The hypothalamo-pituitary-adrenal (HPA) axis comprises interactions between the hypothalamus, the pituitary and the adrenal glands and its activation results in the release of corticosteroid hormones. Corticosteroids are secreted from the adrenal gland in a distinct 24-h circadian rhythm overarching an ultradian rhythm, which consists of hourly corticosteroid pulses exposing target tissues to rapidly changing steroid levels. On top of these rhythms surges can take place after stress. HPA-axis rhythms promote adaptation to predictable (i.e. the earth's rotation) and unpredictable (i.e. stressors) changes in environmental factors. Two steroid hormone receptors, the mineralocorticoid receptor (MR) and the glucocorticoid receptor (GR), are activated by corticosteroids and mediate effects at fast and slow timescales on e.g. glucose availability, gene transcription and synaptic plasticity. The current review discusses the origin of the circadian and ultradian corticosteroid rhythms and their relevance for gene regulation, neuroendocrine and physiological responses to stress and the involvement in the maintenance of brain functionality in rodents.

中文翻译：

---

啮齿动物HPA轴活动的昼夜节律和超昼夜模式：对脑功能的意义。

下丘脑-垂体-肾上腺（HPA）轴包括下丘脑，垂体和肾上腺之间的相互作用，其激活导致皮质类固醇激素的释放。皮质类固醇是肾上腺分泌的一种独特的24小时昼夜节律，覆盖整个超昼夜节律，该节律由每小时一次的皮质类固醇脉冲组成，使目标组织暴露于快速变化的类固醇水平。在这些节律之上，压力过后可能会激增。HPA轴节律促进适应环境因素的可预测（即地球自转）和不可预测（即压力源）变化。糖皮质激素激活两种类固醇激素受体，盐皮质激素受体（MR）和糖皮质激素受体（GR），并在快速和慢速范围内介导例如葡萄糖的可利用性，基因转录和突触可塑性。本篇综述讨论了昼夜节律和超昼夜节律性皮质激素的节律及其与基因调节，神经内分泌和对应激的生理反应以及在啮齿动物中维持脑功能的相关性。