Changes in Cerebral Mitochondrial Function in Postpartum Dams Exposed to a Low-resource Environment during Weaning

Background: Postpartum depression is a serious mental-health condition, affecting over 14% of all mothers in the U.S. Poverty, a lack of educational and economic resources, is a major determinant of adult mental health. In the U.S., poverty impacts 11% of adults, with a greater incidence in women of childbearing age (roughly 16%) and postpartum women (roughly 14%). While pregnancy and poverty separately increase risks of developing depression, few studies have combined these conditions to determine their role in the development of depression. Further, no studies have explored mechanisms contributing to depression following pregnancy and poverty. However, cerebral mitochondrial dysfunction (C-mtDys) may be one mechanism. The aim of this study is to examine C-mtDys in postpartum (PP) dams exposed to the limited-bedding-nesting (LBN) model in rats, which reduces their nesting material to simulate a low-resource environment. We hypothesize that PP dams in the LBN model will exhibit C-mtDys and elevated oxidative stress. Methods. Pregnant Sprague-Dawley rats gave birth naturally and were divided randomly into LBN (n =2) or control (n = 2) groups. LBN dams were exposed to the LBN model from PD 2 through PD 9. To validate the success of the LBN model, entropy scores, which are a measure of behavior unpredictability, were recorded for each dam. At 17 weeks PP, equivalent to 8 years PP in humans, brains were collected and used to isolate mitochondria through differential centrifugation. Mitochondrial function was evaluated via respiration (mtRes) using respiratory states. Oxidative stress in the whole brain was examined through H2O2 and total antioxidant capacity biochemical assays. Results. LBN PP dams displayed higher entropy scores (1.10 ± 0.04 v. 0.79 ± 0.04, p < 0.05), as expected based on prior literature, serving as validation of the model. At 17 weeks, PP LBN dams had reduced mtRes in all states, including the basal state (176.09 ± 5.90 v. 360.70 ± 7.73 pmol/s/mg, ns), State 2 (1044.72 ± 14.00 v. 1703.00 ± 18.10 pmol/s/mg, ns), State 3 (3843.27 ± 31.86 v. 6705.72 ± 37.54 pmol/s/mg, ns) and State 4 (776.83 ± 13.65 v. 1533.54 ± 16.46 pmol/s/mg, ns). PP LBN dams exhibited reduced total antioxidant capacity by roughly 20% (54.10 ± 1.24 v. 63.04 ± 0.99 mM Trolox) and elevated H2O2 by roughly 50% (2.12 ± 0.52 v. 1.35 ± 0.28 nM/mg, ns). Summary. In summary, preliminary data shows C-mtDys via reduced mtRes in PP dams exposed to an impoverished environment during weaning. Furthermore, this study suggests that decreased mtRes could contribute to increased oxidative stress in the brain. Elevated oxidative stress may cause damage at the cellular and circuitry levels in the brain that could facilitate the development of depression later in life. Future studies will further examine C-mtDys, oxidative stress, and depressive behaviors in PP dams exposed to LBN. This study is significant because it identifies C-mtDys as a possible mechanism causing depression after exposure to both pregnancy and poverty.