Radioligand binding characterization of putative dopamine D3 receptor in human peripheral blood lymphocytes with [3H]7-OH-DPAT

Disease mechanisms as subtypes: Immune dysfunction in Parkinson's disease

In recent years, the contraposition between inflammatory and neurodegenerative processes has been increasingly challenged. Inflammation has been emphasized as a key player in the onset and progression of Parkinson disease (PD) and other neurodegenerative disorders. The strongest indicators of the involvement of the immune system derived from evidence of microglial activation, profound imbalance in phenotype and composition of peripheral immune cells, and impaired humoral immune responses. Moreover, peripheral inflammatory mechanisms (e.g., involving the gut-brain axis) and immunogenetic factors are likely to be implicated. Even though several lines of preclinical and clinical studies are supporting and defining the complex relationship between the immune system and PD, the exact mechanisms are currently unknown. Similarly, the temporal and causal connections between innate and adaptive immune responses and neurodegeneration are unsettled, challenging our ambition to define an integrated and holistic model of the disease. Despite these difficulties, current evidence is providing the unique opportunity to develop immune-targeted approaches for PD, thus enriching our therapeutic armamentarium. This chapter aims to provide an extensive overview of past and present studies that explored the implication of the immune system in neurodegeneration, thus paving the road for the concept of disease modification in PD.

Potential biomarkers of addiction identified by real-time PCR in human peripheral blood lymphocytes: a narrative review

Addiction-related neurobiological factors could be considered as potential biomarkers. The concentration of peripheral biomarkers in tissues like blood lymphocytes may mirror their brain levels. This review is focused on the mRNA expression of potential addiction biomarkers in human peripheral blood lymphocytes (PBLs). PubMed, EMBASE, Web of Science, Scopus and Google Scholar were searched using the keywords 'addiction', 'biomarker', 'peripheral blood lymphocyte', 'gene expression' and 'real-time PCR'. The results showed the alterations in the regulation of genes such as dopamine receptors, opioid receptors, NMDA receptors, cannabinoid receptors, α-synuclein, DYN, MAO-A, FosB and orexin-A as PBLs biomarkers in addiction stages. Such variations could also be found during abstinence and relapse. PBLs biomarkers may help in drug development and have clinical implications.

Dopamine and Dopamine-Related Ligands Can Bind Not Only to Dopamine Receptors

The dopaminergic system is one of the most important neurotransmitter systems in the central nervous system (CNS). It acts mainly by activation of the D₁-like receptor family at the target cell. Additionally, fine-tuning of the signal is achieved via pre-synaptic modulation by the D₂-like receptor family. Some dopamine drugs (both agonists and antagonists) bind in addition to DRs also to α₂-ARs and 5-HT receptors. Unfortunately, these compounds are often considered subtype(s) specific. Thus, it is important to consider the presence of these receptor subtypes in specific CNS areas as the function virtually elicited by one receptor type could be an effect of other—or the co-effect of multiple receptors. However, there are enough molecules with adequate specificity. In this review, we want to give an overview of the most common off-targets for established dopamine receptor ligands. To give an overall picture, we included a discussion on subtype selectivity. Molecules used as antipsychotic drugs are reviewed too. Therefore, we will summarize reported affinities and give an outline of molecules sufficiently specific for one or more subtypes (i.e., for subfamily), the presence of DR, α₂-ARs, and 5-HT receptors in CNS areas, which could help avoid ambiguous results.

Where Is Dopamine and how do Immune Cells See it?: Dopamine-Mediated Immune Cell Function in Health and Disease

Dopamine is well recognized as a neurotransmitter in the brain, and regulates critical functions in a variety of peripheral systems. Growing research has also shown that dopamine acts as an important regulator of immune function. Many immune cells express dopamine receptors and other dopamine related proteins, enabling them to actively respond to dopamine and suggesting that dopaminergic immunoregulation is an important part of proper immune function. A detailed understanding of the physiological concentrations of dopamine in specific regions of the human body, particularly in peripheral systems, is critical to the development of hypotheses and experiments examining the effects of physiologically relevant dopamine concentrations on immune cells. Unfortunately, the dopamine concentrations to which these immune cells would be exposed in different anatomical regions are not clear. To address this issue, this comprehensive review details the current information regarding concentrations of dopamine found in both the central nervous system and in many regions of the periphery. In addition, we discuss the immune cells present in each region, and how these could interact with dopamine in each compartment described. Finally, the review briefly addresses how changes in these dopamine concentrations could influence immune cell dysfunction in several disease states including Parkinson's disease, multiple sclerosis, rheumatoid arthritis, inflammatory bowel disease, as well as the collection of pathologies, cognitive and motor symptoms associated with HIV infection in the central nervous system, known as NeuroHIV. These data will improve our understanding of the interactions between the dopaminergic and immune systems during both homeostatic function and in disease, clarify the effects of existing dopaminergic drugs and promote the creation of new therapeutic strategies based on manipulating immune function through dopaminergic signaling. Graphical Abstract.

The role of dopaminergic immune cell signalling in poststroke inflammation

Upon ischaemic stroke, brain-resident and peripheral immune cells accumulate in the central nervous system (CNS). Interestingly, these cells express pattern specific to neurotransmitter receptors and, therefore, seem to be susceptible to neurotransmitter stimulation, potentially modulating their properties and functions. One of the principal neurotransmitters in the CNS, dopamine, is involved in the regulation of processes of brain development, motor control and higher brain functions. It is constantly released in the brain and there is experimental and clinical evidence that dopaminergic signalling is involved in recovery of lost neurological function after stroke. Independent studies have revealed specific but different patterns of dopamine receptor subtypes on different populations of immune cells. Those patterns are dependent on the activation status of cells. Generally, exposure to dopamine or dopamine receptor agonists decreases detrimental actions of immune cells. In contrast, a reduction of dopaminergic inputs perpetuates a pro-inflammatory state associated with increased release of pro-inflammatory molecules. In addition, subsets of immune cells have been identified to synthesize and release dopamine, suggesting autoregulatory mechanisms. Evidence supports that inflammatory processes activated following ischaemic stroke are modulated by dopaminergic signalling.

The Concise Guide to PHARMACOLOGY 2013/14: G protein-coupled receptors

The Concise Guide to PHARMACOLOGY 2013/14 provides concise overviews of the key properties of over 2000 human drug targets with their pharmacology, plus links to an open access knowledgebase of drug targets and their ligands (www.guidetopharmacology.org), which provides more detailed views of target and ligand properties. The full contents can be found at http://onlinelibrary.wiley.com/doi/10.1111/bph.12444/full. G protein-coupled receptors are one of the seven major pharmacological targets into which the Guide is divided, with the others being G protein-coupled receptors, ligand-gated ion channels, ion channels, catalytic receptors, nuclear hormone receptors, transporters and enzymes. These are presented with nomenclature guidance and summary information on the best available pharmacological tools, alongside key references and suggestions for further reading. A new landscape format has easy to use tables comparing related targets. It is a condensed version of material contemporary to late 2013, which is presented in greater detail and constantly updated on the website www.guidetopharmacology.org, superseding data presented in previous Guides to Receptors and Channels. It is produced in conjunction with NC-IUPHAR and provides the official IUPHAR classification and nomenclature for human drug targets, where appropriate. It consolidates information previously curated and displayed separately in IUPHAR-DB and the Guide to Receptors and Channels, providing a permanent, citable, point-in-time record that will survive database updates.

