Behavioural and Physiological Signatures of Chronic Unpredictable Mild Stress Models in Mice

The chronic unpredictable mild stress (CUMS) paradigm is one of the most widely used preclinical models to investigate the role of stress in the neurobiology of depression and to evaluate potential antidepressant therapies, owing to its strong translational relevance. However, despite its extensive use, substantial discrepancies and concerns regarding the reproducibility of CUMS outcomes persist in the literature, with many studies reporting inconsistent or unreliable results. In the present comparative study, we implemented several CUMS protocols in mice that differed in the intensity and duration of stress exposure, and systematically evaluated the resulting pathophysiological and behavioural alterations associated with depressive- and anxiety-like phenotypes. We found that progressive escalation in stress intensity and frequency, as well as prolonged exposure, induced increasingly robust disease-related behavioural and physiological changes, including depression- and anxiety-like behaviours, adrenal hypertrophy, and reduced body weight gain.. Moreover, social isolation emerged as a major contributing factor exacerbating stress-induced deficits. Altogether, data suggest that a multidimensional assessment of the behavioural impairments is critical to reinforce the physiological changes indicative of a hyperactive hypothalamic-pituitary-adrenal axis (HPA). Differences in individual stress susceptibility, stressor intensity, frequency, and housing conditions are key determinants of CUMS outcomes. Therefore, precise, detailed, and transparent reporting of protocol parameters is critical to enhance reproducibility and enable meaningful comparisons across studies.