TAAR1

Last updated

TAAR1
TAAR1 organ-specific expression and function.jpg
Identifiers
Aliases TAAR1 , TA1, TAR1, TRAR1, trace amine associated receptor 1, Trace amine receptor
External IDs OMIM: 609333 MGI: 2148258 HomoloGene: 24938 GeneCards: TAAR1
Orthologs
SpeciesHumanMouse
Entrez
Ensembl
UniProt
RefSeq (mRNA)

NM_138327

NM_053205

RefSeq (protein)

NP_612200

NP_444435

Location (UCSC) Chr 6: 132.64 – 132.66 Mb Chr 10: 23.8 – 23.8 Mb
PubMed search [3] [4]
Wikidata
View/Edit Human View/Edit Mouse

Trace amine-associated receptor 1 (TAAR1) is a trace amine-associated receptor (TAAR) protein that in humans is encoded by the TAAR1 gene. [5] TAAR1 is an intracellular amine-activated Gs-coupled and Gq-coupled G protein-coupled receptor (GPCR) that is primarily expressed in several peripheral organs and cells (e.g., the stomach, small intestine, duodenum, and white blood cells), astrocytes, and in the intracellular milieu within the presynaptic plasma membrane (i.e., axon terminal) of monoamine neurons in the central nervous system (CNS). [6] [7] [8] [9] TAAR1 was discovered in 2001 by two independent groups of investigators, Borowski et al. and Bunzow et al. [10] [11] TAAR1 is one of six functional human trace amine-associated receptors, which are so named for their ability to bind endogenous amines that occur in tissues at trace concentrations. [12] [13] TAAR1 plays a significant role in regulating neurotransmission in dopamine, norepinephrine, and serotonin neurons in the CNS; [7] [12] it also affects immune system and neuroimmune system function through different mechanisms. [14] [15] [16] [17]

Contents

TAAR1 is a high-affinity receptor for amphetamine, methamphetamine, dopamine, and trace amines which mediates some of their cellular effects in monoamine neurons within the central nervous system. [7] [12]

The primary endogenous ligands of the human TAAR1 (hTAAR1) receptor, by rank order of potency, are:
tyramine  > β-phenethylamine  > dopamine  = octopamine. [6]

Discovery

TAAR1 was discovered independently by Borowski et al. and Bunzow et al. in 2001. To find the genetic variants responsible for TAAR1 synthesis, they used mixtures of oligonucleotides with sequences related to G protein-coupled receptors (GPCRs) of serotonin and dopamine to discover novel DNA sequences in rat genomic DNA and cDNA, which they then amplified and cloned. The resulting sequence was not found in any database and coded for TAAR1. [10] [11] Further characterization of the functional role of TAAR1 and other receptors from this family was performed by other researchers including Raul Gainetdinov and his colleagues. [18]

Structure

TAAR1 shares structural similarities with the class A rhodopsin GPCR subfamily. [11] It has 7 transmembrane domains with short N and C terminal extensions. [19] TAAR1 is 62–96% identical with TAARs2-15, which suggests that the TAAR subfamily has recently evolved; while at the same time, the low degree of similarity between TAAR1 orthologues suggests that they are rapidly evolving. [10] TAAR1 shares a predictive peptide motif with all other TAARs. This motif overlaps with transmembrane domain VII, and its identity is NSXXNPXX[Y,H]XXX[Y,F]XWF. TAAR1 and its homologues have ligand pocket vectors that utilize sets of 35 amino acids known to be involved directly in receptor-ligand interaction. [13]

Gene

All human TAAR genes are located on a single chromosome spanning 109 kb of human chromosome 6q23.1, 192 kb of mouse chromosome 10A4, and 216 kb of rat chromosome 1p12. Each TAAR is derived from a single exon, except for TAAR2, which is coded by two exons. [13] The human TAAR1 gene is thought to be an intronless gene. [20]

Tissue distribution

This diagram illustrates how TAAR1 activation induces incretin-like effects through the release of gastrointestinal hormones and influences food intake, blood glucose levels, and insulin release. TAAR1 expression in the periphery is indicated with "x". TAAR1 organ-specific expression and function.jpg
This diagram illustrates how TAAR1 activation induces incretin-like effects through the release of gastrointestinal hormones and influences food intake, blood glucose levels, and insulin release. TAAR1 expression in the periphery is indicated with "x".

To date, TAAR1 has been identified and cloned in five different mammal genomes: human, mouse, rat, monkey, and chimpanzee. In rats, mRNA for TAAR1 is found at low to moderate levels in peripheral tissues like the stomach, kidney, intestines [21] and lungs, and at low levels in the brain. [10] Rhesus monkey Taar1 and human TAAR1 share high sequence similarity, and TAAR1 mRNA is highly expressed in the same important monoaminergic regions of both species. These regions include the dorsal and ventral caudate nucleus, putamen, substantia nigra, nucleus accumbens, ventral tegmental area, locus coeruleus, amygdala, and raphe nucleus. [6] [22] hTAAR1 has also been identified in human astrocytes. [6] [14]

Outside of the human central nervous system, hTAAR1 also occurs as an intracellular receptor and is primarily expressed in the stomach, intestines, [21] duodenum, [21] pancreatic β-cells, and white blood cells. [9] [21] In the duodenum, TAAR1 activation increases glucagon-likepeptide-1 (GLP-1) and peptide YY (PYY) release; [9] in the stomach, hTAAR1 activation has been observed to increase somatostatin (growth hormone-inhibiting hormone) secretion from delta cells. [9]

hTAAR1 is the only human trace amine-associated receptor subtype that is not expressed within the human olfactory epithelium. [23]

Location within neurons

TAAR1 is an intracellular receptor expressed within the presynaptic terminal of monoamine neurons in humans and other animals. [7] [12] [24] In model cell systems, hTAAR1 has extremely poor membrane expression. [24] A method to induce hTAAR1 membrane expression has been used to study its pharmacology via a bioluminescence resonance energy transfer cAMP assay. [24]

Because TAAR1 is an intracellular receptor in monoamine neurons, exogenous TAAR1 ligands must enter the presynaptic neuron through a membrane transport protein [note 1] or be able to diffuse across the presynaptic membrane in order to reach the receptor and produce reuptake inhibition and neurotransmitter efflux. [12] Consequently, the efficacy of a particular TAAR1 ligand in producing these effects in different monoamine neurons is a function of both its binding affinity at TAAR1 and its capacity to move across the presynaptic membrane at each type of neuron. [12] The variability between a TAAR1 ligand's substrate affinity at the various monoamine transporters accounts for much of the difference in its capacity to produce neurotransmitter release and reuptake inhibition in different types of monoamine neurons. [12] E.g., a TAAR1 ligand which can easily pass through the norepinephrine transporter, but not the serotonin transporter, will produce – all else equal – markedly greater TAAR1-induced effects in norepinephrine neurons as compared to serotonin neurons.

