773: Mild restraint stress in pregnancy does not impact mouse litter size and pro-inflammatory cytokines

Abstract

This study assessed the changes in mouse litter size and pro-inflammatory cytokines in mice exposed to daily restraint stress using a model of stress that has been shown to induce changes in the non-pregnant mouse. Male B6D2F1/J and nulliparous female C57BL/6 mice were bred at 8-10 weeks of age. Detection of a copulation plug was used to determine embryonic day (E) 0.5. After breeding, females were randomly assigned to either stress or control groups. The mice assigned to the stress group underwent daily 1-hour periods of restraint in a ventilated clear plastic container from E1-E15. On day E17.5, animals were sacrificed. Number of embryos and resorption sites were counted. Blood was obtained for analysis of serum cytokine concentrations. Median values were compared by independent samples Mann-Whitney U tests with a p-value of .05 being considered significant. The mild restraint stress used in this study did not alter litter size or the number of fetal resorptions observed on E17.5. Median litter size was 8.0 in mice exposed to chronic stress compared to 9.0 in control mice (Mann–Whitney U = 12.0, n1 = n2 = 6, P = .39 two-tailed). There were no resorbed embryos noted in either group. There were no significant differences in the serum pro-inflammatory cytokines analyzed, as detailed in Table 1. These data did not demonstrate a significant difference in litter size between mice exposed to 1-hour daily restraint stress and control mice. It also did not demonstrate a change in serum pro-inflammatory cytokines. It is possible that the immunosuppressed state of pregnancy limited the inflammatory response to this mild stress, and it is likely that more aggressive stress protocols are required to induce changes in these parameters in pregnant mice. Future studies should focus on optimizing stress protocols for studying stress-related changes in pregnant mouse models.