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Caffeine and a selective adenosine A2A receptor antagonist induce reward and sensitization behavior associated with increased phospho-Thr75-DARPP-32 in mice. Psychopharmacology (Berl) 2009; 204:313-25. [PMID: 19169672 DOI: 10.1007/s00213-009-1461-3] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/08/2008] [Accepted: 12/31/2008] [Indexed: 01/07/2023]
Abstract
RATIONALE Caffeine, an antagonist of adenosine A(1) and A(2A) receptor, is the most widely used psychoactive substance in the world. Evidence indicates that caffeine interacts with the neuronal systems involved in drug reinforcing. Although adenosine A(1) and/or A(2A) receptor have been found to play important roles in the locomotor stimulation and probably reinforcing effect of caffeine, the relative contribution of the A(1) and/or A(2A) receptors to the acute and chronic motor activation and reinforcing effects of caffeine has not been completely investigated. OBJECTIVE The roles of adenosine A(1) and/or A(2A) receptor and the association of phospho-Thr75-dopamine- and cAMP-regulated phosphoprotein of molecular weight 32 kDa (DARPP-32) in the motor activation and reinforcing effects of caffeine, 8-cyclopentyl-1,3-dipropylxanthine (DPCPX), a selective A(1) antagonist, and 5-amino-7-(beta-phenylethyl)-2-(8-furyl) pyrazolol [4,3-e]-1,2,4-triazolol [1,5-c] pyrimidine (SCH58261), a selective A(2A) receptor antagonist were examined. METHODS Locomotor stimulation and behavioral sensitization of caffeine, DPCPX, and SCH58261 were studied in C57BL/6 male mice following acute and chronic administration. Conditioned place preference (CPP) paradigm was used to evaluate the drug-seeking potential of these compounds. Furthermore, the expression of phospho-Thr75-DARPP-32 in striatal membrane from behaviorally sensitized mice was analyzed by Western blot. RESULTS Caffeine and SCH58261 but not DPCPX induced CPP and locomotor sensitization in C57BL/6 mice. The locomotor sensitization after chronic treatment was associated with increased DARPP-32 phosphorylation at Thr75 in the striatum. CONCLUSION Caffeine-induced reinforcing effect and behavioral sensitization are mediated by antagonism at adenosine A(2A) receptor. These effects are associated with phosphorylation of DARPP-32 at Thr75 in the striatum.
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Kuzmin A, Johansson B, Gimenez L, Ogren SO, Fredholm BB. Combination of adenosine A1 and A2A receptor blocking agents induces caffeine-like locomotor stimulation in mice. Eur Neuropsychopharmacol 2006; 16:129-36. [PMID: 16054807 DOI: 10.1016/j.euroneuro.2005.07.001] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/22/2005] [Revised: 06/10/2005] [Accepted: 07/01/2005] [Indexed: 11/17/2022]
Abstract
The spontaneous locomotor activity of C57BL/6J mice was examined, using an automated detection system based on infra-red beams, after administration of caffeine (3-30 mg/kg, i.p.), the adenosine A(2A) receptor selective antagonist SCH 58261 (0.312-2.5 mg/kg, i.p.) and the A(1) selective antagonist DPCPX (1.25-5 mg/kg, i.p.). SCH 58261 failed to influence motor activity in mice habituated to the test environment. DPCPX produced a small increase in motility and locomotion (significant at the dose of 5.0 mg/kg), much weaker than that produced by caffeine. Combined administration of DPCPX (1.2 mg/kg, i.p.) and SCH 58261 (1.2 mg/kg, i.p.) produced stimulation of motility and locomotion comparable with the effect of caffeine (15 mg/kg, i.p.). In contrast to motility and locomotion, rearing counts were not significantly influenced by DPCPX, SCH 58261, their combination, or by caffeine. Caffeine (15 mg/kg, i.p.) caused an increase in NGFI-A mRNA (an immediate early gene was chosen as an index of neuronal activation) in the piriform cortex 4 h after injection. This effect was reproduced by the combination of A(1) and A(2A) receptor antagonist. It is hypothesised that the stimulatory effect of low doses of caffeine in C57BL/6J mice is due to concomitant blockade of both A(1) and A(2A) adenosine receptors.