The dopaminergic system in peripheral blood lymphocytes: from physiology to pharmacology and potential applications to neuropsychiatric disorders

Besides its action on the nervous system, dopamine (DA) plays a role on neural-immune interactions. Here we review the current evidence on the dopaminergic system in human peripheral blood lymphocytes (PBL). PBL synthesize DA through the tyrosine-hydroxylase/DOPA-decarboxylase pathway, and express DA receptors and DA transporter (DAT) on their plasma membrane. Stimulation of DA receptors on PBL membrane contributes to modulate the development and initiation of immune responses under physiological conditions and in immune system pathologies such as autoimmunity or immunodeficiency.

The characterization of DA system in PBL gave rise to a further line of research investigating the feasibility of PBL as a cellular model for studying DA derangement in neuropsychiatric disorders. Several reports showed changes of the expression of DAT and/or DA receptors in PBL from patients suffering from several neuropsychiatric disorders, in particular parkinsonian syndromes, schizophrenia and drug- or alcohol-abuse. Despite some methodological and theoretical limitations, these findings suggest that PBL may prove a cellular tool with which to identify the derangement of DA transmission in neuropsychiatric diseases, as well as to monitor the effects of pharmacological treatments.

Transactivation of the dopamine receptor 3 gene by a single provirus integration results in development of B-cell lymphoma in transgenic mice generated from retrovirally transduced embryonic stem cells

Gene transfer vectors based on retroviruses are commonly used in gene therapy applications because of their unique ability to integrate efficiently into host genomes. This ability also forms the basis of a transformation event that can be induced in transduced cells by transactivation of proto-oncogenes near the vector integration sites. Here, we report on the development of lymphoma in mice generated from embryonic stem cells transduced with an enhanced green fluorescent protein. The cells expressed B220, CD5, Mac1, and IgM on their surfaces and expressed transcription factors characteristic of B-cell lymphoma. Importantly, each mouse had a single copy of the provirus in its genome; the copy was integrated into the second intron of the dopamine receptor 3 (D3) gene, and high-level expression of D3 was detected only in the lymphoma cells. Ectopic expression of D3 in murine marrow cells resulted in preferential proliferation of cells at the pre-B-cell stage in response to a D3-specific agonist, but this proliferation was not observed in vivo. Cells cotransduced with D3 and Bcl-x(L) genes had a phenotype similar to that of lymphoma in vivo, suggesting that the leukemogenesis induced by retroviral integration required "second hit" mutations of additional genes.

Effects of insulin-like growth factor-1 on rotenone-induced apoptosis in human lymphocyte cells

Human peripheral blood lymphocytes have been useful as a putative model of oxidative stress-induced apoptosis for Parkinson's disease. The present work shows that rotenone, a mitochondrial complex I inhibitor, induced time- and concentration-dependent apoptosis in lymphocytes which was mediated by anion superoxide radicals (O(2)*(-))/hydrogen peroxide, depolarization of mitochondria, caspase-3 activation, concomitantly with the nuclear translocation of transcription factors such as NF-kappaB, p53, c-Jun and nuclei fragmentation. Since insulin-like growth factor-1 (IGF-1) interferes with a cell's apoptotic machinery when subjected to several stressful conditions, it is demonstrated here for the first time that IGF-1 effectively protects lymphocytes against rotenone through PI-3K/Akt activation, down-regulation of p53 and maintenance of mitochondrial membrane potential independently of ROS generation. These data might contribute to understanding the role played by IGF-1 against oxidative stress stimuli.

Dopamine receptors in human lymphocytes: radioligand binding and quantitative RT-PCR assays

Analysis of dopamine receptors (DR) in lymphocytes of the human peripheral blood mononuclear cell (PBMC) fraction is an attractive tool for evaluation of functional properties of dopaminergic function underlying variation in complex psychological/psychopathological traits. Receptor binding assays (RBAs) with selective radioligands, which are widely used in CNS studies, have not produced consistent results when applied to isolated PBMC. We tested the assay conditions that could be essential for detection of DR in human PBMC and their membrane preparations. Using [(3)H]SCH23390, a dopamine D1-like receptor antagonist, we demonstrated the presence of two binding sites in PBMC-derived membrane fraction. One of them is characterized by the K(d) value consistent with that reported for D5 dopamine receptors in human lymphocytes, whereas the other K(d) value possibly corresponds to serotonin receptor(s). Although D5 receptor binding sites in PBMC membranes could be characterized by binding assays, the low protein expression and the large volume of blood needed for membrane preparation render the binding method impracticable for individual phenotyping. In contrast, real-time RT-PCR may be used for this purpose, contingent on the relationship between DR expression in the brain and in lymphocytes. The expression of the DRD2-DRD5 genes, as detected by this method, varied widely among samples, whereas the DRD1 expression was not detected. The expression levels were comparable with those in the brain for DRD3 and DRD4, and were significantly lower for DRD2 and DRD5.

Dopamine D2 receptor polymorphisms in inflammatory bowel disease and the refractory response to treatment

Dopamine and its receptors may be involved in inflammatory reaction. The availability of this molecule depends on its receptors. The DRD2 gene, which codifies for the D2 dopamine receptor, has several polymorphisms. In this study, the DRD2 TaqIA polymorphism, which confers a decreased receptor density, was evaluated in 313 individuals including 220 inflammatory bowel disease patients (143 patients with Crohn's disease and 77 with ulcerative colitis) and in 93 healthy blood donors. The analysis was carried out by PCR-RFLP techniques. The frequencies of A (1) A (1) and A (2) A (2) genotypes were similar among Crohn's disease, ulcerative colitis patients, and health controls. Also, the genotype frequency was similar in different groups of disease localization, behavior, and age of disease onset. However, the Crohn's disease patients carriers of A (2) A (2) genotype showed a lower risk for development refractory Crohn's disease (37 out 65) than A (1) A (1) and A (1) A (2) carriers (28 out of 65) [(OR=0.4, 95% CI 0.21-0.87; p=0.02)]. Our results support an involvement of the dopamine receptor in inflammatory bowel disease and suggest a new potential target for therapy in refractory Crohn's disease patients.

