L-dopa (l-3,4-dihydroxyphenylalanine)-induced dyskinesia (LID) is a debilitating complication of dopamine replacement therapy for Parkinson's disease. The potential contribution of striatal D₂ receptor (D₂R)-positive neurons and downstream circuits in the pathophysiology of LID remains unclear. In this study, we investigated the role of striatal D₂R⁺ neurons and downstream globus pallidus externa (GPe) neurons in a rat model of LID. Intrastriatal administration of raclopride, a D₂R antagonist, significantly inhibited dyskinetic behavior, while intrastriatal administration of pramipexole, a D₂-like receptor agonist, yielded aggravation of dyskinesia in LID rats. Fiber photometry revealed the overinhibition of striatal D₂R⁺ neurons and hyperactivity of downstream GPe neurons during the dyskinetic phase of LID rats. In contrast, the striatal D₂R⁺ neurons showed intermittent synchronized overactivity in the decay phase of dyskinesia. Consistent with the above findings, optogenetic activation of striatal D₂R⁺ neurons or their projections in the GPe was adequate to suppress most of the dyskinetic behaviors of LID rats. Our data demonstrate that the aberrant activity of striatal D₂R⁺ neurons and downstream GPe neurons is a decisive mechanism mediating dyskinetic symptoms in LID rats.
Rats ; Animals ; Levodopa/toxicity* ; Dopamine ; Parkinsonian Disorders/drug therapy* ; Oxidopamine ; Dyskinesia, Drug-Induced ; Corpus Striatum/metabolism* ; Neurons/metabolism* ; Receptors, Dopamine D2/metabolism* ; Antiparkinson Agents/toxicity*

OBJECTIVE: To explore the association between rs2587552 polymorphism (has a strong lin-kage disequilibrium with rs1800497 which had been found in many studies to be related to obesity, r²=0.85) of DRD2 gene and the effect of a childhood obesity intervention in Chinese population, and provide a scientific basis for future personalized childhood obesity intervention based on genetic background. METHODS: From a multi-center cluster randomized controlled trial studying the effect of a childhood obesity intervention, we enrolled 382 children from 8 primary schools (192 and 190 children from intervention and control groups, respectively) in Beijing as study subjects. Saliva was collected and DNA was extracted to detect the rs2587552 polymorphism of DRD2 gene, and the interactions between the gene and study arms on childhood obesity indicators [including body weight, body mass index (BMI), BMI Z-score, waist circumference, hip circumference, waist-to-hip ratio, waist-to-height ratio, and body fat percentage] were analyzed. RESULTS: No association was found between rs2587552 polymorphism and the changes in hip circumference or body fat percentage in the intervention group (P>0.05). However, in the control group, children carrying the A allele at DRD2 rs2587552 locus showed a greater increase in hip circumference and body fat percentage compared with those not carrying A allele (P < 0.001). There were interactions between rs2587552 polymorphism of DRD2 gene and study arms on the changes in hip circumference and body fat percentage (P=0.007 and 0.015, respectively). Compared with the control group, children in the intervention group carrying the A allele at DRD2 rs2587552 locus showed decrease in hip circumference by (-1.30 cm, 95%CI: -2.25 to -0.35, P=0.007) and decrease in body fat percentage by (-1.34%, 95%CI: -2.42 to -0.27, P=0.015) compared with those not carrying A allele. The results were consistent between the dominant model and the additive model (hip circumfe-rence: -0.66 cm, 95%CI: -1.28 to -0.03, P=0.041; body fat percentage: -0.69%, 95%CI: -1.40 to 0.02, P=0.056). No interaction was found between rs2587552 polymorphism and study arms on the changes in other childhood obesity-related indicators (P>0.05). CONCLUSION Children carrying the A allele at rs2587552 polymorphism of DRD2 gene are more sensitive to intervention and showed more improvement in hip circumference and body fat percentage after the intervention, suggesting that future personalized childhood obesity lifestyle intervention can be carried out based on the rs2587552 polymorphism of DRD2 gene.
Humans ; Child ; Pediatric Obesity/therapy* ; Prospective Studies ; Polymorphism, Genetic ; Body Mass Index ; Waist Circumference ; Receptors, Dopamine D2/genetics*

