Department of Physiology, Institute of Pharmacology, Polish Academy of Sciences, Smętna 12, PL 31-343 Kraków, Poland.
Pharmacol Rep. 2013;65(5):1163-75. doi: 10.1016/s1734-1140(13)71474-9.
Disruption of the glucocorticoid negative feedback system evoked in animals by chronic stress can be induced by downregulation of glucocorticoid receptors (GRs) in several brain regions. In the present study, the dynamics of the changes in GRs, in brain structures involved in stress reactions, prefrontal cortex, hippocampus and hypothalamus was compared with the peripheral hypothalamo-pituitary-adrenocortical (HPA) axis hormones response to chronic stress.
Rats were exposed to 10 min restraint or restrained twice a day for 3, 7 or 14 days, and 24 h after the last stress session exposed to homotypic stress for 10 min. Control rats were not restrained. After rapid decapitation at 0, 1, 2, and 3 h after stress termination, trunk blood for plasma adrenocorticotropic hormone (ACTH) and corticosterone determinations was collected and prefrontal cortex, hippocampus and hypothalamus were excised and frozen. Plasma hormones were determined using commercially available kits and glucocorticoids and mineralocorticoids protein levels in brain structure samples were determined by western blot procedure.
Restraint stress alone significantly decreased glucocorticoid receptor (GR) level in prefrontal cortex and hippocampus, and increased mineralocorticoid receptor (MR) level in hypothalamus. Prior repeated stress for 3 days significantly increased GR protein level in hippocampus and diminished that level in hypothalamus in 7 days stressed rats. Acute stress-induced strong increase in plasma ACTH and corticosterone levels decreased to control level after 1 or 2 h, respectively. Prior repeated stress for 3 days markedly diminished the fall in plasma ACTH level and repeated stress for 7 days moderately deepened this decrease. Plasma ACTH level induced by homotypic stress in rats exposed to restraint for 3, 7, and 14 days did not markedly differ from its control level, whereas plasma corticosterone response was significantly diminished. The fast decrease of stress-induced high plasma ACTH and corticosterone levels was accompanied by a parallel decline of GR level only in prefrontal cortex but not in the hippocampus or hypothalamus.
Comparison of the dynamics of changes in plasma ACTH and corticosterone level with respective alterations in GR and MR in brain structures suggests that the buffering effect of repeated stress depends on the period of habituation to stress and the brain structure involved in regulation of these stress response.
慢性应激会导致动物的糖皮质激素负反馈系统紊乱，这种紊乱可以通过下调几个脑区的糖皮质激素受体（GRs）来诱导。在本研究中，我们比较了 GRs 在参与应激反应的脑结构（前额叶皮层、海马体和下丘脑）中的变化与外周下丘脑-垂体-肾上腺皮质（HPA）轴激素对慢性应激的反应。
大鼠暴露于 10 分钟束缚或每天束缚两次，持续 3、7 或 14 天，最后一次应激后 24 小时暴露于同型应激 10 分钟。对照大鼠不被束缚。应激结束后 0、1、2 和 3 小时快速断头，采集血样测定血浆促肾上腺皮质激素（ACTH）和皮质酮，取出前额叶皮层、海马体和下丘脑并冷冻。使用商业试剂盒测定血浆激素，Western blot 法测定脑结构样本中的糖皮质激素和盐皮质激素蛋白水平。
单独的束缚应激显著降低了前额叶皮层和海马体中的糖皮质激素受体（GR）水平，并增加了下丘脑的盐皮质激素受体（MR）水平。重复应激 3 天会显著增加 7 天应激大鼠的海马体 GR 蛋白水平，并降低其下丘脑 GR 蛋白水平。急性应激诱导的血浆 ACTH 和皮质酮水平的强烈增加在 1 或 2 小时后分别降至对照水平。重复应激 3 天显著降低了血浆 ACTH 水平的下降，重复应激 7 天则适度加深了这种下降。暴露于 3、7 和 14 天束缚应激的大鼠的同型应激诱导的血浆 ACTH 水平与对照水平无显著差异，而血浆皮质酮反应明显降低。应激诱导的高血浆 ACTH 和皮质酮水平的快速下降伴随着前额叶皮层中 GR 水平的平行下降，但海马体和下丘脑没有这种变化。
比较血浆 ACTH 和皮质酮水平变化的动态与脑结构中 GR 和 MR 的相应变化表明，重复应激的缓冲效应取决于适应应激的时间和参与调节这些应激反应的脑结构。
