Association of dopamine receptor D3 polymorphism with Levodopa-induced Dyskinesia: A study on Parkinson's disease patients from India.

INTRODUCTION: Levodopa-induced dyskinesia (LID) is a debilitating motor feature in a subset of patients with Parkinson's disease (PD) after prolonged therapeutic administration of levodopa. Preliminary animal and human studies are suggestive of a key role of dopamine type 3 (D3) receptor polymorphism (Ser9Gly; rs6280) in LID. Its contribution to development of LID among Indian PD patients has remained relatively unexplored and merits further investigation. METHODS AND MATERIALS: 200 well-characterised PD patients (100 without LID and 100 with LID) and 100 age-matched healthy controls were recruited from the outpatient department of Institute of Neurosciences Kolkata. MDS-UPDRS (Unified Parkinson's Disease Rating Scale from International Movement Disorder Society) Part III and AIMS (abnormal involuntary movement scale) were performed for estimation of severity of motor features and LID respectively in the ON state of the disease. Participants were analysed for the presence of Ser9Gly single nucleotide variant (SNV) (rs6280) by polymerase chain reaction followed by restriction fragment length polymorphism techniques. RESULTS: The frequency of AA genotype (serine type) was more frequently present in PD patients with LID compared to PD patients without LID (50 % vs 28 %; P = 0.002; OR = 2.57, 95 % CI: 1.43 - 4.62). The abnormal involuntary movement scale score was significantly higher in PD patients with AA genotype compared to carriers of glycine allele (AG + GG) (4.08 ± 3.35; P = 0.002). CONCLUSION: We observed a significant association of serine type SNV (rs6280) in D3 receptor gene in a cohort of PD patients with LID from India. More severe motor severity was found in patients with glycine substitution of the same SNV. The current study emphasised the role of D3 receptor in the pathogenesis of LID.

DRD3 Predicts Cognitive Impairment and Anxiety in Parkinson's Disease: Susceptibility and Protective Effects.

Background: A possible genetic contribution of dopamine D3 receptor (DRD3) to cognitive impairment in Parkinson's disease (PD) has yet to be investigated. Objective: To explore the effects of rs6280 (Ser9Gly) genotype on PD patients' cognitive performance and to clarify possible interactions with psychopathology. Methods: Two hundred and fifty-three consecutive PD patients underwent neurological and neuropsychological evaluations, which included: Unified Parkinson's Disease Rating Scale (UPDRS), Hoehn & Yahr scale (H&Y), Dementia Rating Scale-2 (DRS-2), and Hospital Anxiety and Depression Scale (HADS). rs6280 polymorphism was genotyped for all PD patients and for 270 ethnically matched healthy volunteers (HC). Non-parametric group comparisons and logistic regressions were used for data analyses. Results: rs6280 genotype did not differ between PD and HC groups. PD patients with rs6280 CC genotype had more impaired cognitive performance (i.e., <1st percentile of demographically adjusted norms) on DRS-2 subscales Initiation/Perseveration and Construction than those with TT genotype. These associations remained statistically significant when other covariates (e.g., demographic features, disease duration, severity of motor symptoms in OFF and ON states, anti-parkinsonian medication, and psychopathology symptoms) were taken into consideration. PD patients with rs6280 TC had less anxiety (i.e., HADS Anxiety≥11) than those with TT (p = 0.012). This association was also independent of other covariates. Conclusions: Study findings suggest that rs6280 CC genotype predisposes to executive dysfunction and visuoconstructional deficits, whereas the heterozygous genotype protects from anxiety in PD. These effects do not appear to be dependent of one another. rs6280 is not a genotypic susceptibility factor for PD.

The dopamine 3 receptor as a candidate biomarker and therapeutic for opioid use disorder.

Here, we present recent studies suggesting that specific DRD3 single nucleotide polymorphisms (SNPs, e.g. rs324029 and rs2654754) might serve as prognostic biomarkers for opioid use disorder (OUD). Additionally, preclinical studies with novel dopamine 3 receptor (D3R) partial agonists and antagonists have been evaluated as candidate OUD therapeutics and have shown a reduced risk of cardiovascular toxicity compared with the original D3R antagonist. From these findings, we argue that DRD3 SNPs could serve as a diagnostic tool for assessing OUD risk and that more research is warranted examining the D3R as a safe and effective therapeutic target for treating OUD.