Dopamine plasma membrane transporter (DAT) in rat thymus and spleen: an immunochemical and immunohistochemical study

The expression of the dopamine plasma membrane transporter (DAT) was investigated in rat thymus and spleen by immunochemical and immunohistochemical techniques. Antibodies raised against a peptide mapping near the amino terminus of DAT were bound to a single band of approximately 76 kDa in thymus and spleen membranes as well as in striatal and kidney membranes which were used as dopaminergic reference tissues. Reverse transcription-polymerase chain reaction analysis revealed that both thymus and spleen expressed DAT mRNA. Immunohistochemistry revealed in rat thymus a DAT immune reaction in the wall of arteries located in septa of connective tissue as well as in the medulla, with a reticular localization and an apparent negative reaction of thymocytes. In the spleen, DAT immunoreactivity was located primarily in the red-white pulp marginal zone, within small cells, likely corresponding to lymphocytes and in the wall of white pulp arteries. The presence of a dopamine transporter suggests that dopamine released in the lymphoid microenvironment may contribute to neuroimmune modulation. It cannot be excluded a different activity of dopamine in primary and secondary immune organs, such as maturation and selection of lymphocytes and activation of immune responses in the spleen.

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.

Insulin-like growth factor-1 prevents Abeta[25-35]/(H2O2)- induced apoptosis in lymphocytes by reciprocal NF-kappaB activation and p53 inhibition via PI3K-dependent pathway

The role of insulin-like growth factor (IGF-1) as neural survival factor for the treatment of Alzheimer's disease has recently gained attention. The present study shows that IGF-1 protects lymphocytes from (10, 30 microM) Abeta[(25-35)] and (25, 50, 100 microM) H(2)O(2)-induced apoptosis through NF-kappaB activation and p53 down regulation involving the phosphoinositide 3-kinase (PI-3K)-dependent pathway as demonstrated by using either (25 microM) LY294002 (PI-3K inhibitor), (10 nM) ammonium pyrrolidinedithiocarbamate (PDTC; NF-kappaB inhibitor), 50 nM pifithrin-alpha (PFT; p53 inhibitor) or by using immunocytochemistry detection of NF-kappaB and p53 transcription factors activation. Importantly, IGF-1, PDTC and PFT were able to protect and rescue lymphocytes pre-exposed to 10 muM Abeta[(25-35)], even when the three compounds were added up-to 12 h post- Abeta[(25-35)] exposure. Altogether these results suggest that survival/rescue of lymphocytes from Abeta[(25-35)] toxicity is determined by p53 inactivation via IGF-1/ PI-3K pathway.

D3 dopamine receptor mRNA is elevated in T cells of schizophrenic patients whereas D4 dopamine receptor mRNA is reduced in CD4+ -T cells

The expression of dopamine receptors was examined in purified human neutrophils, monocytes, B cells, natural killer cells and CD4+ - and CD8+ -T lymphocytes by RT-PCR. In healthy subjects, D1 and D2 receptors were not expressed in leukocytes. Real Time PCR for dopamine receptors D3 and D4 disclosed that D3 receptors are expressed in T cells and natural killer cells and D4 receptors in CD4+ -T cells. The comparison of schizophrenic patients with sex- and age-matched controls revealed a significantly higher expression of D3 receptor mRNA in T cells of schizophrenic patients, whereas D4 receptor mRNA in CD4+ -T cells was downregulated.

Dopamine inhibits cytokine release and expression of tyrosine kinases, Lck and Fyn in activated T cells

The effect of dopamine (DA) on the release of cytokines from activated human T cells has been evaluated to analyze the mechanism by which physiological concentration of dopamine inhibits T cell proliferation. Dopamine inhibited anti-CD3 mAb-induced release of both Th1 and Th2 cytokines, IL2, IFN-gamma and IL4 from T cells by specific class of dopamine receptors. This action of dopamine was mediated by a new mechanism. Dopamine suppressed non-receptor tyrosine kinases, Lck and Fyn expression which are the initial and pivotal signaling steps in T cell receptor (TCR) mediated different down stream signaling cascades, leading to cytokine release and subsequent clonal expansion of these immune effector cells.

Immunochemical and immunocytochemical characterization of cholinergic markers in human peripheral blood lymphocytes

Cholinergic markers and the expression of M(2)-M(5) muscarinic cholinergic receptor subtypes were investigated in human peripheral blood lymphocytes by Western blot analysis and immunocytochemistry. The totality of peripheral blood lymphocytes express acetylcholine (ACh) immunoreactivity, choline acetyltransferase (ChAT), acetylcholinesterase (AChE), vesicular ACh transporter (VAChT) and M(2)-M(5) muscarinic cholinergic receptor protein immunoreactivity. Western blot analysis performed independently on T and B lymphocytes using anti-ChAT and anti-AChE antibodies revealed labelling of single bands of approximately 68-70 and 70 kDa, respectively, whereas VAChT was bound to two bands of approximately 80 and 45 kDa. The pattern of immunoblotting was similar in membranes of lymphocytes and striatum, used as a reference brain tissue. Western blot analysis using anti M(2)-M(5) receptor antibodies revealed labelling of single bands of approximately 55, 85-90, 50 and 81 kDa, respectively. Confocal laser immunofluorescence showed the localization of ACh and VAChT immunoreactivity in punctiform areas likely corresponding to cytoplasmic vesicles. ChAT and AChE were diffused to the cytoplasm and plasma membrane. Muscarinic receptor immunoreactivity was located in lymphocyte plasma membrane. Although the role of lymphocyte cholinergic system is still unclear, the demonstration of cholinergic markers in T and B human blood lymphocytes supports the view that a cholinergic systems may contribute to the regulation of immune function. The characterization of these cholinergic markers may also contribute to define if their evaluation can be used for assessing the status of brain cholinergic system.

Postnatal development of dopamine receptor expression in rat peripheral blood lymphocytes

Postnatal development in the expression of dopamine D1-like and D2-like receptors was investigated in peripheral blood lymphocytes of male Wistar rats aged 1, 3, 4, 8, 12 and 16 weeks of age by radioligand binding assay techniques. Sample of frontal cortex, striatum and hippocampus were also investigated as reference tissues. The dopamine D1-like receptor antagonist [3H]SCH 23390 and the dopamine D2-like receptor agonist [3H]7-OH-DPAT were used as radioligands. The affinity (K(d)) of [3H]SCH 23390 or of [3H]7-OH-DPAT binding was unchanged in lymphocytes of rats of different age groups. The density (B(max)) of [3H]SCH 23390 binding sites increased from the 1st to the 3rd week of age, remained constant from the 3rd to the 8th week of age, and then increased slightly at 12 and 16 weeks of age. The B(max) value of [3H]7-OH-DPAT binding to lymphocytes increased from the 1st to the 3rd week of age, remained constant from the 3rd to the 4th week, increased again until the 12th week and then plateaued. Dopamine D1-like and D2-like receptor maturation in frontal cortex, hippocampus and striatum revealed an increased receptor density until the 4th week of age and a relative stabilization of receptor density values between the 4th to the 12th week depending on the area considered. Comparatively postnatal maturation of lymphocyte dopamine D1-like receptors displayed a pattern different from that of brain areas investigated, whereas maturation of D2-like receptors displayed a pattern similar to that of striatum. The quantitative and/or qualitative dissimilarities between development of lymphocyte and brain dopamine receptors suggest that from a developmental point of view lymphocyte dopamine receptors probably cannot be considered as a marker of homologous brain receptors.