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Bové J, Marin C, Bonastre M, Tolosa E. Adenosine A2A antagonism reverses levodopa-induced motor alterations in hemiparkinsonian rats. Synapse 2002; 46:251-7. [PMID: 12373740 DOI: 10.1002/syn.10112] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
To evaluate the possible involvement of adenosine A(2A) receptor-mediated mechanisms in levodopa-induced motor fluctuations, we investigated the effects of CSC (8-(3-chlorostryryl) caffeine), a selective adenosine A(2A) receptor antagonist, on levodopa-induced motor alterations in rats with unilateral 6-OHDA lesion. Acute and chronic administration of CSC was studied to evaluate the possible reversion or prevention of these levodopa effects. In a first set of experiments, rats were treated with levodopa (25 mg/kg with benserazide, twice daily, i.p.) for 22 days and on day 23 CSC (5 mg/kg, i.p.) was administered immediately before levodopa. In a second set of experiments, rats were treated daily for 22 days with levodopa and CSC (5 mg/kg/day, i.p.). The duration of the rotational behavior induced by chronic levodopa decreased after 22 days (P < 0.05). Acute administration of CSC on day 23 reversed levodopa-induced shortening in motor response duration (P < 0.01). Chronic CSC administration did not prevent the shortening in response duration induced by levodopa. Our results demonstrate that the adenosine A(2A) receptor antagonist CSC reverses but does not prevent levodopa-induced motor alterations in parkinsonian rats. These results suggest a role for adenosine A(2A) receptor-mediated mechanisms in the pathophysiology of levodopa-induced motor response complications. These findings suggest that the antagonism of adenosine A(2A) receptors might confer clinical benefit to parkinsonian patients under levodopa therapy suffering from motor complication syndrome.
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Affiliation(s)
- J Bové
- Laboratori de Neurologia Experimental, Fundació Clínic, Institut d'Investigacions Biomèdiques August Pi i Sunyer (IDIBAPS), Hospital Clínic, 08036 Barcelona, Spain
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Dassesse D, Vanderwinden JM, Golberg I, Vanderhaeghen JJ, Schiffmann SN. Blockade of A1 receptors by caffeine induces c-fos, zif-268 and ARC expression in the striatum through different interactions with the dopamine system. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2002; 486:207-16. [PMID: 11783486 DOI: 10.1007/0-306-46843-3_42] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/23/2023]
Affiliation(s)
- D Dassesse
- Laboratory of Neurophysiology, Dept. Neuroscience, Université Libre de Bruxelles, Brussels, Belgium
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Dassesse D, Ledent C, Parmentier M, Schiffmann SN. Acute and chronic caffeine administration differentially alters striatal gene expression in wild-type and adenosine A(2A) receptor-deficient mice. Synapse 2001; 42:63-76. [PMID: 11574941 DOI: 10.1002/syn.1100] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
In order to assess for the respective involvement of adenosine A(1) and A(2A) receptors (A(2A)-R) in the consequences of short- and long-term caffeine exposure on gene expression, the effects of acute caffeine administration on striatal, cortical, and hippocampal expression of immediate early genes (IEG), zif-268 and arc, and the effects of long-term caffeine or 1,3-dipropyl-8-cyclopentylxanthine (DPCPX) exposure (once daily for 15 days) on striatal gene expression of substance P, enkephalin, and glutamic acid decarboxylase isoforms, GAD65 and GAD67, were evaluated in wild-type and A(2A)-R-deficient (A(2A)-R(-/-)) mice. In situ hybridization histochemistry was performed using oligonucleotides followed by quantitative image analysis. Our results demonstrated that a biphasic response of IEG expression to acute caffeine observed in the wild-type striatum was resumed in a monophasic response in the mutant striatum. In the cerebral cortex and hippocampus, the effect of caffeine was weak in wild-type, whereas in mutant mice it induced a 2-3-fold increase in the IEG expression to restore a level similar to the wild-type basal expression. Chronic caffeine and DPCPX-mediated regulation in neuropeptide and GADs striatal gene expression typically showed the mimicking of alterations resulting from the A(2A)-R genetic deficiency in 25 mg/kg caffeine-treated wild-type mice as well as the dose-dependent normalization of substance P and enkephalin expression in A(2A)-R(-/-) mice. These results indicate that, depending on the dose, the blockade of A(2A)-R or A(1) receptors by caffeine is preferentially revealed leading to highly differential alterations in striatal gene expression and they also suggested the central role of these two receptors on the control of dopaminergic functions.