Association of protein distribution and gene expression revealed by positron emission tomography and postmortem gene expression in the dopaminergic system of the human brain.

PURPOSE: The topological distribution of dopamine-related proteins is determined by gene transcription and subsequent regulations. Recent research strategies integrating positron emission tomography with a transcriptome atlas have opened new opportunities to understand the influence of regulation after transcription on protein distribution. Previous studies have reported that messenger (m)-RNA expression levels spatially correlate with the density maps of serotonin receptors but not with those of transporters. This discrepancy may be due to differences in regulation after transcription between presynaptic and postsynaptic proteins, which have not been studied in the dopaminergic system. Here, we focused on dopamine D1 and D2/D3 receptors and dopamine transporters and investigated their region-wise relationship between mRNA expression and protein distribution. METHODS: We examined the region-wise correlation between regional binding potentials of the target region relative to that of non-displaceable tissue (BPND) values of 11C-SCH-23390 and mRNA expression levels of dopamine D1 receptors (D1R); regional BPND values of 11C-FLB-457 and mRNA expression levels of dopamine D2/D3 receptors (D2/D3R); and regional total distribution volume (VT) values of 18F-FE-PE2I and mRNA expression levels of dopamine transporters (DAT) using Spearman's rank correlation. RESULTS: We found significant positive correlations between regional BPND values of 11C-SCH-23390 and the mRNA expression levels of D1R (r = 0.769, p = 0.0021). Similar to D1R, regional BPND values of 11C-FLB-457 positively correlated with the mRNA expression levels of D2R (r = 0.809, p = 0.0151) but not with those of D3R (r = 0.413, p = 0.3095). In contrast to D1R and D2R, no significant correlation between VT values of 18F-FE-PE2I and mRNA expression levels of DAT was observed (r = -0.5934, p = 0.140). CONCLUSION: We found a region-wise correlation between the mRNA expression levels of dopamine D1 and D2 receptors and their respective protein distributions. However, we found no region-wise correlation between the mRNA expression levels of dopamine transporters and their protein distributions, indicating different regulatory mechanisms for the localization of pre- and postsynaptic proteins. These results provide a broader understanding of the application of the transcriptome atlas to neuroimaging studies of the dopaminergic nervous system.

Blocking D2/D3 dopamine receptors in male participants increases volatility of beliefs when learning to trust others.

The ability to learn about other people is crucial for human social functioning. Dopamine has been proposed to regulate the precision of beliefs, but direct behavioural evidence of this is lacking. In this study, we investigate how a high dose of the D2/D3 dopamine receptor antagonist sulpiride impacts learning about other people's prosocial attitudes in a repeated Trust game. Using a Bayesian model of belief updating, we show that in a sample of 76 male participants sulpiride increases the volatility of beliefs, which leads to higher precision weights on prediction errors. This effect is driven by participants with genetically conferred higher dopamine availability (Taq1a polymorphism) and remains even after controlling for working memory performance. Higher precision weights are reflected in higher reciprocal behaviour in the repeated Trust game but not in single-round Trust games. Our data provide evidence that the D2 receptors are pivotal in regulating prediction error-driven belief updating in a social context.

The Role of Dopamine D3 Receptors, Dysbindin, and Their Functional Interaction in the Expression of Key Genes for Neuroplasticity and Neuroinflammation in the Mouse Brain.

