thioinosine and Seizures

Type 1 equilibrative nucleoside transporter (ENT1) promotes glutamate release by inhibition of adenosine signaling. However, whether ENT1 plays a role in epileptic seizure that involves elevated glutamatergic neurotransmission is unknown. Here, we report that both seizure rats and patients show increased expression of ENT1. Intrahippocampal injection of a specific inhibitor of ENT1, nitrobenzylthioinosine (NBTI), attenuates seizure severity and prolongs onset latency. In order to examine whether NBTI would be effective as antiepileptic after peripheral application, we injected NBTI intraperitoneally, and the results were similar to those obtained after intrahippocampal injection. NBTI administration leads to suppressed neuronal firing in seizure rats. In addition, increased mEPSC in seizure are inhibited by NBTI. Finally, NBTI results in deactivation of phosphorylated cAMP-response element-binding protein in the seizure rats. These results indicate that ENT1 plays an important role in the development of seizure. Inhibition of ENT1 might provide a novel therapeutic approach toward the control of epileptic seizure.

Topics: Action Potentials; Adenosine; Adolescent; Adult; Animals; Anterior Temporal Lobectomy; Anticonvulsants; CA1 Region, Hippocampal; Carrier Proteins; Child, Preschool; Convulsants; Cyclic AMP Response Element-Binding Protein; Disease Models, Animal; Drug Resistance; Epilepsy, Temporal Lobe; Equilibrative Nucleoside Transporter 1; Glutamates; Humans; Male; Middle Aged; Nerve Tissue Proteins; Phosphorylation; Pilocarpine; Protein Processing, Post-Translational; Pyramidal Cells; Rats; Rats, Sprague-Dawley; Seizures; Thioinosine; Young Adult

Adenosine is a well-known endogenous modulator of neuronal excitability with anticonvulsant properties. Thus, the modulation exerted by adenosine might be an effective tool to control seizures. In this study, we investigated the effects of drugs that are able to modulate adenosinergic signaling on pentylenetetrazole (PTZ)-induced seizures in adult zebrafish. The adenosine A1 receptor antagonist 8-cyclopentyl-1,3-dipropylxanthine (DPCPX) decreased the latency to the onset of the tonic-clonic seizure stage. The adenosine A1 receptor agonist cyclopentyladenosine (CPA) increased the latency to reach the tonic-clonic seizure stage. Both the adenosine A2A receptor agonist and antagonist, CGS 21680 and ZM 241385, respectively, did not promote changes in seizure parameters. Pretreatment with the ecto-5'nucleotidase inhibitor adenosine 5'-(α,β-methylene) diphosphate (AMPCP) decreased the latency to the onset of the tonic-clonic seizure stage. However, when pretreated with the adenosine deaminase (ADA) inhibitor, erythro-9-(2-hydroxy-3-nonyl)-adenine (EHNA), or with the nucleoside transporter (NT) inhibitors, dipyridamole and S-(4-Nitrobenzyl)-6-thioinosine (NBTI), animals showed longer latency to reach the tonic-clonic seizure status. Finally, our molecular analysis of the c-fos gene expression corroborates these behavioral results. Our findings indicate that the activation of adenosine A1 receptors is an important mechanism to control the development of seizures in zebrafish. Furthermore, the actions of ecto-5'-nucleotidase, ADA, and NTs are directly involved in the control of extracellular adenosine levels and have an important role in the development of seizure episodes in zebrafish.

Topics: Adenine; Adenosine; Adenosine A1 Receptor Antagonists; Adenosine Diphosphate; Animals; Benzyl Compounds; Convulsants; Dipyridamole; Gene Expression Regulation; Genes, fos; Pentylenetetrazole; Phenethylamines; Phosphodiesterase Inhibitors; Seizures; Signal Transduction; Thioinosine; Xanthines; Zebrafish

