Assessment of the Association of D2 Dopamine Receptor Gene and Reported Allele Frequencies With Alcohol Use Disorders: A Systematic Review and Meta-analysis

IMPORTANCE

The association between the D2 dopamine receptor gene (DRD2) Taq1A locus (rs1800497) and alcohol use disorder (AUD) is enduring but the subject of long-standing controversy; meta-analysis of studies across 3 decades shows an association between rs1800497 and AUD, but genome-wide analyses have detected no role for rs1800497 in any phenotype. No evidence has emerged that rs1800497, which is located in ANKK1, perturbs the expression or function of DRD2.

OBJECTIVE

To resolve contradictions in previous studies by identifying hidden confounders and assaying for functional effects of rs1800497 and other loci in the DRD2 region.

DATA SOURCES

PubMed (882 studies), Embase (1056 studies), and Web of Science (501 studies) databases were searched through August 2018. Three clinical populations-Finnish, Native American, and African American participants-were genotyped for 208 to 277 informative single-nucleotide polymorphisms (SNPs) across the DRD2 region to test the associations of SNPs in this region with AUD.

STUDY SELECTION

Eligible studies had diagnosis of AUD made by accepted criteria, reliable genotyping methods, sufficient genotype data to calculate odds ratios and 95% CIs, and availability of control allele frequencies or genotype frequencies.

DATA EXTRACTION AND SYNTHESIS

After meta-analysis of 62 studies, metaregression was performed to detect between-study heterogeneity and to explore the effects of moderators, including deviations of cases and controls from allele frequencies in large population databases (ExAC and 1000 Genomes). Linkage to AUD and the effect on gene expression of rs1800497 were evaluated in the context of other SNPs in the DRD2 region. Data analysis was performed from August 2018 to March 2019. This study follows the Preferred Reporting Items for Systematic Reviews and Meta-analyses reporting guideline.

MAIN OUTCOMES AND MEASURES

The effects of rs1800497 and other SNPs in the DRD2 region on gene expression were measured in human postmortem brain samples via differential allelic expression and evaluated in other tissues via publicly available expression quantitative locus data.

RESULTS

A total of 62 studies of DRD2 and AUD with 16 294 participants were meta-analyzed. The rs1800497 SNP was associated with AUD (odds ratio, 1.23; 95% CI, 1.14-1.31; P < .001). However, the association was attributable to spuriously low allele frequencies in controls in positive studies, which also accounted for some between-study heterogeneity (I2 = 43%; 95% CI, 23%-58%; Q61 = 107.20). Differential allelic expression of human postmortem brain and analysis of expression quantitative loci in public data revealed that a cis-acting locus or loci perturb the DRD2 transcript level; however, rs1800497 does not and is not in strong disequilibrium with such a locus. Across the DRD2 region, other SNPs are more strongly associated with AUD than rs1800497, although no DRD2 SNP was significantly associated in these 3 clinical samples.

CONCLUSIONS AND RELEVANCE

In this meta-analysis, the significant association of DRD2 with AUD was reassessed. The DRD2 association was attributable to anomalously low control allele frequencies, not function, in positive studies. For genetic studies, statistical replication is not verification.

The influence of immune activation at early vs late gestation on fetal NRG1-ErbB4 expression and behavior in juvenile and adult mice offspring

Maternal inflammation during pregnancy is associated with a higher incidence of mental disorders (e.g. schizophrenia and autism) in the offspring. In our study, we investigate the involvement of the NRG-ErbB signaling pathway in rodent fetal brains four hours following maternal immune activation (MIA) insult at two different gestational days (i.e. early vs late). Furthermore, we test the long-term behavioral alteration of the exposed MIA mice at juvenile and adulthood. We demonstrate that MIA at late, but not at early gestation day, altered the expression of NRG1, its receptor ErbB4, and the dopamine D2 receptor four hours post injection of viral or bacterial mimic material in fetal brain. At the behavioral levels, adult late-MIA-exposed female offspring, but not juvenile, display lack preference to a novel object. While working memory alteration observed only in adult male MIA-exposed offspring at late gestation day. In addition, we found that adult females MIA-exposed mice spent more time in the center of the open field than female-saline groups. On the other hand, juvenile male offspring exposed to MIA at early, but not late, gestation day displayed a significant alteration in social interaction. Our results suggest that MIA during late gestation immediately influences the expression levels of the NRG1 and ErbB4 genes, and affects long-term behavioral changes at adulthood. These behavioral changes are time related and sex-specific. Thus, immune activation at late stages of the embryonic brain development initiates the activation of the NRG1-ErbB4 pathway and this disturbance might result in cognitive dysfunction in adulthood.

Prenatal stress-induced increases in placental inflammation and offspring hyperactivity are male-specific and ameliorated by maternal antiinflammatory treatment

Adverse experiences during gestation such as maternal stress and infection are known risk factors for neurodevelopmental disorders, including schizophrenia, autism, and attention deficit/hyperactivity disorder. The mechanisms by which these distinct exposures may confer similar psychiatric vulnerability remain unclear, although likely involve pathways common to both stress and immune responses at the maternal-fetal interface. We hypothesized that maternal stress-induced activation of immune pathways within the placenta, the sex-specific maternal-fetal intermediary, may contribute to prenatal stress programming effects on the offspring. Therefore, we assessed for markers indicative of stress-induced placental inflammation, and examined the ability of maternal nonsteroidal antiinflammatory drug (NSAID) treatment to ameliorate placental effects and thereby rescue the stress-dysregulation phenotype observed in our established mouse model of early prenatal stress (EPS). As expected, placental gene expression analyses revealed increased levels of immune response genes, including the proinflammatory cytokines IL-6 and IL-1β, specifically in male placentas. NSAID treatment partially ameliorated these EPS effects. Similarly, in adult offspring, males displayed stress-induced locomotor hyperactivity, a hallmark of dopaminergic dysregulation, which was ameliorated by maternal NSAID treatment. Fitting with these outcomes and supportive of dopamine pathway involvement, expression of dopamine D1 and D2 receptors was altered by EPS in males. These studies support an important interaction between maternal stress and a proinflammatory state in the long-term programming effects of maternal stress.

Dopamine receptor autoantibodies correlate with symptoms in Sydenham's chorea

BACKGROUND

Sydenham chorea (SC), a neuropsychiatric sequela of group-A streptococcal infection, is associated with basal ganglia autoantibodies. Although autoantibodies have been proposed in neuropsychiatric disorders, little evidence has been shown to link autoimmunity and clinical symptoms. We hypothesized that dopamine receptor-autoantibody interactions may be the basis of neuropsychiatric symptoms in SC.