Receptor oligomers

TAAR1 forms GPCR oligomers with monoamine autoreceptors in neurons in vivo . [25] [26] These and other reported TAAR1 hetero-oligomers include:

Ligands

Trace amine-associated receptor 1
Transduction mechanisms Gs, Gq, GIRKs, β-arrestin 2
Primary endogenous agonists tyramine, β-phenylethylamine , octopamine, dopamine
Agonists Endogenous: trace amines
Exogenous: RO5166017, amphetamine, methamphetamine, others
Neutral antagonists None characterized
Inverse agonists EPPTB
Positive allosteric modulators N/A
Negative allosteric modulators N/A
External resources
IUPHAR/BPS 364
DrugBank Q96RJ0
HMDB HMDBP10805

Agonists

Trace amines

Trace amines are endogenous amines which act as agonists at TAAR1 and are present in extracellular concentrations of 0.1–10  nM Tooltip nanomolar in the brain, constituting less than 1% of total biogenic amines in the mammalian nervous system. [28] Some of the human trace amines include tryptamine, phenethylamine (PEA), N-methylphenethylamine , p-tyramine , m-tyramine , N-methyltyramine , p-octopamine , m-octopamine , and synephrine. These share structural similarities with the three common monoamines: serotonin, dopamine, and norepinephrine. Each ligand has a different potency, measured as increased cyclic AMP (cAMP) concentration after the binding event.

The rank order of potency for the primary endogenous ligands at hTAAR1 is:
tyramine  > β-phenethylamine  > dopamine  = octopamine. [6]

Thyronamines

Thyronamines are molecular derivatives of the thyroid hormone and are very important for endocrine system function. 3-Iodothyronamine (T1AM) is the most potent TAAR1 agonist yet discovered, although it lacks monoamine transporter affinity and therefore has little effect in monoamine neurons of the central nervous system. Activation of TAAR1 by T1AM results in the production of large amounts of cAMP. This effect is coupled with decreased body temperature and cardiac output.

Synthetic

Partial agonists

Inverse agonists

Neutral antagonists

As of early 2018, no neutral antagonists for hTAAR1 have been characterized. [6]

Function

Monoaminergic systems

Before the discovery of TAAR1, trace amines were believed to serve very limited functions. They were thought to induce noradrenaline release from sympathetic nerve endings and compete for catecholamine or serotonin binding sites on cognate receptors, transporters, and storage sites. [28] Today, they are believed to play a much more dynamic role by regulating monoaminergic systems in the brain.

One of the downstream effects of active TAAR1 is to increase cAMP in the presynaptic cell via Gαs G-protein activation of adenylyl cyclase. [10] [11] [13] This alone can have a multitude of cellular consequences. A main function of the cAMP may be to up-regulate the expression of trace amines in the cell cytoplasm. [29] These amines would then activate intracellular TAAR1. Monoamine autoreceptors (e.g., D2 short, presynaptic α2, and presynaptic 5-HT1A) have the opposite effect of TAAR1, and together these receptors provide a regulatory system for monoamines. [12] Notably, amphetamine and trace amines possess high binding affinities for TAAR1, but not for monoamine autoreceptors. [12] [7] The effect of TAAR1 agonists on monoamine transporters in the brain appears to be site-specific. [12] Imaging studies indicate that monoamine reuptake inhibition by amphetamine and trace amines is dependent upon the presence of TAAR1 co-localization in the associated monoamine neurons. [12] As of 2010, co-localization of TAAR1 and the dopamine transporter (DAT) has been visualized in rhesus monkeys, but co-localization of TAAR1 with the norepinephrine transporter (NET) and the serotonin transporter (SERT) has only been evidenced by messenger RNA (mRNA) expression. [12]

In neurons with co-localized TAAR1, TAAR1 agonists increase the concentrations of the associated monoamines in the synaptic cleft, thereby increasing post-synaptic receptor binding. [12] Through direct activation of G protein-coupled inwardly-rectifying potassium channels (GIRKs), TAAR1 can reduce the firing rate of dopamine neurons, in turn preventing a hyper-dopaminergic state. [33] [39] [40] Amphetamine and trace amines can enter the presynaptic neuron either through DAT or by diffusing across the neuronal membrane directly. [12] As a consequence of DAT uptake, amphetamine and trace amines produce competitive reuptake inhibition at the transporter. [12] Upon entering the presynaptic neuron, these compounds activate TAAR1 which, through protein kinase A (PKA) and protein kinase C (PKC) signaling, causes DAT phosphorylation. Phosphorylation by either protein kinase can result in DAT internalization (non-competitive reuptake inhibition), but PKC-mediated phosphorylation alone induces reverse transporter function (dopamine efflux). [12] [43]

Immune system

Expression of TAAR1 on lymphocytes is associated with activation of lymphocyte immuno-characteristics. [16] In the immune system, TAAR1 transmits signals through active PKA and PKC phosphorylation cascades. [16] In a 2012 study, Panas et al. observed that methamphetamine had these effects, suggesting that, in addition to brain monoamine regulation, amphetamine-related compounds may have an effect on the immune system. [16] A recent paper showed that, along with TAAR1, TAAR2 is required for full activity of trace amines in PMN cells. [17]

Phytohaemagglutinin upregulates hTAAR1 mRNA in circulating leukocytes; [6] in these cells, TAAR1 activation mediates leukocyte chemotaxis toward TAAR1 agonists. [6] TAAR1 agonists (specifically, trace amines) have also been shown to induce interleukin 4 secretion in T-cells and immunoglobulin E (IgE) secretion in B cells. [6]

Astrocyte-localized TAAR1 regulates EAAT2 levels and function in these cells; [14] this has been implicated in methamphetamine-induced pathologies of the neuroimmune system. [14]

Clinical significance

Low phenethylamine (PEA) concentration in the brain is associated with major depressive disorder, [10] [28] [44] and high concentrations are associated with schizophrenia. [44] [45] Low PEA levels and under-activation of TAAR1 also appears to be associated with ADHD. [44] [45] [46] It is hypothesized that insufficient PEA levels result in TAAR1 inactivation and overzealous monoamine uptake by transporters, possibly resulting in depression. [10] [28] Some antidepressants function by inhibiting monoamine oxidase (MAO), which increases the concentration of trace amines, which is speculated to increase TAAR1 activation in presynaptic cells. [10] [13] Decreased PEA metabolism has been linked to schizophrenia, a logical finding considering excess PEA would result in over-activation of TAAR1 and prevention of monoamine transporter function. Mutations in region q23.1 of human chromosome 6  – the same chromosome that codes for TAAR1 – have been linked to schizophrenia. [13]

Medical reviews from February 2015 and 2016 noted that TAAR1-selective ligands have significant therapeutic potential for treating psychostimulant addictions (e.g., cocaine, amphetamine, methamphetamine, etc.). [7] [8] Despite wide distribution outside of the CNS and PNS, TAAR1 does not affect hematological functions and the regulation of thyroid hormones across different stages of ageing. Such data represent that future TAAR1-based therapies should exert little hematological effect and thus will likely have a good safety profile. [47]

Research

A large candidate gene association study published in September 2011 found significant differences in TAAR1 allele frequencies between a cohort of fibromyalgia patients and a chronic pain-free control group, suggesting this gene may play an important role in the pathophysiology of the condition; this possibly presents a target for therapeutic intervention. [48]

In preclinical research on rats, TAAR1 activation in pancreatic cells promotes insulin, peptide YY, and GLP-1 secretion; [49] [ non-primary source needed ] therefore, TAAR1 is potentially a biological target for the treatment of obesity and diabetes. [49] [ non-primary source needed ]

Lack of TAAR1 does not significantly affect sexual motivation and routine lipid and metabolic blood biochemical parameters, suggesting that future TAAR1-based therapies should have a favorable safety profile. [50]

Notes

  1. In dopamine, norepinephrine, and serotonin neurons, the primary membrane transporters are DAT, NET, and SERT respectively. [12]
  2. TAAR1–D2sh is a presynaptic heterodimer which involves the relocation of TAAR1 from the intracellular space to D2sh at the plasma membrane, increased D2sh agonist binding affinity, and signal transduction through the calcium–PKCNFAT pathway and G-protein independent PKBGSK3 pathway. [7] [27]

Related Research Articles

<span class="mw-page-title-main">Amphetamine</span> Central nervous system stimulant

Amphetamine is a central nervous system (CNS) stimulant that is used in the treatment of attention deficit hyperactivity disorder (ADHD), narcolepsy, and obesity. Amphetamine was discovered as a chemical in 1887 by Lazăr Edeleanu, and then as a drug in the late 1920s. It exists as two enantiomers: levoamphetamine and dextroamphetamine. Amphetamine properly refers to a specific chemical, the racemic free base, which is equal parts of the two enantiomers in their pure amine forms. The term is frequently used informally to refer to any combination of the enantiomers, or to either of them alone. Historically, it has been used to treat nasal congestion and depression. Amphetamine is also used as an athletic performance enhancer and cognitive enhancer, and recreationally as an aphrodisiac and euphoriant. It is a prescription drug in many countries, and unauthorized possession and distribution of amphetamine are often tightly controlled due to the significant health risks associated with recreational use.

