Postischemic alteration of muscarinic acetylcholine, adenosine A1 and calcium antagonist binding sites in selectively vulnerable areas: an autoradiographic study of gerbil brain.

We performed receptor autoradiography to determine sequential alterations in the binding of muscarinic cholinergic and adenosine A1 receptors and of a voltage dependent L-type calcium channel blocker 1 h-1 month after transient cerebral ischemia in the gerbil brain. [3H]Quinuclidinyl benzilate (QNB), [3H]cyclohexyladenosine (CHA) and [3H]PN200-110 were used to label muscarinic and adenosine A1 receptors and L-type calcium channels, respectively. Transient ischemia was induced for 10 min. [3H]QNB and [3H]CHA binding showed no significant alteration in selectively vulnerable areas at an early stage (1-24 h) of recirculation. However, the dentate molecular layer which was resistant to ischemia revealed a significant decrease in the [3H]CHA binding sites 24 h after ischemia. Thereafter, the [3H]QNB and [3H]CHA binding showed significant reduction in most of selectively vulnerable areas. Marked reduction was especially found in the dorsolateral part of striatum and the hippocampal CA1 sector which was the most vulnerable to ischemia. In contrast, [3H]PN200-110 binding showed a transient elevation in the hippocampal CA1 sector, the dentate molecular layer and the thalamus 1 h of recirculation. However, the striatum and neocortex revealed no alteration in the [3H]PN200-110 binding. Thereafter, the reduction in the [3H]PN200-110 binding was seen only in the dorsolateral part of the striatum and the hippocampal CA1 sector. The results suggest that transient cerebral ischemia can cause the alterations in the binding of muscarinic cholinergic and adenosine A1 receptors and of L-type calcium channel blocker in most of selectively vulnerable areas.(ABSTRACT TRUNCATED AT 250 WORDS)     

Upregulation of Adenosine Al Receptors and Forskolin Binding Sites Following Chronic Treatment with Caffeine or Carbamazepine: A Quantitative Autoradiographic Study

The effects of feeding a diet enriched in caffeine or carbamazepine (CBZ) were investigated in rats in a quantitative autoradiographic study of adenosine A1 receptors (labeled by [3H]cyclohexyladenosine, [3H]CHA) and adenylate cyclase (labeled by [3H]forskolin). Although regional distribution of [3H]CHA and [3H]forskolin binding sites differed in some areas, chronic CBZ as well as chronic caffeine upregulated both of them. The changes in receptor densities occurred in the same brain microregions, suggesting that caffeine and CBZ act as antagonists at similar subpopulations of adenosine A1 receptors and [3H]forskolin binding sites. Therefore, a selective interaction of these two drugs with distinct adenosine A1 receptors (and adenylate cyclase) probably does not explain the differential effects of caffeine and CBZ on neuronal activity.     

Sequential changes in muscarinic acetylcholine, adenosine A1 and calcium antagonist binding sites in the gerbil hippocampus following repeated brief ischemia.

We performed quantitative autoradiography to determine sequential alterations in the binding of muscarinic cholinergic and adenosine A1 receptors and of an L-type calcium channel blocker in the gerbil hippocampus following repeated brief ischemic insults. [3H]Quinuclidinyl benzilate (QNB). [3H]cyclohexyladenosine (CHA) and [3H]PN200-110 were used to label muscarinic and adenosine A1 receptors and L-type calcium channels, respectively. Changes at 1 h, 6 h, 1 day, 4 days and 1 month after three 2-min ischemic insults were compared with changes after single 2- or 6-min ischemia. Two-minute ischemia, which causes no histopathological neuronal damage, produced no persistent alterations in binding sites. We observed a transient and mild increase in binding activities, especially in [3H]CHA binding, at 1 h of recirculation. Following 6-min ischemia and three 2-min ischemic insults. [3H]QNB and [3H]PN200-110 binding decreased by more than 50% in the CA1 subfield by 1 month, but [3H]CHA binding decreased transiently by 20-30% at 4 days when delayed neuronal death of hippocampal CA1 pyramidal cells took place. Reductions in binding, especially in [3H]QNB binding, following three 2-min ischemic insults were greater and appeared earlier than those after 6-min ischemia. Furthermore, alterations extended to the CA3 subfield and the dentate gyrus following repeated insults. Thus, alterations in receptor binding after repeated ischemic insults were greater than those after equivalent single period of ischemia.     

