Dopamine Receptor Binding Sites Research Articles

Dopamine receptor binding sites in the rat superior colliculus.

Following intravenous administration of [3H]spiperone or [3H]N,n-propylnorapomorphine (NPA) to rats, radioactivity derived from the ligands accumulated in the striatum and superior colliculus when compared with cerebellar levels. The accumulation of [3H]spiperone in both areas was prevented by intraperitoneal administration of (+)-butaclamol, haloperidol and sulpiride but not by (-)-butaclamol, cinanserin, propranolol or prazosin. The accumulation of [3H]NPA was prevented by administration of (+)-butaclamol, haloperidol and apomorphine but not by (-)-butaclamol. In in-vitro experiments, membrane preparations from the superior colliculus showed a small number of specific binding sites for both [3H]spiperone and [3H]NPA. The dissociation constant (KD) for [3H]NPA was not different from that for striatal preparations but that for [3H]spiperone was 10-fold higher. We conclude that dopamine receptors may be present within the superior colliculus.

Effects of Chronic Alcohol and Repeated Deprivations on Dopamine D1 and D2 Receptor Levels in the Extended Amygdala of Inbred Alcohol‐Preferring Rats

Dopaminergic (DA) activity in the extended amygdala (EA) has been known to play a pivotal role in mediating drug and alcohol addiction. Alterations of DA activity within the EA after chronic exposure to alcohol or substances of abuse are considered a major mechanism for the development of alcoholism and addiction. To date, it is not clear how different patterns of chronic alcohol drinking affect DA receptor levels. Therefore, the current studies investigated the effects of chronic ethanol consumption, with or without deprivations, on D1 and D2 receptor densities within the EA. Inbred alcohol-preferring (iP) rats were divided into 3 groups with the following treatments: (1) water for 14 weeks; (2) continuous alcohol (C-Alc) for 14 weeks [24-hour concurrent access to 15 and 30% (v/v) ethanol]; or (3) repeatedly deprived of alcohol (RD-Alc) (24-hour concurrent access to 15 and 30% ethanol for 6 weeks, followed by 2 cycles of 2 weeks of deprivation of and 2 weeks of reexposure to ethanol access). At the end of 14 weeks, the rats were killed for autoradiographic labeling of D1 and D2 receptors. Compared with the water control group, both the C-Alc and the RD-Alc groups displayed increases in D1 receptor binding density in the anterior region of the Acb core, whereas the RD-Alc group displayed additional increases in D1 receptor binding density in anterior regions of the lateral and intercalated nuclei of the amygdala. Additionally, both C-Alc and RD-Alc rats displayed increases in D2 receptor binding density in anterior regions of the Acb shell and core, whereas RD-Alc rats displayed additional increases in D2 receptor binding density in the dorsal striatum. The results of this study indicate that 14-week extended alcohol drinking with continuous chronic or repeated deprivations increase binding sites of D1 and D2 receptors in specific regions of the EA with greater sensitivity in the anterior regions. The repeated deprivation has greater effect on altering D1 and D2 receptor binding sites in the Acb, dorsal striatum, and subamygdala regions. The current result indicates that the two drinking paradigms may have common as well as differential mechanisms on alteration of dopamine receptor-binding sites in specific regions of the EA.

Increased dopamine receptor signaling and dopamine receptor-G protein coupling in denervated striatum.