Monoamine neurotoxins-induced apoptosis in lymphocytes by a common oxidative stress mechanism: involvement of hydrogen peroxide (H(2)O(2)), caspase-3, and nuclear factor kappa-B (NF-kappaB), p53, c-Jun transcription factors

The destruction of dopaminergic and serotonergic nerve cells by selective 6-hydroxydopamine (6-OHDA), 5,6-dihydroxytryptamine (5,6-DHT) and 5,7-dihydroxytryptamine (5,7-DHT), respectively, is a commonly used tool to investigate the mapping of neuronal pathways, elucidation of function and to mimic human neurodegenerative disease such as Parkinson's and Alzheimer's diseases. Despite intense investigations, a complete picture of the precise molecular cascade leading to cell death in a single cellular model is still lacking. In this study, we provide evidence that 6-OHDA, 5,6- and 5,7-DHT toxins-induced apoptosis in peripheral blood lymphocytes cells in a concentration-dependent fashion by a common oxidative mechanism involving: (1) the oxidation of toxins into quinones and production of the by-product hydrogen peroxide, reflected by desipramine-a monoamine uptake blocker-and antioxidants inhibition, (2) activation and/or translocation of nuclear factor-kappaB, p53 and c-Jun transcription factors, showed by immunocytochemical diaminobenzidine-positive stained nuclei, (3) caspase-3 activation, reflected by caspase Ac-DEVD-CHO inhibition, (4) mRNA and protein synthesis de novo according to cycloheximide and actinomycin D cell death inhibition. These results are consistent with the notion that uptake and intracellular autoxidation of those toxins precede the apoptotic process and that once H(2)O(2) is generated, it is able to trigger a specific cell death signalisation. Thus, taken together these results, we present an ordered cascade of the major molecular events leading peripheral blood lymphocytes to apoptosis. These results may contribute to explain the importance of H(2)O(2) as a second messenger of death signal in some degenerative diseases linked to oxidative stress stimuli.

Peripheral blood lymphocytes muscarinic cholinergic receptor subtypes in Alzheimer's disease: a marker of cholinergic dysfunction?

Muscarinic M2-M5 muscarinic cholinergic receptors were investigated in peripheral blood lymphocytes of patients with mild cognitive impairment of the Alzheimer's type (MCIAT), probable Alzheimer's disease (AD) and probable vascular dementia (VaD). [3H]-N-methyl scopolamine (NMS) in the presence of muscarinic antagonists and Mamba venom to occlude different receptor subtypes was used as radioligand. Analysis of [3H]-NMS binding curves without receptor subtype assessment resulted in a slight decrease of receptor density in AD patients. Evaluation of receptor subtypes in MCIAT and AD patients revealed a decrease of M3 receptor by more than 50%, an increase of M4 receptor expression by about 20% and no changes of M2 or M5 receptors. The expression of M2-M5 receptors was unaltered in VaD patients. Strong positive and negative correlations respectively were found between the density of lymphocyte M3 and M4 receptors and MMSE score in both MCIAT (0.78 for M3 receptor and 0.80 for M4 receptor) and AD (0.82 for M3 receptor and 0.83 for M4 receptor) patients. These findings suggest that changes in the expression of peripheral blood lymphocyte M3 and M4 receptors in AD are related to the degree of cognitive impairment. Assessment of lymphocyte muscarinic receptor subtypes may contribute to characterization of cholinergic impairment in AD.

Dopamine interacts directly with its D3 and D2 receptors on normal human T cells, and activates beta1 integrin function

Dopamine by itself has not up to now been reported to activate T cell function. We show here that dopamine interacts directly with dopaminergic receptors on normal human T cells and triggers beta1 integrin-mediated T cell adhesion to a major extracellular matrix component, fibronectin (FN). Such adhesion is a characteristic feature of activated T cells, and is critical for trafficking and extravasation of T cells across blood vessels and tissue barriers. Seven dopamine D2/D3 receptor agonists and antagonists were used to identify the receptor subtypes with which dopamine specifically interacts to activate T cells. The D3 dopamine receptor agonist, 7-hydroxy-DPAT (DPAT), mimics the effects of dopamine, and the effects of both dopamine and DPAT are blocked by a specific D3 receptor antagonist, U-maleate. The dopamine receptor agonists bromocriptine and pergolide mimic the direct effect of dopamine on the beta1 integrin function, while the dopamine receptor antagonists butaclamol and haloperidol suppress it, suggesting additional signaling via the dopamine D2 receptor subtype. Our study shows, for the first time, that dopamine can directly activate T cells via ist specific receptors and suggests a possible role for dopamine in integrin-mediated cellular trafficking and extravasation of T cells in the central nervous system and possibly also in the periphery. Finally, we suggest that the reported changes in the D3 and D2 receptor RNA levels in peripheral blood lymphocytes of individuals with schizophrenia, Parkinson's disease, Alzheimer's disease and migraine can serve not only as a 'passive' diagnostic marker, but primarily reflect the dynamic functional dopamine-T cell interactions in these diseases.

Alpha1-adrenergic receptor subtypes in peripheral blood lymphocytes of essential hypertensives

OBJECTIVE

The expression of alpha1-adrenergic receptor subtypes in peripheral blood lymphocytes was investigated in 28 essential hypertensive patients as well as in the peripheral blood lymphocytes and aorta of spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto (WKY) rats.

METHODS

Alpha1-adrenergic receptors were quantified by radioligand binding assays, employing [3H]-prazosin as the radioligand in association with compounds displaying different degrees of selectivity for alpha1A-, alpha1B- and alpha1D-adrenergic receptor subtypes.

RESULTS

The affinity of [3H]-prazosin binding was similar in peripheral blood lymphocytes of different stage essential hypertensive and normotensive subjects or of SHR and age-matched normotensive WKY rats as well as in the aortas of SHR and WKY rats. The radioligand binding assay revealed no change in the expression of alpha1-adrenergic receptors in peripheral blood lymphocytes of essential hypertensives compared with normotensive subjects; a moderate decrease of alpha1B-adrenergic receptors and an increase of alpha1D-adrenergic receptors. The relative densities of the alpha1-adrenergic receptor subtypes were similar in the three groups of essential hypertensives. In peripheral blood lymphocytes and in aorta of SHR, [3H]-prazosin binding was significantly reduced compared with normotensive WKY rats. The expression of alpha1-adrenergic receptor subtypes in peripheral blood lymphocytes of SHR was similar to that found in peripheral blood lymphocytes of essential hypertensives.

CONCLUSIONS

Changes of lymphocyte alpha1-adrenergic receptor subtypes in essential hypertensives are similar to those observed in lymphocytes and vascular tissues of animal models of hypertension. This suggests that assays of lymphocyte alpha1-adrenergic receptors may represent an indirect marker of their involvement in essential hypertension.

