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Biochemistry. a catecholamine neurotransmitter in the central nervous system, retina, and sympathetic ganglia, acting within the brain to help regulate movement and emotion: its depletion may cause Parkinson's disease. Compare dopa.

Pharmacology. a dopamine preparation used to increase the force of contraction of the heart in the treatment of shock.

a neurotransmitter, derived from tryptophan, that is involved in sleep, depression, memory, and other neurological processes.