Stimulation of adenosine A1 receptors attenuates dopamine D1 receptor-mediated increase of NGFI-A, c-fos and jun-B mRNA levels in the dopamine-denervated striatum and dopamine D1 receptor-mediated turning behaviour

Adenosine A1 receptors antagonistically and specifically modulate the binding and functional characteristics of dopamine D1 receptors. In the striatum this interaction seems to take place in the GABAergic strionigro-strioentopeduncular neurons, where both receptors are colocalized. D1 receptors in the strionigro-strioentopeduncular neurons are involved in the increased striatal expression of immediate-early genes induced by the systemic administration of psychostimulants and D1 receptor agonists. Previous results suggest that a basal expression of the immediate-early gene c-fos tonically facilitates the functioning of strionigro-strioentopeduncular neurons and facilitates D1 receptor-mediated motor activation. The role of A1 receptors in the modulation of the expression of striatal D1 receptor-regulated immediate-early genes and the D1 receptor-mediated motor activation was investigated in rats with a unilateral lesion of the ascending dopaminergic pathways. The systemic administration of the A1 agonist N6-cyclopentyladenosine (CPA, 0.1 mg/kg) significantly decreased the number of contralateral turns induced by the D1 agonist SKF 38393 (3 mg/kg). Higher doses of CPA (0.5 mg/kg) were necessary to inhibit the turning behaviour induced by the D2 agonist quinpirole (0.1 mg/kg). By using in situ hybridization it was found that CPA (0.1 mg/kg) significantly inhibited the SKF 38393-induced increase in the expression of NGFI-A and c-fos mRNA levels in the dopamine-denervated striatum. The increase in jun-B mRNA expression could only be inhibited with the high dose of CPA (0.5 mg/kg). A stronger effect of the A1 agonist was found in the ventral striatum (nucleus accumbens) compared with the dorsal striatum (dorsolateral caudate-putamen). The results indicate the existence of antagonistic A1-D1 receptor-receptor interactions in the dopamine-denervated striatum controlling D1 receptor transduction at supersensitive D1 receptors.     

Adenosine A1 receptor-mediated inhibition of dopamine release from rat striatal slices is modulated by D1 dopamine receptors

Dopamine release is regulated by presynaptic dopamine receptors and interactions between adenosine and dopamine receptors have been well documented. In the present study, dopamine release from isolated striatal slices from Wistar rats was measured using fast cyclic voltammetry. Single-pulse stimulation (0.1 ms, 10 V) was applied every 5 min over a 2-h period. Superfusion with the adenosine (A)(1) receptor agonist N(6)-cyclopentyladenosine (CPA), but not the A(2) receptor agonist 3-[4-[2-[[6-amino-9-[(2R,3R,4S,5S)-5-(ethylcarbamoyl)-3,4-dihydroxy-oxolan-2-yl]purin-2-yl]amino]ethyl] phenyl]propanoic acid (CGS 21680), inhibited dopamine release in a concentration-dependent manner (IC(50) 3.80 x 10(-7) m; n = 10). The dose-response curve to CPA was shifted to the right (IC(50) 6.57 x 10(-6) m; n = 6, P < 0.05 vs. control) by the A(1) receptor antagonist 8-cyclopentyl-1,3-dipropylxanthine (DPCPX). Neither the D(1) agonist 6-chloro-APB nor the D(1) antagonist R-(+)-8-chloro-2,3,4,5-tetrahydro-3-methyl-5-phenyl-1H-3- benzazepine-7-ol (SCH 23390) altered dopamine release on their own. However, SCH 23390 (3 microm) significantly attenuated the response to CPA (IC(50) 1.44 x 10(-5) m; n = 6, P < 0.01 vs. control). Furthermore, the inhibitory effect of CPA was significantly increased in the presence of 6-chloro-APB (1 microm). In radioligand binding experiments, CPA interacted with high- and low-affinity states of [(3)H]DPCPX-lableled A(1) receptors. The high-affinity agonist binding to A(1) receptors was inhibited by the stable guanosine triphosphate analogue Gpp(NH)p. In contrast, neither the proportion nor the affinity of high-affinity A(1) receptors was altered by dopamine or SCH 23390. These results provide evidence that the inhibition of dopamine release by adenosine A(1) receptors is dependent, at least in part, on the simultaneous activation of D(1) dopamine receptors. While the mechanism underlying this interaction remains to be determined, it does not appear to involve an intramembrane interaction between A(1) and D(1) receptors.     

