Comparison of the ability of dopamine receptor agonists to inhibit forskolin-stimulated adenosine 3'5'-cyclic monophosphate (cAMP) accumulation via D2L (long isoform) and D3 receptors expressed in Chinese hamster ovary (CHO) cells

Genome-wide association study reveals candidate markers related to field fertility and semen quality traits in Holstein-Friesian bulls

In vitro assessment of bull semen quality is routinely used in bull semen processing centres in order to ensure that semen destined to be used in the field has passed minimum standards. Despite these stringent quality control checks, individual bulls that pass the quality control checks can still vary in field fertility by up to 25%. A genome-wide association study was undertaken to determine genetic markers associated with prefreeze and post-thaw bull sperm quality traits as well as field fertility. Genome-wide association analysis was performed using a single nucleotide polymorphism (SNP) regression mixed linear model in WOMBAT. Genes within a 250 Kb span of a suggestive (P ≤ 1 × 10^-5) SNP were considered as candidate genes. One SNP was associated with adjusted pregnancy rate, and 21 SNPs were associated across the seven semen quality traits (P ≤ 1 × 10^-5). Functional candidate genes include SIPA1L2 which was associated with adjusted pregnancy rate. This encodes a Rap GTPase-activating protein involved in Rap1 signalling pathway and was previously found to play a role in the process of sperm differentiation. Gene ontology (GO) analysis also identified significantly enriched biological processes involved protein tyrosine kinase activity including genes such as DYRK1A, TEC and TXK that were associated with sperm motility prior to freezing. Another candidate gene associated with post-thaw sperm motility was FHDC1 which coordinates actin filament and microtubule dynamics. The induced 11 GO terms in the ejaculates rejected after freezing trait were related to ATPase, phosphatase and hydrolase activity. These results reveal novel specific genomic regions and candidate genes associated with economically important phenotypes such as field fertility and semen quality traits.

Dopamine Receptor Subtypes Differentially Regulate Autophagy

Some dopamine receptor subtypes were reported to participate in autophagy regulation, but their exact functions and mechanisms are still unclear. Here we found that dopamine receptors D2 and D3 (D2-like family) are positive regulators of autophagy, while dopamine receptors D1 and D5 (D1-like family) are negative regulators. Furthermore, dopamine and ammonia, the two reported endogenous ligands of dopamine receptors, both can induce dopamine receptor internalization and degradation. In addition, we found that AKT (protein kinase B)-mTOR (mechanistic target of rapamycin) and AMPK (AMP-activated protein kinase) pathways are involved in DRD3 (dopamine receptor D3) regulated autophagy. Moreover, autophagy machinery perturbation inhibited DRD3 degradation and increased DRD3 oligomer. Therefore, our study investigated the functions and mechanisms of dopamine receptors in autophagy regulation, which not only provides insights into better understanding of some dopamine receptor-related neurodegeneration diseases, but also sheds light on their potential treatment in combination with autophagy or mTOR pathway modulations.

Structural and Functional Effect of an Oscillating Electric Field on the Dopamine-D3 Receptor: A Molecular Dynamics Simulation Study

Dopamine as a neurotransmitter plays a critical role in the functioning of the central nervous system. The structure of D3 receptor as a member of class A G-protein coupled receptors (GPCRs) has been reported. We used MD simulation to investigate the effect of an oscillating electric field, with frequencies in the range 0.6–800 GHz applied along the z-direction, on the dopamine-D3R complex. The simulations showed that at some frequencies, the application of an external oscillating electric field along the z-direction has a considerable effect on the dopamine-D3R. However, there is no enough evidence for prediction of changes in specific frequency, implying that there is no order in changes. Computing the correlation coefficient parameter showed that increasing the field frequency can weaken the interaction between dopamine and D3R and may decrease the Arg128{3.50}-Glu324{6.30} distance. Because of high stability of α helices along the z-direction, applying an oscillating electric field in this direction with an amplitude 10-time higher did not have a considerable effect. However, applying the oscillating field at the frequency of 0.6 GHz along other directions, such as X-Y and Y-Z planes, could change the energy between the dopamine and the D3R, and the number of internal hydrogen bonds of the protein. This can be due to the effect of the direction of the electric field vis-à-vis the ligands orientation and the interaction of the oscillating electric field with the dipole moment of the protein.

