Exploration of Digestive Diseases

Table 1. Pathophysiology and neurologic consequences in IBD.

Mechanism	Pathophysiological features	Neurological consequences
Cytokine-mediated neuroinflammation [118]	Elevated TNF-α, IL-6, and IL-1β cross the BBB or activate microglia; altered serotonin metabolism.	Fatigue, sickness behavior, depressive symptoms.
HPA axis dysregulation [119]	Chronic inflammation activates the HPA axis; cortisol imbalance affects brain function.	Mood instability, cognitive impairment, stress sensitivity.
Tryptophan metabolism shift [120]	IDO activation diverts tryptophan to the kynurenine pathway; reduced serotonin synthesis.	Depression, cognitive dysfunction.
Microbiota alterations [121]	Dysbiosis reduces SCFA-producing bacteria; disrupted microbial neurotransmitter production.	Anxiety-like behavior, impaired stress resilience.
Medication effects [124]	Corticosteroids worsen mood; anti-TNF agents may reduce systemic inflammation.	Exacerbation or improvement of mood symptoms depending on therapy.

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BBB: blood-brain barrier; HPA: hypothalamic–pituitary–adrenal; IBD: inflammatory bowel disease; IDO: indoleamine 2,3-dioxygenase; IL: interleukin; SCFA: short-chain fatty acid; TNF: tumor necrosis factor.

Declarations

Author contributions

AB: Conceptualization, Writing—original draft. SS: Conceptualization, Writing—original draft. KH: Writing—original draft. VR: Conceptualization, Writing—original draft, Writing—review & editing, Supervision. All authors read and approved the submitted version.

Conflicts of interest

The authors declare that there are no conflicts of interest.

Ethical approval

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Consent to participate

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Consent to publication

Not applicable.

Availability of data and materials

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Funding

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