Long-term lack of endogenous glucocorticoids down-regulates glucocorticoid receptor levels in the rat forebrain.

To understand the effect of a chronic lack of endogenous glucocorticoids on glucocorticoid receptor levels, the changes of glucocorticoid receptor content in the rat forebrain five months after adrenalectomy were investigated. In the long-term adrenalectomized rats that showed a hormone deficiency and loss of glucocorticoid receptor immunoreactivity in the forebrain, an intraperitoneal injection of corticosterone was used to elevate the serum hormone levels and recover glucocorticoid receptor immunoreactivity in the forebrain. One hour later, when the blood corticosterone returned to the normal level, the recovery of glucocorticoid receptor immunoreactivity in the forebrain was examined by immunohistochemistry. Since the complete restoration of glucocorticoid receptor immunoreactivity was shown to depend on the presence of normal levels of both serum hormone and intracellular glucocorticoid receptors, the weak reappearance of glucocorticoid receptor immunoreactivity in any forebrain area of the long-term adrenalectomized rats that had normal serum corticosterone might reflect the low intracellular glucocorticoid receptor levels there. Our results revealed a weak reappearance of glucocorticoid receptor immunoreactivity in some forebrain areas of the long-term adrenalectomized rats after corticosterone treatment; the hippocampal granule cell layer and cerebral cortex in particular showed very weak recovery of glucocorticoid receptor immunoreactivity. Conversely, neurons in the CA1/CA2 subfields of the hippocampal pyramidal cell layer, immediately adjacent to the granule cell layer on the same brain section, exhibited a strong reappearance of glucocorticoid receptor immunoreactivity, to near normal levels. These results suggest that, five months after adrenalectomy, the intracellular glucocorticoid receptor content decreased in the rat granule cell layer and cerebral cortex. Therefore, the long-term lack of endogenous glucocorticoids after adrenalectomy might down-regulate but not up-regulate the intracellular glucocorticoid receptor level, and the presence of glucocorticoids is important for the continued synthesis of glucocorticoid receptors.