Adenosine has been shown to play a significant role as a modulator of neuronal activity in convulsion disorders, acting as an endogenous anticonvulsant agent. In the present study, we have investigated in mice the effect of acute tonic-clonic seizures induced by a single Pentylenetetrazol (PTZ)-injection (a) on the time development of adenosine uptake site binding after seizures in membranes of hippocampus, cortex, cerebellum, and striatum, and (b) on the regional distribution of adenosine uptake sites in the mouse brain by using "in vitro" quantitative autoradiography. As radioligand, the specific adenosine uptake blocker [3H]N-9-nitrobenzylthioinosine ([3H]NBI) was used. Acute seizures induced a rapid significant increase in [3H]NBI uptake site binding in hippocampus and cerebellum within 5 min, in cortex within 10 min after seizures, which reached a maximum level at 1 hr and reversed to control levels in about 150 min after seizures. On the contrary, in striatum a significant decrease of [3H]NBI uptake site binding was observed within 10 min after seizures, which reached its maximum at 1 hr and reversed to control levels at 150 min after seizures. With this single exception of striatum the "in vitro" quantitative autoradiography revealed a rather widespread upregulation of [3H]NBI uptake site density in the mouse brain, which was specifically enhanced in certain areas known to mediate seizure activity, such as hippocampus, specific thalamic nuclei, temporal cortex, and substantia nigra. The pattern of increases in [3H]NBI uptake site binding as they develop after acute seizures correlates well in time with the rapid enhancement of endogenous adenosine concentration released during epileptic activity. Since extracellular adenosine levels seem to be regulated by a rapid reuptake system, it seems likely that in our study, the [3H]NBI adenosine uptake system is acutely activated by seizures in order to compensate for the excess of endogenous adenosine. Furthermore, the upregulation of [3H]NBI uptake sites as revealed by the "in vitro" quantitative autoradiography seems to be organized in selective brain areas related to seizure propagation.

Topics: Adenosine; Affinity Labels; Animals; Autoradiography; Binding Sites; Brain; Cell Membrane; Cerebellum; Cerebral Cortex; Corpus Striatum; Epilepsy, Tonic-Clonic; Female; Hippocampus; In Vitro Techniques; Mice; Mice, Inbred BALB C; Organ Specificity; Pentylenetetrazole; Receptors, Purinergic P1; Reference Values; Seizures; Thioinosine; Time Factors; Tissue Distribution; Tritium

A1 adenosine receptors in the rat prepiriform cortex play an important role in the inhibition of bicuculline methiodide-induced convulsions. In the present study we evaluated manipulation of endogenous adenosine in this brain area as a strategy to effect seizure suppression. All compounds evaluated were unilaterally microinjected into the rat prepiriform cortex. Administration of exogenous adenosine afforded a dose-dependent protection (ED50 = 48.1 +/- 8.4 nmol) against bicuculline methiodide-induced seizures, and these anticonvulsant effects were significantly potentiated by treatment with an adenosine kinase inhibitor, 5'-amino-5'-deoxyadenosine; by the adenosine transport blockers, dilazep or nitrobenzylthioinosine 5'-monophosphate; and by an adenosine deaminase inhibitor, 2'-deoxycoformycin. When administered alone, 5'-amino-5'-deoxyadenosine, 5'-iodotubercidin and dilazep were found to be highly efficacious as anticonvulsants with respective ED50 values of 2.6 +/- 0.8, 4.0 +/- 2.7 and 5.6 +/- 1.5 nmol. In contrast, 2'-deoxycoformycin was both less potent and less efficacious. These results suggest that accumulation of endogenous adenosine may contribute to seizure suppression, and that adenosine kinase and adenosine transport may play a pivotal role in the regulation of extracellular levels of adenosine in the central nervous system. The adenosine antagonist, 8-(p-sulfophenyl)theophylline, increased markedly the severity of bicuculline methiodide-induced seizures. Moreover, reduction of extracellular adenosine formation by a focal injection of an ecto-5'-nucleotidase inhibitor, alpha, beta-methyleneadenosine diphosphate, produced generalized seizures (ED50 = 37.3 +/- 22.7 nmol). Together the proconvulsant effect of an adenosine receptor antagonist and the convulsant action of an ecto-5'-nucleotidase inhibitor further support the role of endogenous adenosine as a tonically active antiepileptogenic substance in the rat prepiriform cortex.

Topics: Adenosine; Adenosine Deaminase Inhibitors; Adenosine Diphosphate; Adenosine Kinase; Animals; Bicuculline; Cerebral Cortex; Male; Pentostatin; Rats; Rats, Sprague-Dawley; Receptors, Purinergic; Seizures; Theophylline; Thioinosine