D5 Dopamine Receptor Knockout Mice and Hypertension

Abnormalities in dopamine production and receptor function have been described in human essential hypertension and rodent models of genetic hypertension. All of the five dopamine receptor genes (D₁, D₂, D₃, D₄, and D₅) expressed in mammals and some of their regulators are in loci linked to hypertension in humans and in rodents. Under normal conditions, D₁-like receptors (D₁ and D₅) inhibit sodium transport in the kidney and the intestine. However, in the Dahl salt-sensitive and spontaneously hypertensive rats, and humans with essential hypertension, the D₁-like receptor-mediated inhibition of sodium transport is impaired because of an uncoupling of the D₁-like receptor from its G protein/effector complex. The uncoupling is genetic, and receptor-, organ-, and nephron segment-specific. In human essential hypertension, the uncoupling of the D₁ receptor from its G protein/effector complex is caused by an agonist-independent serine phosphorylation/desensitization by constitutively active variants of the G protein-coupled receptor kinase type 4. The D₅ receptor is also important in blood pressure regulation. Disruption of the D₅ or the D₁ receptor gene in mice increases blood pressure. However, unlike the D₁ receptor, the hypertension in D₅ receptor null mice is caused by increased activity of the sympathetic nervous system, apparently due to activation of oxytocin, V₁ vasopressin, and non-N-methyl D-aspartate receptors in the central nervous system. The cause of the activation of these receptors remains to be determined.     

Dysregulation of dopamine-dependent mechanisms as a determinant of hypertension: studies in dopamine receptor knockout mice

Dopamine plays an important role in the pathogenesis of hypertension by regulating epithelial sodium transport and by interacting with vasoactive hormones/humoral factors, such as aldosterone, angiotensin, catecholamines, endothelin, oxytocin, prolactin pro-opiomelancortin, reactive oxygen species, renin, and vasopressin. Dopamine receptors are classified into D(1)-like (D(1) and D(5)) and D(2)-like (D(2), D(3), and D(4)) subtypes based on their structure and pharmacology. In recent years, mice deficient in one or more of the five dopamine receptor subtypes have been generated, leading to a better understanding of the physiological role of each of the dopamine receptor subtypes. This review summarizes the results from studies of various dopamine receptor mutant mice on the role of individual dopamine receptor subtypes and their interactions with other G protein-coupled receptors in the regulation of blood pressure.     

Impaired renal D(1)-like and D(2)-like dopamine receptor interaction in the spontaneously hypertensive rat

D(1)-like (D(1), D(5)) and D(2)-like (D(2), D(3), D(4)) dopamine receptors interact in the kidney to produce a natriuresis and a diuresis. Disruption of D(1) or D(3) receptors in mice results in hypertension that is caused, in part, by a decreased ability to excrete an acute saline load. We studied D(1)-like and D(2)-like receptor interaction in anesthetized spontaneously hypertensive rats (SHR) by the intrarenal infusion of Z-1046 (a novel dopamine receptor agonist with rank order potency of D(3)> or =D(4)>D(2)>D(5)>D(1)). Z-1046 increased glomerular filtration rate (GFR), urine flow, and sodium excretion in normotensive Wistar-Kyoto rats but not in SHRs. The lack of responsiveness to Z-1046 in SHRs was not an epiphenomenon, because intrarenal cholecystokinin infusion increased GFR, urine flow, and sodium excretion to a similar extent in the two rat strains. We conclude that renal D(1)-like and D(2)-like receptor interaction is impaired in SHRs. The impaired D(1)-like and D(2)-like receptor interaction in SHRs is not caused by alterations in the coding sequence of the D(3) receptor, the D(2)-like receptor expressed in rat renal tubules that has been shown to be involved in sodium transport. Because the diuretic and natriuretic effects of D(1)-like receptors are, in part, caused by an interaction with D(2)-like receptors, it is possible that the decreased Z-1046 action in SHRs is secondary to the renal D(1)-like receptor dysfunction in this rat strain.     

