Dopamine Reuptake Transporter Research Articles

A bupropion modulatory site in the Gloeobacter violaceus ligand-gated ion channel

Bupropion is an atypical antidepressant and smoking cessation drug that causes adverse effects such as insomnia, irritability, and anxiety. Bupropion inhibits dopamine and norepinephrine reuptake transporters and eukaryotic cation-conducting pentameric ligand-gated ion channels, such as nicotinic acetylcholine and serotonin type 3A receptors, at clinically relevant concentrations. Here, we demonstrate that bupropion also inhibits a prokaryotic homolog of pentameric ligand-gated ion channels, the Gloeobacter violaceus ligand-gated ion channel (GLIC). Using the GLIC as a model, we used molecular docking to predict binding sites for bupropion. Bupropion was found to bind to several sites within the transmembrane domain, with the predominant site being localized to the interface between transmembrane segments M1 and M3 of two adjacent subunits. Residues W213, T214, and W217 in the first transmembrane segment, M1, and F267 and I271 in the third transmembrane segment, M3, most frequently reside within a 4 Å distance from bupropion. We then used single amino acid substitutions at these positions and two-electrode voltage-clamp recordings to determine their impact on bupropion inhibitory effects. The substitution T214F alters bupropion potency by shifting the half-maximal inhibitory concentration to a 13-fold higher value compared to wild-type GLIC. Residue T214 is found within a previously identified binding pocket for neurosteroids and lipids in the GLIC. This intersubunit binding pocket is structurally conserved and almost identical to a binding pocket described for neurosteroids in γ-aminobutyric acid type A receptors. Our data thus suggest that the T214 that lines a previously identified lipophilic binding pocket in GLIC and γ-aminobutyric acid type A receptors is also a modulatory site for bupropion interaction with the GLIC.

Chronic high-sugar diet in adulthood protects Caenorhabditis elegans from 6-OHDA-induced dopaminergic neurodegeneration

BackgroundDiets high in saturated fat and sugar, termed “Western diets,” have been associated with several negative health outcomes, including increased risk for neurodegenerative disease. Parkinson’s disease (PD) is the second most prevalent neurodegenerative disease and is characterized by the progressive death of dopaminergic neurons in the brain. We build upon previous work characterizing the impact of high-sugar diets in Caenorhabditis elegans to mechanistically evaluate the relationship between high-sugar diets and dopaminergic neurodegeneration.ResultsAdult high-glucose and high-fructose diets, or exposure from day 1 to 5 of adulthood, led to increased lipid content, shorter lifespan, and decreased reproduction. However, in contrast to previous reports, we found that adult chronic high-glucose and high-fructose diets did not induce dopaminergic neurodegeneration alone and were protective from 6-hydroxydopamine (6-OHDA) induced degeneration. Neither sugar altered baseline electron transport chain function and both increased vulnerability to organism-wide ATP depletion when the electron transport chain was inhibited, arguing against energetic rescue as a basis for neuroprotection. The induction of oxidative stress by 6-OHDA is hypothesized to contribute to its pathology, and high-sugar diets prevented this increase in the soma of the dopaminergic neurons. However, we did not find increased expression of antioxidant enzymes or glutathione levels. Instead, we found evidence suggesting downregulation of the dopamine reuptake transporter dat-1 that could result in decreased 6-OHDA uptake.ConclusionsOur work uncovers a neuroprotective role for high-sugar diets, despite concomitant decreases in lifespan and reproduction. Our results support the broader finding that ATP depletion alone is insufficient to induce dopaminergic neurodegeneration, whereas increased neuronal oxidative stress may drive degeneration. Finally, our work highlights the importance of evaluating lifestyle by toxicant interactions.

Socially Mediated Shift in Neural Circuits Activation Regulated by Synergistic Neuromodulatory Signaling.

