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Tyramine is a trace monoamine with sympathomimetic properties. It is naturally found in foods, plants, and animals. By definition, all monoamines have an amine group separated from an aromatic ring by a 2-carbon chain. Dopamine, norepinephrine, and serotonin are monoamines. Trace monoamines were named for their relatively low frequency in mammalian tissues compared to their more abundant and discussed monoamine neurotransmitter counterparts: epinephrine, norepinephrine, dopamine, and serotonin.[1] Other trace amines include octopamine, phenethylamine, N-methylphenethylamine, and N-methyltyramine. Tyramine is degraded by several enzymes, most notably monoamine oxidase. Tyramine is often found in fermented, aged, cured, and spoiled foods where microbes with decarboxylase enzymes convert the amino acid tyrosine into tyramine.[2] Ingestion of high tyrosine-containing foods in patients taking monoamine oxidase inhibitors produces headaches, blurry vision, chest pain, and palpitations associated with hypertension, intracranial hemorrhages, and myocardial injury.[3] Tyramine has long been shown to cause cardiovascular effects when consumed in large, pathologic amounts.[4]  New evidence suggests endogenous tyramine and other trace amines in lower physiologic levels may have additional roles, including modulating the immune system.[5]

New evidence has also revealed G-protein coupled receptors that tyramine and other biogenic amines bind to directly, called Trace amine-associated receptors (TAARs).[1] Tyramine has a high affinity for binding TAAR1 and TAAR2. These receptors are found in the central nervous system and periphery. These receptors are the focus of recent research on endogenous trace amines.  The function of this class of receptors is still being elucidated and is hypothesized to include olfaction, modulation of other neurotransmitters, regulation of body weight, and immunologic functions.[1][22] TAAR1 signal transduction may modulate the reward circuits, the limbic system, and mood in the central nervous system.[23] TAAR1 has been found in large amounts in the stomach and small intestine and may play a role in the brain-gut-microbiome axis.[24] TAAR1 is the only subtype not represented in the olfactory epithelium; however, the utility of TAAR subtypes in olfaction is still being studied.[24] One study found an association between single-nucleotide polymorphism (SNPs) in the TAAR1 gene and fibromyalgia.[25] The peripheral vascular effects and resulting hypertension with tyramine ingestion, long attributed to norepinephrine displacement, may partly be the result of TAAR1 binding mechanisms as well.[26]