Clow Angela, Law Robin, Evans Phil, Vallence Ann-Maree, Hodyl Nicolette A, Goldsworthy Mitchell R, Rothwell John R, Ridding Michael C
Department of Psychology, University of Westminster , London , UK .
Stress. 2014 May;17(3):219-23. doi: 10.3109/10253890.2014.905533. Epub 2014 Apr 7.
The cortisol awakening response (CAR) is the most prominent, dynamic and variable part of the circadian pattern of cortisol secretion. Despite this, its precise purpose is unknown. Aberrant patterns of the CAR are associated with impaired physical and mental health and reduced cognitive function, suggesting that it may have a pervasive role or roles. It has been suggested that the CAR primes the brain for the expected demands of the day but the mechanisms underlying this process are unknown. We examined temporal covariation of the CAR and rapid transcranial magnetic stimulation (rTMS)-induced long term depression (LTD)-like responses in the motor cortex. Plasticity was evaluated across 180 measures from five time points on four sessions across nine healthy researcher participants, mean age 25 ± 2.5 years. Plasticity estimates were obtained in the afternoon after measurement of the CAR on 4 days, at least 3 days apart. As both CAR magnitude and rTMS-induced responses are variable across days, we hypothesized that days with larger than individual average CARs would be associated with a greater than individual average plasticity response. This was confirmed by mixed regression modelling where variation in the CAR predicted variation in rTMS-induced responses (df: 1, 148.24; F: 10.41; p = 0.002). As the magnitude of the CAR is regulated by the "master" circadian CLOCK, and synaptic plasticity is known to be modulated by peripheral "slave" CLOCK genes, we suggest that the CAR may be a mediator between the master and peripheral circadian systems to entrain daily levels of synaptic plasticity.
皮质醇觉醒反应（CAR）是皮质醇分泌昼夜节律模式中最显著、动态且多变的部分。尽管如此，其确切目的尚不清楚。CAR的异常模式与身心健康受损及认知功能下降有关，这表明它可能具有广泛的作用。有人提出，CAR使大脑为一天中的预期需求做好准备，但这一过程的潜在机制尚不清楚。我们研究了CAR与运动皮层中重复经颅磁刺激（rTMS）诱导的类似长期抑郁（LTD）反应的时间协变关系。在9名健康研究参与者（平均年龄25±2.5岁）的4次实验中，从5个时间点进行了180次测量来评估可塑性。在4天中测量CAR后的下午获得可塑性估计值，每次测量间隔至少3天。由于CAR幅度和rTMS诱导的反应在不同日子里都是可变的，我们假设CAR大于个体平均水平的日子会与大于个体平均水平的可塑性反应相关。混合回归模型证实了这一点，其中CAR的变化预测了rTMS诱导反应的变化（自由度：1, 148.24；F：10.41；p = 0.002）。由于CAR的幅度受“主”昼夜节律时钟调节，且已知突触可塑性受外周“从”时钟基因调节，我们认为CAR可能是主昼夜节律系统和外周昼夜节律系统之间的介质，以调节每日的突触可塑性水平。
