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Journal of Nuclear Medicine Technology Mar 2019Idiopathic Parkinson disease (PD) is a progressive neurologic condition that affects the dopamine transporters in the substantia nigra of the brain. Currently, more than... (Review)
Review
Idiopathic Parkinson disease (PD) is a progressive neurologic condition that affects the dopamine transporters in the substantia nigra of the brain. Currently, more than 10 million people are living with this disease worldwide, with thousands of newly diagnosed and undiagnosed cases added every year. The disease is difficult to differentiate from other similar disorders, as symptoms widely vary and can mimic other conditions. Classic PD symptoms may look similar to essential tremor and other parkinsonian syndromes. The I-ioflupane dopamine transporter (DaT) protocol differentiates PD from essential tremor through in vivo testing with SPECT imaging. The DaT protocol commonly relies on a semiquantitative analysis and visual interpretations of the images, which may produce inaccurate results due to human error. DaTQUANT software (GE Healthcare) was created in 2013 as an adjunct processing tool with advanced quantitative uptake methods and a designated normals database for a more accurate assessment of a patient's case. DaTQUANT has proven to be a vital protocol component for an accurate differentiation of PD from essential tremor. Current use of the software has been rather limited, so a greater push for education and implementation will be key for its success.
Topics: Dopamine Plasma Membrane Transport Proteins; Humans; Image Processing, Computer-Assisted; Parkinson Disease; Software
PubMed: 30683690
DOI: 10.2967/jnmt.118.222349 -
Molecular Psychiatry Feb 2022The human dopamine transporter gene SLC6A3 has been consistently implicated in several neuropsychiatric diseases but the disease mechanism remains elusive. In this risk...
The human dopamine transporter gene SLC6A3 has been consistently implicated in several neuropsychiatric diseases but the disease mechanism remains elusive. In this risk synthesis, we have concluded that SLC6A3 represents an increasingly recognized risk with a growing number of familial mutants associated with neuropsychiatric and neurological disorders. At least five loci were related to common and severe diseases including alcohol use disorder (high activity variant), attention-deficit/hyperactivity disorder (low activity variant), autism (familial proteins with mutated networking) and movement disorders (both regulatory variants and familial mutations). Association signals depended on genetic markers used as well as ethnicity examined. Strong haplotype selection and gene-wide epistases support multimarker assessment of functional variations and phenotype associations. Inclusion of its promoter region's functional markers such as DNPi (rs67175440) and 5'VNTR (rs70957367) may help delineate condensate-based risk action, testing a locus-pathway-phenotype hypothesis for one gene-multidisease etiology.
Topics: Attention Deficit Disorder with Hyperactivity; Dopamine Plasma Membrane Transport Proteins; Haplotypes; Humans; Mutation; Phenotype
PubMed: 34650206
DOI: 10.1038/s41380-021-01341-5 -
Environmental Health Perspectives May 2022Paraquat (PQ) is a pesticide, exposure to which has been associated with an increased risk of Parkinson's disease; however, PQ transport mechanisms in the brain are...
BACKGROUND
Paraquat (PQ) is a pesticide, exposure to which has been associated with an increased risk of Parkinson's disease; however, PQ transport mechanisms in the brain are still unclear. Our previous studies indicated that the organic cation transporter 3 (OCT3) expressed on astrocytes could uptake PQ and protect the dopaminergic (DA) neurons from a higher level of extracellular PQ. At present, it is unknown how OCT3 levels are altered during chronic PQ exposure or aging, nor is it clear how the compensatory mechanisms are triggered by OCT3 deficiency. Dynamic related protein 1 (DRP1) was previously reported to ameliorate the loss of neurons during Parkinson's disease. Nowadays, mounting studies have revealed the functions of astrocyte DRP1, prompting us to hypothesize that DRP1 could regulate the PQ transport capacity of astrocytes.
OBJECTIVES
The present study aimed to further explore PQ transport mechanisms in the nigrostriatal system and identify pathways involved in extracellular PQ clearance.
