Dopamine D1 binding sites in the striatum of the mutant mouse weaver

In the weaver mouse there is a major abnormality in the dopamine-containing innervation of the striatum. Dopamine islands from during development, along with some innervation of the non-islandic matrix; but during the first postnatal month much of the islandic innervation degenerates and there is a failure of the normal postnatal development of the diffuse nigrostriatal innervation. In the experiments reported here we analysed the distribution of D1 dopamine receptor-related binding sites in the weaver striatum in an effort to test the relationship between the dopamine-containing innervation of the striatum and the synthesis and distribution of dopamine receptors there. Dopamine D1 receptor binding sites labeled by the D1 specific antagonist [3H]SCH 23390 were studied in the striatum of 7-day and adult homozygous weaver (wv/wv) and homozygous control (+/+) mice. Saturation analysis of [3H]SCH 23390 binding in adult animals suggested that the dissociation constants of the binding sites are similar in mutants and controls. The Bmax values in the striatum of weavers were 16% higher than in the controls when the data were expressed as fmoles/mg protein. The protein content of the adult weaver's striatum was decreased by 15 to 30%, however, so that when values were expressed as fmoles/section, no significant difference between values in weavers and homozygous controls were found. Quantitative autoradiography supported the results of saturation analysis. We conclude that the apparent increase of [3H]SCH23390 binding sites in the mutants occurred as the result of shrinkage of the weaver's caudoputamen and that dopamine D1 receptor binding sites in the caudoputamen, as assessed with [3H]SCH 23390, are normal. The studies of regional distribution of [3H]SCH 23390 binding sites in 7-day and adult mice indicated that the characteristic postnatal transition of the [3H]SCH 23390 binding pattern from islandic to a diffuse distribution occurred normally in the weaver's caudoputamen. Thus, in spite of the degeneration and failure of development of the nigrostriatal innervation in weaver mice, D1 binding in the weaver's striatum undergoes the elaborate change in distribution of these sites that is a hallmark of normal striatal development.     

Microtopography of D1 dopaminergic binding sites in the human substantia nigra: an autoradiographic study

The autoradiographic distribution of D1 dopaminergic binding sites was studied in the human ventral mesencephalon using the D1 antagonist [3H]SCH 23390. [3H]SCH 23390 binding was characterized by a single class of sites with a Kd of 2.5 nM and a Bmax of 31 fmol/mg of tissue. The density of [3H]SCH 23390 binding sites was high in the substantia nigra, moderate in the ventral tegmental area and low in the peri- and retrorubral field (catecholaminergic region A8). Binding densities were similar in pars compacta and pars reticulata of the substantia nigra, except for a peak value of high [3H]SCH 23390 in the pars reticulata, at a level just ventral to a zone of hyperdensity of melanized dopaminergic neurons in the pars compacta. The anatomical organization of the human ventral mesencephalon was analysed on adjacent sections stained for acetylcholinesterase histochemistry and tyrosine hydroxylase, substance P, dynorphin B, somatostatin and methionine-enkephalin immunohistochemistry, respectively. The similarity in distribution of [3H]SCH 23390 binding sites and substance P or dynorphin B immunoreactivity suggests that D1 binding sites are mainly located on the striatonigral projections. In accordance with these results: (1) the density of [3H]SCH 23390 binding sites was reduced in the substantia nigra of a patient with Huntington's chorea, a disease associated with a degeneration of striatonigral neurons; (2) the density of [3H]SCH 23390 binding sites was unaffected in the substantia nigra of a patient with Parkinson's disease, a disorder characterized by a marked loss in nigral tyrosine hydroxylase-positive neurons. [3H]SCH 23390 binding sites showed a characteristic, heterogeneous distribution within the human ventral mesencephalon, confirming data obtained in other species. The preferential localization of D1 dopamine receptors on striatonigral projections in human brain suggests that pharmacological manipulation of these receptors modulates the activity of striatonigral pathways, thereby affecting the various outputs of the nigral complex.     

Autoradiographic identification of D1 dopamine receptors labelled with [3H]dopamine: distribution, regulation and relationship to coupling.

