The alteration of glucocorticoid receptor-immunoreactivity in the rat forebrain following short-term and long-term adrenalectomy

To examine the effect of short-term and long-term adrenalectomy (ADX) on the glucocorticoid receptor (GR) expression, we performed an immunohistochemical study on the rat forebrain. One day after ADX, the GR-immunoreactivity significantly decreased or disappeared in most forebrain structures, while-relatively strong GR-immunoreactivity was still found within the hypothalamus especially in the arcuate nucleus (ARC) and the parvocellular paraventricular nucleus (PVN). Two weeks following ADX, GR-immunoreactive cells disappeared in many structures of the forebrain including most parts of hypothalamus while moderate GR-immunoreactivity was still observable in the ARC and PVN. More than 3 months after ADX, the rats still survived when they received replacement of corticosterone during the first 2 weeks following the operation. Moderate GR-immunoreactivity in the ARC and PVN of the hypothalamus was exhibited whereas no immunoreactive cells remained in the cerebral cortex, thalamus and other forebrain structures when these-animals showed obvious cell death in the granule cells of the dentate gyrus, identified with the silver impregnation method for degenerating cells. Massive cell loss in this hippocampal region is an indicator of a complete ADX, in addition to the blood corticosterone level. These results demonstrate topographic differences of GR expression in the rat forebrain after ADX with only continuous immunoreactivity in the ARC and PVN of the hypothalamus, suggesting that some neurons in the ARC and PVN could keep active GR probably in order to maintain their survival after removing the adrenal gland.