Animals exhibit context-dependent behavioral decisions that are mediated by specific motor circuits. In social species these decisions are often influenced by social status. Although social status-dependent neural plasticity of motor circuits has been investigated in vertebrates, little is known of how cellular plasticity translates into differences in motor activity. Here, we used zebrafish (Danio rerio) as a model organism to examine how social dominance influences the activation of swimming and the Mauthner-mediated startle escape behaviors. We show that the status-dependent shift in behavior patterns whereby dominants increase swimming and reduce sensitivity of startle escape while subordinates reduce their swimming and increase startle sensitivity is regulated by the synergistic interactions of dopaminergic, glycinergic, and GABAergic inputs to shift the balance of activation of the underlying motor circuits. This shift is driven by socially induced differences in expression of dopaminergic receptor type 1b (Drd1b) on glycinergic neurons and dopamine (DA) reuptake transporter (DAT). Second, we show that GABAergic input onto glycinergic neurons is strengthened in subordinates compared with dominants. Complementary neurocomputational modeling of the empirical results show that drd1b functions as molecular regulator to facilitate the shift between excitatory and inhibitory pathways. The results illustrate how reconfiguration in network dynamics serves as an adaptive strategy to cope with changes in social environment and are likely conserved and applicable to other social species.

The Impact of Heroin Self-Administration and Environmental Enrichment on Ventral Tegmental CRF1 Receptor Expression.

There is a strong link between chronic stress and vulnerability to drug abuse and addiction. Corticotropin releasing factor (CRF) is central to the stress response that contributes to continuation and relapse to heroin abuse. Chronic heroin exposure can exacerbate CRF production, leading to dysregulation of the midbrain CRF-dopamine-glutamate interaction. Here we investigated the role of midbrain CRF1 receptors in heroin self-administration and assessed neuroplasticity in CRF1 receptor expression in key opioid addiction brain regions. Infusions of antalarmin (a CRF1 receptor antagonist) into the ventral tegmental area (VTA) dose dependently reduced heroin self-administration in rats but had no impact on food reinforcement or locomotor activity in rats. Using RNAscope in situ hybridization, we found that heroin, but not saline, self-administration upregulated CRF1 receptor mRNA in the VTA, particularly on dopamine neurons. AMPA GluR1 and dopamine reuptake transporter mRNA in VTA neurons were not affected by heroin. The western-blot assay showed that CRF1 receptors were upregulated in the VTA and nucleus accumbens. No significant changes in CRF1 protein expression were detected in the prefrontal cortex, insula, dorsal hippocampus, and substantia nigra. In addition, we found that 15 days of environmental enrichment implemented after heroin self-administration does not reverse upregulation of VTA CRF1 receptor mRNA but it downregulates dopamine transporter mRNA. Overall, these data suggest that heroin self-administration requires stimulation of VTA CRF1 receptors and upregulates their expression in brain regions involved in reinforcement. Such long-lasting neuroadaptations may contribute to continuation of drug use and relapse due to stress exposure and are not easily reversed by EE exposure.

Integrated regulation of dopaminergic and epigenetic effectors of neuroprotection in Parkinson’s disease models

Whole-exome sequencing of Parkinson's disease (PD) patient DNA identified single-nucleotide polymorphisms (SNPs) in the tyrosine nonreceptor kinase-2 (TNK2) gene. Although this kinase had a previously demonstrated activity in preventing the endocytosis of the dopamine reuptake transporter (DAT), a causal role for TNK2-associated dysfunction in PD remains unresolved. We postulated the dopaminergic neurodegeneration resulting from patient-associated variants in TNK2 were a consequence of aberrant or prolonged TNK2 overactivity, the latter being a failure in TNK2 degradation by an E3 ubiquitin ligase, neuronal precursor cell-expressed developmentally down-regulated-4 (NEDD4). Interestingly, systemic RNA interference protein-3 (SID-3) is the sole TNK2 ortholog in the nematode Caenorhabditis elegans, where it is an established effector of epigenetic gene silencing mediated through the dsRNA-transporter, SID-1. We hypothesized that TNK2/SID-3 represents a node of integrated dopaminergic and epigenetic signaling essential to neuronal homeostasis. Use of a TNK2 inhibitor (AIM-100) or a NEDD4 activator [N-aryl benzimidazole 2 (NAB2)] in bioassays for either dopamine- or dsRNA-uptake into worm dopaminergic neurons revealed that sid-3 mutants displayed robust neuroprotection from 6-hydroxydopamine (6-OHDA) exposures, as did AIM-100 or NAB2-treated wild-type animals. Furthermore, NEDD4 activation by NAB2 in rat primary neurons correlated to a reduction in TNK2 levels and the attenuation of 6-OHDA neurotoxicity. CRISPR-edited nematodes engineered to endogenously express SID-3 variants analogous to TNK2 PD-associated SNPs exhibited enhanced susceptibility to dopaminergic neurodegeneration and circumvented the RNAi resistance characteristic of SID-3 dysfunction. This research exemplifies a molecular etiology for PD whereby dopaminergic and epigenetic signaling are coordinately regulated to confer susceptibility or resilience to neurodegeneration.

