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Query: UMLS:C0036572 (seizures)
 80,221 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Congenital deficiencies of the urea cycle enzyme ornithine transcarbamylase (OTC) result in chronic hyperammonemia and severe neurological dysfunction including seizures and mental retardation. As part of a series of studies to elucidate the pathophysiologic mechanisms responsible for the CNS consequences of OTC deficiency, concentrations of ammonia-related and neurotransmitter amino acids were measured as their o-phthalaldehyde derivatives using high performance liquid chromatography with fluorescence detection in regions of the brains of sparse-fur (spf) mice, a mutant with an X-linked inherited defect of OTC. Compared to CD-1/Y controls, the brains of spf/Y mutant mice contained significant alterations of several amino acids. A generalized, up to 2-fold, increase of brain glutamine was observed, consistent with the exposure of these brains to increased concentrations of ammonia. Significant increases of brain alanine were also observed and, together with previous reports of increased concentrations of alpha-ketoglutarate, are consistent with ammonia-induced inhibition of alpha-ketoglutarate dehydrogenase in the brains of spf/Y mice. Increased brain content of the excitatory amino acid aspartate could be responsible for the seizures frequently encountered in congenital OTC deficiency.
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PMID:Regional amino acid neurotransmitter changes in brains of spf/Y mice with congenital ornithine transcarbamylase deficiency. 791 68

Pretreatment of mice with 5-fluoromethylornithine (5FMOrn), a selective inactivator of ornithine aminotransferase, diminishes the accumulation of ammonia in the brain after administration of ammonium acetate, and antagonizes ammonia-induced fatal tonic extensor convulsions. In about 50% of the treated animals the loss of the righting reflex and coma is prevented. Presumably these effects are based on the enhancement of urea formation by the increased liver ornithine concentrations. However, since brain ornithine concentrations are greatly enhanced by 5FMOrn, it is not excluded that ornithine has direct effects on cellular events involved in ammonia-induced seizure generation, even though 5FMOrn had no anticonvulsant properties in a series of established animal seizure models, including N-methyl-D,L-aspartate-induced convulsions. NMDA receptor antagonists are capable of preventing death, but do not protect against the generation of coma and tonic extensor convulsions in ammonium acetate intoxicated mice. Since no evidence was found for ammonia-induced glutamate release from rat hippocampus, there is no convincing evidence for the idea that the tonic convulsions are mediated by NMDA receptors. L-Methionine-D, L-sulfoximine (MSO)-induced seizures can be partially antagonized by pretreatment with 5FMOrn. However, the effect is considerably smaller than against ammonia-induced convulsions, although at the time of seizure onset brain ammonia levels of MSO-intoxicated mice were lower than in the animals receiving ammonium acetate. This suggests that MSO-convulsions are not entirely due to the elevation of brain ammonia concentrations, even though MSO administration mimics effects of ammonia on cortical inhibitory neuronal interactions.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Enhanced endogenous ornithine concentrations protect against tonic seizures and coma in acute ammonia intoxication. 809 10

The effects on the background quantitative EEG (power spectral analysis) and concentration of valproate in plasma were studied after single-dose (14.3-33.3 mg/kg) oral administration in 12 epileptic patients with generalized nonconvulsive or partial seizures. An increase of the amplitude of the background EEG (diffuse and preponderant on anterior scalp areas) and a decrease of the 12.5-32.0 Hz relative power (limited to the posterior electrode deviations) were observed; the increase in the EEG total power was paralleled by a definite increment in incidence of epileptic phenomena in the EEG. Both effects proved unrelated to shifts in vigilance or changes in the concentration of ammonia or serum glucose in plasma and confirm previous observations from superimposable study designs. These findings are qualitatively opposite to those observed during long-term treatment at comparable doses and are suggested to reflect a direct CNS action of acute administration of valproate.
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PMID:Ammonia-independent modifications of the background EEG signal and paradoxical enhancement of epileptic abnormalities in EEG after acute administration of valproate to epileptic patients. 823 92

