Dexamethasone stimulates human A1 adenosine receptor (A1AR) gene expression through multiple regulatory sites in promoter B

Dioxin Disrupts Thyroid Hormone and Glucocorticoid Induction of klf9, a Master Regulator of Frog Metamorphosis

Frog metamorphosis, the development of an air-breathing froglet from an aquatic tadpole, is controlled by thyroid hormone (TH) and glucocorticoids (GC). Metamorphosis is susceptible to disruption by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), an aryl hydrocarbon receptor (AHR) agonist. Krüppel-like factor 9 (klf9), an immediate early gene in the endocrine-controlled cascade of expression changes governing metamorphosis, can be synergistically induced by both hormones. This process is mediated by an upstream enhancer cluster, the klf9 synergy module (KSM). klf9 is also an AHR target. We measured klf9 mRNA following exposures to triiodothyronine (T3), corticosterone (CORT), and TCDD in the Xenopus laevis cell line XLK-WG. klf9 was induced 6-fold by 50 nM T3, 4-fold by 100 nM CORT, and 3-fold by 175 nM TCDD. Cotreatments of CORT and TCDD or T3 and TCDD induced klf9 7- and 11-fold, respectively, whereas treatment with all 3 agents induced a 15-fold increase. Transactivation assays examined enhancers from the Xenopus tropicalis klf9 upstream region. KSM-containing segments mediated a strong T3 response and a larger T3/CORT response, whereas induction by TCDD was mediated by a region ∼1 kb farther upstream containing 5 AHR response elements (AHREs). This region also supported a CORT response in the absence of readily identifiable GC responsive elements, suggesting mediation by protein-protein interactions. A functional AHRE cluster is positionally conserved in the human genome, and klf9 was induced by TCDD and TH in HepG2 cells. These results indicate that AHR binding to upstream AHREs represents an early key event in TCDD's disruption of endocrine-regulated klf9 expression and metamorphosis.

Effect of dexamethasone on the expression of MMPs, adenosine A1 receptors and NFKB by human trabecular meshwork cells

Objectives Steroid-induced ocular hypertension and glaucoma are associated with extracellular matrix remodeling at the trabecular meshwork (TM) of the eye due to reduced secretion of matrix metalloproteinases (MMPs), a family of enzymes regulating extracellular matrix proteolysis. Several biological functions of steroids are known to involve regulation of adenosine A1 receptors (A1AR) and nuclear factor kappa B (NFKB). Since MMPs expression in TM has been shown to be regulated by A1AR as well as transcription factors, it is likely that dexamethasone-induced changes in aqueous humor dynamics involve reduced MMP and A1AR expression and reduced NFKB activation. Hence, the current study investigated the association of dexamethasone-induced reduction in MMP secretion with reduced NFKB activation and A1AR expression. Methods Human trabecular meshwork cells (HTMCs) were characterized by estimating myocilin and alpha smooth muscle actin expression and then were treated with dexamethasone 100 nM for 2, 5 and 7 days. The MMP secretion was estimated in culture media using Western blot. Immunocytochemistry (ICC) and ELISA were done to investigate the effect of dexamethasone on NFKB phosphorylation. A1AR expression in HTMCs was determined using Western blot and ELISA. Results Dexamethasone caused a significant reduction in both MMP-2 and -9 expression compared to untreated group after five and seven days but not after two days of culture. Significantly reduced phosphorylated NFKB and A1AR protein levels were detected in dexamethasone treated compared to vehicle treated HTMCs after five days of culture. Conclusions Dexamethasone reduces MMP-2 and -9 secretion by HTMCs and this effect of dexamethasone is associated with reduced NFKB phosphorylation and A1AR expression.

Glucocorticoids Induce Stress Oncoproteins Associated with Therapy-Resistance in African American and European American Prostate Cancer Cells

Glucocorticoid receptor (GR) is emerging as a key driver of prostate cancer (PCa) progression and therapy resistance in the absence of androgen receptor (AR) signaling. Acting as a bypass mechanism, GR activates AR-regulated genes, although GR-target genes contributing to PCa therapy resistance remain to be identified. Emerging evidence also shows that African American (AA) men, who disproportionately develop aggressive PCa, have hypersensitive GR signaling linked to cumulative stressful life events. Using racially diverse PCa cell lines (MDA-PCa-2b, 22Rv1, PC3, and DU145) we examined the effects of glucocorticoids on the expression of two stress oncoproteins associated with PCa therapy resistance, Clusterin (CLU) and Lens Epithelium-Derived Growth Factor p75 (LEDGF/p75). We observed that glucocorticoids upregulated LEDGF/p75 and CLU in PCa cells. Blockade of GR activation abolished this upregulation. We also detected increased GR transcript expression in AA PCa tissues, compared to European American (EA) tissues, using Oncomine microarray datasets. These results demonstrate that glucocorticoids upregulate the therapy resistance-associated oncoproteins LEDGF/p75 and CLU, and suggest that this effect may be enhanced in AA PCa. This study provides an initial framework for understanding the contribution of glucocorticoid signaling to PCa health disparities.

