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Molecular Psychiatry Apr 2022Silencing of dopamine transporter (DAT), a main controlling factor of dopaminergic signaling, results in biochemical and behavioral features characteristic for...
Silencing of dopamine transporter (DAT), a main controlling factor of dopaminergic signaling, results in biochemical and behavioral features characteristic for neuropsychiatric diseases with presumed hyperdopaminergia including schizophrenia, attention deficit hyperactivity disorder (ADHD), bipolar disorder, and obsessive-compulsive disorder (OCD). Investigation of DAT silencing thus provides a transdiagnostic approach towards a systems-level understanding of common underlying pathways. Using a high-field multimodal imaging approach and a highly sensitive cryogenic coil, we integrated structural, functional and metabolic investigations in tandem with behavioral assessments on a newly developed preclinical rat model, comparing DAT homozygous knockout (DAT-KO, N = 14), heterozygous knockout (N = 8) and wild-type male rats (N = 14). We identified spatially distributed structural and functional brain alterations encompassing motor, limbic and associative loops that demonstrated strong behavioral relevance and were highly consistent across imaging modalities. DAT-KO rats manifested pronounced volume loss in the dorsal striatum, negatively correlating with cerebellar volume increase. These alterations were associated with hyperlocomotion, repetitive behavior and loss of efficient functional small-world organization. Further, prefrontal and midbrain regions manifested opposite changes in functional connectivity and local network topology. These prefrontal disturbances were corroborated by elevated myo-inositol levels and increased volume. To conclude, our imaging genetics approach provides multimodal evidence for prefrontal-midbrain decoupling and striato-cerebellar neuroplastic compensation as two key features of constitutive DAT blockade, proposing them as transdiagnostic mechanisms of hyperdopaminergia. Thus, our study connects developmental DAT blockade to systems-level brain changes, underlying impaired action inhibition control and resulting in motor hyperactivity and compulsive-like features relevant for ADHD, schizophrenia and OCD.
Topics: Animals; Attention Deficit Disorder with Hyperactivity; Brain; Dopamine Plasma Membrane Transport Proteins; Hyperkinesis; Male; Mesencephalon; Rats
PubMed: 35246636
DOI: 10.1038/s41380-022-01471-4 -
International Journal of Molecular... Jun 2023Alterations in dopamine neurotransmission are associated with obesity and food preferences. Otsuka Long-Evans Tokushima Fatty (OLETF) rats that lack functional...
Alterations in dopamine neurotransmission are associated with obesity and food preferences. Otsuka Long-Evans Tokushima Fatty (OLETF) rats that lack functional cholecystokinin receptor type-1 (CCK-1R), due to a natural mutation, exhibit impaired satiation, are hyperphagic, and become obese. In addition, compared to lean control Long-Evans Tokushima (LETO) rats, OLETF rats have pronounced avidity for over-consuming palatable sweet solutions, have greater dopamine release to psychostimulants, reduced dopamine 2 receptor (D2R) binding, and exhibit increased sensitivity to sucrose reward. This supports altered dopamine function in this strain and its general preference for palatable solutions such as sucrose. In this study, we examined the relationship between OLETF's hyperphagic behavior and striatal dopamine signaling by investigating basal and amphetamine stimulated motor activity in prediabetic OLETF rats before and after access to sucrose solution (0.3 M) compared to non-mutant control LETO rats, as well as availability of dopamine transporter (DAT) using autoradiography. In the sucrose tests, one group of OLETF rats received ad libitum access to sucrose while the other group received an amount of sucrose equal to that consumed by the LETO. OLETFs with ad libitum access consumed significantly more sucrose than LETOs. Sucrose exerted a biphasic effect on basal activity in both strains, i.e., reduced activity for 1 week followed by increased activity in weeks 2 and 3. Basal locomotor activity was reduced (-17%) in OLETFs prior to sucrose, compared to LETOs. Withdrawal of sucrose resulted in increased locomotor activity in both strains. The magnitude of this effect was greater in OLETFs and the activity was increased in restricted compared to ad-libitum-access OLETFs. Sucrose access augmented AMPH-responses in both strains with a greater sensitization to AMPH during week 1, an effect that was a function of the amount of sucrose consumed. One week of sucrose withdrawal sensitized AMPH-induced ambulatory activity in both strains. In OLETF with restricted access to sucrose, withdrawal resulted in no further sensitization to AMPH. DAT availability in the nucleus accumbens shell was significantly reduced in OLETF compared with aged-matched LETO. Together, these findings show that OLETF rats have reduced basal DA transmission and a heightened response to natural and pharmacological stimulation.
