Enhanced Aspartate Release Related to Epilepsy in (EL) Mice

Abstract: Previous studies have shown that potassium-evoked, calcium-dependent, endogenous aspartate release is greater from hippocampal slices of adult epileptic (EL) mice than from nonepileptic control C57BL/6J (B6) mice. To examine further the association between epilepsy and enhanced aspartate release in EL mice, endogenous neurotransmitter release from hippocampal slices was studied in young, seizure-free EL mice and in two nonseizure control mouse strains, DDY and B6. DDY is the parental strain from which EL arose, and it has a genetic background similar to EL. Released amino acid neurotransmitters were quantitated by HPLC with fluorescent detection and were expressed as picomoles of amino acid released per minute of incubation per slice ± SEM. Aspartate release was significantly higher in EL mice (15.8 ± 0.8) than in either the control B6 or DDY mice (8.5 ± 1.4 and 8.4 ± 1.7, respectively). No significant differences were found among the B6, DDY, and EL mice for the release of glutamate (23.0 ± 2.0, 32.3 ± 5.8, and 25.9 ± 2.6, respectively) or GABA (23.5 ± 0.7, 19.5 ± 3.2, and 21.8 ± 3.2, respectively). Thus, enhanced aspartate release precedes the onset of EL seizures and may be related to the cause rather than to the effects of seizure activity.     

81 例顽固性癫痫患者发作分类特点分析

目的:分析81例最终接受手术治疗的顽固性癫痫患者发病特点,了解不同分类癫痫的发病规律。方法:对81例最终接受手术治疗的顽固性癫痫患者进行分类,分析性别、发病年龄、病程、发作频率等与癫痫分类间的关系。结果:81例患者的男女比例为1.45:1,男性的平均发病年龄为13.6,女性为14.3,强直阵挛发作的耐受病程最短,平均为5.8年,大多数患者在20岁以前发病。结论:多种癫痫发作分类在性别、发病年龄、病程、发作频率上存在差异。     

Long lasting effects of audiogenic seizures on synaptosomal neurotransmitter amino acids in Rb mice

Long lasting alterations of synaptosomal amino acid neurotransmitters following a single or several audiogenic seizures and/or acoustic stimulations were investigated in six brain areas-olfactory bulbs (OB), amygdala (A), hippocampus (Hi), cerebellum (C), inferior colliculus (IC), ponsmedulla (P)- of three sublines of Rb mice: audiogenic seizure-prone Rb1 and Rb2, seizure-resistant Rb3. Changes in the synaptosomal levels of aspartate (Asp), glutamate (Glu), taurine (Tau), 4-amino butyrate (GABA), glycine (Gly) and some closely related precursors, serine (Ser) and glutamine (Gln), were recorded 15–18 hours after a single or multiple acoustic stimulations. Changes were more frequent, or larger, after polystimulation. Some alterations appeared to be attributable to an effect of the acoustic stress.In both seizure-prone sublines, after a single or repeated seizures, an increase in synaptosomal Asp was observed in IC. Decreases in Asp and Tau in OB and Ser in A, an increase in Gln in IC were only observed after repeated seizures, in Rb1 and Rb2 mice.Abbreviations used GABA 4-aminobutyrate - Tau taurine - Gly glycine - Ser serine - Asp aspartate - Glu glutamate - Gln glutamine - OB olfactory bulbs - A amygdala - Hi hippocampus - C cerebellum - IC interior colliculus - P pons Professeur Paul Mandel passed away on 6th October, 1992Special issue dedicated to Dr. Bernard W. Agranoff.     

Postnatal development and GABA allosteric modulation of benzodiazepine receptor binding in the vitamin B-6 deficient rat brain

We have measured the postnatal development and GABA modulation of benzodiazepine receptors in neuronal membranes from vitamin B-6 deficient and normal rats. In rats fed vitamin B-6 adequate and deficient diets there were age-dependent changes in [³H]flunitrazepam binding site affinity and in the number of binding sites. Vitamin B-6 deficiency produced a significant reduction in the potency of GABA to enhance [³H]flunitrazepam binding to cortical membranes prepared from 14 day old rats. These results suggests an uncoupling of the GABAa/benzodiazepine receptor at a developmental period when the animals are most susceptible to spontaneous seizures.     