Quantitative autoradiographic analysis of muscarinic cholinergic and adenosine A1 binding sites after transient forebrain ischemia in the gerbil

The influence of transient forebrain ischemia on adenosine A₁ and muscarinic cholinergic receptors in the gerbil brain 1–27 days after recirculation was studied. The topographical distribution and the alteration in the adenosine A₁ and muscarinic receptor sites were analyzed by means of quantitative receptor autoradiography using [³H]cyclohexyladenosine ([³H]CHA) and [³H]quinuclidinyl benzilate ([³H]QNB), respectively. In most regions examined, the temporal profiles of the alteration of the receptor density were in accordance with the histopathological findings. [³H]CHA binding activity decreased suddenly after neuronal damage, while [³H]QNB grain density showed a gradual decrease in the dorsolateral caudate-putamen and in the CA₁ subfield of the hippocampus. In the caudate-putamen, [³H]CHA and [³H]QNB binding activity in the dorsal aspect was markedly reduced 1–27 days after ischemia. [³H]CHA binding activity in the ventromedial region of the caudate-putamen also decreased 1–3 days after ischemia, though neuronal damage was restricted to the dorsolateral aspect. Neuronal death in CA₁ was preceded by the decrease in [³H]QNB binding activity in the stratum radiatum 1 and 2 days after ischemia. Marked decrease in [³H]QNB and [³H]CHA binding activity was noted in the CA₁ subfield 3–27 days after recirculation. Three to 27 days after ischemia, the A₁ binding activities in the CA₃ subfield of the hippocampus and int he dentate gyrus were reduced despite the normal appearance of these areas throughout the reperfusion period. Muscarinic binding sites in the CA₃ subfield were also reduced 27 days after ischemia. Despite minimal neuronal damage in the lateral septal nucleus and in the substantia nigra, the A₁ binding activity in these regions was reduced by 70% and 50%, respectively. These results provide further evidence that the muscarinic receptors in the dorsolateral region of the caudate-putamen are localized postsynaptically on small and medium-sized neurons and that those in the CA₁ subfield of the hippocampus are localized on the CA₁ pyramidal cells.     

Characterization and localization of adenosine receptors in rat spinal cord

Adenosine A1 receptors were characterized in membranes from rat dorsal and ventral spinal cord using [3H] cyclohexyladenosine [( 3H]CHA) and compared with those in brain. For determination of anatomical loci of adenosine A1 receptors in the dorsal and ventral spinal cord, various lesions were employed, including kainic acid injections directly into the lumbar dorsal spinal cord, spinal cord hemitransections, dorsal rhizotomies, and neonatal capsaicin treatment. In control animals a single high affinity binding component was observed in dorsal and ventral spinal cord with KD values of 2.3 and 2.6 nM and Bmax values of 170 and 123 fmol/mg of protein, respectively. In comparison, [3H]CHA binding to whole brain membranes exhibited KD and Bmax values of 2.3 nM and 301 fmol/mg of protein, respectively. The IC50 values for CHA, (-)-phenylisopropyl adenosine, adenosine-5'-ethylcarboxamide, 2-chloroadenosine, (+)-phenylisopropyl adenosine, and theophylline to displace [3H]CHA were 3.6, 2.3, 15, 17, 21, and 30,500 nM for dorsal horn and 5.1, 2.7, 9.8, 24, 25, and 21,000 nM for ventral horn. The potencies of the various ligands are similar to those found for brain tissue. Injection of kainic acid directly into the dorsal spinal cord significantly reduced specific [3H]CHA binding by 33% in this tissue when compared to values from saline-injected control animals. This decrease was accompanied histologically by the depletion of intrinsic neuronal cell bodies and extensive gliosis at the injection site. Terminals of descending or primary afferent systems appear not to contain [3H]CHA-binding sites since lesions which interrupt these systems failed to alter the levels of [3H]CHA receptors in denervated spinal cord tissue.(ABSTRACT TRUNCATED AT 250 WORDS)     