Topics: Animals; Rats; Dopamine; Dopamine Plasma Membrane Transport Proteins; Obesity; Rats, Inbred OLETF; Rats, Long-Evans; Receptors, Cholecystokinin; Sucrose
PubMed: 37298724
DOI: 10.3390/ijms24119773 -
NeuroImage. Clinical 2021To evaluate possible differences between brain dopamine transporter (DAT) binding in a group of symptomatic parkinsonism patients without dopaminergic degeneration and...
OBJECTIVE
To evaluate possible differences between brain dopamine transporter (DAT) binding in a group of symptomatic parkinsonism patients without dopaminergic degeneration and healthy individuals.
BACKGROUND
Dopaminergic neuroimaging studies of Parkinson's disease (PD) have often used control groups formed from symptomatic patients with apparently normal striatal dopamine function. We sought to investigate whether symptomatic patients can be used to represent dopaminergically normal healthy controls.
METHODS
Forty healthy elderly individuals were scanned with DAT [I]FP-CIT SPECT and compared to 69 age- and sex-matched symptomatic patients with nondegenerative conditions (including essential tremor, drug-induced parkinsonism and vascular parkinsonism). An automated region-of-interest based analysis of the caudate nucleus and the anterior/posterior putamen was performed. Specific binding ratios (SBR = [ROI-occ]/occ) were compared between the groups.
RESULTS
DAT binding in symptomatic patients was 8.6% higher in the posterior putamen than in healthy controls (p = 0.03). Binding correlated negatively with age in both groups but not with motor symptom severity, cognitive function or depression ratings.
CONCLUSIONS
Putaminal DAT binding, as measured with [I]FP-CIT SPECT, was higher in symptomatic controls than in healthy individuals. The reason for the difference is unclear but can include selection bias when DAT binding is used to aid clinical diagnosis and possible self-selection bias in healthy volunteerism. This effect should be taken into consideration when designing and interpreting neuroimaging trials investigating the dopamine system with [I]FP-CIT SPECT.
Topics: Aged; Corpus Striatum; Dopamine Plasma Membrane Transport Proteins; Humans; Neuroimaging; Parkinson Disease; Tomography, Emission-Computed, Single-Photon
PubMed: 34482280
DOI: 10.1016/j.nicl.2021.102807 -
The Journal of Biological Chemistry 2021The dopamine transporter (DAT) is essential for the reuptake of the released neurotransmitter dopamine (DA) in the brain. Psychostimulants, methamphetamine and cocaine,...
The dopamine transporter (DAT) is essential for the reuptake of the released neurotransmitter dopamine (DA) in the brain. Psychostimulants, methamphetamine and cocaine, have been reported to induce the formation of DAT multimeric complexes in vivo and in vitro. The interpretation of DAT multimer function has been primarily in the context of compounds that induce structural and functional modifications of the DAT, complicating the understanding of the significance of DAT multimers. To examine multimerization in the absence of DAT ligands as well as in their presence, we developed a novel, optogenetic fusion chimera of cryptochrome 2 and DAT with an mCherry fluorescent reporter (Cry2-DAT). Using blue light to induce Cry2-DAT multimeric protein complex formation, we were able to simultaneously test the functional contributions of DAT multimerization in the absence or presence of substrates or inhibitors with high spatiotemporal precision. We found that blue light-stimulated Cry2-DAT multimers significantly increased IDT307 uptake and MFZ 9-18 binding in the absence of ligands as well as after methamphetamine and nomifensine treatment. Blue light-induced Cry2-DAT multimerization increased colocalization with recycling endosomal marker Rab11 and had decreased presence in Rab5-positive early endosomes and Rab7-positive late endosomes. Our data suggest that the increased uptake and binding results from induced and rapid trafficking of DAT multimers to the plasma membrane. Our data suggest that DAT multimers may function to help maintain DA homeostasis.
