Cannabinoid receptor-mediated modulation of the gut-brain axis under chronic stress: Neuroinflammatory mechanisms, microbial metabolites, and sexual dimorphism.

Chronic stress disrupts the gut-brain axis (GBA) through coordinated dysfunction of the intestinal barrier and of the vascular interfaces that protect the brain, fostering a neuroinflammatory state implicated in mood disorders, neuropsychiatric conditions, and chronic pain. This narrative review synthesizes evidence across five domains. First, the inflammatory cascade by which stress-induced disruption of the epithelial and gut vascular barriers activates the NLRP3 inflammasome and sustains central neuroinflammation. Second, microbial metabolites, namely short-chain fatty acids (SCFAs), tryptophan-kynurenine products, and indole derivatives, as modulators of gut-brain homeostasis. Third, the gut microbiome-endocannabinoidome axis, including the capacity of commensal bacteria to generate endocannabinoid-like N-acyl amides that engage host receptors. Fourth, the receptor-specific pharmacology of phytocannabinoids, distinguishing Δ9-tetrahydrocannabinol (THC), which acts principally at CB1 and CB2 with comparable affinity, from cannabidiol (CBD), which has low affinity for these receptors and signals mainly through TRPV1, TRPA1, GPR55, PPARs, and 5-HT1A. Fifth, sexual dimorphism in barrier vulnerability and treatment response. In rodent models, chronic stress reduces intestinal and blood-brain barrier tight junction expression, elevates circulating lipopolysaccharide, and activates the NLRP3 inflammasome, while tryptophan metabolism shifts toward neurotoxic kynurenine products. Cannabinoid modulation of the kynurenine pathway and cannabinoid-mediated restoration of blood-brain barrier integrity remain mechanistic hypotheses extrapolated from indirect evidence rather than demonstrated mechanisms in chronic psychological stress paradigms. Human data are largely limited to small trials of microbiota-targeted interventions and of CBD in anxiety, and to observational endocannabinoidome-microbiome studies. These observations provide a preclinical rationale for GBA-targeted pharmacological strategies, with translational claims explicitly separated from mechanistic plausibility.