Figure 1.

Primary and secondary autonomic nervous system (ANS) and the hypothalamus-pituitary-adrenal (HPA) axis response to stress. In the table, the molecular mediators and the main effects of primary and secondary responses to stress of ANS and HPA axis are reported. In both systems, the primary response promotes fight-or-flight reaction to properly face the perceived stress. Conversely, different secondary response mechanisms are adopted: ANS actively promotes rest and digest response through the activation of PSNS, whereas HPA axis secondary response consists of negative feedback mechanisms guaranteeing the recovery of resting conditions-inherent axis responsivity. SNS (Sympathetic nervous system); PSNS (Parasympathetic nervous system); PVN (Paraventricular nucleus); CRH (Corticotropin releasing hormone); ACTH (Adrenocorticotropic hormone); GRs (Glucocorticoid receptors); MRs (Mineralocorticoid receptors); CNS (Central nervous system); ECS (Endocannabinoid system).