Unpredictable Chronic Stress Alters Adenosine Metabolism in Zebrafish Brain

Stress is considered a risk factor for several human disorders. Despite the broad knowledge of stress responses in mammals, data on the relationship between unpredictable chronic stress (UCS) and its effects on purinergic signaling are limited. ATP hydrolysis by ectonucleotidases is an important source of adenosine, and adenosine deaminase (ADA) contributes to the control of the nucleoside concentrations. Considering that some stress models could affect signaling systems, the objective of this study was to investigate whether UCS alters ectonucleotidase and ADA pathway in zebrafish brain. Additionally, we analyzed ATP metabolism as well as ada1, ada2.1, ada2.2, adaL, and adaasi gene expression in zebrafish brain. Our results have demonstrated that UCS did not alter ectonucleotidase and soluble ADA activities. However, ecto-ADA activity was significantly decreased (26.8%) in brain membranes of animals exposed to UCS when compared to the control group. Quantitative reverse transcription PCR (RT-PCR) analysis did not show significant changes on ADA gene expression after the UCS exposure. The brain ATP metabolism showed a marked increase in adenosine levels (ADO) in animals exposed to UCS. These data suggest an increase on extracellular adenosine levels in zebrafish brain. Since this nucleoside has neuromodulatory and anxiolytic effects, changes in adenosine levels could play a role in counteracting the stress, which could be related to a compensatory mechanism in order to restore the homeostasis.

Adenosine receptor neurobiology: overview

Adenosine is a naturally occurring nucleoside that is distributed ubiquitously throughout the body as a metabolic intermediary. In the brain, adenosine functions as an important upstream neuromodulator of a broad spectrum of neurotransmitters, receptors, and signaling pathways. By acting through four G-protein-coupled receptors, adenosine contributes critically to homeostasis and neuromodulatory control of a variety of normal and abnormal brain functions, ranging from synaptic plasticity, to cognition, to sleep, to motor activity to neuroinflammation, and cell death. This review begun with an overview of the gene and genome structure and the expression pattern of adenosine receptors (ARs). We feature several new developments over the past decade in our understanding of AR functions in the brain, with special focus on the identification and characterization of canonical and noncanonical signaling pathways of ARs. We provide an update on functional insights from complementary genetic-knockout and pharmacological studies on the AR control of various brain functions. We also highlight several novel and recent developments of AR neurobiology, including (i) recent breakthrough in high resolution of three-dimension structure of adenosine A2A receptors (A2ARs) in several functional status, (ii) receptor-receptor heterodimerization, (iii) AR function in glial cells, and (iv) the druggability of AR. We concluded the review with the contention that these new developments extend and strengthen the support for A1 and A2ARs in brain as therapeutic targets for neurologic and psychiatric diseases.

Regulation of adenosine receptors expression in rat B lymphocytes by insulin

Development of diabetes is associated with altered expression of adenosine receptors (ARs). Some of these alterations might be attributed to changes in insulin concentration. This study was undertaken to investigate the possible insulin effect on ARs level, and to determine the signaling pathway utilized by insulin to regulate the expression of ARs in rat B lymphocytes. Western blot analysis of B lymphocytes protein extracts indicated that all four ARs were present at detectable levels in the cells cultured for 24 h without insulin (<or=10(-11) M), although the protein band of A(2A)-AR was barely visible. Inclusion of insulin (10(-8) M) in the culture medium resulted in an increase of A(1)-AR and A(2A)-AR protein levels and a significant decrease of A(2B)-AR protein, whereas the protein level of A(3)-AR remained unchanged. Alterations in the ARs protein content were accompanied by changes in the ARs mRNA levels. Increase of the insulin concentration from 10(-11) to 10(-8) M resulted in 50% decrease of A(2B)-AR mRNA level and two-, and threefold increase of A(1)-AR and A(2A)-AR mRNA levels, respectively. Pretreatment of B cells with cycloheximide completely blocked the insulin action on A(1)-AR and A(2A)-AR mRNA, but not on A(2B)-AR expression. Detailed pharmacological analysis demonstrated that insulin-induced A(1)-AR and A(2A)-AR mRNA expression through the Ras/Raf-1/MEK/ERK pathway. The insulin effect on A(2B)-AR expression was blocked by p38 MAP kinase inhibitor (SB 203580). Concluding, elevated insulin concentration differentially affects the expression of ARs in B lymphocytes in a fashion that might enhance the various immunomodulatory effects of adenosine.

