Selective Trace Amine-associated Receptor 1 Research Articles

Activation of trace amine-associated receptor 1 ameliorates PTSD-like symptoms

Trace amine-associated receptor 1 (TAAR1) negatively modulates monoaminergic transmission in the mammalian brain and participates in many psychiatric disorders. Preclinical evidence indicate that selective TAAR1 agonists have anxiolytic effects and anti-stress properties. Post-traumatic stress disorder (PTSD) is an anxiety disorder triggered by experiencing or witnessing traumatic stressors. However, it remains unknown whether TAAR1 is involved in PTSD. Here, we investigated the role of TAAR1 in two PTSD animal models, including single prolonged stress (SPS)-induced impairment of fear extinction and stress-enhanced fear learning (SEFL). SPS decreased TAAR1 mRNA levels in the prefrontal cortex and ventral tegmental area. Acute treatment of the TAAR1 partial agonist RO5263397 attenuated SPS-induced anxiety-like behavior evaluated by the elevated-plus maze test. Compared to non-stressed animals, rats that experienced SPS showed higher freezing levels in the extinction retention test, indicating an impairment of fear extinction retention after SPS exposure. Acute and chronic treatment of RO5263397 ameliorated SPS-induced impairment of fear extinction retention. In the SEFL model, compared to the No-shock group, rats that experienced severe foot shock before fear conditioning showed higher freezing levels during the tests, indicating enhanced fear learning after stress exposure. Chronic treatment of RO5263397 partially attenuated the SEFL. Moreover, chronic treatment with the selective TAAR1 full agonist RO5166017 completely prevented the SEFL. Taken together, these data showed that pharmacological activation of TAAR1 could ameliorate PTSD-like symptoms. The present study thus provides the first evidence that TAAR1 might participate in the development of PTSD, and TAAR1 agonists could be potential pharmacological treatments for this disorder.

TAAR1 in dentate gyrus is involved in chronic stress-induced impairments in hippocampal plasticity and cognitive function

Multiple lines of evidence suggest that the trace amine-associated receptor 1 (TAAR1) holds promise as a potential target for stress-related disorders, such as treating major depressive disorder (MDD). The role of TAAR1 in the regulation of adult neurogenesis is recently supported by transcriptomic data. However, it remains unknown whether TAAR1 in dentate gyrus (DG) mediate chronic stress-induced negative effects on hippocampal plasticity and related behavior in mice. The present study consisted of a series of experiments using RNAscope, genetic approaches, behavioral tests, immunohistochemical staining, Golgi-Cox technique to unravel the effects of TAAR1 on alterations of dentate neuronal plasticity and cognitive function in the chronic social defeat stress model. The mice subjected to chronic defeat stress exhibited a noteworthy decrease in the mRNA level of TAAR1 in DG. Additionally, they exhibited compromised social memory and spatial object recognition memory, as well as impaired proliferation and maturation of adult-born dentate granule cells. Moreover, the selective knockout TAAR1 in DG mostly mimicked the cognitive function deficits and neurogenesis impairment induced by chronic stress. Importantly, the administration of the selective TAAR1 partial agonist RO5263397 during stress exposure attenuated the adverse effects of chronic stress on cognitive function, adult neurogenesis, dendritic arborization, and the synapse number of dentate neurons in DG. In summary, our findings suggest that TAAR1 plays a crucial role in mediating the detrimental effects of chronic stress on hippocampal plasticity and cognition. TAAR1 agonists exhibit therapeutic potential for individuals suffering from cognitive impairments associated with MDD.

Robust aversive effects of trace amine-associated receptor 1 activation in mice.