Dopamine D2 Receptor-Mediated Regulation of Pancreatic β Cell Mass

Understanding the molecular mechanisms that regulate β cell mass and proliferation is important for the treatment of diabetes. Here, we identified domperidone (DPD), a dopamine D2 receptor (DRD2) antagonist that enhances β cell mass. Over time, islet β cell loss occurs in dissociation cultures, and this was inhibited by DPD. DPD increased proliferation and decreased apoptosis of β cells through increasing intracellular cAMP. DPD prevented β cell dedifferentiation, which together highly contributed to the increased β cell mass. DRD2 knockdown phenocopied the effects of domperidone and increased the number of β cells. Drd2 overexpression sensitized the dopamine responsiveness of β cells and increased apoptosis. Further analysis revealed that the adenosine agonist 5′-N-ethylcarboxamidoadenosine, a previously identified promoter of β cell proliferation, acted with DPD to increase the number of β cells. In humans, dopamine also modulates β cell mass through DRD2 and exerts an inhibitory effect on adenosine signaling.

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Dopamine inhibits dedifferentiation and proliferation, and promotes apoptosis of β cells

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Dopamine confers its action through binding to DRD2 and decreasing cAMP

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Dopamine-DRD2 signal also functions through interaction with adenosine-ADORA2A signal

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Dopamine-DRD2-cAMP signal is a potential target for β cell regeneration

Dopamine D3 receptor agonists as pharmacological tools

Dysregulation of the dopaminergic innervation in the central nervous system plays a key role in different neurological disorders like Parkinson´s disease, restless legs syndrome, schizophrenia etc. Although dopamine D3 receptors have been recognized as an important target in these diseases, their full pharmacological properties need further investigations. With focus on dopamine D3 receptor full agonists, this review has divided the ergoline and non-ergoline ligands in dissimilar chemical subclasses describing their pharmacodynamic properties on different related receptors, on species differences and their functional properties on different signaling mechanism. This is combined with a short description of structure-activity relationships for each class. Therefore, this overview should support the rational choice for the optimal compound selection based on affinity, selectivity and efficacy data in biochemical and pharmacological studies.

Single and binge methamphetamine administrations have different effects on the levels of dopamine D2 autoreceptor and dopamine transporter in rat striatum

Methamphetamine (METH) is a central nervous system psychostimulant with a high potential for abuse. At high doses, METH causes a selective degeneration of dopaminergic terminals in the striatum. Dopamine D2 receptor antagonists and dopamine transporter (DAT) inhibitors protect against neurotoxicity of the drug by decreasing intracellular dopamine content and, consequently, dopamine autoxidation and production of reactive oxygen species. In vitro, amphetamines regulate D2 receptor and DAT functions via regulation of their intracellular trafficking. No data exists on axonal transport of both proteins and there is limited data on their interactions in vivo. The aim of the present investigation was to examine synaptosomal levels of presynaptic D2 autoreceptor and DAT after two different regimens of METH and to determine whether METH affects the D2 autoreceptor-DAT interaction in the rat striatum. We found that, as compared to saline controls, administration of single high-dose METH decreased D2 autoreceptor immunoreactivity and increased DAT immunoreactivity in rat striatal synaptosomes whereas binge high-dose METH increased immunoreactivity of D2 autoreceptor and had no effect on DAT immunoreactivity. Single METH had no effect on D2 autoreceptor-DAT interaction whereas binge METH increased the interaction between the two proteins in the striatum. Our results suggest that METH can affect axonal transport of both the D2 autoreceptor and DAT in an interaction-dependent and -independent manner.