Role of beta-arrestin1/ERK MAP kinase pathway in regulating adenosine A1 receptor desensitization and recovery

Exposure of cells to adenosine receptor (AR) agonists leads to receptor uncoupling from G proteins and downregulation of the A(1)AR. The receptor levels on the cell surface generally recover on withdrawal of the agonist, because of either translocation of the sequestered A(1)AR back to plasma membrane or de novo synthesis of A(1)AR. To examine the mechanism(s) underlying A(1)AR downregulation and recovery, we treated ductus deferens tumor (DDT(1) MF-2) cells with the agonist R-phenylisopropyladenosine (R-PIA) and showed a decrease in membrane A(1)AR levels by 24 h, which was associated with an unexpected 11-fold increase in A(1)AR mRNA. Acute exposure of these cells to R-PIA resulted in a rapid translocation of beta-arrestin1 to the plasma membrane. Knockdown of beta-arrestin1 by short interfering RNA (siRNA) blocked R-PIA-mediated downregulation of the A(1)AR, suppressed R-PIA-dependent ERK1/2 and activator protein-1 (AP-1) activity, and reduced the induction of A(1)AR mRNA. Withdrawal of the agonist after a 24-h exposure resulted in rapid recovery of plasma membrane A(1)AR. This was dependent on the de novo protein synthesis and on the activity of ERK1/2 but independent of beta-arrestin1 and nuclear factor-kappaB. Together, these data suggest that exposure to A(1)AR agonist stimulates ERK1/2 activity via beta-arrestin1, which subserves receptor uncoupling and downregulation, in addition to the induction of A(1)AR expression. We propose that such a pathway ensures both the termination of the agonist signal and recovery by priming the cell for rapid de novo synthesis of A(1)AR once the drug is terminated.

Anti-inflammatory preconditioning by agonists of adenosine A1 receptor

BACKGROUND

Adenosine levels rise during inflammation and modulate inflammatory responses by engaging with four different G protein-coupled receptors. It is suggested that adenosine exhibits pro-inflammatory effects through its A(1) receptor (A(1)R), and anti-inflammatory effects through A(2A) receptor (A(2A)R). Therefore, understanding of the mechanisms that govern adenosine receptor regulation may advance treatment of various inflammatory disorders. We previously reported that peak A(1)R expression during leukocyte recruitment, is followed by a peak in A(2A)R during inflammation resolution.

PRINCIPAL FINDINGS

Here, we examined whether A(1)R activation sequentially induces A(2A)R expression and by this reverses inflammation. The effect of adenosine on A(1)R mediated A(2A)R expression was examined in peritoneal macrophages (PMPhi) and primary peritoneal mesothelial cells (PMC) in vitro. Induction of A(2A)R was inhibited by pertussis toxin (PTX) and partly dependent on A(2A)R stimulation. Administration of A(1)R agonists to healthy mice reduced A(1)R expression and induced A(2A)R production in PMC. Mice that were preconditioned with A(1)R agonists 24 hours before E. coli inoculation exhibited decreased TNFalpha and IL-6 sera levels and reduced leukocytes recruitment. Preconditioning was blocked by pretreatment with A(1)R antagonist, as well as, or by late treatment with A(2A)R antagonist, and was absent in A(2A)R(-/-) mice.

CONCLUSIONS

Our data suggest that preconditioning by an A(1)R-agonist promotes the resolution of inflammation by inducing the production of A(2A)R. Future implications may include early treatment during inflammatory disorders or pretreatment before anticipated high risk inflammatory events, such as invasive surgery and organ transplantation.

