Catharanthine Modulates Mesolimbic Dopamine Transmission and Nicotine Psychomotor Effects via Inhibition of α6-Nicotinic Receptors and Dopamine Transporters.

Iboga alkaloids, also known as coronaridine congeners, have shown promise in the treatment of alcohol and opioid use disorders. The objective of this study was to evaluate the effects of catharanthine and 18-methoxycoronaridine (18-MC) on dopamine (DA) transmission and cholinergic interneurons in the mesolimbic DA system, nicotine-induced locomotor activity, and nicotine-taking behavior. Utilizing ex vivo fast-scan cyclic voltammetry (FSCV) in the nucleus accumbens core of male mice, we found that catharanthine or 18-MC differentially inhibited evoked DA release. Catharanthine inhibition of evoked DA release was significantly reduced by both α4 and α6 nicotinic acetylcholine receptors (nAChRs) antagonists. Additionally, catharanthine substantially increased DA release more than vehicle during high-frequency stimulation, although less potently than an α4 nAChR antagonist, which confirms previous work with nAChR antagonists. Interestingly, while catharanthine slowed DA reuptake measured via FSCV ex vivo, it also increased extracellular DA in striatal dialysate from anesthetized mice in vivo in a dose-dependent manner. Superfusion of catharanthine or 18-MC inhibited the firing rate of striatal cholinergic interneurons in a concentration dependent manner, which are known to potently modulate presynaptic DA release. Catharanthine or 18-MC suppressed acetylcholine currents in oocytes expressing recombinant rat α6/α3ß2ß3 or α6/α3ß4 nAChRs. In behavioral experiments using male Sprague-Dawley rats, systemic administration of catharanthine or 18-MC blocked nicotine enhancement of locomotor activity. Importantly, catharanthine attenuated nicotine self-administration in a dose-dependent manner while having no effect on food reinforcement. Lastly, administration of catharanthine and nicotine together greatly increased head twitch responses, indicating a potential synergistic hallucinogenic effect. These findings demonstrate that catharanthine and 18-MC have similar, but not identical effects on striatal DA dynamics, striatal cholinergic interneuron activity and nicotine psychomotor effects.

Cocaine hydrolase blocks cocaine-induced dopamine transporter trafficking to the plasma membrane.

Cocaine blocks dopamine uptake via dopamine transporter (DAT) on plasma membrane of neuron cells and, as a result, produces the high and induces DAT trafficking to plasma membrane which contributes to the drug seeking or craving. In this study, we first examined the dose dependence of cocaine-induced DAT trafficking and hyperactivity in rats, demonstrating that cocaine at an intraperitoneal dose of 10 mg/kg or higher led to redistribution of most DAT to the plasma membrane while inducing significant hyperactivity in rats. However, administration of 5-mg/kg cocaine (ip) did not significantly induce DAT trafficking or hyperactivity in rats. So the threshold (intraperitoneal) dose of cocaine that can significantly induce DAT trafficking or hyperactivity should be between 5 and 10 mg/kg. These data suggest that when a cocaine dose is high enough to induce significant hyperactivity, it can also significantly induce DAT trafficking to the plasma membrane. Further, the threshold brain cocaine concentration required to induce significant hyperactivity and DAT trafficking was estimated to be ~2.0 ± 0.8 µg/g. Particularly, for treatment of cocaine abuse, previous studies demonstrated that an exogenous cocaine-metabolizing enzyme, for example, CocH3-Fc(M3), can effectively block cocaine-induced hyperactivity. However, it was unknown whether an enzyme could also effectively block cocaine-induced DAT trafficking to the plasma membrane. This study demonstrates, for the first time, that the enzyme is also capable of effectively blocking cocaine from reaching the brain even with a lethal dose of 60-mg/kg cocaine (ip) and, thus, powerfully preventing cocaine-induced physiological effects such as the hyperactivity and DAT trafficking.

Non-conserved residues dictate dopamine transporter selectivity for the potent synthetic cathinone and psychostimulant MDPV.

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 Ca2+-mobilization assay. In this assay, voltage-gated Ca2+ 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.