Characterisation of AmphiAmR11, an amphioxus (Branchiostoma floridae) D2-dopamine-like G protein-coupled receptor

The evolution of the biogenic amine signalling system in vertebrates is unclear. However, insights can be obtained from studying the structures and signalling properties of biogenic amine receptors from the protochordate, amphioxus, which is an invertebrate species that exists at the base of the chordate lineage. Here we describe the signalling properties of AmphiAmR11, an amphioxus (Branchiostoma floridae) G protein-coupled receptor which has structural similarities to vertebrate α₂-adrenergic receptors but which functionally acts as a D₂ dopamine-like receptor when expressed in Chinese hamster ovary -K1 cells. AmphiAmR11 inhibits forskolin-stimulated cyclic AMP levels with tyramine, phenylethylamine and dopamine being the most potent agonists. AmphiAmR11 also increases mitogen-activated protein kinase activity and calcium mobilisation, and in both pathways, dopamine was found to be more potent than tyramine. Thus, differences in the relative effectiveness of various agonists in the different second messenger assay systems suggest that the receptor displays agonist-specific coupling (biased agonism) whereby different agonists stabilize different conformations of the receptor which lead to the enhancement of one signalling pathway over another. The present study provides insights into the evolution of α₂-adrenergic receptor signalling and support the hypothesis that α₂-adrenergic receptors evolved from D₂-dopamine receptors. The AmphiAmR11 receptor may represent a transition state between D₂-dopamine receptors and α₂-adrenergic receptors.

In vitro pharmacology of aripiprazole, its metabolite and experimental dopamine partial agonists at human dopamine D2 and D3 receptors

Aripiprazole is the first dopamine D(2)/D(3) receptor partial agonist successfully developed and ultimately approved for treatment of a broad spectrum of psychiatric and neurological disorders. Aripiprazole's dopamine D(2) and serotonin 5-HT(1A) receptor partial agonist activities have been postulated to confer clinical efficacy without marked sedation, and a relatively favorable overall side-effect profile. Using aripiprazole's unique profile as a benchmark for new dopamine partial agonist development may facilitate discovery of new antipsychotics. We conducted an in vitro comparative analysis between aripiprazole, and its human metabolite OPC-14857 (7-(4-[4-(2,3-dichlorophenyl)-1-piperazinyl)butoxy)-2(1H)-quinolinone)); RGH-188 (trans-1-[4-[2-[4-(2,3-dichlorophenyl)piperazine-1-yl]ethyl]cyclohexyl]-3,3-dimethylurea), and its metabolite didesmethyl-RGH-188 (DDM-RGH-188); as well as bifeprunox, sarizotan, N-desmethylclozapine (NDMC; clozapine metabolite), and SDZ 208-912 (N-[(8α)-2-chloro-6-methylergolin-8-yl]-2,2-dimethylpropanamide). In vitro pharmacological assessment included inhibition of forskolin-stimulated cAMP accumulation and the reversal of dopamine-induced inhibition in clonal Chinese hamster ovary cell lines expressing D(2S), D(2L), D(3) Ser-9 and D(3) Gly-9 for human dopamine receptors. All test compounds behaved as dopamine D(2)/D(3) receptor partial agonists. Aripiprazole's intrinsic activity at dopamine D(2S) and D(2L) receptors was similar to that of OPC-14857 and RGH-188; lower than that of dopamine and bifeprunox; and higher than that of DDM-RGH-188, SDZ 208-912, sarizotan, and NDMC. Aripiprazole's intrinsic activity at dopamine D(3) Ser-9 and D(3) Gly-9 receptors was similar to that of OPC-14857 and sarizotan; lower than that of dopamine, bifeprunox, RGH-188 and DDM-RGH-188; and higher than that of SDZ 208-912 and NDMC. A consolidated assessment of these findings may help defining the most appropriate magnitude of intrinsic activity at dopamine D(2)/D(3) receptors for clinical efficacy and safety.