Renal dopamine receptors and hypertension

Dopamine has been recognized as an important modulator of central as well as peripheral physiologic functions in both humans and animals. Dopamine receptors have been identified in a number of organs and tissues, which include several regions within the central nervous system, sympathetic ganglia and postganglionic nerve terminals, various vascular beds, the heart, the gastrointestinal tract, and the kidney. The peripheral dopamine receptors influence cardiovascular and renal function by decreasing afterload and vascular resistance and promoting sodium excretion. Within the kidney, dopamine receptors are present along the nephron, with highest density on proximal tubule epithelial cells. It has been reported that there is a defective dopamine receptor, especially D(1) receptor function, in the proximal tubule of various animal models of hypertension as well as in humans with essential hypertension. Recent reports have revealed the site of and the molecular mechanisms responsible for the defect in D(1) receptors in hypertension. Moreover, recent studies have also demonstrated that the disruption of various dopamine receptor subtypes and their function produces hypertension in rodents. In this review, we present evidence that dopamine and dopamine receptors play an important role in regulating renal sodium excretion and that defective renal dopamine production and/or dopamine receptor function may contribute to the development of various forms of hypertension.     

Hydrogen peroxide causes uncoupling of dopamine D1-like receptors from G proteins via a mechanism involving protein kinase C and G-protein-coupled receptor kinase 2

Dopamine, via activation of D1-like receptors, inhibits Na,K-ATPase and Na,H-exchanger in renal proximal tubules and promotes sodium excretion. This effect of dopamine is not seen in conditions associated with oxidative stress such as hypertension, diabetes, and aging due to uncoupling of D1-like receptors from G proteins. To identify the role of oxidative stress in uncoupling of the D1-like receptors, we utilized primary cultures from rat renal proximal tubules. Hydrogen peroxide (H2O2), an oxidant, treatment to the cell cultures increased the level of malondialdehyde, a marker of oxidative damage. Further, H2O2 decreased membranous D1-like receptor numbers and proteins, D1-like agonist (SKF 38393)-mediated [35S]GTPgammaS binding and SKF 38393-mediated inhibition of Na,K-ATPase. Moreover, H2O2 treatment to the cultures caused membranous translocation of G-protein-coupled receptor kinase 2 (GRK 2) and increased serine phosphorylation of D1A receptors accompanied by an increase in protein kinase C (PKC) activity. Interestingly, PKC inhibitors blocked the H2O2-mediated stimulation of GRK 2 and serine phosphorylation of D1A receptors. Further, GRK 2 antisense but not scrambled oligonucleotides attenuated the effect of H2O2 on membranous expression of GRK 2. Moreover, direct activation of PKC with phorbol ester (PMA) resulted in reduction of SKF 38393-mediated [35S]GTPgammaS binding. We conclude that H2O2 stimulates PKC leading to the activation of GRK 2, which causes serine phopshorylation of D1A receptors and receptor G-protein uncoupling in these cells, resulting in impairment in D1-like receptor function.     

Dopaminergic supersensitivity in G protein-coupled receptor kinase 6-deficient mice

Brain dopaminergic transmission is a critical component in numerous vital functions, and its dysfunction is involved in several disorders, including addiction and Parkinson's disease. Responses to dopamine are mediated via G protein-coupled dopamine receptors (D1-D5). Desensitization of G protein-coupled receptors is mediated via phosphorylation by members of the family of G protein-coupled receptor kinases (GRK1-GRK7). Here we show that GRK6-deficient mice are supersensitive to the locomotor-stimulating effect of psychostimulants, including cocaine and amphetamine. In addition, these mice demonstrate an enhanced coupling of striatal D2-like dopamine receptors to G proteins and augmented locomotor response to direct dopamine agonists both in intact and in dopamine-depleted animals. The present study indicates that postsynaptic D2-like dopamine receptors are physiological targets for GRK6 and suggests that this regulatory mechanism contributes to central dopaminergic supersensitivity.     

Inhibitory effect of D1-like and D3 dopamine receptors on norepinephrine-induced proliferation in vascular smooth muscle cells

The sympathetic nervous system plays an important role in the regulation of blood pressure. There is increasing evidence for positive and negative interactions between dopamine and adrenergic receptors; the activation of the alpha-adrenergic receptor induces vasoconstriction, whereas the activation of dopamine receptor induces vasorelaxation. We hypothesize that the D1-like receptor and/or D3 receptor also inhibit alpha1-adrenergic receptor-mediated proliferation in vascular smooth muscle cells (VSMCs). In this study, VSMC proliferation was determined by measuring [3H]thymidine incorporation, cell number, and uptake of 3-(4,5-dimethylthiazol-2-yl)-diphenyltetrazolium bromide (MTT). Norepinephrine increased VSMC number and MTT uptake, as well as [3H]thymidine incorporation via the alpha1-adrenergic receptor in aortic VSMCs from Sprague-Dawley rats. The proliferative effects of norepinephrine were attenuated by the activation of D1-like receptors or D3 receptors, although a D1-like receptor agonist, fenoldopam, and a D3 receptor agonist, PD-128907, by themselves, at low concentrations, had no effect on VSMC proliferation. Simultaneous stimulation of both D1-like and D3 receptors had an additive inhibitory effect. The inhibitory effect of D3 receptor was via protein kinase A, whereas the D1-like receptor effect was via protein kinase C-zeta. The interaction between alpha1-adrenergic and dopamine receptors, especially D1-like and D3 receptors in VSMCs, could be involved in the pathogenesis of hypertension.     

