Association of glucocorticoid receptor immunoreactivity with cell membrane and transport vesicles in hippocampal and hypothalamic neurons of the rat.

The aim of the present study was to reveal at the ultrastructural level cytoplasmic loci that display glucocorticoid receptor (GR) immunoreactivity in pyramidal neurons of the CA1 sector of the hippocampus and in cells of the medial parvicellular subnucleus of the hypothalamic paraventricular nucleus (PVN). Adrenalectomized male rats were injected intraperitoneally with corticosterone (CS) (1 mg/100 g bw) and sacrificed within 4 hr. Vibratome sections of the perfusion-fixed forebrains were processed for immunocytochemical detection of type 2 GR by means of the BuGr, anti-rat liver GR monoclonal antibody and silver-gold-intensified diaminobenzidine chromogen. The corticosterone administration gradually shifted the GR immunoreactivity (IR) from the cytoplasm to the nucleus. Samples taken 20-40 min after the steroid treatment demonstrated pyramidal cells expressing GR IR in both the cytoplasmic and nuclear pools. Although the chromatin-associated appearance of GR in the nucleus was identifiable at the light microscopic level, the nature of immunoreactive intracytoplasmic loci was not. Ultrastructural analysis of the cytoplasm indicated that fine silver-gold grains marking GR-immunoreactive sites associated with the plasma membrane and coated and regular vesicles. Noted occasionally beneath the plasma membrane of the cell bodies and dendrites, the vesicles also appeared at deeper locations in dendritic processes and around the cell nuclei. These results suggest that glucocorticoid receptors participate in signal transduction at the level of the cell membrane, as well as at the level of the genome in the cell nucleus.