The D1 dopamine agonist SKF 38393, but not the D2 agonist LY 171555, decreases the affinity of type II corticosteroid receptors in rat hippocampus and ventral striatum

Type I and type II brain corticosteroid receptors are regulated by adrenal hormones as well as being under neural control. Recent studies have indicated that neurotransmitters such as serotonin and noradrenaline are also involved in the regulation of corticosteroid receptors. In a previous study, we showed that dopamine also modulates activity of the corticosteroid receptor system. In the present study, we examined the roles of the dopamine D₁ and D₂ receptor subtypes in the regulation of corticosteroid receptors. Adrenalectomized rats whose corticosterone levels were maintained within normal limits by corticosterone replacement implants, were injected intraperitoneally with the D₁ agonist SKF 38393 or the D₂ agonist LY 171555. Corticosteroid receptors were assayed in the ventral striatum and hippocampus. We have shown that the D₁ agonist SKF 38393 decreased type II receptor affinity in both regions, whereas the D₂ agonist LY 171555 had no effects.

The results show that the influence of the dopaminergic system on corticosteroid receptors appears to be mediated by D₁ receptors.     

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.     

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     

Inhibition of inositol phospholipid breakdown by D2 dopamine receptors in dissociated bovine anterior pituitary cells

Inositol phospholipids have been labelled with [³H]inositol in a lactotroph-enriched preparation of dissociated bovine anterior pituitary cells. Stimulation of cells with thyrotropin-releasing hormone receptor agonists leads to accumulation of [³H]inositol phosphates, and this effect may be inhibited by dopamine (DA) agonists. The DA agonist effect may be prevented by D₂ DA receptor selective antagonists. Thus the D₂ receptors on these cells are linked to inhibition of inositol phospholipid metabolism, and this provides a functional assay for the receptor.     

Dopamine D2 receptors are restricted to the prolactin cells in the rabbit pituitary gland: a combined autoradiographic and immunocytochemical study

The distribution of dopamine D₂ receptors was studied using the autoradiographic technique on rabbit pituitary gland sections incubated in the presence of [³H]spiroperidol. D₂ receptors were absent from the intermediate lobe as already reported. In the anterior lobe, the location of D₂ receptors exactly overlapped that of the prolactin-producing cells revealed by immunocytochemistry on the sections used for autoradiography. No topographical relationships could be found between the D₂ receptors and the TSH-producing cells which are known to be inhibited by dopamine in the rat.     

Effects of dopamine D3 receptor agonists on pilocarpine-induced limbic seizures in the rat

The discrete localization of D₃ receptors in the nucleus accumbens and subjacent islands of Calleja bears a close resemblance to the dopamine-sensitive anticonvulsant site in the anteroventral striatum. To determine if these D₃ receptors were capable of attenuating limbic motor seizures induced by pilocarpine, dopamine agonists with preferential or non-selective D₃ affinity were injected stereotaxically into these limbic brain regions of the rat via indwelling cannulae prior to pilocarpine challenge. Reliable clonic seizures were obtained by administering the proconvulsive dopamine D₁ agonist SKF 38393 (10mg/kg i.p.) followed by a subconvulsant dose of pilocarpine (280–300 mg/kg i.p.). Bilateral intra-accumbens pretreatment with the D₃ > D₂ agonist RU 24213 (0.2 pmol-7 nmol) significantly delayed the onset of seizures, with a minimum effective dose of 2 pmol, without altering their frequency or severity. The more selective D₃ agonist LY 171555 (0.2 pmol-7.8 nmol) was less potent, and only attenuated pilocarpine-induced seizures at a dose (500 pmol) that would have stimulated accumbens D2 receptors as well. Intra-accumbens injections of the highly potent and selective D₃ agonist 7-OH-DPAT (20 pmol to 7 nmol) afforded no protection against pilocarpine-induced seizures. Apomorphine, a mixed D₁D₂D₃ agonist, delayed seizure onset at 100–500 pmol, but not at higher doses. RU 24213, LY 171555 and 7-OH-DPAT were all modestly anticonvulsant when microinjected into the islands of Calleja at D₂D₃ unselective doses.

These data support the notion that dopamine systems limit seizure propagation through the limbic forebrain, but suggest this protective effect is mediated by D₂ rather than D₃ receptors.     

