TAAR1 activation modulates monoaminergic neurotransmission, preventing hyperdopaminergic and hypoglutamatergic activity

New Drug Treatments for Schizophrenia: A Review of Approaches to Target Circuit Dysfunction

Schizophrenia is a leading cause of global disease burden. Current drug treatments are associated with significant side effects and have limited efficacy for many patients, highlighting the need to develop new approaches that target other aspects of the neurobiology of schizophrenia. Preclinical, in vivo imaging, postmortem, genetic, and pharmacological studies have highlighted the key role of cortical GABAergic (gamma-aminobutyric acidergic)-glutamatergic microcircuits and their projections to subcortical dopaminergic circuits in the pathoetiology of negative, cognitive, and psychotic symptoms. Antipsychotics primarily act downstream of the dopaminergic component of this circuit. However, multiple drugs are currently in development that could target other elements of this circuit to treat schizophrenia. These include drugs for GABAergic or glutamatergic targets, including glycine transporters, D-amino acid oxidase, sodium channels, or potassium channels. Other drugs in development are likely to primarily act on pathways that regulate the dopaminergic system, such as muscarinic or trace amine receptors or 5-HT2A receptors, while PDE10A inhibitors are being developed to modulate the downstream consequences of dopaminergic dysfunction. Our review considers where new drugs may act on this circuit and their latest clinical trial evidence in terms of indication, efficacy, and side effects. Limitations of the circuit model, including whether there are neurobiologically distinct subgroups of patients, and future directions are also considered. Several drugs based on the mechanisms reviewed have promising clinical data, with the muscarinic agonist KarXT most advanced. If these drugs are approved for clinical use, they have the potential to revolutionize understanding of the pathophysiology and treatment of schizophrenia.

Is there a role for biogenic amine receptors in mediating β-phenylethylamine and RO5256390-induced vascular contraction?

BACKGROUND

Substantial evidence indicates trace amines can induce vasoconstriction independently of noradrenaline release. However, the mechanism underlying noradrenaline-independent vasoconstrictor responses to trace amines has not yet been established. This study evaluates the role of trace amine-associated receptor 1 (TAAR1) and other biogenic amine receptors in mediating β-phenylethylamine and the TAAR-1 selective agonist RO5256390-induced vasoconstriction.

METHODS

Vasoconstrictor responses to β-PEA and the TAAR1-selective agonist, RO5256390 were assessed in vitro in endothelium-denuded aortic rings and third-order mesenteric arteries of male Sprague Dawley rats.

RESULTS

β-PEA and RO5256390 induced concentration-dependent vasoconstriction of aortic rings but not third-order mesenteric arteries. Vasoconstrictor responses in aortic rings were insensitive to antagonists of 5-HT. The murine-selective TAAR1 antagonist, EPPTB, had no effect on either β-PEA or RO5256390-induced vasoconstriction. The α1-adrenoceptor antagonist, prazosin, and the α2-adrenoceptor antagonist, yohimbine, induced a shift of the β-PEA concentration response curve too small to be ascribed to antagonism of α1-or α2-adrenoceptors, respectively. The α2-adrenoceptor antagonist atipamezole had no effect on β-PEA or RO5256390-induced vasoconstriction.

CONCLUSION

Vasoconstrictor responses to trace amines are not mediated by classical biogenic amine neurotransmitter receptors. Insensitivity of β-PEA vasoconstrictor responses to EPPTB, may be explained by its low affinity for rat rather than murine TAAR1. Therefore, TAAR1 remains the most likely candidate receptor mediating vasoconstrictor responses to trace amines and that prazosin and yohimbine have low affinity for TAAR1.

Molecular Mechanisms of Methamphetamine-Induced Addiction via TAAR1 Activation

Trace amine-associated receptor 1 (TAAR1), a member of the trace amine receptor family, recognizes various trace amines in the brain, including endogenous β-phenylethylamine (PEA) and methamphetamine (METH). TAAR1 is a novel target for several neurological disorders, including schizophrenia, depression, and substance abuse. Herein, we report the structure of the human TAAR1-Gs protein complex bound to METH. Using functional studies, we reveal the molecular basis of METH recognition by TAAR1, and potential mechanisms underlying the selectivity of TAAR1 for different ligands. Molecular dynamics simulations further elucidated possible mechanisms for the binding of chiral amphetamine (AMPH)-like psychoactive drugs to TAAR1. Additionally, we discovered a hydrophobic core on the transmembrane helices (TM), TM5 and TM6, explaining the unique mechanism of TAAR1 activation. These findings reveal the ligand recognition pattern and activation mechanism of TAAR1, which has important implications for the development of next-generation treatments for substance abuse and various neurological disorders.

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.

Psychedelics and schizophrenia: a double-edged sword

Psychedelics have shown promising effects in several psychiatric diseases as demonstrated by multiple clinical trials. However, no clinical experiments on patients with schizophrenia have been conducted up to date, except for some old semi-anecdotal studies mainly performed in the time-span '50s-'60s. Notably, these studies reported interesting findings, particularly on the improvement of negative symptoms and social cognition. With no doubts the lack of modern clinical studies is due to the psychomimetic properties of psychedelics, a noteworthy downside that could worsen positive symptoms. However, a rapidly increasing body of evidence has suggested that the mechanisms of action of such compounds partially overlaps with the pathogenic underpinnings of schizophrenia but in an opposite way. These findings suggest that, despite being a controversial issue, the use of psychedelics in the treatment of schizophrenia would be based on a strong biological rationale. Therefore, the aim of our perspective paper is to provide a background on the old experiments with psychedelics performed on patients with schizophrenia, interpreting them in the light of recent molecular findings on their ability to induce neuroplasticity and modulate connectivity, the immune and TAARs systems, neurotransmitters, and neurotropic factors. No systematic approach was adopted in reviewing the evidence given the difficulty to retrieve and interpret old findings. Interestingly, we identified a therapeutic potential of psychedelics in schizophrenia adopting a critical point of view, particularly on negative symptoms and social cognition, and we summarized all the relevant findings. We also identified an eligible subpopulation of chronic patients predominantly burdened by negative symptoms, outlining possible therapeutic strategies which encompass very low doses of psychedelics (microdosing), carefully considering safety and feasibility, to pave the way to future clinical trials.

Vibrational spectroscopic interpretation, solvent effect and molecular docking studies of TAAR1 partial agonist RO5263397

Density functional theory studies of TAAR1 (trace amine associated receptor 1) partial agonist RO5263397 carried out with precise and detailed spectroscopic investigation as well as validated experimentally. FT-IR, confocal Raman and UV-visible spectroscopic techniques were used to characterize the compound and corresponding theoretical calculations were carried out using DFT/B3LYP method with 6-311++G (d,p) basis set. Estimated and observed vibrational wavenumbers of the compound were assigned. UV-visible spectrum and FMOs (frontier molecular orbital) analysis reveals that the polarity affects the molecular reactivity and stability of the compound. Donor - acceptor interaction and second order perturbation energy have been explained using natural bond orbital analysis clarify the presence hydrogen bonds in the system. ELF and LOL studies visualises the localized and delocalized electrons in the title compound. RDG analysis evidences the various interactions present in the monomer and dimer of RO5263397. The structural importance of the compound were clearly examined using NMR spectral analysis. The existence of hydrogen bonding is validated by reactive site findings from Mulliken atomic charge distribution and molecule electrostatic potential surface studies. Information about distinct drug-receptor interactions obtained from molecular docking investigation offers the path of further study of molecular activity in various drug-receptor mechanism.

Wakefulness Induced by TAAR1 Partial Agonism is Mediated Through Dopaminergic Neurotransmission

Trace amine-associated receptor 1 (TAAR1) is known to negatively regulate dopamine (DA) release. The partial TAAR1 agonist RO5263397 promotes wakefulness and suppresses NREM and REM sleep in mice, rats, and non-human primates. We tested the hypothesis that the TAAR1-mediated effects on sleep/wake were due, at least in part, to DA release. Male C57BL6/J mice (n=8) were intraperitoneally administered the D1R antagonist SCH23390, the D2R antagonist eticlopride, a combination of D1R+D2R antagonists or saline at ZT5.5, followed 30 min later by RO5263397 or vehicle (10% DMSO in DI water) at ZT6 per os. EEG, EMG, subcutaneous temperature, and activity were recorded in each mouse across the 8 treatment conditions and sleep architecture was analyzed for 6 hours post-dosing. Consistent with our previous reports, RO5263397 increased wakefulness as well as the latency to NREM and REM sleep. D1, D2, and D1+D2 pretreatment reduced RO5263397-induced wakefulness during the first 1-2 hours after dosing, but only the D1+D2 combination attenuated the wake-promoting effect of RO5263397 from ZT6-8, mostly by increasing NREM sleep. Although D1+D2 antagonism blocked the wake-promoting effect of RO5263397, only the D1 antagonist significantly reduced the TAAR1-mediated increase in NREM latency. Neither the D1 nor the D2 antagonist affected TAAR1-mediated suppression of REM sleep. These results suggest that, whereas TAAR1 effects on wakefulness are mediated in part through the D2R, D1R activation plays a role in reversing the TAAR1-mediated increase in NREM sleep latency. By contrast, TAAR1-mediated suppression of REM sleep appears not to involve D1R or D2R mechanisms.