Neurokinin-1 Antagonism Distinguishes the Role of Norepinephrine Transporter from Dopamine Transporter in Mediating Amphetamine Behaviors.

BACKGROUND: Amphetamine (AMPH) and other psychostimulants act on the norepinephrine (NE) transporter (NET) and the dopamine (DA) transporter (DAT) and enhance NE and DA signaling. Both NET and DAT share anatomical and functional characteristics and are regulated similarly by psychostimulants and receptor-linked signaling pathways. We and others have demonstrated that NET and DAT are downregulated by AMPH and substance P/neurokinin-1 receptor (NK1R)-mediated protein kinase C pathway. OBJECTIVES: Since both NET and DAT are downregulated by AMPH and NK1R activation and share high sequence homology, the objective of the study was to determine the catecholamine transporter specificity in NK1R modulation of AMPH-induced behaviors. METHODS: The effect of NK1R antagonism on AMPH-induced conditioned place preference (CPP) as well as AMPH-induced NET and DAT downregulation was examined using NET and DAT knockout mice (NET-KO and DAT-KO) along with their wild-type littermates. RESULTS: Aprepitant (5 mg/kg i.p.) significantly attenuated AMPH (2 mg/kg i.p.)-induced CPP in the wild-type and DAT-KO but not in the NET-KO. Locomotor activity measured during the post-conditioning test (in the absence of AMPH) showed higher locomotor activity in DAT-KO compared to wild-type or NET-KO. However, the locomotor activity of all 3 genotypes remained unchanged following aprepitant. Additionally, in the ventral striatum of wild-type, the AMPH-induced downregulation of NET function and surface expression but not that of DAT was attenuated by aprepitant. CONCLUSIONS: The results from the current study demonstrate that aprepitant attenuates the expression of AMPH-induced CPP in DAT-KO mice but not in NET-KO mice suggesting a role for NK1R-mediated NET regulation in AMPH-induced behaviors.

Pitolisant, a wake-promoting agent devoid of psychostimulant properties: Preclinical comparison with amphetamine, modafinil, and solriamfetol.

Several therapeutic options are currently available to treat excessive daytime sleepiness (EDS) in patients suffering from narcolepsy or obstructive sleep apnea. However, there are no comparisons between the various wake-promoting agents in terms of mechanism of action, efficacy, or safety. The goal of this study was to compare amphetamine, modafinil, solriamfetol, and pitolisant at their known primary pharmacological targets, histamine H3 receptors (H3R), dopamine, norepinephrine, and serotonin transporters, and in various in vivo preclinical models in relation to neurochemistry, locomotion, behavioral sensitization, and food intake. Results confirmed that the primary pharmacological effect of amphetamine, modafinil, and solriamfetol was to increase central dopamine neurotransmission, in part by inhibiting its transporter. Furthermore, solriamfetol increased levels of extracellular dopamine in the nucleus accumbens, and decreased the 3,4-dihydroxyphenyl acetic acid (DOPAC)/DA ratio in the striatum, as reported for modafinil and amphetamine. All these compounds produced hyperlocomotion, behavioral sensitization, and hypophagia, which are common features of psychostimulants and of compounds with abuse potential. In contrast, pitolisant, a selective and potent H3R antagonist/inverse agonist that promotes wakefulness, had no effect on striatal dopamine, locomotion, or food intake. In addition, pitolisant, devoid of behavioral sensitization by itself, attenuated the hyperlocomotion induced by either modafinil or solriamfetol. Therefore, pitolisant presents biochemical, neurochemical, and behavioral profiles different from those of amphetamine and other psychostimulants such as modafinil or solriamfetol. In conclusion, pitolisant is a differentiated therapeutic option, when compared with psychostimulants, for the treatment of EDS, as this agent does not show any amphetamine-like properties within in vivo preclinical models.

MicroPET/CT assessment of neurochemical effects in the brain after long-term methylphenidate treatment in nonhuman primates.

