Effects of Chronic Glucocorticoid Receptor Stimulation on Circadian Locomotor Activity and Serotonergic Neurotransmission in the Basolateral Amygdala of Rats.

Abstract

Clinical studies, especially those in animal models, have provided evidence that chronic stress may play a role in the etiology of psychiatric diseases, such as depression. Because chronic stress activates the hypothalamic-pituitary-adrenal (HPA) axis, resulting in the excessive secretion of glucocorticoids, the chronic stimulation of glucocorticoid receptors (GRs) may be involved in the pathogenesis of depression. To further investigate the relationship between GR activation and depression, we used the synthetic glucocorticoid dexamethasone (DEX) and the GR antagonist mifepristone to examine the effects of chronic GR stimulation on the circadian rhythms of locomotor activity and serotonergic neurotransmission in the basolateral amygdala (BLA) of rats. Chronic treatment with DEX reduced locomotor activity during the dark phase, without changing overall activity patterns. Measuring the basal release of serotonin in the BLA, using in vivo microdialysis, confirmed that chronic treatment with DEX induced serotonergic hypofunction in the BLA. The co-administration of DEX with mifepristone effectively suppressed the depressive-like symptoms caused by chronic treatment with DEX. Our results provided further evidence for a relationship between GR and depression and suggest that the pharmacological blockade of GR may increase the effectiveness of conventional pharmacotherapies used to treat depression.