Desensitization and acute tolerance are terms used to describe the attenuation of receptor responsiveness by prolonged or intermittent exposure to an agonist. Unlike desensitization of G protein-coupled receptors (GPCRs), which is commonly explained by steric hindrance caused by the β-arrestins that are translocated to the activated receptors, molecular mechanisms involved in the acute tolerance of GPCRs remain unclear. Our studies with several GPCRs and related mutants showed that the acute tolerance of GPCRs could occur independently of agonist-induced β-arrestin translocation. A series of co-immunoprecipitation experiments revealed a correlation between receptor tolerance and interactions among receptors, β-arrestin2, and Gβγ. Gβγ displayed a stable interaction with receptors and β-arrestin2 in cells expressing GPCRs that were prone to undergo tolerance compared to the GPCRs that were resistant to acute tolerance. Strengthening the interaction between Gβγ and β-arrestin rendered the GPCRs to acquire the tendency of acute tolerance. Overall, stable interaction between the receptor and Gβγ complex is required for the formation of a complex with β-arrestin, and determines the potential of a particular GPCR to undergo acute tolerance. Rather than turning off the signal, β-arrestins seem to contribute on continuous signaling when they are in the context of complex with receptor and Gβγ.
Immunoprecipitation ; Receptors, Dopamine D3

OBJECTIVES: The aim of this study is to evaluate the association between rs6280 and rs905568 genetic polymorphism of DRD3 gene and the treatment response of amisulpride. METHODS: After six weeks treatment of amisulpride, 125 schizophrenia patients were interviewed based on the Positive and Negative Syndrome Scale (PANSS) and the Clinical Global Impression-Severity (CGI-S). The genotyping for rs6280 and rs905568 was performed using TaqMan single nucleotide polymorphism (SNP) genotyping assay. RESULTS: There was no significant difference in the frequency of genotype and allele of rs6280 between the responders and non-responders based on the total, positive, and general score of PANSS and CGI-S score. However, there was a significant association between this SNP and treatment response in the negative score of PANSS (chi2 = 5.23, p = 0.022). There was no significant association between rs905568 and the response in positive, negative, general, and total PANSS score and CGI-S score. CONCLUSIONS: This is the first positive association study between DRD3 gene and the treatment response of negative symptoms to amisulpride in Korean schizophrenia patients. A larger scale research on more SNP of the DRD3 gene will make a progress in the study of pharmacogenetics on the treatment response of the amisulpride.
Alleles ; Dopamine* ; Genotype ; Humans ; Pharmacogenetics ; Polymorphism, Genetic ; Polymorphism, Single Nucleotide ; Receptors, Dopamine D3* ; Schizophrenia

Opioid use disorder (OUD) has become a considerable global public health challenge; however, potential medications for the management of OUD that are effective, safe, and nonaddictive are not available. Accumulating preclinical evidence indicates that antagonists of the dopamine D₃ receptor (D₃R) have effects on addiction in different animal models. We have previously reported that YQA14, a D₃R antagonist, exhibits very high affinity and selectivity for D₃Rs over D₂Rs, and is able to inhibit cocaine- or methamphetamine-induced reinforcement and reinstatement in self-administration tests. In the present study, our results illustrated that YQA14 dose-dependently reduced infusions under the fixed-ratio 2 procedure and lowered the breakpoint under the progressive-ratio procedure in heroin self-administered rats, also attenuated heroin-induced reinstatement of drug-seeking behavior. On the other hand, YQA14 not only reduced morphine-induced expression of conditioned place preference but also facilitated the extinguishing process in mice. Moreover, we elucidated that YQA14 attenuated opioid-induced reward or reinforcement mainly by inhibiting morphine-induced up-regulation of dopaminergic neuron activity in the ventral tegmental area and decreasing dopamine release in the nucleus accumbens with a fiber photometry recording system. These findings suggest that D₃R might play a very important role in opioid addiction, and YQA14 may have pharmacotherapeutic potential in attenuating opioid-induced addictive behaviors dependent on the dopamine system.
Rats ; Mice ; Animals ; Analgesics, Opioid ; Dopamine ; Heroin/pharmacology* ; Dopamine Antagonists/pharmacology* ; Receptors, Dopamine D3/metabolism* ; Morphine/pharmacology* ; Behavior, Addictive/drug therapy* ; Self Administration