Chronic interruption of the nigrostriatal dopaminergic pathway leads to sensitized dopaminergic responses in striatum. We attempted to explore the mechanism(s) underlying this dopaminergic supersensitivity by assessing dopamine receptor signaling and receptor-G protein coupling in unilateral 6-hydroxydopamine-lesioned rats. Dopamine-stimulated adenylyl cyclase activity as well as dopamine-activated guanosine 5'-O-(3-[(35)S]thiotriphosphate) ([(35)S]GTPgammaS) binding and [(3)H]palmitate incorporation by Galpha proteins were enhanced in tissues obtained from denervated striata without apparent changes in Galpha protein levels. Moreover, high-affinity binding sites of the D(1) dopamine receptor increased in lesioned compared with control striata without altering the expression level of the receptor. These denervation-mediated changes appear to correlate with the increase in D(1) dopamine receptor binding sites that co-immunoprecipitated with Galphas(olf)/q(11) proteins. In contrast, the total number of D(2) receptor binding sites was increased, yielding an increase in absolute number of high-affinity sites without significant changes in the proportion of high-affinity sites. Stimulation of the D(2) dopamine receptor enhanced coupling to Galphai protein; this was increased in the striata lesioned. The results provide an important molecular mechanism by which dopamine receptor-regulated signaling is enhanced following denervation of dopaminergic input to striatum. Although D(1) dopamine receptor supersensitivity appears to be mediated by enhanced coupling of the receptor to its G proteins, sensitization in the D(2) dopamine receptor system is mediated by increased D(2) receptor density and enhanced D(2) receptor-Gi protein coupling.

Defective dopamine receptor function in proximal tubules of obese zucker rats.

Some of the pathophysiological consequences of obesity include insulin resistance, increased renal sodium reabsorption, and the development of hypertension. Dopamine promotes renal sodium excretion via activation of D(1)-like receptors present on the proximal tubules. Reduced dopamine-induced natriuresis and a defect in D(1)-like receptor function have been reported in the proximal tubules of hypertensive animals. The present study investigated D(1)-like dopamine receptors and associated G proteins as the initial signaling components in the proximal tubular basolateral membranes of obese Zucker and control lean Zucker rats. We found that the obese rats were hyperinsulinemic, hyperglycemic, and hypertensive compared with the lean rats. Dopamine produced concentration-dependent inhibition of Na,K-ATPase activity in the proximal tubules of lean rats, whereas the inhibitory effect of dopamine was reduced in obese rats. The D(1)-like receptors measured by [(3)H]SCH 23390 binding revealed an approximately 45% decrease in B(max) without a change in K(d) in the basolateral membranes of obese rats compared with lean rats. Although we found an increase in G(q)/11alpha and no change in G(s)alpha in the basolateral membranes of obese rats, dopamine and SKF 38393 failed to stimulate G proteins as measured by [(35)S]GTPgammaS binding in obese rats, suggesting a receptor-G protein coupling defect. We conclude that decrease in D(1)-like dopamine receptor binding sites and diminished activation of G proteins, resulting perhaps from defective coupling, led to the reduced inhibition by dopamine of Na,K-ATPase activity in the proximal tubules of obese Zucker rats. Such a defect in renal dopamine receptor function may contribute to sodium retention and development of hypertension in obese rats.

Are high-affinity progesterone binding site(s) from porcine liver microsomes members of the σ receptor family?

Membrane progesterone binding sites have been purified recently from pig liver. Since progesterone is considered as an endogenous sigma ( σ) receptor ligand, these sites were characterized pharmacologically by ligands selective for σ receptor and dopamine receptor binding sites, and by other drugs from distinct pharmacological classes. Binding studies using the radioligand [ 3H]progesterone were done in crude membrane preparations and solubilized fractions to determine half-maximal inhibitory concentration (IC 50) values, from which inhibitory constants ( K i values) were calculated. Radioligand binding was inhibited by the σ receptor ligands haloperidol, carbetapentane citrate, 1,3-Di(2-tolyl)guanidine (DTG), R(−)- N-(3-phenyl-1-propyl)-1-phenyl-2 aminopropane HCl ( R(−)-PPAAP HCl), or σ receptor antagonists like (+)-3-(3-hydroxyphenyl)- N-propylpiperidine HCl ( R(+)-PPP HCl) and cis-9-[3-(3,5-dimethyl-1-piperazinyl)propyl]-9 H-carbazole dihydrochloride (rimcazole 2HCl). The hierarchy of inhibitory action was not fully compatible with either σ receptor class I (moderate affinity of pentazocine, diphenylhydantoin (phenytoin) insensitivity) or II sites (high affinity of carbetapentane). The data thus suggest that progesterone binding sites in porcine liver membranes are related to the σ receptor binding site superfamily, but may represent a particular species with progesterone specificity.