Inhibition of N6-[3H]cyclohexyladenosine binding by carbamazepine

The mechanism of action of carbamazepine (CBZ) (Tegretol), despite widespread use in the management of partial and tonic-clonic seizures in adults, is not completely understood. In animals, adenosine and adenosine analogues have anticonvulsant effects that may be due to interactions with central A1 adenosine receptors. CBZ (at therapeutically relevant concentrations) inhibits the binding of agonists and antagonists to brain A1 adenosine receptors, but whether as an agonist/antagonist is not clear. The adenosine agonist, N6-[3H]cyclohexyladenosine ([3H]CHA), binds to membranes from rat cortex and hippocampus at two nanomolar binding sites or states. To clarify the actions of carbamazepine at the A1 adenosine receptor, its inhibitory actions were compared with those of known adenosine agonists and xanthine antagonists using 0.1 nM[3H]CHA, in which almost all binding is to the higher affinity state, or 10 nM [3H]CHA, in which there is a substantial contribution of binding from both states. The ratios of the IC50 values (concentration that inhibits specific binding by 50%) at 10 nM [3H]CHA to the IC50 values at 0.1 nM [3H]CHA were 18-31 for the agonists and 4-10 for the xanthine antagonists. CBZ had a ratio of 3. The inhibitory effects of GTP on [3H]CHA binding were less in the presence of the adenosine agonist, 2-chloroadenosine than were inhibitory effects in the presence of the xanthine antagonist theophylline or CBZ in both cortex and hippocampus. These in vitro studies indicate that CBZ is an antagonist at A1 adenosine receptors in cerebral cortical and hippocampal membranes from rat brain. Agonist activity at A1 adenosine receptors would have been compatible with the sedative anticonvulsant effects of CBZ, but these data do not support a role of the anticonvulsant action of carbamazepine on A1 adenosine receptors in cerebral cortex or hippocampus.     

Alterations of A1 adenosine receptors in different mouse brain areas after pentylentetrazol-induced seizures, but not in the epileptic mutant mouse 'tottering'

Single and repeated Pentylentetrazol (PTZ)-induced convulsions are associated with significant changes of A1 adenosine receptors (detected using the radioligand [3H]cyclohexyladenosine, [3H]CHA) in 4 different brain areas of the mouse, namely cortex, hippocampus, cerebellum and striatum. In hippocampus and cerebellum, a rapid increase in [3H]CHA binding, by 26% and 30% respectively, was observed 1 h after a single PTZ convulsion. In striatum, on the contrary, a significant decrease by 30% in [3H]CHA binding was seen, whereas in cortex no significant change could be detected. After daily repeated PTZ convulsions, a significant increase of A1 receptors by 26% appeared also in cortex, while the changes of A1 receptors observed in the other brain areas after a single PTZ convulsion were maintained in almost the same range. All the alterations observed were due to changes of the total number of A1 receptors (Bmax) without changes in receptor affinity (Kd). A significant increase in the latency of PTZ seizure (time between the PTZ-injection and the beginning of the seizure) was also observed after repeated PTZ-induced convulsions at the time when the changes in A1 adenosine receptors were noted. Considered together, these results provide further evidence for an A1 receptor-mediated modulation of seizure susceptibility and indicate that specific brain areas may play different roles in this modulation. The binding of [3H]CHA to membranes from different cortical and subcortical areas of the epileptic mutant mouse 'tottering' was not different from that in control animals.     

Potential use of DPCPX as probe for in vivo localization of brain A1 adenosine receptors

The suitability of (³H)DPCPX (8-cyclopentyl-1,3-dipropylxanthine), a xanthine derivative, as an vivo probe for labelling adenosine A₁ receptors was studied in rats. [³H]DPCPX (nM) penetrated largely into the brain (0.8% of the injected dose per gram of brain tissue 5 min after injection). Brain concentrations stayed at a plateau level from 5 to 15 min after the injection. The distribution in the different brain regions was heterogeneous with the highest amount of [³H]DPCPX in cerebellum and hippocampus and the lowest concentrations in hypothalamus and brain stem. Displacement (45–70% of total radioactivity) was obtained by the injection of 250 nM of cold DPCPX or cyclopentylxanthine, an analog of DPCPX. The ex vivo autoradiographic distribution of [³H]DPCPX was similar to the in vitro autoradiographic distribution of tritiated A₁ adenosine receptor ligand as [³H]CHA. These results suggest the potential use of DPCPX for further in vivo investigation of A₁ adenosine receptors with techniques such as positron emission tomography.     

1,3-Dipropyl-8-cyclopentylxanthine (DPCPX) inhibition of [3H]N-ethylcarboxamidoadenosine (NECA) binding allows the visualization of putative non-A1 adenosine receptors

The binding of the adenosine receptor agonists, [3H]N-ethylcarboxamidoadenosine (NECA) and [3H]cyclohexyladenosine (CHA) to membrane preparations and to cryostat sections of the rat brain was examined. The xanthine derivative, 1,3-dipropyl-8-cyclopentylxanthine (DPCPX) was ca. 500-fold more effective at A1 than at A2 sites. [3H]CHA binding to A1 adenosine receptors was virtually eliminated by the inclusion of DPCPX (50 nM), while [3H]NECA binding was only partially inhibited. The pattern of DPCPX-insensitive [3H]NECA binding sites was strikingly different from that of A1 receptors and is believed to represent an association with A2 type adenosine receptors and perhaps another or several, previously undescribed non-A1 sites.     