Ligands of the trace amine-associated receptors (TAARs): A new class of anxiolytics

Most cases of anxiety are currently treated with either benzodiazepines or serotonin reuptake inhibitors. These drugs carry with them risks for a multitude of side effects, and patient compliance suffers for this reason. There is thus a need for novel anxiolytics, and among the most compelling prospects in this vein is the study of the TAARs. The anxiolytic potential of ulotaront, a full agonist at the human TAAR1, is currently being investigated in patients with generalized anxiety disorder. Irrespective of whether this compound succeeds in clinical trials, a growing body of preclinical literature underscores the relevance of modulating the TAARs in anxiety. Multiple behavioral paradigms show anxiolytic-like effects in rodents, possibly due to increased neurogenesis and plasticity, in addition to a panoply of interactions between the TAARs and other systems. Crucially, multiple lines of evidence suggest that the TAARs, particularly TAAR1, TAAR2, and TAAR5, are expressed in the extended amygdala and hippocampus. These regions are central in the actuation of anxiety, and are particularly susceptible to neurogenic and neuroplastic effects which the TAARs are now known to regulate. The TAARs also regulate the dopamine and serotonin systems, both of which are implicated in anxiety. Ligands of the TAARs may thus constitute a new class of anxiolytics.

TAAR1 and 5-HT1B receptor agonists attenuate autism-like irritability and aggression in rats prenatally exposed to valproic acid

Despite the rising prevalence of autism spectrum disorder (ASD), there remains a significant unmet need for pharmacotherapies addressing its core and associative symptoms. While some atypical antipsychotics have been approved for managing associated irritability and aggression, their use is constrained by substantial side effects. This study aimed firstly to develop behavioral measures to explore frustration, irritability and aggression phenotypes in the rat prenatal valproic acid (VPA) model of ASD. Additionally, we investigated the potential of two novel mechanisms, 5-HT1B and TAAR1 agonism, to alleviate these behaviors. Male offspring exposed to prenatal VPA were trained to achieve stable performance on a cued operant task, followed by pharmacological assessment in an operant frustration test, bottle brush test and resident intruder test. VPA exposed rats demonstrated behaviors indicative of frustration and irritability, as well as increased aggression compared to controls. The irritability-like behavior and aggression were further exacerbated in animals previously experiencing a frustrative event during the operant test. Single administration of the 5-HT1B agonist CP-94253 or TAAR1 agonist RO5263397 attenuated the frustration-like behavior compared to vehicle. Additionally, both agonists reduced irritability-like behavior under both normal and frustrative conditions. While CP-94253 reduced aggression in the resident intruder test under both conditions, RO5263397 only produced effects in rats that previously experienced a frustrative event. Our study describes previously uncharacterized phenotypes of frustration, irritability, and aggression in the rat prenatal VPA model of ASD. Administration of selective TAAR1 or 5-HT1B receptor agonists alleviated these deficits, warranting further exploration of both targets in ASD treatment.

Serotonergic Drugs for the Treatment of Attention-Deficit/Hyperactivity Disorder: A Review of Past Development, Pitfalls and Failures, and a Look to the Future

Serotonin has been implicated in the neurobiology of attention-deficit/hyperactivity disorder (ADHD) due to its association with impulsivity, attention, and emotional regulation. Many compounds with serotonergic properties have been evaluated in ADHD, but few have been approved by regulatory authorities. Utilizing a search of public databases, we identified interventions studied in ADHD. Prescribing information and peer-reviewed and gray literature helped us to determine which compounds had an underlying mechanism of action associated with changing serotonin levels. Of the 24 compounds that met the search criteria, 16 had either failed clinical studies in an ADHD population or had been discontinued from future development. The available evidence was assessed to identify the developmental history of drugs with serotonergic activity and the outlook for new ADHD drug candidates targeting serotonin. Several treatment candidates floundered due to an inability to balance effectiveness with safety, underscoring the potential importance of potency, and selectivity. Ongoing drug development includes compounds with multimodal mechanisms of action targeting neurotransmission across serotonin, norepinephrine, and dopamine pathways; it appears likely that treatment which balances competing and complementary monoamine effects may provide improved outcomes for patients. It is hoped that continuing research into ADHD treatment will produce new therapeutic options targeting the serotonergic system, which can positively impact a wide range of symptoms, including mood, anxiety, and sleep as well as attention and hyperactivity.

Computational Methods for the Discovery and Optimization of TAAR1 and TAAR5 Ligands

G-protein-coupled receptors (GPCRs) represent a family of druggable targets when treating several diseases and continue to be a leading part of the drug discovery process. Trace amine-associated receptors (TAARs) are GPCRs involved in many physiological functions with TAAR1 having important roles within the central nervous system (CNS). By using homology modeling methods, the responsiveness of TAAR1 to endogenous and synthetic ligands has been explored. In addition, the discovery of different chemo-types as selective murine and/or human TAAR1 ligands has helped in the understanding of the species-specificity preferences. The availability of TAAR1-ligand complexes sheds light on how different ligands bind TAAR1. TAAR5 is considered an olfactory receptor but has specific involvement in some brain functions. In this case, the drug discovery effort has been limited. Here, we review the successful computational efforts developed in the search for novel TAAR1 and TAAR5 ligands. A specific focus on applying structure-based and/or ligand-based methods has been done. We also give a perspective of the experimental data available to guide the future drug design of new ligands, probing species-specificity preferences towards more selective ligands. Hints for applying repositioning approaches are also discussed.

Trace amine associated receptor 1: predicted effects of single nucleotide variants on structure-function in geographically diverse populations

Trace Amine Associated Receptor 1 (TAAR1) is a novel pharmaceutical target under investigation for the treatment of several neuropsychiatric conditions. TAAR1 single nucleotide variants (SNV) have been found in patients with schizophrenia and metabolic disorders. However, the frequency of variants in geographically diverse populations and the functional effects of such variants are unknown. In this study, we aimed to characterise the distribution of TAAR1 SNVs in five different WHO regions using the Database of Genotypes and Phenotypes (dbGaP) and conducted a critical computational analysis using available TAAR1 structural data to identify SNVs affecting ligand binding and/or functional regions. Our analysis shows 19 orthosteric, 9 signalling and 16 micro-switch SNVs hypothesised to critically influence the agonist induced TAAR1 activation. These SNVs may non-proportionally influence populations from discrete regions and differentially influence the activity of TAAR1-targeting therapeutics in genetically and geographically diverse populations. Notably, our dataset presented with orthosteric SNVs D1033.32N (found only in the South-East Asian Region and Western Pacific Region) and T1945.42A (found only in South-East Asian Region), and 2 signalling SNVs (V1253.54A/T2526.36A, found in African Region and commonly, respectively), all of which have previously demonstrated to influence ligand induced functions of TAAR1. Furthermore, bioinformatics analysis using SIFT4G, MutationTaster 2, PROVEAN and MutationAssessor predicted all 16 micro-switch SNVs are damaging and may further influence the agonist activation of TAAR1, thereby possibly impacting upon clinical outcomes. Understanding the genetic basis of TAAR1 function and the impact of common mutations within clinical populations is important for the safe and effective utilisation of novel and existing pharmacotherapies.

TAAR1 agonist ulotaront delays gastric emptying of solids in patients with schizophrenia and concurrent metabolic syndrome with prediabetes

BACKGROUND

Metabolic syndrome (MetS), which can be induced or exacerbated by the current class of antipsychotic drugs, is highly prevalent in patients with schizophrenia and presents significant challenges to lifetime disease management. Supported by initial clinical results, trace amine-associated receptor 1 (TAAR1) agonists have emerged as potential novel treatments for schizophrenia. Notably, non-clinical studies have also shown weight-lowering and glucoregulatory effects of TAAR1 agonists, including the investigational agent ulotaront. However, the translatability of these findings to humans has not been adequately assessed. Given that delayed gastric emptying (GE) was identified as a potential mechanism contributing to the metabolic benefits of TAAR1 agonists in rodents, the aim of this study was to evaluate the effect of ulotaront on GE in patients with schizophrenia and concurrent MetS with prediabetes.

METHODS

Patients with schizophrenia were randomized to receive a single oral dose of ulotaront (150 mg) and their previous antipsychotic (PA) in an open-label, crossover, two-sequence design (NCT05402111). Eligible participants fulfilled at least three of five MetS criteria and had prediabetes defined by elevated glycated haemoglobin (5.7-6.4%) and/or fasting homeostatic model assessment of insulin resistance (i.e. ≥2.22). Following an overnight fast and 4 h post-dose, participants ingested a 99mTc-sulphur colloid radiolabelled egg meal (320 kcal, 30% fat). GE was measured by scintigraphy over 4 h. Endpoints included GE of solids half-time (T1/2) and percentage gastric retention at 1, 2 and 4 h.

RESULTS

Thirty-one adults were randomized and 27 completed the study. Ulotaront significantly delayed GE of solids [median GE T1/2 ulotaront at 139 min (119, 182) vs. the participant's PA of 124 min (109, 132), p = .006]. A significant increase in gastric retention was seen in the ulotaront versus the PA group at 1 h (80% vs. 75%, p = .015), 2 h (61% vs. 50%, p = .023) and 4 h (17% vs. 7%, p = .002) post-meal.