METHODS

Sera from 22 children with SC (age 10.7±4.5 years) and 22 age-matched controls were studied. Clinical neuropsychiatric symptoms were measured in SC at sample collection using the UFMG-Sydenham's-Chorea-Rating-Scale (USCRS). Anti-dopamine D1 receptor (D1R) and anti-dopamine D2 receptor (D2R) autoantibodies were measured by the enzyme linked immunosorbent assay (ELISA) and were correlated with clinical symptoms.

RESULTS

Anti-D1R and anti-D2R autoantibodies were significantly higher in SC compared to controls (n = 44; p = 0.010 and p = 0.017, respectively). We found that the ratio (anti-D2R/D1R) of the two anti-dopaminergic receptor antibodies correlated with neuropsychiatric symptoms as determined by USCRS measurements (n = 18; r = 0.53, p = 0.024). In addition, anti-D2R titers correlated with antistreptolysin-O titers (n = 43; r = 0.49, p = 0.0008).

INTERPRETATION

Our report linked, for the first time, autoimmunity with neuropsychiatric symptoms. The significant correlation was found using ratios of autoantibodies against dopamine receptors (anti-D2R/D1R) rather than the absolute elevated individual anti-D1R or anti-D2R titers. We suggest that autoantibodies may lead to a receptor imbalance and induce greater sensitivity to dopamine signaling potentially leading to neuropsychiatric symptoms in SC. Our novel findings suggesting altered balance in the dopaminergic system may provide a new approach in understanding autoimmune neuropsychiatric disorders with possible implications for diagnosis and treatment.

[Role of dopamine D1- and D2-receptors in the delta1-opioidergic immunostimulation]

The study has shown that activation of delta1-opioid receptors by a highly selective peptide agonist DPDPE (100 microg/kg) results in a significant increase of the immune response to antigen (SRBC, 5 x 10(8)) in CBA mice. SCH-23390 (1 mg/kg), a selective antagonist of the postsynaptic dopamine D1-receptors, and selective D2-blocker haloperidol (1 mg/kg) prevented immunostimulating effect of DPDPE. Comparison of effects of the antagonists suggests that delta1-opioidergic immunostimulation has more significant impact due to involvement of dopamine D1-receptors.

[Functional interplay of dopamine D1 and D2 receptors in the immune response control in different psychoemotional states]

It is established that preliminary blockade ofdopamine (DA) D2 receptors with haloperidol prevents immunostimulation observed upon the activation of D1 receptors with selective agonist SKF 38393 in mice of the CBA and C57BL/6J strains having no experience in social confrontations. These data are indicative of the functional interconnection between DA receptors of the D1 and D2 subtypes in the immune response control. Similar link between these DA receptor subtypes has been also found in C57BL/6J mice conditioned to display aggressive or submissive behaviors during 10-day social encounter testing. The data obtained give evidence that the interaction between D1 and D2 receptors is manifested in animals with various genotypes and psychoemotional states.

Roles of dopamine receptor subtypes in mediating modulation of T lymphocyte function

OBJECTIVE

Dopamine exists in the immune system and has obvious immunomodulating action. However, receptor mechanism underlying the dopamine immunomodulation remains to be clarified. In the present study, we provide the evidence for existence of dopamine receptor subtypes in T lymphocytes and show the roles of the receptors and the receptor-coupled signaling in mediating the dopamine immunomodulation.

METHODS

The purified T lymphocytes from the mesenteric lymph nodes of mice were detected for expressions of all five subtypes of dopamine receptor mRNAs by reverse transcription-polymerase chain reaction. Lymphocyte proliferation and production of interferon-γ (IFN-γ) and interleukin-4 (IL-4) in response to concanavalin A (Con A) were measured by colorimetric methyl-thiazole-tetrazolium assay and cytometric bead array, respectively, after the cells were exposed to dopamine D1-like or D2-like receptor agonists and antagonists. Meanwhile, content of cAMP and phosphorylation of cAMP-response element-binding (CREB) in the lymphocytes were examined by 125I-cAMP radioimmunoassay and Western blot assay, respectively.

RESULTS

T lymphocytes expressed all the five subtypes of dopamine receptor mRNAs, i.e., D1, D2, D3, D4 and D5 receptors. SKF38393, an agonist of dopamine D1-like receptors (D1 and D5 receptors) only reduced the IFN-γ production, but did not significantly affect the proliferative response, IL-4 production, cAMP content or CREB activation of the lymphocytes. The SKF38393-induced decrease in IFN-γ level was blocked by the D1-like receptor antagonist SCH23390. Quinpirole, an agonist of dopamine D2-like receptors (D2, D3 and D4 receptors) attenuated the lymphocyte proliferation to Con A, and decreased the IFN-γ but increased the IL-4 production. Meanwhile, the quinpirole diminished the cAMP content and the phosphorylated CREB level in the lymphocytes. All the quinpirole-induced changes were reversed by dopamine D2-like receptor antagonist haloperidol.

CONCLUSIONS

Five dopamine receptor subtypes of the two families, D1-like and D2-like receptors, exist on T lymphocytes of mice. Of the two families, D2-like receptors are more important in mediating modulation of T cell function than D1-like receptors. D2-like receptors are involved in suppression of T helper 1 (Th1) cell function and enhancement of Th2 cell function through negative link to cAMP-CREB pathway.

Effects of activation and blockade of dopamine D2 receptors on the immune response in mice with different types of behavior

Activation of dopamine D(2) receptors by the selective agonist quinpirole was found to lead to immunostimulation in control (no experience of confrontations) C57BL/6J mice and in mice subjected to psychoemotional tension (aggression and submission). The most marked increase in the immune response was seen on formation of the aggressive and submissive behavioral strategies. The effects of blockade of D(2) dopamine receptors by haloperidol-immunosuppression-were seen only in control and aggressive animals, but were not seen in animals with submissive behavior. The question of the significance of the initial psychoemotional state, which is linked with particular neurotransmitter patterns in the brain (levels of dopamine, serotonin, their metabolites; dopamine receptor activity in subcortical structures), for the effects of agents altering the activity of dopamine D(2) receptors on the immune response is discussed.

Interaction between dopamine D1 and D2 receptors in modulation of the immune response

The interaction between dopamine D1 and D2 receptors plays a role in immunomodulation. The results of thus interaction depends on the degree of receptor activation with selective agonists in different doses. Combined treatment with agonists of D1 and D2 receptors in high doses had a synergistic effect in the mechanisms of immunomodulation. Receptor agonists in low doses suppressed the immune response. Our results suggest that weak activation of one of these receptors is accompanied by inactivation of the other receptor type.