OBJECTIVES: Schizophrenia manifests a variety of interindividual differences in therapeutic response to antipsychotics. This might be attributable to dopamine and serotonin receptors that a important target for various antipsychotics, and the D3 receptor(DRD3) alleles they carry. The purpose of our study was to investigate whether the plasma levels of homovanillic acid(HVA) and 5-hydroxyindoleacetic acid(HIAA), and the polymorphism of DRD3 can be held as a predictor of treatment response ni chronic schizophrenic patients. METHODS: Therapeutic response for 16 korean schizophrenia patient treated during 48 weeks were assessed by PANSS used as the clinical symptom rating scales. The levels of concentration of HVA and 5-HIAA were examined by HPLC at baseline and at 48 weeks. We classified the polymorphism of DRD3 receptor using amplifying by polymerase chain reaction(PCR). RESULTS: Neither concentrations of HVA and 5-HIAA nor genotype of dopamine 3 receptor were not significantly associated with the therapeutic response. But, the patients who has A1 alleles of DRD3 gene showed poor therapeutic responses. CONCLUSION: A1 allele of DRD3 gene is associated with poor prognosis of chronic schizophrenia.
Alleles ; Antipsychotic Agents ; Chromatography, High Pressure Liquid ; Dopamine* ; Genotype ; Homovanillic Acid ; Humans ; Hydroxyindoleacetic Acid ; Plasma* ; Prognosis ; Receptors, Dopamine D3* ; Receptors, Serotonin ; Schizophrenia ; Weights and Measures

Tardive dyskinesia(TD)is one of the serious side effects caused by long-term treatment with neuroleptic medication. It has been known that dopamine D3 receptors are mainly located on the postsynaptic membrane where they display an inhibitory action on locomotor activity. In this study, we investigated the genetic variation of the dopamine D3 receptor gene(DRD3)as a putative risk factor for TD in schizophrenic patients receiving long-term antipsychotic medication. Fifty schizophrenic patients previously treated neuroleptic medication, were assessed for TD severity using Extrapyramidal Symptom Rating Scale(ESRS) Genomic DNA was amplified by PCR and Digestion with MluI yield two bands of 111bp and 47bp in all subjects. Subjects with a 304bp band were classified a1a1, those with 206bp and 98bp bands a2a2, and those with all five bands a1a2. The allelic distributions in TD patients and non-TD patients were not significantly different(x2=.852, df=2, p=.653) The number of each genotype observed in the schizophrenic group, did not differ significantly from the values expected according to Hardy-Weinberg equilibrium(x2=.29, df=2) This result did not support that dopamine D3 receptor gene variant were susceptible to TD in schizophrenic patients. The role of dopamine D3 receptors as a putative risk factors of TD may therefore be less important than previously thought.
Digestion ; DNA ; Genetic Variation ; Genotype ; Humans ; Membranes ; Motor Activity ; Movement Disorders* ; Polymerase Chain Reaction ; Receptors, Dopamine D3 ; Risk Factors ; Schizophrenia

OBJECTIVETo investigate the mechanisms by which hypertension occurs in D(3) dopamine receptor null mice (D(3)-/-).

METHODSSeveral parameters, including blood pressure, renal sodium excretion, D(3) receptor protein and mRNA expression, plasma renin activity, norepinephrine concentration and AT(1) receptor expression were checked in D(3)-/- mice and their littermate wild type mice (D(3)+/+). Moreover, the vasorelaxant effect of D(3) receptor stimulation was measured with ex-vivo mesenteric artery isolated from Wistar-Kyoto rats.

RESULTSBlood pressure was higher in D(3)-/- mice compared with that in D(3)+/+ mice, salt-loading had no effect on blood pressure in both groups, at the last period, sodium excretion was lower in D(3)-/- mice as compared with D(3)+/+ mice, renal renin activity and AT(1) receptor expression were higher in D(3) -/- [corrected] mice than in D(3) +/+ [corrected] mice. In contrast, no difference of renal norepinephrine was found in two groups. When using angiotensin II subtype-1 receptor antagonist, the systolic blood pressure declined for a longer duration in mutant mice than in wild-type mice. Vaso-relaxation was found in ex-vivo isolated mesenteric artery when D(3) receptor was stimulated.