Consequences of Acute or Chronic Methylphenidate Exposure Using Ex Vivo Neurochemistry and In Vivo Electrophysiology in the Prefrontal Cortex and Striatum of Rats.

Methylphenidate (MPH) is among the main drugs prescribed to treat patients with attention-deficit and hyperactivity disease (ADHD). MPH blocks both the norepinephrine and dopamine reuptake transporters (NET and DAT, respectively). Our study was aimed at further understanding the mechanisms by which MPH could modulate neurotransmitter efflux, using ex vivo radiolabelled neurotransmitter assays isolated from rats. Here, we observed significant dopamine and norepinephrine efflux from the prefrontal cortex (PFC) after MPH (100 µM) exposure. Efflux was mediated by both dopamine and norepinephrine terminals. In the striatum, MPH (100 µM) triggered dopamine efflux through both sodium- and vesicular-dependent mechanisms. Chronic MPH exposure (4 mg/kg/day/animal, voluntary oral intake) for 15 days, followed by a 28-day washout period, increased the firing rate of PFC pyramidal neurons, assessed by in vivo extracellular single-cell electrophysiological recordings, without altering the responses to locally applied NMDA, via micro-iontophoresis. Furthermore, chronic MPH treatment resulted in decreased efficiency of extracellular dopamine to modulate NMDA-induced firing activities of medium spiny neurons in the striatum, together with lower MPH-induced (100 µM) dopamine outflow, suggesting desensitization to both dopamine and MPH in striatal regions. These results indicate that MPH can modulate neurotransmitter efflux in brain regions enriched with dopamine and/or norepinephrine terminals. Further, long-lasting alterations of striatal and prefrontal neurotransmission were observed, even after extensive washout periods. Further studies will be needed to understand the clinical implications of these findings.

Efeitos associados ao uso prolongado de metilfenidato para o tratamento de TDAH: uma revisão sistemática / Effects associated with long-term use of methylphenidate for the treatment of ADHD: a systematic review

INTRODUCTION: The mechanism of action of methylphenidate is to block presynaptic noradrenaline and dopamine reuptake transporters, resulting in increased concentration and time of action of neurotransmitters in the postsynaptic cell.OBJECTIVE: To research the effects associated with the long-term use of methylphenidate for the treatment of ADHD.METHODS: The report on the study was organized according to the criteria of preferred reporting items for systematic reviews and meta-analyses (Prisma), being a systematic review. The articles were analyzed between 2009 and July 2021, including original quantitative or qualitative research articles. Exclusion criteria used: opinion or review articles, or written in a language other than English, Portuguese. All research results are properly filed, enabling future consultations, following the inclusion and exclusion criteria described in the work.RESULTS: Of the 3104 articles identified for review, 20 were selected for review. The main effects of the use of methylphenidate were: irritability, tendency to cry and anxiety. Anorexia, nervousness, insomnia, headache, nausea, and weight loss have also been reported in ADHD patients. Risks of miscarriages and elective interruptions, cardiac malformations and pre-eclampsia in pregnancies exposed to methylphenidate. Risk of seizure in patients starting treatment and risk of prehypertension in adults with normal baseline blood pressure.CONCLUSION: With this systematic review it was possible to describe the adverse effects associated with the use of methylphenidate for the treatment of ADHD, as well as the risks associated with the unguided/recreational use of methylphenidate among health care students.

Clinical Outcome and Striatal Dopaminergic Function After Shunt Surgery in Patients With Idiopathic Normal Pressure Hydrocephalus.