[Effect of the activation and blockade of D2 dopamine receptors on the immune response in mice with different types of social behavior]

Activation of D2 dopamine receptors with a selective agonist quinpirol in C57BL/6J mice was found to induce increase in the immune response regardless of the initial psychoemotional state of animals, e. g. in aggressive mice, submissive mice, and mice without victory or defeat experience (control). However, the immune response level in aggressive and submissive mice was significantly higher than that of control animals. At the same time, the blockade of D2 dopamine receptors with haloperidol suppressed immunogenesis in aggressive and control mice, whereas the immune reactions in submissive mice were unchanged. Thus, the effect of activation and blockade of D2 dopamine receptors on immune function is dependent on the initial psychoemotional status of animals which to a greater extent might be provided by the neuromediator pattern of the brain and activity of DA receptors.

[Differential contribution of dopamine D1 and D2 receptors in the mu-opioidergic immunomodulation]

The study has shown that activation of mu-opioid receptors by a highly selective agonist DAGO (100 microg/kg) results in a significant increase of the immune response to antigen (SRBC, 5% 10(8)) in CBA mice. Haloperidol (2 mg/kg), a selective antagonist of the postsynaptic dopamine (DA) receptors, prevented immunostimulating effect of DAGO. In contrast, selective D1--antagonist SCH 23390 (1 mg/kg) did not affect on DAGO-induced enhancing of immune reactivity. At the same time, the blockade of both types of DA receptors (D1 and D2) caused similar immunosuppressing effects. These data suggest a possible differential role for D1 and D2 receptors in mu-opioidergic immunomodulation.

In vivo and in vitro detection of dopamine d2 receptors in uveal melanomas

Scintigraphy with radiolabeled benzamides was used in melanoma patients. Studies with a newer benzamide called 123I-epidepride, a high-affinity D2 receptor (D2R) antagonist, showed high sensitivity in D2R-positive pituitary adenomas. We evaluated the presence of D2R in patients with uveal melanomas in vivo with 123I-epidepride, and in vitro in melanomas, using immunohistochemistry (IHC) and 125I-epidepride autoradiography. We studied the in vivo tumor-to-background (TB) ratios in six patients with posterior uveal melanoma (one previously enucleated). IHC was performed in 3 of 6 tumors after enucleation and in another 20 uveal melanomas, 7 metastatic lymph nodes from skin melanoma, and 2 normal specimens. 125I-epidepride autoradiography was performed in 10 uveal melanomas (3 of which were studied in vivo), 7 metastases, and 2 normal samples. Radioligand uptake was present in the affected eye of 5 patients with uveal melanoma (TB = 3.1-6.1) and absent in the operated one (TB = 1). Eight uveal tumors were positive at IHC (35%), 14 weakly positive (61%), and 1 negative (4%). Two metastases were positive (29%), 2 weakly positive (29%), and 3 negative (42%). Two uveal tumors were positive at autoradiography (20%), 7 had nonspecific binding (70%), and 1 was negative (10%). One metastasis was positive (14%), while 6 were negative (86%). 123I-epidepride scintigraphy in uveal melanomas seems promising for sensitivity and image quality. D2R was demonstrated in a significant proportion of the melanomas, although 123I-epidepride uptake might also be nonspecific and unrelated to D2R binding. Although further studies on larger series are needed, 123I-epidepride could represent a future tool to study the expression of D2R in other classes of neuroendocrine tumors.

Decreased amphetamine-induced locomotion and improved latent inhibition in mice mutant for the M5 muscarinic receptor gene found in the human 15q schizophrenia region

M5 muscarinic receptors are coexpressed with D2 dopamine receptors in the ventral tegmentum and striatum, and are important for reward in rodents. Previously, we reported that disruption of the M5 receptor gene in mice reduced dopamine release in the nucleus accumbens. In this study, we established a polymerase chain reaction (PCR) genotyping method for M5 mutant mice, and, using RT-PCR, found that M5 mRNA expression was highest in the ventral tegmentum, striatum, and thalamus in wild-type mice. In the M5 mutant mice, D2 mRNA expression was increased in several brain structures, including the striatum. Genome mapping studies showed the M5 gene is localized to chromosome 2E4 in mice, and to 15q13 in humans in the region that has been linked to schizophrenia. Amphetamine-induced locomotion, but not baseline locomotion or motor functions, decreased in M5 mutant mice, consistent with lower accumbal dopamine release. Previous reports found latent inhibition improvement in rats following nucleus accumbens lesions, or blockade of dopamine D2 receptors with neuroleptic drugs. Here, latent inhibition was significantly increased in M5 mutant mice as compared with controls, consistent with reduced dopamine function in the nucleus accumbens. In summary, our results showed that M5 gene disruption in mice decreased amphetamine-induced locomotion and increased latent inhibition, suggesting that increased M5 mesolimbic function may be relevant to schizophrenia.

Dopamine D 1 Receptor Augmentation of D 3 Receptor Action in Rat Aortic or Mesenteric Vascular Smooth Muscles

Dopamine is an important modulator of blood pressure, in part, by regulating vascular resistance. To test the hypothesis that D 1 and D 3 receptors interact in vascular smooth muscle cells, we studied A10 cells, a rat aortic smooth muscle cell line, and rat mesenteric arteries that express both dopamine receptor subtypes. Fenoldopam, a D 1 -like receptor agonist, increased both D 1 and D 3 receptor protein in a time-dependent and a concentration-dependent manner in A10 cells. The effect of fenoldopam was specific because a D 1 -like receptor antagonist, SCH23390 (10 −7 M/24 h), completely blocked the stimulatory effect of fenoldopam (10 −7 M/24 h) (D 3 receptor: control=21±1 density units [DU]); SCH23390=23±2 DU; fenoldopam=33±2 DU; fenoldopam+SCH23390=23±2 DU; n=10). D 1 and D 3 receptors physically interacted with each other because fenoldopam (10 −7 M/24 h) increased D 1 /D 3 receptor coimmunoprecipitation (35±5 versus 65±5 DU; n=8). A D 3 receptor agonist, PD128907, relaxed mesenteric arterial rings independent of the endothelium, effects that were blocked by a D 3 receptor antagonist, U99194A. Costimulation of D 1 and D 3 receptors led to additive vasorelaxation. We conclude that the D 1 receptor regulates the D 3 receptor by physical interaction and receptor expression. D 1 receptor stimulation augments D 3 receptor vasorelaxant effects. An interaction of D 1 and D 3 receptors may be involved in the regulation of blood pressure.