Calcium antagonist, adenosine A1, and muscarinic bindings in rat hippocampus after transient ischemia

The protective roles of Ca2+ channel blockers against ischemic hippocampal damage are still debated. We used autoradiography to study postischemic L-type Ca2+ channels (1,4-dihydropyridine Ca2+ channel blocker binding), adenosine A1 receptors, and muscarinic cholinergic receptors in the rat hippocampus using [3H]PN200-110 (PN), [3H]cyclohexyladenosine (CHA), and [3H]quinuclidinyl benzilate (QNB), respectively, in 49 rats subjected to 20 minutes of forebrain ischemia. The rats were decapitated after 1 (n = 7), 3 (n = 7), 6 (n = 8), 12 (n = 7), 24 (n = 6), 48 (n = 6), or 168 (n = 8) hours of recirculation; eight control rats were sham-operated but experienced no cerebral ischemia. Reduced receptor binding preceding the delayed death of CA1 pyramidal cells was first observed in the stratum oriens of the CA1 subfield. Significant reductions in [3H]PN, [3H]CHA, and [3H]QNB bindings of this stratum compared with control were noticed after 3 (35%, p less than 0.01), 12 (31%, p less than 0.01), and 1 (10%, p less than 0.05) hours of recirculation, respectively. By 168 hours after ischemia (when the populations of CA1 pyramidal cells were depleted) all strata in the CA1 subfield had lost most of their receptor sites, and [3H]PN, [3H]CHA, and [3H]QNB bindings in the stratum oriens were decreased to 23%, 30%, and 63% of control (p less than 0.01). Although [3H]PN binding in the CA3 subfield did not change significantly during 168 hours after ischemia, the histologically intact dentate gyrus exhibited a 31% loss of binding sites compared with control (p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)     

Autoradiographic visualization of adenosine A1 receptors in the gerbil hippocampus: changes in the receptor density after transient ischemia

N6-cyclohexyl-[3H]adenosine [( 3H]CHA) was used for the in vitro visualization of the hippocampal adenosine A1 receptors in the gerbil. The strata radiatum and oriens of the hippocampus showed particularly high binding activity. Depletion of pyramidal cells and consequent severe decrease in [3H]CHA binding activity in the CA1 subfield were observed after transient ischemic insult. These results suggest that most adenosine receptors in the CA1 region are localized in association with pyramidal cells.     

Autoradiographic demonstration of peripheral adenosine binding sites using [3H]NECA

Autoradiographic localization of 5'-N-ethylcarboxamido[3H]adenosine ([3H]NECA) binding sites revealed a heterogeneous labeling of guinea-pig intestine with heavy labeling over the enteric ganglia and in clusters over the mucosa; a low level of label was homogeneously distributed over the muscularis externa. Under the conditions employed, no binding sites were revealed using [3H]-N6-cyclohexyladenosine ([3H]CHA), although both [3H]CHA and [3H]NECA binding sites were localized over comparable areas of rat brain. The relationship of the [3H]NECA binding sites to extracellular adenosine receptors is discussed.     

Autoradiographic changes in brain adenosine A1 receptors and their coupling to G proteins following seizures in the developing rat

In the central nervous system, adenosine has been shown to be a major regulator of neuronal activity in convulsive disorders, mainly via the A1 receptor subtype. In a previous work, we have shown that seizures lead to an age-dependent upregulation of cerebral adenosine A1 sites measured in isolated rat cerebral membranes. However, information concerning regional changes in the receptor density was so far lacking. In the present study, the effects of bicuculline-induced seizures were investigated by quantitative autoradiography of central adenosine A1 receptors in developing rats and in adults. Animals were sacrificed 30 min after an intraperitoneal injection of either saline or a convulsive dose of bicuculline. Adenosine A1 receptors in brain sections were labeled by [3H]N6-cyclohexyladenosine (CHA), a potent receptor agonist. Generalized seizures induced a widespread increase in CHA-specific binding, with a marked enhancement in structures that mediate seizure activity, such as substantia nigra, amygdala, septum and hippocampus. Moreover, the addition of guanylyl-5'-imidodiphosphate, a GTP analogue, to the incubation medium reduced CHA binding by the same order of magnitude whether rats were given saline or bicuculline, suggesting that additional adenosine A1 receptors are also functionally linked to G proteins. The age-related postictal increase in adenosine receptors might contribute to facilitate adenosine anticonvulsant effect, especially in newborns.     