CONCLUSIONSElevation of blood pressure in D(3)-/- mice might be related with impaired renal sodium excretion and vaso-relaxation in resistance artery.

Animals ; Hypertension ; genetics ; physiopathology ; Kidney ; Mesenteric Arteries ; physiopathology ; Mice ; Mice, Inbred BALB C ; Mice, Knockout ; Rats ; Receptors, Dopamine D3 ; genetics

OBJECTIVEAttention deficit hyperactivity disorder (ADHD) is one of the most common behavior disorders in childhood and adolescent. The etiology of ADHD is unknown. The aim of this study was to investigate the relationship between each of the 14 polymorphisms in the five candidate genes and ADHD, and between the combination of some polymorphisms in those genes and ADHD, in attempting to examine whether combinations of genotypes would confer a significant susceptibility to ADHD.

METHODSOne hundred and thirty-nine children with ADHD and one hundred and nineteen normal children were enrolled. Eight single nucleotide polymorphisms (SNP) of three candidate genes were examined with PCR and RFLP techniques. 48 bp VNTR in DRD4 gene was examined with PCR, nondenaturing polyacrylamide gel electrophoresis and silver staining. Five microsatellites (MS) of three candidate genes were examined with genotyping. The relationship between the combinations of 12 polymorphisms and ADHD was examined with logistic regression analysis.

RESULTS1.The frequency of 1065T/1065T genotype and the 1065T allele were significantly higher in ADHD children than that in normal controls (P<0.05). The frequency of -48G/-48G genotype of the A-48G polymorphism of DRD1 gene was significantly lower in ADHD children than that in normal controls (P<0.05). 2. A specific combination of three polymorphisms in the two genes showing an association with ADHD gave a prediction level of 77.5%.

CONCLUSIONSThe T1065G polymorphism in the SNAP-25 may be associated with ADHD. The 1065T/1065T genotype and the 1065T allele may be a risk factor for ADHD. The A-48G polymorphism of DRDI may be associated with ADHD. The -48G/-48G genotype may be a protective factor for ADHD. The specific combination of three sites of SNP in SNAP-25 gene and DRDI gene is found and shows an association with ADHD in 12 polymorphisms of the five candidate genes on glutamatergic/dopaminergic pathway.

Adolescent ; Attention Deficit Disorder with Hyperactivity ; genetics ; Child ; Female ; Humans ; Logistic Models ; Male ; Minisatellite Repeats ; Polymorphism, Single Nucleotide ; Receptors, Dopamine D3 ; genetics ; Receptors, Dopamine D4 ; genetics ; Receptors, Dopamine D5 ; genetics ; Receptors, N-Methyl-D-Aspartate ; genetics ; Synaptosomal-Associated Protein 25 ; genetics

BACKGROUNDTourette syndrome (TS) is a complex, heterozygous genetic disorder. The number of molecular genetic studies have investigated several candidate genes, particularly those implicated in the dopamine system. The dopamine D3 receptor (DRD3) gene has been considered as a candidate gene in TS. There was not any report about the association study of TS and DRD3 gene in Han Chinese population. We combined a case-control genetic association analysis and nuclear pedigrees transmission disequilibrium test (TDT) analysis to investigate the association between DRD3 gene rs6280 single nucleotide polymorphisms (SNPs) and TS in a Han Chinese population.

METHODSA total of 160 TS patients was diagnosed by the diagnostic criteria of the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition. The DRD3 gene rs6280 SNPs were genotyped by TaqMan SNP genotyping assay technique in all subjects. We used a case-control genetic association analysis to compare the difference in genotype and allele frequencies between 160 TS patients and 90 healthy controls. At the same time, we used TDT analysis to identify the DRD3 gene rs6280 transmission disequilibrium among 101 nuclear pedigrees.

RESULTSThe genotype and allele frequency of DRD3 gene rs6280 SNPs had no statistical difference between control group (90) and TS group (160) (χ2 = 3.647, P = 0.161; χ2 = 0.643, P = 0.423) using Chi-squared test. At the basis of the 101 nuclear pedigrees, TDT analysis showed no transmission disequilibrium of DRD3 gene rs6280 SNPs (χ2 = 0; P = 1).