Constitutive oligomerization of human D2dopamine receptors expressed inSpodoptera frugiperda9 (Sf9) and in HEK293 cells

Human D2Long (D2L) and D2Short (D2S) dopamine receptor isoforms were modified at their N-terminus by the addition of a human immunodeficiency virus (HIV) or a FLAG epitope tag. The receptors were then expressed in Spodoptera frugiperda 9 (Sf9) cells using the baculovirus system, and their oligomerization was investigated by means of co-immunoprecipitation and time-resolved fluorescence resonance energy transfer (FRET). [3H]Spiperone labelled D2 receptors in membranes prepared from Sf9 cells expressing epitope-tagged D2L or D2S receptors, with a pKd value of approximately 10. Co-immunoprecipitation using antibodies specific for the tags showed constitutive homo-oligomerization of D2L and D2S receptors in Sf9 cells. When the FLAG-tagged D2S and HIV-tagged D2L receptors were co-expressed, co-immunoprecipitation showed that the two isoforms can also form hetero-oligomers in Sf9 cells. Time-resolved FRET with europium and XL665-labelled antibodies was applied to whole Sf9 cells and to membranes from Sf9 cells expressing epitope-tagged D2 receptors. In both cases, constitutive homo-oligomers were revealed for D2L and D2S isoforms. Time-resolved FRET also revealed constitutive homo-oligomers in HEK293 cells expressing FLAG-tagged D2S receptors. The D2 receptor ligands dopamine, R-(-)propylnorapomorphine, and raclopride did not affect oligomerization of D2L and D2S in Sf9 and HEK293 cells. Human D2 dopamine receptors can therefore form constitutive oligomers in Sf9 cells and in HEK293 cells that can be detected by different approaches, and D2 oligomerization in these cells is not regulated by ligands.

Autoantibodies against four kinds of neurotransmitter receptors in psychiatric disorders

There is a hypothesis that autoimmune abnormalities in neurotransmitter receptors might cause some psychiatric disorders. Using a sensitive radioligand assay, we detected serum autoantibodies to recombinant human muscarinic cholinergic receptor 1 (CHRM1, 34.4%), mu-opioid receptor (OPRM1, 13.1%), 5-hydroxytryptamine receptor 1A (HTR1A, 7.4%), and dopamine receptor D2 (DRD2, 4.9%) in 122 psychiatric patients. Positive antibodies to CHRM1 were found in 34.1%, 34.9%, 33.3%, and 9.1% of patients with schizophrenic disorders (n=44), mood disorders (n=63), other psychiatric disorders (n=15) and autoimmune diseases (n=33), respectively. All three patients with neuroleptic maliganant syndrome had high activities of autoantibodies to CHRM1, OPRM1, and/or HTR1A. Our data suggest that autoimmunity to neurotransmitter receptors might be associated with the induction of psychiatric symptoms and have some relation to neuroleptic malignant syndrome.

Autoantibodies against muscarinic cholinergic receptor in chronic fatigue syndrome

The disturbance of the central nervous system and immunological abnormalities have been suggested in patients with chronic fatigue syndrome (CFS). We focused on immunological abnormalities against neurotransmitter receptors in CFS. Using a sensitive radioligand assay, we examined serum autoantibodies to recombinant human muscarinic cholinergic receptor 1 (CHRM1), mu-opioid receptor (OPRM1), 5-hydroxytryptamine receptor 1A (HTR1A), and dopamine receptor D2 (DRD2) in patients with CFS (n=60) and results were compared with those in patients with autoimmune disease (n=33) and in healthy controls (n=30). The mean anti-CHRM1 antibody index was significantly higher in patients with CFS (p<0.0001) and autoimmune disease (p<0.05) than that in healthy controls, and positive reaction was found in 53.3% of patients with CFS. Anti-OPRM1 antibodies, anti-HTR1A antibodies, and anti-DRD2 antibodies were found in 15.2, 1.7, and 5.0% of patients with CFS, respectively. Anti-nuclear antibodies were found in 56.7% (34/60) of patients with CFS, but anti-nuclear antibody titers did not correlate with the activities of the above four autoantibodies. The patients with positive autoantibodies to CHRM1 had a significantly higher mean score (1.81) of 'feeling of muscle weakness' than negative patients (1.18) among CFS patients (p<0.01). Higher scores on 'painful node', 'forgetfulness', and 'difficulty thinking' were also found in CFS patients with anti-CHRM1 antibodies but did not reach statistical significance. In conclusion, autoantibodies to CHRM1 were detected in a large number of CFS patients and were related to CFS symptoms. Our findings suggested that subgroups of CFS are associated with autoimmune abnormalities of CHRM1.

Angiotensin II regulation of AT1 and D3 dopamine receptors in renal proximal tubule cells of SHR

Dopamine and angiotensin II negatively interact to regulate sodium excretion and blood pressure. D3 dopamine receptors downregulate angiotensin type 1 (AT1) receptors in renal proximal tubule cells from normotensive Wistar-Kyoto rats. We determined whether AT1 receptors regulate D3 receptors and whether the regulation is different in cultured renal proximal tubule cells from normotensive and spontaneously hypertensive rats. Angiotensin II (10(-8)M/24 hours) decreased D3 receptors in both normotensive (control, 36+/-3; angiotensin II, 24+/-3 U) and hypertensive (control, 30+/-3; angiotensin II, 11+/-3 U; n=9 per group) rats; effects that were blocked by the AT1 receptor antagonist, losartan (10(-8)M/24 hours). However, the reduction in D3 expression was greater in hypertensive (60+/-10%) than in normotensive rats (32+/-9%). In normotensive rats, angiotensin II (10(-8)M/24hr) also decreased AT1 receptors. In contrast, in cells from hypertensive rats, angiotensin II increased AT1 receptors. AT1 and D3 receptors co-immunoprecipitated in renal proximal tubule cells from both strains. Angiotensin II decreased D3/AT1 receptor co-immunoprecipitation similarly in both rat strains, but basal D3/AT1 co-immunoprecipitation was 6 times higher in normotensive than in hypertensive rats. Therefore, AT1 and D3 receptor interaction is qualitatively and quantitatively different between normotensive and hypertensive rats; angiotensin II decreases AT1 expression in normotensive but increases it in hypertensive rats. In addition, angiotensin II decreases D3 expression to a greater extent in hypertensive than in normotensive rats. Aberrant interactions between D3 and AT1 receptors may play a role in the pathogenesis of hypertension.

Effects of D2-dopamine and alpha-adrenoceptor antagonists in stress induced changes on immune responsiveness of mice

The involvement of catecholamine receptors (alpha-adrenergic, D2-dopamine (DA)) was investigated in restraint stress influenced immune responses with concomitant changes of G-protein signal transduction. Impairment of the spleen morphology, TH1/TH2 cytokine network and natural killer (NK) cell function was observed. In vivo administration of specific antagonists prior to restraint stress reversed the immunosuppression. These findings demonstrate that D2-type dopaminergic mechanism represents the dominant component in regulation of Galphas/Galphai(1,2)/Galphaq/11-protein signal transduction and contribute to cell responses at postreceptor level of both, central nervous and immune systems. G-protein-coupled receptors (GPCRs) can modulate cytokine production and may play a regulatory role in immune effector mechanisms.