METHODS
Models of PQ-induced neurodegeneration were established by intraperitoneal (i.p.) injection of PQ in wild-type (WT) and organic cation transporter-3-deficient () mice. DRP1 knockdown was achieved by viral tools and small interfering RNA (siRNA) . Extracellular PQ was detected by microdialysis. transport assays were used to directly observe the functions of different transporters. PQ-induced neurotoxicity was evaluated by tyrosine hydroxylase immunohistochemistry, microdialysis for striatal DA and behavior tests. Western blotting analysis or immunofluorescence was used to evaluate the expression levels and locations of proteins or .
RESULTS
Older mice and those chronically exposed to PQ had a lower expression of brain OCT3 and, following exposure to a i.p. loading dose, a higher concentration of extracellular PQ. DRP1 levels were higher in astrocytes and neurons of WT and mice after chronic exposure to PQ; this was supported by finding higher levels of DRP1 after PQ treatment of dopamine transporter-expressing neurons with and without OCT3 inhibition and in primary astrocytes of WT and mice. Selective astrocyte DRP1 knockdown ameliorated the neurotoxicity in mice but not in WT mice. GL261 astrocytes with siRNA-mediated DRP1 knockdown had a higher expression of alanine-serine-cysteine transporter 2 (ASCT2), and transport studies suggest that extracellular PQ was transported into astrocytes by ASCT2 when OCT3 was absent.
DISCUSSION
The present study mainly focused on the transport mechanisms of PQ between the dopaminergic neurons and astrocytes. Lower OCT3 levels were found in the older or chronically PQ-treated mice. Astrocytes with DRP1 inhibition (by viral tools or mitochondrial division inhibitor-1) had higher levels of ASCT2, which we hypothesize served as an alternative transporter to remove extracellular PQ when OCT3 was deficient. In summary, our data suggest that OCT3, ASCT2 located on astrocytes and the dopamine transporter located on DA terminals may function in a concerted manner to mediate striatal DA terminal damage in PQ-induced neurotoxicity. https://doi.org/10.1289/EHP9505.
Topics: Animals; Astrocytes; Cations; Dopamine Plasma Membrane Transport Proteins; Dopaminergic Neurons; Dynamins; Mice; Neurotoxicity Syndromes; Octamer Transcription Factor-3; Paraquat; Parkinson Disease; RNA, Small Interfering; Substantia Nigra
PubMed: 35511227
DOI: 10.1289/EHP9505 -
The Journal of Pharmacology and... Jun 2023Synthetic cathinones are a class of new psychoactive substances that display psychomotor stimulant properties, and novel cathinone analogs continue to emerge in illicit...
Synthetic cathinones are a class of new psychoactive substances that display psychomotor stimulant properties, and novel cathinone analogs continue to emerge in illicit drug markets worldwide. The aim of the present study was to characterize the pharmacology of 4-chloro ring-substituted cathinones that are appearing in illicit drug markets compared with the effects of 4-methylmethcathinone (mephedrone). Synaptosomes were prepared from rat caudate for dopamine transporter (DAT) assays or from whole brain minus caudate and cerebellum for norepinephrine transporter (NET) and serotonin transporter (SERT) assays. Findings from transporter uptake inhibition and release assays showed that mephedrone and 4-chloromethcathinone (4-CMC) function as substrates at DAT, NET, and SERT, with similar potency at all three transporters. In contrast, 4-chloro--pyrrolidinopropiophenone (4-CPPP) was an uptake inhibitor at DAT and NET, with similar potency at each site, but had little activity at SERT. 4-Chloroethcathinone (4-CEC) was a low-potency uptake inhibitor at DAT and NET but a substrate at SERT. In rats implanted with telemetry transmitters, mephedrone and 4-CMC increased blood pressure, heart rate, and locomotor activity to a similar extent. 4-CEC and 4-CPPP were less potent at increasing blood pressure and had modest stimulatory effects on heart rate and activity. 4-CMC also transiently decreased temperature at the highest dose tested. All three 4-chloro ring-substituted cathinones are biologically active, but only 4-CMC has potency comparable to mephedrone. Collectively, our findings suggest that 4-CMC and other 4-chloro cathinones may have abuse potential and adverse effects in humans that are analogous to those associated with mephedrone. SIGNIFICANCE STATEMENT: The 4-chloro ring-substituted cathinones all produced significant cardiovascular stimulation, with 4-chloromethcathinone (4-CMC) showing potency similar to mephedrone. All of the drugs are likely to be abused given their effects at the dopamine transporter, particularly 4-CMC.