Drugs that stimulate the trace amine-associated receptor 1 (TAAR1) are under clinical investigation as treatments for several neuropsychiatric disorders. Previous studies in a genetic mouse model of voluntary methamphetamine intake identified TAAR1, expressed by the Taar1 gene, as a critical mediator of aversive methamphetamine effects. Methamphetamine is a TAAR1 agonist, but also has actions at monoamine transporters. Whether exclusive activation of TAAR1 has aversive effects was not known at the time we conducted our studies. Mice were tested for aversive effects of the selective TAAR1 agonist, RO5256390, using taste and place conditioning procedures. Hypothermic and locomotor effects were also examined, based on prior evidence of TAAR1 mediation. Male and female mice of several genetic models were used, including lines selectively bred for high and low methamphetamine drinking, a knock-in line in which a mutant form of Taar1 that codes for a non-functional TAAR1 was replaced by the reference Taar1 allele that codes for functional TAAR1, and their matched control line. RO5256390 had robust aversive, hypothermic and locomotor suppressing effects that were found only in mice with functional TAAR1. Knock-in of the reference Taar1 allele rescued these phenotypes in a genetic model that normally lacks TAAR1 function. Our study provides important data on TAAR1 function in aversive, locomotor, and thermoregulatory effects that are important to consider when developing TAAR1 agonists as therapeutic drugs. Because other drugs can have similar consequences, potential additive effects should be carefully considered as these treatment agents are being developed.

TAAR1 Regulates Purinergic-induced TNF Secretion from Peripheral, But Not CNS-resident, Macrophages.

Trace amine-associated receptor 1 (TAAR1) is an established neuroregulatory G protein-coupled receptor with recent studies suggesting additional functions related to immunomodulation. Our lab has previously investigated TAAR1 expression within cells of the innate immune system and herein we aim to further elucidate TAAR1 function in both peripherally-derived and CNS-resident macrophages. The selective TAAR1 agonist RO5256390 was used in combination with common damage associated molecular patterns (ATP and ADP) to observe the effect of TAAR1 agonism on modulating cytokine secretion and metabolic profiles. In mouse bone-marrow derived macrophages, TAAR1 agonism inhibited TNF secretion following ATP stimulation, which appeared to be downstream of an associated pro-inflammatory shift in metabolic profile and transcriptional regulation of TNF synthesis. In contrast, TAAR1 agonism had no effect on ADP-induced TNF and IL-6 secretion in mouse microglia in either the presence or absence of astrocytes. In summary, we report a novel interaction between TAAR1 and purinergic signaling in peripherally-derived, but not CNS-resident, macrophages. These findings provide the first evidence of trace aminergic and purinergic crosstalk, and support the potential for TAAR1 as a novel therapeutic target in inflammatory disorders.

Selective TAAR1 agonists induce conditioned taste aversion.

Trace amine-associated receptor 1 (TAAR1) is the best-studied receptor of trace amines, a group of biogenic amines expressed at a relatively low level in the mammalian brain. Growing evidence suggests that TAAR1 plays a critical role in various neuropsychiatric disorders. Given that selective TAAR1 agonists were shown to produce pro-cognition and antipsychotic-like effects as well as to suppress drug use and relapse, they have been proposed to be novel treatments for mental disorders such as schizophrenia and addiction. However, the aversive effects of selective TAAR1 agonists remain largely unknown. Here, we evaluated whether the selective TAAR1 full agonist RO5166017 and partial agonist RO5263397 could induce conditioned taste aversion (CTA). We found that RO5166017 and RO5263397 produced significant aversions to both saccharin and NaCl taste novelty. Furthermore, RO5166017 produced CTA to saccharin in TAAR1 heterozygous knockout (taar1±) and wild-type rats but not in TAAR1 homozygous knockout rats (taar1-/-), suggesting that TAAR1 was sufficient for the taste aversive stimulus property of RO5166017. Taken together, our data indicate that selective TAAR1 agonists could produce strong CTA. Our study urges careful evaluations of the aversive effects of TAAR1 agonists before translating them to clinical use for the treatment of mental disorders.