Dopamine D3 receptors expressed by all mesencephalic dopamine neurons

A polyclonal antibody was generated using synthetic peptides designed in a specific sequence of the rat D(3) receptor (D(3)R). Using transfected cells expressing recombinant D(3)R, but not D(2) receptor, this antibody labeled 45-80 kDa species in Western blot analysis, immunoprecipitated a soluble fraction of [(125)I]iodosulpride binding, and generated immunofluorescence, mainly in the cytoplasmic perinuclear region of the cells. In rat brain, the distribution of immunoreactivity matched that of D(3)R binding, revealed using [(125)I]R(+)trans-7-hydroxy-2-[N-propyl-N-(3'-iodo-2'-propenyl)amino] tetralin ([(125)I]7-trans-OH-PIPAT), with dense signals in the islands of Calleja and mammillary bodies, and moderate to low signals in the shell of nucleus accumbens (AccSh), frontoparietal cortex, substantia nigra (SN), ventral tegmental area (VTA) and lobules 9 and 10 of the cerebellum. Very low or no signals could be detected in other rat brain regions, including dorsal striatum, or in D(3)R-deficient mouse brain. Labeling of perikarya of AccSh and SN/VTA appeared with a characteristic punctuate distribution, mostly at the plasma membrane where it was not associated with synaptic boutons, as revealed by synaptophysin immunoreactivity. In SN/VTA, D(3)R immunoreactivity was found on afferent terminals, arising from AccSh, in which destruction of intrinsic neurons by kainate infusions produced a loss of D(3)R binding in both AccSh and SN/VTA. D(3)R-immunoreactivity was also found in all tyrosine hydroxylase (TH)-positive neurons observed in SN, VTA and A8 retrorubral fields, where it could represent D(3) autoreceptors controlling dopamine neuron activities, in agreement with the elevated dopamine extracellular levels in projection areas of these neurons found in D(3)R-deficient mice.

Expression and coreceptor function of APJ for primate immunodeficiency viruses

APJ is a seven transmembrane domain G-protein-coupled receptor that functions as a coreceptor for some primate immunodeficiency virus strains. The in vivo significance of APJ coreceptor function remains to be elucidated, however, due to the lack of an antibody that can be used to assess APJ expression, and because of the absence of an antibody or ligand that can block APJ coreceptor activity. Therefore, we produced a specific monoclonal antibody (MAb 856) to APJ and found that it detected this receptor in FACS, immunofluorescence, and immunohistochemistry studies. MAb 856 also recognized APJ by Western blot, enabling us to determine that APJ is N-glycosylated. Using this antibody, we correlated APJ expression with coreceptor activity and found that APJ had coreceptor function even at low levels of expression. However, we found that APJ could not be detected by FACS analysis on cell lines commonly used to propagate primate lentiviruses, nor was it expressed on human PBMC cultured under a variety of conditions. We also found that some viral envelope proteins could mediate fusion with APJ-positive, CD4-negative cells, provided that CD4 was added in trans. These findings indicate that in some situations APJ use could render primary cell types susceptible to virus infection, although we have not found any evidence that this occurs. Finally, the peptide ligand for APJ, apelin-13, efficiently blocked APJ coreceptor activity.

Neurons exhibiting dopamine D2 receptor immunoreactivity in the substantia nigra of the mutant weaver mouse

Neurons exhibiting D2 receptor-like immunoreactivity were investigated in the substantia nigra pars compacta of weaver mice at the light and electron microscope levels using immunocytochemical techniques. At the light microscope level, there was significant loss of D2-like immunoreactive cells in weaver mice and the remaining labeled cells exhibited less intense immunoreactivity. At the ultrastructural level, there was a decrease in the number of immunoreactive profiles and fewer synapses were observed abutting labeled dendritic profiles. In addition, degenerative changes were noted in some of the D2 receptor-like immunoreactive profiles. Double labeling with D2 and tyrosine hydroxylase indicated that the majority of the labeled profiles were double labeled. Eight-week-old homozygous weavers were paired with wild-type littermates as controls and perfused with a buffered solution of acrolein/paraformadehyde. Midbrain sections were reacted immunocytochemically either with an antiserum to D2 or with antisera to D2 and tyrosine hydroxylase, using a double-labeling technique. Sections were processed for light and electron microscopy by standard methods. The results of this study confirm the autoreceptor-like activity of D2 receptors on nigral dopamine neurons. The cell degeneration, down-regulation of D2 receptors, and decreased dendritic and synaptic components in the neuropil suggest that the synaptic integrity of the substantia nigra has been compromised, which in turn would affect the functional efficacy of the basal ganglia circuitry. This altered circuity is expressed in the Parkinson-like symptoms displayed by this mutant mouse.

Labeling of dopamine D3 and D4 receptor subtypes in human peripheral blood lymphocytes with [3H]7-OH-DPAT: a combined radioligand binding assay and immunochemical study

Molecular biology studies have demonstrated that human peripheral blood lymphocytes express dopamine D2-like receptors belonging to the D3 and D4 receptor subtypes, whereas the characterization of these receptors using radioligand binding assay techniques provided conflicting results. The preferential dopamine D3 receptor agonist [3H]7-hydroxy-N, N-di-n-propyl-2-aminotetralin ([3H]7-OH-DPAT) was used recently for labeling lymphocyte dopamine D3 receptor. However, the selectivity of this compound for the D3 receptor was questioned. In this study we have investigated human peripheral blood lymphocyte dopamine receptor subtypes labeled by [3H]7-OH-DPAT using a conventional radioligand binding assay technique and antibodies against dopamine D2-like receptor subtypes. [3H]7-OH-DPAT was specifically bound to intact human peripheral blood lymphocytes with a dissociation constant (Kd) value of 0.32 + 0.03 nM and a maximum density of binding sites (Bmax) of 18.2 + 0.8 fmol/2 x 10(6) cells. [3H]7-OH-DPAT binding was unaffected by antibodies against dopamine D2 and D2S receptors. Anti-dopamine D3 and D4 receptor antibodies reduced [3H]7-OH-DPAT binding by about 53% and 32% respectively. Combination of anti D3 and D4 receptor antibodies reduced remarkably [3H]7-OH-DPAT binding. The above results suggest that the dopamine receptor agonist [3H]7-OH-DPAT labels dopamine D3 and D4 receptor subtypes in human peripheral blood lymphocytes. The use of antibodies raised against dopamine receptor subtypes in combination with radioligand binding assay may contribute to define receptor subtypes expressed by human peripheral blood lymphocytes in health and disease.