Cognitive impairment in schizophrenia remains a clinically and pharmacologically unsolved challenge. Clinical and preclinical studies have revealed that the concomitant reduction in dysbindin (DYS) and dopamine receptor D3 functionality improves cognitive functions. However, the molecular machinery underlying this epistatic interaction has not yet been fully elucidated. The glutamate NMDA receptors and the neurotrophin BDNF, with their established role in promoting neuroplasticity, may be involved in the complex network regulated by the D3/DYS interaction. Furthermore, as inflammation is involved in the etiopathogenesis of several psychiatric diseases, including schizophrenia, the D3/DYS interaction may affect the expression levels of pro-inflammatory cytokines. Thus, by employing mutant mice bearing selective heterozygosis for D3 and/or DYS, we provide new insights into the functional interactions (single and synergic) between these schizophrenia susceptibility genes and the expression levels of key genes for neuroplasticity and neuroinflammation in three key brain areas for schizophrenia: the prefrontal cortex, striatum, and hippocampus. In the hippocampus, the epistatic interaction between D3 and DYS reversed to the wild-type level the downregulated mRNA levels of GRIN1 and GRIN2A were observed in DYS +/- and D3 +/- mice. In all the areas investigated, double mutant mice had higher BDNF levels compared to their single heterozygote counterparts, whereas D3 hypofunction resulted in higher pro-inflammatory cytokines. These results may help to clarify the genetic mechanisms and functional interactions involved in the etiology and development of schizophrenia.

Location, Location, Location: The Expression of D3 Dopamine Receptors in the Nervous System.

When the rat D3 dopamine receptor (D3R) was cloned and the distribution of its mRNA examined in 1990-1991, it attracted attention due to its peculiar distribution in the brain quite different from that of its closest relative, the D2 receptor. In the rat brain, the D3R mRNA is enriched in the limbic striatum as opposed to the D2 receptor, which is highly expressed in the motor striatal areas. Later studies in the primate and human brain confirmed relative enrichment of the D3R in the limbic striatum but also demonstrated higher abundance of the D3R in the primate as compared to the rodent brain. Additionally, in the rodent brain, the D3R in the dorsal striatum appears to be co-expressed with the D1 dopamine receptor-bearing striatal neurons giving rise to the direct output striatal pathway, although the picture is less clear with respect to the nucleus accumbens. In contrast, in the primate striatum, the D3R co-localizes with the D2 receptor throughout the basal ganglia as well as in extrastriatal brain areas. The relative abundance of the D3R in the limbic striatum, its output structures, secondary targets, and some of the other connected limbic territories may underpin its role in reward, drug dependence, and impulse control. Selective expression of D3R in the brain proliferative areas may point to its important role in the neural development as well as in neurodevelopmental abnormalities associated with schizophrenia and other developmental brain disorders.

The genetic influence of the DRD3 rs6280 polymorphism (Ser9Gly) on functional connectivity and gray matter volume of the hippocampus in patients with first-episode, drug-naïve schizophrenia.

The D3 dopamine receptor (DRD3) plays a major role in cognitive function and is a candidate gene for schizophrenia. DRD3 is widely distributed in the hippocampus, but whether there are potential associations between the rs6280 genotype, the hippocampus, and cognitive function in first-episode, drug-naïve (FES) patients and healthy controls (HCs) is still poorly understood. First, using functional and structural magnetic resonance imaging data, we calculated the gray matter volume (GMV) and functional connectivity (FC) of the hippocampus. Then, we examined the possible interaction effect of the DRD3 genotype and the disease on the FC and GMV of the hippocampus in 52 FES patients and 51 HCs. Finally, the correlation between the FC and GMV in the hippocampus, influenced by rs6280, and the cognitive performance of subjects was analyzed. A significant interaction effect of diagnostic group by genotype of rs6280 on the GMV of the left hippocampus was found, with lower GMV in FES patients that were C carriers compared with TT homozygotes; the opposite pattern was found in the genetic subgroups of HCs. In the FES group, C carriers performed significantly worse on reasoning and problem-solving tests than TT homozygotes. The left hippocampal GMV positively correlated with reasoning and problem-solving performance in TT homozygotes, but this correlation disappeared in FES patients that were C carriers and in genetic subgroups of HCs. Together, these results suggest that FES patients that are C carriers of rs6280 have lower GMV in the hippocampus, resulting in greater cognitive impairment.

Dopamine receptor D3 is related to prognosis in human hepatocellular carcinoma and inhibits tumor growth.