To determine changes in clinical features and striatal dopamine reuptake transporter (DAT) density after shunt surgery in patients with idiopathic normal pressure hydrocephalus (iNPH). Participants with probable iNPH were assessed at baseline by means of clinical rating scales, brain MRI, and SPECT with [123I]-N-ω-fluoropropyl-2β-carbomethoxy-3β-(4-iodophenyl)nortropane (FP-CIT). Levodopa responsiveness was also evaluated. Patients who did or did not undergo lumboperitoneal shunt were clinically followed up and repeated SPECT after 2 years. We enrolled 115 patients with iNPH. Of 102 patients without significant levodopa response and no signs of atypical parkinsonism, 92 underwent FP-CIT SPECT (58 also at follow-up) and 59 underwent surgery. We identified a disequilibrium subtype (phenotype 1) and a locomotor subtype (phenotype 2) of higher-level gait disorder. Gait impairment correlated with caudate DAT density in both phenotypes, whereas parkinsonian signs correlated with putamen and caudate DAT binding in patients with phenotype 2, who showed more severe symptoms and lower striatal DAT density. Gait and caudate DAT binding improved in both phenotypes after surgery (p < 0.01). Parkinsonism and putamen DAT density improved in shunted patients with phenotype 2 (p < 0.001). Conversely, gait, parkinsonian signs, and striatal DAT binding worsened in patients who declined surgery (p < 0.01). This prospective interventional study highlights the pathophysiologic relevance of striatal dopaminergic dysfunction in the motor phenotypic expression of iNPH. Absence of levodopa responsiveness, shunt-responsive parkinsonism, and postsurgery improvement of striatal DAT density are findings that corroborate the notion of a reversible striatal dysfunction in a subset of patients with iNPH.

Striatal Dopamine Deficit and Motor Impairment in Idiopathic Normal Pressure Hydrocephalus.

Idiopathic normal pressure hydrocephalus can present with parkinsonism. However, abnormalities of the striatal dopamine reuptake transporter are unclear. To explore presence and features of striatal dopaminergic deficit in subjects with idiopathic normal pressure hydrocephalus as compared to Parkinson's disease (PD) patients and healthy controls. We investigated 50 subjects with idiopathic normal pressure hydrocephalus, 25 with PD, and 40 healthy controls. All participants underwent [123 I]-N-ω-fluoropropyl-2β-carbomethoxy-3β-(4-iodophenyl)nortropane and single-photon emission computed tomography to quantify the striatal dopamine reuptake transporter binding. All subjects with idiopathic normal pressure hydrocephalus underwent a levodopa (l-dopa) challenge test and magnetic resonance imaging to evaluate ventriculomegaly and white matter changes. Gait, cognition, balance, and continence were assessed with the Idiopathic Normal Pressure Hydrocephalus Rating Scale, and parkinsonism with the motor section of the Movement Disorder Society-Unified Parkinson's Disease Rating Scale. All patients completed a 2-year follow-up. A total of 62% of patients with idiopathic normal pressure hydrocephalus featured a reduced striatal dopamine reuptake transporter binding, which correlated with the severity of parkinsonism but not with features of ventriculomegaly or white matter changes. Unlike PD, this dopaminergic deficit in idiopathic normal pressure hydrocephalus was more symmetric and prominent in the caudate nucleus. Subjects with idiopathic normal pressure hydrocephalus can present a reduction of striatal dopamine reuptake transporter binding, which is consistent with the severity of parkinsonism and qualitatively differs from that found in PD patients. Longitudinal interventional studies are needed to prove a role for striatal dopamine reuptake transporter deficit in the pathophysiology of idiopathic normal pressure hydrocephalus. © 2020 International Parkinson and Movement Disorder Society.

Is contrast sensitivity a physiological marker in attention-deficit hyperactivity disorder?

Attention-deficit hyperactivity disorder (ADHD) is one of the most common childhood-onset psychiatric disorders. Although the etiology is complex and has not yet been clarified, dopamine is thought to play a role in the etiology. Methylphenidate (MPH) is a psychostimulant drug used as first-line treatment for ADHD and it inhibits dopamine and norepinephrine reuptake transporters. Dopamine also has an effect on retina and contrast sensitivity. Despite evidence indicating the effects of dopamine on contrast sensitivity, the results of studies examining contrast sensitivity in ADHD patients are inconsistent. Also, no studies have been encountered examining the possible effect of MPH on contrast sensitivity. The hypotheses of this study are that children with ADHD who have not used MPH will have lower contrast sensitivity levels than the members of the control group, that contrast sensitivity levels increase after the use of MPH, and that contrast sensitivity is a potential physiological marker for ADHD. The study was conducted with 30 children with ADHD and 30 children without ADHD. Psychiatric evaluations of the participants were conducted with the Schedule for Affective Disorders and Schizophrenia for School Age Children–Present and Lifetime—Turkish version, Conner’s Parent Rating Scale–Revised Short form and the Turgay DSM-IV-based Child and Adolescent Behavioral Disorders Screening and Rating Scale. Photopic contrast sensitivity was measured using the Functional Acuity Contrast Test (FACT). Results showed that FACT mean values of the control group were significantly higher than those of the ADHD group (pre-treatment) in all spatial frequencies. In four spatial frequencies (CPD 1.5, 3, 12 and 18), the FACT mean values of the control group were significantly higher than the ADHD group (during the OROS-MPH treatment). At all spatial frequencies, the mean values of the ADHD group during the OROS-MPH treatment were significantly higher than before the OROS-MPH treatment. In conclusion, the present study showed that contrast sensitivity is low in children with ADHD and increases significantly after OROS-MPH medication, but still did not reach the levels of the children without ADHD. Our findings suggest that contrast sensitivity may be a potential physiological marker in ADHD.

