• Biomolecules & Therapeutics
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• v.27 no.6
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• pp.514-521
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• 2019

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 ${\beta}$-arrestin-mediated desensitization, resulting in increased Gs signaling.

• Biomolecules & Therapeutics
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• v.24 no.5
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• pp.475-481
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• 2016

PICK1, a PDZ domain-containing protein, is known to increase the reuptake activities of dopamine transporters by increasing their expressions on the cell surface. Here, we report a direct and functional interaction between PICK1 and dopamine $D_3$ receptors ($D_3R$), which act as autoreceptors to negatively regulate dopaminergic neurons. PICK1 colocalized with both dopamine $D_2$ receptor ($D_2R$) and $D_3R$ in clusters but exerted different functional influences on them. The cell surface expression, agonist affinity, endocytosis, and signaling of $D_2R$ were unaffected by the coexpression of PICK1. On the other hand, the surface expression and tolerance of $D_3R$ were inhibited by the coexpression of PICK1. These findings show that PICK1 exerts multiple effects on $D_3R$ functions.

• Archives of Pharmacal Research
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• v.14 no.2
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• pp.109-113
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• 1991

Two types of aggressive behavior were produced by selective breeding in ICR mimce. NC900 line mice exhibited high level of species-typical, isolation-induced aggression, conversely, NC100 line mice exhibited little aggression. The present study tested the hypothesis that these differences involved brain monoamine systems. Comparisons of microdissected samples from various brain regions showed that NC100 line mice had significantly lower concentrations of dopamine. DOPAC and HVA in the nucleus accumbens (NAB) and caudate nucleus (NCU) than NC900 line. Homogenate binding studies demonstrated that NC100 mice had significantly increased density of $D_1$ dopamine receptor, but not $D_2$ dopamine receptor in the caudate nucleus. These results support the hypothesis that central dopamine pathways play an important role in modulating the genetically selected differences in aggressive behavior, and of which intensity differs from TEX>$D_1$\;and\;$D_2$ dopamine receptors.

• Korean Journal of Biological Psychiatry
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• v.2 no.1
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• pp.57-62
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• 1995

Objects : Clozapine, prototype of the atypical neuroleptics, was known to have unique antipsychotic effect with a few extrapyramidal effects. While most typical antipsychotic agents mainly block $D_2$ receptors, clozapine has higher affinity for dopamine $D_4$ receptor than for $D_2$ receptor. Many researchers have tried to find out the relationship between schizophrenia and the abnormality of the genes coding dopamine receptors. But no consistent findings were reported. Recently, dopamine $D_4$ receptor was fully sequenced, and the alleles of dopamine $D_4$ receptor gene was found in unusual form on the 48th base pair. Our study was performed to identify the distribution of the dopamine $D_4$ receptor alleles of schizophrenics and normal controls, and whether any difference between the dopamine $D_4$ receptor alleles of schizophrenics and that of normal controls exists. Methods : DNA was extracted from the blood of schizophrenic patients(N=60) and normal controls(N=60). Part of the dopamine $D_4$ receptor gene was amplified by PCR, and amplified DNA was electrophoresed. Authors compared the distribution of the alleles of dopamine $D_4$ receptor gene of normal controls and that of schizophrenic patients. Results : Six kinds of alleles of $D_4$ receptor were observed both groups. The fourth repeat form of alleles was the most common in both schizophrenic patients(75.8%) and normal controls(70.3%), so there was not significant difference between two groups. Conclusion : The Difference in the distribution of the dopamine $D_4$ receptor gene alleles is not thought to be responsible for the pathophysiology of the schizophrenia. However, the difference in the expression of the dopamine $D_4$ receptor gene between normal and schizophrenia is left to be scrutinized.

