Drug-Induced Changes in the Central Metabolism of Tyramine and Other Trace Monoamines: Their Possible Role in Brain Functions

Abstract

It has been known for quite a number of years that PE, p-TA, m-TA or T belong to a group of monoamines that are present in neural tissue in small concentrations and for this they have been named trace amines. The trace amines are present in discrete areas of the mammalian brain and possess a high metabolic rate as determined by their accumulation after MAO inhibition. Their concentrations are increased after the administration of their respective precursor amino acids or in some instances by specific activation of l-aromatic amino acid decarboxylase. In contrast, l-aromatic amino acid decarboxylase inhibitors reduce their brain concentrations. The administration of antipsychotics or stimulant drugs have unraveled intriguing interrelations between the concentrations of some trace amines and the metabolism of the classical transmitters. No changes in neuronal firing rate were observed after the iontophoretic administration of small amounts of trace amines. In contrast, these small amounts potentiate the firing rate changes induced by iontophoresing some of the classical transmitters such as DA, NA or 5-HT. These findings suggest that the trace amines possess a role in neural transmission; this may be a regulatory effect on the action of the classical transmitters or as neurotransmitters in some pathways. Future work will have to decide whether any of these occur.