Long-term alterations in glutamate receptor and transporter expression following early-life seizures are associated with increased seizure susceptibility

Prolonged seizures in early childhood are associated with an increased risk of development of epilepsy in later life. The mechanism(s) behind this susceptibility to later development of epilepsy is unclear. Increased synaptic activity during development has been shown to permanently alter excitatory neurotransmission and could be one of the mechanisms involved in this increased susceptibility to the development of epilepsy. In the present study we determine the effect of status-epilepticus induced by lithium/pilocarpine at postnatal day 10 (P10 SE) on the expression of glutamate receptor and transporter mRNAs in hippocampal dentate granule cells and protein levels in dentate gyrus of these animals in adulthood. The results revealed a decrease in glutamate receptor 2 (GluR2) mRNA expression and protein levels as well as an increase in protein levels for the excitatory amino acid carrier 1 (EAAC1) in P10 SE rats compared to controls. Expression of glutamate receptor 1 (GluR1) mRNA was decreased in both P10 SE rats and identically handled, lithium-injected littermate controls compared to naive animals, and GluR1 protein levels were significantly lower in lithium-controls than in naive rats, suggesting an effect of either the handling or the lithium on GluR1 expression. These changes in EAA receptors and transporters were accompanied by an increased susceptibility to kainic acid induced seizures in P10 SE rats compared to controls. The current data suggest that early-life status-epilepticus can result in permanent alterations in glutamate receptor and transporter gene expression, which may contribute to a lower seizure threshold.     

Intracerebroventricular Guanine-Based Purines Protect Against Seizures Induced by Quinolinic Acid in Mice

Acute and chronic administration of the nucleoside guanosine have been shown to prevent quinolinic acid (QA) and -dendrotoxin-induced seizures, as well as to impair memory and anxiety in rats and mice. In this study, we investigated the effect of i.c.v. administration of guanine-based purines (GTP, GDP, GMP, and guanosine) against seizures induced by the NMDA agonist and glutamate releaser quinolinic acid in mice. We also aimed to study the effects of the poorly hydrolysable analogs of GTP (GppNHp and GTPS) and GDP (GDPS) in this seizure model. QA produced seizures in 100% of mice, an effect partially prevented by guanine-based purines. In contrast to GTP (480 nmol), GDP (320–640 nmol), GMP (320–480 nmol) and guanosine (300–400 nmol), the poorly hydrolysable analogs of GTP and GDP did not affect QA-induced seizures. Thus, the protective effects of guanine nucleotides seem to be due to their conversion to guanosine. Altogether, these findings suggest a potential role of guanine-based purines for treating diseases involving glutamatergic excitotoxicity.     

Role of cAMP-Dependent Protein Kinase on Acute Picrotoxin-Induced Seizures

cAMP-dependent protein kinase (PKA) is a major modulator of synaptic transmission likely to be involved in molecular and cellular events leading to epileptogenesis, but little is known about how it affects the onset of acute epileptic seizures. In this study, we determined PKA enzymatic activity in the rat hippocampus during picrotoxin-induced seizures, using H-9 dihydrochloride, a PKA inhibitor, to investigate the in vivo effects of this enzyme on seizures induced by picrotoxin microdialysis in the rat hippocampus. No significant modifications were found in PKA activity during seizures as compared to control rats, but H-9 dihydrochloride microperfusion (100 μM) prevented picrotoxin seizures in 50% of the animals and significantly reduced the mean number of seizures and mean seizure duration. These results suggest that acute picrotoxin-induced seizures occur without an increase in hippocampal PKA activity, but reduced PKA-mediated phosphorylation protects against picrotoxin seizures, probably by increasing the inhibitory potential of GABA_A receptors. The possibility of other targets for H-9 dihydrochloride, such as PKC, PKG or CAMKII, however, cannot be ruled out.     

