Estrogen administration and withdrawal in a model of hormone-simulated pregnancy lead to alterations in behavior and gene expression but do not induce depression-like phenotypes in mice.

Pregnancy and the post-partum period are associated with substantial fluctuations in hormone levels and are frequently associated with significant stress. Many individuals also experience affective disturbances during the peri‑partum period, including anxiety, the 'baby blues,' and post-partum depression. However, the extent to which these affective changes result from rapidly altering hormone levels, increased stress, or the combination of both remains largely unknown. The current study sought to evaluate the consequences of pregnancy-like hormonal changes on behavior and gene expression in c57BL/6 mice in the absence of stress using a hormone-simulated pregnancy model. Our results reveal that animals receiving hormone injections to simulate the high levels of estrogen observed in late pregnancy and animals withdrawn from estrogen to mimic the rapid decline in this hormone following parturition both exhibit increased anxiety-like behavior compared to ovariectomized controls in the novel open field test. However, no other significant anxiety- or depression-like alterations were observed in either hormone-treated group compared to ovariectomized controls. Both hormone administration and estrogen withdrawal were shown to induce several significant alterations in gene expression in the bed nucleus of the stria terminalis and the paraventricular nucleus of the hypothalamus. In contrast to the estrogen withdrawal hypothesis of post-partum depression, our results suggest that this method estrogen withdrawal following hormone-simulated pregnancy in the absence of stress does not induce phenotypes consistent with post-partum depression in c57BL/6 mice. However, given that estrogen withdrawal does lead to significant gene expression changes in two stress-sensitive brain regions, it remains possible that estrogen withdrawal could still contribute to affective dysregulation in the peri-partum period by influencing susceptibility to stress. Future research is required to evaluate this possibility.