• Proceedings of the PSK Conference
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• 2002.10a
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• pp.270.1-270.1
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• 2002

The signaling pathway of D2 dopamine receptor was studied using yeaslt two-hybrid system.. The 3rd cytoplasmic loop of rat D2 dopamine receptor was used to screen the cDNA library of mouse brain. and ALY was found to interact with it. The interaction in the yeast was observed only with the 3rd cytoplasmic loop of D2 dopamine receptor but not with that of D3 or D4 dopamine receptor. The interaction between two proteins was also confirmed by GST pull-down assay. (omitted)

• Toxicological Research
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• v.6 no.1
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• pp.75-88
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• 1990

The characteristics of dopamine uptake, D-1 and D-2 receptors after acute and subacute cocaine administration were determind in striatum from WKY and SHR. Cocaine was administered either acutely (40 mg/kg, s.c.) or twice daily (20 mg/kg, s.c.) for 3 and 7 days in 9-wk old WKY and SHR. Rats were sacrificed 30 min, 2 or 24 h after the single injection and 18 h after the last administration to the subacutely treated group. The changes in dopamine uptake, dopamine uptake sites, D-1 and D-2 receptors were determined using $(^3H)$dopamine, $(^3H)$-GBR-12935, $(^3H)$SCH-23390 and $(^3H)$sulpiride, respectively. In acutely treated rats, significant increases in $V_{max}$of dopamine uptake were observed 30 min after the cocanine injection in both strains without changes in $K_m$ values. The in vitro $IC_{50}$for cocaine was significantly decreased 30 min in WKY and 2 h in SHR. However, that for in vitro GBR-12909 was significantly increased 30 min and 2 h in both strains. Also densities of $(^3H)$-GBR-12935 binding sites were significantly increased 30 min and 2 h without changes in their $K_d$. Significant increases in D-2 receptor density were observed 30 min, 2 or 24 h after acute injection in both strains without changes in their affinities. The density of D-1 receptor was significantly decreased 30 min after the injection in WKY, but not in SHR. In subacutely treated rats, a significant increase in $K_m$ of dopamine uptake was observed in 7-day treated SHR. The in vitro $IC_{50}$fot GBR-12909 was significantly increased in 3-day treated WKY. The density of D-1 receptors was significantly increased in 3- and 7-day treated WKY, but not in SHR. The affinity of both binding sites remained unchanged. The results suggest that cocanine administration alters dopamine uptake, characteristics of dopamine uptake sites and dopamine receptor binding characteristics in rat brain. Furthermore, D-1 and D-2 dopamine receptors appear to be differently regulated.

• Biomolecules & Therapeutics
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• v.2 no.1
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• pp.16-22
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• 1994

Using 2 to 4 day-old postnatal rats, primary brain cell cultures were made from various brain regions (substantia nigra, hippocampus, striatum, and nucleus accumbens). Whole-cell patch clamp technique was used for electrophysiological studies. Neurons cultured from substantia nigra were characterized more in detail to test whether these cultured neurons were appropriate for physiological studies. Immunocytochemical and electrophysiological properties of these cultured neurons agreed with those from other in vivo or in vitro studies suggesting that cultured neurons maintained normal cytological and physiological conditions. Modulation of ionic channels through dopamine receptors were studied from brain areas where dopamine plays important roles on brain functions. When neurons were clamped near resting membrane potential (-74mV), R(+), R(+)-SKF 38393, a specific D$_1$receptor agonist, activated cultured striatal neurons, and dopamine itself produced biphasic responses. Responses of cultured hippocampal neurons to dopamine agonists were kinds of mirror images to those from striatal neurons; D$_1$receptor agonists inhibited hippocampal neurons but quinpirole, a D$_2$receptor agonist, activated them. Neurons cultured from nucleus accumbens were inhibited by dopamine.

• Korean Journal of Biological Psychiatry
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• v.4 no.1
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• pp.43-47
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• 1997

The author attempted to examine the allelic association between the A1 allele of Dopamine $D_2$ receptor and alcoholism in Koreans. The allelic distribution of Taq I polymorphism of the $D_2$ dopamine receptor gene with alcoholism was examined in 67 Korean alcoholics and compared with 100 Korean controls. In alcoholics, the numbers of alcoholics with A1A1, A1A2 and A2A2 were 11(16.4%), 30(44.8%) and 26(38.8%) respectively and in controls with A1A1, A1A2 and A2A2 were 17(17.0%), 42(42.0%) and 41(41.0%), respectively. The prevalence of the A1 allele in alcoholics was 61.2% and 59.0% in controls. And the frequency of the A1 allele in alcoholics and controls were 0.39 and 0.38, respectively. There was not significant difference in the frequency of the A1 allele between alcoholics and controls. This data suggest that the A1 allele is not associated with alcoholism in Koreans. The author conclude that our data do not support an allelic association between the A1 allele at Dopamine $D_2$ receptor and alcoholism. Further systemized studies will be necessary to determine whether the role of allele of Dopamine $D_2$receptor is major effect gene or modifying effect gene in the pathogenesis of alcoholism.

