Prepartum chronic ultramild stress increases corticosterone and estradiol levels in gestating mice: implications for postpartum depressive disorders.

Fluctuations in steroid hormones (glucocorticoids and estradiol) levels during pregnancy and after delivery are thought to contribute to the etiology of postpartum depression. Such changes may be exacerbated by stressful events, which constitute a predisposing factor for postpartum mood disorders. In the present study, blood hormonal variations associated with prepartum Chronic Ultramild Stress (CUMS) exposure were assessed at two times (15th day of pregnancy and 3rd day postpartum) in mice stressed from day 1 of pregnancy to termination of pregnancy. Litter weight and litter size were determined in both groups whereas the duration of pregnancy was determined in the 3-day postpartum group. CUMS increased estradiol and corticosterone levels during pregnancy, but such effects were no longer observed in the postpartum period, where cortisol levels were decreased in control and stressed mice and estradiol levels were reduced in previously stressed mothers. No effects of the CUMS procedure were observed on gestational parameters. Given the link between hormonal variations during pregnancy and subsequent postpartum depression, these results suggest that CUMS applied to gestating female may provide a useful model for the study of the mechanisms of stress, which may lead to postpartum mood disorders.