Dietary effects on tyrosine availability and catecholamine synthesis in the central nervous system: possible relevance to the control of protein intake.

Contemporary neuroscience holds that central nervous system (CNS) function ultimately derives from the organization of neurons into complex associations analogous to electrical circuits. For these circuits to function, however, the neurons must be able to communicate with one another; in fact, they must exchange small electrical impulses. While some neurons accomplish this task by direct cellular contact, the primary mechanism appears to involve neurotransmitters. Neurotransmitters are molecules, released by neurons when they are electrically active, that modify electrical activity on adjacent neurons. Thus, neurotransmitters are key molecules in interneuronal communications, and in the functioning of the brain (Cooper et al. 1991). Because of the central role of neurotransmitters, it is not surprising to find that factors which influence their synthesis and release modify CNS function. Indeed, many therapeutically-useful agents exert their biological effects by influencing the synthesis and/or release of neurotransmitters. Diet also appears to influence the synthesis and release of certain neurotransmitters. Some findings suggest that brain function is modified as a result. In the present article, we discuss the manner in which diet influences transmitter synthesis and release, and possibly function, using a particular example, dopamine (DA). DA is a low-molecular-weight neurotransmitter derived from the non-essential amino acid tyrosine. Its rate of synthesis in neurons is directly influenced by the local supply of tyrosine. Because the ingestion of food modifies the availability of tyrosine to the CNS, diet is thereby able to influence CNS DA synthesis; this diet-neurotransmitter relationship might participate in brain circuits that regulate appetite.