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MESH Headings
- Animals
- Caffeine/pharmacology
- Cytoskeletal Proteins/genetics
- DNA-Binding Proteins/genetics
- Dose-Response Relationship, Drug
- Drug Administration Schedule
- Early Growth Response Protein 1
- Enkephalins/genetics
- Gene Expression Regulation/drug effects
- Gene Expression Regulation/physiology
- Genes, Immediate-Early/drug effects
- Genes, Immediate-Early/physiology
- Glutamate Decarboxylase/genetics
- Hippocampus/drug effects
- Hippocampus/metabolism
- Immediate-Early Proteins
- Isoenzymes/genetics
- Male
- Mice
- Mice, Knockout
- Neostriatum/drug effects
- Neostriatum/metabolism
- Nerve Tissue Proteins/genetics
- Neuropeptides/drug effects
- Neuropeptides/genetics
- Neuropeptides/metabolism
- Phosphodiesterase Inhibitors/pharmacology
- Purinergic P1 Receptor Antagonists
- RNA, Messenger/drug effects
- RNA, Messenger/metabolism
- Receptor, Adenosine A2A
- Receptors, Purinergic P1/deficiency
- Receptors, Purinergic P1/genetics
- Receptors, Purinergic P1/metabolism
- Somatosensory Cortex/drug effects
- Somatosensory Cortex/metabolism
- Substance P/genetics
- Transcription Factors/genetics
- Xanthines/pharmacology
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Affiliation(s)
- D Dassesse
- Laboratory of Neurophysiology, Department of Neuroscience, School of Medicine, Université Libre de Bruxelles, B-1070 Brussels, Belgium.
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El Yacoubi M, Ledent C, Parmentier M, Costentin J, Vaugeois J. SCH 58261 and ZM 241385 differentially prevent the motor effects of CGS 21680 in mice: evidence for a functional 'atypical' adenosine A(2A) receptor. Eur J Pharmacol 2000; 401:63-77. [PMID: 10915839 DOI: 10.1016/s0014-2999(00)00399-x] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
The acute motor effects elicited by drugs acting upon adenosine A(2A) receptors, namely the highly selective agonist CGS 21680 or the antagonists SCH 58261 and ZM 241385, were investigated in mice. CGS 21680 dose-dependently (0.1-2.5 mg/kg i.p.) decreased horizontal and vertical motor activities. The depressant effect of CGS 21680 (0. 5 mg/kg i.p.) was maintained in mice pretreated by the adenosine receptor antagonist 8-(p-sulfophenyl)-theophylline (10-30 mg/kg i.p. ), which poorly penetrates the blood-brain barrier, but was completely lost in adenosine A(2A) receptor knockout mice. Thus, the adenosine A(2A) receptor is critically involved in motor activity. SCH 58261 (1-10 mg/kg i.p.) increased locomotion and rearing with a quick onset, but for a shorter period in mice habituated to the environment than in mice unfamiliar to it. ZM 241385 (7.5-60 mg/kg i. p.) stimulated horizontal and vertical activities with a slow onset at the two highest tested doses, similarly in naive and in habituated mice. The increase in locomotion elicited by ZM 241385 (15-30 mg/kg i.p. and 10-20 nM i.c.v.) was retained in mice treated by CGS 21680 (0.5 mg/kg i.p.) but that elicited by SCH 58261 (1-3-10 mg/kg i.p. and 10-20 nM i.c.v.) partially subsided. In conclusion, both 'striatal-like'/'SCH 58261-sensitive' adenosine A(2A) receptors and 'ZM 241385-sensitive'/'atypical' CGS 21680 binding sites may mediate CGS 21680-induced motor effects. Moreover, our results suggest that 'atypical' CGS 21680 binding sites could be adenosine A(2A) receptors with a peculiar pharmacological profile.