On the basis of experiments made on striatal membranes, Leff and Creese [Molec. Pharmac. (1985) 27, 184-192] have proposed that tritiated dopamine binds to a high-affinity agonist state of D1 dopamine receptors (D1h) which adopt this conformation when they are associated with the GTP-binding protein involved in the transduction process. Quantitative autoradiography was thus used to look for the distribution of these D1h sites in the rat brain and to compare it with that of D1 receptors labelled with [3H]7-chloro-8-hydroxy-3-methyl-1-phenyl-2,3,4,5-tetrahydro-1H-3-benz aze pine [( 3H]SCH23390), a D1 antagonist. The effects of unilateral 6-hydroxydopamine lesion of the ascending dopamine pathways on the density of [3H]dopamine D1h and [3H]SCH23390 binding sites in the striatum and the nucleus accumbens were also analysed. In the striatum, when D2 receptors were blocked by spiroperidol (20 nM), [3H]dopamine was found to bind specifically to dopamine receptors of the D1 type. Complementary experiments made with dopamine uptake blockers indicated that high-affinity dopamine uptake sites were not labelled by [3H]dopamine under our experimental conditions. The anatomical distribution of [3H]dopamine D1h binding sites was found to be markedly different from that of [3H]SCH23390 binding sites. This was particularly the case in the substantia nigra, some amygdaloid nuclei and the prefrontal cortex--structures in which the ratios between [3H]SCH23390 and [3H]dopamine binding sites were more than seven-fold higher than that observed in the striatum. [3H]SCH23390 binding was not significantly affected in either the striatum or the nucleus accumbens six weeks after a complete unilateral destruction of ascending dopamine pathways. In contrast, a marked decrease in [3H]dopamine D1h binding sites was found in both structures, but this effect was lower in the medioventral (-60%) than in the laterodorsal (-81%) part of the striatum, even though dopamine denervation was uniform throughout the structure. Preincubation of the sections with dopamine (0.5 microM) led to a partial recovery (+126%) in the lesioned striatum and an increase of [3H]dopamine labelling in the control striatum (+68%). This suggest that the presence of dopamine stabilizes the D1h state of D1 receptors. The absence or low amount of dopamine, either due to dopamine denervation or naturally occurring (prefrontal cortex), would then impair the [3H]dopamine D1h binding. In addition, a lower coupling of D1 receptors with adenylate cyclase was observed in the substantia nigra when compared to that in the striatum: this may explain the relatively weak [3H]dopamine binding in the substantia nigra.(ABSTRACT TRUNCATED AT 400 WORDS)     

Long-term changes in striatal D1 dopamine receptor distribution after dopaminergic deafferentation

The morphochemical disposition of the adenylate cyclase-linked dopamine receptor (D1 type) in the rat striatum has been assessed at various time points after a neurotoxic lesion of the dopaminergic afferent pathway to the caudate nucleus. D1 receptor binding sites in the caudate nucleus were determined by in vitro autoradiography of the substituted benzazepine D1 antagonists, [3H]SCH 23390 or [125I]SCH 23982, and contrasted to the pattern of striatal immunohistochemical reactivity of the second messenger compound, cyclic 3',5'-adenosine monophosphate. The results demonstrate that the specific association of this dopamine receptor type with cyclic 3',5'-adenosine monophosphate-stained neurons is abolished at 7 days following chemical interruption of the nigrostriatal pathway, and the receptor disruption is persistent for durations as long as 20 weeks. This investigation suggests that once the postsynaptic receptor pathology is produced by deafferentation, it does not recover the selective morphochemical relationship normally established with the target cell containing the second messenger. This is in contrast to modest biochemical recuperation in D1 dopamine receptor binding seen using this experimental paradigm. This change in D1 dopamine receptor morphochemistry is discussed in relation to the neurochemical deficits produced by dopaminergic denervation and in Parkinson's disease.     