Trace amine-associated receptor 1 modulates motor hyperactivity, cognition, and anxiety-like behavior in an animal model of ADHD

Trace amine-associated receptor 1 (TAAR1) is a G protein-coupled receptor that has recently been implicated in several psychiatric conditions related to monoaminergic dysfunction, such as schizophrenia, substance use disorders, and mood disorders. Although attention-deficit/hyperactivity disorder (ADHD) is also related to changes in monoaminergic neurotransmission, studies that assess whether TAAR1 participates in the neurobiology of ADHD are lacking. We hypothesized that TAAR1 plays an important role in ADHD and might represent a potential therapeutic target. Here, we investigate if TAAR1 modulates behavioral phenotypes in Spontaneously Hypertensive Rats (SHR), the most validated animal model of ADHD, and Wistar Kyoto rats (WKY, used as a control strain). Our results showed that TAAR1 is downregulated in ADHD-related brain regions in SHR compared with WKY. While intracerebroventricular (i.c.v.) administration of the selective TAAR1 antagonist EPPTB impaired cognitive performance in SHR, i.c.v. administration of highly selective TAAR1 full agonist RO5256390 decreased motor hyperactivity, novelty-induced locomotion, and induced an anxiolytic-like behavior. Overall, our findings show that changes in TAAR1 levels/activity underlie behavior in SHR, suggesting that TAAR1 plays a role in the neurobiology of ADHD. Although additional confirmatory studies are required, TAAR1 might be a potential pharmacological target for individuals with this disorder.

TAAR1 regulates drug-induced reinstatement of cocaine-seeking via negatively modulating CaMKIIα activity in the NAc.

Relapse remains a major challenge to the treatment of cocaine addiction. Recent studies suggested that the trace amine-associated receptor 1 (TAAR1) could be a promising target to treat cocaine addiction and relapse; however, the underlying mechanism remains unclear. Here, we aimed to investigate the neural mechanism underlying the role of TAAR1 in the drug priming-induced reinstatement of cocaine-seeking behavior in rats, an animal model of cocaine relapse. We focused on the shell subregion of nucleus accumbens (NAc), a key brain region of the brain reward system. We found that activation of TAAR1 by systemic and intra-NAc shell administration of the selective TAAR1 agonist RO5166017 attenuated drug-induced reinstatement of cocaine-seeking and prevented drug priming-induced CaMKIIα activity in the NAc shell. Activation of TAAR1 dampened the CaMKIIα/GluR1 signaling pathway in the NAc shell and reduced AMPAR-EPSCs on the NAc slice. Microinjection of the selective TAAR1 antagonist EPPTB into the NAc shell enhanced drug-induced reinstatement as well as potentiated CaMKIIα activity in the NAc shell. Furthermore, viral-mediated expression of CaMKIIα in the NAc shell prevented the behavioral effects of TAAR1 activation. Taken together, our findings indicate that TAAR1 regulates drug-induced reinstatement of cocaine-seeking by negatively regulating CaMKIIα activity in the NAc. Our findings elucidate a novel mechanism of TAAR1 in regulating drug-induced reinstatement of cocaine-seeking and further suggests that TAAR1 is a promising target for the treatment of cocaine relapse.

The selective TAAR1 partial agonist RO5263397 promoted novelty recognition memory in mice

Trace amine-associated receptor 1 (TAAR1) is a G protein-coupled receptor that has a particular role in regulating dopaminergic, serotonergic, and glutamatergic transmission. TAAR1 agonists have shown pro-cognitive activities. However, it remains largely unknown of the effects of TAAR1 agonists on memory performance. Here, by using the mice novel object recognition (NOR) test, we examined the effects of the selective TAAR1 partial agonist RO5263397 on recognition memory. We found that RO5263397 significantly enhanced the retrieval of short-term memory (STM; 20min after training) both in male and female mice. RO5263397 promoted the retrieval of STM in the wild-type (WT) littermates but not TAAR1-KO mice, indicating that the effects of RO5263397 were dependent on TAAR1. Interestingly, compared to their WT litters, TAAR1-KO mice showed similar levels of STM, suggesting that genetic deletion of taar1 gene did not affect the STM retrieval. Furthermore, RO5263397 also promoted the retrieval of long-term NOR memory (24h after training). These results indicate that TAAR1 activation promotes NOR memory retrieval. Consistent with previous studies, our finding further suggests that TAAR1 agonists have pro-cognitive properties.

