n(6)-cyclohexyladenosine and 8-cyclopentyl-1-3-dimethylxanthine

Hibernation in mammalians such as hamsters is a physiological state characterized by an extreme reduction of various functions such as body temperature and metabolism. Under such severe conditions, the central nervous system (CNS) activity is maintained at a functionally responsive level. Although hibernation is an interesting behavioral state, the physiological mechanisms of the introduction to and/or the arousal from hibernation have not been clearly defined. Intracerebroventricularly (i.c.v.) injected adenosine produces hypothermia in various animals. The effect of adenosine is generated by A1-receptors and is caused by the suppression of the thermogenesis center of the posterior hypothalamus. At on ambient temperature of 5, i.c.v. injected N6-cyclohexyladenosine (CHA) adenosine A1-receptor agonist induces profound hypothermia in hamsters. Although the time course of the descent of body temperature coincided with that of entry into natural hibernation, the effect was not antagonized by 8-cyclopentyltheophyllin (CPT), an adenosine A1-receptor antagonist. However, i.c.v. injection of CPT elevated the body temperature and interrupted hibernation, albeit the deep-phase (post-entry 30 h) was unaffected. This result suggests that a different system may suppress the thermogenesis center in the deep hibernation phase. Interestingly, i.c.v. injected thyrotropin releasing hormone (TRH) elevated the body temperature in both hibernation phases in hamsters. These findings suggest that the central adenosine and TRH play important roles in thermoregulation and that the new thermogenesis system, activating in low-body temperature, is induced in naturally hibernating animals.

Topics: Adenosine; Animals; Body Temperature; Body Temperature Regulation; Central Nervous System; Cricetinae; Hibernation; Purinergic P1 Receptor Agonists; Purinergic P1 Receptor Antagonists; Receptors, Purinergic P1; Theophylline; Thyrotropin-Releasing Hormone

Adenosine has anticonvulsant effects in various models of seizures. Alpha-2 adrenoceptors have also demonstrated different effects in different models of epilepsy. In this study, the role of alpha-2 adrenoceptors in the anticonvulsant effects of adenosine in mice was determined according to the method of intravenous pentylenetetrazole-induced seizure. In this study, N(6)-cyclohexyladenosine (CHA) (a selective A1 receptor agonist), clonidine (an alpha-2 adrenoceptors agonist), yohimbine (an alpha-2 adrenoceptors antagonist) and 8-cyclopentyl-1,3-dimethylxanthine (8-CPT) (a selective A1 receptor antagonist) were used. CHA at doses of 0.5, 1 and 2mg/kg significantly increased seizure threshold with the maximum anticonvulsant effect at 2mg/kg. Yohimbine (0.1, 1 and 10mg/kg), clonidine (0.1, 0.5, 1 and 2mg/kg) and 8-CPT (0.5, 1, 2 and 4mg/kg) had no effect on seizure by itself. Combination of yohimbine (10mg/kg) and CHA (0.25mg/kg) increased clonic seizure latency showing that yohimbine and CHA have an additive effect. Increasing the seizure threshold created by combining ineffective doses of yohimbine (10mg/kg) and CHA (0.25mg/kg) was completely inhibited by 8-CPT (4mg/kg) or clonidine (1 and 2mg/kg). Clonidine (0.5, 1 and 2mg/kg) inhibited the anticonvulsant effects of CHA (2mg/kg). Combination of 8-CPT (1mg/kg) and clonidine (0.5mg/kg) which completely inhibited the anticonvulsant effect of CHA (2mg/kg) indicates that 8-CPT and clonidine have an additive effect. In conclusion, adenosine and yohimbine exhibit an additive effect on the enhancement of the pentylenetetrazole-induced seizure threshold in mice, indicating the interaction of alpha-2 adrenoceptors and A1 adenosine receptors.