BACKGROUND: Dopamine receptors have been reported to play important roles in cancer progression. However, the role of dopamine receptor D3 (DRD3) in hepatocellular carcinoma (HCC) remains unclear. METHODS: The expression of DRD3 was detected by immunohistochemistry and real-time qPCR. The prognostic value of DRD3 in patients was investigated by analyzing selected databases, including cBioPortal and Kaplan-Meier plotter. Cell growth was tested by CCK8 assay, and Transwell assays were performed to assess cancer cell migration and invasion. The cAMP/ERK/CREB signaling pathway was evaluated by Western blot analysis and ELISA. An HCC xenograft model was established for in vivo experiments. RESULTS: DRD3 mRNA expression was significantly higher in nontumor tissues than in tumor tissues. Lower protein expression of DRD3 was related to poor recurrence-free survival (RFS) and overall survival (OS). Kaplan-Meier plotter analysis showed that higher expression of DRD3 mRNA was associated with better OS, RFS, disease-specific survival (DSS), and progression-free survival (PFS). cBioPortal analysis revealed that the alteration group, which harbored genetic mutations in DRD3, exhibited poor OS, RFS, DSS and PFS. According to CCK8 and Transwell assays, stable DRD3 overexpression cell line (ex-DRD3-SK-HEP-1) showed weaker proliferation, migration and invasion behaviors. PD128907, a DRD3 agonist, suppressed proliferation, migration and invasion in HCC cell lines, while U99194, a DRD3 antagonist, enhanced proliferation, migration and invasion in HCC cell lines. Western blot analysis and ELISA revealed that stable DRD3 knock-down cell line (sh-DRD3-PLC/PRF/5) and U99194 both increased the protein levels of cAMP, p-ERK and p-CREB; on the other hand, ex-DRD3-SK-HEP-1 and PD128907 decreased the protein levels of cAMP, p-ERK and p-CREB. SCH772984, an ERK antagonist, abolished the effect of U99194 on the malignant biological behaviors of HCC cells. In vivo, PD128907 suppressed tumor growth, and U99194 enhanced tumor growth. CONCLUSION: Our results suggest that down-regulation of DRD3 is strongly involved in the progression of HCC, and DRD3 might be consider as an independent prognostic factor for HCC. Furthermore, DRD3 agonists may be a promising strategy for HCC therapy.

Approach to the specificity and selectivity between D2 and D3 receptors by mutagenesis and binding experiments part I: Expression and characterization of D2 and D3 receptor mutants.

D3/D2 sub-specificity is a complex problem to solve. Indeed, in the absence of easy structural biology of the G-protein coupled receptors, and despite key progresses in this area, the systematic knowledge of the ligand/receptor relationship is difficult to obtain. Due to these structural biology limitations concerning membrane proteins, we favored the use of directed mutagenesis to document a rational towards the discovery of markedly specific D3 ligands over D2 ligands together with basic binding experiments. Using our methodology of stable expression of receptors in HEK cells, we constructed the gene encoding for 24 mutants and 4 chimeras of either D2 or D3 receptors and expressed them stably. Those cell lines, expressing a single copy of one receptor mutant each, were stably constructed, selected, amplified and the membranes from them were prepared. Binding data at those receptors were obtained using standard binding conditions for D2 and D3 dopamine receptors. We generated 26 new molecules derived from D2 or D3 ligands. Using 8 reference compounds and those 26 molecules, we characterized their binding at those mutants and chimeras, exemplifying an approach to better understand the difference at the molecular level of the D2 and D3 receptors. Although all the individual results are presented and could be used for minute analyses, the present report does not discuss the differences between D2 and D3 data. It simply shows the feasibility of the approach and its potential.

DRD3 Ser9Gly polymorphism and treatment response to antipsychotics in schizophrenia: A meta-analysis.

