The cellular localization of GRmRNA and GR immunoreactivity in the adult rat brain was studied by in situ hybridization and immunocytochemistry. The expression of GR mRNA was detected in the cytoplasm of neurons and observed in the various regions of the rat brain, especially in the hippocampus, the thalamus, hypothalamus, the cerebral cortex. The distributional pattern of GR-immunoreactive cells was well-correlated with that of GR mRNA-containing cells, but in the hippocampus (CA3/CA4) discrepancy of the distribution of mRNAs and immunoreactivities.
Subcellular localization of glucocorticoid receptor (GR) in rat brain was immunocytochemically observed under different conditions of circulating corticosteroids level in conjunction with the specific antibody to GR.In the case of hippocampal pyramidal and granular cells, the GR-immunoreactivity was mainly distributed in the nucleus associated with chromatin in the control (normal) condition. However, the immunoreactivity almost vanished in all area of the cells 2 days after adrenalectomy (ADX). After 10 or 15 min of intraperitoneal (i.p.) injection of dexamethasone (DEX ; 200mg/kg) to these ADX rats, the GR-immunoreactivity reappeared in the cytoplasm associated with cell organelles. After 30 min of DEX i.p.injection, the same GR-immunoreactivity was distributed in nucleus as showing the control condition.
Moreover, the GRmRNA was abundantly expressed in the cytoplasm of anterior pituitary cells, and of scatteringly posterior pituitary being equivalent to pituicytes. The immunoreactivity for GR was detected in the nuclei of cells in anterior and posterior pituitary. Double immunohistochemistry revealed that co-localization of GR and anterior pituitary hormones were observed in the majority of growth hormone (GH) and adreno-corticotropic hormone (ACTH) producing cells, and in about 60 % of thyroid stimulating hormone (TSH) producing cells. Folliculo-stellate cells, marginal layr cells in the anterior pituitary, and pituicytes in the posterior pituitary, immunostained for S100-protein, were also immunostained with GR.These results suggest that glucocorticoids may directly influence certain pituitary cells and regulate the cell function including the synthesis and/or secretion of hormones.