A wealth of evidence has suggested that gastrointestinal dysfunction is associated with the onset and progression of Parkinson's disease (PD). However, the mechanisms underlying these links remain to be defined. Here, we investigated the impact of deregulation of intestinal dopamine D2 receptor (DRD2) signaling in response to 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced dopaminergic neurodegeneration. Dopamine/dopamine signaling in the mouse colon decreased with ageing. Selective ablation of Drd2, but not Drd4, in the intestinal epithelium, caused a more severe loss of dopaminergic neurons in the substantia nigra following MPTP challenge, and this was accompanied by a reduced abundance of succinate-producing Alleoprevotella in the gut microbiota. Administration of succinate markedly attenuated dopaminergic neuronal loss in MPTP-treated mice by elevating the mitochondrial membrane potential. This study suggests that intestinal epithelial DRD2 activity and succinate from the gut microbiome contribute to the maintenance of nigral DA neuron survival. These findings provide a potential strategy targeting neuroinflammation-related neurological disorders such as PD.
1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine/adverse effects* ; Animals ; Disease Models, Animal ; Dopamine ; Dopaminergic Neurons/metabolism* ; Gastrointestinal Microbiome ; Mice ; Mice, Inbred C57BL ; Neuroprotection ; Parkinson Disease ; Pyrrolidines ; Receptors, Dopamine D2/metabolism* ; Substantia Nigra ; Succinates

Functional changes in synaptic transmission from the lateral entorhinal cortex to the dentate gyrus (LEC-DG) are considered responsible for the chronification of pain. However, the underlying alterations in fan cells, which are the predominant neurons in the LEC that project to the DG, remain elusive. Here, we investigated possible mechanisms using a rat model of complete Freund's adjuvant (CFA)-induced inflammatory pain. We found a substantial increase in hyperpolarization-activated/cyclic nucleotide-gated currents (I_h), which led to the hyperexcitability of LEC fan cells of CFA slices. This phenomenon was attenuated in CFA slices by activating dopamine D2, but not D1, receptors. Chemogenetic activation of the ventral tegmental area -LEC projection had a D2 receptor-dependent analgesic effect. Intra-LEC microinjection of a D2 receptor agonist also suppressed CFA-induced behavioral hypersensitivity, and this effect was attenuated by pre-activation of the I_h. Our findings suggest that down-regulating the excitability of LEC fan cells through activation of the dopamine D2 receptor may be a strategy for treating chronic inflammatory pain.
Animals ; Chronic Pain ; Entorhinal Cortex/metabolism* ; Hyperpolarization-Activated Cyclic Nucleotide-Gated Channels ; Neurons/metabolism* ; Rats ; Receptors, Dopamine D1/metabolism* ; Receptors, Dopamine D2

The aim of the present study was to reveal the role of cortical-striatum postsynaptic dopamine D2 receptor (D2R) in improving motor behavioral dysfunction in Parkinson's disease (PD) mice by exercise. C57/BL6 male adult mice were randomly divided into control, PD and PD plus exercise groups. The mice were injected with 6-OHDA in striatum to establish a unilateral injury PD model. The exercise intervention program was uniform speed running (16 m/min, 40 min/d, 5 d per week for 4 weeks). Autonomic activity of mice was tested by open field test. Cortical-striatum synaptic transmission efficiency was assessed by peak amplitude of field excitatory postsynaptic potential (fEPSP) recorded from in vitro brain slides. Meanwhile, the effects of D2R agonist on autonomic activity and cortical-striatal synaptic transmission were observed. The results showed that, compared with PD group, PD plus exercise group exhibited significantly increased autonomic motor distance and proportion of fast-moving (P < 0.05), as well as decreased maximum amplitude of fEPSP under increasing stimulation intensity (0.75-3.00 pA) (P < 0.05) and slope of stimulus-response curve. Compared with PD mice without D2R agonist, the movement distance and rapid movement ratio of PD mice treated with D2R agonist were increased significantly (P < 0.05), whereas fEPSP peak amplitude (P < 0.05) and the slope of stimulus-response curve were decreased. These results indicate that either early exercise intervention or D2R agonist treatment can inhibit the abnormal increase of cortical-striatum synaptic transmission and improve the autonomic motor ability in PD mice, suggesting that the cortical-striatum synaptic D2R may be an important molecular target for exercise to improve the autonomic motor ability of PD mice.
Animals ; Corpus Striatum ; physiology ; Male ; Mice ; Mice, Inbred C57BL ; Oxidopamine ; Parkinson Disease ; physiopathology ; therapy ; Physical Conditioning, Animal ; Random Allocation ; Receptors, Dopamine D2 ; agonists ; physiology ; Synaptic Transmission