Decline in striatal dopamine D1 and D2 receptor activation in aged F344 rats

Aging differentially affects receptor function. In the present electrophysiological study we compared neuronal responsiveness to locally applied dopamine D₁ and D₂ receptor agonist in the striatum of female Fischer 344 rats aged 3 and 26–27 months. In a subgroup of the old rats, the nigrostriatal dopamine bundle was destroyed unilaterally with 6-hydroxydopamine (6-OHDA) to assess receptor plasticity in response to denervation. Spontaneous firing rate of striatal neurons was higher in aged compared to young rats. Higher doses of the D₁ agonist SKF 38393 or the D₂ agonist quinpirole were required to elicit a 50% change in firing rate in aged compared to young rats. No difference with SKF 38393 or quinpirole was detected between 6-OHDA denervated and control (nonlesioned) striatum in aged rats. Supersensitivity to D₂ agonists has been reported following 6-OHDA lesions in young rats. These observations suggest that D₂ receptors in aged rat striatum might not be as plastic as in younger rats.     

Characterization of a neuronal interleukin-1 receptor and the corresponding mRNA in the mouse anterior pituitary cell line AtT-20.

The serotonin (5-HT)_1A agonist, LY 165,163 (1-[2-(4-aminophenyl)ethyl]-4-(3-trifluoromethylphenyl)-piperazine), also known as PAPP, has been suggested to exert effects via an interaction with dopamine receptors. Thus, in this study, we examined its ability to induce rotation in rats sustaining unilateral 6-hydroxy-dopamine lesions of the substantia nigra, an in vivo model of dopaminergic activity. In analogy to the direct dopamine (mixed D₁/D₂) agonist, apomorphine, (0.01–0.63 mg/kg), LY 165,163 (0.16–10.0 mg/kg) dose-dependently elicited robust and substained contralateral rotation. Its maximal effect was comparable to that of apomorphine and its duration of action more extended. Rotation elicited by LY 165,163 (10.0 mg/kg) was resistant to the 5-HT_1A antagonist, (−)-alprenolol. It was also unaffected by the selective D₁ antagonist, SCH 23390 (R(+)-7-chloro-8-hydroxy-3-methyl-1-phenyl-2,3,4,5,tetraphydro-1H-3- benzazepine) (2.5 mg/kg) or the selective D₂ antagonist, raclopride (10.0 mg/kg) when each was administered alone. However, upon joint administration they clearly diminished the effect of LY 165,163. The dopamine antagonist, haloperidol (D₂ > D₁) also reduced the action of LY 165,163. This profile of partial antagonism by mixed D₁ and D₂ receptor blockade has been reported previously for apomorphine and contrasts to that seen with selective D₁ or D₂ agonists, the actions of which are completely blocked by D₁ or D₂ antagonists, respectively. In conclusion, the present data demonstrate that LY 165,163 exerts pronounced rotation in nigral-lesioned rats: this reflects a mixed D₁/D₂ action rather than an activation of 5-HT_1A sites. Thus, in addition to an agonist action at 5-HT_1A receptors, dopaminergic effects contribute to the pharmacological profile of LY 165,163.     

Localization of NADPH-diaphorase activity in the salt gland of the saltwater-acclimated Pekin duck

The pharmacological properties and the anatomical localisation of dopamine D₃ receptor were assessed in the rat cerebellar cortex using radioligand binding techniques associated with light microscope autoradiography and 7-[³H]hydroxy-N,N-di-n-propyl-2-aminotetralin (7-[³H]OH-DPAT) as a ligand. 7-[³H]OH-DPAT was specifically bound to sections of rat cerebellar cortex with a dissociation constant (K_d) of 0.5 nM and a maximum density of binding sites (B_max) of 97 ± 4 fmol/mg tissue. The rank order of potency of competitors of 7-[³H]OH-DPAT binding and the observation that guanosine triphosphate did not affect radioligand binding suggest the labelling of a dopamine D₃ receptor. 7-[³H]OH-DPAT binding sites are located mainly in the molecular layer and in lesser amounts in the Purkinje neuron layer, primarily within the cell body of Purkinje neurons. No specific accumulation of silver grains was observed in the granule neuron layer or in the white matter of the cerebellar cortex. The localisation of a putative dopamine D₃ receptor within Purkinje neurons suggests that this site may have functional relevance in the cerebellar cortex.     

