Abrupt rather than gradual hormonal changes induce postpartum blues-like behavior in rats

Aims: Postpartum blues is thought to be related to hormonal events accompanying delivery. We investigated whether blues-like symptoms depend on the rate of the decline of hormones, by comparing the behavioral consequences of an abrupt versus a gradual decline of gonadal hormones in an animal model.Methods: Female rats were treated with estrogen and progesterone for 23 days, administered either by injections or by subcutaneously implanted tubes filled with hormones. A gradual hormone decline was achieved by discontinuation of the injections: and rapid decline by removal of the tubes. Control groups received either a continued treatment or no hormones. In the period following the decline the stress-reactivity was tested with an acoustic startle test on 3 consecutive days, and anxiety behavior with an open-field test on the 2nd day. The Hypothalamus-, Pituitary-, Adrenal-axis (HPA-axis) response to stress was measured by assessing the corticosterone levels and hypothalamic c-fos expression stress-response at the 4th day.Key findings: The rapid decline of hormones induced an increased startle response lasting for two days, and increased anxiety-like behavior in the open field. This was not found in the gradual-decline and control groups. The HPA-axis response to stress was decreased in all hormone-treated animals.Significance: This animal Study suggests that: 1) abrupt rather than gradual hormonal changes induce increased stress-reactivity and anxiety-like behavior: 2) postpartum blues may result from differences in the capacity to adapt to the changes of gonadal hormones; 3) Recovery of pregnancy-induced diminished HPA-axis response is independent of the postpartum hormone kinetics. (C) 2008 Elsevier Inc. All rights reserved.