Corticosterone and Dexamethasone Act at Different Brain Sites to Inhibit Adrenalectomy-induced Adrenocorticotropin Hypersecretion

To investigate the involvement of different brain sites in the mediation of glucocorticoid feedback action, we implanted dexamethasone or corticosterone containing glass capillaries into the paraventricular and arcuate nuclei of the hypothalamus, into the lateral septum, the dorsal and ventral hippocampus, amygdala and the cerebral cortex of adrenalectomized male rats, and compared the plasma adrenocorticotropin (ACTH) values to those of the sham implanted controls. The ACTH hypersecretion of adrenalectomized (ADX), sham implanted rats (670 fmol/ml) was reduced significantly by dexamethasone implants placed into the paraventricular nucleus (9.97 fmol/ml), arcuate nucleus (20.54 fmol/ml) or lateral septum (44.15 fmol/ml). Corticosterone was effective only when placed into the dorsal hippocampus, but normal ACTH levels were not restored (219.67 fmol/ml). All other implants at other sites had no effect on ACTH secretion. Our results suggest that corticosterone and dexamethasone possess different feedback potencies and act at different sites in the brain to normalize the ADX-induced ACTH secretion.