<span class="mw-page-title-main">Neurotransmitter</span> Chemical substance that enables neurotransmission

A neurotransmitter is a signaling molecule secreted by a neuron to affect another cell across a synapse. The cell receiving the signal, or target cell, may be another neuron, but could also be a gland or muscle cell.

<span class="mw-page-title-main">Monoamine neurotransmitter</span> Monoamine that acts as a neurotransmitter or neuromodulator

Monoamine neurotransmitters are neurotransmitters and neuromodulators that contain one amino group connected to an aromatic ring by a two-carbon chain (such as -CH2-CH2-). Examples are dopamine, norepinephrine and serotonin.

<span class="mw-page-title-main">Phenethylamine</span> Organic compound, a stimulant in humans

Phenethylamine (PEA) is an organic compound, natural monoamine alkaloid, and trace amine, which acts as a central nervous system stimulant in humans. In the brain, phenethylamine regulates monoamine neurotransmission by binding to trace amine-associated receptor 1 (TAAR1) and inhibiting vesicular monoamine transporter 2 (VMAT2) in monoamine neurons. To a lesser extent, it also acts as a neurotransmitter in the human central nervous system. In mammals, phenethylamine is produced from the amino acid L-phenylalanine by the enzyme aromatic L-amino acid decarboxylase via enzymatic decarboxylation. In addition to its presence in mammals, phenethylamine is found in many other organisms and foods, such as chocolate, especially after microbial fermentation.

<span class="mw-page-title-main">Tryptamine</span> Metabolite of the amino acid tryptophan

Tryptamine is an indolamine metabolite of the essential amino acid, tryptophan. The chemical structure is defined by an indole—a fused benzene and pyrrole ring, and a 2-aminoethyl group at the second carbon (third aromatic atom, with the first one being the heterocyclic nitrogen). The structure of tryptamine is a shared feature of certain aminergic neuromodulators including melatonin, serotonin, bufotenin and psychedelic derivatives such as dimethyltryptamine (DMT), psilocybin, psilocin and others. Tryptamine has been shown to activate trace amine-associated receptors expressed in the mammalian brain, and regulates the activity of dopaminergic, serotonergic and glutamatergic systems. In the human gut, symbiotic bacteria convert dietary tryptophan to tryptamine, which activates 5-HT4 receptors and regulates gastrointestinal motility. Multiple tryptamine-derived drugs have been developed to treat migraines, while trace amine-associated receptors are being explored as a potential treatment target for neuropsychiatric disorders.

<span class="mw-page-title-main">Monoamine transporter</span> Proteins that function as integral plasma-membrane transporters

Monoamine transporters (MATs) are proteins that function as integral plasma-membrane transporters to regulate concentrations of extracellular monoamine neurotransmitters. The three major classes are serotonin transporters (SERTs), dopamine transporters (DATs), and norepinephrine transporters (NETs) and are responsible for the reuptake of their associated amine neurotransmitters. MATs are located just outside the synaptic cleft (peri-synaptically), transporting monoamine transmitter overflow from the synaptic cleft back to the cytoplasm of the pre-synaptic neuron. MAT regulation generally occurs through protein phosphorylation and post-translational modification. Due to their significance in neuronal signaling, MATs are commonly associated with drugs used to treat mental disorders as well as recreational drugs. Compounds targeting MATs range from medications such as the wide variety of tricyclic antidepressants, selective serotonin reuptake inhibitors such as fluoxetine (Prozac) to stimulant medications such as methylphenidate (Ritalin) and amphetamine in its many forms and derivatives methamphetamine (Desoxyn) and lisdexamfetamine (Vyvanse). Furthermore, drugs such as MDMA and natural alkaloids such as cocaine exert their effects in part by their interaction with MATs, by blocking the transporters from mopping up dopamine, serotonin, and other neurotransmitters from the synapse.

A biogenic amine is a biogenic substance with one or more amine groups. They are basic nitrogenous compounds formed mainly by decarboxylation of amino acids or by amination and transamination of aldehydes and ketones. Biogenic amines are organic bases with low molecular weight and are synthesized by microbial, vegetable and animal metabolisms. In food and beverages they are formed by the enzymes of raw material or are generated by microbial decarboxylation of amino acids.

<span class="mw-page-title-main">Tyramine</span> Chemical compound

Tyramine, also known under several other names, is a naturally occurring trace amine derived from the amino acid tyrosine. Tyramine acts as a catecholamine releasing agent. Notably, it is unable to cross the blood-brain barrier, resulting in only non-psychoactive peripheral sympathomimetic effects following ingestion. A hypertensive crisis can result, however, from ingestion of tyramine-rich foods in conjunction with the use of monoamine oxidase inhibitors (MAOIs).

<span class="mw-page-title-main">Adderall</span> Drug mixture used mainly to treat ADHD and narcolepsy

Adderall and Mydayis are trade names for a combination drug called mixed amphetamine salts containing four salts of amphetamine. The mixture is composed of equal parts racemic amphetamine and dextroamphetamine, which produces a (3:1) ratio between dextroamphetamine and levoamphetamine, the two enantiomers of amphetamine. Both enantiomers are stimulants, but differ enough to give Adderall an effects profile distinct from those of racemic amphetamine or dextroamphetamine, which are marketed as Evekeo and Dexedrine/Zenzedi, respectively. Adderall is used in the treatment of attention deficit hyperactivity disorder (ADHD) and narcolepsy. It is also used illicitly as an athletic performance enhancer, cognitive enhancer, appetite suppressant, and recreationally as a euphoriant. It is a central nervous system (CNS) stimulant of the phenethylamine class.

<span class="mw-page-title-main">Dopamine transporter</span> Mammalian protein found in Homo sapiens

The dopamine transporter (DAT) also is a membrane-spanning protein coded for in the human by the SLC6A3 gene,, that pumps the neurotransmitter dopamine out of the synaptic cleft back into cytosol. In the cytosol, other transporters sequester the dopamine into vesicles for storage and later release. Dopamine reuptake via DAT provides the primary mechanism through which dopamine is cleared from synapses, although there may be an exception in the prefrontal cortex, where evidence points to a possibly larger role of the norepinephrine transporter.

An autoreceptor is a type of receptor located in the membranes of nerve cells. It serves as part of a negative feedback loop in signal transduction. It is only sensitive to the neurotransmitters or hormones released by the neuron on which the autoreceptor sits. Similarly, a heteroreceptor is sensitive to neurotransmitters and hormones that are not released by the cell on which it sits. A given receptor can act as either an autoreceptor or a heteroreceptor, depending upon the type of transmitter released by the cell on which it is embedded.