CONCLUSION

Ulotaront delayed the GE of solids in patients with schizophrenia and concurrent MetS with prediabetes. Additional studies are needed to assess whether treatment with TAAR1 agonists is associated with weight loss and glucoregulatory improvement.

TAAR1 agonist ulotaront modulates striatal and hippocampal glutamate function in a state-dependent manner

Aberrant dopaminergic and glutamatergic function, particularly within the striatum and hippocampus, has repeatedly been associated with the pathophysiology of schizophrenia. Supported by preclinical and recent clinical data, trace amine-associated receptor 1 (TAAR1) agonism has emerged as a potential new treatment approach for schizophrenia. While current evidence implicates TAAR1-mediated regulation of dopaminergic tone as the primary circuit mechanism, little is known about the effects of TAAR1 agonists on the glutamatergic system and excitation-inhibition balance. Here we assessed the impact of ulotaront (SEP-363856), a TAAR1 agonist in Phase III clinical development for schizophrenia, on glutamate function in the mouse striatum and hippocampus. Ulotaront reduced spontaneous glutamatergic synaptic transmission and neuronal firing in striatal and hippocampal brain slices, respectively. Interestingly, ulotaront potentiated electrically-evoked excitatory synaptic transmission in both brain regions, suggesting the ability to modulate glutamatergic signaling in a state-dependent manner. Similar striatal effects were also observed with the TAAR1 agonist, RO5166017. Furthermore, we show that ulotaront regulates excitation-inhibition balance in the striatum by specifically modulating glutamatergic, but not GABAergic, spontaneous synaptic events. These findings expand the mechanistic circuit hypothesis of ulotaront and TAAR1 agonists, which may be uniquely positioned to normalize both the excessive dopaminergic tone and regulate abnormal glutamatergic function associated with schizophrenia.

Trace amine-associated receptor 1 (TAAR1) agonism for psychosis: a living systematic review and meta-analysis of human and non-human data

Background

Trace amine-associated receptor 1 (TAAR1) agonism shows promise for treating psychosis, prompting us to synthesise data from human and non-human studies.

Methods

We co-produced a living systematic review of controlled studies examining TAAR1 agonists in individuals (with or without psychosis/schizophrenia) and relevant animal models. Two independent reviewers identified studies in multiple electronic databases (until 17.11.2023), extracted data, and assessed risk of bias. Primary outcomes were standardised mean differences (SMD) for overall symptoms in human studies and hyperlocomotion in animal models. We also examined adverse events and neurotransmitter signalling. We synthesised data with random-effects meta-analyses.

Results

Nine randomised trials provided data for two TAAR1 agonists (ulotaront and ralmitaront), and 15 animal studies for 10 TAAR1 agonists. Ulotaront and ralmitaront demonstrated few differences compared to placebo in improving overall symptoms in adults with acute schizophrenia (N=4 studies, n=1291 participants; SMD=0.15, 95%CI: -0.05, 0.34), and ralmitaront was less efficacious than risperidone (N=1, n=156, SMD=-0.53, 95%CI: -0.86, -0.20). Large placebo response was observed in ulotaront phase-III trials. Limited evidence suggested a relatively benign side-effect profile for TAAR1 agonists, although nausea and sedation were common after a single dose of ulotaront. In animal studies, TAAR1 agonists improved hyperlocomotion compared to control (N=13 studies, k=41 experiments, SMD=1.01, 95%CI: 0.74, 1.27), but seemed less efficacious compared to dopamine D 2 receptor antagonists (N=4, k=7, SMD=-0.62, 95%CI: -1.32, 0.08). Limited human and animal data indicated that TAAR1 agonists may regulate presynaptic dopaminergic signalling.

Conclusions

TAAR1 agonists may be less efficacious than dopamine D 2 receptor antagonists already licensed for schizophrenia. The results are preliminary due to the limited number of drugs examined, lack of longer-term data, publication bias, and assay sensitivity concerns in trials associated with large placebo response. Considering their unique mechanism of action, relatively benign side-effect profile and ongoing drug development, further research is warranted.

Registration

PROSPERO-ID: CRD42023451628.

Up-regulation of the Trace Amine Receptor, TAAR-1, in the Prefrontal Cortex of Individuals Affected by Schizophrenia

BACKGROUND AND HYPOTHESIS

Type-1 trace amine-associated receptors (TAAR1) modulate dopaminergic and glutamatergic neurotransmission and are targeted by novel antipsychotic drugs. We hypothesized that schizophrenia (SCZ) causes adaptive changes in TAAR1 expression in the prefrontal cortex.

STUDY DESIGN

We measured TAAR1 mRNA and protein levels by quantitative PCR and immunoblotting in post-mortem prefrontal cortical samples obtained from 23 individuals affected by SCZ and 23 non-schizophrenic controls (CTRL). Data were correlated with a number of variables in both groups.

STUDY RESULTS

TAAR1 mRNA levels were largely increased in the SCZ prefrontal cortex, and did not correlate with age, age at onset and duration of SCZ, or duration of antipsychotic treatment. For the analysis of TAAR1 protein levels, CTRL and SCZ were divided into 2 subgroups, distinguished by the extent of neuropathological burden. CTRL with low neuropathological burden (LNB) had lower TAAR1 protein levels than CTRL with high neuropathological burden (HNB), whereas no changes were found between LNB and HNB in the SCZ group. TAAR1 protein levels were lower in CTRL with LNB with respect to all SCZ samples or to SCZ samples with LNB. In the SCZ group, levels showed an inverse correlation with the duration of antipsychotic treatment and were higher in individuals treated with second-generation antipsychotics as compared with those treated with first-generation antipsychotics.

CONCLUSIONS

The up-regulation of TAAR1 observed in the SCZ prefrontal cortex supports the development of TAAR1 agonists as new promising drugs in the treatment of SCZ.

TAAR1 agonists improve glycemic control, reduce body weight and modulate neurocircuits governing energy balance and feeding

OBJECTIVE

Metabolic Syndrome, which can be induced or exacerbated by current antipsychotic drugs (APDs), is highly prevalent in schizophrenia patients. Recent preclinical and clinical evidence suggest that agonists at trace amine-associated receptor 1 (TAAR1) have potential as a new treatment option for schizophrenia. Intriguingly, preclinical tudies have also identified TAAR1 as a novel regulator of metabolic control. Here we evaluated the effects of three TAAR1 agonists, including the clinical development candidate ulotaront, on body weight, metabolic parameters and modulation of neurocircuits implicated in homeostatic and hedonic feeding.

METHODS

Effects of TAAR1 agonists (ulotaront, RO5166017 and/or RO5263397) on body weight, food intake and/or metabolic parameters were investigated in rats fed a high-fat diet (HFD) and in a mouse model of diet-induced obesity (DIO). Body weight effects were also determined in a rat and mouse model of olanzapine-, and corticosterone-induced body weight gain, respectively. Glucose tolerance was assessed in lean and diabetic db/db mice and fasting plasma glucose and insulin examined in DIO mice. Effects on gastric emptying were evaluated in lean mice and rats. Drug-induced neurocircuit modulation was evaluated in mice using whole-brain imaging of c-fos protein expression.

RESULTS

TAAR1 agonists improved oral glucose tolerance by inhibiting gastric emptying. Sub-chronic administration of ulotaront in rats fed a HFD produced a dose-dependent reduction in body weight, food intake and liver triglycerides compared to vehicle controls. In addition, a more rapid reversal of olanzapine-induced weight gain and food intake was observed in HFD rats switched to ulotaront or RO5263397 treatment compared to those switched to vehicle. Chronic ulotaront administration also reduced body weight and improved glycemic control in DIO mice, and normalized corticosterone-induced body weight gain in mice. TAAR1 activation increased neuronal activity in discrete homeostatic and hedonic feeding centers located in the dorsal vagal complex and hypothalamus with concurrent activation of several limbic structures.

CONCLUSION

The current data demonstrate that TAAR1 agonists, as a class, not only lack APD-induced metabolic liabilities but can reduce body weight and improve glycemic control in rodent models. The underlying mechanisms likely include TAAR1-mediated peripheral effects on glucose homeostasis and gastric emptying as well as central regulation of energy balance and food intake.

Neurobiology of Stress-Induced Nicotine Relapse

Tobacco smoking is the leading cause of preventable death and disease. Although there are some FAD-approved medicines for controlling smoking, the relapse rate remains very high. Among the factors that could induce nicotine relapse, stress might be the most important one. In the last decades, preclinical studies have generated many new findings that lead to a better understanding of stress-induced relapse of nicotine-seeking. Several molecules such as α3β4 nicotinic acetylcholine receptor, α2-adrenergic receptors, cannabinoid receptor 1, trace amine-associated receptor 1, and neuropeptide systems (corticotropin-releasing factor and its receptors, dynorphine and kappa opioid receptor) have been linked to stress-induced nicotine relapse. In this review, we discuss recent advances in the neurobiology, treatment targets, and potential therapeutics of stress-induced nicotine relapse. We also discuss some factors that may influence stress-induced nicotine relapse and that should be considered in future studies. In the final section, a perspective on some research directions is provided. Further investigation on the neurobiology of stress-induced nicotine relapse will shed light on the development of new medicines for controlling smoking and will help us understand the interactions between the stress and reward systems in the brain.