Methylphenidate (MPH) is a psychostimulant approved by the FDA to treatment Attention-Deficit Hyperactivity Disorder (ADHD). MPH is believed to exert its pharmacological effects via preferential blockade of the dopamine transporter (DAT) and the norepinephrine transporter (NET), resulting in increased monoamine levels in the synapse. We used a quantitative non-invasive PET imaging technique to study the effects of long-term methylphenidate use on the central nervous system (CNS). We conducted microPET/CT scans on young adult male rhesus monkeys to monitor changes in the dopaminergic system. We used [18F] AV-133, a ligand for the vesicular monoamine transporter 2 (VMAT2), and [18F]FESP a ligand for the D2 and 5HT2 receptors. In this study we evaluated the effects if chronic MPH treatment in the nonhuman primates (NHP). Two-year-old, male rhesus monkeys were orally administered MPH diluted in the electrolyte replenisher, Prang, twice a day, five days per week (M-F) over an 8-year period. The dose of MPH was gradually escalated from 0.15 mg/kg initially to 2.5 mg/kg/dose for the low dose group, and 1.5 mg/kg to 12.5 mg/kg/dose for the high dose group (Rodriguez et al., 2010). Scans were performed on Mondays, about 60 h after their last treatment, to avoid the acute effects of MPH. Tracers were injected intravenously ten minutes before microPET/CT scanning. Sessions lasted about 120 min. The Logan reference tissue model was used to determine the Binding Potential (BP) of each tracer in the striatum with the cerebellar cortex time activity curve as an input function. Both MP treatment groups had a lower [18F] AV-133 BP, although this failed to reach statistical significance. MPH treatment did not have a significant effect on The BP of [18F] FESP in the striatum. Long-term administration of MPH did not significant change any of the marker of monoamine function used here. These data suggest that, despite lingering concerns, long-term use of methylphenidate does not negatively impact monoamine function. This study also demonstrates that microPET imaging can distinguish differences in binding potentials of a variety of radiotracers in the CNS of NHPs. This approach may provide minimally-invasive biomarkers of neurochemical processes associated with chronic exposure to CNS medications. (Supported by NCTR).

Functional validation of a finding from a mouse genome-wide association study shows that Azi2 influences the acute locomotor stimulant response to methamphetamine.

In a previous genome-wide association study (GWAS) using outbred Carworth Farms White (CFW) mice, we identified a locus that influenced the stimulant response to methamphetamine and colocalized with an eQTL for Azi2. Based on those findings, we hypothesized that heritable differences in Azi2 expression were causally related to the differential response to methamphetamine. To test that hypothesis, we created a mutant Azi2 allele on an inbred C57BL/6J background. The mutant allele enhanced the locomotor response to methamphetamine. However, the GWAS had suggested that lower Azi2 would decrease the locomotor response to methamphetamine. We also sought to explore the mechanism by which Azi2 influenced methamphetamine sensitivity. A recent publication reported that the 3'UTR of Azi2 mRNA downregulates the expression of Slc6a3, which encodes the dopamine transporter, which is a key target of methamphetamine. We evaluated the relationship between Azi2, Azi2 3'UTR and Slc6a3 expression in the ventral tegmental area of wildtype, mutant Azi2 heterozygotes and mutant Azi2 homozygotes and in a new cohort of outbred CFW mice where both allele mapped in our prior GWAS were segregating. We did not observe any correlation between Azi2 and Slc6a3 in either cohort. However, RNA sequencing confirmed that the Azi2 mutation altered Azi2 expression and also revealed a number of potentially important genes and pathways that were regulated by Azi2, including the metabotropic glutamate receptor group III pathway and nicotinic acetylcholine receptor signaling pathway. Our results support a role for Azi2 in methamphetamine sensitivity; however, the exact mechanism does not appear to involve regulation of Slc6a3.

SLC26A6-selective inhibitor identified in a small-molecule screen blocks fluid absorption in small intestine.

