Effect of Hypothalamic and Mesencephalic Steroid Implantations on ACTH Feedback Mechanisms1

Abstract

Mature male rats received implants of dexamethasone, cortisol or testosterone into various central nervous system sites, or into the pituitary; 1 wk postimplantation animals were sacrificed and plasma and adrenal corticosterone assays were performed. Midline dexamethasone placement into the median eminence was effective in significantly reducing plasma and adrenal corticosterone levels, and adrenal weight; cortisol was also significantly inhibitory, but not to the same extent as dexamethasone. Testosterone was without effect. Dexamethasone implants into the pituitary, cerebral cortex or midbrain periventricular gray proved to be ineffective. In contrast, dexamethasone (but not cortisol), when bilaterally placed into the midbrain lateral reticular formation, lowered plasma and adrenal corticosterone levels; adrenal weight was unaltered. The results are discussed in light of the hypothesis that the midbrain, as well as the median eminence, contains receptors sensitive to variations in blood corticoid levels, and that the midbrain should therefore be incorporated into the neuroendocrine scheme underlying the control of ACTH. (Endocrinology76: 811, 1965)