TAAR1 as an emerging target for the treatment of psychiatric disorders

Trace amines, a group of amines expressed at the nanomolar level in the mammalian brain, can modulate monoamine transmission. The discovery of and the functional research on the trace amine-associated receptors (TAARs), especially the most well-characterized TAAR1, have largely facilitated our understanding of the function of the trace amine system in the brain. TAAR1 is expressed in the mammalian brain at a low level and widely distributed in the monoaminergic system, including the ventral tegmental area and substantial nigra, where the dopamine neurons reside in the mammalian brain. Growing in vitro and in vivo evidence has demonstrated that TAAR1 could negatively modulate monoamine transmission and play a crucial role in many psychiatric disorders, including schizophrenia, substance use disorders, sleep disorders, depression, and anxiety. Notably, in the last two decades, many studies have repeatedly confirmed the pharmacological effects of the selective TAAR1 ligands in various preclinical models of psychiatric disorders. Recent clinical trials of the dual TAAR1 and serotonin receptor agonist ulotaront also revealed a potential efficacy for treating schizophrenia. Here, we review the current understanding of the TAAR1 system and the recent advances in the elucidation of behavioral and physiological properties of TAAR1 agonists evaluated both in preclinical animal models and clinical trials. We also discuss the potential TAAR1-dependent signaling pathways and the cellular mechanisms underlying the inhibitory effects of TAAR1 activation on drug addiction. We conclude that TAAR1 is an emerging target for the treatment of psychiatric disorders.

Emerging trends in antipsychotic and antidepressant drug development: Targeting nonmonoamine receptors and innovative mechanisms

The domain of psychiatric drug development is currently witnessing a notable transformation, with a paramount emphasis on targeting nonmonoamine receptors and exploring inventive mechanisms of action. This paper presents an overview of the ongoing advancements in antipsychotic and antidepressant drug development. Historically, antipsychotics predominantly targeted dopamine receptors, but there is now an escalating interest in drugs that act on alternative receptors, exemplified by the TAAR1 receptor. One noteworthy candidate is Ulotaront (SEP-363856), an agent acting as a TAAR1 agonist with 5-HT1A agonist activity, demonstrating promising outcomes in the treatment of schizophrenia, devoid of extrapyramidal symptoms or metabolic side-effects. Similarly, MIN-101 (Roluperidone) and KarXT are currently in development, with its focus on addressing the symptoms in schizophrenia. In the domain of antidepressants, novel therapeutic approaches have surfaced, such as Auvelity, a Food and Drug Administration (FDA)-approved NMDA receptor antagonist synergistically combined with Bupropion to enhance its effects. Another notable candidate is Zuranolone, operating as a GABA A receptor-positive allosteric modulator, showcasing efficacy in treating major depressive disorder (MDD) and postpartum depression. Additionally, TAK-653 (NBI-1065845) and MJI821 (Onfasprodil) have emerged as potential antidepressants targeting AMPA receptors and NMDA receptor 2B (NR2B) negative allosteric modulation, respectively. This paper underscores the transformative potential of these novel drug candidates in psychiatric treatment and their ability to address cases that were previously treatment-resistant. By focusing on nonmonoamine receptors and introducing innovative mechanisms, these drugs offer a promising prospect of improved outcomes for individuals suffering from schizophrenia and MDD. Thus, sustained attention and dedication to the development of such drugs are essential to augmenting the therapeutic options available for psychiatric patients.

Versatile lactate signaling via HCAR1: a multifaceted GPCR involved in many biological processes

G-coupled protein receptors (GPCRs) are the ultimate refuge of pharmacology and medicine as more than 40% of all marketed drugs are directly targeting these receptors. Through cell surface expression, they are at the forefront of cellular communication with the outside world. Metabolites among the conveyors of this communication are becoming more prominent with the recognition of them as ligands for GPCRs. HCAR1 is a GPCR conveyor of lactate. It is a class A GPCR coupled to Gαi which reduces cellular cAMP along with the downstream Gβγ signaling. It was first found to inhibit lipolysis, and lately has been implicated in diverse cellular processes, including neural activities, angiogenesis, inflammation, vision, cardiovascular function, stem cell proliferation, and involved in promoting pathogenesis for different conditions, such as cancer. Other than signaling from the plasma membrane, HCAR1 shows nuclear localization with different location-biased activities therein. Although different functions for HCAR1 are being discovered, its cell and molecular mechanisms are yet ill understood. Here, we provide a comprehensive review on HCAR1, which covers the literature on the subject, and discusses its importance and relevance in various biological phenomena.

Trace Amine-Associated Receptors and Monoamine-Mediated Regulation of Insulin Secretion in Pancreatic Islets

Currently, metabolic syndrome treatment includes predominantly pharmacological symptom relief and complex lifestyle changes. Trace amines and their receptor systems modulate signaling pathways of dopamine, norepinephrine, and serotonin, which are involved in the pathogenesis of this disorder. Trace amine-associated receptor 1 (TAAR1) is expressed in endocrine organs, and it was revealed that TAAR1 may regulate insulin secretion in pancreatic islet β-cells. For instance, accumulating data demonstrate the positive effect of TAAR1 agonists on the dynamics of metabolic syndrome progression and MetS-associated disease development. The role of other TAARs (TAAR2, TAAR5, TAAR6, TAAR8, and TAAR9) in the islet's function is much less studied. In this review, we summarize the evidence of TAARs' contribution to the metabolic syndrome pathogenesis and regulation of insulin secretion in pancreatic islets. Additionally, by the analysis of public transcriptomic data, we demonstrate that TAAR1 and other TAAR receptors are expressed in the pancreatic islets. We also explore associations between the expression of TAARs mRNA and other genes in studied samples and demonstrate the deregulation of TAARs' functional associations in patients with metabolic diseases compared to healthy donors.

Ulotaront: review of preliminary evidence for the efficacy and safety of a TAAR1 agonist in schizophrenia

Ulotaront is a trace amine-associated receptor 1 (TAAR1) agonist in Phase 3 clinical development for the treatment of schizophrenia. Ulotaront was discovered through a unique, target-agnostic approach optimized to identify drug candidates lacking D2 and 5-HT2A receptor antagonism, while demonstrating an antipsychotic-like phenotypic profile in vivo. The mechanism of action (MOA) of ulotaront is thought to be mediated by agonism at TAAR1 and serotonin 5-HT1A receptors. Ulotaront has completed two Phase 2 trials (4-week acute study and 26-week open-label extension) which led to Breakthrough Therapy Designation from the US Food and Drug Administration for the treatment of schizophrenia. In the double-blind, placebo-controlled, acute study, ulotaront was associated with significant (p < 0.001) improvement in Positive and Negative Syndrome Scale (PANSS) total score (effect size [ES]: 0.45), with improvements vs. placebo also observed across secondary endpoints. Post-hoc analyses of the acute trial revealed additional evidence to support the effect of ulotaront on negative symptoms. In the 4-week study, ulotaront was well-tolerated, with an incidence of adverse events (AEs) numerically lower compared to placebo (45.8% vs. 50.4%; with a number needed to harm [NNH] for individual ulotaront AEs all > 40). The open-label extension demonstrated further improvement across schizophrenia symptoms and confirmed the tolerability of ulotaront, with a 6-month completion rate of 67%. Based on current data, ulotaront shows potential to be a first-in-class TAAR1 agonist for the treatment of schizophrenia with a safety and efficacy profile distinct from current antipsychotics.

Metabolic and cardiovascular benefits and risks of 4-hydroxy guanabenz hydrochloride: α2-adrenoceptor and trace amine-associated receptor 1 ligand

BACKGROUND

α2-adrenoceptor ligands have been investigated as potential therapeutic agents for the treatment of obesity. Our previous studies have shown that guanabenz reduces the body weight of obese rats, presumably through its anorectic action. This demonstrates an additional beneficial effect on selected metabolic parameters, including glucose levels. The purpose of this present research was to determine the activity of guanabenz's metabolite-4-hydroxy guanabenz hydrochloride (4-OH-Guanabenz).

METHODS

We performed in silico analyses, involving molecular docking to targets of specific interest as well as other potential biological targets. In vitro investigations were conducted to assess the selectivity profile of 4-OH-Guanabenz binding to α-adrenoceptors, along with intrinsic activity studies involving α2-adrenoceptors and trace amine-associated receptor 1 (TAAR1). Additionally, the effects of 4-OH-Guanabenz on the body weight of rats and selected metabolic parameters were evaluated using the diet-induced obesity model. Basic safety and pharmacokinetic parameters were also examined.

