Maternal dexamethasone treatment in late gestation alters glucocorticoid and mineralocorticoid receptor mRNA in the fetal guinea pig brain.

Development of the fetal hypothalamo-pituitary-adrenocortical (HPA) axis is critical for fetal maturation and responses to stress. Guinea pigs, unlike rats, give birth to mature young, and peak brain growth occurs around days 48-52 (75%) of gestation. There is extensive development of the glucocorticoid receptor (GR) and mineralocorticoid receptor (MR) systems at the time of rapid brain growth in guinea pigs. Since approximately 10% of pregnant women are treated with synthetic glucocorticoids in late gestation, to promote fetal organ maturation, we tested the hypothesis that fetal exposure to glucocorticoids modifies developing GR and MR systems in the brain. Pregnant guinea pigs were subcutaneously injected with dexamethasone (dex; 1 mg/kg) or vehicle on days 50 and 51 of gestation (term=70 days). On day 52, guinea pigs were killed and the fetuses rapidly removed. Maternal dex treatment resulted in increased plasma cortisol concentrations in female fetuses, but decreased cortisol in male fetuses. Plasma thyroxine levels were increased in both female and male fetuses following maternal dex-treatment. Exposure to dex resulted in significant increases in MR and GR mRNA in the CA1-2 region of the hippocampus, and MR mRNA in the dentate gyrus in female fetuses. There was no effect of dex on GR or MR mRNA in the male fetuses. In conclusion, the effect of synthetic glucocorticoid on the developing brain GR and MR systems is sex-specific and is confined to very specific regions of the hippocampus. Since the hippocampus plays a central role in mediating glucocorticoid negative feedback of HPA function, alterations in the fetal development of corticosteroid receptors may form the basis of permanently modified HPA activity following fetal exposure to endogenous or synthetic glucocorticoid.