G protein-coupled receptors (GPCRs) are membrane receptors whose agonist-induced dynamic conformational changes trigger heterotrimeric G protein activation, followed by GRK-mediated phosphorylation and arrestin-mediated desensitization. Cytosolic regions of GPCRs have been studied extensively because they are direct contact sites with G proteins, GRKs, and arrestins. Among various cytosolic regions, the role of helix 8 is least understood, although a few studies have suggested that it is involved in G protein activation, receptor localization, and/or internalization. In the present study, we investigated the role of helix 8 in dopamine receptor signaling focusing on dopamine D1 receptor (D1R) and dopamine D2 receptor (D2R). D1R couples exclusively to Gs, whereas D2R couples exclusively to Gi. Bioinformatic analysis implied that the sequences of helix 8 may affect GPCR-G protein coupling selectivity; therefore, we evaluated if swapping helix 8 between D1R and D2R changed G protein selectivity. Our results suggest that helix 8 is not involved in D1R-Gs or D2R-Gi coupling selectivity. Instead, we observed that D1R with D2R helix 8 or D1R with an increased number of hydrophobic residues in helix 8 relative to wild-type showed diminished β-arrestin-mediated desensitization, resulting in increased Gs signaling.
Arrestin ; Arrestins ; Computational Biology ; Cytosol ; Dopamine ; Family Characteristics ; GTP-Binding Proteins ; Membranes ; Phosphorylation ; Receptors, Dopamine D1 ; Receptors, Dopamine D2 ; Receptors, Dopamine

OBJECTIVE: This study aimed to investigate the long-term effects of aripiprazole treatment during adolescence on behavior, cognitive function, and dopamine D2 receptor (D2R) expression in adult rats. METHODS: Adolescent male Sprague-Dawley rats were injected intraperitoneally with aripiprazole, risperidone, or vehicle control for 3 weeks (postnatal day 36–56). After a 2-week washout period, locomotion, anxiety, and spatial working memory were evaluated in adulthood (postnatal day 71–84), using an open field test, elevated plus maze, and Y-maze, respectively. In addition, we assessed D2R levels in the dorsolateral and medial prefrontal cortex (PFC), dorsal and ventral striatum, and hippocampus using western blot analysis. RESULTS: Spontaneous alternation performance (SAP) in the Y-maze, a measure of spatial working memory, differed significantly among the 3 groups (F = 3.89, p = 0.033). A post-hoc test confirmed that SAP in the aripiprazole group was significantly higher than that in the risperidone group (post-hoc test p = 0.013). D2R levels in the medial PFC (F = 8.72, p = 0.001) and hippocampus (F = 13.54, p < 0.001) were different among the 3 groups. D2R levels in the medial PFC and hippocampus were significantly lower in the aripiprazole-treated rats than that in the risperidone-treated rats (post-hoc test p = 0.025 and p < 0.001, respectively) and controls (post-hoc test p < 0.001, all). CONCLUSION: This study showed that aripiprazole treatment in adolescence could influence cognitive function and dopaminergic neurotransmission into early adulthood.
Adolescent ; Adult ; Animals ; Anxiety ; Aripiprazole ; Blotting, Western ; Cognition ; Dopamine ; Hippocampus ; Humans ; Locomotion ; Male ; Memory, Short-Term ; Models, Animal ; Prefrontal Cortex ; Rats ; Rats, Sprague-Dawley ; Receptors, Dopamine D2 ; Risperidone ; Synaptic Transmission ; Ventral Striatum