The association between dopamine D3 receptor (DRD3) Ser9Gly polymorphism and treatment response to antipsychotic drugs (APDs) in schizophrenia (SCZ) has been widely reported with inconsistent results, thus we performed an updated meta-analysis to derive a more precise estimation of the relationship. PubMed, Cochrane Library, Medline, Embase, CNKI, Weipu and Wanfang databases were searched for eligible studies published until March 2022. Odds ratios (ORs) with 95 % confidence intervals (CIs) were used to assess the strength of the associations in four genetic models. A total of 13 studies with 1769 patients were included in this meta-analysis. Our findings suggested that Ser9Gly polymorphism was significantly associated with treatment response to APDs in SCZ in allele model (Ser vs Gly, OR = 0.72, 95 % CI = 0.58-0.89, P = 0.002), recessive model (Ser/Ser vs Ser/Gly + Gly/Gly, OR = 0.55, 95 % CI = 0.36-0.86, P = 0.008) and co-dominant model (Ser/Ser vs Gly/Gly, OR = 0.57, 95 % CI = 0.33-0.99, P = 0.045) in Caucasians, but not in Asians. meta-regression revealed that the associations were not confounded by mean age, male ratio and treatment duration (P > 0.05). In summary, our results indicated the DRD3 Ser9Gly may influence the efficacy of APDs in specific genetic models, of which Ser allele and Ser/Ser genotype contributed to poor treatment response in Caucasians.

[Association of gene polymorphisms DRD3 rs6280, COMT rs4680 and HTR2A rs7322347 with schizophrenia]. / Assotsiatsiya geneticheskikh polimorfizmov rs6280 gena DRD3, rs4680 gena COMT, rs7322347 gena HTR2A s shizofreniei.

OBJECTIVE: To check the association of genetic polymorphisms rs6280 of the DRD3 gene, rs4680 of the COMT gene, rs7322347 of the HTR2A gene with schizophrenia. MATERIAL AND METHODS: The sample included 300 inpatients with paranoid schizophrenia. Inclusion criteria: age 18-50 years, established diagnosis «Schizophrenia, paranoid form¼, duration of psychiatric disorders not less than 5 years. The healthy control group consisted of 290 subjects. The association between polymorphisms and the study groups was assessed by logistic regression. RESULTS: The CC genotype of the rs6280 polymorphism is associated with schizophrenia (OR 3.37 (1.50; 8.03)). The TT genotype of the rs7322347 polymorphism is associated with controls (OR 1.83 (1.25; 2.68)). CONCLUSION: These analyses confirmed the hypothesis that the genetic polymorphisms rs7322347 of the HTR2A gene (p=0.006) and rs6280 of the DRD3 gene (p=0.004) were associated with the disease. The hypothesis of an association of the rs4680 polymorphism of the COMT gene could not be confirmed.

Decreased taste sensitivity to sucrose in dopamine D3 receptor mutant mice.

Dopamine plays a key role in food rewards and sweet-taste stimulation. We examined the basis for behavioral responses to sweet taste in dopamine D3 receptor-deficient (D3-/-) mice by determining whether the absence of D3 receptors affects the sensitivity to dilute sucrose solutions. In experiment 1, we measured the intensity generalization threshold of conditioned taste aversion (CTA) to a 0.2 M sucrose solution. Results showed that the generalization thresholds were 0.025-0.05 M in D3-/- mice and 0.0025-0.005 M in wild-type (WT) mice. In experiment 2, we found that D3-/- and WT mice had similar capabilities to form and extinguish CTAs. Since the intensity generalization threshold is mainly due to a combination of sweet-taste sensitivity and the robust nature of CTA formation, the results showed that taste sensitivity to sucrose in D3-/- mice was lower than that in WT mice. In experiment 3, to test whether the peripheral sensory signaling may also be affected by the disruption of the dopamine D3 receptors, the mRNA expression levels of sweet-taste-related proteins in taste buds of D3-/- mice were determined. The T1R1 and BDNF mRNA expression levels in D3-/- mice were higher than the controls, whereas T1R2, T1R3, α-gustducin, and TRPM5 mRNA were similar. These findings suggest that disruption of dopamine D3 receptor-mediated signaling decreases the sweet-taste sensitivity and alters the mRNA expression levels of some taste-related molecules.

Role of dopamine D3 receptors in methamphetamine-induced behavioural sensitization and the characterization of dopamine receptors (D1R-D5R) gene expression in the brain.