Reinforcing Effects of the Synthetic Cathinone α-Pyrrolidinopropiophenone (α-PPP) in a Repeated Extended Access Binge Paradigm.

Synthetic cathinones are designer psychostimulants that are derivatives of the natural alkaloid cathinone, and produce effects similar to more traditional illicit stimulants such as cocaine and methamphetamine. The pyrovalerone cathinones methylenedioxypyrovalerone (MDPV) and α-pyrrolidinopropiophenone (α-PPP) exert their effects via inhibition of presynaptic dopamine and norepinephrine reuptake transporters. While the reinforcing effects of MDPV in rodents are well-established, very few studies have examined self-administration patterns of α-PPP. Users of synthetic cathinones often engage in repeated binge episodes of drug intake that last several days. We therefore sought to determine the reinforcing effects of three doses of α-PPP (0.05, 0.1 and 0.32 mg/kg/infusion) under conditions of prolonged binge-like access conditions, with three 96-h periods of drug access interspersed with 72 h of abstinence. MDPV (0.05 mg/kg/infusion) was used as a comparison drug. Our results show that both MDPV and the high (0.32 mg/kg/infusion) dose of α-PPP are readily self-administered at high levels across all three extended access periods, whereas lower doses of α-PPP produce variable and less robust levels of self-administration. These results indicate that higher doses of α-PPP have reinforcing effects under conditions of extended access, suggesting the potential for abuse and a need for consideration in drug control policies.

Hazard Characterization of Synthetic Cathinones Using Viability, Monoamine Reuptake, and Neuronal Activity Assays.

Synthetic cathinones are the second largest class of new psychoactive substances (NPS) on the drug market. Despite the large number of different cathinones and their abundant use, hazard characterization is mainly limited to their potential to inhibit monoamine transporters. To expand the current hazard characterization, we first investigated the acute effects of several synthetic cathinones [4-methylethcathinone (4-MEC), 3-methylmethcathinone (3-MMC), 4-MMC, methylone, pentedrone, α-pyrrolidinovalerophenone (α-PVP), and 3,4-methylenedioxypyrovalerone (MDPV)] on human dopamine, norepinephrine, and serotonin reuptake transporters (hDAT, hNET, and hSERT), which were stably transfected in human embryonic kidney (HEK) 293 cells. Next, we examined effects on spontaneous neuronal activity in rat primary cortical cultures grown on microelectrode arrays (MEAs) as an integrated endpoint for neurotoxicity. Changes in neuronal activity were assessed after acute (30 min) and prolonged (4.5 h) exposure. Moreover, we investigated whether neuronal activity recovered after washout of the exposure (24 h after the start of the 5 h exposure). Low micromolar concentrations of synthetic cathinones inhibited monoamine uptake via hDAT and hNET, while higher cathinone concentrations were needed to inhibit uptake via hSERT. Comparable high concentrations were needed to inhibit spontaneous neuronal activity during acute (30 min) and prolonged (4.5 h) exposure. Notably, while the inhibition of neuronal activity was reversible at low concentrations, only partial recovery was seen following high, but non-cytotoxic, concentrations of synthetic cathinones. Synthetic cathinones with either a pyrrolidine moiety or long alkyl-tail carbon chain more potently inhibit monoamine uptake via hDAT and neuronal activity. Monoamine uptake via hNET was most potently inhibited by synthetic cathinones with a pyrrolidine moiety. The combination of integrated measurements (MEA recordings of neuronal activity) with single target assays (monoamine reuptake transporter inhibition) indicates inhibition of hDAT and hNET as the primary mode of action of these synthetic cathinones. Changes in neuronal activity, indicative for additional mechanisms, were observed at higher concentrations.

Bupropion Inhibits Serotonin Type 3AB Heteromeric Channels at Clinically Relevant Concentrations.

