptors might underlie the hyperactivity of the HPA axis described in patients with major depression. Animal studies have shown that long-term in-vivo treatment with antidepressants up-regulates hippocampal GR and/or MR, but it is not clear whether this up-regulation is evoked through a direct action of antidepressants on these receptors. We therefore examined the direct effects of long-term antidepressant treatment on GR binding and the levels of GR messenger RNA (mRNA) in primary cultures of rat hippocampal neurones. The time course of the effects of the tricyclic antidepressants desipramine and amitriptyline on GR binding, as assessed by [3H]dexamethasone binding using RU 28362, a specific agonist for GR, showed a biphasic mode of stimulation: desipramine significantly increased the GR binding with 2-day exposure by 36% over that in controls and by 99% and 60% with 10- and 14-day exposures, respectively. Amitriptyline also led to a significant increase in GR binding, with peaks at 2 (by 60%) and 14 days of exposure (by 60%). The effects of 14-day treatment with desipramine required at least the first 4-day exposure, and the first 10-day exposure was required for the full effect. Northern blot analysis demonstrated that the GR mRNA level was significantly increased by 14-day treatment with desipramine (+142% over control), amitriptyline (+108%), mianserin (+124%), paroxetine (+42%) and sulpiride (+92%), but not with haloperidol. Immunocytochemistry for GR revealed that 2- or 14-day treatment with desipramine significantly increased the number of GR-positive cells with dominant immunoreactivity in the nuclei of granule cell-like neurones or in perikarya of pyramidal cell- and granule cell-like neurones. These findings suggest that tricyclic antidepressants directly increase hippocampal GR by short-term (2-day) and long-term (14-day) exposure, and that the increase by long-term exposure is evoked commonly with different classes of antidepressants through transcriptional up-regulation of GR expression.