Quinolinic Acid-induced Seizures Research Articles

Increased susceptibility to quinolinic acid-induced seizures and long-term changes in brain oscillations in an animal model of glutaric acidemia type I.

Glutaric acidemia type I (GA-I) is an inborn error of metabolism of lysine, hydroxylysine, and tryptophan, caused by glutaryl-CoA-dehydrogenase (GCDH) deficiency, characterized by the buildup of toxic organic acids predominantly in the brain. After acute catabolic states, patients usually develop striatal degeneration, but the mechanisms behind this damage are still unknown. Quinolinic acid (QA), a metabolite of the kynurenine pathway, increases especially during infections/inflammatory processes, and could act synergically with organic acids, contributing to the neurological features of GA-I. The aim of this study was to investigate whether QA increases seizure susceptibility and modifies brain oscillation patterns in an animal model of GA-I, the Gcdh-/- mice taking high-lysine diet (Gcdh-/- -Lys). Therefore, the characteristics of QA-induced seizures and changes in brain oscillatory patterns were evaluated by video-electroencephalography (EEG) analysis recorded in Gcdh-/- -Lys, Gcdh+/+ -Lys, and Gcdh-/- -N (normal diet) animals. We found that the number of seizures per animal was similar for all groups receiving QA, Gcdh-/- -Lys-QA, Gcdh+/+ -Lys-QA, and Gcdh-/- -N-QA. However, severe seizures were observed in the majority of Gcdh-/- -Lys-QA mice (82%), and only in 25% of Gcdh+/+ -Lys-QA and 44% of Gcdh-/- -N-QA mice. All Gcdh-/- -Lys animals developed spontaneous recurrent seizures (SRS), but Gcdh-/- -Lys-QA animals had increased number of SRS, higher mortality rate, and significant predominance of lower frequency oscillations on EEG. Our results suggest that QA plays an important role in the neurological features of GA-I, as Gcdh-/- -Lys mice exhibit increased susceptibility to intrastriatal QA-induced seizures and long-term changes in brain oscillations.

ConBr, a Lectin from Canavalia brasiliensis Seeds, Protects Against Quinolinic Acid-Induced Seizures in Mice

Lectins are proteins capable of reversible binding to carbohydrates or glycoconjugates. In the central nervous system of mammals, lectins with affinity for mannose/glucose or galactose can modulate cellular communication. ConBr, a lectin isolated from the seeds of Canavalia brasiliensis, previously showed antidepressant effect in the forced swimming test in mice, with involvement of the monoaminergic system. In this study, we investigated the neuroprotective effects of ConBr against quinolinic acid (QA), a well-known NMDA agonist that produces severe neurotoxicity when administered in vivo. ConBr (10 μg/site) administered via intracerebroventricular (i.c.v.) showed a neuroprotective activity against seizures induced by QA (36.8 nmol/site; i.c.v.) when administered 15 min prior to QA, with a percentage of protection around 50%. ConBr was also able to significantly decrease the severity of the seizures but without changes in the latency of the first convulsion or the duration of the seizures. This effect was dependent on the structural integrity of the ConBr protein and its binding capacity to oligosaccharides residues. ConA, a lectin with high similarity to ConBr, did not reverse the QA-induced seizures. Moreover, ConBr was able to protect against hippocampal cell death caused by QA, which was measured by propidium iodide incorporation. QA caused activation of JNK2 and improved the phosphorylation of Ser831 and 845 on the AMPA receptor GluR1 subunit, and both of these effects were counteracted by ConBr. Our data suggest that the lectin ConBr may exert a modulatory action on NMDA receptors, which inhibits its activity in response to QA.

Intracerebroventricular administration of inosine is anticonvulsant against quinolinic acid-induced seizures in mice: An effect independent of benzodiazepine and adenosine receptors

