Treatment of mouse brain cytosol with dextran-coated charcoal and high salt does not reveal a new glucocorticoid binder

Effects of prenatal ethanol exposure on glucocorticoid receptors in rat hippocampus

Animals exposed to ethanol in utero are typically hyperresponsive to stressors in adulthood as indicated by increased adrenocortical activation and/or deficits in response inhibition or recovery following stress. In the present study we reasoned that a deficit in feedback control of pituitary-adrenal activity might underlie this hyperresponsiveness in fetal ethanol-exposed (FEE) animals. Further, we hypothesized that a long-term decrease in hippocampal glucocorticoid receptor concentration, induced by prenatal ethanol exposure, might mediate such a deficit in pituitary-adrenal feedback regulation. Male and female Sprague-Dawley rats from prenatal ethanol (E), pair-fed (PF), and control (C) treatment groups were tested in adulthood for determination of cytosolic hippocampal glucocorticoid receptor binding. No significant differences in specific binding (Bmax) or binding affinity (Kd) of either type I or type II glucocorticoid receptors were found among animals from E, PF, and C conditions. There were, however, significant sex differences in receptor concentration and binding affinity; females showed significantly greater maximal binding and significantly lower binding affinity than males. These data do not support the hypothesis that prenatal ethanol exposure induces a long-term decrease in hippocampal glucocorticoid receptors in animals tested under basal nonstressed conditions. However, these data do not preclude the possibility that receptor binding capacity may be differentially affected in E, PF, and C animals during stress.

Presence of type I and type II/IB receptors for adrenocorticosteroid hormones in the inner ear

Aldosterone-Type I and dexamethasone-Type II/IB receptor complexes were identified in cytosol prepared from both cochlear and vestibular tissue samples. The specific binding capacity of Type I receptors in the cochlear tissues was approximately equal to that in the vestibular tissues. Likewise, the binding capacity of Type II/IB receptors in the cochlea was approximately equal to that in the vestibular endorgans. Based on the total specific binding measured with dexamethasone, the Type II/IB receptors appeared to outnumber the Type I receptors in cochlear and vestibular tissues by a factor of approximately 2.6; however, when adjustments were made for the probable cross-binding of dexamethasone to Type I receptors, these ratios were decreased to approximately 1.6. The existence of protein receptors for adrenocorticosteroid hormones demonstrated in the present study clearly suggests a mechanism whereby such hormones may directly regulate fluid and ionic gradients in the inner ear.