RESULTS

4-OH-guanabenz is a partial agonist of α2A-adrenoceptor. The calculated EC50 value for it is 316.3 nM. It shows weak agonistic activity at TAAR1 too. The EC50 value for 4-OH-Guanabenz calculated after computer simulation is 330.6 µM. Its primary mode of action is peripheral. The penetration of 4-OH-Guanabenz into the brain is fast (tmax = 15 min), however, with a low maximum concentration of 64.5 ng/g. 4-OH-Guanabenz administered ip at a dose of 5 mg/kg b.w. to rats fed a high-fat diet causes a significant decrease in body weight (approximately 14.8% compared to the baseline weight before treatment), reduces the number of calories consumed by rats, and decreases plasma glucose and triglyceride levels.

CONCLUSIONS

The precise sequence of molecular events within the organism, linking the impact of 4-OH-Guanabenz on α2A-adrenoceptor and TAAR1 with weight reduction and the amelioration of metabolic disturbances, remains an unresolved matter necessitating further investigation. Undoubtedly, the fact that 4-OH-Guanabenz is a metabolite of a well-known drug has considerable importance, which is beneficial from an economic point of view and towards its further development as a drug candidate.

In Vitro Comparison of Ulotaront (SEP-363856) and Ralmitaront (RO6889450): Two TAAR1 Agonist Candidate Antipsychotics

BACKGROUND

Trace amine-associated receptor-1 (TAAR1) agonists have been proposed as potential antipsychotics, with ulotaront and ralmitaront having reached clinical trials. While ulotaront demonstrated efficacy in a recent Phase II trial, a corresponding study studies of ralmitaront failed to show efficacy as a monotherapy or as an adjunct to atypical antipsychotics. In addition to TAAR1 agonism, ulotaront is a partial agonist at the serotonin 1A receptor (5-HT1AR). However, little is known about ralmitaront.

METHODS

We compared ulotaront and ralmitaront at TAAR1, 5-HT1AR, and dopamine D2 using luciferase complementation-based G protein recruitment, cAMP accumulation, and G protein-coupled inward rectifier potassium channel activation assays.

RESULTS

Ralmitaront showed lower efficacy at TAAR1 in G protein recruitment, cAMP accumulation, and GIRK activation assays. Moreover, ralmitaront lacked detectable activity at 5-HT1AR and dopamine D2.

CONCLUSIONS

Compared with ulotaront, ralmitaront shows lower efficacy and slower kinetics at TAAR1 and lacks efficacy at 5-HT1AR. These data may be relevant to understanding differences in clinical profiles of these 2 compounds.

The Expression of Trace Amine-Associated Receptors (TAARs) in Breast Cancer Is Coincident with the Expression of Neuroactive Ligand-Receptor Systems and Depends on Tumor Intrinsic Subtype

Currently, the contribution of trace amine-associated receptors (TAARs) to breast cancer (BC) is recognized, but their associations with various pathological characteristics are not yet understood. There is accumulated transcriptomic data for BC tumors, which are represented in publicly accessible databases. We estimated TAARs' (including TAAR1, TAAR2, TAAR5, TAAR6, TAAR8, and TAAR9) associations with BC stage, grade, and molecular subtypes in these data and identified that the expression of all TAARs was associated with more unfavorable cancer subtypes, including basal-like and HER2-positive tumors. Also, the significant upregulation of all TAARs was demonstrated in circulating tumor cells compared to the metastatic lesions. Considering that co-expressed genes are more likely to be involved in the same biologic processes, we analyzed genes that are co-expressed with TAARs in BC. These gene sets were enriched with the genes of the olfactory transduction pathway and neuroactive ligand-receptor interaction participants. TAARs are co-expressed with G-protein-coupled receptors of monoamine neurotransmitters including dopamine, norepinephrine, and serotonin as well as with other neuroactive ligand-specific receptors. Since TAAR1 is able to modulate the activity of monoamine receptors that are involved in the regulation of BC growth, TAAR1 and potentially other TAARs may be regarded as prospective therapeutic targets for breast cancer.

Negative symptoms in schizophrenia: Newly emerging measurements, pathways, and treatments

The negative symptoms of schizophrenia, which often appear earlier than any other symptom, are prominent and clinically relevant in the majority of patients. As a result, interest in their treatment has increased. Patients who exhibit significant negative symptoms have worse functional outcomes than those without, resulting in impairments in occupational, household, and recreational functioning, as well as difficulties in relationships. Yet treatment with currently available medications does not lead to any significant improvements in this core component of schizophrenia. An increased understanding of the pathophysiology underlying negative symptoms and the discovery of novel treatments that do not directly target dopamine offer the potential to develop therapies that may reduce negative symptoms and increase quality of life for patients. The current article will discuss the impact of negative symptoms, outline current measurement tools for the assessment of negative symptoms, and examine how these measures may be improved. Insights into the neural circuitry underlying negative symptoms will be discussed, and promising targets for the development of effective treatments for these symptoms will be identified. As more prospective, large-scale, randomized studies focus on the effects of treatments on negative symptoms, progress in this area is foreseeable. However, improvements in clinical assessment instruments, a better understanding of the underlying neural mechanisms, development of novel treatments with varied targets, and a greater focus on personalized treatment are all important to produce significant benefits for patients with negative symptoms of schizophrenia.

T1AM/TAAR1 System Reduces Inflammatory Response and β-Amyloid Toxicity in Human Microglial HMC3 Cell Line

Microglial dysfunction is one of the hallmarks and leading causes of common neurodegenerative diseases (NDDs), including Alzheimer's disease (AD) and Parkinson's disease (PD). All these pathologies are characterized by aberrant aggregation of disease-causing proteins in the brain, which can directly activate microglia, trigger microglia-mediated neuroinflammation, and increase oxidative stress. Inhibition of glial activation may represent a therapeutic target to alleviate neurodegeneration. Recently, 3-iodothyronamine (T1AM), an endogenous derivative of thyroid hormone (TH) able to interact directly with a specific GPCR known as trace amine-associated receptor 1 (TAAR1), gained interest for its ability to promote neuroprotection in several models. Nevertheless, T1AM's effects on microglial disfunction remain still elusive. In the present work we investigated whether T1AM could inhibit the inflammatory response of human HMC3 microglial cells to LPS/TNFα or β-amyloid peptide 25-35 (Aβ25-35) stimuli. The results of ELISA and qPCR assays revealed that T1AM was able to reduce microglia-mediated inflammatory response by inhibiting the release of proinflammatory factors, including IL-6, TNFα, NF-kB, MCP1, and MIP1, while promoting the release of anti-inflammatory mediators, such as IL-10. Notably, T1AM anti-inflammatory action in HMC3 cells turned out to be a TAAR1-mediated response, further increasing the relevance of the T1AM/TAAR1 system in the management of NDDs.

Unlocking the Therapeutic Potential of Ulotaront as a Trace Amine-Associated Receptor 1 Agonist for Neuropsychiatric Disorders

All antipsychotics currently used in clinic block D2 dopamine receptors. Trace amine-associated receptor 1 is emerging as a new therapeutic target for schizophrenia and several other neuropsychiatric disorders. SEP-363856 (International Nonproprietary Name: Ulotaront) is an investigational antipsychotic drug with a novel mechanism of action that does not involve antagonism of dopamine D2 receptors. Ulotaront is an agonist of trace amine-associated receptor 1 and serotonin 5-HT1A receptors, but can modulate dopamine neurotransmission indirectly. In 2019, the United States Food and Drug Administration granted Breakthrough Therapy Designation for ulotaront for the treatment of schizophrenia. Phase 2 clinical studies indicated that ulotaront can reduce both positive and negative symptoms of schizophrenia without causing the extrapyramidal or metabolic side effects that are inherent to most currently used antipsychotics. At present, it is in phase 3 clinical development for the treatment of schizophrenia and is expected to be introduced into clinical practice in 2023-2024. Clinical studies evaluating the potential efficacy of ulotaront in Parkinson's disease psychosis, generalized anxiety disorder, and major depressive disorder have also been started. The aim of this scoping review is to summarize all currently available preclinical and clinical evidence on the utility of ulotaront in the treatment of schizophrenia. Here, we show the main characteristics and distinctive features of this drug. Perspectives and limitations on the potential use of ulotaront in the pharmacotherapy of several other neuropsychiatric disorders are also discussed.

Activation of trace amine-associated receptor 1 (TAAR1) transiently reduces alcohol drinking in socially housed mice

Alcohol dependence is characterized by the abnormal release of dopamine in the brain reward-related areas. Trace amine-associated receptor 1 (TAAR1) is a G protein-coupled receptor that negatively regulates dopamine neurotransmission and thus is a promising target in the treatment of drug addiction. However, the role of TAAR1 in the regulation of alcohol abuse remains understudied. Here, we assessed the effect of TAAR1 activation on alcohol drinking behaviours of C57Bl/6J female mice housed in IntelliCages. The animals were administered with either vehicle or TAAR1 full selective agonist, RO5256390, and tested for alcohol consumption, alcohol preference and motivation for alcohol seeking. We found that mice with the highest preference for alcohol (high drinkers) in the RO5256390 group consumed less alcohol and had lower alcohol preference in comparison with high drinkers in the vehicle group, during 20 h of free alcohol access (FAA). We also found decreased alcohol consumption and alcohol preference comparing all animals in the RO5256390 to all animals in the vehicle group, during 20 h of FAA performed after the abstinence. These effects of RO5256390 lasted for the first 24 h after administration that roughly corresponded to the compound level in the brain, measured by mass spectrometry. Finally, we found that administration of RO5256390 may attenuate motivation for alcohol seeking. Taken together, our findings reveal that activation of TAAR1 may transiently reduce alcohol drinking; thus, TAAR1 is a promising target for the treatment of alcohol abuse and relapse.