Inosine (INO) has an anticonvulsant effect against seizures induced by antagonists of GABAergic system. Quinolinic acid (QA) is an agonist NMDA receptors implicated in the neurobiology of seizures. In the present study, we investigated the anticonvulsant effect of intracerebroventricular (i.c.v.) INO administration against QA-induced seizures in adult mice. We also investigated whether the benzodiazepines (BZ) or adenosine (ADO) receptors were involved in the INO effects. Animals were pretreated with an i.c.v. injection of either vehicle or INO before an i.c.v. administration of 4μl QA (36.8nmol). All animals pretreated with vehicle followed by QA presented seizures. INO protected against QA-induced seizures in a time and dose dependent manner (up to 60% at 400nmol, 5min before QA injection). Diazepam (DZ) and ADO (i.c.v.) also exhibited anticonvulsant effect against QA induced seizures. Additionally, i.p. administration of either flumazenil, a BZ receptor antagonist, or caffeine, an ADO receptor antagonist, did not change the anticonvulsant potency of INO i.c.v. injection, but completely abolished the DZ and ADO anticonvulsant effects, respectively. In conclusion, this study demonstrated that INO exert anticonvulsant effect against hyperactivity of the glutamatergic system independently of BZ or ADO receptors activation.

NMDA preconditioning protects against quinolinic acid-induced seizures via PKA, PI3K and MAPK/ERK signaling pathways

Preconditioning by N-methyl-d-aspartate (NMDA) may be promoted in vivo by the administration of a sub-convulsing dose of NMDA, with a neuroprotective effect against seizures and neuronal death induced by the infusion of quinolinic acid (QA) in mice. This study aimed to evaluate the participation of protein kinase C (PKC), cyclic AMP-dependent protein kinase (PKA), mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase (ERK) kinase (MEK), Ca2+/calmodulin dependent protein kinase II (CaMKII) and phosphatidilinositol-3 kinase (PI3K) signaling pathways in this neuroprotection model. Adult Swiss male mice were preconditioned with NMDA 24h before the infusion of QA, and were treated with inhibitors of the aforementioned signaling pathways either 15min before the preconditioning or infusion of QA. Inhibition of the PKA and PI3K pathways abolished the protection evoked by NMDA, and inhibition of the MEK pathway significantly diminished this protection. Treatment with PKC and CaMKII inhibitors did not alter the protection rate. Inhibition of the MEK and PKC pathways resulted in an increased mortality rate when followed by the infusion of QA, or NMDA preconditioning and QA infusion, respectively. These results suggest that the PKA, PI3K and MEK pathways have a crucial role in the achievement of a neuroprotective state following preconditioning.

Atorvastatin Prevents Hippocampal Cell Death due to Quinolinic Acid-Induced Seizures in Mice by Increasing Akt Phosphorylation and Glutamate Uptake

Statins are cholesterol-lowering agents due to the inhibition of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase. Recent studies have shown statins possess pleiotropic effects, which appear to be independent from its cholesterol-lowering action. In this study, we investigated whether atorvastatin would have protective effects against hippocampal cell death promoted by quinolinic acid (QA)-induced seizures in mice. Mice were pretreated with Atorvastatin (1 or 10 mg/kg) or vehicle (saline, 0.9%), orally, once a day for 7 days before the intracerebroventricular (i.c.v.) QA infusion (36.8 nmol/site). Atorvastatin treatment with 1 mg/kg/day did not significantly prevent QA-induced seizures (13.34%). However, administration of atorvastatin 10 mg/kg/day prevented the clonic and/or tonic seizures induced by QA in 29.41% of the mice. Additionally, administration of atorvastatin 10 mg/kg/day significantly prevented QA-induced cell death in the hippocampus. Atorvastatin treatment promoted an increased Akt phosphorylation, which was sustained after QA infusion in both convulsed and non-convulsed mice. Moreover, atorvastatin pretreatment prevented the reduction in glutamate uptake into hippocampal slices induced by QA i.c.v. infusion. These results show that atorvastatin attenuated QA-induced hippocampal cellular death involving the Akt pathway and glutamate transport modulation. Therefore, atorvastatin treatment might be a useful strategy in the prevention of brain injury caused by the exacerbation of glutamatergic toxicity in neurological diseases such as epilepsy.

Evaluation of glutathione metabolism in NMDA preconditioning against quinolinic acid-induced seizures in mice cerebral cortex and hippocampus