Forebrain D1 function and sensorimotor gating in rats: effects of D1 blockade, frontal lesions and dopamine denervation

Prefrontal D1 hypoactivity is implicated in the pathophysiology of schizophrenia, and might contribute to sensorimotor gating deficits in schizophrenia patients, based on evidence that D1 blockade in the medial prefrontal cortex (MPFC) reduces prepulse inhibition of startle (PPI) in animal models. PPI is disrupted by systemic and intra-MPFC infusion of the D1 antagonist, SCH23390. We investigated the role of the MPFC in the PPI-disruptive effects of systemic SCH23390 administration, and more generally, in the dopaminergic regulation of PPI. PPI was measured in rats after forebrain manipulations, including systemic administration of SCH23390, ibotenic acid lesions of the MPFC, and 6OHDA-induced dopamine (DA) depletion from MPFC or nucleus accumbens. Systemic SCH23390 disrupted PPI; these effects were not opposed by ibotenic acid lesions of the MPFC. PPI remained intact after MPFC DA depletion, but--as predicted by Bubser and Koch [M. Bubser, M. Koch, Prepulse inhibition of the acoustic startle response of rats is reduced by 6 hydroxydopamine lesions of the medial prefrontal cortex, Psychopharmacology 113 (1994) 487-492]--a reduction in PPI from pre- to post-surgery correlated significantly with MPFC DA loss. The effects of systemic SCH23390 were not opposed by NAC DA depletion. D1 receptors regulate PPI in rats, but this effect does not appear to be mediated either by the MPFC or by increased mesolimbic DA activity.     

D1-receptor antagonists: comparison of [3H]SCH39166 to [3H]SCH23390.

A radiolabeled form of the benzonaphthazephine, SCH39166 was used to characterize the binding of this D1 antagonist in cortex, and an autoradiographic comparison of the localization of [3H]SCH39166 to [3H]SCH23390 (D1 antagonist and forerunner of SCH39166) binding was performed. The Kd for [3H]SCH39166, calculated from dissociation and association rate constants (1.09 nM), was comparable to the Kd value derived from Scatchard analyses of saturation data (1.74 nM). [3H]SCH39166 binds to brain tissue in a saturable manner with high affinity and low non-specific binding. Inhibition of [3H]SCH39166 binding by dopaminergic and serotonergic agents supports the hypothesis that this is indeed a D1-specific compound with little overlap onto serotonin (5-HT) receptors. The affinity of [3H]SCH39166 for 5-HT2 and 5-HT1c receptors is at least an order of magnitude lower than the affinity of [3H]SCH23390 for these same receptor sites. Quantitative autoradiographic analysis of [3H]SCH39166 and [3H]SCH23390 binding indicates high D1-receptor density in the caudate-putamen, nucleus accumbens, olfactory tubercle, substantia nigra and entopeduncular nucleus. Low levels of binding (not significantly above background) were detected with [3H]SCH39166 in lamina IV of the cortex and in choroid plexus; areas which had significant [3H]SCH23390 binding and are known to have a high density of 5-HT (5-HT2 and 5-HT1c respectively) receptors.     

Different plasticity changes in D1 and D2 receptors in rat striatal subregions following impairment of dopaminergic transmission

The precise topographical changes in striatal D1 and D2 dopamine receptor density that occurred after chronic treatment with haloperidol or SCH 23390 or after 6-hydroxydopamine-induced lesion of the mesostriatal dopaminergic pathway have been studied autoradiographically in the rat. Repeated treatment with SCH 23390 (0.5 mg/kg i.p., 21 days) caused an almost similar increase in [3H]SCH 23390 binding sites in the different striatal subregions whereas lesion of the dopaminergic pathway was ineffective. Subacute administration of haloperidol (2 mg/kg i.p., 18 days) or lesion of dopaminergic afferents provoked an increase in [3H]spiperone binding which was restricted to the ventro- and dorsolateral striatal sectors.     

Different neuronal location of [3H]SCH 23390 binding sites in pars reticulata and pars compacta of the substantia nigra in the rat

The precise neuronal localization of D1 receptors in the substantia nigra has been studied autoradiographically in the rat by measuring the alterations of [3H]SCH 23390 binding site densities in this brain area after 6-hydroxydopamine (6-OHDA) induced destruction of nigrostriatal dopaminergic neurons and after ibotenate-induced lesion of striatal afferents. 6-OHDA-induced nigral lesion provoked a total loss of [3H]SCH 23390 binding sites in the pars compacta and pars lateralis (but not in the pars reticulata) of the substantia nigra. In contrast, ibotenate-induced striatal lesion caused a large diminution of the [3H]ligand binding site density in the pars reticulata but not in the pars compacta and pars lateralis of the substantia nigra. These results suggest that D1 receptors in the pars compacta or pars lateralis of the substantia nigra are located on the dopaminergic perikarya whereas those D1 receptors present in the pars reticulata of the substantia nigra lie on the terminals of nigral afferents of striatal origin.     

