Chronic unpredictable stress during adolescence exerts sex-specific effects on depressive-like behavior and neural activation triggered by tail suspension test

During adolescence, acute stress can modify neuronal excitability in various brain regions, leading to negative behavioral outcomes. However, the impact of chronic stress during adolescence on neuronal responses to acute stimuli remains unclear. To address this, we subjected adolescent mice to 12 days of chronic unpredictable stress (CUS). Anxiety and depressive behaviors were evaluated, along with changes in c-Fos expression, which is one of the most widely used markers of neuronal activation. By comparing c-Fos immunoreactivity between the CUS and control groups both before and after the tail suspension test (TST), we found that adolescent CUS induced depressive behaviors in male mice, but not in female mice. Adolescent CUS primarily affected the excitability of neurons in the infralimbic cortex (IL), the dorsomedial and dorsolateral area of the bed nucleus of the stria terminalis (BNST), and the ventral hippocampus CA3. TST exerted a significant main effect on the density of c-Fos⁺ neurons in the prelimbic cortex (PL), infralimbic cortex (IL), cingulate areas 1 and 2 (Cg1, Cg2), the lateral septum (LS), BNST, and lateral habenular (LHb). Furthermore, the excitability of neurons in the paraventricular thalamic nucleus (PVT) was impacted by sex. These data suggest that adolescent CUS elicits region- and sex-specific modifications in TST-induced c-Fos expression, establishing a theoretical basis for understanding the pathophysiological alterations in mood disorders following adolescent stress.