D1 receptors mediate dopamine action in the fetal suprachiasmatic nuclei: studies of mice with targeted deletion of the D1 dopamine receptor gene

Studies in rodents suggest the presence of a dopaminergic system that influences the function of a biological clock in the hypothalamic suprachiasmatic nuclei (SCN). To provide insights into mechanisms of dopamine action in the SCN, we studied transgenic mice that had either one allele (+\\−) or both alleles (−/−) of the D1 dopamine receptor gene deleted, along with normal (+/+) littermates. As expected, receptor labelling autoradiography studies using [ 125I ] SCH 23982 showed a complete absence of D1 dopamine receptor binding sites in the SCN of −/− animals. When pregnant mice from +\\−×+\\− matings were injected with the D1 receptor agonist SKF 38393, or the dopamine reuptake blocker GBR 12909 at day 19 of gestation, c- fos mRNA expression was observed in the SCN of +/+ fetuses. In contrast, c- fos mRNA induction was not seen in −/− or +\\− litter mates. Injection of cocaine into pregnant dams also resulted in robust SCN c- fos mRNA expression in +/+ mice. Increases in SCN c- fos mRNA expression were also seen in +\\− and −/− mice suggesting that cocaine action in the SCN involves both D1 receptor-dependent and -independent mechanisms. Collectively, our studies of transgenic mice deficient in D1 receptors support the presence of a functional dopaminergic system in the fetal SCN. We also identify D1 receptors as the prominent transducer of dopamine action in the fetal SCN.

Mitochondrial toxins in models of neurodegenerative diseases. II: elevated zif268 transcription and independent temporal regulation of striatal D1 and D2 receptor mRNAs and D1 and D2 receptor-binding sites in C57BL/6 mice during MPTP treatment

Sporadic Parkinson's disease (PD) may arise from a defect in complex I of the mitochondrial electron transport chain (ETC), transmitted through mitochondrial DNA mutations. The N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) model of experimental PD is believed to arise from loss of complex I activity in dopamine (DA) neurons after accumulation of MPP+, a potent complex I inhibitor and the two electron monoamine oxidase B oxidation product of MPTP. Acute MPP+ infusion into striatum, possibly mimicking the in vivo situation after MPTP treatment, increases release of DA and production of hydroxyl radical ( ⋅OH). We treated C57BL/6 mice with MPTP and followed the expression of the immediate-early gene zif268 in striatum as a marker of DA synaptic activity, determined the pharmacology of its activation during MPTP toxicity, and assayed the time course of MPTP effects on striatal DA transporter (DAT), and D1 and D2 DA receptor-binding sites and their mRNAs. MPTP (24 mg/kg b.i.d. for 4 doses) increased striatal zif268 expression, with peak effects observed 24 h after starting MPTP. Increased striatal zif268 was dependent mainly on DA D1 and to a lesser extent on non-NMDA glutamate receptors and was not altered by inhibition of nitric oxide synthase (NOS). Our MPTP schedule resulted in a loss of about one-third of nigral DA neurons. We observed with [ 3H]mazindol autoradiography that loss of striatal DAT sites after starting MPTP was heterogenous and greatest in centromedial striatum, reached a maximum at 48 h and showed a slight recovery at 2 weeks. Striatal D1 and D2 receptor-binding sites (measured with [ 3H]SCH23390 and [ 3H]spiperone binding, respectively) and mRNA levels for D1 and D2 receptors (determined with quantitative in situ hybridization) were altered after MPTP treatment in temporally independent manners. MPTP toxicity to the nigrostriatal system likely induces substantial striatal DA release in vivo and stimulates transcription of at least one major IEG, zif268, in striatal neurons. Increased striatal zif268 expression after MPTP appears to derive mainly from DA released onto D1 receptors, not by a NO-dependent process which has been described in striatal neurons in vitro. The rapid loss of striatal DA terminals after MPTP treatment alters D1 and D2 receptor sites independently of changes in their mRNA levels. Increased D1 and D2 gene transcription in this model may depend on re-innervation by DA terminals of striatal neurons and likely is not related to the increased zif268 transcription observed after MPTP.