<span class="mw-page-title-main">Trace amine</span> Amine receptors in the mammalian brain

Trace amines are an endogenous group of trace amine-associated receptor 1 (TAAR1) agonists – and hence, monoaminergic neuromodulators – that are structurally and metabolically related to classical monoamine neurotransmitters. Compared to the classical monoamines, they are present in trace concentrations. They are distributed heterogeneously throughout the mammalian brain and peripheral nervous tissues and exhibit high rates of metabolism. Although they can be synthesized within parent monoamine neurotransmitter systems, there is evidence that suggests that some of them may comprise their own independent neurotransmitter systems.

Trace amine-associated receptors (TAARs), sometimes referred to as trace amine receptors, are a class of G protein-coupled receptors that were discovered in 2001. TAAR1, the first of six functional human TAARs, has gained considerable interest in academic and proprietary pharmaceutical research due to its role as the endogenous receptor for the trace amines phenethylamine, tyramine, and tryptamine – metabolic derivatives of the amino acids phenylalanine, tyrosine and tryptophan, respectively – ephedrine, as well as the synthetic psychostimulants, amphetamine, methamphetamine and methylenedioxymethamphetamine. In 2004, it was shown that mammalian TAAR1 is also a receptor for thyronamines, decarboxylated and deiodinated relatives of thyroid hormones. TAAR2–TAAR9 function as olfactory receptors for volatile amine odorants in vertebrates.

<i>N</i>-Methylphenethylamine Chemical compound

N-Methylphenethylamine (NMPEA) is a naturally occurring trace amine neuromodulator in humans that is derived from the trace amine, phenethylamine (PEA). It has been detected in human urine and is produced by phenylethanolamine N-methyltransferase with phenethylamine as a substrate, which significantly increases PEA's effects. PEA breaks down into phenylacetaldehyde which is further broken down into phenylacetic acid by monoamine oxidase. When this is inhibited by monoamine oxidase inhibitors, it allows more of the PEA to be metabolized into nymphetamine (NMPEA) and not wasted on the weaker inactive metabolites.

<span class="mw-page-title-main">TAAR2</span> Protein-coding gene in the species Homo sapiens

Trace amine-associated receptor 2 (TAAR2), formerly known as G protein-coupled receptor 58 (GPR58), is a protein that in humans is encoded by the TAAR2 gene. TAAR2 is coexpressed with Gα proteins; however, as of February 2017, its signal transduction mechanisms have not been determined.

<span class="mw-page-title-main">3-Methoxytyramine</span> Chemical compound

3-Methoxytyramine (3-MT), also known as 3-methoxy-4-hydroxyphenethylamine, is a human trace amine that occurs as a metabolite of the neurotransmitter dopamine. It is formed by the introduction of a methyl group to dopamine by the enzyme catechol-O-methyl transferase (COMT). 3-MT can be further metabolized by the enzyme monoamine oxidase (MAO) to form homovanillic acid (HVA), which is then typically excreted in the urine.

<span class="mw-page-title-main">Monoamine releasing agent</span> Class of compounds

A monoamine releasing agent (MRA), or simply monoamine releaser, is a drug that induces the release of a monoamine neurotransmitter from the presynaptic neuron into the synapse, leading to an increase in the extracellular concentrations of the neurotransmitter. Many drugs induce their effects in the body and/or brain via the release of monoamine neurotransmitters, e.g., trace amines, many substituted amphetamines, and related compounds.

<span class="mw-page-title-main">Norepinephrine–dopamine reuptake inhibitor</span> Drug that inhibits the reuptake of norepinephrine and dopamine

A norepinephrine–dopamine reuptake inhibitor (NDRI) is a drug used for the treatment of clinical depression, attention deficit hyperactivity disorder (ADHD), narcolepsy, and the management of Parkinson's disease. The drug acts as a reuptake inhibitor for the neurotransmitters norepinephrine and dopamine by blocking the action of the norepinephrine transporter (NET) and the dopamine transporter (DAT), respectively. This in turn leads to increased extracellular concentrations of both norepinephrine and dopamine and, therefore, an increase in adrenergic and dopaminergic neurotransmission.

<span class="mw-page-title-main">RO5166017</span> Chemical compound

RO-5166017 is a drug developed by Hoffmann-La Roche which acts as a potent and selective agonist for the trace amine-associated receptor 1, with no significant activity at other targets. This is important for the study of the TAAR1 receptor, as while numerous other compounds are known which act as TAAR1 agonists, such as methamphetamine, MDMA and 3-iodothyronamine, all previously known TAAR1 agonists are either weak and rapidly metabolized, or have strong pharmacological activity at other targets, making it very difficult to assess which effects are due to TAAR1 activation. The discovery of RO-5166017 allows purely TAAR1 mediated effects to be studied, and in animal studies it was shown to prevent stress-induced hyperthermia and block dopamine-dependent hyperlocomotion, as well as blocking the hyperactivity which would normally be induced by an NMDA antagonist. The experiment was done in dopamine transporter knockout mice, and since TAAR1 affects the dopamine transporter, the results could be very different in humans.

An excitatory amino acid reuptake inhibitor (EAARI) is a type of drug which inhibits the reuptake of the excitatory neurotransmitters glutamate and aspartate by blocking one or more of the excitatory amino acid transporters (EAATs).

