Impact of social defeat stress on depressive-like behavior, cognitive impairment, and autonomic dysregulation in male rats

Social stress is a critical risk factor for depression, impacting millions of individuals globally. This study investigated the behavioral and cardiovascular effects of a chronic social defeat model in male Wistar rats, focusing on identifying cardiovascular markers associated with depressive-like phenotypes. Male Wistar rats were subjected to a 7-day resident-intruder social defeat paradigm, followed by behavioral assessments (open field test, novel object recognition test, and forced swimming test) and cardiovascular recordings (mean arterial pressure, heart rate, and heart rate variability). Socially defeated rats exhibited increased immobility in the forced swimming test, indicative of depressive-like behavior. While locomotion and anxiety-like behaviors in the open field were unchanged, both defeated and isolated groups showed impaired short-term memory. Cardiovascular analysis revealed that defeated animals had a significantly elevated basal heart rate and a reduced high-frequency (HF) component of heart rate variability, suggesting decreased parasympathetic activity. No significant changes were observed in blood pressure or baroreflex sensitivity across groups. Correlation analysis highlighted a strong positive correlation between short-term memory and HF power in the control group, a relationship that was disrupted in both isolated and defeated groups. These findings suggest that chronic social defeat induces specific behavioral alterations, such as increased immobility and impaired memory, coupled with cardiovascular dysregulation characterized by basal tachycardia and reduced parasympathetic tone. This study underscores the potential of heart rate variability as a physiological marker for stress-induced depressive phenotypes and emphasizes the association between behavioral and cardiovascular systems under social stress.