Topics: Animals; Biological Transport; Cell Membrane; Dopamine; Dopamine Plasma Membrane Transport Proteins; Gene Expression; HEK293 Cells; Humans; Neurons; Optogenetics; Protein Multimerization
PubMed: 34015332
DOI: 10.1016/j.jbc.2021.100787 -
Journal of Chemical Information and... Jul 2023Human dopamine transporter (hDAT) regulates the reuptake of extracellular dopamine (DA) and is an essential therapeutic target for central nervous system (CNS) diseases....
Human dopamine transporter (hDAT) regulates the reuptake of extracellular dopamine (DA) and is an essential therapeutic target for central nervous system (CNS) diseases. The allosteric modulation of hDAT has been identified for decades. However, the molecular mechanism underlying the transportation is still elusive, which hinders the rational design of allosteric modulators against hDAT. Here, a systematic structure-based method was performed to explore allosteric sites on hDAT in inward-open (IO) conformation and to screen compounds with allosteric affinity. First, the model of the hDAT structure was constructed based on the recently reported Cryo-EM structure of the human serotonin transporter (hSERT) and Gaussian-accelerated molecular dynamics (GaMD) simulation was further utilized for the identification of intermediate energetic stable states of the transporter. Then, with the potential druggable allosteric site on hDAT in IO conformation, virtual screening of seven enamine chemical libraries (∼440,000 compounds) was processed, resulting in 10 compounds being purchased for assay and with Z1078601926 discovered to allosterically inhibit hDAT (IC = 0.527 [0.284; 0.988] μM) when nomifensine was introduced as an orthosteric ligand. Finally, the synergistic effect underlying the allosteric inhibition of hDAT by Z1078601926 and nomifensine was explored using additional GaMD simulation and postbinding free energy analysis. The hit compound discovered in this work not only provides a good starting point for lead optimization but also demonstrates the usability of the method for the structure-based discovery of novel allosteric modulators of other therapeutic targets.
Topics: Humans; Dopamine Plasma Membrane Transport Proteins; Nomifensine; Molecular Dynamics Simulation; Allosteric Site; Ligands
PubMed: 37410882
DOI: 10.1021/acs.jcim.3c00477 -
Biomolecules Jun 2022Dopamine (DA), the most abundant human brain catecholaminergic neurotransmitter, modulates key behavioral and neurological processes in young and senescent brains,...
Dopamine (DA), the most abundant human brain catecholaminergic neurotransmitter, modulates key behavioral and neurological processes in young and senescent brains, including motricity, sleep, attention, emotion, learning and memory, and social and reward-seeking behaviors. The DA transporter (DAT) regulates transsynaptic DA levels, influencing all these processes. Compounds targeting DAT (e.g., cocaine and amphetamines) were historically used to shape mood and cognition, but these substances typically lead to severe negative side effects (tolerance, abuse, addiction, and dependence). DA/DAT signaling dysfunctions are associated with neuropsychiatric and progressive brain disorders, including Parkinson's and Alzheimer diseases, drug addiction and dementia, resulting in devastating personal and familial concerns and high socioeconomic costs worldwide. The development of low-side-effect, new/selective medicaments with reduced abuse-liability and which ameliorate DA/DAT-related dysfunctions is therefore crucial in the fields of medicine and healthcare. Using the rat as experimental animal model, the present work describes the synthesis and pharmacological profile of ()-MK-26, a new modafinil analogue with markedly improved potency and selectivity for DAT over parent drug. Ex vivo electrophysiology revealed significantly augmented hippocampal long-term synaptic potentiation upon acute, intraperitoneally delivered ()-MK-26 treatment, whereas in vivo experiments in the hole-board test showed only lesser effects on reference memory performance in aged rats. However, in effort-related FR5/chow and PROG/chow feeding choice experiments, ()-MK-26 treatment reversed the depression-like behavior induced by the dopamine-depleting drug tetrabenazine (TBZ) and increased the selection of high-effort alternatives. Moreover, in in vivo microdialysis experiments, ()-MK-26 significantly increased extracellular DA levels in the prefrontal cortex and in nucleus accumbens core and shell. These studies highlight ()-MK-26 as a potent enhancer of transsynaptic DA and promoter of synaptic plasticity, with predominant beneficial effects on effort-related behaviors, thus proposing therapeutic potentials for ()-MK-26 in the treatment of low-effort exertion and motivational dysfunctions characteristic of depression and aging-related disorders.