Chronic eticlopride and dopamine denervation induce equal nonadditive increases in striatal D2 receptor density: autoradiographic evidence against the dual mechanism hypothesis.

In an attempt to resolve experimental discrepancies regarding the mode of action of D2 receptor regulation following denervation or chronic receptor blockade, rats with extensive unilateral destruction of the mesotelencephalic dopaminergic projections induced by intracerebral 6-hydroxydopamine were injected daily for 21 days with either saline or the potent, selective D2 antagonist eticlopride (0.5 mg/kg, i.p.). Four days after the last injection of eticlopride or saline, rats were killed, and brain sections through the caudate-putamen and nucleus accumbens septi were incubated with [3H]spiroperidol or (R)-(+)-8-chloro-2,3,4,5-tetrahydro-3-methyl-5- phenyl-1H-3-benzazepin-7-ol ([3H]SCH 23390) to assay D2 and D1 receptors, respectively. Autoradiographic analysis revealed that chronic eticlopride treatment increased the density of D2 sites in the intact hemisphere for all regions examined without further augmenting the already increased density of D2 receptors seen in the dopamine-denervated hemisphere. D2 receptor density was independent of functional sensitivity as evidenced by the fact that rats treated chronically with eticlopride rotated contralateral to the 6-hydroxydopamine lesion following systemic administration of the selective D2 agonist quinpirole during the neuroleptic wash-out period, despite the fact that D2 receptor binding was not significantly different in the left and right hemispheres of these subjects. D1 receptor density was not affected by eticlopride treatment but was significantly reduced reduced in the dopamine-denervated hemisphere. [3H]Mazindol labeling of high-affinity DA uptake sites indicated that the extent of dopamine denervation was greater than 97% in both saline- and eticlopride-treated rats.(ABSTRACT TRUNCATED AT 250 WORDS)     

Distribution and postnatal ontogeny of adenosine A2A receptors in rat brain: comparison with dopamine receptors

In adult rat brain, adenosine A_2A receptors and dopamine D₂ receptors are known to be located on the same cells where they interact in an antagonistic manner. In the present study we wanted to examine when this situation develops and compared the postnatal ontogeny of the binding of the adenosine A_2A receptor agonist [³H]CGS 21680, the binding of the dopamine D₁ receptor antagonist [³H]SCH 23390 and the dopamine D₂ receptor antagonist [³H]raclopride.

All three radioligands bound to the striatum at birth and this binding increased several-fold during the postnatal period. [³H]SCH 23390 binding developed first (mostly during the first week), followed by [³H]raclopride binding (first to third week) and [³H]CGS 21680 binding (only during second and third week). For all three radioligands the binding tended to decrease between 21 days and adulthood. This occurred earlier and was more pronounced in the globus pallidus than in the other examined structures. The increase in [³H]CGS 21680 binding from newborn to adult was mainly due to four-fold increase in the number of binding sites. The pharmacology of [³H]CGS 21680 binding to caudate–putamen was similar in newborn, one-week-old and adult animals, and was indicative of A_2A receptors. The binding was inhibited by guanylyl imidodiphosphate at all ages, indicating that A_2A receptors are G-protein-coupled already at birth. In contrast to the large increase in [³H]CGS 21680 binding, there was a decrease in the levels of A_2A messenger RNA during the postnatal period in the caudate–putamen. In cerebral cortex [³H]CGS 21680 bound to a different site than the A_2A receptor. From birth to adulthood cortical binding of [³H]CGS 21680 increased four-fold and that of the adenosine A₁ agonist [³H]cyclohexyladenosine 19-fold. During early postnatal development [³H]SCH 23390 binding was higher in deep than in superficial cortical layers, but this difference disappeared in adult animals. There was binding of both [³H]CGS 21680 and [³H]cyclohexyladenosine to the olfactory bulb, suggesting a role of the two adenosine receptors in processing of olfactory information. [³H]CGS 21680 binding was present in the external plexiform layer and glomerular layer, and increased during development, but the density of binding sites was about one tenth of that seen in caudate–putamen. [³H]cyclohexyladenosine showed a very different labelling pattern, resembling that observed with [³H]SCH 23390.