Hyperthermia-Induced Seizures Modify the GABA<Subscript><Emphasis Type="Bold">A</Emphasis></Subscript> and Benzodiazepine Receptor Binding in Immature Rat Brain

Summary Effects of hyperthermia-induced seizures (HS) on GABA_A and benzodiazepine (BDZ) receptor binding in immature rat brain were evaluated using in vitro autoradiography. HS were induced in 10-day-old rats by a regulated stream of moderately heated air directed 50 cm above the animals. Rats were killed 30 min, 24 h, or 20 days after HS and their brains were used for in vitro autoradiography experiments to determine GABA_A and BDZ receptor binding. GABA_A binding was significantly enhanced in all brain areas evaluated 30 min after HS, an effect that endures 24 h and 20 days after seizures. Concerning BDZ receptor binding, a significant increase was detected in entorhinal and perirhinal cortices and decreased in basolateral amygdala 30 min following HS. One day after HS, animals demonstrated enhanced BDZ binding in the cingulate, frontal, posterior parietal, entorhinal, temporal, and perirhinal cortices; striatum, accumbens, substantia nigra pars compacta, and amygdala nuclei. Twenty days after HS enhanced BDZ binding was restricted in the cingulated, frontal, anterior and posterior parietal cortices, as well as in substantia nigra pars reticulata, whereas decreased values were found in accumbens nucleus and substantia nigra pars compacta. Our data indicate differential effects of HS in GABA_A and BDZ binding in immature brain. HS-induced GABA_A and BDZ changes are different from those previously described in experimental models of temporal lobe epilepsy in adult animals.     

Made for "anchorin": Kv7.2/7.3 (KCNQ2/KCNQ3) channels and the modulation of neuronal excitability in vertebrate axons

Kv7.2 and Kv7.3 (encoded by KCNQ2 and KCNQ3) are homologous subunits forming a widely expressed neuronal voltage-gated K(+) (Kv) channel. Hypomorphic mutations in either KCNQ2 or KCNQ3 cause a highly penetrant, though transient, human phenotype-epilepsy during the first months of life. Some KCNQ2 mutations also cause involuntary muscle rippling, or myokymia, which is indicative of motoneuron axon hyperexcitability. Kv7.2 and Kv7.3 are concentrated at axonal initial segments (AISs), and at nodes of Ranvier in the central and peripheral nervous system. Kv7.2 and Kv7.3 share a novel ～80 residue C-terminal domain bearing an "anchor" motif, which interacts with ankyrin-G and is required for channel AIS (and likely, nodal) localization. This domain includes the sequence IAEGES/TDTD, which is analogous (not homologous) to the ankyrin-G interaction motif of voltage-gated Na(+) (Na(V)) channels. The KCNQ subfamily is evolutionarily ancient, with two genes (KCNQ1 and KCNQ5) persisting as orthologues in extant bilaterian animals from worm to man. However, KCNQ2 and KCNQ3 arose much more recently, in the interval between the divergence of extant jawless and jawed vertebrates. This is precisely the interval during which myelin and saltatory conduction evolved. The natural selection for KCNQ2 and KCNQ3 appears to hinge on these subunits' unique ability to be coordinately localized with Na(V) channels by ankyrin-G, and the resulting enhancement in the reliability of neuronal excitability.     

A recurrent KCNT1 mutation in two sporadic cases with malignant migrating partial seizures in infancy

We performed analysis of KCNT1 in two unrelated patients with malignant migrating partial seizures in infancy. Both patients had intractable focal seizures since two months of age. Their seizures were characterized by a shift of epileptic focus during a single seizure and were resistant to most antiepileptic drugs but responded to vagus nerve stimulation in one and clorazepate in the other. Bidirectional sequencing for KCNT1 was analyzed by standard Sanger sequencing method. A de novo c.862G > A (p.Gly288Ser) missense mutation was identified at the pore region of KCNT1 channel in both patients, whereas all KCNT1 mutations in the previous reports were identified mostly in the intracellular C-terminal region. Computational analysis suggested possible changes in the molecular structure and the ion channel property induced by the Gly288Ser mutation. Because the G-to-A transition was located at CG dinucleotide sequences as previously reported for KCNT1 mutations, the recurrent occurrence of de novo KCNT1 mutations indicated the hot spots of these locations.