Topics: Adenosine; Adrenergic alpha-1 Receptor Agonists; Adrenergic alpha-1 Receptor Antagonists; Adrenergic alpha-2 Receptor Agonists; Adrenergic alpha-2 Receptor Antagonists; Animals; Anticonvulsants; Clonidine; Dose-Response Relationship, Drug; Drug Interactions; Male; Mice; Pentylenetetrazole; Receptor, Adenosine A1; Receptors, Adrenergic, alpha-2; Seizures; Theophylline; Yohimbine

Torpor in hibernating mammals defines the nadir in mammalian metabolic demand and body temperature that accommodates seasonal periods of reduced energy availability. The mechanism of metabolic suppression during torpor onset is unknown, although the CNS is a key regulator of torpor. Seasonal hibernators, such as the arctic ground squirrel (AGS), display torpor only during the winter, hibernation season. The seasonal character of hibernation thus provides a clue to its regulation. In the present study, we delivered adenosine receptor agonists and antagonists into the lateral ventricle of AGSs at different times of the year while monitoring the rate of O(2) consumption and core body temperature as indicators of torpor. The A(1) antagonist cyclopentyltheophylline reversed spontaneous entrance into torpor. The adenosine A(1) receptor agonist N(6)-cyclohexyladenosine (CHA) induced torpor in six of six AGSs tested during the mid-hibernation season, two of six AGSs tested early in the hibernation season, and none of the six AGSs tested during the summer, off-season. CHA-induced torpor within the hibernation season was specific to A(1)AR activation; the A(3)AR agonist 2-Cl-IB MECA failed to induce torpor, and the A(2a)R antagonist MSX-3 failed to reverse spontaneous onset of torpor. CHA-induced torpor was similar to spontaneous entrance into torpor. These results show that metabolic suppression during torpor onset is regulated within the CNS via A(1)AR activation and requires a seasonal switch in the sensitivity of purinergic signaling.

Topics: Adenosine; Animals; Arctic Regions; Body Temperature; Body Temperature Regulation; Brain; Hibernation; Injections, Intraventricular; Oxygen Consumption; Purinergic Antagonists; Purinergic P1 Receptor Agonists; Receptor, Adenosine A1; Sciuridae; Seasons; Telemetry; Theophylline; Xanthines

Adenosine exerts its anticonvulsants effect through different brain regions including piriform cortex. In this study, the effect of amygdala kindled seizures on adenosine A1 receptor-mediated neuromodulation in piriform cortex pyramidal neurons was tested at 24 h and 1 month after kindling. Animals were kindled by daily electrical stimulation of amygdala. Field potentials were recorded from layer II of piriform cortex pyramidal cells following stimulation of the lateral olfactory tract. Obtained results showed that N6-cyclohexyladenosine (CHA), a selective adenosine A1 receptor agonist (1, 10 and 100 microM; i.c.v.), reduced A1 slope and B1 amplitude of field potentials in both kindled and non-kindled (control) rats. However, its effects on kindled animals were more potent at 24 h, but not 1 month post-kindling. 8 cyclopenthyl-1,3-dimethylxanthine (CPT), a selective adenosine A1 receptor antagonist (50 microM, i.c.v.), had no significant effect on the field potential parameters. However, CPT (50 microM, i.c.v.) pretreatment eliminated effects of CHA (10 microM; i.c.v.) on the field potentials. These results indicate that activation of adenosine A1 receptors has an inhibitory effect on the field potentials of piriform cortex pyramidal neurons and the efficiency of adenosine A1 receptor neuromodulation in piriform cortex is increased at short-term (24 h) but return to normal at long-term (1 month) after kindling implementation.

