During the prenatal period, the neuronal system develops rapidly and is thus vulnerable to external influences. Maternal stress hormones (glucocorticoids) can "reprogram" the fetal nervous system, thereby altering its normal development. A common target of maternal glucocorticoids is the fetal neuro-endocrine axis between the hypothalamus, the pituitary and the adrenal gland (HPA axis). Changes in the amount of receptors or hormones on this axis can produce long term consequences in animal behaviour. In our experiment, we exposed pregnant mice to stress and then tested their male offspring for sexual and aggressive behaviour. Three groups of pregnant mice were exposed to stress by syringe injection on different days of pregnancy. The first group was injected on days 13, 14, and 15 p. c. (lat. post coitum), the second group was injected on days 17 and 18 p. c., and the third group was injected daily from days 13 to 18 p. c. Male offspring that were exposed to stress on days 13–18 and 17–18 p. c., were less aggressive and had lower testosterone levels in blood, compared to the control group. In male sexual behaviour, there were no statistically significant differences between the groups. After behavioural testing, brains were processed for immunohistochemical staining with antibodies against vasopressin (AVP) and calbindin (CALB). The expression of AVP and CALB in the lateral septum and the preoptic area, respectively, did not differ between groups, suggesting that these two masculinisation markers were not affected by prenatal stress. Our research showed that stress on days 13–15 p. c. affects the increase of body weight in the adult period, while stress in the later period, on days 16–18 p. c., weakens aggressive behaviour of adult males.
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