Although L-carnitine has been reported to have protective effects against ammonia toxicity, conflicting results have also been presented and the mechanisms underlying the protection, if any, are not clear. In the present study, we examined the effects of L-carnitine, D-carnitine and acetyl-L-carnitine on the neurotoxicity of ammonia. Administration of ammonium acetate (15 mmol/kg) to mice caused seizures, elevation of blood ammonia and urea concentrations, and marked alterations of brain energy metabolites. Pretreatment with either L-carnitine, D-carnitine or acetyl-L-carnitine reduced the frequency of the seizures, prolonged the time until the first fit, lowered the levels of ammonia in the blood and brain, and suppressed the alterations of brain energy metabolites caused by hyperammonemia. there was no significant difference between L- and D-carnitine in the potency to inhibit the seizures. In addition, there was no difference between the two chemicals in the potency to decrease the ammonia contents in the blood and brain, or to suppress the alterations of energy metabolites in the brain. When compared with L-carnitine, however, acetyl-L-carnitine better preserved ATP in the brain, while it lowered ammonia in the blood and brain less markedly. These results show that L-carnitine and its analogues do have the potential to suppress the neurotoxicity of ammonia. Moreover, the results suggest that the protective effects of carnitine against the toxicity of ammonia are systemic, that the action of acetyl-L-carnitine may differ from that of L- or D-carnitine, and that the "classical" function of carnitine is not the sole mechanism underlying the suppression of the neurotoxicity of ammonia.
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PMID:Comparison of the effects of L-carnitine, D-carnitine and acetyl-L-carnitine on the neurotoxicity of ammonia. 834 26

CNS oxygen (O2) toxicity is complex, and the etiology of its most severe manifestation, O2 convulsions, is yet to be determined. A role for depletion of the brain GABA pool has been proposed, although recent data have implicated production of reactive O2 species, e.g. H2O2, in this process. We hypothesized that the production of H2O2 and NH3 produced by monoamine oxidase (MAO) would lead to depletion of GABA and production of nitric oxide (NO.) respectively, and thereby enhance CNS O2 toxicity. In this study, rats treated with an MAO inhibitor (pargyline) or a nitric oxide synthase inhibitor (LNNA) were protected against O2-induced convulsions. Selected cerebral amino acids including arginine were measured in control and O2 treated rats (6 ATA, 20 min) with or without drug pretreatment. After O2 exposure, the cerebral pools of glutamate, aspartate, and GABA decreased significantly while glutamine content increased relative to control (P < 0.05). After treatment with either enzyme inhibitor, glutamine, glutamate and aspartate concentrations were maintained near control levels. Remarkably, GABA depletion by O2 was not prevented despite protection from seizures by both pargyline and LNNA. The NO. precursor, arginine, was increased significantly in the brain by toxic O2 exposure, but both pargyline and LNNA inhibited this effect. Simultaneous norepinephrine measurements indicated that its storage substantially decreased during hyperoxia (P < 0.05), but this effect too was blocked by either pargyline or LNNA. These data indicate that protection against O2 by these inhibitors is not related to preservation of the GABA pool. More importantly, O2 dependent norepinephrine metabolism and NO. synthesis appear to be interactive during CNS O2 toxicity.
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PMID:Cerebral amino acid, norepinephrine and nitric oxide metabolism in CNS oxygen toxicity. 846 4

This paper describes the signs of toxicity when seed-bearing flatpea (Lathyrus sylvestris L) hay is fed to sheep. Signs of intoxication (including seizure, muscular trembling and spasmotic torticollis) are similar to those observed for ammonia toxicity in ruminants. Accumulation of ammonia may be a direct consequence of flatpea ingestion, given that 2,4-diaminobutyric acid (DABA, a toxic constituent of flatpea) is known to inhibit hepatic urea synthesis. However, other modes of toxicity for DABA as well as other flatpea toxins may also contribute to this process of intoxication. Our evidence suggests that ruminal microbes are responsible for flatpea detoxification and host animal protection. The adaptation of sheep to flatpea may be a consequence of enhanced ruminal detoxification activity. Ruminal protective functions can be disrupted, however, through abrupt monensin feeding or the replacement of nonadapted for adapted rumen contents. This disruption temporarily suppresses mechanisms of ruminal detoxification. As a consequence sheep can again be made vulnerable to flatpea intoxication.
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PMID:Flatpea intoxication in sheep and indications of ruminal adaptation. 847 Mar 53