Brain preconditioning refers to a wide range of treatments that induce a neuronal tolerance state where neuronal tissue become more resistant to a subsequent lethal insult. The mechanisms underlying the preconditioning-induced brain tolerance are not fully understood, but up-regulation of antioxidant enzymes activity has been suggested to play an important role. In order to test this hypothesis, evaluation of glutathione (GSH) scavenger system was carried out in mice showing the neuroprotective effect of NMDA preconditioning against quinolinic acid (QA)-induced seizures. NMDA is known to prevent seizures in 53% of the animals and completely prevent neural damage against QA. Mice were preconditioned by a non-convulsant NMDA dose (75 mg/kg, 10 ml/kg i.p.) 24 h before QA infusion (4 μl, 9.2 mM i.c.v.). GSH content and enzymatic activities of glutathione peroxidase (GPx), glutathione reductase (GR), glutathione S-transferase (GST) and glucose-6-phosphate dehydrogenase (G6PDH) were evaluated in the cerebral cortex and hippocampus 24 h after QA infusion. NMDA preconditioning and QA infusion did not alter GSH content, GR and G6PDH activities, however, an increase in GST activity was observed in the cerebral cortex from mice. Moreover, NMDA pretreatment was able to prevent the QA-induced decrease in hippocampal GPx activity, but it was not effective against the decreased cortical GPx activity. These results indicate that, although NMDA preconditioning and QA toxicity modulate the activity of some GSH related enzymes, GSH metabolism is not directly linked to the neuroprotective effect induced by NMDA preconditioning.

Quinolinic Acid-induced Seizures Stimulate Glutamate Uptake into Synaptic Vesicles from Rat Brain: Effects Prevented by Guanine-based Purines

Glutamate uptake into synaptic vesicles is a vital step for glutamatergic neurotransmission. Quinolinic acid (QA) is an endogenous glutamate analog that may be involved in the etiology of epilepsy and is related to disturbances on glutamate release and uptake. Guanine-based purines (GBPs) guanosine 5'-monophosphate (GMP and guanosine) have been shown to exert anticonvulsant effects against QA-induced seizures. The aims of this study were to investigate the effects of in vivo administration of several convulsant agents on glutamate uptake into synaptic vesicles and investigate the role of MK-801, guanosine or GMP (anticonvulsants) on glutamate uptake into synaptic vesicles from rats presenting QA-induced seizures. Animals were treated with vehicle (saline 0.9%), QA 239.2 nmoles, kainate 30 mg/kg, picrotoxin 6 mg/kg, PTZ (pentylenetetrazole) 60 mg/kg, caffeine 150 mg/kg or MES (maximal transcorneal electroshock) 80 mA. All convulsant agents induced seizures in 80-100% of animals, but only QA stimulated glutamate uptake into synaptic vesicle. Guanosine or GMP prevented seizures induced by QA (up to 52% of protection), an effect similar to the NMDA antagonist MK-801 (60% of protection). Both GBPs and MK-801 prevented QA-induced glutamate uptake stimulation. This study provided additional evidence on the role of QA and GBPs on glutamatergic system in rat brain, and point to new perspectives on seizures treatment.

Quinolinic acid promotes seizures and decreases glutamate uptake in young rats: reversal by orally administered guanosine

Quinolinic acid (QA) has been used as a model for experimental overstimulation of the glutamatergic system. Glutamate uptake is the main mechanism involved in the maintenance of extracellular glutamate below toxic levels. Guanosine systemically administered prevents quinolinic acid-induced seizures in adult mice and increases basal glutamate uptake by cortical astrocyte culture and slices from young rats. The immature brain differs from the adult brain in its susceptibility to seizures, seizure characteristics, and responses to antiepileptic drugs (AED). Here we investigated the effect of guanosine p.o. on QA-induced seizures in young rats (P12–14) and upon ex vivo glutamate uptake by cortical slices from these animals. I.c.v. infusion of 250 nmol QA induced seizures in all animals and decreased glutamate uptake. I.p. injection of MK-801 and phenobarbital 30 min before QA administration prevented seizures in all animals. Guanosine (7.5 mg/kg) 75 min before QA prevented seizures in 50% of animals as well as prevented the decrease of glutamate uptake in the protected animals. To investigate if the anticonvulsive effect of guanosine was specific for QA-induced seizures, the picrotoxin-induced seizures model was also performed. Pretreatment with phenobarbital i.p. (60 mg/kg–30 min) prevented picrotoxin-induced seizures in all animals, whereas guanosine p.o. (7.5 mg/kg–75 min) and MK-801 i.p. (0.5 mg/kg–30 min) had no effect. Thus, guanosine protection on the QA-induced seizures in young rats and on the decrease of glutamate uptake showed some specificity degree towards the QA-induced toxicity. This points that guanosine could be considered for treatments of epilepsy, and possibly other neurological disorders in children.

