Modifications of glucocorticoid receptors mRNA expression in the HPA axis in response to early life stress in female Japanese quail

Abstract

Stress exposure during early life development can program individual brain and physiology. The hypothalamic-pituitary-adrenal (HPA) axis is one of the primary targets of this programming which is generally associated with a hyperactive HPA axis, indicative of a reduced negative feedback. This reduced feedback efficiency usually results from a reduced level of the glucocorticoid receptor (GR) and/or the mineralocorticoid receptor (MR) within the HPA axis. However, a few studies have shown that early life stress exposure results in an attenuated physiological stress response, suggesting an enhance feedback efficiency. Here, we aimed to determine if early life stress had long-term consequences on GR and MR levels in quail and if the effects on the physiological response to acute stress observed in pre-natally stressed individuals were underpinned by changes in GR and/or MR levels in one or more HPA axis components. We determined GR and MR mRNA expression in the hippocampus, hypothalamus and pituitary gland in quail exposed to elevated CORT during pre-natal development, post-natal development or both and in control individuals exposed to none of the stressors. We showed that pre-natal stress increased the GR:MR ratio in the hippocampus, GR and MR expression in the hypothalamus and GR expression in the pituitary gland. Post-natal stress resulted in a reduced MR expression in the hippocampus. Both early life treatments permanently affected the expression of both receptor types in HPA axis regions. The effects of pre-natal stress are in accordance with a more efficient negative feedback within the HPA axis and thus can explain the attenuated stress response observed in these birds. Therefore, these changes in receptor density or number as a consequence of early life stress exposure might be the mechanism that allows an adaptive response to later life stressful conditions. This article is protected by copyright. All rights reserved.