Bupropion, a Food and Drug Administration–approved antidepressant and smoking cessation aid, blocks dopamine and norepinephrine reuptake transporters and noncompetitively inhibits nicotinic acetylcholine and serotonin (5-HT) type 3A receptors (5-HT3ARs). 5-HT3 receptors are pentameric ligand-gated ion channels that regulate synaptic activity in the central and peripheral nervous system, presynaptically and postsynaptically. In the present study, we examined and compared the effect of bupropion and its active metabolite hydroxybupropion on mouse homomeric 5-HT3A and heteromeric 5-HT3AB receptors expressed in Xenopus laevis oocytes using two-electrode voltage clamp experiments. Coapplication of bupropion or hydroxybupropion with 5-HT dose dependently inhibited 5-HT–induced currents in heteromeric 5-HT type 3AB receptors (5-HT3ABRs) (IC50 = 840 and 526 μM, respectively). The corresponding IC50s for bupropion and hydroxybupropion for homomeric 5-HT3ARs were 10- and 5-fold lower, respectively (87 and 113 μM). The inhibition of 5-HT3ARs and 5-HT3ABRs was non–use dependent and voltage independent, suggesting bupropion is not an open channel blocker. The inhibition by bupropion was reversible and time-dependent. Of note, preincubation with a low concentration of bupropion that mimics therapeutic drug conditions inhibits 5-HT–induced currents in 5-HT3A and 5-HT3AB receptors considerably. In summary, we demonstrate that bupropion inhibits heteromeric 5-HT3ABRs as well as homomeric 5-HT3ARs. This inhibition occurs at clinically relevant concentrations and may contribute to bupropion’s clinical effects.SIGNIFICANCE STATEMENTClinical studies indicate that antagonizing serotonin (5-HT) type 3AB (5-HT3AB) receptors in brain areas involved in mood regulation is successful in treating mood and anxiety disorders. Previously, bupropion was shown to be an antagonist at homopentameric 5-HT type 3A receptors. The present work provides novel insights into the pharmacological effects that bupropion exerts on heteromeric 5-HT3AB receptors, in particular when constantly present at low, clinically attainable concentrations. The results advance the knowledge on the clinical effects of bupropion as an antidepressant.

Differential effects of psychoactive substances on human wildtype and polymorphic T356M dopamine transporters (DAT)

Many psychoactive substances affect the human dopamine (DA) reuptake transporter (hDAT). Polymorphisms in the encoding gene could affect the functionality of the transporter and consequently alter effects of psychotropic and recreational drugs. Recently, a T356 M single nucleotide polymorphism in the human SLC6A3 gene was described, which resulted in functional impairments of DA uptake. Therefore, we investigated the effects of 10 psychoactive substances (0.01–1000 μM)) on DA uptake in human embryonic kidney (HEK) 293 cells transiently overexpressing wildtype (WT) or T356 M hDAT.Our data shows that T356 M hDAT has a 3 times lower Vmax and a 3 times higher Km compared to WT hDAT. Additionally, all psychoactive substances inhibited DA uptake by T356 M and WT hDAT. The DA reuptake inhibitors (methylphenidate, cocaine, and bupropion) inhibited DA uptake by WT hDAT most potently, followed by amphetamine-type stimulants [4-fluoroamphetamine (4-FA), amphetamine and MDMA], selective serotonin reuptake inhibitors (SSRI; fluoxetine and citalopram) and arylcyclohexylamines [methoxetamine (MXE) and ketamine].Compared to DA uptake by WT hDAT, bupropion, methylphenidate, cocaine, and MXE less potently inhibited DA uptake by T356 M hDAT, while citalopram more potently inhibited uptake. The differences in IC50 values between T356 M and WT hDAT were considerable (3–45 fold). As such, the presence of this polymorphism could affect treatment efficiency with these substances as well as susceptibly for toxicity and addiction for individuals carrying this polymorphism.

An opsin 5-dopamine pathway mediates light-dependent vascular development in the eye.