Increased Metabolic Potential, Efficacy, and Safety of Emerging Treatments in Schizophrenia

Patients with schizophrenia experience a broad range of detrimental health outcomes resulting from illness severity, heterogeneity of disease, lifestyle behaviors, and adverse effects of antipsychotics. Because of these various factors, patients with schizophrenia have a much higher risk of cardiometabolic abnormalities than people without psychiatric illness. Although exposure to many antipsychotics increases cardiometabolic risk factors, mortality is higher in patients who are not treated versus those who are treated with antipsychotics. This indicates both direct and indirect benefits of adequately treated illness, as well as the need for beneficial medications that result in fewer cardiometabolic risk factors and comorbidities. The aim of the current narrative review was to outline the association between cardiometabolic dysfunction and schizophrenia, as well as discuss the confluence of factors that increase cardiometabolic risk in this patient population. An increased understanding of the pathophysiology of schizophrenia has guided discovery of novel treatments that do not directly target dopamine and that not only do not add, but may potentially minimize relevant cardiometabolic burden for these patients. Key discoveries that have advanced the understanding of the neural circuitry and pathophysiology of schizophrenia now provide possible pathways toward the development of new and effective treatments that may mitigate the risk of metabolic dysfunction in these patients. Novel targets and preclinical and clinical data on emerging treatments, such as glycine transport inhibitors, nicotinic and muscarinic receptor agonists, and trace amine-associated receptor-1 agonists, offer promise toward relevant therapeutic advancements. Numerous areas of investigation currently exist with the potential to considerably progress our knowledge and treatment of schizophrenia.

Dopamine Transporter Deficient Rodents: Perspectives and Limitations for Neuroscience

The key element of dopamine (DA) neurotransmission is undoubtedly DA transporter (DAT), a transmembrane protein responsible for the synaptic reuptake of the mediator. Changes in DAT's function can be a key mechanism of pathological conditions associated with hyperdopaminergia. The first strain of gene-modified rodents with a lack of DAT were created more than 25 years ago. Such animals are characterized by increased levels of striatal DA, resulting in locomotor hyperactivity, increased levels of motor stereotypes, cognitive deficits, and other behavioral abnormalities. The administration of dopaminergic and pharmacological agents affecting other neurotransmitter systems can mitigate those abnormalities. The main purpose of this review is to systematize and analyze (1) known data on the consequences of changes in DAT expression in experimental animals, (2) results of pharmacological studies in these animals, and (3) to estimate the validity of animals lacking DAT as models for discovering new treatments of DA-related disorders.

G protein-coupled receptors in neurodegenerative diseases and psychiatric disorders

Neuropsychiatric disorders are multifactorial disorders with diverse aetiological factors. Identifying treatment targets is challenging because the diseases are resulting from heterogeneous biological, genetic, and environmental factors. Nevertheless, the increasing understanding of G protein-coupled receptor (GPCR) opens a new possibility in drug discovery. Harnessing our knowledge of molecular mechanisms and structural information of GPCRs will be advantageous for developing effective drugs. This review provides an overview of the role of GPCRs in various neurodegenerative and psychiatric diseases. Besides, we highlight the emerging opportunities of novel GPCR targets and address recent progress in GPCR drug development.

A multicenter, double-blind, placebo-controlled, randomized, Phase 1b crossover trial comparing two doses of ulotaront with placebo in the treatment of narcolepsy-cataplexy

BACKGROUND

Ulotaront (SEP-363856) is a novel agonist at trace amine-associated receptor 1 and serotonin 5-HT_1A receptors in clinical development for the treatment of schizophrenia. Previous studies demonstrated ulotaront suppresses rapid eye movement (REM) sleep in both rodents and healthy volunteers. We assessed acute and sustained treatments of ulotaront on REM sleep and symptoms of cataplexy and alertness in subjects with narcolepsy-cataplexy.

METHODS

In a multicenter, double-blind, placebo-controlled, randomized, 3-way crossover study, ulotaront was evaluated in 16 adults with narcolepsy-cataplexy. Two oral doses of ulotaront (25 mg and 50 mg) were administered daily for 2 weeks and compared with matching placebo (6-treatment sequence, 3-period, 3-treatment).

RESULTS

Acute treatment with both 25 mg and 50 mg of ulotaront reduced minutes spent in nighttime REM compared to placebo. A sustained 2-week administration of both doses of ulotaront reduced the mean number of short-onset REM periods (SOREMPs) during daytime multiple sleep latency test (MSLT) compared to placebo. Although cataplexy events decreased from the overall mean baseline during the 2-week treatment period, neither dose of ulotaront statistically separated from placebo (p = 0.76, 25 mg; p = 0.82, 50 mg), and no significant improvement in patient and clinician measures of sleepiness from baseline to end of the 2-week treatment period occurred in any treatment group.

CONCLUSIONS

Acute and sustained treatment with ulotaront reduced nighttime REM duration and daytime SOREMPs, respectively. The effect of ulotaront on suppression of REM did not demonstrate a statistical or clinically meaningful effect in narcolepsy-cataplexy.

REGISTRATION

ClinicalTrials.gov identifier: NCT05015673.

Neural mechanism of acute stress regulation by trace aminergic signalling in the lateral habenula in male mice

Stress management is necessary for vertebrate survival. Chronic stress drives depression by excitation of the lateral habenula (LHb), which silences dopaminergic neurons in the ventral tegmental area (VTA) via GABAergic neuronal projection from the rostromedial tegmental nucleus (RMTg). However, the effect of acute stress on this LHb-RMTg-VTA pathway is not clearly understood. Here, we used fluorescent in situ hybridisation and in vivo electrophysiology in mice to show that LHb aromatic L-amino acid decarboxylase-expressing neurons (D-neurons) are activated by acute stressors and suppress RMTg GABAergic neurons via trace aminergic signalling, thus activating VTA dopaminergic neurons. We show that the LHb regulates RMTg GABAergic neurons biphasically under acute stress. This study, carried out on male mice, has elucidated a molecular mechanism in the efferent LHb-RMTg-VTA pathway whereby trace aminergic signalling enables the brain to manage acute stress by preventing the hypoactivity of VTA dopaminergic neurons.

Efficacy, safety, and tolerability of ulotaront (SEP-363856, a trace amine-associated receptor 1 agonist) for the treatment of schizophrenia and other mental disorders with similar pathophysiology: a systematic review of preclinical and clinical trials

INTRODUCTION

Schizophrenia is a mental illness that can disrupt emotions, perceptions, cognition, and reduce quality of life. The classical approach to treat schizophrenia uses typical and atypical antipsychotics; however, limitations include low efficacy in mitigating negative symptoms and cognitive dysfunctions, and a range of adverse effects. Evidence has accumulated on trace amine-associated receptor 1 (TAAR1) as a novel therapeutic target for treating schizophrenia. This systematic review investigates the available evidence on a TAAR1 agonist, ulotaront, as a treatment for schizophrenia.

METHODS

A systematic search was conducted on PubMed/MEDLINE, and Ovid databases for English-published articles from inception to December 18, 2022. Literature focusing on the association between ulotaront and schizophrenia were evaluated based on an inclusion/exclusion criterion. Selected studies were assessed for risk of bias, using Cochrane Collaboration tool, and summarized in a table to generate discussion topics.

RESULTS

Three clinical, two comparative, and five preclinical studies examining ulotaront's pharmacology, tolerability and safety, and/or efficacy were identified. Results indicate that ulotaront has a differing adverse effects profile from other antipsychotics, may mitigate metabolic-related adverse effects commonly associated with antipsychotics, and may be effective for treating positive and negative symptoms.

CONCLUSIONS

Findings from available literature present ulotaront as a potential and promising alternative treatment method for schizophrenia. Despite this, our results were limited due to lack of clinical trials on ulotaront's long-term efficacy and mechanisms of action. Future research should focus on these limitations to elucidate ulotaront's efficacy and safety for the treatment of schizophrenia and other mental disorders with similar pathophysiology.

Dopamine Dynamics and Neurobiology of Non-Response to Antipsychotics, Relevance for Treatment Resistant Schizophrenia: A Systematic Review and Critical Appraisal

Treatment resistant schizophrenia (TRS) is characterized by a lack of, or suboptimal response to, antipsychotic agents. The biological underpinnings of this clinical condition are still scarcely understood. Since all antipsychotics block dopamine D2 receptors (D2R), dopamine-related mechanisms should be considered the main candidates in the neurobiology of antipsychotic non-response, although other neurotransmitter systems play a role. The aims of this review are: (i) to recapitulate and critically appraise the relevant literature on dopamine-related mechanisms of TRS; (ii) to discuss the methodological limitations of the studies so far conducted and delineate a theoretical framework on dopamine mechanisms of TRS; and (iii) to highlight future perspectives of research and unmet needs. Dopamine-related neurobiological mechanisms of TRS may be multiple and putatively subdivided into three biological points: (1) D2R-related, including increased D2R levels; increased density of D2Rs in the high-affinity state; aberrant D2R dimer or heteromer formation; imbalance between D2R short and long variants; extrastriatal D2Rs; (2) presynaptic dopamine, including low or normal dopamine synthesis and/or release compared to responder patients; and (3) exaggerated postsynaptic D2R-mediated neurotransmission. Future points to be addressed are: (i) a more neurobiologically-oriented phenotypic categorization of TRS; (ii) implementation of neurobiological studies by directly comparing treatment resistant vs. treatment responder patients; (iii) development of a reliable animal model of non-response to antipsychotics.