Glucocorticoids regulate innate immunity in a model of multiple sclerosis: reciprocal interactions between the A1 adenosine receptor and beta-arrestin-1 in monocytoid cells

Desensitization of seven transmembrane receptors (7TMRs), which are modulated by the beta-arrestins, leads to altered G protein activation. The A1 adenosine receptor (A1AR) is an antiinflammatory 7TMR exhibiting reduced expression and activity in both multiple sclerosis (MS) and the murine MS model, experimental autoimmune encephalomyelitis (EAE) in monocytoid cells. Herein, we report that beta-arrestin-1 expression was increased in brains of MS patients relative to non-MS brains, whereas A1AR expression was concomitantly reduced. This inverse relationship between beta-arrestin-1 and A1AR was confirmed in cultured monocytoid cells as beta-arrestin-1 overexpression resulted in a down-regulation of A1AR together with the internalization of the surface receptor. Moreover, a physical interaction between beta-arrestin-1 and A1AR was demonstrated in monocytoid cells. Proinflammatory cytokines regulated the A1AR/beta-arrestin-1 interactions, while A1AR activation also modulated proinflammatory cytokines expression. During EAE, beta-arrestin-1 and A1AR expression in the spinal cord displayed a similar pattern compared to that observed in MS brains. EAE-induced neuroinflammation and neurobehavioral deficits were suppressed by glucocorticoid treatments, accompanied by concurrent reduced beta-arrestin-1 and enhanced A1AR expression. Thus, the interplay between beta-arrestin-1 and A1AR in the central nervous system during neuroinflammation represents a reciprocal regulatory mechanism through which neuroprotective therapeutic strategies for neuroinflammatory diseases might be further developed.

IL-1 beta and TNF-alpha regulation of the adenosine receptor (A2A) expression: differential requirement for NF-kappa B binding to the proximal promoter

Adenosine is a potent endogenous regulator of airway inflammation that acts through specific receptor subtypes that can either cause constriction (A1R, A2BR, and A3R) or relaxation (A2AR) of the airways. We therefore examined the effects of key inflammatory mediators on the expression of the A2AR in a lung epithelial cell line (A549). IL-1beta and TNF-alpha increased the expression of the A2AR gene at the mRNA and protein levels. In contrast, LPS had no effect on A2AR gene expression. IL-1beta and TNF-alpha rapidly activated p50 and p65, but not C-Rel, RelB, or p52, and both IL-1beta- and TNF-alpha-stimulated A2AR expression was inhibited by the IkappaB kinase 2 inhibitor AS602868 in a concentration-dependent manner. Using chromatin immunoprecipitation assays, we demonstrate that IL-1beta can enhance p65 association with putative kappaB binding sites in the A2AR promoter in a temporal manner. In contrast, TNF-alpha failed to enhance p65 binding to these putative sites. Functionally, the two most 5' kappaB sites were important for IL-1beta-, but not TNF-alpha-, induced A2AR promoter reporter gene activity. Finally, neither TNF-alpha nor Il-1beta had any effect on A2AR mRNA transcript degradation. These results directly implicate a major role for NF-kappaB in the regulation of A2AR gene transcription by IL-1beta and TNF-alpha but suggest that the effects of TNF-alpha on A2AR gene transcription are not mediated through the proximal promoter.

Increased density and synapto-protective effect of adenosine A2A receptors upon sub-chronic restraint stress

Stress initially causes adaptive changes in the brain and can lead to neurodegeneration if continuously present. Noxious brain conditions trigger the release of adenosine that can control brain function and neurodegeneration through inhibitory A(1) and facilitatory A(2A) receptors. We tested the effect of restraint stress on the density of adenosine receptors and their effect on the outcome of stress, focusing in a known affected region, the hippocampus. Sub-chronic restraint stress (6 h/day for 7 days) caused a parallel decrease of the density of A(1) receptors (15-20%) and an increase (near 250%) of A(2A) receptor density in rat hippocampal nerve terminals. This indicates that sub-chronic stress unbalances adenosine receptors, up-regulating A(2A) and down-regulating A(1) receptors. Sub-chronic stress did not cause hippocampal neurodegeneration but decreased the immunoreactivity (immunohistochemistry and Western blot) of a synaptic marker, synaptophysin. The blockade of A(2A) receptors with 7-(2-phenylethyl)-5-amino-2-(2-furyl)-pyrazolo-[4,3-e]-1,2,4-triazolo[1,5-c]pyrimidine (0.05 mg/kg, daily i.p. injection) attenuated the loss of synaptophysin immunoreactivity observed in the hippocampus of rats subjected to sub-chronic restraint stress. This ability of A(2A) receptor antagonists to prevent the earliest stress-induced synaptic modifications provides a neurochemical and morphological correlate for the interest of A(2A) receptor antagonists to attenuate the burden of chronic stress.

