Adolescent envy-like social comparison stress induces HPA axis hypoactivity and anxiety in female mice: implications for somatic symptom disorder.

Adolescence is a critical developmental window marked by heightened neuroplasticity and maturation of the stress response system, conferring vulnerability to psychosocial stress. Chronic stress during this period increases the risk of anxiety and depressive disorders and may contribute to somatic symptom disorder (SSD), which is characterized by medically unexplained physical complaints and shows a striking female predominance. The impact of envy-like stress arising from social comparison, a pervasive psychosocial factor in modern society, remains poorly understood. Male and female C57BL/6N mice were exposed to chronic envy-like stress from postnatal day (P)21 to P52 by housing them adjacent to enriched cages, while control mice were housed without such exposure. From P52 onward, mice underwent behavioral testing of anxiety-like behavior, exploratory activity, social interaction, spatial working memory, motor coordination, nociception, and depression-like behavior. Serum corticosterone and adrenocorticotropic hormone (ACTH) concentrations were measured to assess hypothalamic–pituitary–adrenal (HPA) axis function. Envy-like stress induced sex-specific phenotypes. Male mice exhibited hyperactivity, reduced social interaction, and impaired spatial working memory. In contrast, female mice displayed robust increases in anxiety-like behavior, impaired motor coordination, and significant reductions in basal corticosterone and ACTH levels. Chronic envy-like stress during adolescence elicits distinct, sex-dependent behavioral and endocrine alterations. The phenotype observed in female mice—characterized by heightened anxiety and lower basal HPA axis hormone levels—shares some biological features with clinical observations in SSD. This model may serve as a starting point for elucidating the mechanisms linking psychosocial stress and somatic symptoms in a sex-dependent manner.