Two receptor systems for corticosterone (CORT) can be distinguished in rat brain: mineralocorticoidlike or CORT receptors (CR) and glucocorticoid receptors (GR). The microdistribution and extent of occupation of each receptor population by CORT were studied. The CR system is restricted predominantly to the lateral septum and hippocampus. Within the hippocampus, the highest density occurs in the subiculum ± CA1 cell field (144 fmol/mg protein) and the dentate gyrus (104 fmol/mg protein). Affinity of CR for CORT was very high (Kd, ∼0.5 nm). The GR system has a more widespread distribution in the brain. The highest density for GR is in the lateral septum (195 fmol/mg protein), the dentate gyrus (133 fmol/mg protein), the nucleus tractus solitarii and central amygdala. Substantial amounts of GR are present in the paraventricular nucleus and locus coeruleus and low amounts in the raphe area and the subiculum + CA1 cell field. The affinity of GR for CORT (Kd, ∼2.5–5 nm) was 6- to 10-fold lower than that of CR. ...

Two Receptor Systems for Corticosterone in Rat Brain: Microdistribution and Differential Occupation

The acute effects of corticosteroids on cognition: integration of animal and human model studies

Publisher Summary This chapter discusses the regulation of function in the adrenocortical system. There are three major characteristics that describe most changes in activity of the system: (1) the circadian rhythm in basal activity, (2) stress-induced activation, and (3) corticosteroid feedback regulation. The first two may occur on very different timescales, and it is probably a consequence of the differing temporal demands that the third, corticosteroid feedback inhibition, is exerted by a variety of mechanisms over time. At any time of the day, the adrenocortical system can be activated by application of stressors. These include alteration of the value of a regulated variable or may be invoked by subjecting an animal to sudden disturbances of its environment, for example, noise, flashing lights, handling, strange environment, mild heat or cold. The adrenocortical system may be activated by traumatic stimuli or by psychological stimuli—in man, examinations, or mental arithmetic, or medical school admissions exams; in rats, unexpected decreases in food rewards.

Regulation of ACTH secretion: variations on a theme of B.

The effect of estrogen (E) on the hypothalamic-pituitary-adrenal axis was investigated in female Sprague-Dawley rats. Animals were bilaterally ovariectomized (OVX), and a Silastic capsule (0.5 cm) containing 17 beta-estradiol was sc implanted. Control animals received a blank capsule. Animals were killed 21 days later. In E-treated rats, we found significantly higher corticosterone (CORT) peak levels 20 min after a 5-sec footshock (1.0 mamp) or exposure to ether vapors (P less than 0.05) compared to those in OVX controls. In addition, the recovery of the ACTH and CORT responses to footshock stress was significantly prolonged (P less than 0.05) in the presence of E. Furthermore, the ACTH and CORT secretory responses to ether stress could be suppressed by exogenous RU 28362 (a specific glucocorticoid receptor agonist; 40 micrograms/100 g BW for 4 days) in OVX controls (P less than 0.05), but not in E-treated animals. These data suggest that E can impair glucocorticoid receptor-mediated delayed or slow negative feedback. Consequently, we examined the influence of E on mineralocorticoid and glucocorticoid receptor concentrations using in vitro binding assays. E did not alter mineralocorticoid or glucocorticoid receptor concentrations in any of the brain regions examined. The administration of RU 28362 (40 micrograms/100 g BW for 4 days) to OVX control or E-treated rats significantly down-regulated hippocampal glucocorticoid receptor (P less than 0.02) in control rats only. In contrast, aldosterone administration (40 micrograms/100 g BW for 4 days) significantly down-regulated hippocampal glucocorticoid receptor (P less than 0.0008) in both control and E-treated animals. Thus, E treatment results in a loss of the glucocorticoid receptor's ability to autoregulate; this suggests that E may cause a functional impairment of the glucocorticoid receptor even though receptor binding appears normal. These findings suggest that hyperactivation of the hypothalamic-pituitary-adrenal axis after stress in E-treated rats is due in part to impaired glucocorticoid receptor-mediated slow negative feedback.

Chronic estrogen-induced alterations in adrenocorticotropin and corticosterone secretion, and glucocorticoid receptor-mediated functions in female rats.

B.I. Grosser

Papers

The autoradiographic localization of (3H)dexamethasone in the brain and pituitary of the rat.