Postnatal changes in adenosine receptors may explain age-dependent differences in stimulatory caffeine effects and endogenous protection against seizures. Since A_2A receptors show a co-distribution with D₂ receptors throughout development, caffeine may partly exert such actions by regulating the activity of D₂ receptor-containing striatopallidal neurons     

The effects of D1 or D2 dopamine receptor antagonism in the medial preoptic area, ventral pallidum, or nucleus accumbens on the maternal retrieval response and other aspects of maternal behavior in rats

The medial preoptic area (MPOA), ventral pallidum (VP), and nucleus accumbens (NA) receive dopaminergic afferents and are involved in maternal behavior. Experiments investigated whether dopamine (DA) receptor antagonism in NA disrupts maternal behavior, determined the type of DA receptor involved, and investigated the involvement of drug spread to VP or MPOA. Injection of SCH 23390 (D1 DA receptor antagonist) into NA of postpartum rats disrupted retrieving at dosage levels that were ineffective when injected into MPOA or VP. Motor impairment was not the cause of the deficit. Injection of eticlopride (D2 DA receptor antagonist) into NA or VP was without effect. Results emphasize the importance of DA action on D1 receptors in NA for retrieval behavior.     

The D1 dopamine receptor in the rat brain: quantitative autoradiographic localization using an iodinated ligand

The distribution of dopamine D1 receptors in the rat, labeled with [125I]SCH 23982, was studied using a quantitative in-vitro light-microscopic autoradiographic method. The binding of [125I]SCH 23982 to slide-mounted tissue sections and membrane preparations of prefrontal cortex was saturable, specific and of high affinity. Scatchard analysis revealed a Kd of 1.15 +/- 0.47 nM and Bmax of 8.76 +/- 0.34 fmol/mg tissue in prefrontal cortex membranes and a Kd of 1.27 +/- 0.14 nM and Bmax of 67.6 +/- 3.75 fmol/mg tissue in slide-mounted tissue sections at the level of the striatum. [125I]SCH 23982 was found to predominantly label D1 receptors, but a small fraction of the binding was to serotonin receptors. D1 receptors were found throughout the forebrain and were concentrated in the substantia nigra pars reticulata, accumbens nucleus, caudate putamen, entopeduncular nucleus, olfactory tubercle and the major island of Calleja. [125I]SCH 23982 binding to serotonin receptors was concentrated in the cortices, dorsal raphe, central gray, anterior hypothalamic area and the molecular cell layer of the cerebellum. Knowledge of the distribution of D1 receptors may increase our understanding of the role of D1 receptors in central nervous system dopaminergic function. Furthermore, data on the potential sites of interaction of [125I]SCH 23982 with serotonin receptors may help to understand the complex physiology and pharmacology of the primarily D1 selective compound.     

Prefrontal D1 and ventral hippocampal N-methyl-D-aspartate regulation of startle gating in rats

BACKGROUND: Sensorimotor gating, as measured by prepulse inhibition of the startle reflex, is deficient in schizophrenia patients, and in rats after specific manipulations of limbic cortico-striato-pallido-thalamic circuitry. For example, prepulse inhibition in rats is disrupted after D1 blockade in the medial prefrontal cortex, and after N-methyl-D-aspartate infusion into the ventral hippocampus. In the present study, we examined whether these two substrates form part of an integrated circuit regulating sensorimotor gating, which might contribute to the loss of prepulse inhibition in patient populations. METHODS: Prepulse inhibition was assessed in male Sprague-Dawley rats after systemic or intra-medial prefrontal cortex administration of the D1 antagonist, SCH 23390. Separate rats received intra-medial prefrontal cortex infusion of the retrograde transported label Fluoro-Gold. In rats with sham or electrolytic lesions of the medial prefrontal cortex, prepulse inhibition was tested after infusion of N-methyl-D-aspartate or vehicle into ventral hippocampus regions that were determined to send projections to the medial prefrontal cortex. RESULTS: Prepulse inhibition was disrupted after systemic SCH 23390 treatment and after infusion of SCH 23390 into medial prefrontal cortex sites within the prelimbic and cingulate cortices. Fluoro-Gold infusion into these medial prefrontal cortex sites labeled cells in the ventral hippocampus complex, including regions CA1 and entorhinal cortex. N-methyl-D-aspartate infusions into these ventral hippocampus regions disrupted prepulse inhibition in rats after sham but not electrolytic lesions of the medial prefrontal cortex. CONCLUSIONS: Prepulse inhibition appears to be regulated by interacting substrates within the ventral hippocampus and MPFC. Specifically, NMDA activation of the ventral hippocampus appears to disrupt prepulse inhibition in a manner that is dependent on the integrity of infralimbic or cingulate cortical regions that also support a D1-mediated regulation of prepulse inhibition. Conceivably, dysfunction within these hippocampal-frontal circuits may contribute to sensorimotor gating deficits in schizophrenia.     