脑缺血再灌流［~3H］—三磷酸肌醇放射活性及突触体游离Ca~（2＋）的变化

本文研究了大鼠脑缺血再灌流时［３Ｈ］—三磷酸肌醇（［３Ｈ］－ＩＰ３）放射活性及突触体游离Ｃａ２＋（［Ｃａ２＋］ｉ）的变化，并用苯甲基磺酰氟化物（ＰＭＳＦ）治疗，观察其对［３Ｈ］－ＩＰ３放射活性及突触体［Ｃａ２＋］ｉ的影响。结果：脑缺血１ｍｉｎ［３Ｈ］－ＩＰ３放射活性非常显著地增高。缺血２０ｍｉｎ、缺血２０ｍｉｎ再灌流１ｈ、６ｈ、２ｄ［３Ｈ］－ＩＰ３放射活性非常显著地降低。缺血２０ｍｉｎ突触体［Ｃａ２＋］ｉ非常显著地增高，至再灌流６ｈ达到最高水平。应用ＰＭＳＦ治疗能显著地抑制突触体［Ｃａ２＋］ｉ的升高。     

Induction of tolerance to ischemia: Alterations in second-messenger systems in the gerbil hippocampus

Preconditioning the brain with sublethal ischemia protects against neuronal damage following subsequent ischemic insult. Using [3H]inositol 1,4,5-triphosphate (IP3), [3H]phorbol 12,13-dibutyrate (PDBu), [3H]cyclic adenosine monophosphate (cAMP) and [3H]rolipram, we performed quantitative autoradiography to determine postischemic alterations in second-messenger systems in the gerbil hippocampus following preconditioning the brain with sublethal ischemia. At 7 days of reperfusion, no alterations were observed in brains subjected to 2 min of forebrain ischemia which produced no neuronal damage. However, 3-min ischemia caused a 75% reduction in [3H]IP3 binding (p < 0.01 vs. control) and 15-25% reductions in [3H]forskolin (p < 0.01 vs. control), [3H]cAMP (p < 0.05 vs. control), and [3H]rolipram (p < 0.01 vs. control) binding in the CA1 subfield coincident with histopathological CA1 pyramidal cell destruction, but no significant alterations in [3H]PDBu binding. Preconditioning the brain with 2 min of ischemia followed by 4 days of reperfusion prevented both histopathological cell death and the reductions in binding following subsequent 3 min of ischemia. Interestingly, [3H]IP3 and [3H]rolipram binding in CA1 showed a transient reduction, by 30% and 20% (both p < 0.01 vs. control), respectively, in the early reperfusion period. This downregulation of the IP3 system may play a role in the protection against cell death.     

Localization of [3H]cyclohexyladenosine and [3H]nitrobenzylthioinosine binding sites in rat striatum and superior colliculus

The localization of adenosine receptors labelled with [3H]cyclohexyladenosine ([3H]CHA) and adenosine transport sites labelled with [3H]nitrobenzylthioinosine ([3H]NBI) was examined in striatum and superior colliculus (SC) using radioligand binding and lesioning methods. Striatal kainic acid lesions significantly reduced the number (Bmax) of a single class of high affinity binding sites for [3H]CHA by 50% and that for [3H]NBI by 15% without altering Kd values for either ligand. In SC, enucleations significantly reduced both high and low affinity [3H]CHA binding sites by about 60% while levels of [3H]NBI binding were unaffected. Thus, adenosine receptors are present on striatal interneurons and retinal projections to the SC and some [3H]NBI binding sites are located on striatal interneurons.     