Topics: Animals; Dopamine; Dopamine Plasma Membrane Transport Proteins; Hippocampus; Humans; Motivation; Neuronal Plasticity; Rats
PubMed: 35883437
DOI: 10.3390/biom12070881 -
Neuropharmacology Dec 2021Clandestine chemists are currently exploiting the pyrrolidinophenone scaffold to develop new designer drugs that carry the risk of abuse and overdose. These drugs...
Clandestine chemists are currently exploiting the pyrrolidinophenone scaffold to develop new designer drugs that carry the risk of abuse and overdose. These drugs promote addiction through the rewarding effects of increased dopaminergic neurotransmission. 3,4-Methylenedioxypyrovalerone (MDPV) and its analogs are illicit psychostimulants of this class that are ∼50-fold more potent than cocaine at inhibiting the human dopamine transporter (hDAT). In contrast, MDPV is a weak inhibitor at both the human serotonin transporter (hSERT) and, as it is shown here, the Drosophila melanogaster DAT (dDAT). We studied three conserved residues between hSERT and dDAT that are unique in hDAT (A117, F318, and P323 in dDAT), and one residue that is different in all three transporters (D121 in dDAT). hDAT residues were replaced in the dDAT sequence at these positions using site-directed mutagenesis and stable cell lines were generated expressing these mutant transporters. The potencies of MDPV and two of its analogs were determined using a Ca-mobilization assay. In this assay, voltage-gated Ca channels are expressed to sense the membrane electrical depolarization evoked when dopamine is transported through DAT. Each individual mutant slightly improved MDPV's potency, but the combination of all four increased its potency ∼100-fold (2 log units) in inhibiting dDAT activity. Molecular modeling and docking studies were conducted to explore the possible mode of interaction between MDPV and DAT in silico. Two of the studied residues (F318 and P323) are at the entrance of the S1 binding site, whereas the other two (A117 and D121) face the aryl moiety of MDPV when bound to this site. Therefore, these four non-conserved residues can influence MDPV selectivity not only by stabilizing binding, but also by controlling access to its binding site at DAT.
Topics: Animals; Benzodioxoles; Biological Transport; Calcium Channels; Cell Line; Designer Drugs; Dopamine Plasma Membrane Transport Proteins; Dopamine Uptake Inhibitors; Drosophila melanogaster; Molecular Docking Simulation; Pyrrolidines; Serotonin Plasma Membrane Transport Proteins; Synthetic Cathinone
PubMed: 34619165
DOI: 10.1016/j.neuropharm.2021.108820 -
Neuroscience and Biobehavioral Reviews Jan 2016The gene coding for the dopamine transporter (DAT), SLC6A3, contains a 40-base pair variable number of tandem repeats (VNTR) polymorphism (rs28363170) in its 3'... (Meta-Analysis)
Meta-Analysis Review
The gene coding for the dopamine transporter (DAT), SLC6A3, contains a 40-base pair variable number of tandem repeats (VNTR) polymorphism (rs28363170) in its 3' untranslated region. This VNTR has been associated with attention deficit hyperactivity disorder (ADHD) and has been investigated in relation to cognition and brain function. Here, we report the results of a comprehensive meta-analysis with meta-regression examining the association of the VNTR with different domains of cognition in healthy adults. We extracted data from 28 independent studies and carried out meta-analyses for associations with working memory (k=10 samples, N=1193 subjects), inhibition (k=8 samples, N=829 subjects), executive functions including inhibition (k=10 samples, N=984 subjects), attention (k=6 samples, N=742 subjects) and declarative long-term memory (k=5 samples, N=251 subjects). None of the investigated dimensions showed significant associations with the VNTR (all p>0.26). Meta-regression including year of publication, gender, age, ethnicity and percentage of 10R-homozygotes similarly did not attain significance. We conclude that there is no evidence that rs28363170 may be a significant predictor of cognitive function in healthy adults.
