Chronic unpredictable mild stress-induced anxiety is linked to inflammatory responses and disruptions in tryptophan metabolism in male C57BL/6N mice

Abstract

Chronic stress can affect brain function through various mechanisms, leading to the development of anxiety disorders. The chronic unpredictable mild stress (CUMS) is a classic model of chronic stress. This study evaluated the effects of different durations of CUMS on anxiety-like behavior, inflammation, and tryptophan metabolism in C57BL/6N mice. The results of behavioral assessments showed that after 3 and 4 weeks of CUMS exposure, the mice exhibited significant decreases in open arms ratio and time ratio in the elevated plus maze (EPM), prolonged latency in the novelty-suppressed feeding test (NSFT), and reduced transitions in the light/dark box (LDB), all indicative of anxiety-like behavior. The inflammatory factors expressions were quantified using qPCR, showing that pro-inflammatory and anti-inflammatory markers began to rise following 1–2 weeks of CUMS exposure. After 3 weeks of stress, TNF-α significantly increased, TGF-β levels started to decrease, and by 4 weeks of CUMS, Arg-1 expression also declined. In terms of tryptophan metabolism, 5-HT content in the hippocampus of the mice began to decrease after 3 weeks of CUMS, while the levels of neuroprotective kynurenic acid (KYNA) continued to rise. Concurrently, neurotoxic substances, including 3-hydroxykynurenine (3-HK) and quinolinic acid (QA), accumulated; after 4 weeks of CUMS, the KYNA content also started to decline. In conclusion, CUMS exposure for 3–4 weeks in male C57BL/6 N mice induces anxiety-like behavior alongside the occurrence of inflammatory responses and disturbances in tryptophan metabolism. These findings highlight the complex interplay between stress, inflammation, and metabolic pathways in the etiology of anxiety-related behaviors.