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.

Astrocyte changes in aging cerebral cortex and hippocampus: a quantitative immunohistochemical study

Glial cells are sensitive to aging, but the real extent of age-related quantitative and qualitative changes of these brain cellular elements has not yet been clarified. Brain volume undergoes age-related changes, but several studies on the number of glial cells have not taken this important variable into account. In this study we quantitatively evaluated the number and morphology of glial fibrillary acidic protein (GFAP)-immunoreactive astroglia in the frontal cortex and in the CA1 subfield of the hippocampus of male Sprague-Dawley rats of aged 12 and 24 months, considered adult and aged, respectively. The volume of frontal cortex was unchanged in the two age groups investigated, whereas the volume of hippocampus was higher in aged rats. An increase in the number and size of GFAP-immunoreactive astrocytes was observed in the frontal cortex and in the CA1 subfield of the hippocampus of aged rats. The numeric increase in astrocytes was more pronounced in the hippocampus than in the frontal cortex, whereas age-related hypertrophy of astroglia was more accentuated in the frontal cortex. The possible significance of hyperplasia and hypertrophy of GFAP-immunoreactive astrocytes in the frontal cortex and in the CA1 subfield of the hippocampus of aged rats is discussed.

Association of circulating endothelium and noradrenaline with increased calcium-channel binding sites in the placental bed in pre-eclampsia

OBJECTIVE

To evaluate factors contributing to both placental hypoperfusion and maternal vasoconstriction in pre-eclampsia.

DESIGN

Single centre, comparative study of calcium-channel density and affinity in the placental bed of pregnant women with normotension and pre-eclampsia.

SETTING

Teaching hospital.

PARTICIPANTS

Twenty-two primigravidae in the third trimester of pregnancy: 10 with pre-eclampsia and 12 normotensive.

METHODS

Plasma levels of endothelin-1 (by RIA) and noradrenaline (by HPLC-ED) were measured. Both pharmacological characterisation and anatomical localisation of dihydropyridine-sensitive binding sites (using radioligand-binding studies and autorradiographic techniques) were determined with 3H-isradipine in placental bed tissues to determine both the density (Bmax) and the affinity (Kd) of receptor sites.

RESULTS

Higher plasma levels of endothelin-1 and noradrenalin were found in women with pre-eclampsia compared with normotensive women. Placental bed tissues bound 3H-isradipine in a saturable, reversible time and temperature-dependent manner with very low Kd values. Study of the 3H-isradipine specificity binding included the use of several dihydropyridine displacers. In the group with pre-eclampsia the Scatchard analysis of the results showed a significant increase (P < 0.001) both in the affinity [Kd = 0.23 nmol (0.04) vs 0.45 nmol (0.03), pre-eclampsia vs normotensive] and in the density of calcium-channel binding sites [Bmax = 77.70 fmol/mg (1.30) vs 64.30 fmol/mg (1 80) tissue, pre-eclampsia vs normotensive]. Autoradiography confirmed that in the placental bed tissue of those with pre-eclampsia there was a much higher silver grain density in the arteries walls, compared with normotensive women.

CONCLUSIONS

In pre-eclampsia there is an increase in the maternal circulation of two strong vasoconstrictor factors (endothelin-1 and noradrenalin) and a sharp increase both in the density and the affinity of calcium-channel binding sites in placental bed central area. The latter may strongly contribute to the perpetuation of the uteroplacental hypoperfusion either by itself or by amplifying the local actions of circulating factors, such as endothelin-1 and noradrenalin.