Topics: Adenosine; Amygdala; Animals; Excitatory Postsynaptic Potentials; Kindling, Neurologic; Male; Olfactory Pathways; Rats; Rats, Sprague-Dawley; Receptor, Adenosine A1; Seizures; Theophylline

In this study, the effect of A1 and A2A adenosine receptor activity of the piriform cortex (PC) on amygdala-kindled seizures was investigated in rats. Animals were kindled by daily electrical stimulation of the amygdala. In fully kindled rats, N6-cyclohexyladenosine (CHA, a selective A1 agonist), 8-cyclopentyl-1,3-dimethylxanthine (CPT, a selective A1 antagonist), CGS21,680 hydrochloride (CGS, a selective A2A agonist), and ZM241,385 (ZM, a selective A2A antagonist) were microinjected bilaterally into the PC. Rats were stimulated 5 min post-drug microinjection and seizure parameters were measured. Results showed that intra-PC CHA (10 and 100 micromol/L) decreased the duration of both afterdischarge and stage 5 seizure and significantly increased the latency to stage 4 seizure. Intra-PC CPT increased afterdischarge and stage 5 seizure duration at the dose of 20 micromol/L. The anticonvulsant effect of CHA (100 micromol/L) was eliminated by CPT (10 micromol/L) pretreatment. On the other hand, neither intra-PC CGS nor ZM had a significant effect on kindled seizures. These results suggest that activity of A1, but not A2A, receptors of the PC have anticonvulsant effects on kindled seizures elicited from electrical stimulation of the amygdala.

Topics: Adenosine; Adenosine A1 Receptor Agonists; Adenosine A1 Receptor Antagonists; Adenosine A2 Receptor Agonists; Adenosine A2 Receptor Antagonists; Amygdala; Analysis of Variance; Animals; Anticonvulsants; Dose-Response Relationship, Drug; Electric Stimulation; Evoked Potentials; Kindling, Neurologic; Male; Microinjections; Models, Anatomic; Phenethylamines; Rats; Rats, Sprague-Dawley; Theophylline; Triazines; Triazoles

Studies have shown that the activation of adenosine A(1) receptors lower intraocular pressure primarily by increasing total outflow facility. The purpose of this study was to investigate the actions of the adenosine A(1) agonist N(6)-cyclohexyladenosine (CHA) on conventional outflow facility.. Conventional outflow facility was evaluated in isolated bovine anterior segments, perfused at a constant pressure of 10 mm Hg. After overnight perfusion to establish a stable baseline, the concentration- and time-dependent changes in outflow facility induced by CHA were determined. To confirm the involvement of adenosine A(1) receptors and matrix metalloproteinases (MMP) in any change in facility, the responses to CHA were evaluated in preparations treated with the adenosine A(1) receptor antagonist, 8-cyclopentyl-1,3-dimethylxanthine (CPT), or the nonselective MMP inhibitor GM-6001.. The administration of CHA (10 microM) to perfused anterior segments produced a 28% increase in outflow facility over basal levels. This response was relatively slow to develop with no significant change in outflow facility measured until after 60 minutes of CHA infusion. The peak response to CHA infusion occurred between 3 and 4 hours after CHA administration. Analysis of the CHA concentration-response curves demonstrated that this increase in outflow facility was concentration-dependent, with an EC(50) of 0.28 microM. Pretreatment with the adenosine A(1) receptor antagonist CPT (10 microM) or the nonselective MMP inhibitor GM-6001 (10 microM) blocked the response to CHA (1 microM). When compared with control eyes, no significant change in baseline facility was measured in eyes perfused with CPT or GM-6001.. These studies demonstrate that the adenosine agonist CHA significantly increases conventional outflow facility in the perfused bovine eye. Analysis of the CHA concentration-response curve and inhibition of the CHA-induced increase in outflow facility by the adenosine A(1) antagonist confirms that this response is mediated by the activation of adenosine A(1) receptors. The inhibition of the CHA-induced increase in outflow facility by the MMP inhibitor GM-6001 provides evidence that the secretion and activation of MMPs within the conventional outflow pathway play a central role in the ocular hypotensive action of adenosine A(1) agonists.