A synergistic approach towards understanding the functional significance of dopamine receptor interactions

The importance of the neurotransmitter dopamine (DA) in the nervous system is underscored by its role in a wide variety of physiological and neural functions in both vertebrates and invertebrates. Binding of dopamine to its membrane receptors initiates precise signaling cascades that result in specific cellular responses. Dopamine receptors belong to a super-family of G-protein coupled receptors (GPCRs) that are characterized by seven trans-membrane domains. In mammals, five dopamine receptors have been identified which are grouped into two different categories D1- and D2-like receptors. The interactions of DA receptors with other proteins including specific Gα subunits are critical in deciding the fate of downstream molecular events carried out by effector proteins. In this mini-review we provide a synopsis of known protein-protein interactions of DA receptors and a perspective on the potential synergistic utility of Caenorhabditis elegans as a model eukaryote with a comparatively simpler nervous system to gain insight on the neuronal and behavioral consequences of the receptor interactions.     

D5 dopamine receptor regulation of phospholipase D

D(1)-like receptors have been reported to decrease oxidative stress in vascular smooth muscle cells by decreasing phospholipase D (PLD) activity. However, the PLD isoform regulated by D(1)-like receptors (D(1) or D(5)) and whether abnormal regulation of PLD by D(1)-like receptors plays a role in the pathogenesis of hypertension are unknown. The hypothesis that the D(5) receptor is the D(1)-like receptor that inhibits PLD activity and serves to regulate blood pressure was tested using D(5) receptor mutant mice (D(5)(-/-)). We found that in the mouse kidney, PLD2, like the D(5) receptor, is mainly expressed in renal brush-border membranes, whereas PLD1 is mainly expressed in renal vessels with faint staining in brush-border membranes and collecting ducts. Total renal PLD activity is increased in D(5)(-/-) mice relative to congenic D(5) wild-type (D(5)(+/+)) mice. PLD2, but not PLD1, expression is greater in D(5)(-/-) than in D(5)(+/+) mice. The D(5) receptor agonist fenoldopam decreases PLD2, but not PLD1, expression and activity in human embryonic kidney-293 cells heterologously expressing the human D(5) receptor, effects that are blocked by the D(5) receptor antagonist SCH-23390. These studies show that the D(5) receptor regulates PLD2 activity and expression. The hypertension in the D(5)(-/-) mice is associated with increased PLD expression and activity. Impaired D(5) receptor regulation of PLD2 may play a role in the pathogenesis of hypertension.     

多巴胺D5受体转基因小鼠的建立

目的建立人多巴胺D5受体突变基因F173 L（D5F173L）,S390G（D5S390G）及正常人D5基因（hD5 WT）的转基因小鼠,利用该转基因动物模型来研究D5受体在原发性高血压中的发病机制。方法利用显微注射的技术将插入CMV启动子下游的D5F173L,D5S390G及hD5 WT基因的转基因载体注射入C57BL/6小鼠体内,建立多巴胺D5F173L,D5S390G及hD5 WT的转基因小鼠。通过PCR鉴定转基因小鼠的基因型。利用Western Blotting方法鉴定该受体蛋白在肾脏的表达情况。使用智能无创血压测量仪测量转基因小鼠的血压值。结果分别建立了多巴胺D5F173L,D5S390G及hD5 WT转基因C57BL/6小鼠,Western Blotting方法鉴定结果显示,与非转基因C57BL/6小鼠比较,D5转基因小鼠D5受体在肾脏有较高的表达。3-6月龄D5 F173L转基因小鼠的收缩压、舒张压和平均动脉血压均明显高于多巴胺D5S390G及hD5 WT转基因小鼠（n=6-8,P〈0.05）。结论多巴胺D5受体在原发性高血压发病中具有重要作用,但作用机理还有待于进一步研究。     