References

  1. 1 2 3 GRCh38: Ensembl release 89: ENSG00000146399 - Ensembl, May 2017
  2. 1 2 3 GRCm38: Ensembl release 89: ENSMUSG00000056379 - Ensembl, May 2017
  3. "Human PubMed Reference:". National Center for Biotechnology Information, U.S. National Library of Medicine.
  4. "Mouse PubMed Reference:". National Center for Biotechnology Information, U.S. National Library of Medicine.
  5. "Entrez Gene: TAAR1 trace amine associated receptor 1".
  6. 1 2 3 4 5 6 7 8 9 10 Maguire JJ, Davenport AP (20 February 2018). "Trace amine receptor: TA1 receptor". IUPHAR/BPS Guide to PHARMACOLOGY. International Union of Basic and Clinical Pharmacology. Retrieved 16 July 2018.
    Tissue Distribution
    CNS (region specific) & several peripheral tissues:
    Stomach > amygdala, kidney, lung, small intestine > cerebellum, dorsal root ganglion, hippocampus, hypothalamus, liver, medulla oblongata, pancreas, pituitary gland, pontine reticular formation, prostate, skeletal muscle, spleen. ...
    Leukocytes ...Pancreatic islet β cells ... Primary Tonsillar B Cells ... Circulating leukocytes of healthy subjects (upregulation occurs upon addition of phytohaemagglutinin).
    Species: Human ...
    In the brain (mouse, rhesus monkey) the TA1 receptor localises to neurones within the momaminergic pathways and there is emerging evidence for a modulatory role for TA1 on function of these systems. Co-expression of TA1 with the dopamine transporter (either within the same neurone or in adjacent neurones) implies direct/indirect modulation of CNS dopaminergic function. In cells expressing both human TA1 and a monoamine transporter (DAT, SERT or NET) signalling via TA1 is enhanced [26,48,50–51]. ...
    Functional Assays ...
    Mobilization of internal calcium in RD-HGA16 cells transfected with unmodified human TA1
    Response measured: Increase in cytopasmic calcium ...
    Measurement of cAMP levels in human cultured astrocytes.
    Response measured: cAMP accumulation ...
    Activation of leukocytes
    Species: Human
    Tissue: PMN, T and B cells
    Response measured: Chemotactic migration towards TA1 ligands (β-Phenylethylamine, tyramine and 3-iodothyronamine), trace amine induced IL-4 secretion (T-cells) and trace amine induced regulation of T cell marker RNA expression, trace amine induced IgE secretion in B cells.
  7. 1 2 3 4 5 6 7 8 Grandy DK, Miller GM, Li JX (February 2016). ""TAARgeting Addiction"-The Alamo Bears Witness to Another Revolution: An Overview of the Plenary Symposium of the 2015 Behavior, Biology and Chemistry Conference". Drug Alcohol Depend. 159: 9–16. doi:10.1016/j.drugalcdep.2015.11.014. PMC   4724540 . PMID   26644139. TAAR1 is a high-affinity receptor for METH/AMPH and DA ... This original observation of TAAR1 and DA D2R interaction has subsequently been confirmed and expanded upon with observations that both receptors can heterodimerize with each other under certain conditions ... Additional DA D2R/TAAR1 interactions with functional consequences are revealed by the results of experiments demonstrating that in addition to the cAMP/PKA pathway (Panas et al., 2012) stimulation of TAAR1-mediated signaling is linked to activation of the Ca++/PKC/NFAT pathway (Panas et al.,2012) and the DA D2R-coupled, G protein-independent AKT/GSK3 signaling pathway (Espinoza et al., 2015; Harmeier et al., 2015), such that concurrent TAAR1 and DA DR2R activation could result in diminished signaling in one pathway (e.g. cAMP/PKA) but retention of signaling through another (e.g., Ca++/PKC/NFA)
  8. 1 2 Jing L, Li JX (August 2015). "Trace amine-associated receptor 1: A promising target for the treatment of psychostimulant addiction". Eur. J. Pharmacol. 761: 345–352. doi:10.1016/j.ejphar.2015.06.019. PMC   4532615 . PMID   26092759. TAAR1 is largely located in the intracellular compartments both in neurons (Miller, 2011), in glial cells (Cisneros and Ghorpade, 2014) and in peripheral tissues (Grandy, 2007) ... Existing data provided robust preclinical evidence supporting the development of TAAR1 agonists as potential treatment for psychostimulant abuse and addiction. ... Given that TAAR1 is primarily located in the intracellular compartments and existing TAAR1 agonists are proposed to get access to the receptors by translocation to the cell interior (Miller, 2011), future drug design and development efforts may need to take strategies of drug delivery into consideration (Rajendran et al., 2010).
  9. 1 2 3 4 5 6 7 8 9 Berry MD, Gainetdinov RR, Hoener MC, Shahid M (December 2017). "Pharmacology of human trace amine-associated receptors: Therapeutic opportunities and challenges". Pharmacology & Therapeutics. 180: 161–180. doi: 10.1016/j.pharmthera.2017.07.002 . PMID   28723415.
  10. 1 2 3 4 5 6 7 8 Borowsky B, Adham N, Jones KA, Raddatz R, Artymyshyn R, Ogozalek KL, Durkin MM, Lakhlani PP, Bonini JA, Pathirana S, Boyle N, Pu X, Kouranova E, Lichtblau H, Ochoa FY, Branchek TA, Gerald C (July 2001). "Trace amines: identification of a family of mammalian G protein-coupled receptors". Proceedings of the National Academy of Sciences of the United States of America. 98 (16): 8966–8971. Bibcode:2001PNAS...98.8966B. doi: 10.1073/pnas.151105198 . PMC   55357 . PMID   11459929.
  11. 1 2 3 4 5 6 Bunzow JR, Sonders MS, Arttamangkul S, Harrison LM, Zhang G, Quigley DI, Darland T, Suchland KL, Pasumamula S, Kennedy JL, Olson SB, Magenis RE, Amara SG, Grandy DK (December 2001). "Amphetamine, 3,4-methylenedioxymethamphetamine, lysergic acid diethylamide, and metabolites of the catecholamine neurotransmitters are agonists of a rat trace amine receptor". Molecular Pharmacology. 60 (6): 1181–1188. doi:10.1124/mol.60.6.1181. PMID   11723224.
  12. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 Miller GM (January 2011). "The emerging role of trace amine-associated receptor 1 in the functional regulation of monoamine transporters and dopaminergic activity". Journal of Neurochemistry. 116 (2): 164–176. doi:10.1111/j.1471-4159.2010.07109.x. PMC   3005101 . PMID   21073468.
  13. 1 2 3 4 5 6 Lindemann L, Ebeling M, Kratochwil NA, Bunzow JR, Grandy DK, Hoener MC (March 2005). "Trace amine-associated receptors form structurally and functionally distinct subfamilies of novel G protein-coupled receptors". Genomics. 85 (3): 372–385. doi:10.1016/j.ygeno.2004.11.010. PMID   15718104.
  14. 1 2 3 4 Cisneros IE, Ghorpade A (October 2014). "Methamphetamine and HIV-1-induced neurotoxicity: role of trace amine associated receptor 1 cAMP signaling in astrocytes". Neuropharmacology. 85: 499–507. doi:10.1016/j.neuropharm.2014.06.011. PMC   4315503 . PMID   24950453. TAAR1 overexpression significantly decreased EAAT-2 levels and glutamate clearance ... METH treatment activated TAAR1 leading to intracellular cAMP in human astrocytes and modulated glutamate clearance abilities. Furthermore, molecular alterations in astrocyte TAAR1 levels correspond to changes in astrocyte EAAT-2 levels and function.
  15. Rogers TJ (2012). "The molecular basis for neuroimmune receptor signaling". J Neuroimmune Pharmacol. 7 (4): 722–724. doi:10.1007/s11481-012-9398-4. PMC   4011130 . PMID   22935971.
  16. 1 2 3 4 Panas MW, Xie Z, Panas HN, Hoener MC, Vallender EJ, Miller GM (December 2012). "Trace amine associated receptor 1 signaling in activated lymphocytes". Journal of Neuroimmune Pharmacology. 7 (4): 866–876. doi:10.1007/s11481-011-9321-4. PMC   3593117 . PMID   22038157.
  17. 1 2 Babusyte A, Kotthoff M, Fiedler J, Krautwurst D (March 2013). "Biogenic amines activate blood leukocytes via trace amine-associated receptors TAAR1 and TAAR2". Journal of Leukocyte Biology. 93 (3): 387–394. doi:10.1189/jlb.0912433. PMID   23315425. S2CID   206996784.
  18. Gainetdinov RR, Hoener MC, Berry MD (July 2018). "Trace Amines and Their Receptors". Pharmacological Reviews. 70 (3): 549–620. doi: 10.1124/pr.117.015305 . PMID   29941461.
  19. Xie Z, Miller GM (November 2009). "Trace amine-associated receptor 1 as a monoaminergic modulator in brain". Biochemical Pharmacology. 78 (9): 1095–1104. doi:10.1016/j.bcp.2009.05.031. PMC   2748138 . PMID   19482011.
  20. "TAAR1". The Human Protein Atlas. Retrieved 24 August 2017.
  21. 1 2 3 4 Bugda Gwilt K, González DP, Olliffe N, Oller H, Hoffing R, Puzan M, El Aidy S, Miller GM (December 2019). "Actions of Trace Amines in the Brain-Gut-Microbiome Axis via Trace Amine-Associated Receptor-1 (TAAR1)" (PDF). Cellular and Molecular Neurobiology. 40 (2): 191–201. doi:10.1007/s10571-019-00772-7. PMID   31836967. S2CID   209339614.
  22. Xie Z, Westmoreland SV, Bahn ME, Chen GL, Yang H, Vallender EJ, Yao WD, Madras BK, Miller GM (April 2007). "Rhesus monkey trace amine-associated receptor 1 signaling: enhancement by monoamine transporters and attenuation by the D2 autoreceptor in vitro". The Journal of Pharmacology and Experimental Therapeutics. 321 (1): 116–127. doi:10.1124/jpet.106.116863. PMID   17234900. S2CID   578835.
  23. Liberles SD, Buck LB (August 2006). "A second class of chemosensory receptors in the olfactory epithelium". Nature. 442 (7103): 645–650. Bibcode:2006Natur.442..645L. doi:10.1038/nature05066. PMID   16878137. S2CID   2864195.
  24. 1 2 3 Barak LS, Salahpour A, Zhang X, Masri B, Sotnikova TD, Ramsey AJ, Violin JD, Lefkowitz RJ, Caron MG, Gainetdinov RR (September 2008). "Pharmacological characterization of membrane-expressed human trace amine-associated receptor 1 (TAAR1) by a bioluminescence resonance energy transfer cAMP biosensor". Molecular Pharmacology. 74 (3): 585–594. doi:10.1124/mol.108.048884. PMC   3766527 . PMID   18524885.
  25. 1 2 3 Lam VM, Espinoza S, Gerasimov AS, Gainetdinov RR, Salahpour A (June 2015). "In-vivo pharmacology of Trace-Amine Associated Receptor 1". Eur. J. Pharmacol. 763 (Pt B): 136–42. doi:10.1016/j.ejphar.2015.06.026. PMID   26093041.
    TAAR1 peripheral and immune localization/functions: It is important to note that in addition to the brain, TAAR1 is also expressed in the spinal cord (Gozal et al., 2014) and periphery (Revel et al., 2012c). It has been shown that TAAR1 is expressed and regulates immune function in rhesus monkey leukocytes (Babusyte et al., 2013; Nelson et al., 2007; Panas et al., 2012). In granulocytes, TAAR1 is necessary for chemotaxic migration of cells towards TAAR1 agonists. In addition, TAAR1 signaling in B and T cells can trigger immunoglobulin and cytokine release, respectively (Babusyte et al., 2013). TAAR1 is also expressed in the islets of Langerhans, stomach and intestines based on LacZ staining patterns carried out on TAAR1-KO LacZ mice (Revel et al., 2012c). Interestingly, the administration of selective TAAR1 partial agonist RO5263397 reverses the side effect of weight gain observed with the antipsychotic olanzapine, indicating that peripheral TAAR1 signalling can regulate metabolic homeostasis (Revel et al., 2012b). ...