Topics: Humans; Rats; Animals; Dopamine Plasma Membrane Transport Proteins; Synthetic Cathinone; Methamphetamine; Central Nervous System Agents; Serotonin Plasma Membrane Transport Proteins; Illicit Drugs; Norepinephrine Plasma Membrane Transport Proteins; Central Nervous System Stimulants
PubMed: 36669877
DOI: 10.1124/jpet.122.001478 -
Pharmacology & Therapeutics Mar 2018HIV-associated neurocognitive disorder (HAND) remains highly prevalent in HIV infected individuals and represents a special group of neuropathological disorders, which... (Review)
Review
HIV-associated neurocognitive disorder (HAND) remains highly prevalent in HIV infected individuals and represents a special group of neuropathological disorders, which are associated with HIV-1 viral proteins, such as transactivator of transcription (Tat) protein. Cocaine abuse increases the incidence of HAND and exacerbates its severity by enhancing viral replication. Perturbation of dopaminergic transmission has been implicated as a risk factor of HAND. The presynaptic dopamine (DA) transporter (DAT) is essential for DA homeostasis and dopaminergic modulation of the brain function including cognition. Tat and cocaine synergistically elevate synaptic DA levels by acting directly on human DAT (hDAT), ultimately leading to dysregulation of DA transmission. Through integrated computational modeling and experimental validation, key residues have been identified in hDAT that play a critical role in Tat-induced inhibition of DAT and induce transporter conformational transitions. This review presents current information regarding neurological changes in DAT-mediated dopaminergic system associated with HIV infection, DAT-mediated adaptive responses to Tat as well as allosteric modulatory effects of novel compounds on hDAT. Understanding the molecular mechanisms by which Tat induces DAT-mediated dysregulation of DA system is of great clinical interest for identifying new targets for an early therapeutic intervention for HAND.
Topics: AIDS Dementia Complex; Animals; Dopamine; Dopamine Plasma Membrane Transport Proteins; Humans; tat Gene Products, Human Immunodeficiency Virus
PubMed: 28987321
DOI: 10.1016/j.pharmthera.2017.10.007 -
Biomolecules Nov 2023L-DOPA is the mainstay of treatment for Parkinson's disease (PD). However, over time this drug can produce dyskinesia. A useful acute PD model for screening novel...
L-DOPA is the mainstay of treatment for Parkinson's disease (PD). However, over time this drug can produce dyskinesia. A useful acute PD model for screening novel compounds for anti-parkinsonian and L-DOPA-induced dyskinesia (LID) are dopamine-depleted dopamine-transporter KO (DDD) mice. Treatment with α-methyl--tyrosine rapidly depletes their brain stores of DA and renders them akinetic. During sensitization in the open field (OF), their locomotion declines as vertical activities increase and upon encountering a wall they stand on one leg or tail and engage in climbing behavior termed "three-paw dyskinesia". We have hypothesized that L-DOPA induces a stereotypic activation of locomotion in DDD mice, where they are unable to alter the course of their locomotion, and upon encountering walls engage in "three-paw dyskinesia" as reflected in vertical counts or beam-breaks. The purpose of our studies was to identify a valid index of LID in DDD mice that met three criteria: (a) sensitization with repeated L-DOPA administration, (b) insensitivity to a change in the test context, and (c) stimulatory or inhibitory responses to dopamine D1 receptor agonists (5 mg/kg SKF81297; 5 and 10 mg/kg MLM55-38, a novel compound) and amantadine (45 mg/kg), respectively. Responses were compared between the OF and a circular maze (CM) that did not hinder locomotion. We found vertical counts and climbing were specific for testing in the OF, while oral stereotypies were sensitized to L-DOPA in both the OF and CM and responded to D1R agonists and amantadine. Hence, in DDD mice oral stereotypies should be used as an index of LID in screening compounds for PD.