Effects of long-term theophylline treatment on adenosine A1-receptors in rat brain: autoradiographic evidence for increased receptor number and altered coupling to G-proteins

The effects of 2 weeks' treatment with theophylline (20 mg/kg i.p.) on the binding to adenosine A1-receptors was studied by autoradiography using the agonist [3H]N6-cyclohexyladenosine ([3H]CHA) and the antagonist [3H]8-cyclopentyl-1,3-dipropylxanthine ([3H]DPCPX) as ligands. A significant increase (10%) in [3H]CHA binding was measured only in the frontoparietal cortex. However, if the brain sections were incubated in the presence of 5 microM guanosine-5'-triphosphate (GTP), which by itself decreased binding by between 15 and 80% depending on the region, the increase in the frontoparietal cortex was larger (30%) and significant increases of the same magnitude were also seen in several other structures, e.g. the caudate putamen and the central gray matter of the midbrain. In some regions, for example the hippocampus and the cerebellar cortex, small or no increases were seen. GTP 100 microM practically eliminated [3H]CHA binding in both control and treated animals, suggesting that these receptors are all coupled to G-proteins. The binding of [3H]DPCPX was increased significantly only in the frontoparietal and striate cortex (5-10%). These results suggest that the theophylline treatment had little on the total receptor number but may have altered the coupling between A1-receptors and regulatory GTP-binding proteins.     

Pharmacological characterization of adenosine A1 receptors and its functional role in brown trout (Salmo trutta) brain

The adenosine receptor agonist N⁶-cyclohexyl[³H]adenosine ([³H]CHA) was used to identify and pharmacologically characterize adenosine A1 receptors in brown trout (Salmo trutta) brain. In membranes prepared from trout whole brain, the A1 receptor agonist [³H]CHA bound saturably, reversibly and with high affinity (K_d=0.69±0.04 nM; B_max=0.624±0.012 pmol/mg protein) to a single class of binding sites. In equilibrium competition experiments, the adenosine agonists and antagonists all displaced [³H]CHA from high-affinity binding sites with the rank order of potency characteristic for an adenosine A1 receptors. A1 receptor density appeared not age-related (from 3 months until 4 years), and was similar in different brain areas. The specific binding was inhibited by guanosine 5′-triphosphate (IC₅₀=0.778±0.067 μM). GTP (5 μM) induced a low affinity state of A1 receptors. In superfused trout cerebral synaptosomes, 30 mM K⁺ stimulated the release of glutamate in a calcium dependent manner. Glutamate-evoked release was dose-dependently reduced by CHA, and the inhibition was reversed by the A1 antagonist 8-cyclopentyltheophylline (CPT). In the same synaptosomal preparation, 30 mM K⁺ as well as 1 mM glutamate stimulated the release of adenosine in a Ca²⁺-independent manner and tetrodotoxin insensitive. These findings show that in trout brain adenosine A1 receptors are present which are involved in the modulation of glutamate transmitter release. Moreover, the stimulation of adenosine release by K⁺ depolarisation or glutamate support the hypothesis that, as in mammalian brain, a cross-talk between adenosine and glutamate systems exists also in trout brain.     

Cyclohexyladenosine binding in rat striatum

N6-Cyclohexyl-[3H]adenosine [( 3H]CHA) binds specifically to rat brain membranes prepared from the caudate-putamen complex with a Kd value of 2.50 +/- 0.39 nM and Bmax of 458 +/- 51 fmol/mg protein. Lesioning the nigrostriatal dopaminergic pathway using 6-hydroxydopamine failed to alter [3H]CHA binding characteristics. Intrastriatal kainate lesions reduced the binding capacity of [3H]CHA by 28% though this was not statistically significant (0.1 less than P greater than 0.05). In kainate-lesioned striata, however, 2-deoxyglucose uptake was reduced by only 39%.     

Chronic Carbamazepine Treatment Increases Brain Adenosine Receptors

The effect of carbamazepine on adenosine receptors in vitro has been well documented, with findings from several groups showing that therapeutic doses of this drug are sufficient to inhibit binding to the major portion of adenosine receptors in brain. In this study, we describe the effects of chronic carbamazepine on central adenosine receptors from several areas of rat brain using [3H]diethylphenylxanthine [( 3H]DPX) and [3H]cyclohexyladenosine [( 3H]CHA) as ligands. Carbamazepine was administered to rats orally in the diet at doses of 2.25 g/kg of diet and 5.0 g/kg of diet for periods of 3 and 11 days, respectively. Carbamazepine-treated animals displayed higher levels of adenosine receptors in virtually all brain areas tested, most of which reached significance in the 11-day treatment group. Scatchard analysis revealed increases in the number of receptors. There was no change in peripheral and central type benzodiazepine receptors or beta-adrenergic receptors in the carbamazepine-treated animals. Therefore, carbamazepine treatment in vivo appears to upregulate adenosine receptors, suggesting that this drug may act as an adenosine antagonist.