SLC26A6 (also known as putative anion transporter 1 [PAT1]) is a Cl-/HCO3- exchanger expressed at the luminal membrane of enterocytes where it facilitates intestinal Cl- and fluid absorption. Here, high-throughput screening of 50,000 synthetic small molecules in cells expressing PAT1 and a halide-sensing fluorescent protein identified several classes of inhibitors. The most potent compound, the pyrazolo-pyrido-pyrimidinone PAT1inh-B01, fully inhibited PAT1-mediated anion exchange (IC50 ~350 nM), without inhibition of the related intestinal transporter SLC26A3 (also known as DRA). In closed midjejunal loops in mice, PAT1inh-B01 inhibited fluid absorption by 50%, which increased to >90% when coadministered with DRA inhibitor DRAinh-A270. In ileal loops, PAT1inh-B01 blocked fluid absorption by >80%, whereas DRAinh-A270 was without effect. In colonic loops, PAT1inh-B01 was without effect, whereas DRAinh-A270 completely blocked fluid absorption. In a loperamide constipation model, coadministration of PAT1inh-B01 with DRAinh-A270 increased stool output compared with DRAinh-A270 alone. These results provide functional evidence for complementary and region-specific roles of PAT1 and DRA in intestinal fluid absorption, with PAT1 as the predominant anion exchanger in mouse ileum. We believe that PAT1inh-B01 is a novel tool to study intestinal ion and fluid transport and perhaps a drug candidate for small intestinal hyposecretory disorders such as cystic fibrosis-related meconium ileus and distal intestinal obstruction syndrome.

Psychomotor impairments and therapeutic implications revealed by a mutation associated with infantile Parkinsonism-Dystonia.

Parkinson disease (PD) is a progressive, neurodegenerative disorder affecting over 6.1 million people worldwide. Although the cause of PD remains unclear, studies of highly penetrant mutations identified in early-onset familial parkinsonism have contributed to our understanding of the molecular mechanisms underlying disease pathology. Dopamine (DA) transporter (DAT) deficiency syndrome (DTDS) is a distinct type of infantile parkinsonism-dystonia that shares key clinical features with PD, including motor deficits (progressive bradykinesia, tremor, hypomimia) and altered DA neurotransmission. Here, we define structural, functional, and behavioral consequences of a Cys substitution at R445 in human DAT (hDAT R445C), identified in a patient with DTDS. We found that this R445 substitution disrupts a phylogenetically conserved intracellular (IC) network of interactions that compromise the hDAT IC gate. This is demonstrated by both Rosetta molecular modeling and fine-grained simulations using hDAT R445C, as well as EPR analysis and X-ray crystallography of the bacterial homolog leucine transporter. Notably, the disruption of this IC network of interactions supported a channel-like intermediate of hDAT and compromised hDAT function. We demonstrate that Drosophila melanogaster expressing hDAT R445C show impaired hDAT activity, which is associated with DA dysfunction in isolated brains and with abnormal behaviors monitored at high-speed time resolution. We show that hDAT R445C Drosophila exhibit motor deficits, lack of motor coordination (i.e. flight coordination) and phenotypic heterogeneity in these behaviors that is typically associated with DTDS and PD. These behaviors are linked with altered dopaminergic signaling stemming from loss of DA neurons and decreased DA availability. We rescued flight coordination with chloroquine, a lysosomal inhibitor that enhanced DAT expression in a heterologous expression system. Together, these studies shed some light on how a DTDS-linked DAT mutation underlies DA dysfunction and, possibly, clinical phenotypes shared by DTDS and PD.

An efficient and label-free LC-MS/MS method for assessing drug's activity at dopamine and serotonin transporters using transporter-transfected HEK293T cells.

BACKGROUND: Dopamine transporter (DAT) and serotonin transporter (SERT) are targets for many psychoactive substances. Functional assays including uptake inhibition and release assays often involve radiolabeled compounds like [3H]-dopamine and [3H]-serotonin to assess drug activity at transporters, which have high requirements on handling radioactive samples. AIMS: The aim of this study was to establish a label-free method to assess drug activity at DAT and SERT. METHODS: A liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) method was established using transporter-transfected human embryonic kidney 293T (HEK293T) cells. This method was evaluated by testing the effects of amphetamine and cocaine in the assay procedure. RESULTS: The limits of detection of this method were 0.2 nM for both dopamine (DA) and serotonin (5-HT), with good linearities in the range of 0.5-160 nM. Amphetamine and cocaine's IC50 and EC50 on DAT and SERT determined by this method were consistent with previous reports. CONCLUSIONS: A rapid, reliable and label-free LC-MS/MS method for assessing drug activity was established, which affords an attractive alternative for those laboratories that do not have a radiation license or capabilities.