Development of striatal dopaminergic function. I. Pre- and postnatal development of mRNAs and binding sites for striatal D1 (D1a) and D2 (D2a) receptors.

Quantitative receptor autoradiography with iodinated ligands, quantitative in situ hybridization histochemistry and reverse transcriptase-polymerase chain reaction (RT-PCR) were used to describe the prenatal and early postnatal ontogeny (embryonic day 14 to postnatal day 7, or E14 to P7) of striatal D1 and D2 dopamine receptor binding sites and mRNA levels, respectively, in relation to the development of dopaminergic nigrostriatal innervation D1 dopamine receptor, measured by [125I]SCH23982 binding, and dopamine transporter binding sites, measured by [125I]RTI-55 binding, were present in low amounts beginning on E14 (2-3% and 0.3-0.6% of adult values, respectively) and increased slowly during the prenatal period. D2 receptor binding sites, measured with [125I]spiperone, were also detected on E14 but in higher relative quantities (17% of adult values) than D1 receptor and dopamine transporter binding sites at the same age. Other than abrupt declines in the late prenatal period for D1 and D2 receptor binding sites, all three binding sites increased throughout development and increased maximally between P7 and adulthood. On P5, both D1 and D2 receptors were functionally coupled to their respective G proteins, based on GTP-induced decreases in affinity of dopamine for [125I]SCH23982 and [125I]spiperone binding. D1 receptor mRNA was present in E14 striatal anlage, increased prenatally, declined on P0, then increased to a peak on P5, after which it declined to its lowest levels (20% of peak values) in the adult. In contrast, D2 receptor mRNA levels were presented also on E14, increased to a peak on P0, declined until P5, and increased thereafter to adulthood. Anatomically, nigrostriatal innervation and D1 and D2 receptor mRNA levels increased from the medial to lateral striatal quadrants. In contrast, D1 and D2 receptor binding site ontogency exhibited fairly homogenous distributions from E18 to P7. D1 and D2 receptor mRNAs appear to be expressed early in prenatal development before there is any significant dopaminergic innervation. In contrast, the majority of D1 and D2 receptor binding activity, representing expressed receptor proteins, develops in the postnatal period and correlates well with the increase in dopaminergic innervation. Intrinsic genetic programming is more likely to be responsible for D1 and D2 receptor gene transcription in striatal neuroblasts and newly born neurons, while factors derived from ingrowing dopaminergic afferents may direct post-transcriptional dopamine receptor development. The dissociation between the ontogeny of dopamine receptor binding sites and mRNAs suggests that the developmental regulation of D1 and D2 receptor synthesis is independent of D1 and D2 receptor gene transcription.

Development of striatal dopaminergic function. I. Pre- and postnatal development of mRNAs and binding sites for striatal D1 (D1a) and D2 (D2a) receptors