Effect of lesions of the nucleus basalis magnocellularis and of treatment with posatirelin on cholinergic neurotransmission enzymes in the rat cerebral cortex

The effect of 4 and 8 weeks of treatment with the thyrotropin releasing hormone (TRH), analogue posatirelin (L-6-ketopiperidine-2-carbonyl-L-leucyl-proline amide), on the changes of cholinergic neurotransmission enzymes, choline acetyltransferase (ChAT) and acetylcholinesterase (AChE), caused by lesions of the nucleus basalis magnocellularis (NBM), was investigated in the rat frontal cortex. ChAT and AChE were demonstrated with immunohistochemical and histochemical techniques, respectively associated with image analysis and microdensitometry. Monolateral and bilateral lesions of NBM area caused a significant loss of ChAT-immunoreactive nerve cell bodies in the NBM, as well as a remarkable decrease of ChAT-immunoreactive fibres and of AChE reactivity in the frontal cortex ipsilateral to the lesion or of both sides, respectively. The number of ChAT-immunoreactive nerve cell bodies in the lesioned NBM was higher in posatirelin-treated rats for 8 weeks in comparison with control NBM-lesioned rats. Moreover, the compound increased the number of ChAT-immunoreactive fibres in the frontal cortex of monolaterally and bilaterally NBM-lesioned rats at 8 weeks after lesion, but was without effect on these fibres in sham-operated rats. The same is true for AChE reactivity, developed in the neuropil of the frontal cortex, which was restored in part by an 8-week treatment with posatirelin in NBM-lesioned rats. These findings suggest that treatment with posatirelin rescues cholinergic neurons of the NBM and cholinergic projections to the cerebral cortex affected by lesioning of the NBM. The functional relevance of these observations and their possible applications should be evaluated in future studies.

Peripheral blood lymphocyte muscarinic cholinergic receptors in airway hyperresponsiveness: a marker of cholinergic dysfunction?

1. Muscarinic cholinergic receptors were assayed in human peripheral blood lymphocytes of healthy control and airway hyperresponsive subjects using a radioligand binding assay technique and the muscarinic cholinergic receptor antagonist [3H]-quinuclidinyl benzilate (QNB) as a radioligand. Subjects investigated were divided in four different groups based on threshold responses to methacholine inhaled as challenge test. 2. [3H]-QNB was bound to human peripheral blood lymphocytes in a manner consistent with the labelling of muscarinic cholinergic receptors. Dissociation constant (Kd) values of [3H]-QNB binding were similar in the different groups examined, whereas maximum density of binding sites (Bmax) was increased in airway hyperresponsive subjects in comparison with healthy controls. 3. The above findings indicate that the density of muscarinic cholinergic receptors is increased in peripheral blood lymphocytes of airway hyperresponsive subjects. 4. This suggests that airway hyperresponsiveness is associated with cholinergic hyperreactivity and is probably a systemic cholinergic dysfunction since it is accompanied by changes in the density of muscarinic cholinergic receptors expressed by peripheral blood lymphocytes.

Telemedicine and medical care to ships without a doctor on board

Providing medical assistance to ships at sea was probably one of the first practical applications of telemedicine. At present, about 200 different organizations worldwide give medical assistance to ships without a doctor on board. The activity of the Foundation Centro Internazionale Radio Medico (CIRM), which probably has the largest experience in the world of telemedicine applied to seafarers, is reviewed. Medical assistance to seafarers has not improved in parallel with advances in medicine and telecommunications. Possible initiatives for improving teledelivery of medical assistance to seafarers are discussed.

Influence of neonatal treatment with the pyrethroid insecticide cypermethrin on the development of dopamine receptors in the rat kidney

