Role of the brain-gut axis in gastrointestinal cancer

Table 1 Summary of the most relevant neurotransmitters and neurotrophic factors related to progression of gastrointestinal cancer

Family	Member	Signaling receptor	Role in GI cancer
Neurotransmitters	Epinephrine (Adrenaline)	α/β adrenergic receptors	Promote proliferation, invasion, and angiogenesis
	Acetylcholine	Muscarinic and nicotinic acetylcholine receptor	Increase stemness activity
			Promote migration and invasion
	5-hydroxytryptamine	5-HT1-7 receptors	Promote mitogen and angiogenesis
	Dopamine	Dopamine 1–5 receptors	Suppress invasion and migration
			Reduce tumor microvessel density
	Gamma-aminobutyric acid	GABAB GABAA, GABAA-ρ receptor	Reduce migration (GABAA)
			Promote proliferation (GABAB)
Neurotrophic factors	Brain-derived neurotrophic factor	TrkB	Promote proliferation and migration
			Decrease apoptosis
	Nerve growth factor	TrkA	Promote survival, proliferation, differentiation, and angiogenesis
			Involved in cancer-induced bone pain
	Insulin-like growth factor	IGF type I/II receptor	Promote proliferation
	Fibroblast growth factors	FGFR-1–4	Promote growth, survival, and metastasis

GI: Gastrointestinal; 5-HT: 5-hydroxytryptamine; IGFR: Insulin-like growth factor; FGF: Fibroblast growth factor receptor; TrkB: Tropomyosin receptor kinase B.