Ethanol alters local cellular levels of (3?,5?)-3-hydroxypregnan-20-one (3?,5?-THP) independent of the adrenals in subcortical brain regions.
The neuroactive steroid (3?,5?)-3-hydroxypregnan-20-one (3?,5?-THP or allopregnanolone) is a positive modulator of GABAA receptors synthesized in the brain, adrenal glands, and gonads. In rats, ethanol activates the hypothalamic-pituitary-adrenal axis and elevates 3?,5?-THP in plasma, cerebral cortex, and hippocampus. In vivo, these effects are dependent on both the pituitary and adrenal glands. In vitro, however, ethanol locally increases 3?,5?-THP in hippocampal slices, in the absence of adrenal influence. Therefore, it is not known whether ethanol can change local brain levels of 3?,5?-THP in vivo, independent of the adrenals. To directly address this controversy, we administered ethanol (2 g/kg) or saline to rats that underwent adrenalectomy (ADX) or received sham surgery and performed immunohistochemistry for 3?,5?-THP. In the medial prefrontal cortex (mPFC), ethanol increased 3?,5?-THP after sham surgery, compared with saline controls, with no ethanol-induced change in 3?,5?-THP following ADX. In subcortical regions, 3?,5?-THP was increased independent of adrenals in the CA1 pyramidal cell layer, dentate gyrus polymorphic layer, bed nucleus of the stria terminalis, and paraventricular nucleus of the hypothalamus. Furthermore, ethanol decreased 3?,5?-THP labeling in the nucleus accumbens shore and central nucleus of the amygdala, independent of the adrenal glands. These data indicate that ethanol dynamically regulates local 3?,5?-THP levels in several subcortical regions; however, the adrenal glands contribute to 3?,5?-THP elevations in the mPFC. Using double immunofluorescent labeling we determined that adrenal dependence of 3?,5?-THP induction by ethanol is not due to a lack of colocalization of 3?,5?-THP with the cholesterol transporters steroidogenic acute regulatory protein (StAR) or translocator protein (TSPO).