Distinct Gut–brain Axis Dysregulation in Episodic versus Chronic Migraine: Insights from NTG-induced Mouse Models

Background The gut–brain axis influences various brain functions and plays a crucial role in maintaining central nervous system homeostasis and the intestinal environment. Migraine patients show increased risk of gastrointestinal (GI) disorders, with stronger links between GI comorbidities and chronic migraine (CM) compared to episodic migraine (EM). This study was performed to evaluate differences in migraine-related GI manifestations using nitroglycerin (NTG)-induced EM and CM mouse models. Methods To generate mouse models of EM or CM, male C57BL/6J mice received either a single injection or five injections (every other day for 9 days) of NTG at a concentration of 10 mg/kg. Vehicle controls received saline with propylene glycol. On the day of sacrifice, GI tract length was measured, and tissues were collected for analysis. We assessed pro- and antiinflammatory marker transcript expression (tumor necrosis factor [TNF]-α, transforming growth factor [TGF]-β, interleukin [IL]-1β, IL-6, IL-8, IL-4, and IL-10), along with calcitonin gene-related peptide (CGRP) expression, in the GI tract by immunofluorescence analysis. FACS analysis was performed to evaluate immune cell distribution in the colon. Results NTG-induced migraine groups exhibited significantly reduced food intake and body weight compared with controls. Colon length was notably shorter in the CM model compared to the EM model and controls. Molecular analysis revealed increased proinflammatory cytokine expression in the EM model and antiinflammatory cytokine expression in the CM model, particularly in the colon. CGRP expression was significantly elevated in the GI tract, especially in the colon of the CM model. Immune cell analysis showed increased Th17 and B cells in the EM model, whereas T cells, regulatory T (Treg) cells, and macrophages were more abundant in the CM model, with marked immune changes in the distal colon. Conclusion This study showed that CM is associated with more pronounced gut–brain axis dysregulation than EM, as evidenced by distinct patterns of GI inflammation, CGRP expression, immune cell alterations, and morphological changes in the GI tract, especially the colon. These results warrant further translational research to explore gut-targeted therapies as potential adjuncts in CM therapy.