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.     

Dopamine inhibition of evoked IPSCs in rat prefrontal cortex.

Rat prefrontal cortex (PFC) receives substantial dopamine (DA) input. This DA innervation appears critical for modulation of PFC cognitive functions. Clinical and experimental studies have also implicated DA in the pathogenesis of a number of neurological and psychiatric disorders including epilepsy and schizophrenia. However, the actions of DA at the cellular level are incompletely understood. Both inhibitory interneurons and pyramidal cells are targets of DA and may express different DA receptor types. Our recent findings suggest that DA can directly excite cortical interneurons and increase the frequency of spontaneous inhibitory postsynaptic currents (IPSCs). The present study was undertaken to determine the effect of specific DA receptor agonists on evoked (e) IPSCs. Visually identified pyramidal neurons were studied using whole cell voltage-clamp techniques. Bath application of DA 30 microM reduced IPSC amplitude to 80 +/- 4% (mean +/- SE) of control without any significant change in IPSC kinetics or passive membrane properties. The D1-like DA receptor agonist SKF 38393 reduced IPSC amplitude to 71.5 +/- 8%, whereas the D2-like specific agonist quinpirole has no effect on amplitude (94.5 +/- 5%). The D1-like receptor antagonist SCH 23390 prevented DA inhibition of IPSC amplitude (98.2 +/- 4%), whereas IPSCs were still reduced in amplitude (79.7 +/- 4%) by DA in the presence of the D2-like receptor antagonist sulpiride. DA increased significantly paired-pulse inhibition, whereas responses to puff applied GABA were unaffected. Addition of the PKA inhibitor H-8 blocked the effect of DA on IPSCs. These results suggest that DA can decrease IPSCs in layer II-III PFC neocortical pyramidal cells by activating presynaptic D1-like receptors.     

D1 dopamine receptors distribution following photothrombotic stroke in rat cerebral cortex

The effect of focal photothrombotic stroke on the distribution of D1 dopamine receptor (D1R) sites was examined in different cortical areas of rat brain with quantitative receptor autoradiography using [3H]SCH23390 as a ligand. Unilateral cortical stroke was located in the primary somatosensory cortex. After different survival times (1, 7 and 28 days) D1R binding levels were determined in the lesion core, penumbra, frontoparietal motor (FrPaM) and somatosensory (FrPaSS) areas as well as in homotopic regions in the contralateral hemisphere. One day after stroke, D1R density decreased by 36% (P < 0.01) in the lesion core relative to sham-operated controls. At 7th day binding density was further reduced by 56% (P < 0.002). Twenty-eight days after infarction, D1R binding returned to control level. No alterations in D1R binding levels were found in penumbra and other investigated regions. We suggest that the return of D1R binding to control level in the area initially corresponding to the infarct results from the shrinkage of the lesion volume.     

Effect of unilateral perinatal hypoxic-ischemic brain injury on striatal dopamine uptake sites and D1 and D2 receptors in adult rats.

The effect of unilateral perinatal hypoxic-ischemic brain injury on striatal dopamine uptake sites and on D1 and D2 receptors was investigated in rat by using in vitro quantitative receptor binding autoradiography, 9-11 weeks after the insult. Saturation experiments revealed a significant 20% decrease in maximal binding capacity (Bmax) for [3H]spiperone-labeled D2 receptors on the side of the lesion in comparison to the non-lesioned contralateral side or to either side of control animals. There was no significant change in [3H]mazindol-labeled dopamine uptake sites or in [3H]SCH 23390-labeled D1 receptor characteristics (Bmax and Kd) on the lesioned side. We conclude that the decrease in D2 receptor binding previously observed in immature animals is persistent, whereas the decrease in D1 binding is not.     