Oligodendrocytes express functional A1 adenosine receptors that stimulate cellular migration

A1 adenosine receptors (A1ARs) exert important effects in the central nervous system. However, the expression and function of A1ARs in oligodendrocyte precursor cells (OPCs) and oligodendrocytes (OLGs) is unclear. To address this issue, we examined A1AR expression during different stages of oligodendrocyte development. Radioreceptor studies showed that membranes prepared from OPCs and OLGs expressed high-affinity A1ARs with Kd values of 1.35 +/- 0.33 and 1.2 +/- 0.27 nM for [3H]CCPA, 1.17 +/- 0.24 and 1.4 +/- 0.34 nM for [3H]DPCPX, respectively. Bmax values were 64.31 +/- 6.14 and 75 +/- 6 fmol/mg protein for [3H]CCPA, and 153 +/- 12 and 205 +/- 17.8 fmol/mg protein for [3H]DPCPX, respectively. Activation of A1ARs using N6-cyclopentyladenosine (CPA) reduced both forskolin- and N-ethylcarboxyamidoadenosine (NECA)-stimulated cAMP accumulation, but did not affect basal cAMP levels. Activation of A1ARs by CPA stimulated OPC migration, but did not affect cell viability, proliferation, or differentiation. These results show that OPCs and OLGs express functional A1ARs that can stimulate the migration of OPCs.     

Caffeine-mediated induction of c-fos, zif-268 and arc expression through A1 receptors in the striatum: different interactions with the dopaminergic system

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.     

Development of A1 adenosine receptors in the chick embryo retina

Adenosine inhibits cyclic AMP synthesis induced by dopamine in embryonic but not in post-hatched chick retinas. N6-Cyclohexyladenosine (CHA), which preferentially activates A1 receptors as well as 2-chloroadenosine, inhibits cyclic AMP accumulation induced by dopamine in retinas from 10-day-old embryos (E10) with IC50's of 0.1 and 0.5 microM, respectively, but this effect is not detectable after hatching. In order to verify if this developmental change reflects variations in the number or affinity of A1 adenosine receptors, their development during chick retina ontogeny was studied. Binding studies using 3(H)CHA revealed the presence of A1 receptors at all stages of development examined, including the post-hatched retina. The number of binding sites increased between E10 and E17, and then decreased in post-hatched animals. In the latter, 3(H)CHA binding was to a single site with a Bmax of 128.6 +/- 13.4 fmol/mg protein and a Kd of 2.1 + 0.2 nM. Various ligands showed similar hierarchies of affinity for the A1 receptor in embryonic and post-hatched retinas, namely, CHA greater than R-N6-phenylisopropyladenosine (1-PIA) greater than 5'-N-ethylcarboxamideadenosine (NECA) greater than isobuthylemethyl-xanthine (IBMX). Given that CHA inhibited forskolin-induced cyclic AMP production and Gpp(NH)p inhibited 3(H)CHA binding in both embryonic and post-hatched retinas, it appears that receptor coupling to adenylate cyclase is present since early embryonic stages. The results suggest that the A1 receptors may have different functions in the embryonic as compared to the mature chick retina.     

Upregulation of striatal adenosine A2A receptor mRNA in 6-hydroxydopamine-lesioned rats intermittently treated with L-DOPA

To determine whether the adenosine A2A receptor might play a role in L-DOPA-induced dyskinesia in Parkinson's disease, we analyzed changes in the expression of A2A receptor mRNA in response to intermittent treatment with L-DOPA in rats with dopaminergic denervation by 6-hydroxydopamine (OHDA) infusion into the medial forebrain bundle. Intermittent treatment with L-DOPA increased A2A receptor mRNA levels in the dopamine-depleted striatum of 6-OHDA-lesioned rats exhibiting behavioral sensitization to L-DOPA. These results suggest that A2A receptor activation is associated with the development of motor complications induced by L-DOPA treatment.     