The influence of neonatal treatment with the pyrethroid insecticide cypermethrin ((R,S)alpha-cyano-3-phenoxybenzyl (1R,S)-cis-trans-3-(2,2-dichloro-vinyl)-2,2-dimethylcyclopropane carboxylate) on postnatal development of renal dopamine receptors was investigated by radioligand binding assay techniques. Treatment with cypermethrin was made on rats from the 10th to the 16th day after birth. Dopamine D1- and D2-like receptors were assayed in frozen sections of kidney of 21-, 30-, 60- and 90-day-old rats using as ligands of dopamine D1- and D2-like receptors [3H]([R](+)-(chloro-2,3,4,5,-tetrahydro-5-phenyl-1,4,-benzazepinal hemimaleate) (SCH 23390) and [3H]spiperone, respectively. Treatment with cypermethrin was without effect on the affinity (Kd value) or the density (Bmax value) of dopamine D1- and D2-like receptors of rats of 21 days of age. In older groups, treatment with the compound reduced the affinity and increased the density of dopamine D1-like receptors, whereas it was without effect on the affinity of dopamine D2-like receptors and decreased their density. These findings indicate that neonatal treatment with the pyrethroid insecticide cypermethrin induces long-lasting impairment of renal dopamine D1- and D2-like receptors and that kidney is a target of the toxic action of the compound. Renal dopamine receptor changes caused by cypermethrin are consistent with possible alterations of renal tubular function and of sympathetic neuroeffector modulation. The above data suggest also that, different from the adult, neonatal exposure to pyrethroid insecticides may induce toxic effects.

Autoradiographic localisation of muscarinic cholinergic receptor subtypes in human placenta

The localisation of M1-M4 muscarinic cholinergic receptor subtypes was investigated in sections of normal human term placenta by light microscope autoradiography. Muscarinic cholinergic receptor subtypes were found almost exclusively in syncytiotrophoblast. Neither other cellular components of placenta, nor blood vessels were labelled. Quantitative analysis of the density of silver grains developed in sections incubated with the different protocols for labelling M1-M4 receptor subtypes, revealed that syncytiotrophoblast expresses all subtypes of muscarinic cholinergic receptor investigated. A higher density of binding sites was found in the apical than in the basal portion of syncytiotrophoblast. The demonstration of muscarinic cholinergic receptors in syncytiotrophoblast suggests that a cholinergic system may have a role in regulating transport of compounds from maternal to foetal interface.

Density and localization of calcium channels of the L-type in human pulmonary artery

The pharmacological profile and the anatomical localization of Ca2+ channels of the L-type were investigated in the human pulmonary artery to identify possible mechanisms involved in the regulation of the pulmonary vascular tone. Analysis was performed on slide-mounted frozen sections of human pulmonary artery using radioligand binding assay techniques associated with light microscope autoradiography. [3H]-Nicardipine was used as ligand. Human renal and right coronary arteries also were used as systemic reference arteries. Binding of [3H]-nicardipine to sections of human pulmonary artery was time-, temperature- and concentration-dependent, saturable and reversible. In the human pulmonary artery, the apparent equilibrium dissociation constant (Kd) was 0.12+/-0.02 nM and the maximum density of binding sites (Bmax) was 38.15+/-2.25 fmol/mg tissue. Kd values were 0.3+/-0.01 nM and 0.5+/-0.02 in the human renal artery and right coronary artery respectively. Bmax values were 248+/-16 fmol/mg tissue and 173+/-9.5 fmol/mg tissue in the human renal artery and right coronary artery respectively. The pharmacological profile of [3H]-nicardipine binding to sections of human pulmonary artery was consistent with the labeling of Ca2+ channels of the L-type. It was similar in the pulmonary artery and in the human renal and right coronary arteries. Light microscope autoradiography revealed a high density of [3H]-nicardipine binding sites within smooth muscle of the tunica media of human pulmonary artery as well as of human renal and right coronary arteries. A lower accumulation of the radioligand occurred in the tunica adventitia. No specific binding was noticeable in the tunica intima. Our data suggest that human pulmonary artery expresses Ca2+ channels of the L-type sensitive to dihydropyridines. These sites have similar affinity and lower density than those expressed by systemic arteries. The presence of Ca2+ channels of the L-type in human pulmonary artery suggests that their pharmacological manipulation may be considered in the treatment of pulmonary hypertension.