Coexpressed D1- and D2-like dopamine receptors antagonistically modulate acetylcholine release in Caenorhabditis elegans

Dopamine acts through two classes of G protein-coupled receptor (D1-like and D2-like) to modulate neuron activity in the brain. While subtypes of D1- and D2-like receptors are coexpressed in many neurons of the mammalian brain, it is unclear how signaling by these coexpressed receptors interacts to modulate the activity of the neuron in which they are expressed. D1- and D2-like dopamine receptors are also coexpressed in the cholinergic ventral-cord motor neurons of Caenorhabditis elegans. To begin to understand how coexpressed dopamine receptors interact to modulate neuron activity, we performed a genetic screen in C. elegans and isolated mutants defective in dopamine response. These mutants were also defective in behaviors mediated by endogenous dopamine signaling, including basal slowing and swimming-induced paralysis. We used transgene rescue experiments to show that defects in these dopamine-specific behaviors were caused by abnormal signaling in the cholinergic motor neurons. To investigate the interaction between the D1- and D2-like receptors specifically in these cholinergic motor neurons, we measured the sensitivity of dopamine-signaling mutants and transgenic animals to the acetylcholinesterase inhibitor aldicarb. We found that D2 signaling inhibited acetylcholine release from the cholinergic motor neurons while D1 signaling stimulated release from these same cells. Thus, coexpressed D1- and D2-like dopamine receptors act antagonistically in vivo to modulate acetylcholine release from the cholinergic motor neurons of C. elegans.     

Dopamine selectively induces migration and homing of naive CD8+ T cells via dopamine receptor D3

The nervous systems affect immune functions by releasing neurohormones and neurotransmitters. A neurotransmitter dopamine signals via five different seven-transmembrane G protein-coupled receptors termed D1 to D5. The secondary lymphoid tissues are highly innervated by sympathetic nerve fibers that store dopamine at high contents. Lymphocytes also produce dopamine. In this study, we examined expression and function of dopamine receptors in lymphocytes. We found that D3 was the predominant subtype of dopamine receptors in the secondary lymphoid tissues and selectively expressed by naive CD8+ T cells of both humans and mice. Dopamine induced calcium flux and chemotaxis in mouse L1.2 cells stably expressing human D3. These responses were almost completely inhibited by pertussis toxin, indicating that D3 was coupled with the Galphai class of G proteins. Consistently, dopamine selectively induced chemotactic responses in naive CD8+ T cells of both humans and mice in a manner sensitive to pertussis toxin and D3 antagonists. Dopamine was highly synergistic with CCL19, CCL21, and CXCL12 in induction of chemotaxis in naive CD8+ T cells. Dopamine selectively induced adhesion of naive CD8+ T cells to fibronectin and ICAM-1 through activation of integrins. Intraperitoneal injection of mice with dopamine selectively attracted naive CD8+ T cells into the peritoneal cavity. Treatment of mice with a D3 antagonist U-99194A selectively reduced homing of naive CD8+ T cells into lymph nodes. Collectively, naive CD8+ T cells selectively express D3 in both humans and mice, and dopamine plays a significant role in migration and homing of naive CD8+ T cells via D3.     

Dopamine Receptors Antagonistically Regulate Behavioral Choice between Conflicting Alternatives in C. elegans

Caenorhabditis elegans is a useful model to study the neuronal or molecular basis for behavioral choice, a specific form of decision-making. Although it has been implied that both D1-like and D2-like dopamine receptors may contribute to the control of decision-making in mammals, the genetic interactions between D1-like and D2-like dopamine receptors in regulating decision-making are still largely unclear. In the present study, we investigated the molecular control of behavioral choice between conflicting alternatives (diacetyl and Cu²⁺) by D1-like and D2-like dopamine receptors and their possible genetic interactions with C. elegans as the assay system. In the behavioral choice assay system, mutation of dop-1 gene encoding D1-like dopamine receptor resulted in the enhanced tendency to cross the Cu²⁺ barrier compared with wild-type. In contrast, mutations of dop-2 or dop-3 gene encoding D2-like dopamine receptor caused the weak tendency to cross the Cu²⁺ barrier compared with wild-type. During the control of behavioral choice, DOP-3 antagonistically regulated the function of DOP-1. The behavioral choice phenotype of dop-2; dop-1dop-3 triple mutant further confirmed the possible antagonistic function of D2-like dopamine receptor on D1-like dopamine receptor in regulating behavioral choice. The genetic assays further demonstrate that DOP-3 might act through Gα_o signaling pathway encoded by GOA-1 and EGL-10, and DOP-1 might act through Gα_q signaling pathway encoded by EGL-30 and EAT-16 to regulate the behavioral choice. DOP-1 might function in cholinergic neurons to regulate the behavioral choice, whereas DOP-3 might function in GABAergic neurons, RIC, and SIA neurons to regulate the behavioral choice. In this study, we provide the genetic evidence to indicate the antagonistic relationship between D1-like dopamine receptor and D2-like dopamine receptor in regulating the decision-making of animals. Our data will be useful for understanding the complex functions of dopamine receptors in regulating decision-making in animals.     