Quantitative autoradiographical analysis of the age-related modulation of central dopamine D1 and D2 receptors

Quantitative autoradiography of [3H]SCH 23390 and [3H](-)-sulpiride binding was performed in the brain of rats of various ages (3, 11 and 24 months) in order to study the changes in D1 and D2 receptor density with age. Binding of [3H]SCH 23390 in the caudate-putamen decreased progressively and markedly at rostral levels in 11- and 24- compared with 3-month-old rats (max. decrease -63%) while at caudal levels significant decrease was observed only in 24-month-old rats. [3H](-)-Sulpiride binding progressively decreased during aging in the caudate-putamen at rostral levels and the decrease was more pronounced laterally (-70% at 24 months), while at caudal levels no significant decrease was observed. D1 and D2 binding sites also decreased in the nucleus accumbens and olfactory tubercle of aged rats, while in the substantia nigra only the D1 receptors appeared to be modified with aging. No change was found in the entopeduncular nucleus, amygdala, frontoparietal, suprarinal-prefrontal and anterior cingulate cortex. The results indicate that the age-associated decrease of D1 and D2 receptors is not widespread, being confined to dopaminergic areas with high density of dopamine receptors.     

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.     

Distribution of dopaminergic receptors in the primate cerebral cortex: Quantitative autoradiographic analysis using [H]raclopride, [H]spiperone and [H]SCH23390

A widespread distribution of dopamine D₁ receptors in the neocortex is well recognized. However, the presence of dopamine D₂ receptors in this structure has only recently been established [Martres et al. (1985) Eur. J. Pharmac.118, 211–219; Lidow et al. (1989) Proc. natn. Acad. Sci. U.S.A.86, 6412–6416]. In the present paper, a highly specific antagonist, [³H]raclopride, was used for autoradiographic determination of the distribution of D₂ receptors in 12 cytoarchitectonic areas of the frontal, parietal, and occipital lobes of the rhesus monkey. A low density of D₂-specific [³H]raclopride binding (1.5–4.0 fmol/mg tissue) was detected in all layers of all cortical areas studied. Throughout the entire cortex, the highest density of binding was consistently found in layer V. This is a unique distribution not observed so far for any other neurotransmitter receptor subtype in monkey cerebral cortex, including D₁ receptor. In addition, a comparison was made of the distribution of [³H]raclopride and [³H]spiperone, which has been commonly used in previous attempts to label cortical D₂ receptors. We found marked differences in the distribution of these two radioligands. In the prefrontal cortex, the pattern of [³H]spiperone binding in the presence of ketanserin resembled the combined distribution of 5-HT_ic serotoninergic and ₂-adrenergic sites as well as D₂ receptors. Thus, [³H]raclopride provides a better estimation of the D₂ receptor distribution than does [³H]spiperone. The distribution of D₂-specific binding of [³H]raclopride was also compared with the D₁-specific binding of [³H]SCH23390 in the presence of mianserin to block labeling to 5-HT₂ and 5-HT_IC sites. The density of D₁-specific [³H]SCH23390 binding was 10–20 times higher than that of D₂-speciflc [³H]raclopride binding throughout the cortex. The densities of both [³H]raclopride and [³H]SCH23390 binding sites display a rostral-caudal gradient with the highest concentrations in prefrontal and the lowest concentrations in the occipital cortex. However, the binding sites of these two ligands had different laminar distributions in all areas examined. In contrast to preferential [³H]raclopride binding in layer V, a bilaminar pattern of [³H]SCH23390 labeling was observed in most cytoarchitectonic areas, with the highest concentrations in supragranular layers I, II and IIIa and infragranular layers V and VI. Whereas [³H]raclopride binding was similar in all cytoarchitectonic areas, [³H]SCH23390 exhibited some region-specific variations in the primary visual and motor cortex.

The different regional and laminar distributions of D₁ and D₂ dopaminergic receptors indicates that they may subserve different aspects of dopamine function in the cerebral cortex.