Effect of orally administered guanosine on seizures and death induced by glutamatergic agents

Intraperitoneal guanosine has been shown to prevent quinolinic acid-induced seizures in mice. In this study, we investigated the effect of orally administered guanosine on seizures induced by the glutamate agonists quinolinic acid and kainate, and the endogenous glutamate releaser α-dendrotoxin. Guanosine (7.5 mg/kg, per os), administered 75 min in advance, prevented 70% of seizures induced by i.c.v. quinolinic acid, being as efficient as the NMDA channel blocker MK-801 administered intraperitoneally. Guanosine was ineffective against kainate-induced seizures, but significantly reversed the potentiation of seizures and death caused by the concomitant injection of MK-801. Guanosine also significantly prevented seizures and death induced by i.c.v. α-dendrotoxin, whereas MK-801 and phenobarbital only prevented death. Altogether, our findings underscore the therapeutic potential of oral administration of guanosine for treating diseases involving glutamatergic excitotoxicity, including epilepsy.

Effect of catecholaminergic drugs on quinolinate- and kynurenine-induced seizures in mice

Administration of reserpine, trifluperidol, chlorpromazine, haloperidol, spiroperidol, and thioproperazine to adult mice shortened the latency and increased the number of animals with clonic seizures induced by 1-kynurenine sulfate or its metabolite quinolinic acid. Haloperidol dose-dependently intensified kynurenine-induced seizures and did not alter pentylenetetrazole seizures. Dopamine abolished the effect of haloperidol while serotonin was ineffective. Pretreatment with 6-hydroxydopamine potentiated kynurenine-induced seizures, but not quinolinic acid-induced seizures. The seizure thresholds of kynurenine and quinolinic acid were not affected by pretreatments with yohimbine, clonidine, piperoxan, phentolamine and tricyclic antidepressants. Apomorphine and amphetamine (i.p.), noradrenaline and adrenaline (i.c.v.) possess anticonvulsant action against kynurenine and not against quinolinic acid. The data obtained suggest a similarity of kynurenine and known convulsants in the involvement of the catecholaminergic processes in their convulsant action. Quinolinic acid markedly differs from kynurenine in its mechanism of action as indicated by their interactions with numerous endogenous substances.

Quinolinic acid-induced seizures, but not nerve cell death, are associated with extracellular Ca 2+ decrease assessed in the hippocampus by brain dialysis

Seizures, neuronal damage and extracellular Ca 2+ concentration were studied in rats unilaterally injected in the dorsal hippocampus with quinolinic acid, a brain metabolite with excitotoxic properties. In freely moving animals, in the first 2 h after the injection of a convulsant and neurotoxic dose (156 nmol), quinolinic acid induced a tetrodotoxin-insensitive decrease in the extracellular Ca 2+ concentration (nadir 40%) in the injected area, as assessed by brain dialysis coupled to a fluorimetric method for Ca 2+ detection. Blockade of quinolinic acid-induced decrements in Ca 2+ by 15.6 nmol d-(−)2-amino-7-phosphonoheptanoic acid indicated that this effect was receptor-mediated. Dose-response relationships showed a close association between seizure activity (measured by EEG) and extracellular Ca 2+ changes in the injected area. Changes in Ca 2+ were apparent at the site of injection prior to the onset of focal seizures and they were not found in the homotypic structure where siezures were conducted. Drugs effective in blocking seizures (carbamazepine and flunarizine) prevented the fall in extracellular Ca 2+, while drugs without anticonvulsant activity (ethosuximide and nifedipine) did not. Destruction of nerve cells by quinolinic acid was not prevented by treatment with carbamazepine and flunarizine. The results suggest that the fall in extracellular Ca 2+ observed in the first 2 h after quinolinic acid, probably reflecting the ion influx into neurons, is involved in triggering focal seizures but is not related to the occurrence of nerve cell death.

A noradrenergic component of quinolinic acid-induced seizures

Unilateral application of the convulsant brain metabolite, quinolinic acid, to unanesthetized rats resulted in a transient dramatic decrease in norepinephrine levels (nadir—70% after 2 h) in both the injected and the contralateral hippocampus. Dose-response relationships and the temporal sequence of this effect indicated a close functional association between seizure events and the decrease in hippocampal norepinephrine content. Massive release of the inhibitory transmitter, norepinephrine, may thus constitute the brain's defensive response to quinolinic acid-induced seizures.