Dopamine is a neurotransmitter in the brain that is synthesised in a chemical pathway originating from the amino acid L-phenylalanine. The enzyme phenylalanine hydroxylase converts L-phenylalanine to L-tyrosine, and then the enzyme tyrosine hydroxylase converts L-tyrosine to L-DOPA. Finally, L-DOPA decarboxylase removes a carbon dioxide from L-DOPA to form dopamine. Dopamine synthesis is concentrated mainly in the part of the brain called the nucleus accumbens, which is a primitive part of the brain that is involved in stimulating feelings of euphoria, motivation and pleasure. Increasing dopamine synthesis in the nucleus accumbens is associated with increased motivational behaviour, assertiveness, and an increase in labido. Dopamine may also be involved in the regulation of appetite through affecting secretion of prolactin and may be required for short term memory and other cognitive functions. Dopamine deficiency may also be related in some way to the onset of depressive symptoms.
Other symptoms of dopamine deficiency in the brain can include apathy, long sleep duration, irritability and the addiction to recreational drugs such as alcohol, caffeine, or illegal street drugs. The addiction to drugs is worthy of note because it is the seeking of such drugs to boost dopamine levels that may be the first indication that brain levels of dopamine are insufficient. While many drugs do increase the release of dopamine from dopamine containing neurones, they do not address the underlying cause of the low dopamine levels, and in this way often have deleterious effects in the long term. One of the best ways to ensure that the brain can produce adequate dopamine is through good nutrition. For example, the rate limiting step in the synthesis of dopamine requires a molecule of iron, and so iron deficiencies can inhibit flux through the pathway. In addition, supplying the amino acid L-tyrosine in amounts greater than normally found in the diet can also increase the synthesis of dopamine naturally.