Pharmacological characterization and autoradiographic localization of a putative dopamine D4 receptor in the heart

1. 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 [3H]-spiperone as a ligand. 2. [3H]-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. 3. The pharmacological profile of [3H]-spiperone binding to sections of both rat and human atria and ventricles was consistent with the labelling of dopamine D2-like receptors. [3H]-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 sections with a dopamine D4 receptor antibody and subsequent exposure to [3H]-spiperone caused a remarkable decrease of radioligand binding to sections of atria, but only a slight reduction of binding to sections of ventricles. 4. 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 humans. 5. The above findings suggest the expression of a dopamine D4 receptor in rat atria, but not in ventricles. A similar site was identified in human atria. The possible relevance of a dopamine D4 receptor in the heart is discussed.

Dopamine D2-like receptors in the kidney of spontaneously hypertensive rats: a radioligand binding assay and light microscope autoradiography study

1. Dopamine D2-like receptors were investigated in sections of kidney from male spontaneously hypertensive rats (SHRs) at 6 and 14 weeks of age using radioligand binding assay and autoradiographic techniques with [3H]-spiperone as a ligand. 2. Systolic blood pressure values were slightly higher in 6-week-old SHRs in comparison with age-matched normotensive Wistar-Kyoto (WKY) rats and considerably higher in 14-week-old SHRs in comparison with the other groups investigated. Renal dopamine levels were higher in SHRs aged 6 and 14 weeks in comparison with age-matched WKY rats. Noradrenaline concentrations were similar in 6-week-old SHRs and normotensive WKY rats, and increased slightly in SHRs aged 14 weeks. 3. The density of [3H]-spiperone binding sites was similar in SHRs and WKY rats at 6 weeks of age, and decreased in SHRs at 14 weeks in comparison with age-matched normotensive animals. Light microscope autoradiography revealed the accumulation of silver grains in the tunica adventitia, in the adventitia-media border of intrarenal arteries and within cortical tubules. A few specific silver grains were also developed in the glomerular tuft. No changes in the density and pattern of silver grains were noticeable between SHRs and WKY rats at 6 weeks of age, whereas a reduction in silver grains largely affecting vascular binding sites was observed at 14 weeks of age. 4. Renal denervation considerably decreased the density of [3H]-spiperone binding sites in sections of rat kidney, with an almost complete loss of vascular binding sites. 5. The above findings indicate the occurrence of a decrease of dopamine D2-like receptors in the kidney of SHRs with the progress of hypertension. Dopamine D2-like receptors which are mainly prejunctional are involved in the modulation of sympathetic neurotransmission in the kidney. The loss of these receptors in SHRs may contribute to the pathophysiology of hypertension.

Organization and activities of the International Radio Medical Centre (CIRM)

The International Radio Medical Centre (CIRM) was founded in 1935, to provide free medical assistance by radio to ships with no doctor on board and others who cannot be reached by a doctor. In 1950 CIRM was established as a non-profit-making foundation and has benefited since 1957 from an annual contribution from the Italian government. The results achieved by the Centre over 61 years include medical assistance to 42,935 patients on board ships (as well as on small islands and aircraft), with 375,264 medical messages received and transmitted. CIRM is organized into a medical service, a telecommunications service and a studies section. The 24-h continuous medical service is provided by doctors at the CIRM headquarters. The doctor on duty gives instructions for managing the case. If necessary the medical service will coordinate the patient's hospitalization at the nearest port with suitable medical facilities or arrange the patient's transfer to another ship with a doctor on board, or an airlift. The telecommunications service receives requests for assistance, locates the ship or whoever made the request, passes the call to the doctor on duty, and relays the doctor's response to those requesting assistance. The studies section, established in 1957-58, researches occupational pathologies of sailors and contributes to their prevention. This provides a scientific basis for improving medical assistance to sailors at sea.

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.