Role of trace amine‑associated receptor 1 in the medial prefrontal cortex in chronic social stress-induced cognitive deficits in mice

Emerging evidence supports an essential role of trace amine-associated receptor 1 (TAAR1) in neuropsychiatric disorders such as depression and schizophrenia. Stressful events are critical contributors to various neuropsychiatric disorders. This study examined the role of TAAR1 in mediating the negative outcomes of stressful events. In mice that experienced chronic social defeat stress but not acute stress, a significant reduction in the TAAR1 mRNA level was found in the medial prefrontal cortex (mPFC), a brain region that is known to be vulnerable to stress experience. Conditional TAAR1 knockout in the mPFC mimicked the cognitive deficits induced by chronic stress. In addition, chronic treatment with the selective TAAR1 partial agonist RO5263397 ameliorated chronic stress-induced changes in cognitive function, dendritic arborization, and the synapse number of pyramidal neurons in the mPFC but did not affect chronic stress-induced anxiety-like behaviors. Biochemically, chronic stress reduced the ratio of vesicular transporters of glutamate-1 (VGluT1) / vesicular GABA transporter (VGAT) in the mPFC，most prominently in the prelimbic cortex, and RO5263397 restored the excitatory-inhibitory (E/I) imbalance. Together, the results of this study reveal an essential role of TAAR1 in mediating chronic stress-induced cognitive impairments and suggest that TAAR1 agonists may be uniquely useful to treat MDD-related cognitive impairments.

TAAR1 agonists attenuate extended-access cocaine self-administration and yohimbine-induced reinstatement of cocaine-seeking.

The trace amine-associated receptor 1 (TAAR1) negatively modulates dopamine transmission. Our previous studies demonstrated that TAAR1 agonists attenuated cue- and drug-induced cocaine-seeking and increased the elasticity of the cocaine demand curve, in the short-access cocaine self-administration model. Compulsive use of cocaine, which is an essential criterion of cocaine use disorder, can be induced by extended access to cocaine self-administration. To characterize the role of TAAR1 in compulsive cocaine use, we evaluated the effects of activation of TAAR1 on cocaine intake, cocaine binge and cue-induced cocaine-seeking using the extended-access cocaine self-administration model in adult male Sprague-Dawley rats. We also investigated the role of TAAR1 in stress-triggered cocaine relapse by using the α2 -adrenoceptor antagonist yohimbine-induced reinstatement of cocaine-seeking. The selective TAAR1 partial agonist RO5263397 attenuated cocaine intake and did not develop tolerance during the 10-day extended-access cocaine self-administration. RO5263397 reduced a 12-h binge intake of cocaine after forced abstinence. RO5263397 also decreased cue-induced cocaine-seeking after prolonged abstinence from extended-access cocaine self-administration. Furthermore, RO5263397 and the selective TAAR1 full agonist RO5166017 reduced yohimbine-induced reinstatement of cocaine-seeking behaviour. Activation of TAAR1 attenuated extended-access cocaine self-administration and stress-induced cocaine reinstatement. These results suggest that TAAR1 agonists are promising pharmacological interventions to treat cocaine use disorder and relapse.

The Action of TAAR1 Agonist RO5263397 on Executive Functions in Rats.