Quantitative autoradiography of dopamine D2 sites in rat caudate-putamen: Localization to intrinsic neurons and not to neocortical afferents

Dopamine D₂ receptors, labeled with [³H]spiroperidol or [³H]sulpiride, show a lateral-to-medial gradient in the caudate-putamen, with a more than two-fold greater density laterally than medially. It has been thought that D₂ receptors are located on at least two neuronal elements of the caudate-putamen, neurons intrinsic to this structure and axons whose cell bodies reside in the cortex. As a first step in establishing what neuronal elements underlie this heterogeneous organization of D₂ receptors, we took advantage of quantitative autoradiography to examine the association of these receptors with those elements. The present findings show that the D₂ sites are almost exclusively located on neurons whose somata reside in the caudate-putamen and are not located on terminals of corticostriatal axons. A detailed comparison of the distribution of histochemically identified acetylcholinesterase neurons with that of D₂ receptors in serially adjoining sections suggests a common organizational pattern.

The density of [³H]spiroperidol sites in rat caudate-putamen was determined after unilateral injection of the neurotoxin quinolinic acid into this structure or after ablation of neocortical regions. Quantification of the tissue damage was achieved by acetylcholinesterase histochemistry (following diisopropylfluoro-phosphate treatment), as well as by thionin and luxol fast staining of sections adjacent to those used for [³H]spiroperidol autoradiography. In identically treated animals, biochemical determination of the extent of tissue damage was made utilizing assays for high-affinity [³H]choline and [³H]glutamate uptake in the caudate-putamen. In quinolinic acid-injected rats, the density of D₂ sites was decreased by 90–95% at the site of complete loss of large acetylcholinesterase-positive neurons. Other animals, given ablations of specific neocortical fields (medial prefrontal, motor, somatosensory) or of the entire parietal-frontal cortex of one hemisphere, showed no loss of caudate-putamen D₂ sites unless the cortical ablation caused accompanying damage of the caudate-putamen. In the caudate-putamen of all animals there was a close correspondence between the D₂ sites and the striatal neurons (and processes) that show strong acetylcholinesterase reactivity.

We suggest that the caudate-putamen topography of D₂ sites is based largely on the internal organization of this structure and may preferentially involve acetylcholine-containing intrinsic neurons.     

Chronic ganglioside treatment counteracts the biochemical signs of dopamine receptor supersensitivity induced by chronic haloperidol treatment

Chronic ganglioside treatment (10 mg/kg, i.p.) using the molecular species with only one neuroaminic acid residue (GM1) given together with haloperidol (0.3 and 5 mg/kg, i.p.) once daily in male rats, counteracted the haloperidol-induced increase in the number of [³H]spiperone binding sites in striatal membranes when the low dosse of haloperidol, but not the high dose, was administered. The present results therefore indicate that chronic GM1 treatment can partially counteract the increase in the number of dopamine receptors having a high affinity for neuroleptics (D₂ type) induced by chronic haloperidol treatment in striatal membranes, and therefore may also partially counteract the development of neuroleptic-induced dopamine receptor supersensitivity.     

Stimulation of adenosine A2 receptors induces catalepsy.

The central administration of the adenosine A₂ agonist CGS 21680 induced catalepsy in the rat. This effect was counteracted by the previous systemic administration of the adenosine antagonist theophylline or the D₂ agonist BHT-920. These results are in agreement with the view that adenosine A₂ receptors regulate central dopamine D₂ transmission and underline the potential antipsychotic activity of A₂ agonists.     

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.     

大麻素受体二聚化及其激活机理

Cannabinoid receptor 1 (CB₁) and cannabinoid receptor 2 (CB₂) are important members of G protein-coupled receptors (GPCRs). Numerous studies have shown that CB₁ receptor can form heterodimers with dopamine receptors (D₂), μ-opioid receptor (μOR), orexin-1 receptor, adenosine receptor (A_2A) or β2 adrenergic receptors, and then forming an essential functional entity. This review summarizes the research progress on heterodimers of cannabinoid CB₁ or CB₂, the function of heterodimers as well as the downstream signalings. The different pharmacological properties of the receptor heterodimer lead to bringing a change in receptor pharmacology, which will have a profound impact on drug development.     

Ontogeny of the dopamine D2 receptor mRNA expressing cells in the human hippocampal formation and temporal neocortex