INTRODUCTION: As a central nervous system stimulant, methamphetamine (METH) can cause lasting changes after being abused, including possible changes of gene expression in the brain. The dopamine (DA) system plays a fundamental role in METH-induced behavioural changes, but the expression levels of various subtypes of DA receptors, especially the dopamine D3 receptor (D3R), remains unclear. MATERIAL AND METHODS: We explored the effect of the D3R on METH-induced behavioural sensitization by comparing D3R knockout (D3R-/-) mice with wild type (WT) mice. The quantitative real-time polymerase chain reaction (qRT-PCR) was used to detect the expression levels of the five DA receptor (D1R, D2R, D3R, D4R, and D5R) genes in four brain regions: the prefrontal cortex (PFc), nucleus accumbens (NAc), caudate-putamen (CPu), and hippocampus (Hip). RESULTS: The behavioural test results revealed that METH could induce behavioural sensitization both in WT and D3R-/- mice. Moreover, in D3R-/- mice, the increase in movement distance induced by methamphetamine was significantly less than that of wild-type mice. The response of the five DA receptors to METH exposure varies in different brain regions. To be more specific, METH increased the expression of the D3R gene in most brain regions of WT mice, decreased D1R and D2R gene expression both in the NAc and CPu of WT mice and in CPu of D3R-/- mice. CONCLUSIONS: These results suggested that D3R may play a positive regulatory role in the locomotor effects of METH, and five DA receptors, especially D1R, D2R, and D3R, may concurrently participate in the adaptive changes and the regulation of METH-induced behavioural sensitization.

HUMAN STUDY COMT and DRD3 haplotype-associated pain intensity and acute care utilization in adult sickle cell disease.

A previous exploratory analysis of a COMT gene single-nucleotide polymorphism (SNP) and a DRD3 SNP by our group suggested possible contributions to pain-related acute care utilization in people with sickle cell disease (SCD). Our aim was to extend the analysis to gene-spanning haplotypes of COMT SNPs and DRD3 SNPs to investigate possible associations with pain intensity and pain-related acute care utilization in an SCD cohort. Genotyping was conducted, and clinical data were collected, including self-reported pain intensity using PAINReportIt® (average of current pain and least and worst in past 24 hours, average pain intensity [API]) and medical record-extracted, pain-related acute care utilization data of 130 adults with SCD. Haplotype blocks were identified based on linkage disequilibria (COMT = 7 haploblocks; DRD3 = 8 haploblocks). Regression analyses were tested for association between haplotypes and API and utilization, yielding several significant findings. For COMT block 1 (rs2075507, rs4646310, rs737865), the A-G-G haplotype was associated with higher API compared to the reference A-G-A (p = 0.02), whereas the A-A-A haplotype was associated with higher utilization (p = 0.02). For DRD3 block 2 (rs9817063, rs2134655, rs963468, and rs3773679), relative to reference T-C-G-C, the T-T-G-C haplotype was associated with higher utilization (p = 0.01). For DRD3 block 4 (rs167770, rs324029, and rs324023), the A-G-T haplotype was associated with higher API (p = 0.04) and utilization (p < 0.001) relative to reference G-A-T, whereas the A-A-T haplotype was associated with higher utilization (p = 0.01). We found COMT and DRD3 haplotypes associated with pain-related SCD features, suggesting that in future studies more emphasis be placed on cis effects of SNP alleles in evaluating genetic contributions to SCD pain and acute care utilization for pain.

New Insight into the human genetic diversity in North African populations by genotyping of SNPs in DRD3, CSMD1 and NRG1 genes.