Prominence of the dopamine D2 short isoform in dopaminergic pathways

As a result of alternative splicing, the D2 gene of the dopamine receptor family exists in two isoforms. The D2 long is characterized by the insertion of 29 amino acids in the third cytoplasmic loop, which is absent in the short isoform. We have produced subtype-specific antibodies against both the D2 short and D2 long isoforms and found a unique compartmentalization between these two isoforms in the primate brain. The D2 short predominates in the cell bodies and projection axons of the dopaminergic cell groups of the mesencephalon and hypothalamus, whereas the D2 long is more strongly expressed by neurons in the striatum and nucleus accumbens, structures targeted by dopaminergic fibers. These results show that the splice variants of the dopamine D2 receptor are differentially distributed and possess distinct functions. The strategic localization of the D2 short isoform in dopaminergic cell bodies and axons strongly suggests that this isoform is the likely dopamine autoreceptor, whereas the D2 long isoform is primarily a postsynaptic receptor.

[Effect of opioid peptides on immunomodulation]

Activation of the opioid receptors by delta-agonist DSLET and by kappa-agonist rimorphin led to a significant inhibition of plaque-forming and rosette-forming cells in the CBA mice. On the other hand, mu-agonist DAGO stimulated the immune response on the 4th and 5th days after immunization with SRBC (5 x 10(8)). Lesion of the hypothalamo-hypophyseal connection prevented immuno-stimulating as well as immuno-depressive effects. The latter seems to be due to an interaction with the serotoninergic system, whereas immuno-stimulating effect involves the dopaminergic system.

Development and characterization of antibodies directed against the mouse D4 dopamine receptor

Polyclonal antibodies against the mouse D4 dopamine receptor have been developed in order to investigate the anatomical localization of this receptor in the mouse brain. Two antibodies were generated against specific peptides corresponding to predicted extracellular and intracellular regions of the D4 protein. Specificity of these antibodies was demonstrated on human embryonic kidney 293 (HEK 293) cells transfected with different dopamine receptor subtypes; immunoreactivity was detected only in cells transfected with the mouse D4 dopamine receptor cDNA. Following in vitro transcription/translation of the mouse D4 cDNA, a single protein band of 36 kDa was selectively immunoprecipitated with the anti-D4 antibodies. The antibodies also detected a single protein of 36 kDa in Western blot of HEK 293 cells transiently transfected with the mouse D4 receptor. These antibodies were able to detect the D4 receptor in several regions of the mouse brain. In the regions examined, D4 immunoreactivity was found in neurones located in layers II-VI of the frontal and piriform cortices, with the highest concentration in layer II; in scattered neurones in the caudate putamen and in larger neurones in the globus pallidus. In all experiments, both antibodies exhibit the same specificity, and all immunoreactivity could be abolished by preincubation with the corresponding peptide antigen.

Expression of dopamine D3 receptor dimers and tetramers in brain and in transfected cells

The expression and characteristics of the dopamine D3 receptor protein were studied in brain and in stably transfected GH3 cells. Monoclonal antibodies were used for immunoprecipitation and immunoblot experiments. Immunoprecipitates obtained from primate and rodent brain tissues contain a low molecular weight D3 protein and one or two larger protein species whose molecular mass are integral multiples of the low molecular weight protein and thus appear to have resulted from dimerization and tetramerization of a D3 monomer. Whereas D3 receptor multimers were found to be abundantly expressed in brain, the major D3 immunoreactivity expressed in stable D3-expressing rat GH3 cells was found to be a monomer. However, multimeric D3 receptor species with electrophoretic mobilities similar to those expressed in brain were also seen in D3-expressing GH3 cells when a truncated D3-like protein (named D3nf) was co-expressed in these cells. Furthermore, results from immunoprecipitation experiments with D3- and D3nf-specific antibodies show that the higher-order D3 proteins extracted from brain and D3/D3nf double transfectants also contain D3nf immunoreactivity, and immunocytochemical studies show that the expression of D3 and D3nf immunoreactivities overlaps substantially in monkey and rat cortical neurons. Altogether, these data show oligomeric D3 receptor protein expression in vivo and they suggest that at least some of these oligomers are heteroligomeric protein complexes containing D3 and the truncated D3nf protein.

Development and characterization of antibodies against the N terminus of the human dopamine D4 receptor

The human dopamine D4 receptor (hD4R), which has been implicated in human diseases such as schizophrenia and in a personality trait called "novelty seeking," has not yet been characterized at the protein level. Following epitope scanning of the hD4R, we have produced a highly specific monoclonal antibody named DFR1 raised against an amino-terminal peptide in a predicted extracellular region of the receptor. DFR1 decorated recombinant hD4Rs on the surface of intact Chinese hamster ovary (CHO) cells by flow cytometry and fluorescence microscopy and also recognized recombinant hD4.2, hD4.4, and hD4.7 receptor isoforms by western blot analysis. When expressed stably in CHO cells, all three hD4R isoforms contained N-linked glycosylation and showed apparent molecular masses of 48, 55, and 67 kDa for hD4.2, hD4.4, and hD4.7, respectively. DFR1 immunoreactivity representing hD4R protein or dopamine D4 receptor-like antigens was observed in crude membrane extracts of postmortem human brain tissue by immunoblotting. The DFR1 antibody provides a new immunological tool with the potential to further our understanding of the human dopamine D4 receptor protein.

Cellular distribution of the rat D4 dopamine receptor protein in the CNS using anti-receptor antisera

A polyclonal antiserum was generated against a unique peptide fragment in the rat D4 dopamine (DA) receptor. The titer was monitored using solid-phase ELISA and once it was established, specificity was assessed using Chinese Hamster Ovary (CHO) cells, stably transfected with the full-length cDNA for the rat D4 DA receptor. Immunofluorescent staining produced by incubation with the anti-D4 DA receptor antiserum was selective for D4 DA receptor-transfected CHO cells, and was expressed at their cell membranes and cytoplasm. Attenuated staining for D4 DA receptor protein was visible in untransfected, K1 CHO cells, and in D2 or D3 DA receptor-transfected CHO cells. The regional and cellular CNS distribution patterns for the D4 DA receptor subtype were examined, and illustrated significant protein levels within the frontal (FCx) and parietal cortices. Lesser amounts of receptor protein staining occurred in the thalamus, globus pallidus, hippocampus, cerebellar vermis, and very low expression was detected in the striatum (CPu). D4 DA receptor protein staining was correlated with the cellular expression of its mRNA transcripts in these same brain regions using concurrent fluorescent analyses. The homologous coincidence in staining patterns for the D4 DA receptor transcripts and encoded proteins in identified neurons of the FCx and CPu showed variations in receptor expression in these identified basal ganglia pathways.

