In the brain, dopamine functions as a neurotransmitter —a chemical released by nerve cells to send signals to other nerve cells. The brain includes several distinct dopamine systems, one of which plays a major role in reward-motivated behavior.opamine itself is used as precursor in the synthesis of the neurotransmitter norepinephrine and the hormone epinephrine. Dopamine is converted into norepinephrine by the enzyme dopamine β-hydroxylase (DBH), with O 2 and L-ascorbic acid as cofactors.