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Affiliation(s)
- M El Yacoubi
- UPRESA CNRS 6036, IFRMP 23, U.F.R. de Médecine and Pharmacie, 22 Boulevard Gambetta, 76183 Cédex, Rouen, France
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Dassesse D, Vanderwinden JM, Goldberg I, Vanderhaeghen JJ, Schiffmann SN. Caffeine-mediated induction of c-fos, zif-268 and arc expression through A1 receptors in the striatum: different interactions with the dopaminergic system. Eur J Neurosci 1999; 11:3101-14. [PMID: 10510174 DOI: 10.1046/j.1460-9568.1999.00725.x] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Adenosine and the adenosine receptor antagonist, caffeine, modulate locomotor activity and striatal neuropeptide expression through interactions with the dopaminergic system by mechanisms which remain partially undetermined. We addressed this question by using quantitative immunocytochemistry and in situ hybridization, combined with retrograde tracing of striatal neurons, to characterize the mechanism(s) leading to the striatal increase in the immediate early genes (IEG), c-fos, zif-268 and arc, following a single injection of caffeine or the A1 antagonist, 1,3-dipropyl-8-cyclopentylxanthine (DPCPX). Caffeine and DPCPX induced c-fos, zif-268 and arc expression, both at mRNA and protein levels, in large proportions of striatonigral and striatopallidal neurons. The involvement of dopamine systems was evaluated by manipulations of the dopaminergic transmission. Quinpirole, a D2 agonist, almost completely blocked the caffeine-induced IEG increase in both striatopallidal and striatonigral neurons. Conversely, the lesion of the nigrostriatal pathway and the D1 antagonist SCH23390 abolished the caffeine effects in striatonigral neurons but had no or slight effect, respectively, on its action in striatopallidal neurons. These observations demonstrate that caffeine- and DPCPX-mediated IEG inductions involved different mechanisms in striatonigral and striatopallidal neurons through blockade of A1 receptors. Immediate early gene inductions result from a stimulation of dopamine release in striatonigral neurons and from activation of glutamate release and probably also acetylcholine release in striatopallidal neurons. These results also support the idea that, besides A2A receptors, adenosine acting at the A1 receptor plays pivotal functions in the basal ganglia physiology and that blockade of these receptors by specific or nonspecific antagonists, DPCPX and caffeine, may influence a broad range of neuronal functions in the striatum.
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Affiliation(s)
- D Dassesse
- Brain Research Unit and Laboratory of Neuropathology and Neuropeptides Research, School of Medicine, Université Libre de Bruxelles, Campus Erasme, Brussels, Belgium.