Identification of dopamine plasma membrane and vesicular transporters in human peripheral blood lymphocytes

Plasma membrane dopamine transporter (DAT), vesicular monoamine transporters (VMAT) type-1 and -2 and the expression of the dopaminergic markers dopamine and tyrosine hydroxylase were assessed in membranes and/or in cytospin centrifuged human peripheral blood lymphocytes. The radiolabeled DAT ligand [3H]GBR12935 was bound to peripheral lymphocytes in a manner consistent with the specific binding to a dopamine uptake system, with a dissociation constant similar to that found in striatum, but with a lower density of binding sites. On the other hand, no specific binding occurred in cerebellum used as a test tissue not expressing DAT. Western blot analysis using antibodies raised against amino or carboxy terminus of DAT or against VMAT-1 or VMAT-2 revealed labeling of single bands of approximately 76, 55 or 68 KDa, respectively, displaying similar migration characteristics in lymphocytes and test tissues used for comparison. Immunofluorescence revealed that anti-dopamine, anti-tyrosine hydroxylase, anti-DAT, anti-VMAT-1 and anti-VMAT-2 antibodies labeled the total population of cytospin-centrifuged lymphocytes mounted on microscope slides. Confocal laser microscopy demonstrated that dopamine and VMAT-2 immunoreactivity was developed mainly in cytoplasmic punctiform areas likely corresponding to vesicles and to a lower extent was associated to plasma membrane. Tyrosine hydroxylase immunoreactivity was diffused to cytoplasm and to plasma membrane of lymphocytes, whereas DAT and VMAT-1 immunoreactivity were located almost exclusively in lymphocyte plasma membrane and cytoplasm, respectively. Lymphocyte DAT characterized in this study has probably functional relevance as [3H]dopamine was taken up by intact lymphocytes and uptake was inhibited specifically by compounds known to affect dopamine transport. These findings indicate that human peripheral blood lymphocytes possess DAT plasma membrane and VMAT-1 and VMAT-2 transporters. Increasing evidence indicates that dopamine transporter changes may be related to neuronal injury. In view of this assessment of lymphocyte DAT and VMAT transporters can be considered for identifying pathologies characterized by impaired dopaminergic neurotransmission.

The dopaminergic system in hypertension

Dopamine exerts cardiovascular and renal actions mediated through interaction with specific dopamine receptors. Dopamine receptors are cell surface receptors coupled to G-proteins and classified into two main super families based on biochemical, pharmacological and molecular characteristics. The dopamine D1-like receptor super family includes D1 and D5 receptors, known also in rodents as D1A and D1B sites. These receptors are linked to stimulation of adenylate cyclase. The dopamine D2-like receptor super family includes D2, D3 and D4 receptors. These receptors are linked to inhibition of adenylate cylase or not related with this enzyme activity. They also interfere with opening of Ca+2 channels and are linked to stimulation of K+ receptors. Dopamine receptor subtypes are expressed in brain as well as in extracerebral structures such as the heart, blood vessels, carotid body, kidney, adrenal gland, parathyroid gland and gastrointestinal tract. In the kidney, which represents the peripheral organ where dopamine receptors were more extensively investigated, dopamine receptors are involved in regulation of hemodynamic, electrolyte and water transport, as well as renin secretion. Hypertension-related dopamine receptor changes were also investigated primarily in the kidney. Defective renal dopamine production and/or dopamine receptor function have been reported in human primary hypertension as well as in genetic models of animal hypertension. There may be a primary defect in D1-like receptors and an altered signalling system in the proximal tubules that lead to reduced dopamine-mediated effects on renal sodium excretion in hypertension. Studies on the influence of hypertension on dopamine D2-like receptors are sparse Disruption of either D1A or D3 receptors at the gene level causes hypertension in mice. Using peripheral blood lymphocytes as possible markers of the status of dopamine receptors in essential hypertension, no changes of dopamine D1-like receptors were noticeable, whereas an increase of dopamine D2-like receptors likely representing an up-regulation mechanism was reported. Available information collectively indicates an involvement of peripheral dopaminergic system in hypertension consisting either in impaired receptor transduction mechanisms and/or in receptor loss. A better knowledge of molecular bases of these changes may contribute to the development of specific therapeutic approaches in the future.

Reduced density of dopamine D2-like receptors on peripheral blood lymphocytes in Alzheimer's disease

Clinical and pathological evidence points to an involvement of dopamine in Alzheimer's disease (AD). The present study was designed to assay dopamine D1-like and D2-like receptors on peripheral blood lymphocytes (PBL) in 20 patients with AD and in 25 healthy controls by radioligand binding assay techniques with [3H][R]-(+)-(-)chloro-2,3,4,5 tetrahydro-5-phenyl-1H-3-benzazepin-al-hemimaleate (SCH 23390) and [3H]7-hydroxy-N,N-di-n-propyl-2-aminotetraline (7OH-DPAT) as radioligands. The density of dopamine D1-like receptors and the affinity of [3H]SCH 23390 and [3H]7OH-DPAT binding to PBL were similar in both groups investigated. AD patients revealed a lower density of dopamine D2-like receptors on PBL than controls (P=0. 0016). The pharmacological profile of [3H]SCH 23390 and [3H]7OH-DPAT binding to PBL was consistent with the labeling of dopamine D5 and D3 receptor subtypes, respectively. The reduced density of dopamine D2-like receptors on PBL is consistent with the observation of changes in the expression of D2-like receptors in dopaminergic brain areas in AD. Our findings support the hypothesis of an involvement of dopamine in AD, even in those patients with no evidence of Parkinsonism, behavioral abnormalities or psychosis.

In situ hybridization and immunocytochemistry of alpha1-adrenoceptors in human peripheral blood lymphocytes

1 alpha1-Adrenoceptor subtypes were investigated in cytospin centrifuged preparations of human peripheral blood lymphocytes by in situ hybridization and immunocytochemistry. 2 In situ hybridization cytochemistry revealed alpha1A-, alpha1B-, and alpha1D-receptor mRNA in human peripheral blood lymphocytes. Lymphocytes hybridized for alpha1A receptor subtype represented approximately 30% of total lymphocytes, those hybridized for alpha1Beta- and alpha1D-receptor subtypes averaged 42 and 25% of total lymphocytes, respectively. 3 Cytospin centrifuged lymphocytes exposed to anti-alpha1A-, alpha1Beta- or alpha1D-receptor protein antibodies, developed specific immunostaining. Approximately 27% of total lymphocytes were immunoreactive for alpha1A-receptor protein, 40% displayed alpha1B-receptor protein immunoreactivity and 22% alpha1D-receptor protein immunoreactivity. Analysis of percentages as well as of lymphocyte morphology of in situ hybridized and immunolabelled lymphocytes suggests the co-expression of mRNA receptor signal and protein receptor immunostaining in the same lymphocyte. 4 The demonstration of both alpha1-adrenoceptor mRNA and receptor protein subtypes suggests that alpha1-adrenoceptors may have a role in regulating lymphocyte function. 5 The possibility of demonstrating receptor protein immunoreactivity in a small amount of blood, such as that required for preparing cytospin-centrifuged lymphocytes, may stimulate research to evaluate the role of these receptors in lymphocytes and to establish if assessment of lymphocyte alpha1-adrenoceptors may represent a marker of their status in health and disease.