Fine-mapping reveals novel alternative splicing of the dopamine transporter

The dopamine transporter gene (SLC6A3, DAT) has been implicated in the pathogenesis of numerous psychiatric and neurodevelopmental disorders, including schizophrenia (SZ). We previously detected association between SZ and intronic SLC6A3 variants that replicated in two independent Caucasian samples, but had no obvious function. In follow-up analyses, we sequenced the coding and intronic regions of SLC6A3 to identify complete linkage disequilibrium patterns of common variations. We genotyped 78 polymorphisms, narrowing the potentially causal region to two correlated clusters of associated SNPs localized predominantly to introns 3 and 4. Our computational analysis of these intronic regions predicted a novel cassette exon within intron 3, designated E3b, which is conserved among primates. We confirmed alternative splicing of E3b in post-mortem human substantia nigra (SN). As E3b introduces multiple in-frame stop codons, the SLC6A3 open reading frame is truncated and the spliced product may undergo nonsense mediated decay. Thus, factors that increase E3b splicing could reduce the amount of unspliced product available for translation. Observations consistent with this prediction were made using cellular assays and in post-mortem human SN. In mini-gene constructs, the extent of splicing is also influenced by at least two common haplotypes, so the alternative splicing was evaluated in relation to SZ risk. Meta-analyses across genome-wide association studies did not support the initial associations and further post-mortem studies did not suggest case-control differences in splicing. These studies do not provide a compelling link to schizophrenia. However, the impact of the alternative splicing on other neuropsychiatric disorders should be investigated. © 2010 Wiley-Liss, Inc.

Pharmacological characterization of 2-methoxy-N-propylnorapomorphine's interactions with D2 and D3 dopamine receptors

Dopaminergic signaling pathways have been extensively investigated using PET imaging, primarily with antagonist radioligands of D(2) and D(3) dopamine receptors (DARs). Recently, agonist radioligands of D(2)/D(3) DARs have begun to be developed and employed. One such agonist is (R)-2-(11)CH(3)O-N-n-propylnorapomorphine (MNPA). Here, we perform a pharmacological characterization of MNPA using recombinant D(2) and D(3) DARs expressed in HEK293 cells. MNPA was found to robustly inhibit forskolin-stimulated cAMP accumulation to the same extent as dopamine in D(2) or D(3) DAR-transfected cells, indicating that it is a full agonist at both receptors. MNPA is approximately 50-fold more potent than dopamine at the D(2) DAR, but equally potent as dopamine at the D(3) DAR. MNPA competition binding curves in membrane preparations expressing D(2) DARs revealed two binding states of high and low-affinity. In the presence of GTP, only one binding state of low affinity was observed. Direct saturation binding assays using [(3)H]MNPA revealed similar results as with the competition experiments leading to the conclusion that MNPA binds to the D(2) DAR in an agonist-specific fashion. In contrast to membrane preparations, using intact cell binding assays, only one site of low affinity was observed for MNPA and other agonists binding to the D(2) DAR. MNPA was also found to induce D(2) DAR internalization to an even greater extent than dopamine as determined using both cell surface receptor binding assays and confocal fluorescence microscopy. Taken together, our data indicate that the PET tracer, MNPA, is a full and potent agonist at both D(2) and D(3) receptors.