Muscarinic cholinergic receptors and acetylcholinesterase activity in umbilical artery and vein in pregnancy-induced hypertension (pre-eclampsia)

The influence of pregnancy-induced hypertension (pre-eclampsia) on muscarinic cholinergic receptors and on acetylcholinesterase (AChE) activity was investigated using frozen sections of the umbilical artery and vein. Pre-eclamptic patients undergoing Caesarean delivery and normotensive pregnant control woman undergoing Caesarean delivery with similar parity, gestation length and age were examined. Muscarinic cholinergic receptors were assayed in frozen sections of the umbilical artery and vein by a radioligand binding assay technique, using [3H]-N-methyl scopolamine (NMS) as a ligand. AChE was demonstrated with a histochemical technique associated with microdensitometry. [3H]-NMS was specifically bound to sections of both umbilical artery and vein in a manner consistent with the labelling of muscarinic cholinergic receptors. The affinity of the radioligand was similar in the two vessels, whereas the maximum density of binding sites (Bmax) was higher in the umbilical vein than in the artery. A faint AChE reactivity was observed in the tunica media of both umbilical artery and vein. In pre-eclampsia, a loss of [3H]-NMS binding sites not accompanied by changes in the affinity of radioligand was found. The decrease of muscarinic cholinergic receptors involved to a greater extent the umbilical artery than the vein. No differences in AChE activity were found at the level of umbilical artery and vein between control and pre-eclamptic subjects. These findings suggest that pre-eclampsia is characterized by a loss of muscarinic cholinergic receptors in the umbilical circulation not accompanied by changes of the acetylcholine catabolizing enzyme AChE. It is possible that the decreased density of vascular muscarinic cholinergic receptors in pregnancy-induced hypertension contribute to the increased resistance of the umbilical circulation occurring in pre-eclampsia.

Pharmacological characterisation and autoradiographic localisation of a putative dopamine D3 receptor in the rat kidney

The pharmacological profile and the microanatomical localisation of a putative dopamine D3 receptor in the rat renal cortex were investigated using radioligand binding assay and light microscope autoradiography techniques. [3H]7-hydroxy-N,N-di-n-propyl-2-aminotetraline ([3H]7-OH-DPAT) was used as a ligand. [3H]7-OH-DPAT was bound specifically to sections of renal cortex. The binding was time-, temperature- and concentration-dependent, of high affinity and guanine nucleotide-insensitive. The dissociation constant (Kd) value was 0.57 +/- 0.02 nM and the maximum density of binding sites (Bmax) was 62.4 +/- 3.5 fmol/mg tissue. The pharmacological profile of [3H]7-OH-DPAT binding to sections of rat renal cortex suggests the labelling of a dopamine D3 receptor. Light microscope autoradiography revealed the accumulation of the radioligand primarily within cortical tubules and to a lesser extent in the glomerular tuft. In glomeruli, binding sites were found mainly in mesangium and mesangial cells. The demonstration of a putative dopamine D3 receptor in slide-mounted sections of rat renal cortex suggests that appropriate radioligand binding assay techniques combined with autoradiography, may contribute to characterise peripheral dopamine receptor subtypes.

Effect of treatment with the neuroactive peptide posatirelin on microanatomical changes of frontal cortex and hippocampus caused by lesions of the locus coeruleus

The influence of monolateral and bilateral lesions of the Locus coeruleus (LC) on the number of nerve cell and glial fibrillary acidic protein (GFAP)-immunoreactive astrocyte profiles, on silver-gold impregnated fibres and on tyrosine hydroxylase (TH) immunoreactivity was assessed in the rat frontal cortex and hippocampus. The influence of treatment for 4 and 8 weeks with a 10 mg/kg/day dose of the neuroactive peptide posatirelin on the above parameters was also investigated. Lesions of the LC decreased the number of nerve cell profiles in the frontal cortex 8 weeks after lesioning and were without effect on nerve cell profiles in the frontal cortex 4 weeks after lesioning and in the hippocampus at both 4 and 8 weeks after LC lesioning. Glial fibrillary acidic protein (GFAP)-immunoreactive astrocytes were not affected by lesions of LC. Silver-gold impregnated fibres were decreased in the frontal cortex but not in the hippocampus of LC-lesioned rats at 8 weeks after lesioning. TH immunoreactivity, which was localized in nerve fibre-like structures both in the frontal cortex and in the hippocampus was decreased in the frontal cortex and in the hippocampus from the 4th week after LC lesioning. Treatment with posatirelin was without effect on the number of nerve cell and of GFAP-immunoreactive astrocyte profiles at both 4 and 8 weeks after LC lesioning, with the exception of nerve cells of the frontal cortex in monolaterally-lesioned rats which were increased 8 weeks after lesioning. The compound increased silver-gold impregnated fibres in the frontal cortex of monolaterally lesioned rats after 8 weeks of treatment, but did not affect TH immunoreactivity both in the frontal cortex or in the hippocampus. The above results suggest that treatment with posatirelin exerts a neuroprotective effect on the frontal cortex consisting of the partial restoration of some microanatomical changes caused by lesions of LC. The possible significance of this effect is discussed.