Muscarinic cholinergic receptor-mediated modulation on striatal c-fos mRNA expression induced by levodopa in rat brain

Summary To clarify the interactions between dopamine receptors and muscarinic cholinergic receptors by which neurotransmitters may affect genetic responses, we studied the effects of the muscarinic cholinergic agonist, carbachol, and the muscarinic cholinergic antagonist, trihexyphenidyl, on levodopa-induced c-fos messenger RNA (mRNA) expression in rat striatum. Animals were administered levodopa (levodopa with one-tenth dosage of carbidopa), carbachol or thrihexyphenidyl alone or administered in combination as levodopa (100 mg/kg) + carbachol, or levodopa + trihexyphenidyl given as a single bolus. Levodopa given alone increase the expression of c-fos mRNA. Although carbachol or trihexyphenidyl alone was ineffective in inducing c-fos mRNA, the combination of levodopa and carbachol ( 0.1 mg/kg) significantly suppressed the induction of c-fos mRNA as compared with levodopa given alone. The combined administration of levodopa and trihexyphenidyl showed a trend toward an additive effect on the induction of c-fos mRNA vs levodopa alone. These findings suggest that the muscarinic cholinergic system may modulate the levodopa-induced c-fos mRNA expression which then regulates the expression of other mRNAs.     

Neurotensin facilitates dopamine release in vitro from rat striatal slices

Neurotensin, (0.1-10 microM) stimulated the release of [3H]dopamine from rat striatal slices in a calcium-dependent manner, and potentiated the K+-evoked release of [3H]dopamine and endogenous dopamine. This effect was dose-dependent, (1 nM-1 microM) with an EC50 of approximately 10 nM, and was mediated by means of a receptor of similar structure-activity profile to those described in other tissues.     

Acute and chronic caffeine administration differentially alters striatal gene expression in wild-type and adenosine A(2A) receptor-deficient mice

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.     

Involvement of corticostriatal glutamatergic terminals in striatal dopamine release elicited by stimulation of delta-opioid receptors

We have previously shown that striatal dopamine release induced locally by a delta-opioid receptor agonist was totally inhibited by a glutamate N-methyl-D-aspartate receptor antagonist, indicating the involvement of glutamatergic receptors in this effect. The aim of the present study was to specify this mechanism. Firstly, we investigated the effect of [D-Pen2,D-Pen5]-enkephalin (DPDPE) on glutamate release in rats by intrastriatal microdialysis. The infusion of DPDPE (10 microm) enhanced the glutamate content in dialysate by approximately 34%, an effect which did not appear to result from inhibition of glutamate uptake. We then considered the consequences of a unilateral thermocoagulation of the frontal cortex on either glutamate or dopamine release induced by stimulation of delta-opioid receptors 2 days later. This lesion, which decreased the glutamate content in ipsilateral striatum by approximately 30%, totally prevented the increase in dialysate levels of glutamate induced by DPDPE. Moreover, whereas DPDPE (10 microm) was found to increase the striatal dopamine release in intact animals by approximately 59%, this effect was also completely suppressed by the cortical lesion. Finally, we studied the effect of the lesion on the [3H]-DPDPE binding to striatal membranes prepared from the whole striatum. In the ipsilateral striatum a significant decrease in this [3H]-DPDPE binding (by approximately 18%) was found 2 days after the lesion. Our results indicate that the increase in striatal dopamine release induced by DPDPE probably depends on glutamate release from corticostriatal glutamatergic afferents in response to the stimulation of delta-opioid receptors located on terminals of these neurons.     

A simple method for characterizing passive and active neuronal properties: application to striatal neurons

The study of active and passive neuronal dynamics usually relies on a sophisticated array of electrophysiological, staining and pharmacological techniques. We describe here a simple complementary method that recovers many findings of these more complex methods but relies only on a basic patch-clamp recording approach. Somatic short and long current pulses were applied in vitro to striatal medium spiny (MS) and fast spiking (FS) neurons from juvenile rats. The passive dynamics were quantified by fitting two-compartment models to the short current pulse data. Lumped conductances for the active dynamics were then found by compensating this fitted passive dynamics within the current-voltage relationship from the long current pulse data. These estimated passive and active properties were consistent with previous more complex estimations of the neuron properties, supporting the approach. Relationships within the MS and FS neuron types were also evident, including a graduation of MS neuron properties consistent with recent findings about D1 and D2 dopamine receptor expression. Application of the method to simulated neuron data supported the hypothesis that it gives reasonable estimates of membrane properties and gross morphology. Therefore detailed information about the biophysics can be gained from this simple approach, which is useful for both classification of neuron type and biophysical modelling. Furthermore, because these methods rely upon no manipulations to the cell other than patch clamping, they are ideally suited to in vivo electrophysiology.     