Dopamine D(2/3) receptor occupancy of apomorphine in the nonhuman primate brain--a comparative PET study with [11C]raclopride and [11C]MNPA

Binding studies in vitro have demonstrated that the dopamine D2 receptor may exist in two affinity states for agonists. The high affinity state is thought to represent the functional state of the receptor and proportions might alter during disease. In vitro studies further indicate that agonists induce measurable D(2) receptor occupancy at clinically relevant concentrations but only when measured at the high affinity state. Recently developed PET-radioligands, such as [11C]MNPA, have now made it possible to directly study agonist binding in vivo. The aim of this study was to compare the inhibition by apomorphine of agonist and antagonist radioligand binding to D(2/3) receptors in vivo. A total of 36 PET measurements were performed with the D(2/3) antagonist [11C]raclopride or the D(2/3) agonist [11C]MNPA in two cynomolgus monkeys. On each study day, a baseline measurement was followed by two consecutive pretreatment studies with rising doses of apomorphine (0.01, 0.05, 0.15, 0.5, 1.0, and 3.0 mg/kg). Binding potential (BP(ND)) values were calculated for the striatum with cerebellum as reference region. Apomorphine inhibited [11C]raclopride and [11C]MNPA binding in a dose-dependent manner and to a similar extent. ID(50) and K(i) values were 0.26 mg/kg and 29 ng/ml for [11C]raclopride and 0.50 mg/kg and 31 ng/ml for [11C]MNPA. The present observations do not support the existence of two affinity states in vivo. It might thus be speculated that all D(2/3) receptors are in the high affinity state at in vivo conditions.

The presence and function of dopamine type 2 receptors in boar sperm: a possible role for dopamine in viability, capacitation, and modulation of sperm motility

Several studies have shown that dopamine and other catecholamines are present in oviduct luminal fluid. We recently reported that dopamine type 2 receptors (DRD2) are present in a wide range of mammalian sperm, suggesting a role for dopaminergic signaling in events such as fertilization, capacitation, and sperm motility. In the present study, we used Western blot analysis to show that boar sperm express DRD2 and that their activation with dopamine (100 nM) has a positive effect on cell viability that can be correlated with AKT/PKB phosphorylation. Bromocriptine (100 nM) and dopamine (100 nM and 10 muM) increased tyrosine phosphorylation during the capacitation period. Immunofluorescence analysis indicated that DRD2 localization is dynamic and depends on the capacitation stage, colocalizing with tyrosine phosphorylated proteins in the acrosome and midpiece region of capacitated boar sperm. This association was confirmed by coimmunoprecipitation analysis. We also showed that bromocriptine (100 nM) and low-concentration dopamine (100 nM and 10 muM) increased total and progressive motility of sperm. However, high concentrations of dopamine (1 mM) decreased tyrosine phosphorylation and motility in in vitro sperm capacitation assays. This can be explained by the presence of the dopamine transporters (DAT, official symbol SLC6A3) in sperm, as demonstrated by Western blot analysis and immunocytochemistry. Taken together, our results support the idea that dopamine may have a fundamental role during sperm capacitation and motility in situ in the female upper reproductive tract.

Characterization of aripiprazole partial agonist activity at human dopamine D3 receptors