α-PPP and its derivatives are selective partial releasers at the human norepinephrine transporter: A pharmacological characterization of interactions between pyrrolidinopropiophenones and high and low affinity monoamine transporters.

While classical cathinones, such as methcathinone, have been shown to be monoamine releasing agents at human monoamine transporters, the subgroup of α-pyrrolidinophenones has thus far solely been characterized as monoamine transporter reuptake inhibitors. Herein, we report data from previously undescribed α-pyrrolidinopropiophenone (α-PPP) derivatives and compare them with the pharmacologically well-researched α-PVP (α-pyrrolidinovalerophenone). Radiotracer-based in vitro uptake inhibition assays in HEK293 cells show that the investigated α-PPP derivatives inhibit the human high-affinity transporters of dopamine (hDAT) and norepinephrine (hNET) in the low micromolar range, with α-PVP being ten times more potent. Similar to α-PVP, no relevant pharmacological activity was found at the human serotonin transporter (hSERT). Unexpectedly, radiotracer-based in vitro release assays reveal α-PPP, MDPPP and 3Br-PPP, but not α-PVP, to be partial releasing agents at hNET (EC50 values in the low micromolar range). Furthermore, uptake inhibition assays at low-affinity monoamine transporters, i.e., the human organic cation transporters (hOCT) 1-3 and human plasma membrane monoamine transporter (hPMAT), bring to light that all compounds inhibit hOCT1 and 2 (IC50 values in the low micromolar range) while less potently interacting with hPMAT and hOCT3. In conclusion, this study describes (i) three new hybrid compounds that efficaciously block hDAT while being partial releasers at hNET, and (ii) highlights the interactions of α-PPP-derivatives with low-affinity monoamine transporters, giving impetus to further studies investigating the interaction of drugs of abuse with OCT1-3 and PMAT.

Direct coupling of oligomerization and oligomerization-driven endocytosis of the dopamine transporter to its conformational mechanics and activity.

Dopamine transporter (DAT) mediates the reuptake of synaptically released dopamine, and thus controls the duration and intensity of dopamine neurotransmission. Mammalian DAT has been observed to form oligomers, although the mechanisms of oligomerization and its role in DAT activity and trafficking remain largely unknown. We discovered a series of small molecule compounds that stabilize trimers and induce high-order oligomers of DAT and concomitantly promote its clathrin-independent endocytosis. Using a combination of chemical cross-linking, fluorescence resonance energy transfer microscopy, antibody-uptake endocytosis assay, live-cell lattice light sheet microscopy, ligand binding and substrate transport kinetics analyses, and molecular modeling and simulations, we investigated molecular basis of DAT oligomerization and endocytosis induced by these compounds. Our study showed that small molecule-induced DAT oligomerization and endocytosis are favored by the inward-facing DAT conformation and involve interactions of four hydrophobic residues at the interface between transmembrane (TM) helices TM4 and TM9. Surprisingly, a corresponding quadruple DAT mutant displays altered dopamine transport kinetics and increased cocaine-analog binding. The latter is shown to originate from an increased preference for outward-facing conformation and inward-to-outward transition. Taken together, our results demonstrate a direct coupling between conformational dynamics of DAT, functional activity of the transporter, and its oligomerization leading to endocytosis. The high specificity of such coupling for DAT makes the TM4-9 hub a new target for pharmacological modulation of DAT activity and subcellular localization.

Optogenetic brain-stimulation reward: A new procedure to re-evaluate the rewarding versus aversive effects of cannabinoids in dopamine transporter-Cre mice.