Effect of cocaine self-administration on striatal dopamine D1 receptors in rhesus monkeys

An array of evidence indicates that long-term exposure to cocaine alters several components of the brain dopamine system. Because the release of dopamine in the nucleus accumbens (NAc) has been implicated in mediating the reinforcing effects of cocaine, changes in dopamine function can have profound effects on drug-seeking and drug-taking behavior. The present study examined the effects of the chronic self-administration of cocaine on the D₁ family of dopamine receptors in the rhesus monkey. The brains of three rhesus monkeys that had intravenously self-administered an average of 1.35 mg/kg cocaine per day for 18–22 months were compared to the brains of three cocaine-naive controls. The in vitro quantitative autoradiographic technique was used to quantify binding densities of the D₁ ligand [³H]SCH-23390 on cryostat-cut sections of fresh frozen tissue. In animals that self-administered cocaine, the density of D₁ binding was significantly lower in the regions of the striatum at the level where the nucleus accumbens is most fully developed. The shell of the NAc showed the largest difference with significantly lower D₁ binding also detected in adjacent regions of the caudate nucleus and the putamen. No differences were found in the rostral pole of the NAc or the dorsal striatum at that level. These findings suggest that chronic self-administration of cocaine can modulate the density of dopamine D₁ receptors in specific portions of the primate striatum. Such changes might underlie some of the behavioral consequences, like drug dependence and craving, of long-term cocaine use. Synapse 28:1–9, 1998. © 1998 Wiley-Liss, Inc.     

Neonatal tail posture and its relationship to striatal dopamine asymmetry in the rat

Previous research has demonstrated a link between rotational behavior and striatal dopamine asymmetry in the rat (rats rotate contralateral to the side of higher striatal dopamine concentration) and that the direction of a rat pup's tail posture will predict rotational bias. The present study hypothesized that neonatal tail posture would also predict adult striatal dopamine asymmetry. This hypothesis was confirmed for animals with a left but not right tail posture.     

Blockade of neurotensin receptors suppresses the dopamine D1/D2 synergism on immediate early gene expression in the rat brain

A remarkable feature of dopamine functioning is that the concomitant activation of D1-like and D2-like receptors acts to intensify the expression of various dopamine-dependent effects, in particular the expression of the immediate-early genes, c-fos and zif268. Using non-peptide neurotensin receptor antagonists, including SR48692, we have determined that blockade of neurotensin receptors reduced the cooperative responses of direct acting D2-like (quinpirole) and partial D1-like (SKF38393) dopamine agonists on the expression of Fos-like antigens and zif268 mRNA. Pretreatment with SR48692 (3 and 10 mg/kg) reduced the number of Fos-like immunoreactive cells produced by the combined administration of SKF38393 (20 mg/kg) and quinpirole (1 mg/kg) in the caudate-putamen, nucleus accumbens, globus pallidus and ventral pallidum. High-affinity neurotensin receptors are likely to be involved in these D1-like/D2-like cooperative responses, as compounds structurally related to SR48692, SR48527 (3 mg/kg) and its (-)antipode, SR49711 (3 mg/kg), exerted a stereospecific antagonism in all selected brain regions. Pretreatment with SR48692 (10 mg/kg) also diminished Fos induction by the indirect dopamine agonist, cocaine (25 mg/kg), particularly at the rostral level of the caudate-putamen. In situ hybridization experiments in the caudate-putamen indicated that SR48692 (10 mg/kg) markedly reduced zif268 mRNA labelling produced by SKF38393 plus quinpirole in cells not expressing enkephalin mRNA, but was unable to affect the concomitant decrease of zif268 mRNA labelling in enkephalin-positive cells. Taken together, the results of the present study indicate that neurotensin is a key element for the occurrence of cooperative responses of D2-like and partial D1-like agonists on immediate-early gene expression.     