    Monoamine transporters and SLC22A carrier subfamily transport TAAR1 ligand: Studies using the rhesus monkey TAAR1 have shown that this receptor interacts with the monoamine transporters DAT, SERT, and NET in HEK cells (Miller et al., 2005; Xie and Miller, 2007; Xie et al., 2007). It has been hypothesized that TAAR1 interaction with these transporters might provide a mechanism by which TAAR1 ligands can enter the cytoplasm and bind to TAAR1 in intracellular compartments. A recent study has shown that in rat neonatal motor neurons, trace-amine specific signalling requires the presence and function of the transmembrane solute carrier SLC22A but not that of monoamine transporters (DAT, SERT, and NET) (Gozal et al., 2014). Specifically, it was shown that addition of β-PEA, tyramine, or tryptamine induced locomotor like activity (LLA) firing patterns of these neurons in the presence of N-Methyl D-Aspartate. Temporally, it was found that the trace amine induction of LLA is delayed compared to serotonin and norepinephrine induced LLA, indicating the target site for the trace amines is not located on the plasma membrane and could perhaps be intracellular. Importantly, blocking of SLC22A with pentamidine abolished trace amine induced LLA, indicating that trace amine induced LLA does not act on receptors found on the plasma membrane but requires their transport to the cytosol by SLC22A for induction of LLA.
  26. 1 2 Dinter J, Mühlhaus J, Jacobi SF, Wienchol CL, Cöster M, Meister J, Hoefig CS, Müller A, Köhrle J, Grüters A, Krude H, Mittag J, Schöneberg T, Kleinau G, Biebermann H (June 2015). "3-iodothyronamine differentially modulates α-2A-adrenergic receptor-mediated signaling". J. Mol. Endocrinol. 54 (3): 205–216. doi: 10.1530/JME-15-0003 . PMID   25878061. Moreover, in ADRA2A/TAAR1 hetero-oligomers, the capacity of NorEpi to stimulate Gi/o signaling is reduced by co-stimulation with 3-T1AM. The present study therefore points to a complex spectrum of signaling modification mediated by 3-T1AM at different G protein-coupled receptors.
  27. Harmeier A, Obermueller S, Meyer CA, Revel FG, Buchy D, Chaboz S, Dernick G, Wettstein JG, Iglesias A, Rolink A, Bettler B, Hoener MC (2015). "Trace amine-associated receptor 1 activation silences GSK3β signaling of TAAR1 and D2R heteromers". Eur Neuropsychopharmacol. 25 (11): 2049–2061. doi:10.1016/j.euroneuro.2015.08.011. PMID   26372541. S2CID   41667764. Interaction of TAAR1 with D2R altered the subcellular localization of TAAR1 and increased D2R agonist binding affinity.
  28. 1 2 3 4 Zucchi R, Chiellini G, Scanlan TS, Grandy DK (December 2006). "Trace amine-associated receptors and their ligands". British Journal of Pharmacology. 149 (8): 967–978. doi:10.1038/sj.bjp.0706948. PMC   2014643 . PMID   17088868. Other biogenic amines are present in the central nervous system at very low concentrations in the order of 0.1–10 nm, representing <1% of total biogenic amines (Berry, 2004). For these compounds, the term 'trace amines' was introduced. Although somewhat loosely defined, the molecules generally considered to be trace amines include para-tyramine, meta-tyramine, tryptamine, β-phenylethylamine, para-octopamine and meta-octopamine (Berry, 2004) (Figure 2).
  29. 1 2 Xie Z, Miller GM (July 2009). "A receptor mechanism for methamphetamine action in dopamine transporter regulation in brain". The Journal of Pharmacology and Experimental Therapeutics. 330 (1): 316–325. doi:10.1124/jpet.109.153775. PMC   2700171 . PMID   19364908.
  30. Rickli A, Kopf S, Hoener MC, Liechti ME (July 2015). "Pharmacological profile of novel psychoactive benzofurans". British Journal of Pharmacology. 172 (13): 3412–3425. doi:10.1111/bph.13128. PMC   4500375 . PMID   25765500.
  31. 1 2 Wainscott DB, Little SP, Yin T, Tu Y, Rocco VP, He JX, Nelson DL (January 2007). "Pharmacologic characterization of the cloned human trace amine-associated receptor1 (TAAR1) and evidence for species differences with the rat TAAR1". The Journal of Pharmacology and Experimental Therapeutics. 320 (1): 475–485. doi:10.1124/jpet.106.112532. PMID   17038507. S2CID   10829497. Several series of substituted phenylethylamines were investigated for activity at the human TAAR1 (Table 2). A surprising finding was the potency of phenylethylamines with substituents at the phenyl C2 position relative to their respective C4-substituted congeners. In each case, except for the hydroxyl substituent, the C2-substituted compound had 8- to 27-fold higher potency than the C4-substituted compound. The C3-substituted compound in each homologous series was typically 2- to 5-fold less potent than the 2-substituted compound, except for the hydroxyl substituent. The most potent of the 2-substituted phenylethylamines was 2-chloro-β-PEA, followed by 2-fluoro-β-PEA, 2-bromo-β-PEA, 2-methoxy-β-PEA, 2-methyl-β-PEA, and then 2-hydroxy-β-PEA.
    The effect of β-carbon substitution on the phenylethylamine side chain was also investigated (Table 3). A β-methyl substituent was well tolerated compared with β-PEA. In fact, S-(–)-β-methyl-β-PEA was as potent as β-PEA at human TAAR1. β-Hydroxyl substitution was, however, not tolerated compared with β-PEA. In both cases of β-substitution, enantiomeric selectivity was demonstrated.
    In contrast to a methyl substitution on the β-carbon, an α-methyl substitution reduced potency by ~10-fold for d-amphetamine and 16-fold for l-amphetamine relative to β-PEA (Table 4). N-Methyl substitution was fairly well tolerated; however, N,N-dimethyl substitution was not.
  32. Galley G, Beurier A, Décoret G, Goergler A, Hutter R, Mohr S, Pähler A, Schmid P, Türck D, Unger R, Zbinden KG, Hoener MC, Norcross RD (2016). "Discovery and Characterization of 2-Aminooxazolines as Highly Potent, Selective, and Orally Active TAAR1 Agonists". ACS Med Chem Lett. 7 (2): 192–197. doi:10.1021/acsmedchemlett.5b00449. PMC   4753552 . PMID   26985297.
  33. 1 2 Revel FG, Moreau JL, Gainetdinov RR, Bradaia A, Sotnikova TD, Mory R, Durkin S, Zbinden KG, Norcross R, Meyer CA, Metzler V, Chaboz S, Ozmen L, Trube G, Pouzet B, Bettler B, Caron MG, Wettstein JG, Hoener MC (May 2011). "TAAR1 activation modulates monoaminergic neurotransmission, preventing hyperdopaminergic and hypoglutamatergic activity". Proc. Natl. Acad. Sci. U.S.A. 108 (20): 8485–8490. Bibcode:2011PNAS..108.8485R. doi: 10.1073/pnas.1103029108 . PMC   3101002 . PMID   21525407.