Localization of dopamine D4 receptors in GABAergic neurons of the primate brain

Dopamine receptors are the principal targets of drugs used in the treatment of schizophrenia. Among the five mammalian dopamine-receptor subtypes, the D4 subtype is of particular interest because of its high affinity for the atypical neuroleptic clozapine. Interest in clozapine stems from its effectiveness in reducing positive and negative symptoms in acutely psychotic and treatment-resistant schizophrenic patients without eliciting extrapyramidal side effects. We have produced a subtype-specific antibody against the D4 receptor and localized it within specific cellular elements and synaptic circuits of the central nervous system. The D4-receptor antibody labelled GABAergic neurons in the cerebral cortex, hippocampus, thalamic reticular nucleus, globus pallidus and the substantia nigra (pars reticulata). Labelling was also observed in a subset of cortical pyramidal cells. Our findings suggest that clozapine's beneficial effects in schizophrenia may be achieved, in part, through D4-mediated GABA modulation, possibly implicating disinhibition of excitatory transmission in intrinsic cortical, thalamocortical and extrapyramidal pathways.

In vitro translation of D2 dopamine receptors and their chimaeras: analysis by subtype-specific antibodies

We have developed a range of specific anti-peptide antibodies directed against the D2 and D3 dopamine receptors, and their alternatively spliced isoforms. To demonstrate the subtype- and isoform-specificities of these antibodies we have expressed the receptors in an in vitro translation system and have immunoprecipitated the expressed proteins. We have shown that the D2 and D3 receptors unexpectedly exhibit different migration properties on SDS-PAGE, in addition to displaying a significant difference between their predicted and apparent molecular weights. We have used D2/D3 chimaeric receptors to show that the differential migration between the subtypes can be attributed to the N-terminal half of the receptor and propose that the highly hydrophobic nature of the receptor proteins underlies their anomalous migration properties.

D2 dopamine receptor protein location: Golgi impregnation-gold toned and ultrastructural analysis of the rat neostriatum

The neostriatal distribution of D2 dopamine receptor protein has been assessed using subtype-selective polyclonal antibodies generated against three unique polypeptide sequences of the receptor. The experimental tissues were processed by peroxidase based immunohistochemical procedures for routine light microscopy, Golgi impregnation-gold toned morphological characterization, and correlative light/electron microscopy. The results demonstrated a regional gradient of D2-like dopamine receptor expression in the neostriatum, where lateral portions in the nucleus exhibited more reactive cell bodies than medial portions. D2-like expression was detected in the three populations of neostriatal neurons, i.e., the medium-sized spiny projection neurons, and the medium- and large-sized aspiny interneuron types. Morphometric measurements of labeled neurons verified that medium and large diameter neurons expressed the D2-like receptor subtype. D2-like immunoreactivity was distributed throughout the cytoplasm in dendritic processes, and in presynaptic terminal boutons. Immunoreactivity for the receptor protein was also detected in small, thinly myelinated axons, suggesting the possibilities of anterograde transport of the receptor from cell bodies in the substantia nigra to their neostriatal terminal fields, as well as from local axon collaterals of neostriatal projections neurons. These findings provide evidence of widespread distribution of the D2-like receptor protein in neostriatal neurons, and showed that the presynaptic D2 receptors contain analogous epitopes to the postsynaptic receptor subtype.

Anti-idiotypes against an anti-haloperidol antibody bind to sigma receptors

Anti-idiotypic monoclonal antibodies that interact with the binding site of sigma receptors were generated. First, BALB/c mice were immunized with a haloperidol-bovine serum albumin conjugate, and monoclonal anti-haloperidol antibodies that recognize the piperidinyl moiety of haloperidol molecule were obtained. Second, for generation of anti-idiotypic antibodies, BALB/c mice were immunized with the anti-haloperidol monoclonal antibodies coupled to keyhole limpet hemocyanin. Anti-idiotypic antisera and three hybridomas secreting anti-idiotypic monoclonal antibodies were obtained. All of them were shown to inhibit [3H]haloperidol binding to the anti-haloperidol antibodies. The anti-idiotypes were potent in displacing the binding of [3H]haloperidol to rat brain sigma receptors. Furthermore, they significantly immunoprecipitated the sigma receptors from a detergent-solubilized preparation. These findings demonstrate the generation of anti-idiotypic monoclonal antibodies specifically interacting with membrane-bound and solubilized sigma receptors.

Radioimmunoligand characterization and immunohistochemical localization of dopamine D2 receptors on rods in the rat retina

The retinal neurotransmitter dopamine (DA), elaborated from intrinsic dopaminergic neurons as amacrine and interplexiform cells, is known to modulate several complex functions mediated by D1 and D2 receptors in the vertebrate retina. In this paper, we characterized and localized DA receptors of the D2 family on rod outer segments (ROS) of the rat retina by a radioimmunoligand binding assay and by immunohistochemistry. Anti-anti-DA conjugated antibodies (or anti-idiotypic antibodies Ab2) were used as ligand; BSA-glutaraldehyde-conjugated spiperone, eticlopride (D2 antagonists) and DA were used as displacers. The linear Scatchard transformation indicated that data were best fit to the one-site model. By using the peroxidase-antiperoxidase technique, an intense labeling was located on rods. These results supported the paracrine action of DA on the photoreceptor cell.

Development of polyclonal anti-D2 dopamine receptor antibodies to fusion proteins: inhibition of D2 receptor-G protein interaction

Portions of the cDNA encoding the third intracellular loop (i3 loop) of the long and short isoforms of the rat D2 dopamine receptor were subcloned into the vector pNMHUBpoly and expressed in Escherichia coli as fusion proteins. The fusion proteins were gel-purified and used to immunize rabbits for the production of polyclonal anti-receptor antisera. The anti-fusion protein antisera recognized synthetic peptides corresponding to segments of the i3 loops of D2 dopamine receptors in a solid-phase radioimmunoassay. Antisera were tested in an immunoprecipitation assay using the reversible D2 antagonist [125I]NCQ 298 and digitonin-solubilized extracts of canine and rat caudate. [125I]-NCQ 298 bound reversibly and with high affinity (KD = 0.14 nM) to receptors in solubilized extracts enriched by chromatography on heparin-agarose. The anti-UBI-D2i3L and anti-UBI-D2i3s antisera were able to immunoprecipitate quantitatively D2 dopamine receptors labeled with [125I]NCQ 298 from solubilized rat caudate. The antibodies were tested for their ability to affect the coupling of D2 dopamine receptors to GTP-binding proteins in digitonin-solubilized rat caudate. Both anti-UBI-D2i3L and anti-UBI-Di3s antisera were able to inhibit the high-affinity binding of the agonist N-propylnorapomorphine to digitonin-solubilized rat caudate. These findings indicate that the i3 loop of the D2 dopamine receptor is an important determinant for coupling of the G protein.

