Adrenal steroids and extinction behavior: antagonism by progesterone, deoxycorticosterone and dexamethasone of a specific effect of corticosterone

Decreased serotonin turnover in the dorsal hippocampus of rat brain shortly after adrenalectomy: selective normalization after corticosterone substitution

Pargyline-induced accumulation of serotonin (5-HT) was used as an index of 5-HT turnover rate in the dorsal hippocampus. One hour after bilateral removal of the adrenals, 5-HT turnover was significantly reduced when compared to that of the sham-operated controls. A low dose of corticosterone given immediately after adrenalectomy restored the 5-HT response, while the same dose of dexamethasone was ineffective. Pretreatment with dexamethasone blocked the 5-HT response to corticosterone in the acutely adrenalectomized rat. The specificity of the 5-HT response in the hippocampus corresponds to the properties of the glucocorticoid receptor system in rat hippocampal neurons.

Ornithine decarboxylase induction by glucocorticoids in brain and liver of adrenalectomized rats

Ornithine decarboxylase (ODC), the rate-limiting enzyme in the biosynthesis of polyamines, was measured in the brain and the liver of adrenalectomized rats after an acute s.c. treatment with glucocorticoids. The effects of corticosterone and dexamethasone were compared in three brain areas, the cerebral cortex, hippocampus, and cerebellum. These structures have similar concentrations of cytosolic glucocorticoid receptor, as measured by an in vitro exchange assay using a specific glucocorticoid ligand, [3H]RU 26988, but contain different amounts of mineralocorticoid receptor. Corticosterone and dexamethasone increased ODC activity in the liver and brain areas in a dose-dependent manner, dexamethasone being more active than corticosterone in all tissues. Moreover, estradiol, progesterone, and testosterone were inactive. Aldosterone, at high doses, increased brain ODC activity. Glucocorticoids, selected for their weak binding, or lack of binding to the mineralocorticoid receptor, were tested and found to be highly active in inducing brain and liver ODC, thus showing that ODC induction by steroids is specific for glucocorticoids. These results are among the first to suggest biochemically a central action of glucocorticoids following an acute treatment and confirm that the brain is a glucocorticoid target organ.