Blockade of A2A adenosine receptors prevents basic fibroblast growth factor-induced reactive astrogliosis in rat striatal primary astrocytes

Previous literature data show that blockade of A(2A) adenosine receptors via selective antagonists induces protection in various models of neurodegenerative diseases. The mechanisms underlying this effect are still largely unknown. Since it is known that excessive reactive astrogliosis is a factor contributing to cell death in diseases characterized by neurodegenerative events, the present study has been aimed at determining whether selective A(2A) receptor antagonists can counteract the formation of reactive astrocytes induced in vitro by basic fibroblast growth factor (bFGF), a typical trigger of this reaction. Exposure of primary rat striatal astrocytes to the selective A(2A) antagonist SCH58261 resulted in concentration-dependent abolition of bFGF induction of astrogliosis in vitro. This effect could also be reproduced with the chemically unrelated A(2A) antagonist KW-6002. The direct activation of A(2A) adenosine receptors by selective receptor agonists was not sufficient per se to induce astrogliosis, suggesting that the A(2A) receptor needs to act in concert with other bFGF-induced genes to trigger the formation of reactive astrocytes. These results provide a mechanism at the basis of the neuroprotection induced by A(2A) receptor antagonists in models of brain damage and highlight this adenosine receptor subtype as a novel target for the pharmacological modulation of the gliotic reaction.     

Methamphetamine induces striatal neurokinin‐1 receptor endocytosis primarily in somatostatin/NPY/NOS interneurons and the role of dopamine receptors in mice

Methamphetamine (METH) is a psychostimulant that induces long‐term deficits of dopamine terminal markers and apoptotic cell death in the striatum. Our laboratory demonstrated that pharmacological blockade of the neurokinin‐1 receptor attenuated the METH‐induced damage to the striatal dopamine terminals and the apoptotic cell death of some striatal neurons. Here, we used histological methods to assess the effect of METH on neurokinin‐1 receptor trafficking in the striatum as an indirect index of signaling by the neuropeptide substance P (natural ligand for this receptor). Male mice received a single injection of METH (30 mg/kg, i.p.) and were sacrificed 30 min later. Immunohistofluorescence confocal microscopy confirmed that the neurokinin‐1 receptor is located on cholinergic and somatostatin interneurons of the striatum. METH induced the trafficking of the neurokinin‐1 receptor from the membrane into cytoplasmic endosomes primarily in the somatostatin/NPY/NOS interneurons, and this phenomenon was attenuated by antagonists of the dopamine D1 (SCH‐23390), D2 (raclopride), or neurokinin‐1 (WIN‐51,708) receptors. These data demonstrate that METH induces the trafficking of the striatal neurokinin‐1 receptors principally in the somatostatin/NPY/NOS interneurons and that this phenomenon is dependent on the activity of dopamine D1 and D2 receptors. Synapse, 2011. © 2010 Wiley‐Liss, Inc.     

Amphetamine and cocaine induce different patterns of c-fos mRNA expression in the striatum and subthalamic nucleus depending on environmental context

In the dorsal striatum, there are two major populations of medium spiny projection neurons. One population is positive for dynorphin mRNA (DYN+), and these cells project preferentially to the substantia nigra, forming the so-called 'direct pathway'. A second population is positive for enkephalin mRNA (ENK+), and these cells influence the substantia nigra indirectly, via the globus pallidus and subthalamic nucleus. Psychostimulant drugs, such as amphetamine and cocaine, are reported to induce immediate early genes (IEGs) in only one subpopulation of dorsal striatal projection neurons, DYN+ cells. However, this apparent selectivity appears to be a function of environmental context. We found that when given in the animal's home cage, amphetamine and cocaine increased expression of the IEG, c-fos, almost exclusively in DYN+ cells. However, when given in a novel environment, amphetamine and cocaine increased c-fos mRNA in both DYN+ and ENK+ cells. Furthermore, amphetamine and cocaine increased c-fos mRNA expression in the subthalamic nucleus when administered in the novel environment, but not when given at home. We conclude that the neural circuitry engaged by psychostimulant drugs, and their ability to induce specific patterns of gene expression, are determined by the environmental context in which they are experienced. This may be related to the ability of environmental novelty to facilitate psychostimulant drug-induced neuroplasticity.