Distribution of D(5) dopamine receptor mRNA in rat ventromedial hypothalamic nucleus

Estrogen induces lordosis through, in part, estrogen receptor (ER)-mediated synthesis of progesterone receptors (PR) in the ventromedial nucleus (VMN). In vitro, PR is activated by the neurotransmitter dopamine through D1-like receptors (1). In vivo, lordosis is induced by dopamine, an effect mediated in part by PR and D(5) dopamine receptors. The purpose of the present study was to determine mRNA distribution of D1-like receptors in the female rat brain using RT-PCR combined with punchout microdissection techniques. Employing specific primers to D(5) and D(1) dopamine receptors, we found detectable expression levels of D(5) dopamine receptor mRNA in VMN as well as the arcuate nucleus/median eminence (ArcN/ME). In contrast, D(1) dopamine receptor mRNA was detected only in VMN. By using this highly sensitive and specific RT-PCR methodology, we have confirmed the presence of D(5) dopamine receptor mRNA in an area of the brain that regulates reproductive behavior through PR. The data support the previous observation that D(5) dopamine receptors in VMN contribute to facilitation of female reproductive behavior by D1-like agonists.     

Dopamine receptor regulation of Ca2+ levels in individual isolated nerve terminals from rat striatum: comparison of presynaptic D1-like and D2-like receptors

We have directly observed the effects of activating presynaptic D1-like and D2-like dopamine receptors on Ca2+ levels in isolated nerve terminals (synaptosomes) from rat striatum. R-(+)-SKF81297, a selective D1-like receptor agonist, and (-)-quinpirole, a selective D2-like receptor agonist, induced increases in Ca2+ levels in different subsets of individual striatal synaptosomes. The SKF81297- and quinpirole-induced effects were blocked by R-(+)-SCH23390, a D1-like receptor antagonist, and (-)-sulpiride, a D2-like receptor antagonist, respectively. SKF81297- or quinpirole-induced Ca2+ increases were inhibited following blockade of voltage-gated calcium channels or sodium channels. In a larger subset of synaptosomes, quinpirole decreased baseline Ca2+. Quinpirole also inhibited veratridine-induced increases in intrasynaptosomal Ca2+ level. Immunostaining confirmed the presynaptic expression of D1, D5, D2 and D3 receptors, but not D4 receptors. The array of neurotransmitter phenotypes of the striatal nerve endings expressing D1, D5, D2 or D3 varied for each receptor subtype. These results suggest that presynaptic D1-like and D2-like receptors induce increases in Ca2+ levels in different subsets of nerve terminals via Na+ channel-mediated membrane depolarization, which, in turn, induces the opening of voltage-gated calcium channels. D2-like receptors also reduce nerve terminal Ca2+ in a different but larger subset of synaptosomes, consistent with the predominant presynaptic action of dopamine in the striatum being inhibitory.     

The dopamine D(2) receptor is expressed and sensitizes adenylyl cyclase activity in airway smooth muscle