Quantitative receptor autoradiography with iodinated ligands, quantitative in situ hybridization histochemistry and reverse transcriptase-polymerase chain reaction (RT-PCR) were used to describe the prenatal and early postnatal ontogeny (embryonic day 14 to postnatal day 7, or E14 to P7) of striatal D1 and D2 dopamine receptor binding sites and mRNA levels, respectively, in relation to the development of dopaminergic nigrostriatal innervation. D1 dopamine receptor, measured by [ 125I]SCH23982 binding, and dopamine transporter binding sites, measured by [ 125I]RTI-55 binding, were present in low amounts beginning on E14 (2–3% and 0.3–0.6% of adult values, respectively) and increased slowly during the prenatal period. D2 receptor binding sites, measured with [ 125I]spiperone, were also detected on E14 but in higher relative quantities (17% of adult values) than D1 receptor and dopamine transporter binding sites at the same age. Other than abrupt declines in the late prenatal period for D1 and D2 receptor binding sites, all three binding sites increased throughout development and increased maximally between P7 and adulthood. On P5, both D1 and D2 receptors were functionally coupled to their respective G proteins, based on GTP-induced decreases in affinity of dopamine for [ 125I]SCH23982 and [ 125I]spiperone binding. D1 receptor mRNA was present in E14 striatal anlage, increased prenatally, declined on P0, then increased to a peak on P5, after which it declined to its lowest levels (20% of peak values) in the adult. In contrast, D2 receptor mRNA levels were present also on E14, increased to a peak on P0, declined until P5, and increased thereafter to adulthood. Anatomically, nigrostriatal innervation and D1 and D2 receptor mRNA levels increased from the medial to lateral striatal quadrants. In contrast, D1 and D2 receptor binding site ontogeny exhibited fairly homogeneous distributions from E18 to P7. D1 and D2 receptor mRNAs appear to be expressed early in prenatal development before there is any significant dopaminergic innervation. In contrast, the majority of D1 and D2 receptor binding activity, representing expressed receptor proteins, develops in the postnatal period and correlates well with the increase in dopaminergic innervation. Intrinsic genetic programming is more likely to be responsible for D1 and D2 receptor gene transcription in striatal neuroblasts and newly born neurons, while factors derived from ingrowing dopaminergic afferents may direct post-transcriptional dopamine receptor development. The dissociation between the ontogeny of dopamine receptor binding sites and mRNAs suggests that the developmental regulation of D1 and D2 receptor synthesis is independent of D1 and D2 receptor gene transcription.

Sulfhydryl groups of renal D1A dopamine receptors: differential sensitivity of receptors to N-ethylmaleimide in normotensive and hypertensive rats.

To determine whether sulfhydryl groups are present on D1A receptors of spontaneously hypertensive rats (SHR) and to test the hypothesis that failure of agonists to bind to such receptors is linked to microstructural changes involving sulfhydryl groups. Alkylation of renal proximal tubule membranes by N-ethylmaleimide caused 70% loss of D1A dopamine receptor binding sites in the normotensive Wistar-Kyoto (WKY) rat and the SHR. The concentration of N-ethylmaleimide (IC50) required to produce half-maximal loss of receptor binding was 5.2 and 1200 mumol/l in WKY rats and SHR, respectively. Previous receptor occupancy of WKY rat D1A sites by the D1A agonist SKF R-38393 completely protected the binding sites from N-ethylmaleimide-mediated inactivation. Occupancy with the D1A antagonist SCH 23390 partially protected the binding sites and produced a 500-fold increase in the IC50 of N-ethylmaleimide. In SHR, receptor occupancy either by SKF R-38393 or by SCH 23390 failed to protect the D1A sites from N-ethylmaleimide or to alter the IC50 of N-ethylmaleimide-mediated inactivation. These results indicate that D1A dopamine receptors both of WKY rats and of SHR contain sulfhydryl groups at or near the ligand binding site, which display differential sensitivity to N-ethylmaleimide.