Aripiprazole is the first dopamine D2/D3 receptor partial agonist approved for use in the treatment of psychiatric disorders, including schizophrenia, bipolar disorder, and unipolar depression in the US. To explore the functional activity of aripiprazole at dopamine D3 receptors, we established Chinese hamster ovary (CHO) cell lines stably expressing high and low densities of Ser-9 and Gly-9 variants of human dopamine D3 receptors and compared aripiprazole's dopamine D3 pharmacological properties with other marketed and non-approved dopamine D3 receptor modulating agents on inhibition of forskolin-stimulated cAMP accumulation. Maximal cell responses for dopamine were dependent on receptor expression levels, and all cells had similar potency for dopamine responses. Aripiprazole, terguride, bifeprunox, OPC-4392 (7-(3-[4-(2,3-dimethylphenyl)piperazinyl]propoxy)-2(1H)-quinolinone), (-)-3-PPP ((-)-3-(3-hydroxyphenyl)-N-n-propylpiperidine), SDZ 208-912 (N-[(8 alpha)-2-chloro-6-methylergolin-8-yl]-2,2-dimethylpropanamide), BP897 (N-[4-[4-(2-Methoxyphenyl)-1-piperazinyl]butyl]naphthalene-2-carboxamide) and GR103691 (4'-Acetyl-N-[4-[4-(2-methoxyphenyl)piperazin-1-yl]butyl]biphenyl-4-carboxamide) behaved as partial agonists. Aripiprazole's intrinsic activity was similar to that of BP897 and GR103691, lower than that of terguride, bifeprunox, OPC-4392, and (-)-3-PPP, and higher than that of SDZ 208-912. The Gly-9 variant did not differ from the Ser-9 variant with respect to those agonist potencies and intrinsic activities. These compounds blocked the action of dopamine with a maximum effect equal to that of each compound alone. ACR16 (4-(3-Methanesulfonyl-phenyl)-1-propyl-piperidine), quetiapine, clozapine, olanzapine, ziprasidone, risperidone, and haloperidol acted as antagonists. Aripiprazole's unique activity at dopamine D3 receptors may translate into clinically relevant outcomes in patients with a variety of neuropsychiatric disorders.

The structural evolution of dopamine D3 receptor ligands: structure-activity relationships and selected neuropharmacological aspects

"Evolution consists largely of molecular tinkering."-Following the famous concept of the molecular geneticist and medicine Nobel laureate François Jacob, in this review we describe the structural evolution of dopamine D3 receptor ligands from the natural agonist dopamine (DA) to highly potent and subtype selective new agents by bioisosteric tinkering with well-established and privileged or novel and fancy chemical functionalities and scaffolds. Some of the more than 200 ligands presented herein have already achieved therapeutic or scientific value up to now, some will most likely achieve it in the future. Hence, great importance is not only attached to the relationship between structure and activity of the ligands, but also to their utility as pharmacological tools in animal models or as therapeutics in patients with neurological diseases or other disorders.

Signaling Mechanisms of the D3Dopamine Receptor

A substantial body of evidence shows the capacity of the dopamine D3 receptor to couple functionally to G proteins when expressed in an appropriate milieu in heterologous expression systems. In these systems, activation of D3 receptors inhibits adenylate cyclase, modulates ion flow through potassium and calcium channels, and activates kinases, most notably mitogen-activated protein kinase. Coupling to Gi/Go is implicated in many of these effects, but other G proteins may contribute. Studies with chimeric receptors implicate the third intracellular loop in the mediation of agonist-induced signal transduction. Finally, D3-preferring drugs modulate expression of c-fos in neuronal cultures and brain. Signaling mechanisms of the D3 receptor in brain, however, remain to be definitively determined.

Comparative pharmacology of human dopamine D(2)-like receptor stable cell lines coupled to calcium flux through Galpha(qo5)

The goal of this study was to develop a new approach to study the pharmacology of the dopamine D(4) receptor that could be used in comparative studies with dopamine D(2) and D(3) receptors. Stable HEK-293 cell lines co-expressing recombinant human D(2L), D(3) or D(4) receptors along with Galpha(qo5) cDNA were prepared. Dopamine induced a robust, transient calcium signal in these cell lines with EC(50)s for D(2L), D(3) and D(4) of 18.0, 11.9 and 2.2 nM, respectively. Reported D(4)-selective agonists CP226269 and PD168077 were potent, partial D(4) agonists exhibiting 31-1700-fold selectivity for D(4) over D(3) or D(2). Non-selective D(2)-like agonists apomorphine and quinpirole showed full efficacy but did not discriminate across the three receptors. D(3)-selective agonists 7-hydroxy-DPAT and PD128907 were potent but non-selective D(2)-like agonists. The reported D(3) partial agonist BP-897 exhibited minimal agonist activity at D(3) but was a potent D(3) antagonist and a partial D(4) agonist. Other D(2)-like antagonists, haloperidol, clozapine, and domperidone showed concentration-dependent inhibition of dopamine responses at all three receptors with K(i) ranging from 0.05 to 48.3 nM. The D(3) selective antagonist S33084 and D(4)-selective antagonist L-745870 were highly selective for D(3) and D(4) receptors with K(b) of 0.7 and 0.1 nM, respectively. Stable co-expression of D(2)-like receptors with chimeric Galpha(qo5) proteins in HEK-293 cells is an efficient method to study receptor activation in a common cellular background and an efficient method for direct comparison of ligand affinity and efficacy across human D(2L), D(3) and D(4) receptors.