Topics: Mice; Animals; Levodopa; Dopamine Agonists; Dopamine; Dopamine Plasma Membrane Transport Proteins; Dyskinesia, Drug-Induced; Mice, Knockout; Parkinson Disease; Amantadine
PubMed: 38002340
DOI: 10.3390/biom13111658 -
ACS Chemical Neuroscience May 2022Fast-scan cyclic voltammetry (FSCV) is an effective tool for measuring dopamine release and clearance throughout the brain, especially the striatum where dopamine...
Fast-scan cyclic voltammetry (FSCV) is an effective tool for measuring dopamine release and clearance throughout the brain, especially the striatum where dopamine terminals are abundant and signals are heavily regulated by release machinery and the dopamine transporter (DAT). Peak height measurement is perhaps the most common method for measuring dopamine release, but it is influenced by changes in clearance. Michaelis-Menten-based modeling has been a standard in measuring dopamine clearance, but it is problematic in that it requires experimenter fitted modeling subject to experimenter bias. This study presents the use of the first derivative (velocity) of evoked dopamine signals as an alternative approach for measuring and distinguishing dopamine release from clearance. Maximal upward velocity predicts reductions in dopamine peak height due to D and GABA receptor stimulation and by alterations in calcium concentrations. The Michaelis-Menten maximal velocity () measure, an approximation for DAT levels, predicts maximal downward velocity in slices and in vivo. Dopamine peak height and upward velocity were similar between wild-type and DAT knock-out (DATKO) mice. In contrast, downward velocity was lower and exponential decay (tau) was higher in DATKO mice, supporting the use of both measures for extreme changes in DAT activity. In slices, the competitive DAT inhibitors cocaine, PTT, and WF23 increased peak height and upward velocity differentially across increasing concentrations, with PTT and cocaine reducing these measures at high concentrations. Downward velocity and tau values decreased and increased respectively across concentrations, with greater potency and efficacy observed with WF23 and PTT. In vivo recordings demonstrated similar effects of WF23, PTT, and cocaine on measures of release and clearance. Tau was a more sensitive measure at low concentrations, supporting its use as a surrogate for the Michaelis-Menten measure of apparent affinity (). Together, these results inform on the use of these various measures for dopamine release and clearance.
Topics: Animals; Cocaine; Corpus Striatum; Dopamine; Dopamine Plasma Membrane Transport Proteins; Dopamine Uptake Inhibitors; Mice; Rats; Rats, Sprague-Dawley
PubMed: 35482592
DOI: 10.1021/acschemneuro.2c00033 -
Brain, Behavior, and Immunity May 2018The second-most common neurodegenerative disease, Parkinson's Disease (PD) has three hallmarks: dysfunctional dopamine transmission due, at least in part, to dopamine... (Review)
Review
The second-most common neurodegenerative disease, Parkinson's Disease (PD) has three hallmarks: dysfunctional dopamine transmission due, at least in part, to dopamine neuron degeneration; intracellular inclusions of α-synuclein aggregates; and neuroinflammation. The origin and interplay of these features remains a puzzle, as does the underlying mechanism of PD pathogenesis and progression. When viewed in the context of neuroimmunology, dopamine also plays a role in regulating peripheral immune cells. Intriguingly, plasma dopamine levels are altered in PD, suggesting collateral dysregulation of peripheral dopamine transmission. The dopamine transporter (DAT), the main regulator of dopaminergic tone in the CNS, is known to exist in lymphocytes and monocytes/macrophages, but little is known about peripheral DAT biology or how DAT regulates the dopaminergic tone, much less how peripheral DAT alters immune function. Our review is guided by the hypothesis that dysfunctional peripheral dopamine signaling might be linked to the dysfunctional immune responses in PD and thereby suggests a potential bidirectional communication between central and peripheral dopamine systems. This review seeks to foster new perspectives concerning PD pathogenesis and progression.
