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Dopamine (DA) is a catecholamine neurotransmitter and
neurohormone involved in movement, motivation, reward, cognition, memory,
attention and endocrine regulation. Dopamine acts primarily through five
G-protein-coupled receptors, DRD1–DRD5, which can produce
different and sometimes opposing biological effects. In Alzheimer’s disease,
dopaminergic dysfunction and reduced dopamine signalling have been associated
with cognitive decline, memory impairment and neuropsychiatric symptoms,
suggesting that the typical AD-associated direction is generally
down or dysregulated. In cancer, dopamine signalling is
context-dependent: dopamine receptors can regulate tumour-cell
proliferation, stemness, angiogenesis, migration, apoptosis and antitumour
immunity, but individual receptors may be either tumour-promoting or
tumour-suppressive depending on the cancer type.
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