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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.

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The protective effects of hypoxic preconditioning on the development of depressive states in rat models were studied. Three episodes of intermittent preconditioning using hypobaric hypoxia (360 mmHg, 2 h) prevented the onset of depressive behavioral reactions, hyperfunction of the hypophyseal-adrenal system, and impairments in its suppression in the dexamethasone test in rats following unavoidable aversive stress in a model of endogenous depression. The anxiolytic and antidepressant actions of hypoxic preconditioning in experiments on rats were no less marked than those of the tetracyclic antidepressant ludiomil. The results obtained here provide evidence that preconditioning with intermittent hypobaric hypoxia increases resistance to psychoemotional stresses, has marked anxiolytic and antidepressant effects, and can be used for the prophylaxis of depressive episodes.

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This report presents studies of the effects of immobilization stress applied to pregnant female rats during the last third of pregnancy on anxiety levels and neurosteroid synthesis in brain structures of adult offspring. Neurosteroid synthesis was assessed in terms of changes in the activity of 5alpha-reductase, the enzyme which converts progesterone into active metabolites. Prenatal stress results in a significant decrease in the level of anxiety and an increase in movement activity among adult males. Stressed rats showed increases in progesterone-5alpha-reductase activity in the hypothalamus, hippocampus, and frontal cortex. These results provide evidence that changes in the behavior of adult male rats due to stress in the prenatal period of development may be due to the formation of active progesterone metabolites in the brain.

The effects of daily 1-h immobilization of female rats from days 15 to 18 of pregnancy on the levels of anxiety, orientational-investigative activity in an open field test, and the dynamics of the stress response of the hypophyseal-adrenal system were studied in the male and female adult offspring of these rats. Maternal stress was found to induce significant reductions in the level of orientational-investigative activity of females in the stage of diestrus, and to increase anxiety as measured in an elevated cross maze. Prenatally stressed males, conversely, had decreased levels of anxiety, and behavior in the open field test was virtually unaltered. As a result, prenatally stressed rats showed smoothing out of the intergender differences in these forms of behavior, seen in control animals in normal conditions. Prenatal stress had a significant influence on the dynamics of the stress response of the hypophyseal-adrenal system in males and females; males showed impairment of the feedback control of this system in conditions of stress activation, while females showed significant increases in the maximum level of adrenal corticosterone secretion into the blood in response to immobilization lasting 20 min. These data provide evidence that maternal stress has significant influences on behavior and the stress response in both male and female rats.