Topics: Cognition; Dopamine Plasma Membrane Transport Proteins; Humans; Minisatellite Repeats; Polymorphism, Genetic
PubMed: 26593110
DOI: 10.1016/j.neubiorev.2015.09.021 -
The Journal of Biological Chemistry Jan 2017Extracellular dopamine and serotonin concentrations are determined by the presynaptic dopamine (DAT) and serotonin (SERT) transporters, respectively. Numerous studies...
Extracellular dopamine and serotonin concentrations are determined by the presynaptic dopamine (DAT) and serotonin (SERT) transporters, respectively. Numerous studies have investigated the DAT and SERT structural elements contributing to inhibitor and substrate binding. To date, crystallographic studies have focused on conserved transmembrane domains, where multiple substrate binding and translocation features are conserved. However, it is unknown what, if any, role the highly divergent intracellular N and C termini contribute to these processes. Here, we used chimeric proteins to test whether DAT and SERT N and C termini contribute to transporter substrate and inhibitor affinities. Replacing the DAT N terminus with that of SERT had no effect on DA transport V but significantly decreased DAT substrate affinities for DA and amphetamine. Similar losses in uptake inhibition were observed for small DAT inhibitors, whereas substituting the DAT C terminus with that of SERT affected neither substrate nor inhibitor affinities. In contrast, the N-terminal substitution was completely tolerated by the larger DAT inhibitors, which exhibited no loss in apparent affinity. Remarkably, all affinity losses were rescued in DAT chimeras encoding both SERT N and C termini. The sensitivity to amino-terminal substitution was specific for DAT, because replacing the SERT N and/or C termini affected neither substrate nor inhibitor affinities. Taken together, these findings provide compelling experimental evidence that DAT N and C termini synergistically contribute to substrate and inhibitor affinities.
Topics: Amino Acid Substitution; Biological Transport, Active; Cell Line; Dopamine Plasma Membrane Transport Proteins; Humans; Mutation, Missense; Protein Domains; Serotonin Plasma Membrane Transport Proteins
PubMed: 27986813
DOI: 10.1074/jbc.M116.762872 -
Drug and Alcohol Dependence Feb 2015Treatment of stimulant-use disorders remains a formidable challenge, and the dopamine transporter (DAT) remains a potential target for antagonist or agonist-like... (Review)
Review
BACKGROUND
Treatment of stimulant-use disorders remains a formidable challenge, and the dopamine transporter (DAT) remains a potential target for antagonist or agonist-like substitution therapies.
METHODS
This review focuses on DAT ligands, such as benztropine, GBR 12909, modafinil, and DAT substrates derived from phenethylamine or cathinone that have atypical DAT-inhibitor effects, either in vitro or in vivo. The compounds are described from a molecular mechanistic, behavioral, and medicinal-chemical perspective.
RESULTS
Possible mechanisms for atypicality at the molecular level can be deduced from the conformational cycle for substrate translocation. For each conformation, a crystal structure of a bacterial homolog is available, with a possible role of cholesterol, which is also present in the crystal of Drosophila DAT. Although there is a direct relationship between behavioral potencies of most DAT inhibitors and their DAT affinities, a number of compounds bind to the DAT and inhibit dopamine uptake but do not share cocaine-like effects. Such atypical behavior, depending on the compound, may be related to slow DAT association, combined sigma-receptor actions, or bias for cytosol-facing DAT. Some structures are sterically small enough to serve as DAT substrates but large enough to also inhibit transport. Such compounds may display partial DA releasing effects, and may be combined with release or uptake inhibition at other monoamine transporters.
CONCLUSIONS
Mechanisms of atypical DAT inhibitors may serve as targets for the development of treatments for stimulant abuse. These mechanisms are novel and their further exploration may produce compounds with unique therapeutic potential as treatments for stimulant abuse.
Topics: Animals; Benzhydryl Compounds; Benztropine; Central Nervous System Stimulants; Cocaine; Dopamine Plasma Membrane Transport Proteins; Drug Delivery Systems; Humans; Ligands; Modafinil; Protein Binding; Protein Structure, Secondary; Protein Structure, Tertiary
PubMed: 25548026
DOI: 10.1016/j.drugalcdep.2014.12.005