Abstract

Background: Stress is considered to be a major factor in the development of depressive illness. Pregnancy is also a kind of physical stress, and the rate of pregnancy-induced depression is increasing. This study analyzed alterationsin the levels of peptide hormones in the gestational period in order to evaluate the prevalence of a depressed state during pregnancy.

Methods: Specific pathogen-free C57BL/6j gestation female mice were used for the experiments. In order to investigate the prevalence of a depressed state in the gestational period, we conducted forced swim test (FST) and open field test (OFT) and measured the levels of plasma adrenocorticotropic hormone (ACTH), β-endorphin (β-End), corticosterone and dopamine (DA) in the gestational period. In addition, we measured the expression of prohormone convertase 2 (PC2) in the pituitary gland.

Results: In the FST, the akinesia time (floating time) during the gestational period was the longest on gestational day (gd) 6, then gradually decreasd toward parturition. On the other hand, in the OFT, the motor activity during the gestational period increased gradually to gd 17 after being the lowest on gd 6. The plasma levels of ACTH and corticosterone fell gradually to gd 18 after a peak on gd 6. In contrast, the plasma levels of β-End and DA and the expression of PC2 in the pituitary gland increased throughout the gestational period, peaking by gd 18.

Conclusions: These observations suggest that the levels of ACTH and corticosterone change in parallel with those of β-End and DA during the gestational period and function to regulate a depressed state.

Keywords: Depression, β-Endorphin, adrenocorticotropic hormone, dopamine, forced swim test, open field test