17 beta-estradiol protects lymphocytes against dopamine and iron-induced apoptosis by a genomic-independent mechanism. Implication in Parkinson's disease

Dopamine (DA) in combination with iron (Fe(2+)) has been demonstrated to induce apoptosis in neuronal-like PC12 cells by an oxidative stress mechanism. To get a better insight of cell death and protective mechanisms in DA/Fe(2+)-induced toxicity, we investigated the effects of DA/Fe(2+) and the antioxidant action of 17 beta-estradiol (E2) in peripheral blood lymphocytes (PBL). We found that DA/Fe(2+)-induces apoptosis in PBL via a hydrogen peroxide (H(2)O(2))-mediated oxidative mechanism, which in turn triggers a cascade of molecular events requiring RNA and de novo protein synthesis. We have also demonstrated that E2 prevents significantly DA/Fe(2+)-induced apoptosis in PBL by directly inhibiting the intracellular accumulation of peroxides generated by DA/Fe(2+)-reaction. This protective activity is independent of the presence or activation of the estrogen receptors (ERs). These data further support and validate our previous hypothesis that DA/Fe(2+)/H(2)O(2) could be a general mediator of oxidative stress through a common cell death mechanism in both neuronal and nonneuronal cells. These findings may be particularly relevant to the potential approaches to rescue and prolong the survival of neurons by estrogens in patients with Parkinson's disease (PD).

Migraine patients show an increased density of dopamine D3 and D4 receptors on lymphocytes

Recent studies have revealed peculiar functional and genetic features of dopamine receptors in migraine. As peripheral blood lymphocytes (PBL) may represent a tool for peripheral detection of neuroreceptors, we compared the expression of dopamine D3 (DRD3) and D4 (DRD4) receptors on PBL in migraine patients and in healthy controls using radioligand binding assay techniques in the presence of antidopamine D2-like receptor antibodies. The dopamine D2-like receptor agonist [3H]7-OH-DPAT was used as a radioligand. An increased density of both DRD3 (P=0.0006) and DRD4 (P=0.002) on PBL was observed in migraineurs compared with controls. This up-regulation might reflect central and/or peripheral dopamine receptor hypersensitivity due to hypofunction of the dopaminergic system. These findings support the view that dopamine D2-like receptors are involved in the determination of the so-called migraine trait, which may help to elucidate several clinical features of the disease.

Dopamine, a neurotransmitter, influences the immune system

Dopamine (DA) is a monoamine neurotransmitter of both central and peripheral nervous system. Its role in the neural-immune communication has been discussed in the present review. Results reveal that in vivo damage or stimulation of specific central dopaminergic system suppresses or enhances functional activities of the immune effector cells. The possible influences of other immunomodulators of the brain by altering brain DA may be the underlying mechanism. Direct effects of DA on the immune effector cells are also contradictory, it is suppressive in vitro, while in pharmacological doses, it is mostly stimulatory in vivo. The possible mechanisms have been discussed. Lastly, future areas of relevance on DA and immunity have been highlighted to advance our knowledge regarding DA as an immune regulator.

Radioligand binding assay of M1-M5 muscarinic cholinergic receptor subtypes in human peripheral blood lymphocytes

Analysis of lymphocyte muscarinic cholinergic receptors using quantitative techniques such as radioligand binding assay is made difficult due to the low density of these sites and the lack of subtype-specific selectivity of most available muscarinic ligands. In this study, a combined kinetic and equilibrium labeling technique recently developed for brain tissue was used for labeling the five muscarinic cholinergic receptor subtypes in intact human peripheral blood lymphocytes. No specific muscarinic M1 receptor binding was detectable in human peripheral blood lymphocytes using [3H]-pirenzepine as a ligand. Labeling of M2-M5 muscarinic receptors using [3H]N-methyl-scopolamine (NMS) by occluding various receptor subtypes with muscarinic antagonist and mamba venom resulted in the labeling of M2-M5 receptors in brain as well as in human peripheral blood lymphocytes. The relative density of different receptor subtypes was M3 > M5 > M4 > M2. The development of a reproducible technique for assaying muscarinic cholinergic receptor subtypes expressed by human peripheral blood lymphocytes may contribute to clarify their role in lymphocyte function.

Increased expression of dopamine receptors on lymphocytes in Parkinson's disease

Dopamine D1-like and D2-like receptors on peripheral blood lymphocytes (PBL) were assayed in 50 de novo patients with idiopathic Parkinson's disease (PD), in 36 neurologic control subjects (multiple-system atrophy, n = 16; essential tremor, n = 10; other neurodegenerative diseases, n = 10), and in 26 healthy control subjects by radioligand binding assay techniques using [3H]SCH 23390 and [3H]7OH-DPAT as ligands. Patients with PD revealed a higher density (Bmax) of dopamine D1-like (p <0.001) and D2-like (p <0.00001) receptors on PBL than either neurologic or healthy control subjects, whereas no differences in Bmax were observed among patients affected by other neurologic diseases and healthy control subjects. The affinity (Kd) of both radioligands was similar in the groups investigated. The pharmacologic profile of [3H]SCH 23390 and [3H]7OH-DPAT binding was consistent with the labeling of dopamine D5 and D3 receptor subtypes, respectively. Twenty-five of the 50 patients with PD were retested after 3 months of therapy with levodopa or bromocriptine. Both treatments reduced the density of D1-like (p <0.001) and D2-like (p <0.001) receptors on PBL to values comparable to those of control subjects. The increased density of D1-like and D2-like receptors on PBL in de novo PD patients may represent an upregulation mechanism resulting from the diffuse impairment of the dopaminergic system in PD.

Relative amounts of mRNA encoding four subtypes of muscarinic receptors (m2-m5) in human peripheral blood mononuclear cells

It is known that lymphocytes express functional muscarinic cholinergic receptors. In this study, RT-PCR method was applied to study the presence and relative levels of mRNA encoding muscarinic receptor subtypes in human peripheral blood mononuclear cells (PBMCs). Our results, confirmed by DNA sequencing, demonstrate the presence of m2, m3, m4, and m5 receptor subtypes in human PBMCs. The relative levels of muscarinic receptor subtypes fit the following pattern: m3 > m5 > m4 > m2. Our data provide strong evidence confirming previous pharmacological studies that suggested the existence of several subtypes of muscarinic receptors on human PBMCs. We cannot exclude the possibility that expression of receptor subtype depends on the lineage and/or activation status of the cell.