BACKGROUND: The single nucleotide polymorphisms (SNPs) of the dopamine D3 receptor (DRD3), the CUB and sushi multiple domains 1 (CSMD1) and the neuregulin 1 (NRG1) genes were used to study the genetic diversity and affinity among North African populations and to examine their genetic relationships in worldwide populations. METHODS: The rs3773678, rs3732783 and rs6280 SNPs of the DRD3 gene located on chromosome 3, the rs10108270 SNP of the CSMD1 gene and the rs383632, rs385396 and rs1462906 SNPs of the NRG1 gene located on chromosome 8 were analysed in 366 individuals from seven North African populations (Libya, Kairouan, Mehdia, Sousse, Kesra, Smar and Kerkennah). RESULTS: The low values of FST indicated that only 0.27%-1.65% of the genetic variability was due to the differences between the populations. The Kairouan population has the lowest average heterozygosity among the North African populations. Haplotypes composed of the ancestral alleles ACC and ACAT were more frequent in the Kairouan population than in other North African populations. The PCA and the haplotypic analysis showed that the genetic structure of populations in North Africa was closer to that of Europeans, Admixed Americans, South Asians and East Asians. However, analysis of the rs3732783 and rs6280 SNPs revealed that the CT microhaplotype was specific to the North African population. CONCLUSIONS: The Kairouan population exhibited a relatively low rate of genetic variability. The North African population has undergone significant gene flow but also evolutionary forces that have made it genetically distinct from other populations.

Prefrontal and striatal dopamine D2/D3 receptors correlate with fMRI BOLD activation during stopping.

D2-like dopamine receptors in animals and humans have been shown to be linked to impulsive behaviors that are highly relevant for several psychiatric disorders. Here, we investigate the relationship between the fronto-striatal D2/D3 dopamine receptor availability and response inhibition in a selected population of healthy OPRM1 G-allele carriers. Twenty-two participants successively underwent blood-oxygen level dependent functional magnetic resonance imaging (fMRI) while performing a stop-signal task and a separate positron emission tomography (PET) scan. Striatal and extrastriatal D2/D3 dopamine receptor availability was measured using the radiotracer [18F]fallypride. Caudate D2/D3 dopamine receptor availability positively correlated with stopping-related fronto-striatal fMRI activation. In addition, right prefrontal D2/D3 dopamine receptor availability correlated positively with stopping-related striatal fMRI BOLD signal. Our study partially replicates previous findings on correlations between striatal D2/D3 dopamine receptor availability and response inhibition in a population selected for its genetic determination of dopamine response to alcohol and as a modulator of impulse control via the endogenous opioid system. We confirm the important role of D2/D3 dopamine receptor availability in the fronto-striatal neural circuit for response inhibition. Moreover, we extend previous findings suggesting that dopamine receptor availability in the right inferior frontal cortex, a crucial region of the stopping network, is also strongly associated with stopping-related striatal fMRI activity in healthy OPRM1 G-allele carriers.

Dopaminergic stimulation leads B-cell infiltration into the central nervous system upon autoimmunity.

BACKGROUND: Recent evidence has shown dopamine as a major regulator of inflammation. Accordingly, dopaminergic regulation of immune cells plays an important role in the physiopathology of inflammatory disorders. Multiple sclerosis (MS) is an inflammatory disease involving a CD4+ T-cell-driven autoimmune response to central nervous system (CNS) derived antigens. Evidence from animal models has suggested that B cells play a fundamental role as antigen-presenting cells (APC) re-stimulating CD4+ T cells in the CNS as well as regulating T-cell response by mean of inflammatory or anti-inflammatory cytokines. Here, we addressed the role of the dopamine receptor D3 (DRD3), which displays the highest affinity for dopamine, in B cells in animal models of MS. METHODS: Mice harbouring Drd3-deficient or Drd3-sufficient B cells were generated by bone marrow transplantation into recipient mice devoid of B cells. In these mice, we compared the development of experimental autoimmune encephalomyelitis (EAE) induced by immunization with a myelin oligodendrocyte glycoprotein (MOG)-derived peptide (pMOG), a model that leads to CNS-autoimmunity irrespective of the APC-function of B cells, or by immunization with full-length human MOG protein (huMOG), a model in which antigen-specific activated B cells display a fundamental APC-function in the CNS. APC-function was assessed in vitro by pulsing B cells with huMOG-coated beads and then co-culturing with MOG-specific T cells. RESULTS: Our data show that the selective Drd3 deficiency in B cells abolishes the disease development in the huMOG-induced EAE model. Mechanistic analysis indicates that although DRD3-signalling did not affect the APC-function of B cells, DRD3 favours the CNS-tropism in a subset of pro-inflammatory B cells in the huMOG-induced EAE model, an effect that was associated with higher CXCR3 expression. Conversely, the results show that the selective Drd3 deficiency in B cells exacerbates the disease severity in the pMOG-induced EAE model. Further analysis shows that DRD3-stimulation increased the expression of the CNS-homing molecule CD49d in a B-cell subset with anti-inflammatory features, thus attenuating EAE manifestation in the pMOG-induced EAE model. CONCLUSIONS: Our findings demonstrate that DRD3 in B cells exerts a dual role in CNS-autoimmunity, favouring CNS-tropism of pro-inflammatory B cells with APC-function and promoting CNS-homing of B cells with anti-inflammatory features. Thus, these results show DRD3-signalling in B cells as a critical regulator of CNS-autoimmunity.

