Cortisol Awakening Response: An Ancient Adaptive Feature

Author(s): Carlos M. Contreras, Ana G. Gutierrez-Garcia

Similar to other endocrine substances, cortisol secretion follows a pulsating rhythm. The cortisol awakening response (CAR) occurs upon awakening in the absence of any apparent stressful situation or imminent danger, which is a very intriguing feature. When confronting any stressful situation, two systems are activated. One system is regulated by the hypothalamic-pituitary-adrenal axis (HPA), and the other system is regulated by cerebral structures that control the activity of the autonomic sympathetic nervous system. Both systems receive inputs from emotional memory circuits, namely the amygdala, the hippocampus, the medial prefrontal cortex, and lateral septal nuclei, among others. This circuit integrates sensory information that comes from thalamic nuclei. The acquisition, retention, and evocation of recent and remote memories that are processed by the emotional memory circuit allow the selection of strategies for survival. The diurnal secretion of cortisol occurs near the time of awakening (i.e., after a period of rest or sleeping) and persists for several hours in the absence of any current stressful situation. The CAR seems to represent an ancient adaptive-allostatic feature that prepares an individual to face eventualities that are forthcoming during the day. The CAR is regulated by hypothalamic nuclei that modulate circadian rhythm, namely the suprachiasmatic nucleus and its connections with the paraventricular nucleus, and then activate the HPA axis. The CAR may represent a useful preparatory process that occurs before a stressful situation. The participation of emotional memory circuits may modify the CAR and contribute to resilient or vulnerable reactions when coping with threatening situations.

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