Topics: Adenosine; Adenosine A1 Receptor Agonists; Adenosine A1 Receptor Antagonists; Animals; Anterior Eye Segment; Aqueous Humor; Cattle; Dipeptides; Dose-Response Relationship, Drug; Matrix Metalloproteinase Inhibitors; Matrix Metalloproteinases; Protease Inhibitors; Receptor, Adenosine A1; Theophylline; Time Factors

Adenosine is considered an endogenous neuroprotective metabolite that through activation of the A(1) receptor results in reduction of neuronal damage following cerebral ischemia. Protein kinase B, also known as Akt/PKB, is part of an endogenous pathway that exerts effective neuroprotection from both necrotic and apoptotic cell death. Using a rat model of unilateral common carotid artery occlusion coupled with hypoxia, and using in vitro rat hippocampal slices, we examined the ability of adenosine to directly activate Akt/PKB. Western blot analysis revealed that levels of phosphorylated Akt/PKB were elevated in vivo under ischemic conditions in an adenosine A(1)-dependent manner and elevated in hippocampal slices treated with an adenosine A(1) agonist. We conclude from these studies that the activation of an adenosine A(1) receptor-mediated signal transduction pathway, either by endogenous adenosine (in vivo) or by an adenosine A(1) agonist (in vitro), results in the activation of the neurotrophic kinase Akt/PKB.

Topics: Adenosine; Animals; Cell Death; Cerebrovascular Circulation; Hippocampus; Hypoxia-Ischemia, Brain; Immunohistochemistry; Male; Nerve Degeneration; Neurons; Organ Culture Techniques; Phosphorylation; Protein Serine-Threonine Kinases; Proto-Oncogene Proteins; Proto-Oncogene Proteins c-akt; Purinergic P1 Receptor Agonists; Purinergic P1 Receptor Antagonists; Rats; Rats, Sprague-Dawley; Receptors, Purinergic P1; Subcellular Fractions; Synaptic Transmission; Theophylline; Up-Regulation

Studies have shown that adenosine A(1) agonists can lower IOP in rabbits, mice, and monkeys, and this response is mediated in part by increases in outflow facility. The purpose of this project was to evaluate the response of trabecular meshwork cells to the addition of the adenosine A(1) receptor agonist N(6)-cyclohexyladenosine (CHA).. The human trabecular meshwork (HTM-3) cell line and primary cultures of bovine trabecular meshwork (BTM) cells were used in these studies. Cells were treated with CHA, and the secretion of matrix metalloproteinase (MMP)-2 or the activation of extracellular signal-regulated kinase (ERK1/2) was determined.. Treatment of HTM-3 and BTM cells with CHA (0.1 micro M) resulted in a time-dependent secretion of MMP-2 that was measurable as early as 30 minutes after treatment and reached a maximum by 2 hours. This CHA-induced secretion of MMP-2 was inhibited by the adenosine A(1) receptor antagonist 8-cyclopentyl-1,3-dimethylxanthine (CPT) and by the ERK1/2 pathway inhibitor U0126. Treatment of HTM-3 cells with CHA produced a rapid dose-dependent activation of ERK1/2 with an EC(50) of 5.7 nM. The CHA-induced activation of ERK1/2 was inhibited by pretreatment with the adenosine A(1) antagonist CPT and by the ERK pathway inhibitor U0126.. The addition of the adenosine A(1) agonist CHA stimulates the secretion of MMP-2 from trabecular meshwork cells. This secretory response involves the activation of adenosine A(1)-linked stimulation of ERK1/2. These results provide evidence for the existence of functional adenosine A(1) receptors in the trabecular cells and that the activation of these receptors stimulates secretion of MMP-2.

Topics: Adenosine; Animals; Cattle; Cell Line, Transformed; Cells, Cultured; Dose-Response Relationship, Drug; Enzyme Inhibitors; Humans; Matrix Metalloproteinase 2; Mitogen-Activated Protein Kinase 1; Mitogen-Activated Protein Kinase 3; Mitogen-Activated Protein Kinases; Purinergic P1 Receptor Antagonists; Receptors, Purinergic P1; Theophylline; Time Factors; Trabecular Meshwork

Peripheral administration of adenosine A(1) receptor selective agonists is generally thought to protect the hippocampus against ischemic damage via central actions. We examined the effects of two peripherally administered A(1) agonists, cyclohexyladenosine (CHA) and adenosine amine congener (ADAC), on synaptic transmission in the hippocampus and on indices of cardiovascular function. We conclude that the permeability of these agonists is not sufficient to result in concentrations necessary to activate central adenosine A(1) receptors within the hippocampus.