Trace amine-associated receptor 1 (TAAR1) is a widely recognized new perspective target for the neuropsychiatric pharmacological treatment. Despite a growing number of studies investigating TAAR1 role in the animal models of different pathologies, information of TAAR1 agonists impact on executive cognitive functions is limited. The goal of the present study was to evaluate the activity of highly selective partial TAAR1 agonist RO5263397 on various executive cognitive functions. The results of the present study demonstrated that the pretreatment with RO5263397 was able to increase attention and decrease cognitive flexibility in rats. The analysis of the RO5263397 action on impulsivity demonstrated that the TAAR1 activation failed to affect premature responding but was able to slightly modify impulsive choice. Problem solving was resistant to the pharmacological intervention.

Activation of trace amine-associated receptor 1 attenuates schedule-induced polydipsia in rats

Trace Amine Associated Receptor 1 (TAAR1) is a novel pharmacological target. TAAR1 are well-documented to play a modulatory role in the dopaminergic system. In spite of a growing number of studies of TAAR1 effects, little is still known about the behavioral pharmacology of TAAR1 ligands, including effects of repeated TAAR1 agonist administration. The present study appears to be the first that estimated the action of TAAR1 agonists on schedule-induced polydipsia, a type of adjunctive behavior, which is considered to be useful for evaluating certain aspects of obsessive-compulsive and related disorders (OCD) and schizophrenia.Our results have demonstrated that the wide range of RO5263397, the highly selective partial TAAR1 agonist, doses (1–10 mg/kg) attenuated the polydipsia induced by two different schedules of food delivery in rats. The effect remained unchanged for the 7 days of repeated treatment. However, the highest tested doses of RO5263397 (6 and 10 mg/kg) decreased the vertical locomotor activity of the animals and the volume of water intake of thirsty rats following the acute treatment. Also, though, the repeated RO5263397 administration is exhibited to diminish the volume of consumed water and weight of rats without SIP, on the other hand, the tolerance was observed to these drug effects.In general, the RO5263397 decreases specifically the adjunctive drinking and this effect is maintained with repeated drug administration without the development of tolerance. The interpretation of these results as an evidence for the RO5263397 anticompulsive-like action, however, should be taken with caution because the drug also influenced the drinking behavior and only weakly affected the other parameters of SIP used to reveal the potential anticompulsive-like effects of drugs.

Biochemical and Functional Characterization of the Trace Amine-Associated Receptor 1 (TAAR1) Agonist RO5263397.

Trace amine-associated receptor 1 (TAAR1) is a G protein-coupled receptor, which signals through elevating intracellular cAMP levels, and expressed in most vertebrates, including rodents and humans. In recent years, several lines of evidence indicated the role of TAAR1 in the regulation of dopaminergic system and its importance in physiological processes such as locomotion, control of emotional states and cognition. In our study, we used RO5263397, a selective TAAR1 agonist, as a tool and characterized its pharmacology in vitro in HEK293 cells and its effects in vivo in tests assessing potential antidepressant and antipsychotic actions. We found that RO5263397 not only increases cAMP levels at very low concentrations but also can induce the phosphorylation of ERK and CREB in a concentration- and time-dependent manner. Like other TAAR1 agonists, RO5263397 potently suppressed high dopamine-dependent hyperactivity in mice lacking the dopamine transporter. Moreover, RO5263397 produced a strong antidepressant-like effect in the forced swim test comparable to fluoxetine. Furthermore, the antidepressant-like activity was blocked by pretreatment with SCH23390 (dopamine D1 receptor antagonist) or NBQX (glutamate AMPA receptor antagonist) but only in part by WAY100635 (serotonin 5HT1A receptor antagonist). In conclusion, our study confirms some previous in vitro and in vivo findings in relation to the pharmacological effects of RO5263397 but more importantly provides new insight on intracellular signaling pathway and other neurotransmitter receptors modulated by TAAR1 receptor activation.

Deletion of Trace Amine-Associated Receptor 1 Attenuates Behavioral Responses to Caffeine.