Use of frozen sections for the pharmacological characterization of compounds active on neurotransmitter receptors

Radioligand binding assay represents an important technique in pharmacological and pharmaceutical research for assessing the receptor profile of new drugs or of compounds under development. In this study, the pharmacological profile and the receptor specificity of compounds active on dopamine and muscarinic cholinergic receptor subtypes were evaluated using as a receptor source, membrane preparations or frozen sections. Dopamine D1-like receptors were assayed in membrane preparations or frozen sections of rat striatum and kidney with [3H]-SCH 23390 as a ligand. Rat striatum, kidney and atrium were used as a source of dopamine D2-like receptors with [3H]-spiperone as a ligand. The non-selective muscarinic cholinergic receptor antagonist [3H]-N-methyl-scopolamine was used to label muscarinic cholinergic receptors in the rat. Frontal cortex represented the source of M1 receptor subtype, heart the source of M2 receptor subtype, sub maxillary gland the source of M3 receptor subtype and striatum the source of M4 receptor subtype. With the exception of cardiac tissue, no significant differences were noticeable in the affinity of dopaminergic or muscarinic cholinergic compounds tested using membrane particles or 8 microns thick slide-mounted section. In the heart, frozen sections gave lower dissociation constant and inhibition constant values than membranes. The above findings suggest that radioligand binding assay on slide-mounted tissue sections may represent a suitable technique for assessing the receptor profile of drugs under development for the treatment of disorders characterised by dopaminergic or muscarnic cholinergic dysfunction.

Dopamine D2-like receptors in the rat kidney: effect of denervation

The effects of monolateral denervation induced by renal artery occlusion on dopamine D2-like receptors were assessed in rat kidney using radioligand binding assay and autoradiographic techniques. [3H]spiperone was used as a ligand. [3H]spiperone was bound specifically to sections of control innervated kidneys with a dissociation constant (Kd) value of 0.07 +/- 0.003 nM and a maximum density of binding sites (Bmax) value of 35.4 +/- 0.16 fmol/mg tissue. Light microscope autoradiography showed the accumulation of silver grains both in the arterial tree and in cortical tubules. At the vascular level, [3H]spiperone binding sites were accumulated primarily in the adventitia and in adventitia-media transitional zone. In cortical tubules, the higher density of [3H]spiperone binding sites was noticeable in proximal convoluted tubules. A few binding sites were also found in the glomerular tuft. In denervated kidneys, noradrenaline and dopamine levels were reduced by about 90% and 60% respectively in comparison with control innervated kidneys. Denervation reduced the density of [3H]spiperone binding sites by more than 85%. In denervated kidneys, light microscope autoradiography showed the disappearance of specific vascular binding sites and a remarkable reduction of tubular [3H]spiperone binding sites. The above results indicate that the largest majority of renal dopamine D2-like receptors labelled by [3H]spiperone is prejunctional in location.