Dopamine D2-like receptors on human peripheral blood lymphocytes: a radioligand binding assay and immunocytochemical study

1. Peripheral blood lymphocytes express dopamine D1-like and D2-like receptors which were investigated using radioligand binding assay and molecular biology techniques. Analysis of dopamine D2-like receptors expressed by human peripheral blood lymphocytes with radioligand binding assay may offer a rapid technique for assessing receptor changes in disorders characterized by involvement of the dopaminergic system. However, the suitability of radioligand binding assay techniques to measure dopamine D2-like receptors is questioned. 2. In view of the discrepancy between data of dopamine D2-like receptor determination with molecular biology and radioligand binding assay techniques, we have assayed dopamine D2-like receptors expressed by human peripheral blood lymphocytes using as radioligands the dopamine receptor agonist 7-[3H]-hydroxy-N,N-di-n-propyl-2-aminotetraline ([3H]-7-OH-DPAT) and two antagonists ([3H]-spiperone and [3H]-nemonapride). 3. Analysis of saturation curves revealed a concentration-dependent binding of all compounds to human peripheral blood lymphocytes. Dissociation constant (Kd) values averaged between 0.15 and 0.40 nM for different radioligands. The maximum density of binding sites (Bmax) was low, ranging from 4.15 +/- 0.05 fmol/10(6) cells with [3H]-spiperone and 8.66 +/- 0.04 fmol/10(6) cells with [3H]-7-OH-DPAT. 4. Displacement curves of [3H]-7-OH-DPAT, [3H]-spiperone and [3H]-nemonapride binding to human peripheral blood lymphocytes revealed, using radioligand concentrations giving the highest specific:non-specific binding ratio, a pharmacological profile consistent with the labelling of dopamine D2-like receptors. The use of higher radioligand concentrations resulted in a poorly displaceable and characterizable binding. 5. Detection of dopamine D2, D3 and D4 receptor immunoreactivity in cytospin centrifuged peripheral blood lymphocytes revealed dopamine D3 and D4 but not D2 receptor immunostaining. 6. The above findings indicate in agreement with molecular biology studies, that dopamine D2-like receptors expressed by human peripheral blood lymphocytes belong to the D3 and D4 receptor subtypes. These receptors are detectable using either dopamine D2-like receptor agonists and antagonists as radioligands if controlled experimental conditions are followed. The standardisation of immunocytochemical techniques for detecting human peripheral blood lymphocyte dopamine receptors may contribute to clarify their role in lymphocyte function or as a peripheral marker of the status of the dopaminergic system.

Dopamine D1-like receptor subtypes in human peripheral blood lymphocytes

Molecular biology studies have shown that human peripheral blood lymphocytes express a dopamine D5 receptor, whereas no information is available on dopamine D receptor, the other dopamine D1-like receptor subtype. Radioligand binding assay investigations with the nonsubtype selective dopamine D1-like receptor antagonist [3H]SCH 23390 as radioligand have suggested the presence of a dopamine D5 receptor in human peripheral blood lymphocytes. However, so far no evidence was provided as whether or not human peripheral blood lymphocytes express a dopamine D1 receptor. In this study, we have investigated dopamine D1 and D5 receptor mRNA and the influence of antibodies against dopamine D1 and D5 receptors on [3H]SCH 23390 binding to intact human peripheral blood lymphocytes. The two receptors were also analyzed by immunocytochemistry. Dopamine D5 receptor, but not D1 mRNA, was detected in human peripheral blood lymphocytes. Anti-dopamine D5 receptor antibodies, but not anti-dopamine D1 receptor antibodies, significantly decreased [3H]SCH 23390 binding to human peripheral blood lymphocytes. A dark-brown immunoreactivity was visualized in cytospin centrifuged human peripheral blood lymphocytes exposed to anti-dopamine D5, but not to anti-dopamine D1 receptor antibodies. These data collectively indicate that dopamine D5 receptor is the only dopamine D1-like receptor subtype expressed by human peripheral blood lymphocytes.

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.

Inhibition of immune cell proliferation with haloperidol and relationship of tyrosine hydroxylase expression to immune cell growth

Previous studies indicated that exogenous dopamine and its agonists directly regulated mitogen-induced immune cell proliferation. In this study, we further investigated role of endogenous dopamine in immune cell growth. Haloperidol, a general antagonist for dopamine receptors, could reduce the cell growth rate of T cell hybridoma (10I) and rat nervous pheochromocytoma cells (PC12). Tyrosine hydroxylase (TH) catalyzes the initial rate-limiting step of catecholamine biosynthesis in the nervous system. Flow cytometric analysis indicated the expression of TH in various immune cells. The presence of TH in PC12 cells was used as a control. Temporal studies indicated that the expression of TH increased during 10I cell growth. Both alpha-methyl-p-tyrosine and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine reduced TH expression and cell growth in a dose-dependent manner. These results suggest that immune T cells express TH which is correlated to cell growth, and that dopamine released from these cells may bind to the receptors to act in an autocrine or paracrine way.

Effect of dopamine on immune cell proliferation in mice

Dopamine is known as a precursor of catecholamine and one of the neurotransmitters in brain and peripheral tissues. Recent studies suggest an important role of dopamine in immune responses. In the present study, intraperitoneal administration of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) which lowered endogenous dopamine suppressed splenocyte proliferation in response to mitogens such as lipopolysaccharide (LPS) and concanavalin A (Con A). Moreover, intravenous injection of the specific agonists of dopamine DA-1 receptor (SKF38393) or DA-2 receptor (LY171555) into mice enhanced the splenocyte proliferation stimulated by LPS or Con A. In the in vitro cultures, dopamine, SKF38393 and LY171555 directly promoted cell proliferation to LPS or Con A. These results indicate that dopamine has an ability to regulate B- and T-cell proliferation both in vivo and in vitro.

Quantitative autoradiographic studies of dopamine D3 receptors in rat cerebellum using [125I]S(-)5-OH-PIPAT

Recently, [125I]S(-)5-OH-PIPAT (5-hydroxy-2-(N-n-propyl-N-3'-iodo-2'-propenyl)amino-tetralin) was reported to be a selective radioiodinated ligand for dopamine D2-like receptors. This ligand displayed a high binding affinity (Kd = 0.3-0.4 nM) and an agonist binding profile to dopamine D2 and D3 receptors expressed in HEK293 cells and dopamine D4 receptors expressed in CHO cells. Herein, a series of studies to characterize D3 receptors in native tissues is presented. Based on studies of the distribution of receptor mRNA, D3, but not D2, receptors are present in the rat cerebellum. Quantitative autoradiographic experiments using [125I]S(-)5-OH-PIPAT to label molecular layers 9 and 10 of rat cerebellum were conducted. Saturation experiments demonstrated that [125I]S(-)5-OH-PIPAT bound with high affinity (Kd = 0.1 nM) to a low density (approximately 3 fmol/mg protein) of sites in molecular layers 9 and 10 of rat cerebellum. Increasing concentrations of Gpp(NH)p, but not ATP, decreased the specific binding of [125I]S(-)5-OH-PIPAT in rat cerebellum slices. In comparison studies, binding of [125I]NCQ298, a dopamine D2/D3 receptor antagonist, with a similar affinity (Kd = 0.2 nM) for D3 receptors as [125]S(-)5-OH-PIPAT, was not sensitive to Gpp(NH)p. Analysis of inhibition by S(-)5-OH-PIPAT of [125I]NCQ298 binding to rat cerebellum resulted in two-site binding with IC50 values of 0.07 nM and 6.0 nM. In the presence of GTP (300 microM), the data best fit a one-site model with an IC50 value of 1.6 nM. Agonists and antagonists inhibited the binding of [125I]S(-)5-OH-PIPAT in the cerebellum with a rank order of potency consistent with an interaction at D3 receptors. These results indicate that [125I]S(-)5-OH-PIPAT binds to D3 receptors in rat cerebellum. Furthermore, [125I]S(-)5-OH-PIPAT binds to GTP sensitive and GTP insensitive states of D3 receptors with distinctive high and low affinity states, respectively.