Dopamine receptors are G protein-coupled receptors that are divided into two subgroups, "D(1)-like" receptors (D(1) and D(5)) that couple to the G(s) protein and "D(2)-like" receptors (D(2), D(3), and D(4)) that couple to G(i). Although inhaled dopamine has been reported to induce bronchodilation in patients with asthma, functional expression of dopamine receptor subtypes has never been described on airway smooth muscle (ASM) cells. Acute activation of G(i)-coupled receptors inhibits adenylyl cyclase activity and cAMP synthesis, which classically impairs ASM relaxation. In contrast, chronic activation of G(i)-coupled receptors produces a paradoxical enhancement of adenylyl cyclase activity referred to as heterologous sensitization. We questioned whether the dopamine D(2)-like receptor is expressed on ASM, whether it exhibits classical G(i)-coupling, and whether it modulates ASM function. We detected the mRNA encoding the dopamine D(2) receptor in total RNA isolated from native human ASM and from cultured human airway smooth muscle (HASM) cells. Immunoblots identified the dopamine D(2) receptor protein in both native human and guinea pig ASM and cultured HASM cells. The dopamine D(2) receptor protein was immunohistochemically localized to both human and guinea pig ASM. Acute activation of the dopamine D(2) receptor by quinpirole inhibited forskolin-stimulated adenylyl cyclase activity in HASM cells, which was blocked by the dopamine D(2) receptor antagonist L-741626. In contrast, the chronic pretreatment (1 h) with quinpirole potentiated forskolin-stimulated adenylyl cyclase activity, which was inhibited by L-741626, the phospholipase C inhibitor U73122, or the protein kinase C inhibitor GF109203X. Quinpirole also stimulated inositol phosphate synthesis, which was inhibited by L-741626 or U73122. Chronic pretreatment (1 h) of the guinea pig tracheal rings with quinpirole significantly potentiated forskolin-induced airway relaxation, which was inhibited by L-741626. These results demonstrate that functional dopamine D(2) receptors are expressed on ASM and could be a novel therapeutic target for the relaxation of ASM.     

D1-like dopamine receptor-mediated function in congenic mutants with D1 vs. D5 receptor "knockout"

Current understanding of the functional roles of individual dopamine D1-like [D1, D5] and D2-like [D2L/s, D3, D4] receptor subtypes remains incomplete. In particular, the lack of pharmacological agonists and antagonists able to distinguish between D1 and D5 receptors means that any differential roles in the regulation of behavior are poorly understood. Mutant mice with targeted gene deletion ("knockout") of individual dopamine receptor subtypes offer an important alternative approach to resolving these functional roles. In congenic D1 mutants examined ethologically, progressive increases in specific topographies of behavior over wildtypes were considerably greater than those in D1 mutants on a mixed genetic background; D1 knockout appears to influence the neuronal substrate(s) of habituation to disrupt sculpture of the changing topography of behavior from initial exploration through to quiescence. Similarly, the D1 receptor appears to regulate specific topographies of orofacial movement in the mouse as these are "sculpted" in a time-dependent manner. Although the well-recognized role of the D1-like family in regulating several aspects of behavioral topography has been assumed to involve primarily D1 receptors, this presumption may require modification to accommodate a subtle but not negligible role for their D5 counterparts as evidenced in the phenotype of congenic D5 mutants.     

Dopamine induces IL-6-dependent IL-17 production via D1-like receptor on CD4 naive T cells and D1-like receptor antagonist SCH-23390 inhibits cartilage destruction in a human rheumatoid arthritis/SCID mouse chimera model

A major neurotransmitter dopamine transmits signals via five different seven-transmembrane G protein-coupled receptors termed D1-D5. Several studies have shown that dopamine not only mediates interactions into the nervous system, but can contribute to the modulation of immunity via receptors expressed on immune cells. We have previously shown an autocrine/paracrine release of dopamine by dendritic cells (DCs) during Ag presentation to naive CD4(+) T cells and found efficacious results of a D1-like receptor antagonist SCH-23390 in the experimental autoimmune encephalomyelitis mouse model of multiple sclerosis and in the NOD mouse model of type I diabetes, with inhibition of Th17 response. This study aimed to assess the role of dopaminergic signaling in Th17-mediated immune responses and in the pathogenesis of rheumatoid arthritis (RA). In human naive CD4(+) T cells, dopamine increased IL-6-dependent IL-17 production via D1-like receptors, in response to anti-CD3 plus anti-CD28 mAb. Furthermore, dopamine was localized with DCs in the synovial tissue of RA patients and significantly increased in RA synovial fluid. In the RA synovial/SCID mouse chimera model, although a selective D2-like receptor antagonist haloperidol significantly induced accumulation of IL-6(+) and IL-17(+) T cells with exacerbated cartilage destruction, SCH-23390 strongly suppressed these responses. Taken together, these findings indicate that dopamine released by DCs induces IL-6-Th17 axis and causes aggravation of synovial inflammation of RA, which is the first time, to our knowledge, that actual evidence has shown the pathological relevance of dopaminergic signaling with RA.