CONCLUSIONSOur findings provide no evidence for an association between DRD3 gene rs6280 and TS in the Han Chinese population.

Adolescent ; Child ; Female ; Gene Frequency ; genetics ; Genetic Predisposition to Disease ; genetics ; Genotype ; Humans ; Male ; Polymorphism, Single Nucleotide ; genetics ; Receptors, Dopamine D3 ; genetics ; Tourette Syndrome ; etiology

OBJECTIVETo study the role of dopamine receptors in the regulation of the activity of transcription factor cAMP response element-binding protein (CREB) after cocaine treatment.

METHODSBy using dopamine receptor antagonists SCH23390 and nafadotride, the activation of CREB by D1 and D3 dopamine receptors after cocaine treatment and role of extracellular signal-regulated kinase (ERK) in cocaine-induced CREB activation were examined by Western blotting, which was also employed for determination of the effect of SCH23390 and nafadotride on CREB activation.

RESULTSD1 receptor antagonist could inhibit cocaine-induced CREB activation, while D3 receptor antagonist enhanced cocaine-induced CREB activation. Dopamine receptor antagonists SCH23390 and nafadotride did not induce CREB activation. SL327, a MEK inhibitor, inhibited cocaine-induced CREB activation.

CONCLUSIOND1 and D3 dopamine receptors can oppositely regulate CREB activation after cocaine treatment and this regulation depends on ERK signaling pathway.

Animals ; Benzazepines ; pharmacology ; Blotting, Western ; Cocaine ; pharmacology ; Cyclic AMP Response Element-Binding Protein ; metabolism ; Dopamine Antagonists ; pharmacology ; Dopamine Uptake Inhibitors ; pharmacology ; Extracellular Signal-Regulated MAP Kinases ; metabolism ; Mice ; Naphthalenes ; pharmacology ; Pyrrolidines ; pharmacology ; Receptors, Dopamine D1 ; antagonists & inhibitors ; physiology ; Receptors, Dopamine D3 ; antagonists & inhibitors ; physiology ; Signal Transduction ; drug effects

BACKGROUNDCocaine addiction may involve complex neuroadaptations, including many changes of genes expression. Dopamine D3 receptors play an important role in cocaine addiction; however, its role in cocaine induced gene expression change is poorly understood. To identify the changes in gene expression induced by repeated cocaine exposure through D3 dopamine receptors, we compared the expression of four molecules: Janus kinase 2 (Jak2), g-aminobutanoic acid receptor subunit alpha 1 (GABAAalpha1), glutamate receptor AMPA3 alpha 3 (GluR 3) and stromal cell derived factor 1 (SDF1). These four have been implicated in mediating the actions of cocaine in the nucleus accumbens (NAc) and caudoputamen (CPu) in mice after acute and repeated cocaine exposure.

METHODSFor the acute and repeated injections, the mice were divided into four groups: 30 mg/kg cocaine, nafadotride 0.5 mg/kg + cocaine 30 mg/kg, nafadotride 0.5 mg/kg, and saline as the basal group. The expression of Jak2, GABAAalpha1, GluR 3 and SDF1 were assayed by Western blot, quantitative real-time RT-PCR and immunohistochemistry.

RESULTSTwenty-four hours after seven consecutive days of repeated cocaine exposure, the expression of GABAAalpha1 decreased in cocaine group compared with basal line and further decreased in the cocaine + nafadotride group and remained at basal level in the nafadotride group. Similarly, the Jak2 expression decreased in cocaine group compared with base line. However, the levels of Jak2 increased in cocaine + nafadotride group compared with cocaine group, while remained at basal level in nafadotride group.

CONCLUSIONSGABAAalpha1 and Jak2 may be involved in chronic cocaine induced neuroadaptations. D3 dopamine receptors play an important role in the expression of these genes.

Animals ; Brain ; drug effects ; metabolism ; Cocaine ; pharmacology ; Female ; Gene Expression Regulation ; drug effects ; Immunohistochemistry ; Janus Kinase 2 ; analysis ; genetics ; Male ; Mice ; Receptors, Dopamine D3 ; physiology ; Receptors, GABA-A ; analysis ; genetics ; Reverse Transcriptase Polymerase Chain Reaction