Despite extensive research, the rewarding effects of cannabinoids are still debated. Here, we used a newly established animal procedure called optogenetic intracranial self-stimulation (ICSS) (oICSS) to re-examine the abuse potential of cannabinoids in mice. A specific adeno-associated viral vector carrying a channelrhodopsin gene was microinjected into the ventral tegmental area (VTA) to express light-sensitive channelrhodopsin in dopamine (DA) neurons of transgenic dopamine transporter (DAT)-Cre mice. Optogenetic stimulation of VTA DA neurons was highly reinforcing and produced a classical "sigmoidal"-shaped stimulation-response curve dependent upon the laser pulse frequency. Systemic administration of cocaine dose-dependently enhanced oICSS and shifted stimulation-response curves upward, in a way similar to previously observed effects of cocaine on electrical ICSS. In contrast, Δ9 -tetrahydrocannabinol (Δ9 -THC), but not cannabidiol, dose-dependently decreased oICSS responding and shifted oICSS curves downward. WIN55,212-2 and ACEA, two synthetic cannabinoids often used in laboratory settings, also produced dose-dependent reductions in oICSS. We then examined several new synthetic cannabinoids, which are used recreationally. XLR-11 produced a cocaine-like increase, AM-2201 produced a Δ9 -THC-like reduction, while 5F-AMB had no effect on oICSS responding. Immunohistochemistry and RNAscope in situ hybridization assays indicated that CB1 Rs are expressed mainly in VTA GABA and glutamate neurons, while CB2 Rs are expressed mainly in VTA DA neurons. Together, these findings suggest that most cannabinoids are not reward enhancing, but rather reward attenuating or aversive in mice. Activation of CB1 R and/or CB2 R in different populations of neurons in the brain may underlie the observed actions.

Cannabidiol prevents priming- and stress-induced reinstatement of the conditioned place preference induced by cocaine in mice.

BACKGROUND: Cocaine dependence is an important problem without any effective pharmacological treatment. Some preclinical studies have suggested that cannabidiol (CBD), a component of the Cannabis sativa plant, could be useful for the treatment of cocaine use disorders. AIMS: This work aims to evaluate the ability of CBD to reduce priming- and stress-induced reinstatement of the conditioned place preference (CPP) induced by cocaine. METHODS: Young adult CD-1 male mice were allocated to 10 groups (n = 12/group), conditioned with cocaine (10 mg/kg) and exposed to extinction of CPP (two sessions per week). When extinction was achieved, each group received the corresponding treatment before the reinstatement test. In experiment 1, six groups were used: vehicle+saline (Veh+Sal), 5 mg/kg cocaine alone (Veh+Coc) or with CBD 30 or 60 mg/kg (CBD30+Coc, CBD60+Coc) and CBD alone (CBD30+Sal, CBD60+Sal). In experiment 2, four groups were used: exploration (Veh+Expl), social defeat (Veh+SD) and social defeat with CBD (CBD30+SD and CBD60+SD). Furthermore, the relative gene expression of the dopamine transporter (DAT) in the ventral tegmental area was measured. RESULTS: All mice acquired cocaine CPP and extinguished it after three or four weeks. Only the groups treated with cocaine priming (Veh+Coc) or exposed to social defeat (Veh+SD) showed reinstatement of CPP. Interestingly, CBD itself did not induce reinstatement and blocked the reinstating effects of cocaine priming and social defeat. Furthermore, cocaine priming increased DAT gene expression in the ventral tegmental area and CBD completely reversed this effect. CONCLUSION: These results suggest that CBD could reduce reinstatement to cocaine seeking after a period of abstinence.

Human neuronal signaling and communication assays to assess functional neurotoxicity.

Prediction of drug toxicity on the human nervous system still relies mainly on animal experiments. Here, we developed an alternative system allowing assessment of complex signaling in both individual human neurons and on the network level. The LUHMES cultures used for our approach can be cultured in 384-well plates with high reproducibility. We established here high-throughput quantification of free intracellular Ca2+ concentrations [Ca2+]i as broadly applicable surrogate of neuronal activity and verified the main processes by patch clamp recordings. Initially, we characterized the expression pattern of many neuronal signaling components and selected the purinergic receptors to demonstrate the applicability of the [Ca2+]i signals for quantitative characterization of agonist and antagonist responses on classical ionotropic neurotransmitter receptors. This included receptor sub-typing and the characterization of the anti-parasitic drug suramin as modulator of the cellular response to ATP. To exemplify potential studies on ion channels, we characterized voltage-gated sodium channels and their inhibition by tetrodotoxin, saxitoxin and lidocaine, as well as their opening by the plant alkaloid veratridine and the food-relevant marine biotoxin ciguatoxin. Even broader applicability of [Ca2+]i quantification as an end point was demonstrated by measurements of dopamine transporter activity based on the membrane potential-changing activity of this neurotransmitter carrier. The substrates dopamine or amphetamine triggered [Ca2+]i oscillations that were synchronized over the entire culture dish. We identified compounds that modified these oscillations by interfering with various ion channels. Thus, this new test system allows multiple types of neuronal signaling, within and between cells, to be assessed, quantified and characterized for their potential disturbance.

