Microbiota-derived tryptophol attenuates chronic stress-induced pain- and depression-like phenotypes in female mice via colonic aryl hydrocarbon receptor signaling through reduced neuroinflammation.

Chronic stress contributes to comorbid hyperalgesia and depression-like behaviors, but the microbial-metabolic mediators linking stress to these phenotypes remain unclear. Using a chronic restraint stress (CRS) model, we found that CRS induced hyperalgesia and depression-like behaviors together with gut microbial dysbiosis and remodeling of fecal tryptophan metabolites. Fecal microbiota transplantation from CRS donors to antibiotic-treated recipients reproduced these behavioral abnormalities, supporting a causal contribution of the gut microbiota. Targeted metabolomics identified reduced fecal tryptophol (IEt) in both female and male mice. Because IEt is a reported aryl hydrocarbon receptor (AHR) ligand, we evaluated it pharmacologically in vivo. Oral IEt alleviated CRS-induced behavioral abnormalities in females, but not males, under the dose and regimen tested, and this effect was abolished by the gastrointestinal-specific AHR antagonist GNF351. In females, IEt increased colonic AHR signaling-related proteins, improved barrier-associated markers, and reduced the degree of colonic and systemic inflammation. These changes were accompanied by preservation of blood-brain barrier tight-junction markers' expression and attenuation of neuroinflammatory and neuronal/synaptic alterations in the medial prefrontal cortex and ventral hippocampus. Together, these findings support a female-selective, gut AHR-associated mechanism linking chronic stress-induced pain- and depression-like phenotypes to coordinated enteric and neuroinflammation.