Objective: To investigate the association between three single nucleotide polymorphism (SNP) genes DRD2 (rs1800497, rs6275, and rs1799978) and the dosage used on methadone maintenance treatment (MMT). Methods: From the methadone maintenance treatment centers, 257 MMT patients were recruited to participate in a case-control study and divided into two groups-control groups under low dosage (n=89) and case (n=168) group with high dosage. Quanto software was used to estimate the sample size as 180. Information related to social-demographic status, history on drug use and medication were collected. And DRD2 SNPs were genotyped to explore the relationship between polymorphism of DRD2 gene and the dosage of methadone maintenance treatment. Results: Distributions of DRD2 rs6275 between different groups were significantly different. Patients carrying TC genotype needed lower dose of methadone when compared to the patients that carrying CC genotype counterparts (OR=0.338, 95% CI: 0.115-0.986). Patients that carrying C allele at rs6275 needed lower methadone dose than those that carrying genotype TT (OR=0.352, 95% CI: 0.127-0.975). Distributions of genotypes, alles in the other two SNPs (rs1800497, rs1799978) were not significantly different between groups under different dosages. Conclusion: DRD2 rs6275 was associated with dosage of methadone used for the MMT patients. However, no significant associations were found between rs1800497, rs1799978 and the dosage of methadone.
Alleles ; Case-Control Studies ; Drug Dosage Calculations ; Genotype ; Humans ; Methadone/therapeutic use* ; Opiate Substitution Treatment ; Opioid-Related Disorders/rehabilitation* ; Polymorphism, Single Nucleotide/genetics* ; Receptors, Dopamine D2/genetics*

OBJECTIVE: The aim of this study was to explore the association of dopamine receptor D2 (DRD2) polymorphism and alleviation of obesity in children and adolescents after 8-year follow-up. METHODS: This retrospective cohort study included obese children and adolescents with a follow-up period of 8 years. Baseline clinical characteristics and DRD2 polymorphisms (including rs1076562, rs2075654, and rs4586205) were extracted from medical records. A follow-up visit was performed in May 2017 to collect related data including height, weight, diet compliance, and exercise compliance. RESULTS: One hundred and nine obese children and adolescents were included in the current study. Among three DRD2 single nucleotide polymorphisms, only rs2075654 had a statistically significant association with alleviation of obesity, as the alleviation rate for minor allele carriers (68.6% for TC+TT) was higher compared to the major allele homozygote (43.3% for CC). After adjusting for all related factors, the hazard ratio of rs2075654 minor allele carriers for the alleviation of obesity was 3.34 (95% confidence interval (CI): 1.30‒8.58). CONCLUSIONS The rs2075654 polymorphism of DRD2 is related to long-term obesity alleviation in obese Chinese children and adolescents.
Adolescent ; Body Mass Index ; Child ; Female ; Humans ; Male ; Obesity/genetics* ; Polymorphism, Single Nucleotide ; Receptors, Dopamine D2/genetics* ; Retrospective Studies

PURPOSE: Prolactinoma (prolactin-secreting pituitary adenoma) is one of the most common estrogen-related functional pituitary tumors. As an agonist of the dopamine D2 receptor, bromocriptine is used widely to inhibit prolactinoma progression. On the other hand, it is not always effective in clinical application. Although a dopamine D2 receptor deficiency contributes to the impaired efficiency of bromocriptine therapy to some extent, it is unknown whether there some other underlying mechanisms leading to bromocriptine resistance in prolactinoma treatment. That is the main point addressed in this project. MATERIALS AND METHODS: Human prolactinoma samples were used to analyze the S-phase kinase associated protein 2 (SKP2) expression level. Nutlin-3/adriamycin/cisplatin-treated GH3 and MMQ cells were used to analyze apoptosis in SKP2 overexpression or knockdown cells. SKP2 expression and the interaction partners of SKP2 were also detected after a bromocriptine treatment in 293T. Apoptosis was analyzed in C25 and bromocriptine-treated GH3 cells. RESULTS: Compared to normal pituitary samples, most prolactinoma samples exhibit higher levels of SKP2 expression, which could inhibit apoptosis in a p53-dependent manner. In addition, the bromocriptine treatment prolonged the half-life of SKP2 and resulted in SKP2 overexpression to a greater extent, which in turn compromised its pro-apoptotic effect. As a result, the bromocriptine treatment combined with C25 (a SKP2 inhibitor) led to the maximal apoptosis of human prolactinoma cells. CONCLUSION: These findings indicated that SKP2 inhibition sensitized the prolactinoma cells to bromocriptine and helped promote apoptosis. Moreover, a combined treatment of bromocriptine and C25 may contribute to the maximal apoptosis of human prolactinoma cells.
Apoptosis* ; Bromocriptine ; Half-Life ; Hand ; Humans* ; Pituitary Neoplasms ; Prolactinoma* ; Receptors, Dopamine D2 ; S-Phase Kinase-Associated Proteins