Trace amines (TAs), endogenous amino acid metabolites that are structurally similar to the biogenic amines, are endogenous ligands for trace amine-associated receptor 1 (TAAR1), a GPCR that modulates dopaminergic, serotonergic, and glutamatergic activity. Selective TAAR1 full and partial agonists exhibit similar pro-cognitive, antidepressant- and antipsychotic-like properties in rodents and non-human primates, suggesting TAAR1 as a novel target for the treatment of neurological and psychiatric disorders. We previously reported that TAAR1 partial agonists are wake-promoting in rats and mice, and that TAAR1 knockout (KO) and overexpressing mice exhibit altered sleep-wake and EEG spectral composition. Here, we report that locomotor and EEG spectral responses to the psychostimulants modafinil and caffeine are attenuated in TAAR1 KO mice. TAAR1 KO mice and WT littermates were instrumented for EEG and EMG recording and implanted with telemetry transmitters for monitoring locomotor activity (LMA) and core body temperature (Tb). Following recovery, mice were administered modafinil (25, 50, 100 mg/kg), caffeine (2.5, 10, 20 mg/kg) or vehicle p.o. at ZT6 in balanced order. In WT mice, both modafinil and caffeine dose-dependently increased LMA for up to 6 h following dosing, whereas only the highest dose of each drug increased LMA in KO mice, and did so for less time after dosing. This effect was particularly pronounced following caffeine, such that total LMA response was significantly attenuated in KO mice compared to WT at all doses of caffeine and did not differ from Vehicle treatment. Tb increased comparably in both genotypes in a dose-dependent manner. TAAR1 deletion was associated with reduced wake consolidation following both drugs, but total time in wakefulness did not differ between KO and WT mice. Furthermore, gamma band EEG activity following both modafinil and caffeine treatment was attenuated in TAAR1 KO compared to WT mice. Our results show that TAAR1 is a critical component of the behavioral and cortical arousal associated with two widely used psychostimulants with very different mechanisms of action. Together with our previous findings, these data suggest that TAAR1 is a previously unrecognized component of an endogenous wake-modulating system.

0014 TRACE AMINE-ASSOCIATED RECEPTOR 1 REGULATES WAKEFULNESS, BEHAVIORAL ACTIVATION AND EEG SPECTRAL COMPOSITION

Trace amines (TAs) are endogenous amino acid metabolites that are structurally similar to the biogenic amines. TAs are endogenous ligands for trace amine-associated receptor 1 (TAAR1), a GPCR that modulates dopaminergic, serotonergic, and glutamatergic activity. Selective TAAR1 agonists have been shown to have pro-cognitive, antipsychotic-like, anti-addiction, stress-reducing, weight-reducing, glucose-lowering and wake-promoting activities. We used Taar1 knockout (KO) and over-expressing (OE) mice and TAAR1 agonists to elucidate the role of TAAR1 in sleep/wake. EEG, EMG, body temperature (Tb) and locomotor activity (LMA) were recorded in Taar1 KO, OE and WT mice. Following a 24h recording to characterize baseline sleep/wake, mice were sleep-deprived (SD) for 6h. In separate experiments, mice were given three doses of the TAAR1 partial agonist RO5263397, caffeine, modafinil or vehicle p.o. Baseline wakefulness was modestly increased in OE compared to WT mice. Baseline theta (4.5-9Hz) and low gamma (30-60Hz) activity was elevated in KO compared to OE mice in NREM and REM sleep. Following SD, both KO and OE mice exhibited a homeostatic sleep rebound. In WT mice, RO5263397 increased waking and reduced NREM and REM sleep, decreased gamma power during wake and NREM, and decreased Tb without affecting LMA; these effects were absent in KO mice and potentiated in OE mice. By contrast, caffeine increased wake time, NREM gamma power, and LMA in all strains compared to vehicle; this effect was attenuated in KO and potentiated in OE mice. Subsequent studies confirmed that motor activation and gamma band activity increases induced by caffeine or modafinil are attenuated in KO mice compared to WT. TAAR1 overexpression increases wakefulness whereas TAAR1 partial agonism strongly increases wakefulness and reduces NREM and REM sleep. These results indicate a modulatory role for TAAR1 in sleep/wake and cortical activity and suggest TAAR1 as a novel target for wake-promoting therapeutics. NIH R01 NS082876.