  34. Revel FG, Moreau JL, Gainetdinov RR, Ferragud A, Velázquez-Sánchez C, Sotnikova TD, Morairty SR, Harmeier A, Groebke Zbinden K, Norcross RD, Bradaia A, Kilduff TS, Biemans B, Pouzet B, Caron MG, Canales JJ, Wallace TL, Wettstein JG, Hoener MC (June 2012). "Trace Amine-Associated Receptor 1 Partial Agonism Reveals Novel Paradigm for Neuropsychiatric Therapeutics". Biol Psychiatry. 72 (11): 934–942. doi:10.1016/j.biopsych.2012.05.014. PMID   22705041. S2CID   27334223.
  35. Cichero E, Francesconi V, Casini B, Casale M, Kanov E, Gerasimov AS, et al. (November 2023). "Discovery of Guanfacine as a Novel TAAR1 Agonist: A Combination Strategy through Molecular Modeling Studies and Biological Assays". Pharmaceuticals. 16 (11): 1632. doi: 10.3390/ph16111632 . PMC   10674299 . PMID   38004497.
  36. Bradaia A, Trube G, Stalder H, Norcross RD, Ozmen L, Wettstein JG, Pinard A, Buchy D, Gassmann M, Hoener MC, Bettler B (November 2009). "The selective antagonist EPPTB reveals TAAR1-mediated regulatory mechanisms in dopaminergic neurons of the mesolimbic system". Proceedings of the National Academy of Sciences of the United States of America. 106 (47): 20081–20086. Bibcode:2009PNAS..10620081B. doi: 10.1073/pnas.0906522106 . PMC   2785295 . PMID   19892733.
  37. 1 2 Eiden LE, Weihe E (January 2011). "VMAT2: a dynamic regulator of brain monoaminergic neuronal function interacting with drugs of abuse". Ann. N. Y. Acad. Sci. 1216 (1): 86–98. Bibcode:2011NYASA1216...86E. doi:10.1111/j.1749-6632.2010.05906.x. PMC   4183197 . PMID   21272013. VMAT2 is the CNS vesicular transporter for not only the biogenic amines DA, NE, EPI, 5-HT, and HIS, but likely also for the trace amines TYR, PEA, and thyronamine (THYR) ... [Trace aminergic] neurons in mammalian CNS would be identifiable as neurons expressing VMAT2 for storage, and the biosynthetic enzyme aromatic amino acid decarboxylase (AADC). ... AMPH release of DA from synapses requires both an action at VMAT2 to release DA to the cytoplasm and a concerted release of DA from the cytoplasm via "reverse transport" through DAT.
  38. Sulzer D, Cragg SJ, Rice ME (August 2016). "Striatal dopamine neurotransmission: regulation of release and uptake". Basal Ganglia. 6 (3): 123–148. doi:10.1016/j.baga.2016.02.001. PMC   4850498 . PMID   27141430. Despite the challenges in determining synaptic vesicle pH, the proton gradient across the vesicle membrane is of fundamental importance for its function. Exposure of isolated catecholamine vesicles to protonophores collapses the pH gradient and rapidly redistributes transmitter from inside to outside the vesicle. ... Amphetamine and its derivatives like methamphetamine are weak base compounds that are the only widely used class of drugs known to elicit transmitter release by a non-exocytic mechanism. As substrates for both DAT and VMAT, amphetamines can be taken up to the cytosol and then sequestered in vesicles, where they act to collapse the vesicular pH gradient.
  39. 1 2 Ledonne A, Berretta N, Davoli A, Rizzo GR, Bernardi G, Mercuri NB (2011). "Electrophysiological effects of trace amines on mesencephalic dopaminergic neurons". Frontiers in Systems Neuroscience. 5: 56. doi: 10.3389/fnsys.2011.00056 . PMC   3131148 . PMID   21772817. inhibition of firing due to increased release of dopamine; (b) reduction of D2 and GABAB receptor-mediated inhibitory responses (excitatory effects due to disinhibition); and (c) a direct TA1 receptor-mediated activation of GIRK channels which produce cell membrane hyperpolarization.
  40. 1 2 mct (28 January 2012). "TAAR1". GenAtlas. University of Paris. Retrieved 29 May 2014.
    " tonically activates inwardly rectifying K(+) channels, which reduces the basal firing frequency of dopamine (DA) neurons of the ventral tegmental area (VTA)"
  41. Underhill SM, Wheeler DS, Li M, Watts SD, Ingram SL, Amara SG (July 2014). "Amphetamine modulates excitatory neurotransmission through endocytosis of the glutamate transporter EAAT3 in dopamine neurons". Neuron. 83 (2): 404–416. doi:10.1016/j.neuron.2014.05.043. PMC   4159050 . PMID   25033183. AMPH also increases intracellular calcium (Gnegy et al., 2004) that is associated with calmodulin/CamKII activation (Wei et al., 2007) and modulation and trafficking of the DAT (Fog et al., 2006; Sakrikar et al., 2012). ... For example, AMPH increases extracellular glutamate in various brain regions including the striatum, VTA and NAc (Del Arco et al., 1999; Kim et al., 1981; Mora and Porras, 1993; Xue et al., 1996), but it has not been established whether this change can be explained by increased synaptic release or by reduced clearance of glutamate. ... DHK-sensitive, EAAT2 uptake was not altered by AMPH (Figure 1A). The remaining glutamate transport in these midbrain cultures is likely mediated by EAAT3 and this component was significantly decreased by AMPH
  42. Vaughan RA, Foster JD (September 2013). "Mechanisms of dopamine transporter regulation in normal and disease states". Trends Pharmacol. Sci. 34 (9): 489–496. doi:10.1016/j.tips.2013.07.005. PMC   3831354 . PMID   23968642. AMPH and METH also stimulate DA efflux, which is thought to be a crucial element in their addictive properties [80], although the mechanisms do not appear to be identical for each drug [81]. These processes are PKCβ– and CaMK–dependent [72, 82], and PKCβ knock-out mice display decreased AMPH-induced efflux that correlates with reduced AMPH-induced locomotion [72].
  43. Maguire JJ, Parker WA, Foord SM, Bonner TI, Neubig RR, Davenport AP (March 2009). "International Union of Pharmacology. LXXII. Recommendations for trace amine receptor nomenclature". Pharmacological Reviews. 61 (1): 1–8. doi:10.1124/pr.109.001107. PMC   2830119 . PMID   19325074.