The study details the cellular expression of the dopamine D₂ receptor mRNA in the human temporal lobe during prenatal development. At 13 embryonic weeks (E13) D₂ mRNA was widely expressed in the temporal lobe. At this time point in the dentate gyrus D₂ mRNA positive cells first appeared at the outer border of the granular layer and their number increased with development. The CA1 exhibited the highest level of D₂ mRNA expression. By E19–25 the hippocampal formation underwent rapid morphological maturation. D₂ mRNA expression became more uniform and dense in the ammonic subfield. At all ages the subiculum appeared more mature morphologically but less intensely stained for D₂ mRNA than the ammonic fields. In the entorhinal cortex D₂ mRNA expression was most conspicuous in the future layer II at all ages. In the temporal neocortex D₂ mRNA-positive cells were detected in the subplate and cortical plate. Differentiation of the cortical plate was accompanied by concentration of D₂ mRNA-positive cells in layer V. The most conspicuous cells expressing D₂ mRNA were found in the marginal zone of all regions and resembled Cajal–Retzius cells in morphology and location. Density of putative Cajal–Retzius cells expressing D₂ mRNA decreased with development. They all but disappeared from the hippocampal areas by mid gestation, but in the temporal neocortex occasional cells were seen even at term. Early and widespread but region and cell type specific expression of D₂ receptor mRNA suggests an important role of this DA receptor subtype in prenatal development of the human temporal lobe.     

Pressure reversed extracellular striatal dopamine decrease produced by D1 receptor agonist SKF 38393, and D2 receptor agonist LY 171555, but failed to change the effect of the activation of both D1 and D2 receptors.

When human divers or experimental animals are exposed to high pressure, they develop the high-pressure neurological syndrome which is characterized by electroencephalographic changes, and behavioral disturbances. Recently, neurochemical disorders such as a pressure-induced increase in dopamine release have been demonstrated. In the present study, pharmacological experiments, using dopamine receptor agonists such as D1 receptor agonist SKF 38393, D2 receptor agonist LY 171555, and D1/D2 receptor agonist apomorphine, were performed to investigate dopamine receptor function at the neurochemical level. Only apomorphine and mixed SKF 38393 + LY 171555 prevented the pressure-induced increase in dopamine release while SKF 38393 or LY 171555 administered alone failed to do so. The results suggest that the D1-D2 link would be reduced under high pressure because of an abnormal function of D1 receptors which would allow high-affinity D2 states for dopamine. If so, such a preponderance of high-affinity states in D2 postsynaptic receptors could be associated with hyperbaric hyperlocomotor activity. Elsewhere, results also suggested that the pressure-induced disorders in dopamine receptor function could be involved in the pressure-induced elevation in dopamine release.     

Modulation of cell-cell and cell-antigen interactions by 1,25-dihydroxyvitamin D3 and vitamin D3 sulfate in vitro: a study on pregnancy lymphocytes and hybridoma cells

The effect of 1,25-dihydroxyvitamin D₃ (1,25(OH)₂D₃ was investigated in single cell cytotoxicity assays, using K-562 target cells. The action of vitamin D₃ sulfate (VD₃S) in natural cytotoxicity assays as well as its effect on the antigen-specific adherence of hybridoma cells has also been studied. In the single cell cytotoxicity assay 1,25(OH₂)D₃ dose-dependently and significantly increased the binding of PBMC to target, the number of lysed target cells and NK activity, RU486, a compound known as a potent blocker of progesterone and glucocorticoid receptors, suppressed the effect of 1,25(OH₂)D₃ in all systems. VD₃S dose-dependently decreased the natural cytotoxicity of PBMC and the binding of hybridoma cells to antigen immobilized on plastic surfaces. The results suggest that both 1,25(OH₂)D₃ and VD₃S are potent     

Corticotropin-releasing hormone-containing neurons in the hypothalamo-hypophyseal system in rats six weeks after bilateral lesions of the paraventricular nucleus

Adenosine is now considered as a major regulatory agent in the mammalian central nervous system. Its actions are mediated by specific receptors which are coupled with an adenylate cyclase system via a G protein. The postnatal development of adenosine A₁ receptors was studied by quantitative autoradiography using [³H]N⁶-cyclohexyladenosine, a potent receptor agonist in 42 rat brain structures. The coupling of these sites to G proteins was examined by measuring the effects of in vitro addition of guanylyl-5′-imidodiphosphate, a stable analogue of guanosine triphosphate, on N⁶-cyclohexyladenosine binding. [³H]N⁶-Cyclohexyladenosine-specific binding was quite low at birth, around 10% of adult levels, and exhibited a rather homogeneous distribution pattern, except in thalamic nuclei. Data showed a sequential development of adenosine A₁ receptors in relation to the time course of maturation of cerebral structures with a proliferation peak which paralleled rapid brain growth.

The time period by which adult levels are reached differed according to the cerebral region studied. N⁶-Cyclohexyladenosine-specific binding sites appeared to be functionally linked to G proteins in all structures and at all postnatal stages. However, the potency of guanylyl-5′-imidodiphosphate to displace N⁶-cyclohexyladenosine binding was significantly lower before 5 days of age, suggesting functional changes during postnatal maturation in cerebral pathways modulated by adenosine.