Upregulation of A2A adenosine receptor expression by TNF-alpha in PBMC of patients with CHF: a regulatory mechanism of inflammation

BACKGROUND

Tumor necrosis factor (TNF)-alpha plays a role in congestive heart failure (CHF). A2A adenosine receptor (A(2A)R) activation on immune cells putatively reduces the release of cytokines contributing to CHF progression. The study is aimed at determining the role of the A(2A)R in the modulation of TNF-alpha production, and the ex vivo effect of TNF-alpha on A(2A)R in peripheral blood mononuclear cells (PBMC) from CHF patients.

METHODS AND RESULTS

Plasma levels of TNF-alpha and TNF-alpha production from lipopolysaccharide (LPS)-stimulated PBMC were evaluated in 26 CHF patients in comparison to controls. The effects of the A(2A)R agonist CGS-21680 and antagonist ZM-241385 on TNF-alpha production from PBMC were also evaluated. Finally, reverse transcriptase-polymerase chain reaction and Western blot analyses of A(2A)R in PBMC were performed in TNF-alpha-treated and untreated cells. TNF-alpha production from LPS-stimulated PBMC was enhanced in CHF patients with respect to controls. CGS-21680 blunted TNF-alpha production in both groups; ZM-241385 reverted this effect. A(2A)R expression in PBMC was higher in CHF patients than in controls. TNF-alpha addition produced an increase in A(2A)R in PBMC from controls but not in PBMC from CHF patients.

CONCLUSIONS

PBMC from CHF patients show an upregulation of A(2A)R-mediated inhibition of TNF-alpha, which may represents a mechanism of protection against inappropriate cytokine production.

A1 adenosine receptor upregulation and activation attenuates neuroinflammation and demyelination in a model of multiple sclerosis

The neuromodulator adenosine regulates immune activation and neuronal survival through specific G-protein-coupled receptors expressed on macrophages and neurons, including the A1 adenosine receptor (A1AR). Here we show that A1AR null (A1AR-/-) mice developed a severe progressive-relapsing form of experimental allergic encephalomyelitis (EAE) compared with their wild-type (A1AR+/+) littermates. Worsened demyelination, axonal injury, and enhanced activation of microglia/macrophages were observed in A1AR-/- animals. In addition, spinal cords from A1AR-/- mice demonstrated increased proinflammatory gene expression during EAE, whereas anti-inflammatory genes were suppressed compared with A1AR+/+ animals. Macrophages from A1AR-/- animals exhibited increased expression of the proinflammatory genes, interleukin-1beta, and matrix metalloproteinase-12 on immune activation when matched with A1AR+/+ control cells. A1AR-/- macrophage-derived soluble factors caused significant oligodendrocyte cytotoxicity compared with wild-type controls. The A1AR was downregulated in microglia in A1AR+/+ mice during EAE accompanied by neuroinflammation, which recapitulated findings in multiple sclerosis (MS) patients. Caffeine treatment augmented A1AR expression on microglia, with ensuing reduction of EAE severity, which was further enhanced by concomitant treatment with the A1AR agonist, adenosine amine congener. Thus, modulation of neuroinflammation by the A1AR represents a novel mechanism that provides new therapeutic opportunities for MS and other demyelinating diseases.

Th1 Cytokines Regulate Adenosine Receptors and Their Downstream Signaling Elements in Human Microvascular Endothelial Cells