GC-TOF-MS-Based Metabolomic Analysis and Evaluation of the Effects of HX106, a Nutraceutical, on ADHD-Like Symptoms in Prenatal Alcohol Exposed Mice.

Attention deficit hyperactivity disorder (ADHD) is a neurodevelopmental disorder that occurs in children characterized by inattention and hyperactivity. Prenatal alcohol exposure (PAE) can disrupt fetal neuronal development and cause an ADHD-like hyperactive behavior in the offspring. In this study, we hypothesized that metabolic disturbance would involve in ADHD neuropathology and aimed to investigate the changes in metabolite profile in PAE-induced ADHD-like model and the effects of HX106, a nutraceutical, on ADHD-like pathophysiology and metabolite changes. To this end, we administered HX106 to the mouse offspring affected by PAE (OPAE) and assessed the hyperactivity using the open field test. We observed that HX106-treated OPAE showed less hyperactive behavior than vehicle-treated OPAE. The effects of HX106 were found to be related to the regulation of dopamine transporter and D2 dopamine receptor expression. Furthermore, using gas chromatography time-of-flight mass spectrometry-based metabolomics, we explored the metabolite changes among the experimental groups. The metabolite profile, particularly related with the amino acids, linoleic acid and amino sugar pathways, was altered by PAE and reversed by HX106 treatment partially similar to that observed in the control group. Overall, this study suggest that metabolite alteration would be involved in ADHD pathology and that HX106 can be an efficient supplement to overcome ADHD by regulating dopamine signaling-related protein expression and metabolite changes.

Chemogenetic Manipulation of Dopamine Neurons Dictates Cocaine Potency at Distal Dopamine Transporters.

The reinforcing efficacy of cocaine is largely determined by its capacity to inhibit the dopamine transporter (DAT), and emerging evidence suggests that differences in cocaine potency are linked to several symptoms of cocaine use disorder. Despite this evidence, the neural processes that govern cocaine potency in vivo remain unclear. In male rats, we used chemogenetics with intra-VTA microinfusions of the agonist clozapine-n-oxide to bidirectionally modulate dopamine neurons. Using ex vivo fast scan cyclic voltammetry, pharmacological probes of the DAT, biochemical assessments of DAT membrane availability and phosphorylation, and cocaine self-administration, we tested the effects of chemogenetic manipulations on cocaine potency at distal DATs in the nucleus accumbens as well as the behavioral economics of cocaine self-administration. We discovered that chemogenetic manipulation of dopamine neurons produced rapid, bidirectional modulation of cocaine potency at DATs in the nucleus accumbens. We then provided evidence that changes in cocaine potency are associated with alterations in DAT affinity for cocaine and demonstrated that this change in affinity coincides with DAT conformation biases and changes in DAT phosphorylation state. Finally, we showed that chemogenetic manipulation of dopamine neurons alters cocaine consumption in a manner consistent with changes in cocaine potency at distal DATs. Based on the spatial and temporal constraints inherent to our experimental design, we posit that changes in cocaine potency are driven by alterations in dopamine neuron activity. When considered together, these observations provide a novel mechanism through which GPCRs regulate cocaine's pharmacological and behavioral effects.SIGNIFICANCE STATEMENT Differences in the pharmacological effects of cocaine are believed to influence the development and progression of cocaine use disorder. However, the biological and physiological processes that determine sensitivity to cocaine remain unclear. In this work, we use a combination of chemogenetics, fast scan cyclic voltammetry, pharmacology, biochemistry, and cocaine self-administration with economic demand analysis to demonstrate a novel mechanism by which cocaine potency is determined in vivo These studies identify a novel process by which the pharmacodynamics of cocaine are derived in vivo, and thus this work has widespread implications for understanding the mechanisms that regulate cocaine consumption across stages of addiction.