• Animal cells and systems
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• v.1 no.3
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• pp.497-505
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• 1997

Dopamine plays diverse roles in the fetal brain development and differentiation. However, the development of the dopaminergic neurons and its receptors has not been fully understood. In our studies, in situ hybridization and immunohistochemical methods were used to investigate the ontogeny of dopaminergic neurons and its receptor subtypes during the fetal development of the rat. In situ hybridization data showed that dopamine $D_1$ and $D_2$ receptor mRNAs were expressed in the ventricular and subventricular zones of ganglionic eminence, thalamus, hypothalamus, and cortical neuroepithelium on gestational day 13. Expression of dopamine $D_1$ and $D_2$ receptors during gestational days 17 and 19 reached the same or similar level of that in the adult brain. Expression of $D_1$ receptor mRNA preceded that of $D_2$ receptor mRNA in the early developmental stage, although this pattern was reversed with the sharp increase of $D_2$ receptor mRNA soon after. $D_2$ receptor mRNA was expressed in substantia nigra of mesencephalon of the fetal rat brain. However, $D_1$ receptor mRNA was not detected in substantia nigra. Our results indicate that dopamine might function in the fetal brain during the early gestational period.

• Journal of Korean Neurosurgical Society
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• v.29 no.7
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• pp.868-876
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• 2000

Objective : Parkinsonian rat models have generally been characterized by unilateral destruction of both the nigrostriatal pathway and the mesolimbic pathway using the neurotoxin 6-hydroxydopamine. The induction of contraversive turning by apomorphine in these models is thought to reflect the stimulation of supersensitive dopamine D2 receptor or receptor-mediated mechanisms in denervated neostriatum. The present study was undertaken to investigate the expression of dopamine D2 receptor in denervated striatum according to modalities of apomorphine(dopamine agonist) treatment after creating a hemiparkinsonian rat model in which there is 6-hydroxydopamine induced destruction of the unilateral dopaminergic nigrostriatal pathway. Methods : After making complete lesion in left side substantia nigra pars compacta(SNpc) by stereotactic injection of 6-hydroxydopamine into medial and lateral areas of SNpc, and confirming successful animal model by apomorphine induced contraversive turning behavior without recovery and complete destruction of ipsilateral SNpc with tyrosine hydroxylase immunostaining in 7th day after operation, 15 rats of parkinsonian model were studied with or without administration of apomorphine at varying doses and durations. According to the modalities of apomorphine treatment for 4 days, these rats were divided into 3 groups, as not-treated group, intermittently treated group and constantly treated group. For investigating the extent of the expression of dopamine D2 receptor in denervated striatum, immunohistochemical staining by dopamine D2 receptor antibody and Western blot were performed. Results : In the D2 receptor antibody immunohistochemical staining, the mean number of positive stained neurons was highest in not-treated group($20.5{\pm}1.14$) of 3 groups. In constantly treated group, the mean number of positive stained neurons was less($3.9{\pm}1.79$) than intermittently treated group(p<0.05). The Western blotting with the D2 receptor antibody revealed that expression of receptors was also highest in not-treated group and less in constantiy treated group than intermittently treated group. Conclusion : Dopamine D2 receptors in denervated striatum of parkinsonian rat models, which were not treated with apomorphine, revealed to be most highly expressed. And, according to doses and durations of apomorphine administration, desensitization of the receptor was more apt to develop with constant treatment than intermittent treatment. In clinical setting, the authors believe that, in long-term treated parkinsonian patients, desensitization of dopamine receptors due to chronic dopaminergic stimulation seems to be partially related to mechanisms of drug tolerance.