CARDIAC PREDICTORS OF STRESS SUSCEPTIBILITY: LONGITUDINAL EVIDENCE FROM THE CHRONIC SOCIAL DEFEAT MODEL

Emotional processing is fundamental across species, shaping perception, decision-making, and behavioural adaptation. During stressful situations, emotional responses coordinate physiological mechanisms that support coping, but prolonged stress can overload this system, resulting in maladaptive behavioural and physiological responses. Emotional processing is organized in a top-down manner involving limbic structures converging on crucial brainstem relay sites, affecting cardiac, respiratory, hormonal and motor functions to prepare for threats. These brain centres modulate cardiac emotional responses through sympatho-vagal efferents, allowing heart activity adjustments to environmental demands. This balance is indexed by heart-rate variability (HRV), a promising biomarker of autonomic balance and predictor of stress-related disorders susceptibility. Nevertheless, longitudinal studies investigating how chronic stress dynamically alters cardiac-behavioural interactions remain scarce. In this study, we evaluated the effects of chronic stress on heart rate (HR) and heart reactivity. Additionally, we evaluated the biomarker potential of HRV to predict stress susceptibility. To address this, we combined wireless electrocardiogram recordings in mice exposed to the chronic social defeat stress model with longitudinal behavioural assessment using the elevated O-maze and social interaction tests. Our results demonstrate that chronic stress induces enduring brain-heart dysfunction during emotional contexts. Furthermore, pre-stress cardiac parameters appear to predict individual vulnerability to stress exposure. Together, these results provide new insights into the dynamic interaction between chronic stress, cardiac autonomic regulation, and emotional behaviour, advancing our understanding of the physiological bases of resilience and susceptibility.