30th Annual GP2A Medicinal Chemistry Conference

The Group for the Promotion of Pharmaceutical Chemistry in Academia (GP2A) held their 30th annual conference in August 2022 in Trinity College Dublin, Ireland. There were 9 keynote presentations, 10 early career researcher presentations and 41 poster presentations.

Chemogenetic Enhancement of cAMP Signaling Renders Hippocampal Synaptic Plasticity Resilient to the Impact of Acute Sleep Deprivation

Sleep facilitates memory storage and even brief periods of sleep loss lead to impairments in memory, particularly memories that are hippocampus dependent. In previous studies, we have shown that the deficit in memory seen after sleep loss is accompanied by deficits in synaptic plasticity. Our previous work has also found that sleep deprivation (SD) is associated with reduced levels of cyclic adenosine monophosphate (cAMP) in the hippocampus and that the reduction of cAMP mediates the diminished memory observed in sleep-deprived animals. Based on these findings, we hypothesized that cAMP acts as a mediator for not only the cognitive deficits caused by sleep deprivation, but also the observed deficits in synaptic plasticity. In this study, we expressed the heterologous Drosophila melanogaster Gαs-protein-coupled octopamine receptor (DmOctβ1R) in mouse hippocampal neurons. This receptor is selectively activated by the systemically injected ligand (octopamine), thus allowing us to increase cAMP levels in hippocampal neurons during a 5-h sleep deprivation period. Our results show that chemogenetic enhancement of cAMP during the period of sleep deprivation prevents deficits in a persistent form of long-term potentiation (LTP) that is induced at the Schaffer collateral synapses in the hippocampal CA1 region. We also found that elevating cAMP levels in either the first or second half of sleep deprivation successfully prevented LTP deficits. These findings reveal that cAMP-dependent signaling pathways are key mediators of sleep deprivation at the synaptic level. Targeting these pathways could be useful in designing strategies to prevent the impact of sleep loss.

Biological evaluation and in silico studies of novel compounds as potent TAAR1 agonists that could be used in schizophrenia treatment

Introduction: Schizophrenia is a serious mental illness that requires effective treatment with minimal adverse effects. As preclinical and clinical research progresses, trace amine-associated receptor 1 (TAAR1) is becoming a potential new target for the treatment of schizophrenia. Methods: We used molecular docking and molecular dynamics (MD) simulations to discover TAAR1 agonists. The agonistic or inhibitory effects of compounds on TAAR1, 5-HT1A, 5-HT2A, and dopamine D₂-like receptors were determined. We used an MK801-induced schizophrenia-like behavior model to assess the potential antipsychotic effects of compounds. We also performed a catalepsy assay to detect the adverse effects. To evaluate the druggability of the compounds, we conducted evaluations of permeability and transporter substrates, liver microsomal stability in vitro, human ether-à-go-go-related gene (hERG), pharmacokinetics, and tissue distribution. Results: We discovered two TAAR1 agonists: compounds 50A and 50B. The latter had high TAAR1 agonistic activity but no agonistic effect on dopamine D₂-like receptors and demonstrated superior inhibition of MK801-induced schizophrenia-like behavior in mice. Interestingly, 50B had favorable druggability and the ability to penetrate the blood-brain barrier (BBB) without causing extrapyramidal symptoms (EPS), such as catalepsy in mice. Conclusion: These results demonstrate the potential beneficial role of TAAR1 agonists in the treatment of schizophrenia. The discovery of a structurally novel TAAR1 agonist (50B) may provide valuable assistance in the development of new treatments for schizophrenia.

Trace amine-associated receptor 1 (TAAR1) agonism as a new treatment strategy for schizophrenia and related disorders

Schizophrenia remains a major health burden, highlighting the need for new treatment approaches. We consider the potential for targeting the trace amine (TA) system. We first review genetic, preclinical, and clinical evidence for the role of TAs in the aetiopathology of schizophrenia. We then consider how the localisation and function of the trace amine-associated receptor 1 (TAAR1) position it to modulate key brain circuits for the disorder. Studies in rodents using Taar1 knockout (TAAR1-KO) and overexpression models show that TAAR1 agonism inhibits midbrain dopaminergic and serotonergic activity, and enhances prefrontal glutamatergic function. TAAR1 agonists also reduce hyperactivity, attenuate prepulse inhibition (PPI) deficits and social withdrawal, and improve cognitive measures in animal models. Finally, we consider findings from clinical trials of TAAR1 agonists and how this approach may address psychotic and negative symptoms, tolerability issues, and other unmet needs in the treatment of schizophrenia.

Effects of acute and chronic administration of trace amine-associated receptor 1 (TAAR1) ligands on in vivo excitability of central monoamine-secreting neurons in rats

Trace amine-associated receptor 1 (TAAR1) has been recently identified as a target for the future antidepressant, antipsychotic, and anti-addiction drugs. Full (e.g. RO5256390) and partial (e.g. RO5263397) TAAR1 agonists showed antidepressant-, antipsychotic- and anti-addiction-like behavioral effects in rodents and primates. Acute RO5256390 suppressed, and RO5263397 stimulated serotonin (5-HT) neurons of the dorsal raphe nucleus (DRN) and dopamine neurons of the ventral tegmental area (VTA) in brain slices, suggesting that the behavioral effects of TAAR1 ligands involve 5-HT and dopamine. For more comprehensive testing of this hypothesis, we examined acute and chronic effects of RO5256390 and RO5263397 on monoamine neurons in in vivo conditions. Excitability of 5-HT neurons of the DRN, noradrenaline neurons of the locus coeruleus (LC), and dopamine neurons of the VTA was assessed using single-unit electrophysiology in anesthetized rats. For acute experiments, RO5256390 and RO5263397 were administered intravenously; neuronal excitability after RO5256390 and RO5263397 administration was compared to the basal activity of the same neuron. For chronic experiments, RO5256390 was administered orally for fourteen days prior to electrophysiological assessments. The neuronal excitability in RO5256390-treated rats was compared to vehicle-treated controls. We found that acute RO5256390 inhibited 5-HT and dopamine neurons. This effect of RO5256390 was reversed by the subsequent and prevented by the earlier administration of RO5263397. Acute RO5256390 and RO5263397 did not alter the excitability of LC noradrenaline neurons in a statistically significant way. Chronic RO5256390 increased excitability of 5-HT neurons of the DRN and dopamine neurons of the VTA. In conclusion, the putative antidepressant and antipsychotic effects of TAAR1 ligands might be mediated, at least in part, via the modulation of excitability of central 5-HT and dopamine neurons.

TAAR1 dependent and independent actions of the potential antipsychotic and dual TAAR1/5-HT1A receptor agonist SEP-383856

SEP-383856 (SEP-856) is a novel antipsychotic under clinical development. It displays a unique pattern of receptor interaction, with only weak (partial agonist) activity at dopamine D₂ receptors, yet more potent agonist activity at the trace amine associated receptor (TAAR1) and 5-hydroxytryptamine 1 A receptor (5-HT_1A). Nonetheless, these observations await independent confirmation and more detailed characterization of the in vitro and in vivo actions of SEP-856 at TAAR1 and 5-HT_1A receptors would be instructive. Herein, we employed luminescence complementation technology in heterologous live cell systems, confocal microscopy, voltage clamp electrophysiology, behavioral readouts and TAAR1 knockout (KO) mice to study SEP-856 in further detail. We provide evidence for the ability of SEP-856 to activate TAAR1 at the surface plasma membrane, and show that this interaction results in Gα_s recruitment (pEC₅₀: 6.08 ± 0.22 E_MAX: 96.41% ± 15.26) and by extension, to G-protein inwardly rectifying potassium (GIRK) channel activation. Using TAAR1-KO mice, we find TAAR1 to be indispensable for SEP-856 control of body temperature, baseline locomotion reduction and for "antipsychotic-like" efficacy as characterized by a reversal of dizocilipine (MK-801) mediated disruption of pre-pulse inhibition. Conversely, the inhibition by SEP-856 of MK-801 induced locomotion was unaffected in TAAR1 KO mice. SEP-856 behaved as a low-potency, partial agonist at the 5-HT_1A receptor, while it partially inhibited recruitment of D₂ receptor-coupled Gα and GIRK by DA and acted as a weak partial agonist with low potency at the same receptor when applied alone. Our findings corroborate and extend previous observations on the molecular substrates engaged by this unique, dual TAAR1/5-HT_1A receptor agonist and potential antipsychotic that could prove to have major advantages in the treatment of schizophrenia and other psychotic disorders.