We and others have shown that adenosine, acting at its receptors, is a potent modulator of inflammation and angiogenesis. To better understand the regulation of adenosine receptors during these processes we studied the effects of IL-1, TNF-alpha, and IFN-gamma on expression and function of adenosine receptors and select members of their coupling G proteins in human dermal microvascular endothelial cells (HMVEC). HMVEC expressed message and protein for A(2A) and A(2B), but not A(1) or A(3) receptors. IL-1 and TNF-alpha treatment increased message and protein expression of A(2A) and A(2B) receptor. IFN-gamma treatment also increased the expression of A(2B) receptors, but decreased expression of A(2A) receptors. Resting HMVEC and IFN-gamma-treated cells showed minimal cAMP response to the selective A(2A) receptor agonist 2-[2-(4-chlorophenyl)ethoxy]adenosine (MRE0094). In contrast, MRE0094 stimulated a dose-dependent increase in cAMP levels in TNF-alpha-treated cells that was almost completely blocked by the A(2A) receptor antagonist ZM-241385 (4-[2-[7-amino-2-(2-furyl)[1,2,4]triazolo-[2,3-a][1,3,5]triazin-5-ylamino]ethyl]phenol). The nonselective adenosine receptor agonist 5'-(N-ethylcarboxamido)adenosine increased cAMP levels in both TNF-alpha- and IFN-gamma-treated cells, but not control cells, and its effect was only partially reversed by ZM-241385 in TNF-alpha-treated cells and not affected in IFN-gamma-treated cells. HMVEC expressed a higher level of G protein beta1 isoform than beta4 isoform. Although none of the cytokines tested affected G(beta1) expression, both IL-1 and TNF-alpha significantly up-regulated G(beta4) expression. These findings indicate that inflammatory cytokines modulate adenosine receptor expression and function on HMVECs and suggest that the interaction between proinflammatory cytokines and adenosine receptors may affect therapeutic responses to anti-inflammatory drugs that act via adenosine-dependent mechanisms.

Inflammatory cytokines regulate function and expression of adenosine A(2A) receptors in human monocytic THP-1 cells

Adenosine, acting at its receptors, particularly A(2A) receptors, is a potent endogenous anti-inflammatory agent that modulates the functions and differentiation of inflammatory and immune cells. Because the inflammatory milieu abounds in proinflammatory cytokines, we investigated the effects of Th1-inflammatory cytokines on function and expression of adenosine A(2A) receptors in the human monocytic cell line THP-1. We found that, consistent with previous reports, adenosine and 2-[p-(2-carnonylethyl)phenylethylamino]-5'-N-ethylcarboxamidoadenosine (CGS-21680), a selective A(2A) receptor agonist, suppress IL-12 production but increase IL-10 production in LPS-activated THP-1 cells. These effects were blocked by the A(2A) receptor antagonist 4-(2-[7-amino-2-(2-furyl)[1,2,4-triazolo[2,3-a][1,3,5]triazin-5-ylamino]ethyl)phenol (ZM-241385). More importantly, the suppressive effect of adenosine and CGS-21680 on IL-12 production was significantly enhanced in cells pretreated with either IL-1 (10 U/ml) or TNF-alpha (100 U/ml) but markedly attenuated in cells pretreated with IFN-gamma (100 U/ml). Similarly, IL-1 and TNF-alpha treatment potentiated the stimulatory effect of adenosine and CGS-21680 on IL-10 production, whereas IFN-gamma treatment almost completely abolished this effect. CGS-21680 stimulated an increase in intracellular cAMP in a time- and dose-dependent manner in IL-1- and TNF-alpha-treated cells but not in control or IFN-gamma-treated cells. Both IL-1 and TNF-alpha increased A(2A) receptor mRNA and protein. In parallel with its effect on A(2A) receptor function, IFN-gamma down-regulated A(2A) receptor message and protein. Because adenosine mediates many of the antiinflammatory effects of drugs such as methotrexate, these observations suggest that local changes in the cytokine milieu may influence the therapeutic response to those drugs by altering the expression and function of adenosine receptors on inflammatory cells.

Subchronic treatment with methamphetamine and phencyclidine differentially alters the adenosine A1 and A2A receptors in the prefrontal cortex, hippocampus, and striatum of the rat

Subchronic treatment with MAP (4.6 mg/kg, i.p., once daily for 11 days) significantly decreased the Kd, but not Bmax, values of [3H]1,3-dipropyl-8-cyclopentylxanthine ([3H]DPCPX) binding to adenosine A1 receptors in the prefrontal cortex and hippocampus, but not striatum, of rat brain. However, subchronic treatment with PCP (10 mg/kg, i.p., once daily for 11 days) did not alter the Kd and Bmax values of [3H]DPCPX binding to adenosine A1 receptors in these three regions. Subchronic treatment with MAP or PCP did not alter the Bmax and Kd values of [3H]2-p-(2-carboxyehyl)phenethylamino-5'-N-ethylcarboxyamidoadenosine ([3H]CGS21680) binding to adenosine A2A receptors in the striatum. Furthermore, subchronic treatment with MAP or PCP significantly decreased the specific binding of [3H]CGS21680 to adenosine A2A receptors in the hippocampus, but not in the prefrontal cortex. Thus, these results suggest that MAP and PCP may produce differential effects on the adenosine A2A receptors, but not adenosine A1 receptors in rat brain.