Short and long-term changes in dopamine and serotonin receptor binding sites in amphetamine-sensitized rats: a quantitative autoradiographic study

The biochemical changes in DA and 5HT systems were investigated in amphetamine (AMPH)-sensitized rats, 1 and 15 days after cessation of treatment (5 mg/kg AMPH, i.p., twice a day for 6 days). At both times, AMPH-treated rats exhibited behavioral sensitization, as revealed by an enhancement of the stereotypic response to a challenge dose of 2 mg/Kg, ip. AMPH. Basal dopamine (DA) and serotonin (5-HT) metabolism was not significantly modified in different brain areas of AMPH-sensitized rats. Quantitative autoradiographic analysis of DA and serotonin 5-HT receptor subtypes was performed in the following brain regions: medial prefrontal cortex, nucleus accumbens, striatum, substantia nigra, ventral tegmental area, dorsal and median raphe nuclei. A significant increase of [ 3H]SCH 23390 binding to D 1 DA receptors was observed in the substantia nigra pars reticulata 1 day but not 15 days after the cessation of AMPH treatment, whereas [ 3H]8-OH-DPAT binding to 5-HT 1A sites was found to be significantly enhanced in the dorsal raphe nucleus at both time points. No change in D 2 DA nor in 5-HT 1B or 5-HT 2A receptors was found in any of the brain structures examined at either time point. The obtained results suggest that DA and 5-HT systems are differently and time-dependently involved in AMPH-induced behavioral sensitization.

Characterization of dopamine receptor binding sites in the subthalamic nucleus.

Experiments were undertaken to determine the distribution and binding profile of dopamine (DA) receptors within a key extra-striatal region of the rat basal ganglia, the subthalamic nucleus (STh). Analysis of [125I]NCQ-298 autoradiograms showed that binding sites of the D2-receptor family are abundant in the STh. Competition studies indicated that these sites were specifically of the D2 subtype. However, contrary to previously published data, [125I]SCH-23982 autoradiograms failed to reveal D1 receptor binding in the STh. These data suggest that DA acting at D2 receptors may directly modulate STh neural activity and furthermore that the antagonism of STh D2 receptor binding by neuroleptics may be involved in the expression of extrapyramidal motor disturbances.

Dopamine receptor binding on identified striatonigral neurons

Dopamine receptors have been divided into two families, known as D 1 and D 2, based on their ability to bind distinct ligands, and their use of separate post-synaptic transduction systems. Determining the specific cellular location for these dopamine receptors in the striatum is important to the design of drug treatments for disorders with suspected dopaminergic involvement such as Parkinson's disease. This study examined the binding of D 1 and D 2 antagonist ligands on identified striatonigral neurons using in vitro fluorescent techniques. The results indicate that striatonigral neurons express both pharmacological subfamilies of dopamine receptor binding sites.

Effect of age on D2 dopamine receptors in normal human brain measured by positron emission tomography and 11C-raclopride.

Human postmortem and animal experimental results suggest a decline of the cerebral dopaminergic neuronal system with age. In this study, the radiotracer carbon 11-labeled-raclopride and positron emission tomography were applied to determine the effect of age on striatal D2 dopamine receptors in 32 healthy volunteer subjects (age range, 21 to 68 years; median, 31 years). An index of specific 11C-raclopride binding was calculated for putamen, caudate nucleus, and other brain regions in each subject. A significant decrease with age of the index for specific tracer uptake was found in putamen and caudate nucleus. The decrease was steep until 30 years, but slower afterward. After approximately 30 years of age, the decline of specific 11C-raclopride binding in putamen was found to be 0.6% per year. Our results suggest that D2 dopamine receptor binding sites (mainly postsynaptically located) decrease as a consequence of normal aging in parallel with the decline of the presynaptic nigrostriatal dopaminergic neuronal system.

