Meijer O C, Van Oosten R V, De Kloet E R
Division of Medical Pharmacology, Leiden/Amsterdam Center for Drug Research, University of Leiden, The Netherlands.
Neuroscience. 1997 Sep;80(2):419-26. doi: 10.1016/s0306-4522(97)00008-0.
Several studies with adrenalectomized rats have shown that the suppressive effects of exogenous corticosteroids on 5-hydroxytryptamine(1A) receptor function are mediated by the high-affinity mineralocorticoid receptor, rather than the lower affinity glucocorticoid receptor. In the present study, adrenally intact rats were subcutaneously implanted for six days with pellets containing a small amount of corticosterone, which leads to a flattening of the circadian rhythm in the level of circulating hormone. The peak in daily corticosterone is suppressed, the basal trough is increased, and the hormone levels remain at a constant value equivalent to the daily average of about 5 microg/dl, which is usually observed in rats. Accordingly, this regime of corticosterone treatment did not enhance exclusively glucocorticoid receptor-controlled parameters, such as the weight of the thymus. Effects involving mineralocorticoid receptor activation were enhanced, since reductions were observed in stress-induced plasma corticosterone levels and adrenal weight. 5-Hydroxytryptamine(1A) receptor messenger RNA levels were found to be suppressed by approximately 25% in the dentate gyrus of the hippocampus of these corticosterone pellet-implanted rats. This suppression was reflected in significantly reduced [3H]8-hydroxy-2-(di-n-propylamino)tetralin binding in the hippocampal region. We propose therefore that this suppressive effect on 5-hydroxytryptamine(1A) receptor expression involves enhanced occupation of mineralocorticoid receptors, under a condition of elevated basal trough corticosteroid levels as is commonly observed in human depression.
