Dynamic Aspects of Glucocorticoid Receptors in the Spinal Cord of the Rat

In spite of biochemical and autoradiographic evidence for glucocorticoid binding sites in the spinal cord (SC), events occurring after the preliminary step of hormone binding were not studied. In this investigation, we have examined the transformation (activation) of the cytosolic receptor coupled to 3H]dexamethasone (DEX) and the in vivo interaction of adrenal hormone corticosterone (CORT)] with purified nuclei from the SC, in addition to the CORT content of the SC before and after stress. Binding of 3H]DEX in the SC was 40% lower than in the hippocampus (HC), although the KD values were comparable. Transformation of 3H]DEX-receptor complexes in the cytosol was demonstrated by diethylaminoethane-cellulose chromatography, by DNA-cellulose binding, and by a combined minicolumn procedure including hydroxyapatite in addition to the last two techniques for separation of transformed, nontransformed, and meroreceptor complexes. In all these situations, SC glucocorticoid binding sites behaved similarly to those in the HC. Nuclear uptake of a tracer dose of 3H]CORT was much lower in the SC than in the HC; nuclear retention of CORT was more easily detected by radioimmunoassay after injection of 1 mg of CORT into adrenalectomized rats. Substantial amounts of CORT, which increased in level after stress, were measured in five regions in the SC, with higher concentrations in the cervical regions. These studies suggest that although SC and HC receptors show similar properties in vitro, differences emerged at the level of nuclear uptake in vivo, in that glucocorticoid action in the SC was similar to that in the optic nerve, where receptors seem to be localized mostly in glial cells.