Single Cocaine Exposure Inhibits GABA Uptake via Dopamine D1-Like Receptors in Adolescent Mice Frontal Cortex.

Cocaine (COC) is a psychostimulant that acts by increasing catecholaminergic neurotransmission mainly due to its effects on the dopamine transporter (DAT). However, other neurotransmitter systems may also be regulated by COC, including the GABAergic system. Since the effect of COC in modulating gamma-aminobutyric acid (GABA) reuptake is not defined, we investigated the molecular mechanisms related to the increase in GABA uptake induced by acute COC exposure and its effects on locomotor activity in adolescent mice. Behavioral experiments showed that COC increased locomotor activity and decreased immobilization time in mice. A single COC exposure reduced both GABA uptake and GAT-1 protein levels. On the other hand, cyclic adenosine monophosphate (cAMP) levels increased after a COC challenge. The major changes induced by acute COC on behavioral and neurochemical assays were avoided by previous treatment with the selective D1 receptor antagonist SCH-23390 (0.5 mg/kg). Our findings suggest that GABA uptake naturally decreases during mice development from preadolescence until adulthood and that dopamine (DA) D1-like receptors are key players in the regulation of GABA uptake levels following a single COC exposure in adolescent mice.

Blockade of D3 receptor prevents changes in DAT and D3R expression in the mesolimbic dopaminergic circuit produced by social stress- and cocaine prime-induced reinstatement of cocaine-CPP.

BACKGROUND: Cocaine may cause persistent changes in the brain, which are more apparent in DA transporter (DAT) and DA receptor availability within the nucleus accumbens (NAc). On the other hand, the DA D3 receptor (D3R) has emerged as a promising pharmacotherapeutic target for substance use disorders. AIMS: This study aims to assess the impact of selective D3R antagonism on DAT and D3R after reinstatement of cocaine preference (CPP) induced by an acute session of social defeat stress (SDS) and a cocaine prime in mice after a period of abstinence. METHODS: Male mice were conditioned with 25 mg/kg of cocaine for 4 days. After 60 days of extinction training mice were pretreated with the selective D3R antagonist SB-277011A before the re-exposure to a priming dose of cocaine or to a single SDS session. CPP scores were determined and levels of DAT, D3R, phospho Akt (pAkt) and phospho mTOR (pmTOR) were assessed in the NAc shell. RESULTS: An increase in DAT and D3R expression was seen in the NAc after both a cocaine prime- and SDS-induced reinstatement of CPP. Pretreatment with SB-277011A blocked elevated DAT and D3R expression as well as SDS-induced reinstatement. By contrast, the blockade of D3R did not modified the cocaine prime-induced CPP. Changes in DAT and D3R expression do not seem to occur via the canonic pathway involving Akt/mTOR. CONCLUSIONS: Our results suggest that the selective D3R antagonist ability to inhibit DAT and D3R up-regulation could represent a possible mechanism for its behavioral effects in cocaine-memories reinstatement induced by social stress.

Glyphosate exposure exacerbates the dopaminergic neurotoxicity in the mouse brain after repeated administration of MPTP.

Parkinson's disease (PD) is a chronic and progressive neurodegenerative disorder. Epidemiological studies suggest that the exposure of the herbicide glyphosate may influence the development of PD in humans. In this study, we examined whether the exposure of glyphosate can affect the reduction of dopamine transporter (DAT) in the striatum and tyrosine hydroxylase (TH) in the substantial nigra (SNr) of mouse brain after repeated administration of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). Repeated injections of MPTP (10 mg/kg × 3, 2-h interval) significantly decreased the density of DAT-immunoreactivity in the striatum and the number of TH-immunoreactivity in the SNr. Glyphosate exposure for 14 days significantly potentiated MPTP-induced dopaminergic neurotoxicity in the striatum and SNr of mouse brain. This study suggests that glyphosate exposure might exacerbate MPTP-induced dopaminergic neurotoxicity in the striatum and SNr of adult mice. It is likely that exposure of glyphosate may be an environmental risk factor for PD since glyphosate has been used widely in the world.