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Doriat JF, Humbert AC, Daval JL. Brain maturation of high-affinity adenosine A2 receptors and their coupling to G-proteins. BRAIN RESEARCH. DEVELOPMENTAL BRAIN RESEARCH 1996; 93:1-9. [PMID: 8804686 DOI: 10.1016/0165-3806(96)00009-0] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
The neuromodulator adenosine is acting through specific receptors, A1 and A2, coupled to their effector systems via G-proteins. The regulatory effects of adenosine on locomotor activity have been attributed to an interaction with A2 striatal receptors. The postnatal development of adenosine A2a receptors was analysed in rat striatal membranes and by quantitative autoradiography in brain sections using [3H]CGS 21680 as specific probe. At the concentration of radioligand used (5 nM), A2a sites were concentrated in the striatum at all ages, with minor developmental alterations in the expression pattern within the striatal regions. In membrane preparations, Scatchard analysis showed that the density of CGS 21680 binding sites was low at birth, around 3% of the adult value, and then increased, mostly between birth and 5 days and then from 15 days to adulthood. Concomitantly, the receptor affinity decreased sharply during brain development, Kd values varying from 2 to 15.5 nM. The addition of a GTP analogue, guanylyl-5'-imidodiphosphate (Gpp(NH)p, 10 microM), to the assay medium reduced significantly the receptor affinity throughout the postnatal development, reflecting a coupling to G-proteins at all ages, but it also suggested a weaker association at birth. These data show that the developmental properties of A2a receptors contrast with those of A1 receptors, and emphasize the role played by adenosine through its A2 receptors in the maturation of striatum-related cerebral pathways.
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Affiliation(s)
- J F Doriat
- INSERM U.272, Université de Nancy, France
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Hooper N, Fraser C, Stone TW. Effects of purine analogues on spontaneous alternation in mice. Psychopharmacology (Berl) 1996; 123:250-7. [PMID: 8833418 DOI: 10.1007/bf02246579] [Citation(s) in RCA: 45] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
The Y-maze was used to examine the effects of purines acting at A1 and A2 adenosine receptors upon spontaneous alternation, a model of working memory, in mice. In support of previous work, scopolamine produced a loss of spontaneous alternation behaviour to the 0.5 chance level. The A1 receptor selective agonist N6- cyclopentyladenosine (CPA) did not change spontaneous alternation behaviour alone, but it prevented the decrease of spontaneous alternation scores produced by scopolamine. The A1 receptor selective antagonist 1,3-dipropyl-8-cyclopentylxanthine (CPX) blocked the effect of CPA in combination with scopolamine but had no effect alone. The A2 receptor selective agonist (N6-[2-(3,5-dimethoxyphenyl)-2-(2- methylphenyl)ethyl] adenosine (DPMA), and the A2 receptor selective antagonist 3,7-dimethyl-1-propargylxanthine (DMPX) had no effect of alternation behaviour alone and did not modify the effect of scopolamine. The results indicate the ability of A1 but not A2 receptor activation to modify working memory deficits induced by scopolamine, but suggest that endogenous adenosine does not normally participate in working memory processes.
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Affiliation(s)
- N Hooper
- Neuroscience Research Group, Institute of Biomedical and Life Sciences, University of Glasgow, UK
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Abstract
Adenosine participates in the physiology of central and peripheral tissues through several subtypes of G-protein-coupled receptors. Positively linked to adenylate cyclase, A2 receptors have been subdivided into A2a and A2b sites on the basis of their molecular, biochemical and pharmacological properties. They exhibit selective distribution, and are implicated in the modulation of psychomotor activity, circulation, respiration, and metabolism. Recent data support the evidence that adenosine A2 receptor properties may prove useful in future drug development, and selective manipulation of receptor-associated biologic effects might be relevant in the treatment of various disorders, including psychiatric diseases, hypoxia/ischemia, inflammation or erythrocytosis.
