Search

1 Earlier studies have demonstrated a high density of dopamine D1-like receptor binding in the choroid plexus by light microscope autoradiography, but the dopaminergic specificity of this binding was questioned. 2 In this study the localization of dopamine receptor subtypes was investigated in the rat choroid plexus by Western blot analysis and immunohistochemistry using antibodies raised against dopamine D1–D5 receptor protein. 3 Western blot analysis revealed reactivity with immune bands of approximately 50 and 51 KDa corresponding to dopamine D1 and D5 receptors, respectively. Dopamine D1-like (D1 and D5) receptor protein immunoreactivity insensitive to superior cervical ganglionectomy was located in smooth muscle of choroid arteries and to a larger extent within choroid plexus epithelium. 4 Western blot analysis revealed reactivity with immune bands of approximately 53 KDa and 40–42 KDa corresponding to dopamine D2 and D4 receptors, respectively, and no dopamine D3 receptor reactivity. Dopamine D2-like receptor protein immunoreactivity displayed a distribution similar to that of tyrosine-hydroxylase (TH)-immunoreactive sympathetic fibres and disappeared after superior cervical ganglionectomy. It consisted in the expression of dopamine D2 and to a lesser extent of D4 receptor protein immunoreactivity perivascularly and associated with choroid epithelium. No D3 receptor protein immunoreactivity was found in rat choroid plexus. 5 The above results indicate that rat choroid plexus expresses dopamine receptor protein, being dopamine D1-like receptors predominant in epithelium and arterial smooth muscle and D2-like receptors in sympathetic nerve fibres supplying choroid plexus epithelium and vasculature. 6 These findings suggests that dopamine receptors with a different anatomical localization may modulate production of cerebrospinal fluid. [ABSTRACT FROM AUTHOR]

Summary The pharmacological profile and the anatomical localization of a putative dopamine D4 receptor were assessed in sections of rat and human atria and ventricles using combined radioligand binding and autoradiographic techniques with [3 H]-spiperone as a ligand. [3 H]-Spiperone was bound specifically to sections of human and rat atria and ventricles. The binding was time-, temperature- and concentration-dependent, belonging to a single class of high affinity sites. In atria, the dissociation constant value (Kd ) was 0.45 nM in rats and 0.32 nM in humans, and the maximum density of binding sites (Bmax ) was 31.6 ± 2.9 fmol mg-1 tissue in rats and 18.8 ± 0.7 fmol mg-1 tissue in humans. In ventricles, Kd was 0.38 nM in rats and 0.39 nM in humans, and the Bmax was 43.5 ± 3.0 fmol mg-1 tissue in rats and 56.4 ± 3.2 fmol mg-1 tissue in humans. The pharmacological profile of [3 H]-spiperone binding to sections of both rat and human atria and ventricles was consistent with the labelling of dopamine D2 -like receptors. [3 H]-Spiperone binding was more sensitive to displacement by the neuroleptic clozapine in sections of atria than of ventricles, suggesting the expression of a dopamine D4 receptor in atrial tissue. Moreover, preincubation of some section with a dopamine D4 receptor antibody and subsequent exposure to [3 H]-spiperone caused a remarkable decrease of radioligand binding to sections of atria, but only a slight reduction of binding to section of ventricles. Light microscope autoradiography revealed the accumulation of silver grains over atrial tissue within atrial myocardiocytes. A higher density of silver grains was developed in rat than in human atria. In ventricles, silver grains were accumulated primarily in cluster areas both in rats and in... [ABSTRACT FROM AUTHOR]

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/106 cells with [3H]-spiperone and 8.66 ± 0.04 fmol/106 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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]