Effects of prenatal stress on the activity of an enzyme involved in neurosteroid synthesis during the "critical period" of sexual differentiation of the brain in male rats.

The effects of daily immobilization stress applied to female rats on days 15 to 18 of pregnancy on the activity of the enzyme 5 alpha-reductase (isoform I), involved in the synthesis of brain neurosteroids were studied in male offspring. The results demonstrated a decrease in enzyme activity in the cerebral cortex and hypothalamus of male fetuses one day after the last session of stress, while enzyme activity was elevated in the cortex of neonates. Increases in 5 alpha-reductase activity in the cortex, hippocampus, and hypothalamus were also seen in prenatally stressed males on day 5 of life. There were reductions in plasma testosterone and progesterone levels in experimental animals on day 19 of embryonic life and in neonatal rats, the blood progesterone level in prenatally stressed rats remaining decreased at age five days. The possible involvement of neurosteroids in the actions of prenatal stress on sexual differentiation of the brain is discussed.