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Affiliation(s)
- J L Daval
- INSERM U.272, Université de Nancy I, France
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Nehlig A, Daval JL, Boyet S. Effects of selective adenosine A1 and A2 receptor agonists and antagonists on local rates of energy metabolism in the rat brain. Eur J Pharmacol 1994; 258:57-66. [PMID: 7925600 DOI: 10.1016/0014-2999(94)90057-4] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
The quantitative [14C]2-deoxyglucose autoradiographic technique was applied to the measurement of the cerebral metabolic effects of adenosine A1 and A2 receptor agonists and antagonists in adult rats. The adenosine A1 receptor agonist and antagonist, 2-chloro-N6-cyclopentyladenosine (CCPA) and 8-cyclopentyl-1,3-dipropylxanthine (DPCPX) as well as the adenosine A2 receptor agonist, 2-[p-(2-carboxyethyl)phenylethylamino]-5'-ethylcarboxamidoadenosin e (CGS 21680), were injected at the dose of 0.01 mg/kg. The adenosine A2 receptor antagonist, 3,7-dimethyl-1-proparglyxanthine (DMPX) was injected at the dose of 0.3 mg/kg. These doses were chosen in accordance with the known affinity of the drugs for their respective receptor and to avoid peripheral effects. The adenosine A1 receptor agonist, CCPA, induced decreases in glucose utilization in three brain areas, the globus pallidus and two hypothalamic nuclei. The adenosine A2 receptor agonist, CGS 21680, induced more general depressant effects on energy metabolism which were significant in 17 brain areas, such as cerebral cortex, hippocampal and white matter regions plus motor and limbic structures. The adenosine A2 receptor antagonist, DMPX, decreased glucose utilization in the globus pallidus while increasing energy metabolism in the cochlear nucleus. The adenosine A1 receptor antagonist, DPCPX, depressed glucose utilization in the globus pallidus and dentate gyrus, and increased rates of energy metabolism in six regions, mainly hypothalamic, thalamic areas and in the cochlear nucleus. There was a mismatch between cerebral metabolic consequences of adenosine A1 and A2 receptor agonists and the localization of corresponding adenosine receptors. The metabolic effects of the adenosine A2 receptor agonist and antagonist were consistent with the known involvement of that type of receptor in the control of locomotion and its effects on neuronal firing in the hippocampus and cerebral cortex. The effects of the adenosine A1 receptor agonist were very discrete and mostly related to the transient decrease in blood pressure induced by the drug. The increases in glucose utilization induced in limbic regions by the adenosine A1 receptor antagonist are probably linked to the regulation by adenosine of arousal and cardiorespiratory function. These results are in good agreement with the neuroregulatory function of the adenosine system as previously shown by other methods.
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Affiliation(s)
- A Nehlig
- INSERM U 272, Université de Nancy I, France
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Jacobson KA, Nikodijević O, Padgett WL, Gallo-Rodriguez C, Maillard M, Daly JW. 8-(3-Chlorostyryl)caffeine (CSC) is a selective A2-adenosine antagonist in vitro and in vivo. FEBS Lett 1993; 323:141-4. [PMID: 8495727 PMCID: PMC3468328 DOI: 10.1016/0014-5793(93)81466-d] [Citation(s) in RCA: 141] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
An adenosine antagonist, 8-(3-chlorostyryl)caffeine (CSC), was shown previously to be 520-fold selective for A2a-adenosine receptors in radioligand binding assays in the rat brain. In reversing agonist effects on adenylate cyclase, CSC was 22-fold selective for A2a receptors in rat phenochromocytoma cells (Kb 60 nM) vs. A1 receptors in rat adipocytes (Kb 1.3 microM). Administered i.p. in NIH mice at a dose of 1 mg/kg, CSC shifted the curve for locomotor depression elicited by the A2a-selective agonist APEC to the right (ED50 value for APEC shifted from 20 micrograms/kg i.p. to 190 micrograms/kg). CSC had no effect on locomotor depression elicited by an ED50 dose of the A1-selective agonist CHA. CSC alone at a dose of 5 mg/kg stimulated locomotor activity by 22% over control values. Coadministration of CSC and the A1-selective antagonist CPX, both at non-stimulatory doses, increased activity by 37% (P < 0.001) over CSC alone, suggesting a behavioral synergism of A1- and A2-antagonist effects in the CNS.
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Affiliation(s)
- K A Jacobson
- Laboratory of Bioorganic Chemistry, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892
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