A novel method for rapid enrichment of lactotrophs from dispersed anterior pituitary cells of the rat

A polyclonal antibody to the rat D2 dopamine (DA) receptor was rapidly and covalently attached to surface-activated polystyrene cultureware (MicroCEL-Lector plates). Addition of a suspension of dispersed rat anterior pituitary cells resulted in the rapid (within 1 h) selection of cells possessing D2 DA receptors (i.e. lactotrophs). Four-fold enrichment (from about 20% in the suspension to about 80%) was routinely obtained, as judged by prolactin (PRL) immunostaining. The enriched cells were virtually free of fibroblasts and were much more homogeneous in appearance than untreated cells after 3 days in culture. Lactotroph-enriched cell cultures displayed similar functional characteristics as untreated cells when assessed by determining dose-response curves for inhibition of PRL secretion by the DA agonist N-propylnorapomorphine. This method may be generally applicable for the selective enrichment and purification of desired cell types from heterogeneous mixtures in tissue dispersions.

Development of polyclonal anti-D2 dopamine receptor antibodies using sequence-specific peptides

Multiple subtypes of dopamine receptors with similar properties have been described. Ligands that have been shown to interact with a single subtype of receptor do not yet exist. The use of immunologic methods provides an alternative approach to distinguish receptors and receptor isoforms. Synthetic peptides corresponding to portions of the third intracellular loops of the two isoforms of the rat D2 dopamine receptor were used to elicit polyclonal antipeptide antibodies. Peptide D2-244 is unique to the D2L isoform, whereas peptide D2-284 is present in both the D2L and the D2S isoforms. Rabbits were immunized monthly with peptide coupled to keyhole limpet hemocyanin. The immunogenicity of the peptides was established using a solid-phase radioimmunoassay. Both immunogens elicited antipeptide antibodies within 10 weeks of the primary immunization, with titers of at least 1/10(4). An immunoprecipitation assay using receptors in digitonin-solubilized extracts of rat or canine caudate labeled with the high affinity D2 antagonist 125I-NCQ 298 showed that antipeptide antisera could recognize solubilized D2 receptors. At a dilution of 1/1000, antisera to peptide D2-284 quantitatively immunoprecipitated 125I-NCQ 298 binding sites from both rat and canine striatal tissue, whereas antisera against peptide D2-244 immunoprecipitated 40% of the D2 receptors solubilized from rat caudate. The selectivity of the antisera was determined using 293 cells transfected with cDNA encoding the D2L or the D2S isoform of receptor. Antisera to D2-284, at a dilution of 1/1000, were able to quantitatively immunoprecipitate receptor from both 293-D2L and 293-D2S cells. Antisera to D2-244 were specific for the D2L isoform, immunoprecipitating 125I-NCQ 298 binding sites from 293-D2L cells but not from 293-D2S cells. Anti-D2-284 specifically recognized multiple bands of 100 kDa, 68 kDa, and 50 kDa in immunoblots of denatured preparations of rat caudate. Immunohistochemical studies with anti-D2-284 demonstrated the presence of the D2 receptor in several regions of rat brain. Immunostaining was most dense in the striatum, with a lateral to medial gradient and patches of lighter staining. Immunoreactivity was negligible with preimmune serum or peptide-blocked immune serum. Immunoreactive processes were seen in the nucleus accumbens and ventral pallidum, as well as in the hypothalamus. The high affinity binding of agonist to D2 dopamine receptors was disrupted by anti-D2-284 but not anti-D2-244 antisera, implicating the internal region of the third intracellular loop represented by peptide D2-284 as a potential determinant of receptor-guanine nucleotide-binding protein coupling.

D2 dopamine receptor distribution in the rodent CNS using anti-peptide antisera

D2 dopamine receptors were identified immunohistochemically in rodent tissues using anti-peptide antisera to distinguish regional and cellular staining patterns. These subtype selective polyclonal antibodies were directed against both extracellular and intracellular regions of the native protein and showed that the D2 dopamine receptors are widely distributed within the nervous system. The highest expression of D2-like dopamine receptor immunoreactivity was visualized in the forebrain and components of the basal ganglia, supportive of previous investigations of the D2 dopamine receptor distribution using in vitro autoradiographic ligand binding or in situ hybridization for its messenger RNA. The anti-peptide antisera could detect the dopamine receptor in both perfusion-fixed and fresh-frozen tissue preparations. The reactive cells and their processes could be distinguished using experimental incubations from 1:8,000 (in immunofluorescence processing) to 1:80,000 (in immunoperoxidase processing) in the most reactive nervous system region, the neostriatum. The antisera are selectively directed against extracellular or intracellular epitopes in both the long and short isoforms of the D2 dopamine receptor, and should prove useful in subsequent studies of the subcellular distribution of this receptor in particular, and the dopamine system in general.

Preparation and characterization of an antibody specific to the rat dopamine D2 receptor

Antibodies specific to the dopamine D2 receptor have been raised in rabbits using synthetic peptides. The resulting antiserum was sensitive to picogram quantities of peptide as measured by enzyme-linked immunoassay and was shown to have a 33% cross-reactivity with partially purified D2 receptor protein. No detectable cross-reactivity with similarly prepared fungal membranes was observed. D2 receptor preparations from normal rat pituitary cells were used in Western blot analysis. Bands of M(r) = 95,000 and 34,000 were detected in these preparations with a third faint band at 120,000. These correspond to the pituitary D2 receptor.

An antibody to dopamine D2 receptor inhibits dopamine antagonist and agonist binding to dopamine D2 receptor cDNA transfected mouse fibroblast cells

A polyclonal antibody to dopamine D2 receptor (D2-receptor) has been used to examine the immuno-inhibition in the binding of a D2 antagonist, [3H]YM09151-2 and an agonist, PPHT-fluorescein to dopamine receptor DNA transfected mouse fibroblast cells. The specific activity of the [3H]YM09151-2 binding to transfected (Ltk-RGB) cells is 4-5 fold higher than untransfected (Ltk-) cells. The antibody is able to inhibit the [3H]YM09151-2 binding to the cell membranes from Ltk-RGB cells (Bmax 110.56 +/- 5.26 and 76.20 +/- 5.18 fmoles/mg protein in the presence of preimmune and immune sera, respectively, with no change in the Kd). The flow cytometric analysis of the PPHT-fluorescein labeled Ltk- and Ltk-RGB cells indicated that ligand specific fluorescence is associated only with small Ltk-RGB cells (second peak) and autofluorescence with large cells (first peak). Preincubation of the Ltk-RGB cells with antibody, reduced the fluorescence intensity of the PPHT-fluorescein by 20-25% without changing the auto-fluorescence. These results suggest that peptide antibody recognize D2-receptor in both membranes and in intact cells and interact at or near the ligand binding site of the receptor.