During mouse postnatal eye development, the embryonic hyaloid vascular network regresses from the vitreous as an adaption for high acuity vision. This process occurs with precisely controlled timing. Here we show that an Opsin 5 (OPN5, Neuropsin)-dependent retinal light response regulates vascular development in the postnatal eye. In Opn5 null mice hyaloid vessels regress precociously. We demonstrate that 380 nm light stimulation via OPN5 and VGAT (the vesicular GABA/glycine transporter) in retinal ganglion cells enhances activity of inner retinal DAT/SLC6A3 (a dopamine reuptake transporter) and thus suppresses vitreal dopamine. In turn, dopamine acts directly on hyaloid vascular endothelial cells to suppress activity of VEGFR2 and promote hyaloid vessel regression. With OPN5 loss-of-function, vitreous dopamine is elevated and results in premature hyaloid regression. These investigations identify violet light as a developmental timing cue that, via an OPN5-dopamine pathway, regulates optic axis clearance in preparation for visual function.

Task-Dependent Differences in Operant Behaviors of Rats With Acute Exposure to High Ambient Temperature: A Potential Role of Hippocampal Dopamine Reuptake Transporters.

Behavioral or cognitive functions are known to be influenced by thermal stress from the change in ambient temperature (Ta). However, little is known about how increased Ta (i.e., when the weather becomes warm or hot) may affect operant conditioned behavior and the neural substrates involved. The present study thus investigated the effects of high Ta on operant behaviors maintained on a fixed-ratio 1 (FR1) and a differential reinforcement for low-rate responding 10 s (DRL 10-s) schedule of reinforcement. The rats were randomly assigned to three groups receiving acute exposure to Ta of 23°C, 28°C, and 35°C, respectively, for evaluating the effects of high Ta exposure on four behavioral tests. Behavioral responses in an elevated T-maze and locomotor activity were not affected by Ta treatment. Regarding operant tests, while the total responses of FR1 behavior were decreased only under 35°C when compared with the control group of 23°C, those of DRL 10-s behavior were significantly reduced in both groups of 28°C and 35°C. Distinct patterns of inter-response time (IRT) distribution of DRL behavior appeared among the three groups; between-group differences of behavioral changes produced by high Ta exposure were confirmed by quantitative analyses of IRT data. Western blot assays of dopamine (DA) D1 and D2 receptor, DA transporter (DAT) and brain-derived neurotrophic factor (BDNF) were conducted for the sample tissues collected in six brain areas from all the subjects after acute high Ta exposure. Significant Ta-related effects were only revealed in the dorsal hippocampus (dHIP). In which, the DAT levels were increased in a Ta-dependent fashion that was associated with operant behavior changes under high Ta exposure. And, there as an increased level of D1 receptors in the 28°C group. In summary, these data indicate that the performance of operant behavior affected by the present high Ta exposure is task-dependent, and these changes of operant behaviors cannot be attributed to gross motor function or anxiety being affected. The regulation of dHIP DAT may be involved in this operant behavioral change under high Ta exposure.

Effect of microinjections of dopamine into the nucleus accumbens shell on emission of 50 kHz USV: Comparison with effects of d-amphetamine

Systemic pharmacological manipulation of dopamine (DA) signaling has been central to many investigations of 50 kHz ultrasonic vocalizations (USVs) in the rat. In particular, the indirect DA releaser d-amphetamine (AMPH) has been used extensively in many such investigations. The possible unique character of the native transmitter relative to DA-stimulating drugs such as AMPH in inducing and modulating emission of 50 kHz USVs has not been investigated. Adult male Long Evans rats were tested with intracerebral application of DA into the nucleus accumbens shell at several doses (3.75 μg–120 μg) to determine its capacity to induce 50 kHz USV emission. Additionally, the call profile characteristics of intracerebral DA injections were compared with those of intracerebral application of AMPH. Results indicated that local increases in DA signaling within the nucleus accumbens shell are sufficient to increase 50 kHz call rate, reduce latency to call, and increase the degree of frequency modulation of emitted USVs. However, our results found that microinjections of DA were not as efficacious in either inducing 50 kHz USVs or increasing frequency modulation without antagonism of the dopamine reuptake transporter when compared with AMPH. In summary, these results support the notion that the native transmitter DA is driving the increase in frequency modulation seen after administration of DA stimulating drugs. These results also suggest that drugs affecting dopamine may be altering the 50 kHz call profile in a distinct manner from the native transmitter and thus caution should be used in interpreting their effects.

Activation of RHO-1 in cholinergic motor neurons competes with dopamine signalling to control locomotion.