Topics: Dopamine; Dopamine Plasma Membrane Transport Proteins; Dopaminergic Neurons; Humans; Lymphocytes; Macrophages; Monocytes; Nerve Degeneration; Neurodegenerative Diseases; Parkinson Disease; Signal Transduction; alpha-Synuclein
PubMed: 29551693
DOI: 10.1016/j.bbi.2018.03.020 -
Internal Medicine (Tokyo, Japan) Jun 2019Parkinson disease (PD) is a slowly progressive neurodegenerative disease characterized by the loss of dopaminergic neurons and terminals in the nigrostriatal system.... (Review)
Review
Parkinson disease (PD) is a slowly progressive neurodegenerative disease characterized by the loss of dopaminergic neurons and terminals in the nigrostriatal system. Dopamine transporter (DAT) imaging is widely performed for the differential diagnosis of PD and other degenerative parkinsonism from essential tremor, vascular parkinsonism, and drug-induced parkinsonism. DAT is the plasma membrane carrier specific to dopamine neurons that are responsible for re-uptaking dopamine from the synaptic cleft back into the nerve ending. DAT binding might reflect striatal presynaptic dysfunction or DAT expression in PD patients. Longitudinal studies of DAT imaging have reported progressive changes from early PD patients. This imaging may be used as a progressive biomarker. Follow-up DAT imaging for therapeutic interventions has been applied for several anti-parkinsonian drugs. We herein review the progressive changes and therapeutic modification of DAT binding by anti-PD medications in early PD patients.
Topics: Aged; Brain; Corpus Striatum; Dopamine Plasma Membrane Transport Proteins; Humans; Parkinson Disease; Tomography, Emission-Computed, Single-Photon
PubMed: 30799370
DOI: 10.2169/internalmedicine.2489-18 -
Journal of Neuroscience Research Aug 2022Modulatory mechanisms of neurotransmitter release and clearance are highly controlled processes whose finely tuned regulation is critical for functioning of the nervous...
Modulatory mechanisms of neurotransmitter release and clearance are highly controlled processes whose finely tuned regulation is critical for functioning of the nervous system. Dysregulation of the monoamine neurotransmitter dopamine can lead to several neuropathies. Synaptic modulation of dopamine is known to involve pre-synaptic D2 auto-receptors and acid sensing ion channels. In addition, the dopamine membrane transporter (DAT), which is responsible for clearance of dopamine from the synaptic cleft, is suspected to play an active role in modulating release of dopamine. Using functional imaging on the Caenorhabditis elegans model system, we show that DAT-1 acts as a negative feedback modulator to neurotransmitter vesicle fusion. Results from our fluorescence recovery after photo-bleaching (FRAP) based experiments were followed up with and reaffirmed using swimming-induced paralysis behavioral assays. Utilizing our numerical FRAP data we have developed a mechanistic model to dissect the dynamics of synaptic vesicle fusion, and compare the feedback effects of DAT-1 with the dopamine auto-receptor. Our experimental results and the mechanistic model are of potential broader significance, as similar dynamics are likely to be used by other synaptic modulators including membrane transporters for other neurotransmitters across species.
Topics: Animals; Caenorhabditis elegans; Caenorhabditis elegans Proteins; Dopamine; Dopamine Plasma Membrane Transport Proteins; Homeostasis; Neurotransmitter Agents; Receptors, Dopamine
PubMed: 34747520
DOI: 10.1002/jnr.24965