Topics: Adenosine; Animals; Cardiovascular Physiological Phenomena; Excitatory Postsynaptic Potentials; Hippocampus; Hypoxia-Ischemia, Brain; Male; Neurons; Neuroprotective Agents; Purinergic P1 Receptor Agonists; Rats; Rats, Sprague-Dawley; Receptors, Purinergic P1; Synapses; Synaptic Transmission; Theophylline

The cholinergic agonist carbachol (1.1 mM) and the adenosinergic agonist cyclohexyladenosine (0.1 mM) were microinjected (60 nl) into the region of the caudal, oral pontine reticular formation of the rat. Local intracerebral infusion of each receptor agonist resulted in significant, long-lasting (at least 8 h) elevations in rapid eye movement sleep without reduction in latency to onset. The effects of carbachol were reduced by the muscarinic receptor antagonist atropine, while those of cyclohexyladenosine were reduced by the adenosinergic receptor antagonist 8-cyclopentyltheophylline. Atropine failed to antagonize the long-term induction of rapid eye movement sleep following cyclohexyladenosine, but did appear to suppress increases in the first 2 h. Similarity of effects on sleep parameters and the lack of additivity when injected consecutively are consistent with these agonist ligands targeting the same cellular mechanisms through their respective receptors. These findings suggest that transitory increases in the pons of either acetylcholine or adenosine may underlie long-lasting elevations in the amount of rapid eye movement sleep. Adenosine may play a role in the increased rapid eye movement sleep following prolonged wakefulness, as well as following conditions of stress and learning.

Topics: Adenosine; Animals; Atropine; Brain Mapping; Carbachol; Infusions, Parenteral; Male; Microinjections; Muscarinic Antagonists; Pons; Purinergic P1 Receptor Agonists; Purinergic P1 Receptor Antagonists; Rats; Reticular Formation; Sleep; Sleep, REM; Theophylline; Time Factors; Wakefulness

The effect of adenosine and related compounds on the proliferation of cultured TM4 cells, a Sertoli-like cell line, has been examined. Adenosine, as well as A1 and A2 adenosine receptor agonists (cyclohexyladenosine and N6-[2-(3,5-dimethoxyphenyl)-2-(2-methylphenyl)ethyl]adenosine) inhibited cell proliferation. These effects were prevented by 8-cyclopentyl theophylline, 1,3-dimethyl-propargylxanthine and caffeine, antagonists at the A1, A2 and both receptors, respectively. The xanthines had no effect by themselves and, consistent with this, the bathing medium was found not to contain detectable levels of adenosine. It is concluded that TM4 cell proliferation can be regulated by receptors for adenosine.

Topics: Adenosine; Animals; Caffeine; Cell Division; Cells, Cultured; Male; Mice; Purinergic P1 Receptor Antagonists; Purines; Receptors, Purinergic P1; Sertoli Cells; Theobromine; Theophylline