Autoradiographic evaluation of forskolin and D 1 dopamine receptor binding in a rat model of focal cerebral ischaemia

Post-ischaemic changes in forskolin and D 1 dopamine receptor (labelled with SCH23390) binding sites were evaluated in a rat unilateral middle cerebral artery occlusion (MCA) model. The changes in binding were assessed acutely (2 h post-MCA occlusion) in relation to local cerebral blood flow (lCBF) and chronically (24 h post-MCA occlusion) in relation to histopathological alterations. Two hours following occlusion lCBF was significantly reduced throughout the territory of the MCA. Despite the widespread hypoperfusion, significant reductions in binding were only observed in the dorsolateral caudate nucleus — the region with the most profound reduction in blood flow (6% of the control contralateral lCBF value). Forskolin binding sites were reduced to 40% of the contralateral value while D 1 binding sites were reduced to 80% of the contralateral value. Analysis of the relationship between forskolin binding and CBF in the caudate nucleus revealed that the ischaemic threshold for alteration in forskolin binding sites 2 h after MCA occlusion was approximately 34 ml/100 g/min. Twenty-four h post-occlusion forskolin binding sites were further reduced in the dorsolateral caudate nucleus (to 6% of contralateral) while D 1 binding showed minimal reduction from that observed at 2 h. The areas of reduced binding corresponded to the area of histopathological change in the caudate nucleus and rostral neocortex. In conclusion, reduction in forskolin binding progresses further than reduction in D 1 binding within the first 24 h following focal cerebral ischaemia. For both forskolin and D 1 binding sites, the areas of reduced binding 24 h post-MCA occlusion predicted the area of histopathological change.

Multiple fluorescent ligands for dopamine receptors. II. Visualization in neural tissues

Selective dopamine receptor ligands, ( R,S)-5-(4′-aminophenyl)-8-chloro-2,3,4,5-tetrahydro-3-methyl-[1H]-3-benzazepin-7-ol, the 4′-amino derivative of the high affinity D 1 receptor antagonist SCH 23390, the high affinity D 2 receptor antagonist N-( p-aminophenethyl)-spiperone or NAPS, and the D 2 selective agonist, 2-( N-phenethyl- N-propyl)-amino-5-hydroxytetralin or PPHT were chemically coupled to the fluorescent compounds, Bodipy, Cascade blue, coumarin, fluorescein, rhodamine, or Texas red. The utility of the 6 fluorescent moieties linked to the 3 dopamine receptor binding ligands for anatomical study of regional and cellular distribution patterns of the two dopaminergic receptor subtypes has been assessed in frozen sections of the rat striatum and compared to our previous report using the rhodamine-labeled antagonists. The regional staining for the two dopaminergic receptor binding sites supports previous work using in vitro receptor autoradiographic analyses; the D 1 receptor binding was more robust than that of D 2 receptors in the caudate nucleus. The cellular element which most frequently expressed striatal D 1 binding sites had a medium-diameter cell body. Medium-sized cells also exhibited fluorescence for the D 2 binding site, as did a much larger diameter element; potentially the cholinergic interneuron of the caudate nucleus. The pharmacological specificity for each of the different D 1 fluorescent antagonist ligands in the tissues was determined by competition with 100-fold excess of unlabeled SCH 23390 (non-specific binding), spiroperidol (binding selectivity), the stereoactive paired isomers of butaclamol, and the serotonin 5-HT 2 receptor antagonist ketanserin. The same criteria were used to assess the different D 2 fluorescent agonist and antagonist ligand derivatives. The anatomical efficacy of these novel ligands was determined using selective dichroic filters to stimulate the fluorescent moieties in the optimal excitation wavelength, and the amount of fluorescent dopamine receptor binding was photographically measured and contrasted for each of the newly synthesized fluoroprobes. Using the most pharmacologically specific and anatomically efficient of these novel fluoroprobes, we determined the localization pattern of the D 1 and D 2 dopamine receptor binding sites in tissues reported to exhibit both subtypes of the receptor. The cellular distribution of the dopamine receptor binding sites was determined concurrently using fluoroprobes in the forebrain, mesencephalon, pituitary, retina, and superior cervical ganglion of the rodent, and bovine adrenal medullary chromaffin cells were examined using the rhodamine-labeled antagonists.