Use of [3H]-clozapine as a ligand of the dopamine D4 receptor subtype in peripheral tissues

1. Molecular biology studies have documented the presence of peripheral dopamine D4 receptors. This site has not been characterized yet with classical radioligand binding assay techniques because of the lack of selective radioligands. 2. The atypical neuroleptic clozapine labelled with tritium ([3H]-clozapine) has been proposed and sold as a radioligand for brain dopamine D4 receptors. However, the selectivity of [3H]-clozapine for D4 receptor subtypes, and its specificity for brain dopamine receptors, have been questioned. 3. In this study dopamine D4 receptors were assayed in peripheral organs known to express them, such as rat atria and kidney, by using a radioligand binding assay technique with [3H]-clozapine as the radioligand. Parallel experiments were performed using Chinese hamster ovary (CHO) cells transfected with the D4 receptor clone (variant D4.2). 4. [3H]-Clozapine was bound to sections of rat atria and kidney. After appropriate blockade of sites other than dopamine receptors to which it can bind (i.e. muscarinic cholinergic, serotonergic and alpha-adrenergic receptors), the radioligand was bound to a site displaying a pharmacological profile similar to that expressed by CHO cells transfected with the D4 receptor. 5. The above findings indicate that with appropriate protocols, [3H]-clozapine may represent a radioligand for peripheral dopamine D4 receptors.

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.

Postnatal development of dopamine D1-like and D2-like receptors in the rat kidney: a radioligand binding study

Dopamine exerts important natriuretic and renal haemodynamic changes mediated through the interaction with dopamine D1-like and D2-like receptors. Dopamine-mediated natriuresis and renal vascular effects are less in younger than in older animals. The pharmacological profile and the density of dopamine D1-like and D2-like receptors were assessed in the kidney of rats ranging from 2 to 90 days of age by using radioligand binding assay techniques. [3H]SCH 23390 was used as ligand of dopamine D1-like receptors. [3H]Spiperone was used as a ligand of dopamine D2-like receptors. The dissociation constant (Kd) value of [3H]SCH 23390 binding was slightly decreased from the 21st day of age in comparison with animals of 2 and 7 days of age. The maximum density (Bmax) of [3H]SCH 23390 binding sites increased progressively until the 21st day of age and then plateauned. A similar trend was found for [3H]Spiperone binding sites. In [3H]Spiperone binding experiments, the Kd value was remarkably decreased from the 21st to the 90th day of life. Bmax value of [3H]Spiperone binding sites were similar in rats of 2 and 7 days of age and subsequently increased to values similar to those found in adult rats from the 21st day of life. The pharmacological profile of [3H]SCH 23390 and [3H]Spiperone was similar in rats of the different ages investigated. These findings suggest that renal dopamine D1-like and D2-like receptors undergo maturational changes in the first 3 weeks after birth and then are stabilized at the adult levels. The possibility that the increased expression of renal dopamine receptors postnatally may be linked with the gradual appearance of dopamine-mediated renal responses after birth is discussed.

Muscarinic cholinergic receptor subtypes expression by human placenta

The presence of a cholinergic system in the placenta is suggested by several data, but no information is available concerning cholinergic receptor expression by placenta. The present study was designed to investigate muscarinic cholinergic receptors in sections of human placenta using a radioligand binding techniques with [3H]N-methyl scopolamine ([3H]NMS) as a ligand. [3H]NMS was bound to sections of human placenta in a manner consistent with the labelling of muscarinic cholinergic receptors. The dissociation constant (Kd) value was 0.1 +/- 0.03 nM and the maximum density of binding site (Bmax) value was 10.82 +/- 0.09 fmol/mg of tissue. The binding was time-, temperature- and concentration-dependent, belonging to one class of high affinity sites. Analysis of [3H]NMS displacement curves by compounds acting on the different subtypes of muscarinic cholinergic receptor subtypes suggests that human placenta expresses the four subtypes (M1-M4) of muscarinic cholinergic receptor assayable with radioligand binding assay techniques. The demonstration of muscarinic cholinergic recognition sites in human placenta may contribute to define the possible significance of placental cholinergic system. Moreover, human placenta can be used as an easily obtainable human source of M1-M4 muscarinic cholinergic receptor subtypes.