A partial trace amine-associated receptor 1 agonist exhibits properties consistent with a methamphetamine substitution treatment.

Recent evidence suggests that the trace amine-associated receptor 1 (TAAR1) plays a pivotal role in the regulation of dopamine (DA) transmission and psychostimulant action. Several selective TAAR1 agonists have previously shown efficacy in models of cocaine addiction. However, the effects of TAAR1 activation on methamphetamine (METH)-induced behaviours are less well understood, as indeed are the underlying neurochemical mechanisms mediating potential interactions between TAAR1 and METH. Here, in a progressive ratio schedule of reinforcement the partial TAAR1 agonist, RO5263397, reduced the break-point for METH self-administration, while significantly increasing responding maintained by food reward. Following self-administration and extinction training, RO5263397 completely blocked METH-primed reinstatement of METH seeking. Moreover, when used as a substitute, unlike a low dose of METH, which sustained vigorous responding when substituting for the training dose of METH, RO5263397 was not self-administered at any dose, thus exhibiting no apparent abuse liability. Fast-scan cyclic voltammetry experiments showed that RO5263397 prevented METH-induced DA overflow in slices of the nucleus accumbens, while having no effect on DA transmission in its own right. Collectively, the present observations demonstrate that partial TAAR1 activation decreases the motivation to self-administer METH, blocks METH-primed reinstatement of METH seeking and prevents METH-induced DA elevations in the nucleus accumbens, and strongly support the candidacy of TAAR1-based medications as potential substitute treatment in METH addiction.

Trace amine-associated receptor 1 activation silences GSK3β signaling of TAAR1 and D2R heteromers

Trace amine-associated receptor 1 (TAAR1) activation by selective endogenous agonists modulates dopaminergic neurotransmission. This results in antipsychotic-like behavior in vivo which might be initiated by an interaction of TAAR1 and dopamine D2L receptor (D2R). Here we analyzed the functional link between TAAR1 and D2R using highly potent and selective TAAR1 agonists, and newly generated tools such as TAAR1 knock-out and TAAR1 overexpressing rats as well as specific anti-rat TAAR1 antibodies. We provide data from co-immunoprecipitation experiments supporting a functional interaction of the two receptors in heterologous cells and in brain tissue. Interaction of TAAR1 with D2R altered the subcellular localization of TAAR1 and increased D2R agonist binding affinity. Using specific β-arrestin 2 (βArr2) complementation assays we show that the interaction of TAAR1 with D2R reduced βArr2 recruitment to D2R. In addition, we report that besides Gαs-protein signaling TAAR1 also signals via βArr2. In the presence of D2R, cAMP signaling of TAAR1 was reduced while its βArr2 signaling was enhanced, resulting in reduced GSK3β activation. These results demonstrate that βArr2 signaling may be an important pathway for TAAR1 function and that the activation of the TAAR1-D2R complex negatively modulates GSK3β signaling. Given that patients with schizophrenia or bipolar disorder show increased GSK3β signaling, such a reduction of GSK3β signaling triggered by the interaction of D2R with activated TAAR1 further supports TAAR1 as a target for the treatment of psychiatric disorders.

Design, Synthesis, and Evaluation of Thyronamine Analogues as Novel Potent Mouse Trace Amine Associated Receptor 1 (mTAAR1) Agonists.