Dopamine D3 receptor in peripheral mononuclear cells of essential hypertensives

Dopamine D3 receptor was studied in peripheral mononuclear cells of high-normal, stage 1, stage 2, and stage 3 essential hypertensives using a radioligand binding assay technique with [3H]-7-hydroxy-N,N-di-n-propyl-2-aminotetraline (7-OH-DPAT) as a radioligand. A group of de novo Parkinsonian patients was also examined as a reference group of impaired dopaminergic function. [3H]-7-OH-DPAT was bound specifically to human peripheral mononuclear cells in a manner consistent with the labeling of a dopamine D3 receptor. No changes in free dopamine, norepinephrine, epinephrine and aldosterone levels, renin activity, dissociation constant of [3H]-7-OH-DPAT binding, or the pharmacological profile of [3H]-7-OH-DPAT binding were found between normotensive control subjects and essential hypertensives or Parkinsonians. The density of peripheral mononuclear cell [3H]-7-OH-DPAT binding sites increased in essential hypertensives parallel to blood pressure value augmentation. A higher density of [3H]-7-OH-DPAT binding sites was found in Parkinsonians. In these patients, the density of [3H]-7-OH-DPAT binding sites was similar to that observed in high-normal subjects and in stage 1 essential hypertensives. The increased density of peripheral mononuclear cell dopamine D3 receptor in hypertension as well as in Parkinson's disease may represent an upregulation mechanism consequent to impaired dopaminergic function. In view of the difficulty in identifying markers of peripheral dopamine function, analysis of dopamine D3 receptor in peripheral mononuclear cells may help evaluate whether the dopaminergic system is involved in hypertension.

Dopamine D4 receptor in human peripheral blood lymphocytes: a radioligand binding assay study

The expression of dopamine D4 receptor was investigated in human peripheral blood lymphocytes with a radioligand binding assay technique, using [3H]clozapine as radioligand. [3H]Clozapine was specifically bound to human peripheral blood lymphocytes. The binding was time-, temperature-, and concentration-dependent and of high affinity, with a dissociation constant (K(d)) value of 0.34 +/- 0.02 nM and a maximum density of binding sites (B(max)) value of 27 +/- 1.4 fmol/10(6) cells. The pharmacological profile of [3H]clozapine binding to human peripheral blood lymphocytes was similar to that found in Chinese hamster ovary (CHO) cells transfected with the D4 clone (D4.2 variant). The above results are consistent with molecular biology studies demonstrating the expression of a dopamine D4 receptor in immune cells and in human peripheral blood lymphocytes. The availability of a rapid and sensitive radioligand binding assay technique for the dopamine D4 receptor in human peripheral blood lymphocytes may contribute to better define the role of this dopamine receptor subtype in neurological and psychiatric disorders.

Age-dependent changes in the expression of dopamine receptor subtypes in human peripheral blood lymphocytes

The pharmacological profile and the density of dopamine D3 and D5 receptor subtypes expressed by human peripheral blood lymphocytes of subjects of different ages (ranging from 20 to 75 years) were assessed using radioligand binding techniques. Dopamine D3 receptor was assayed with [3H]7-hydroxy-N,N-di-n-propyl-2-aminotetraline ([3H]7-OH-DPAT) as a ligand. Dopamine D5 receptor was assayed using [3HIR]-(+)-(-chloro-2,3,4,5, tetrahydro-5-phenyl-1H-3-benzazepin-al-hemimaleate) ([3H]SCH 23390) as a ligand. The affinity and the pharmacological profile of [3H]7-OH-DPAT and [3H]SCH 23390 at dopamine D3 and D5 receptor, respectively, were similar in subjects of different ages. The density of dopamine D3 receptor binding sites was slightly decreased in subjects of 30-39 years in comparison with younger individuals. A remarkable loss of dopamine D3 receptor was then found between 40 and 49 years of age in comparison with younger subjects. A further slight decrease was noticeable between 50 and 59 years of age. The number of [3H]7-OH-DPAT binding sites was then stabilized after 60 years of age. The density of dopamine D5 receptor binding sites did not show age-dependent changes. The above findings indicate the occurrence of a decline in the density of lymphocyte dopamine D3 but not D5 receptor between adult and mature subjects. The possibility that dopamine D3 receptor assay in peripheral blood lymphocytes may represent a tool for investigating dopamine receptor function in aging and age-related neurological disorders is discussed.

Identification of dopamine D4 receptor mRNA in circulating human lymphocytes using nested polymerase chain reaction

There is a long standing controversy if dopamine receptors are present on human lymphocytes. In recent years the expression of dopamine D3 and D5 receptors was demonstrated with molecular biological methods. Using reverse transcription and polymerase chain reaction (RT-PCR) we were able to demonstrate the expression of the dopamine D4 receptor (DRD4) mRNA in human circulating lymphocytes. Direct sequencing of the RT-PCR product assured that it corresponds to the human DRD4 sequence. However, because of the unusual high G/C content of the DRD4, several precautions have to be applied for reliable results.

D2-like dopamine receptors are not detectable on human peripheral blood lymphocytes

The binding of [3H]-nemonapride to human peripheral blood lymphocytes (PBL) was studied using various competing ligands specific for D2-like dopamine receptors. There is no detectable stereoselectivity for the stereoisomers of butaclamol, and competitions with haloperidol and sulpiride also show no evidence of specific binding to D2-like dopamine receptors. RT-PCR of RNA from human lymphocytes showed that there is no detectable D2 mRNA (even with nested PCR). D3 mRNA was, however, detectable by RT-PCR, but only at low levels that could not be detected by Northern blots of PBL total RNA.

Haloperidol and spiperone potentiate murine splenic B cell proliferation

The neuroleptics haloperidol and spiperone potentiated anti-mu induced murine B-lymphocyte proliferation in vitro and lowered the threshold of anti-mu antibody needed to trigger proliferation. Because haloperidol and spiperone are best known for actions at D2, 5HT2, alpha 1 and sigma (sigma) receptors, a series of agonists and antagonists of these receptors were tested. Dopamine and norepinephrine inhibited, and serotonin (5HT) enhanced B-cell proliferation. Spiperone opposed the suppression of proliferation by dopamine and norepinephrine. However, antagonists of D1, D2, D3, D5, 5HT2, 5HT1A, and alpha 1 receptors did not mimic the effect of haloperidol and spiperone. Furthermore, a series of sigma agonists failed to affect B-cell proliferation. Therefore it is likely that the effects of haloperidol and spiperone are not due to actions at known dopamine, 5HT, alpha 1, or sigma receptors. These findings indicate neuroleptics act not only in the CNS, but also directly on B-lymphocytes of the immune system. The pharmacological site of this action is not clear at this time.