Functional coupling of the human dopamine D2 receptor with G alpha i1, G alpha i2, G alpha i3 and G alpha o G proteins: evidence for agonist regulation of G protein selectivity

(1) The human dopamine D(2long) (D(2L)) receptor was expressed with four different G proteins in Sf9 cells using the baculovirus expression system. When co-expressed with G(i)/G(o) G proteins (G(i1)alpha, G(i2)alpha, G(i3)alpha, or G(o)alpha, plus Gbeta(1) and Ggamma(2)), the receptor displayed a high-affinity binding site for the agonists (dopamine and NPA), which was sensitive to GTP (100 micro M), demonstrating interaction between the receptor and the different G proteins. (2) The receptor to G protein ratio (R : G ratio) was evaluated using [(3)H]-spiperone saturation binding (R) and [(35)S]-GTPgammaS saturation binding (G). R : G ratios of 1 : 12, 1 : 3, 1 : 14 and 1 : 5 were found for G(i1), G(i2), G(i3), and G(o) preparations, respectively. However, when R : G ratios of 1 : 2 and 1 : 12 were compared for G(i2) and G(o), no difference was found for the stimulation of [(35)S]-GTPgammaS binding. (3) Several agonists were tested for their ability to stimulate [(35)S]-GTPgammaS binding to membranes co-expressing the receptor and various G proteins. All the compounds tested showed agonist activity in preparations expressing G(i3) and G(o). However, for G(i2) and G(i1) preparations, compounds such as S-(-)-3-PPP and p-tyramine were unable to stimulate [(35)S]-GTPgammaS binding. (4) Most of the compounds showed higher relative efficacies (compared to dopamine) and higher potencies in the preparation expressing G(o). Comparison of the effects of different agonists in the different preparations showed that each agonist differentially activates the four G proteins. (5) We conclude that the degree of selectivity of G protein activation by the D(2L) receptor can depend on the conformation of the receptor stabilised by an agonist.

Identification of functional dopamine receptors in human teratocarcinoma NT2 cells

In search of a cellular model suitable for studying molecular events contributing to brain disorders, we have characterised the expression and functionality of dopamine receptors in human teratocarcinoma NT2 cells. The cells were differentiated by a 4-week retinoic acid treatment, followed by a 3-week mitotic inhibitor treatment in the absence of retinoic acid. The messages of two D(2)-like family members, D(2L) and D(3), were expressed in undifferentiated NT2 cells. The retinoic acid treatment resulted in increased expression of both spliced variants of the D(2) receptor, D(2L) and D(2S) isoforms and a significant induction of D(1) and D(5) gene transcripts. The same treatment turned off expression of the D(3) gene. Further induction of the D(5) gene was observed in the post-mitotic NT2N neurons. The NT2N cells stained positively for D(2) and D(5) receptor proteins, and the intracellular cyclic AMP level increased in response to forskolin, dopamine and the D(1)-receptor agonist SKF-81297. Furthermore, dopamine was ineffective in the presence of the D(2) receptor agonist PPHT and the D(1) receptor antagonist cis-(z)-flupenthixol. These results indicated that upon ligand/agonist/antagonist binding, the receptors could be coupled to the adenylyl cyclase system, hence were functional. To our knowledge, NT2 is the only human immortalized cell line expressing functional dopamine receptors of both families.