Enhanced Aggression, Reduced Self-Grooming Behavior and Altered 5-HT Regulation in the Frontal Cortex in Mice Lacking Trace Amine-Associated Receptor 1 (TAAR1)

The Trace Amine-Associated Receptor 1 (TAAR1) is one of the six functional receptors belonging to the family of monoamine-related G protein-coupled receptors (TAAR1-TAAR9) found in humans. However, the exact biological mechanisms of TAAR1 central and peripheral action remain to be fully understood. TAAR1 is widely expressed in the prefrontal cortex and several limbic regions, interplaying with the dopamine system to modulate the reward circuitry. Recent clinical trials suggest the efficacy of TAAR1 agonists as potential novel antipsychotic agents. Here, we characterize behavioral and neurochemical phenotypes of TAAR1 knockout mice, focusing on aggression and self-grooming behavior that both strongly depend on the monoaminergic signaling and cortico-striatal and cortico-limbic circuits. Overall, we report increased aggression in these knockout mice in the resident-intruder test, accompanied by reduced self-grooming behavior in the novelty-induced grooming test, and by higher cortical serotonin (5-HT) tissue levels. Further studies are necessary to explore whether TAAR1-based therapies can become potential novel treatments for a wide range of neuropsychiatric disorders associated with aggression.

Class A and C GPCR Dimers in Neurodegenerative Diseases

Neurodegenerative diseases affect over 30 million people worldwide with an ascending trend. Most individuals suffering from these irreversible brain damages belong to the elderly population, with onset between 50 and 60 years. Although the pathophysiology of such diseases is partially known, it remains unclear upon which point a disease turns degenerative. Moreover, current therapeutics can treat some of the symptoms but often have severe side effects and become less effective in long-term treatment. For many neurodegenerative diseases, the involvement of G proteincoupled receptors (GPCRs), which are key players of neuronal transmission and plasticity, has become clearer and holds great promise in elucidating their biological mechanism. With this review, we introduce and summarize class A and class C GPCRs, known to form heterodimers or oligomers to increase their signalling repertoire. Additionally, the examples discussed here were shown to display relevant alterations in brain signalling and had already been associated with the pathophysiology of certain neurodegenerative diseases. Lastly, we classified the heterodimers into two categories of crosstalk, positive or negative, for which there is known evidence.

Selective TAAR1 agonists induce conditioned taste aversion

RATIONALE

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.

OBJECTIVES

Here, we evaluated whether the selective TAAR1 full agonist RO5166017 and partial agonist RO5263397 could induce conditioned taste aversion (CTA).

RESULTS

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.

CONCLUSIONS

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.

A New Treatment Paradigm: Targeting Trace Amine-Associated Receptor 1 (TAAR1) in Schizophrenia

This continuing education supplement is jointly provided by Medical Education Resources and CMEology. The supplement is supported by an independent educational grant from Sunovion Pharmaceuticals Inc. It was edited and peer reviewed by the Journal of Clinical Psychopharmacology.After reviewing the learning objectives and reading the supplement, please complete the Activity Evaluation/Credit Request form online at https://www.cmesurvey.site/TAAR1.

ABSTRACT

All currently available antipsychotics work via essentially the same mechanism: by antagonizing the dopamine D2 receptor. However, schizophrenia is an extremely heterogeneous condition, and antipsychotics do not adequately control symptoms for all patients. Negative and cognitive symptoms are especially difficult to manage with existing medications. Therefore, antipsychotic agents with novel mechanisms of action are urgently needed. Recently, a phase 2 clinical trial and extension study demonstrated that, relative to placebo, the trace amine-associated receptor 1 (TAAR1) agonist ulotaront was effective at controlling the positive, negative, and cognitive symptoms of schizophrenia. In addition, ulotaront seems to lack the weight gain, metabolic issues, and extrapyramidal symptoms associated with traditional antipsychotics. This agent is currently undergoing multiple phase 3 trials for the treatment of schizophrenia. Another TAAR1 agonist, ralmitaront, is being investigated for the treatment of schizophrenia and schizoaffective disorders. Two phase 2 clinical trials are underway, evaluating ralmitaront both as a monotherapy and an add-on therapy to traditional antipsychotics. In this supplement, we review the biologic, preclinical, and clinical data available for TAAR1 agonists, so that if and when they are approved for the treatment of schizophrenia, psychiatry specialists will be ready to use them to optimize patient outcomes. We also briefly review other emerging therapies in late-stage development for the treatment of schizophrenia.

Improved cognitive performance in trace amine-associated receptor 5 (TAAR5) knock-out mice

Trace amine-associated receptors (TAARs) are a family of G protein-coupled receptors present in mammals in the brain and several peripheral organs. Apart from its olfactory role, TAAR5 is expressed in the major limbic brain areas and regulates brain serotonin functions and emotional behaviours. However, most of its functions remain undiscovered. Given the role of serotonin and limbic regions in some aspects of cognition, we used a temporal decision-making task to unveil a possible role of TAAR5 in cognitive processes. We found that TAAR5 knock-out mice showed a generally better performance due to a reduced number of errors and displayed a greater rate of improvement at the task than WT littermates. However, task-related parameters, such as time accuracy and uncertainty have not changed significantly. Overall, we show that TAAR5 modulates specific domains of cognition, highlighting a new role in brain physiology.

Enhancer Regulation of Dopaminergic Neurochemical Transmission in the Striatum

The trace amine-associated receptor 1 (TAAR1) is a Gs protein-coupled, intracellularly located metabotropic receptor. Trace and classic amines, amphetamines, act as agonists on TAAR1; they activate downstream signal transduction influencing neurotransmitter release via intracellular phosphorylation. Our aim was to check the effect of the catecholaminergic activity enhancer compound ((−)BPAP, (R)-(−)-1-(benzofuran-2-yl)-2-propylaminopentane) on neurotransmitter release via the TAAR1 signaling. Rat striatal slices were prepared and the resting and electrical stimulation-evoked [³H]dopamine release was measured. The releaser (±)methamphetamine evoked non-vesicular [³H]dopamine release in a TAAR1-dependent manner, whereas (−)BPAP potentiated [³H]dopamine release with vesicular origin via TAAR1 mediation. (−)BPAP did not induce non-vesicular [³H]dopamine release. N-Ethylmaleimide, which inhibits SNARE core complex disassembly, potentiated the stimulatory effect of (−)BPAP on vesicular [³H]dopamine release. Subsequent analyses indicated that the dopamine-release stimulatory effect of (−)BPAP was due to an increase in PKC-mediated phosphorylation. We have hypothesized that there are two binding sites present on TAAR1, one for the releaser and one for the enhancer compounds, and they activate different PKC-mediated phosphorylation leading to the evoking of non-vesicular and vesicular dopamine release. (−)BPAP also increased VMAT2 operation enforcing vesicular [³H]dopamine accumulation and release. Vesicular dopamine release promoted by TAAR1 evokes activation of D2 dopamine autoreceptor-mediated presynaptic feedback inhibition. In conclusion, TAAR1 possesses a triggering role in both non-vesicular and vesicular dopamine release, and the mechanism of action of (−)BPAP is linked to the activation of TAAR1 and the signal transduction attached.

Trace Amine Associate Receptor 1 (TAAR1) as a New Target for the Treatment of Cognitive Dysfunction in Alzheimer's Disease

Worldwide, approximately 27 million people are affected by Alzheimer’s disease (AD). AD pathophysiology is believed to be caused by the deposition of the β-amyloid peptide (Aβ). Aβ can reduce long-term potentiation (LTP), a form of synaptic plasticity that is closely associated with learning and memory and involves postsynaptic glutamate receptor phosphorylation and trafficking. Moreover, Aβ seems to be able to reduce glutamatergic transmission by increasing the endocytosis of NMDA receptors. Trace amines (TAs) are biogenic amines that are structurally similar to monoamine neurotransmitters. TAs bind to G protein-coupled receptors, called TAARs (trace amine-associated receptors); the best-studied member of this family, TAAR1, is distributed in the cortical and limbic structures of the CNS. It has been shown that the activation of TAAR1 can rescue glutamatergic hypofunction and that TAAR1 can modulate glutamate NMDA receptor-related functions in the frontal cortex. Several lines of evidence also suggest the pro-cognitive action of TAAR1 agonists in various behavioural experimental protocols. Thus, we studied, in vitro, the role of the TAAR1 agonist RO5256390 on basal cortical glutamatergic transmission and tested its effect on Aβ-induced dysfunction. Furthermore, we investigated, in vivo, the role of TAAR1 in cognitive dysfunction induced by Aβ infusion in Aβ-treated mice. In vitro data showed that Aβ 1–42 significantly decreased NMDA cell surface expression while the TAAR1 agonist RO5256390 promoted their membrane insertion in cortical cells. In vivo, RO5256390 showed a mild pro-cognitive effect, as demonstrated by the better performance in the Y maze test in mice treated with Aβ. Further studies are needed to better understand the interplay between TAAR1/Aβ and glutamatergic signalling, in order to evaluate the eventual beneficial effect in different experimental paradigms and animal models. Taken together, our data indicate that TAAR1 agonism may provide a novel therapeutic approach in the treatments of disorders involving Aβ-induced cognitive impairments, such as AD.