The catecholamine neurotransmitters dopamine, noradrenaline and adrenaline are found in nervous tissue of animals. They are synthesized in catecholaminergic neurons by four enzymes from tyrosine to adrenaline: tyrosine hydroxylase (TH); aromatic L-amino acid decarboxylase (AADC); dopamine beta-hydroxylase (DBH); and phenylethanolamine N-methyltransferase (PNMT).