The small GTPase RhoA plays a crucial role in the regulation of neuronal signalling to generate behaviour. In the developing nervous system RhoA is known to regulate the actin cytoskeleton, however the effectors of RhoA-signalling in adult neurons remain largely unidentified. We have previously shown that activation of the RhoA ortholog (RHO-1) in C. elegans cholinergic motor neurons triggers hyperactivity of these neurons and loopy locomotion with exaggerated body bends. This is achieved in part through increased diacylglycerol (DAG) levels and the recruitment of the synaptic vesicle protein UNC-13 to synaptic release sites, however other pathways remain to be identified. Dopamine, which is negatively regulated by the dopamine re-uptake transporter (DAT), has a central role in modulating locomotion in both humans and C. elegans. In this study we identify a new pathway in which RHO-1 regulates locomotory behaviour by repressing dopamine signalling, via DAT-1, linking these two pathways together. We observed an upregulation of dat-1 expression when RHO-1 is activated and show that loss of DAT-1 inhibits the loopy locomotion phenotype caused by RHO-1 activation. Reducing dopamine signalling in dat-1 mutants through mutations in genes involved in dopamine synthesis or in the dopamine receptor DOP-1 restores the ability of RHO-1 to trigger loopy locomotion in dat-1 mutants. Taken together, we show that negative regulation of dopamine signalling via DAT-1 is necessary for the neuronal RHO-1 pathway to regulate locomotion.

Impact of maternal high fat diet on hypothalamic transcriptome in neonatal Sprague Dawley rats.

Maternal consumption of a high fat diet during early development has been shown to impact the formation of hypothalamic neurocircuitry, thereby contributing to imbalances in appetite and energy homeostasis and increasing the risk of obesity in subsequent generations. Early in postnatal life, the neuronal projections responsible for energy homeostasis develop in response to appetite-related peptides such as leptin. To date, no study characterises the genome-wide transcriptional changes that occur in response to exposure to high fat diet during this critical window. We explored the effects of maternal high fat diet consumption on hypothalamic gene expression in Sprague Dawley rat offspring at postnatal day 10. RNA-sequencing enabled discovery of differentially expressed genes between offspring of dams fed a high fat diet and offspring of control diet fed dams. Female high fat diet offspring displayed altered expression of 86 genes (adjusted P-value<0.05), including genes coding for proteins of the extra cellular matrix, particularly Collagen 1a1 (Col1a1), Col1a2, Col3a1, and the imprinted Insulin-like growth factor 2 (Igf2) gene. Male high fat diet offspring showed significant changes in collagen genes (Col1a1 and Col3a1) and significant upregulation of two genes involved in regulation of dopamine availability in the brain, tyrosine hydroxylase (Th) and dopamine reuptake transporter Slc6a3 (also known as Dat1). Transcriptional changes were accompanied by increased body weight, body fat and body length in the high fat diet offspring, as well as altered blood glucose and plasma leptin. Transcriptional changes identified in the hypothalamus of offspring of high fat diet mothers could alter neuronal projection formation during early development leading to abnormalities in the neuronal circuitry controlling appetite in later life, hence priming offspring to the development of obesity.

Cholinergic activity and levodopa-induced dyskinesia: a multitracer molecular imaging study.

ObjectiveTo investigate the association between levodopa‐induced dyskinesias and striatal cholinergic activity in patients with Parkinson's disease.MethodsThis study included 13 Parkinson's disease patients with peak‐of‐dose levodopa‐induced dyskinesias, 12 nondyskinetic patients, and 12 healthy controls. Participants underwent 5‐[123I]iodo‐3‐[2(S)‐2‐azetidinylmethoxy]pyridine single‐photon emission computed tomography, a marker of nicotinic acetylcholine receptors, [123I]N‐ω‐fluoropropyl‐2β‐carbomethoxy‐3β‐(4‐iodophenyl)nortropane single‐photon emission computed tomography, to measure dopamine reuptake transporter density and 2‐[18F]fluoro‐2‐deoxyglucose positron emission tomography to assess regional cerebral metabolic activity. Striatal binding potentials, uptake values at basal ganglia structures, and correlations with clinical variables were analyzed.ResultsDensity of nicotinic acetylcholine receptors in the caudate nucleus of dyskinetic subjects was similar to that of healthy controls and significantly higher to that of nondyskinetic patients, in particular, contralaterally to the clinically most affected side.InterpretationOur findings support the hypothesis that the expression of dyskinesia may be related to cholinergic neuronal excitability in a dopaminergic‐depleted striatum. Cholinergic signaling would play a role in maintaining striatal dopaminergic responsiveness, possibly defining disease phenotype and progression.