Amino acid levels in plasma were measured by amino acid autoanalyser in 130 convulsive children. The levels of taurine, serine and tryptophan were significantly lower in convulsive children as compared to normal control; in contrast, isoleucine, homocystine, GABA, histidine, arginine and ammonia were higher. The children with paroxysmal disorders (headache, dizziness and abdominal epilepsy) had the highest levels of isoleucine, histidine and arginine and the lowest levels of glutamate and cystein. Clinical seizure activity within 6 months prior to the test seemed to have no obvious effect on the plasma amino acid pattern, except for the levels of glycine and arginine tended to return to normal, and the level of GABA was significantly increased in patients with the seizure being controlled. The patients treated with carbamazepin as a single anticonvulsant had the highest GABA level compared to those with other anticonvulsants. Hyperglycinemia and hyperammonaemia were also noted in patients who took valproic acid. The levels of serine, isoleucine and phenylalanine in the CSF within 6 hours after convulsion were significantly lower than the normal control; while asparagine, tyrosine, lysine and arginine were significantly higher. The concentration of ammonia in the CSF was also elevated after convulsion as compared to the normal control. Amino acids play an important role in the generation of epilepsy and recently there has been an increasing number of studies to help determine their effects during an epileptic attack. However, there still is much debate and controversy on this topic. Therefore, further studies are needed and researchers should carefully consider factors that might affect the accurate assessment of the results.
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PMID:Alteration of amino acid in plasma and cerebrospinal fluid of children with seizure disorders. 851 Jan 96

Previous studies in our laboratory have shown that L-carnitine suppresses seizures and alterations of brain energy metabolism in mice caused by hyperammonemia. The present study was done to exclude the effects of seizures on brain energy metabolism. When sublethal dose of ammonium acetate (12 mmol/kg b.wt.) was injected to mice, all mice survived without developing seizures, while clear increase of brain ammonia and alterations of brain energy metabolites were seen. In L-carnitine-treated animals, the levels of ammonia, AMP and lactate were lower and those of ATP and phosphocreatine were higher than in untreated animals. Treatment with D-carnitine also preserved the phosphocreatine level. This indicates that the improvement of brain energy metabolism by L-carnitine in hyperammonemia is not simply a result of the suppression of seizures, and that the "physiological" function of carnitine may not be the sole mechanism underlying this effect.
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PMID:Effects of L and D-carnitine on brain energy metabolites in mice given sublethal doses of ammonium acetate. 851 63

The enantiomers of the anticonvulsant DL-2-hydroxy-2-phenylbutyramide (1) were prepared by resolving the (-)-quinine and (+)-1-phenylethylamine salts of the acids. The optically active acids were then esterified and reacted with ammonia to give (+)-1 and (-)-1. Optical purity of the amides was greater than 99.9% enantiomeric excess by chiral HPLC. Examination of the infrared spectra of the enantiomers and the racemate of 1 in chloroform solution showed identical spectra, but the spectrum of the racemate in a KBr disc was somewhat different from those of the pure enantiomers. Pharmacologically, 1 and its enantiomers have a similar significant anticonvulsant activity at peak drug effect against pentylenetetrazol seizures, but a variation in time between the enantiomers was found with the anticonvulsant activity. In the rotarod ataxia test (-)-1-possessed the lowest neurotoxicity.
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PMID:Stereoselective anticonvulsant activity of the enantiomers of (+/-)-2-hydroxy-2-phenylbutyramide. 857 17

Injection of large doses of ammonia (1.2g/kg, i.p.) was used to induce acute toxicity in mice which was characterized by hyperresponsiveness, taquipnea, clonic and tonic seizures and death. Pretreatment with 20, 40, or 80 mg/Kg, i.p., of ketamine increased 30 to 55% survival rate. This pretreatment significantly retarded the beginning of the first tonic convulsion attenuating its intensity and delayed the time of the animal death; but did not alter the onset of the first clonic seizures. These experiments may be an evidence that support the hypothesis that seizures due to hyperammonemia involve activation of excitatory amino acid receptors.
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PMID:Ketamine reduces lethality on the acute ammonia intoxication in mice. 871 23


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