Traumatic events have been proposed to be associated with hypo-activity of the hypothalamic-pituitary-adrenal (HPA) axis, but data in animal models exposed to severe stressors are controversial and have important methodological concerns. Individual differences in resting or stress levels of corticosterone might explain some of the inconsistencies. We then studied this issue in male rats exposed to 2 h immobilization on boards (IMO), a severe stressor.

Thirty-six rats were blood sampled under resting conditions four times a day on three non-consecutive days. Then, they were assigned to control (n = 14) or IMO (n = 22) to study the HPA response to IMO, the stressor-induced alterations in the circadian pattern of corticosterone (CPCORT), and the behavioral and HPA responsiveness to an open-field.

Individual differences in pre-IMO resting corticosterone were inconsistent, but averaging data markedly improved consistency. The CPCORT was markedly altered on day 1 post-IMO (higher trough and lower peak levels), less altered on day 3 and apparently normal on day 7. Importantly, when rats were classified in low and high resting corticosterone groups (LCORT and HCORT, respectively), on the basis of the area under the curve (AUC) of the averaged pre-IMO data, AUC differences between LCORT and HCORT groups were maintained in controls but disappeared in IMO rats during the post-IMO week. Open-field hypo-activity and corticosterone sensitization were similar in LCORT and HCORT groups nine days after IMO. A single IMO exposure causes long-lasting HPA alterations, some of them dependent on pre-stress resting corticosterone levels, with no evidence for post-IMO resting corticosterone hypo-activity.

已经提出创伤事件与下丘脑-垂体-肾上腺（HPA）轴的活动不足有关，但是暴露于严重应激源的动物模型中的数据存在争议，并且具有重要的方法论关注。皮质酮的静息或压力水平的个体差异可能解释了一些不一致之处。然后，我们在暴露于严重应激源木板（IMO）2小时的雄性大鼠中研究了这个问题。

在不连续的三天中，每天在静止条件下对四十六只大鼠进行四次血液采样。然后，他们被分配到对照组（n  = 14）或IMO（n  = 22），以研究HPA对IMO的反应，应激源引起的皮质酮昼夜节律模式的改变（CPCORT）以及行为和HPA对人的反应。开放领域。

IMO前静息皮质酮的个体差异不一致，但平均数据明显改善了一致性。IMO后第1天CPCORT发生了明显变化（波谷较高且峰值较低），第3天变化较小，第7天明显正常。重要的是，将大鼠分为低和高静息皮质酮组（LCORT和HCORT，分别），根据平均IMO前数据的曲线下面积（AUC），对照组中LCORT和HCORT组之间的AUC差异得以维持，但在IMO后一周内在IMO大鼠中消失。IMO后9天，LCORT和HCORT组的野外运动减退和皮质酮敏感性增高。一次IMO暴露会导致持久的HPA改变，其中一些取决于压力前静息的皮质酮水平，