  44. 1 2 3 Lindemann L, Hoener MC (May 2005). "A renaissance in trace amines inspired by a novel GPCR family". Trends Pharmacol. Sci. 26 (5): 274–281. doi:10.1016/j.tips.2005.03.007. PMID   15860375. The dysregulation of TA levels has been linked to several diseases, which highlights the corresponding members of the TAAR family as potential targets for drug development. In this article, we focus on the relevance of TAs and their receptors to nervous system-related disorders, namely schizophrenia and depression; however, TAs have also been linked to other diseases such as migraine, attention deficit hyperactivity disorder, substance abuse and eating disorders [7,8,36]. Clinical studies report increased β-PEA plasma levels in patients suffering from acute schizophrenia [37] and elevated urinary excretion of β-PEA in paranoid schizophrenics [38], which supports a role of TAs in schizophrenia. As a result of these studies, β-PEA has been referred to as the body's 'endogenous amphetamine' [39]
  45. 1 2 Sotnikova TD, Caron MG, Gainetdinov RR (August 2009). "Trace amine-associated receptors as emerging therapeutic targets". Mol. Pharmacol. 76 (2): 229–235. doi:10.1124/mol.109.055970. PMC   2713119 . PMID   19389919. Although the functional role of trace amines in mammals remains largely enigmatic, it has been noted that trace amine levels can be altered in various human disorders, including schizophrenia, Parkinson's disease, attention deficit hyperactivity disorder (ADHD), Tourette syndrome, and phenylketonuria (Boulton, 1980; Sandler et al., 1980). It was generally held that trace amines affect the monoamine system indirectly via interaction with plasma membrane transporters [such as plasma membrane dopamine transporter (DAT)] and vesicular storage (Premont et al., 2001; Branchek and Blackburn, 2003; Berry, 2004; Sotnikova et al., 2004). ...
    Furthermore, DAT-deficient mice provide a model to investigate the inhibitory actions of amphetamines on hyperactivity, the feature of amphetamines believed to be important for their therapeutic action in ADHD (Gainetdinov et al., 1999; Gainetdinov and Caron, 2003). It should be noted also that the best-established agonist of TAAR1, β-PEA, shared the ability of amphetamine to induce inhibition of dopamine-dependent hyperactivity of DAT-KO mice (Gainetdinov et al., 1999; Sotnikova et al., 2004).
    Furthermore, if TAAR1 could be proven as a mediator of some of amphetamine's actions in vivo, the development of novel TAAR1-selective agonists and antagonists could provide a new approach for the treatment of amphetamine-related conditions such as addiction and/or disorders in which amphetamine is used therapeutically. In particular, because amphetamine has remained the most effective pharmacological treatment in ADHD for many years, a potential role of TAAR1 in the mechanism of the "paradoxical" effectiveness of amphetamine in this disorder should be explored.
  46. Berry MD (January 2007). "The potential of trace amines and their receptors for treating neurological and psychiatric diseases". Rev Recent Clin Trials. 2 (1): 3–19. CiteSeerX   10.1.1.329.563 . doi:10.2174/157488707779318107. PMID   18473983. changes in trace amines, in particular PE, have been identified as a possible factor for the onset of attention deficit/hyperactivity disorder (ADHD) [5, 27, 43, 78]. PE has been shown to induce hyperactivity and aggression, two of the cardinal clinical features of ADHD, in experimental animals [100]. Hyperactivity is also a symptom of phenylketonuria, which as discussed above is associated with a markedly elevated PE turnover [44]. Further, amphetamines, which have clinical utility in ADHD, are good ligands at trace amine receptors [2]. Of possible relevance in this aspect is modafanil, which has shown beneficial effects in ADHD patients [101] and has been reported to enhance the activity of PE at TAAR1 [102]. Conversely, methylphenidate, which is also clinically useful in ADHD, showed poor efficacy at the TAAR1 receptor [2]. In this respect it is worth noting that the enhancement of functioning at TAAR1 seen with modafanil was not a result of a direct interaction with TAAR1 [102].
    More direct evidence has been obtained recently for a role of trace amines in ADHD. Urinary PE levels have been reported to be decreased in ADHD patients in comparison to both controls and patients with autism [103-105]. Evidence for a decrease in PE levels in the brain of ADHD patients has also recently been reported [4]. In addition, decreases in the urine and plasma levels of the PE metabolite phenylacetic acid and the precursors phenylalanine and tyrosine have been reported along with decreases in plasma tyramine [103]. Following treatment with methylphenidate, patients who responded positively showed a normalization of urinary PE, whilst non-responders showed no change from baseline values [105].
  47. Zhukov IS, Kubarskaya LG, Tissen IY, Kozlova AA, Dagayev SG, Kashuro VA, et al. (March 2020). "Minimal Age-Related Alterations in Behavioral and Hematological Parameters in Trace Amine-Associated Receptor 1 (TAAR1) Knockout Mice". Cellular and Molecular Neurobiology. 40 (2): 273–282. doi:10.1007/s10571-019-00721-4. PMID   31399838. S2CID   199511689.
  48. Smith SB, Maixner DW, Fillingim RB, Slade G, Gracely RH, Ambrose K, Zaykin DV, Hyde C, John S, Tan K, Maixner W, Diatchenko L (February 2012). "Large candidate gene association study reveals genetic risk factors and therapeutic targets for fibromyalgia". Arthritis and Rheumatism. 64 (2): 584–593. doi:10.1002/art.33338. PMC   3237946 . PMID   21905019.
  49. 1 2 Raab S, Wang H, Uhles S, Cole N, Alvarez-Sanchez R, Künnecke B, Ullmer C, Matile H, Bedoucha M, Norcross RD, Ottaway-Parker N, Perez-Tilve D, Conde Knape K, Tschöp MH, Hoener MC, Sewing S (2016). "Incretin-like effects of small molecule trace amine-associated receptor 1 agonists". Mol Metab. 5 (1): 47–56. doi:10.1016/j.molmet.2015.09.015. PMC   4703809 . PMID   26844206.
  50. Zhukov IS, Ptukha MA, Zolotoverkhaja EA, Sinitca EL, Tissen IY, Karpova IV, Volnova AB, Gainetdinov RR (May 2022). "Evaluation of Approach to a Conspecific and Blood Biochemical Parameters in TAAR1 Knockout Mice". Brain Sciences. 12 (5): 614. doi: 10.3390/brainsci12050614 . PMC   9139149 . PMID   35625001.

This article incorporates text from the United States National Library of Medicine, which is in the public domain.