Renal Dopamine and Changes in Dopamine Receptor Ligand Binding During High Sodium Intake

This study was designed to measure changes in plasma levels of atrial natriuretic peptides (ANP), urine volume (UV), urinary excretion of dopamine (UDAV) and sodium (UNaV), and dopamine (DA) receptor affinity (Kd) and binding sites (Bmax) in kidneys of rats drinking normal saline for a period of 7 days. The saline intake significantly increased UV, UNaV, plasma ANP, UDAV, and its primary metabolite dihydroxyphenyl acetic acid (DOPAC) for the period of 7 days. Bmax increased significantly 1 day after the initiation of saline intake, however, the increase appeared to be transient since measurements of Bmax made after 7 days of saline intake were not significantly different from the control group. No changes in Kd were observed. These results indicate that renal DA contributes to maintenance of Na balance during increased Na intake and that renal DA receptors undergo transient changes during this period.

Localized alterations of dopamine receptor binding in rat brain by repeated electroconvulsive shock: an autoradiographic study

The effects of repeated electroconvulsive shock (ECS) on binding parameters of D 1 and D 2 type dopamine (DA) receptors were investigated in different brain regions of male rats using quantitative autoradiography. D 1 binding was studied with [ 3H]SCH 23390 as the ligand and D 2 binding with [ 3H]spiroperidol. The distribution patterns of both D 1and D 2 receptor sites were in good agreement with previously published reports. Repeated ECS induced upregulation of D 1 receptors in the olfactory tubercle, the endopiriform nucleus and the substantia nigra without appreciably affecting D 1 binding sites in the striatum, n. accumbens or in other brain regions containing D 1 binding sites. Upregulation of D 2 binding sites, after ECS, was seen in the accumbens, the olfactory tubercle, the amygdaloid nuclei, the claustrum and the endopiriform nucleus, but not in the caudate-putamen or in other brain regions containing D 2 binding sites. The present finding that repeated ECS can selectively upregulate DA receptor binding sites in discrete brain areas, including limbic structures, renders important support to a large number of previous studies that demonstrated effects of repeated ECS on DA receptor function in behavioral models.

Dopamine receptor subsensitivity in the substantia nigra after chronic morphine treatment in rats

Several classes of 5-HT and dopamine (DA) receptor binding sites, and the levels of 5-HT, 5-hydroxyindoleacetic acid (5-HIAA), DA and dihydroxyphenylacetic acid (DOPAC) were examined in various brain regions 24 h after a 10-day treatment with morphine (2 × 15 mg/kg s.c. daily) in adult rats. Quantitative autoradiography of receptor binding sites revealed only a significant reduction of [ 3H]SCH-23390 and [ 3H]spiperone binding to D-1 and D-2 sites, respectively, in the substantia nigra pars compacta of morphine-treated rats. 5-HT and 5-HIAA levels remained unchanged in the substantia nigra and striatum, but the nigral levels of DA and DOPAC and the levels of DOPAC in the striatum were reduced significantly by morphine treatment. Apomorphine, at a dose (0.05 mg/kg s.c.) known to stimulate DA autoreceptors, decreased nigral and striatal DOPAC levels in controls but not in morphine-treated rats. It is concluded that chronic morphine treatment probably induces a down regulation of nigral D-1 and D-2 binding sites and reduces the negative feed-back mechanisms triggered by DA autoreceptors.

The effects of REM sleep deprivation on striatal dopamine receptor sites

3H-Spiroperidol binding to dopamine receptor sites of rat striatal tissue was studied following 24, 48, 72 and 96 hr of rapid eye movement sleep deprivation (REM dep.). The density of dopamine receptor binding sites (B max) was decreased after 48, 72, and 96 hr of REM dep. The apparent dissociation constant (K D) decreased after 96 hr, indicating an increase in apparent affinities. The control experimental animals also presented a time-dependent decrease of B max and K D as compared to unhandled controls. These results suggest that dopaminergic mechanisms may indeed be involved in the effects of REM sleep deprivation and/or slress.