In goldfish brain, [3H]cyclohexyladenosine binding sites are ubiquitously distributed with a maximum in the hypothalamus and a minimum in the spinal cord. The binding parameters measured in cerebellar membranes (Kd = 0.88 +/- 0.08 nM; Bmax = 59.65 +/- 2.62 fmol/mg protein) are not significantly different from those of the whole brain. In perfused goldfish cerebellar slices, stimulation of cyclic AMP accumulation by 10(-5) M forskolin was markedly reduced (58.7%) by treatment with 10(-4) M cyclohexyladenosine, an adenosine A1 receptor agonist, and the reduction was reversed in the presence of 10(-4) M 8-cyclopentyltheophylline, a selective A1 receptor antagonist. In the same brain preparation, 30 mM K+ stimulated the release of glutamate, glutamine, glycine and GABA in a Ca(2+)-dependent manner, whereas the aspartate and taurine release was Ca(2+)-independent. Cyclohexyladenosine inhibited the 30 mM K(+)-evoked release of glutamate in a dose-related manner. This effect was reversed by 8-cyclopentyltheophylline. These results support the hypothesis that adenosine A1 receptors present in goldfish cerebellum are involved in the modulation of glutamate transmitter release.

Topics: Adenosine; Adenylyl Cyclases; Amino Acids; Animals; Calcium; Cerebellum; Colforsin; Cyclic AMP; Glutamates; Glutamic Acid; Goldfish; In Vitro Techniques; Membranes; Potassium; Receptors, Purinergic P1; Theophylline

The adenosine modulation of glutamate exocytosis from guinea pig cerebrocortical synaptosomes is investigated. Endogenously leaked adenosine is sufficient to cause a partial tonic inhibition of 4-aminopyridine-evoked glutamate release, which can be relieved by adenosine deaminase. The adenosine A1 receptor is equally effective in mediating inhibition of glutamate exocytosis evoked by 4-aminopyridine (where K(+)-channel activation would inhibit release) and by elevated KCl (where K(+)-channel activation would have no effect), arguing for a central role of Ca(2+)-channel modulation. In support of this, the plateau phase of depolarization-evoked free Ca2+ elevation is decreased by adenosine with both depolarization protocols. No effect of adenosine agonists is seen on membrane potential in polarized or KCl- or 4-aminopyridine-stimulated synaptosomes. The interaction of protein kinase C with the A1 receptor-mediated inhibition is examined. Activation of protein kinase C by 4 beta-phorbol dibutyrate has been shown previously by this laboratory to modulate glutamate release via K(+)-channel inhibition, and is shown here to have an additional action of decoupling the adenosine inhibition of glutamate exocytosis.

Topics: 4-Aminopyridine; Adenosine; Animals; Cerebral Cortex; Enzyme Activation; Exocytosis; Fura-2; Glutamates; Glutamic Acid; Guinea Pigs; Potassium Chloride; Protein Kinase C; Receptors, Purinergic; Synaptosomes; Theophylline

Binding of [3H]cyclohexyladenosine (CHA) to the cellular fractions and P2 subfractions of the goldfish brain was studied. The A1 receptor density was predominantly in synaptosomal membranes. In goldfish brain synaptosomes (P2), 30 mM K+ stimulated glutamate, taurine and GABA release in a Ca(2+)-dependent fashion, whereas the aspartate release was Ca(2+)-independent. Adenosine, R-phenylisopropyladenosine (R-PIA) and CHA (100 microM) inhibited K(+)-stimulated glutamate release (31%, 34% and 45%, respectively). All of these effects were reversed by the selective adenosine A1 receptor antagonist, 8-cyclopentyltheophylline (CPT). In the same synaptosomal preparation, K+ (30 mM) stimulated Ca2+ influx (46.8 +/- 6.8%) and this increase was completely abolished by pretreatment with 100 nM omega-conotoxin. Pretreatment with 100 microM R-PIA or 100 microM CHA, reduced the evoked increase of intra-synaptosomal Ca2+ concentration, respectively by 37.7 +/- 4.3% and 39.7 +/- 9.0%. A possible correlation between presynaptic A1 receptor inhibition of glutamate release and inhibition of calcium influx is discussed.

Topics: Adenosine; Amino Acids; Animals; Brain; Calcium; Calcium Channel Blockers; Fura-2; Glutamates; Glutamic Acid; Goldfish; Kinetics; omega-Conotoxins; Peptides; Phenylisopropyladenosine; Potassium; Receptors, Purinergic; Synaptosomes; Theophylline