Exploring regulation and function of dopamine D3 receptors in alcohol use disorder. A PET [11C]-(+)-PHNO study.

Preclinical studies support an important role of dopamine D3 receptors (DRD3s) in alcohol use disorder (AUD). In animals, voluntary alcohol consumption increases DRD3 expression, and pharmacological blockade of DRD3s attenuates alcohol self-administration and reinstatement of alcohol seeking. However, these findings have yet to be translated in humans. This study used positron emission tomography (PET) and [11C]-(+)-PHNO to compare receptor levels in several dopamine D2 receptor (DRD2) and DRD3 regions of interest between AUD subjects in early abstinence (n = 17; 6.59 ± 4.14 days of abstinence) and healthy controls (n = 18). We recruited non-treatment seeking subjects meeting DSM-5 criteria for AUD. We examined the relationship between DRD2/3 levels and both alcohol craving and alcohol motivation/wanting, using a cue reactivity procedure and an intravenous alcohol self-administration (IVASA) paradigm, respectively. [11C]-(+)-PHNO binding levels in AUD subjects were significantly lower than binding in HCs when looking at all DRD2/3 ROIs jointly (Wilk's Λ = .58, F(6,28) =3.33, p = 0.013, η2p = 0.42), however there were no region-specific differences. Binding values demonstrate -12.3% and -16.1% lower [11C]-(+)-PHNO binding in the SMST and SN respectively, though these differences did not withstand Bonferroni corrections. There was a positive association between [11C]-(+)-PHNO binding in the SN (almost exclusively reflective of DRD3) and alpha (lower values reflect higher alcohol demand) in the APT after Bonferroni corrections (r = 0.66, p = 0.0080). This demonstrates that AUD subjects with lower DRD3 levels in the SN exhibit increased demand for alcohol. These results replicate previous findings demonstrating reduced DRD2/3 levels while also supporting a lack of DRD3 upregulation and potential downregulation in early abstinent AUD. Furthermore, the finding that binding in the SN is associated with alcohol demand warrants further examination.

Evidence for Protein-Protein Interaction between Dopamine Receptors and the G Protein-Coupled Receptor 143.

Protein-protein interactions between G protein-coupled receptors (GPCRs) can augment their functionality and increase the repertoire of signaling pathways they regulate. New therapeutics designed to modulate such interactions may allow for targeting of a specific GPCR activity, thus reducing potential for side effects. Dopamine receptor (DR) heteromers are promising candidates for targeted therapy of neurological conditions such as Parkinson's disease since current treatments can have severe side effects. To facilitate development of such therapies, it is necessary to identify the various DR binding partners. We report here a new interaction partner for DRD2 and DRD3, the orphan receptor G protein-coupled receptor 143 (GPR143), an atypical GPCR that plays multiple roles in pigment cells and is expressed in several regions of the brain. We previously demonstrated that the DRD2/ DRD3 antagonist pimozide also modulates GPR143 activity. Using confocal microscopy and two FRET methods, we observed that the DRs and GPR143 colocalize and interact at intracellular membranes. Furthermore, co-expression of wildtype GPR143 resulted in a 57% and 67% decrease in DRD2 and DRD3 activity, respectively, as determined by ß-Arrestin recruitment assay. GPR143-DR dimerization may negatively modulate DR activity by changing affinity for dopamine or delaying delivery of the DRs to the plasma membrane.