Trace amine associated receptor 1 (TAAR1) is a G protein coupled receptor (GPCR) expressed in brain and periphery activated by a wide spectrum of agonists that include, but are not limited to, trace amines (TAs), amphetamine-like psychostimulants, and endogenous thyronamines such as thyronamine (T0AM) and 3-iodothyronamine (T1AM). Such polypharmacology has made it challenging to understand the role and the biology of TAAR1. In an effort to understand the molecular basis of TAAR1 activation, we rationally designed and synthesized a small family of thyronamine derivatives. Among them, compounds 2 and 3 appeared to be a good mimic of the parent endogenous thyronamine, T0AM and T1AM, respectively, both in vitro and in vivo. Thus, these compounds offer suitable tools for studying the physiological roles of mouse TAAR1 and could represent the starting point for the development of more potent and selective TAAR1 ligands.

The Discovery of Novel TAAR1 Ligands through the use of a Homology Model and in silico Screening

Trace amines (TA) are by‐products of the synthesis of classical neurotransmitters within the brain. TA's exert their effect by activating a class of GPCRs including, trace amine associated receptor 1 (TAAR1) where TAAR1 signalling has been shown to be a negative regulator of dopamine transmission. In this study, we aimed to identify novel selective TAAR1 compounds for TAAR1 for in vivo testing. To this end, a TAAR1 homology model was generated and an in silico screen of 3 million commercially available compounds was conducted. The top 42 compounds, based on predicted affinities, were ordered and screened for TAAR1 activity using a cAMP BRET biosensor. From the 42 compounds tested, a mix of antagonists (seven compounds) and agonists (nine compounds) were found, yielding an initial hit rate of 35%. Of the nine identified agonists, three compounds (8, 16, and 25) displayed high potency for TAAR1 with EC50 values of 18, 1.0, and 52 µM respectively. In order to identify compounds with improved affinity for TAAR1, five analogs of compounds 8 and 16 were tested. Of the five analogs of compound 8 tested, only one compound (8b) displayed agonist activity with no improvements on efficacy or potency compared to compound 8. Two of the five compound 16 analogs (16a and 16b) had a left shift of ~10 fold in their EC50 for activation of cAMP signalling by TAAR. Furthermore the analog 16b had higher efficacy for TAAR1 activation than compound 16. In conclusion we have discovered three unique novel partial TAAR1 agonists with new chemical backbones where compound 16 and its analogs had the most optimal pharmacological profile. The in vivo effects as well as identification of higher affinity analogs of these compounds will be undertaken in the future.

The trace amine-associated receptor 1 modulates methamphetamine's neurochemical and behavioral effects.

The newly discovered trace amine-associated receptor 1 (TAAR1) has the ability to regulate both dopamine function and psychostimulant action. Here, we tested in rats the ability of RO5203648, a selective TAAR1 partial agonist, to modulate the physiological and behavioral effects of methamphetamine (METH). In experiment 1, RO5203468 dose- and time-dependently altered METH-induced locomotor activity, manifested as an early attenuation followed by a late potentiation of METH's stimulating effects. In experiment 2, rats received a 14-day treatment regimen during which RO5203648 was co-administered with METH. RO5203648 dose-dependently attenuated METH-stimulated hyperactivity, with the effects becoming more apparent as the treatments progressed. After chronic exposure and 3-day withdrawal, rats were tested for locomotor sensitization. RO5203648 administration during the sensitizing phase prevented the development of METH sensitization. However, RO5203648, at the high dose, cross-sensitized with METH. In experiment 3, RO5203648 dose-dependently blocked METH self-administration without affecting operant responding maintained by sucrose, and exhibited lack of reinforcing efficacy when tested as a METH's substitute. Neurochemical data showed that RO5203648 did not affect METH-mediated DA efflux and uptake inhibition in striatal synaptosomes. In vivo, however, RO5203648 was able to transiently inhibit METH-induced accumulation of extracellular DA levels in the nucleus accumbens. Taken together, these data highlight the significant potential of TAAR1 to modulate METH's neurochemical and behavioral effects.