Transient Morphological Alterations in the Hippocampus After Pentylenetetrazole-Induced Seizures in Rats

The relationships between seizures, neuronal death, and epilepsy remain one of the most disputed questions in translational neuroscience. Although it is broadly accepted that prolonged and repeated seizures cause neuronal death and epileptogenesis, whether brief seizures can produce a mild but similar effect is controversial. In the present work, using a rat pentylenetetrazole (PTZ) model of seizures, we evaluated how a single episode of clonic–tonic seizures affected the viability of neurons in the hippocampus, the area of the brain most vulnerable to seizures, and morphological changes in the hippocampus up to 1 week after PTZ treatment (recovery period). The main findings of the study were: (1) PTZ-induced seizures caused the transient appearance of massively shrunken, hyperbasophilic, and hyperelectrondense (dark) cells but did not lead to detectable neuronal cell loss. These dark neurons were alive, suggesting that they could cope with seizure-related dysfunction. (2) Neuronal and biochemical alterations following seizures were observed for at least 1 week. The temporal dynamics of the appearance and disappearance of dark neurons differed in different zones of the hippocampus. (3) The numbers of cells with structural and functional abnormalities in the hippocampus after PTZ-induced seizures decreased in the following order: CA1?>?CA3b,c?>?hilus?>?dentate gyrus. Neurons in the CA3a subarea were most resistant to PTZ-induced seizures. These results suggest that even a single seizure episode is a potent stressor of hippocampal neurons and that it can trigger complex neuroplastic changes in the hippocampus.     

Anticonvulsant activity of topiramate and phenytoin in a rat model of ischemia-induced epilepsy

Topiramate, a structurally novel anticonvulsant, and phenytoin were evaluated in a rat model of ischemia-induced epilepsy. In this model a transient global cerebral ischemia is induced by cardiac compression. By precisely controlling the experimental conditions the procedure causes reproducible neurological deficits that include audiogenic epileptic seizures. The seizures can be broadly separated into three types reflecting the degree of severity: wild running, clonic seizures, and tonic extension seizures of the forelimbs and hindlimbs. Topiramate and phenytoin blocked all three types of seizures. Calculated ED₅₀ values for topiramate 1 hr after oral administration were 8.2, 13.0 and 36.1 mg/kg for blockade of tonic extension seizures, clonic seizures and wild running, respectively. Corresponding ED₅₀ values for phenytoin were 5.0, 10.8 and 20.7 mg/kg. These results support the concept that the anticonvulsant activity of these drugs is due primarily to an ability to block the spread of seizures.     

Experimental febrile seizures are precipitated by a hyperthermia-induced respiratory alkalosis

Febrile seizures are frequent during early childhood, and prolonged (complex) febrile seizures are associated with an increased susceptibility to temporal lobe epilepsy. The pathophysiological consequences of febrile seizures have been extensively studied in rat pups exposed to hyperthermia. The mechanisms that trigger these seizures are unknown, however. A rise in brain pH is known to enhance neuronal excitability. Here we show that hyperthermia causes respiratory alkalosis in the immature brain, with a threshold of 0.2-0.3 pH units for seizure induction. Suppressing alkalosis with 5% ambient CO2 abolished seizures within 20 s. CO2 also prevented two long-term effects of hyperthermic seizures in the hippocampus: the upregulation of the I(h) current and the upregulation of CB1 receptor expression. The effects of hyperthermia were closely mimicked by intraperitoneal injection of bicarbonate. Our work indicates a mechanism for triggering hyperthermic seizures and suggests new strategies in the research and therapy of fever-related epileptic syndromes.     

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.     

Neurotropic viral infections leading to epilepsy: focus on Theiler's murine encephalomyelitis virus

Neurotropic viruses cause viral encephalitis and are associated with the development of seizures/epilepsy. The first infection-driven animal model for epilepsy, the Theiler's murine encephalomyelitis virus-induced seizure model is described herein. Intracerebral infection of C57BL/6 mice with Theiler's murine encephalomyelitis virus induces acute seizures from which the animals recover. However, once the virus is cleared, a significant portion of the animals that experienced acute seizures later develop epilepsy. Components of the innate immune response to viral infection, including IL-6 and complement component 3, have been implicated in the development of acute seizures. Multiple mechanisms, including neuronal cell destruction and cytokine activation, play a role in the development of acute seizures. Future studies targeting the innate immune response will lead to new therapies for seizures/epilepsy.     

Prognostic index for recurrence of seizures after remission of epilepsy. Medical Research Council Antiepileptic Drug Withdrawal Study Group.

OBJECTIVES--To develop and test a prognostic index for the recurrence of seizures after a minimum remission of seizures of two years in people with a history of epilepsy. DESIGN--Information from a large prospective randomised study of withdrawal of antiepileptic drugs was used to identify clinical and treatment factors of prognostic importance in determining the recurrence of seizures. A split sample approach was used to test the internal validity of predictions made on the basis of identified prognostic factors. SETTING--Centres in six European countries. MAIN OUTCOME MEASURES--Comparison of predicted and observed rates of recurrence of seizure. SUBJECTS--1013 patients randomised to the Medical Research Council study for antiepileptic drug withdrawal. RESULTS--The Cox proportional hazards model identified several factors that increased the risk of seizures recurring. These included being 16 years or older; taking more than one antiepileptic drug; experiencing seizures after starting antiepileptic drug treatment; a history of primary or secondarily generalised tonic-clonic seizures; a history of myoclonic seizures; and having an abnormal electroencephalogram. The risks of seizures recurring decreased with increasing time without seizures. The model allowed estimation of the risk of seizures recurring in the next one and two years under the policies of continued antiepileptic drug treatment and slow withdrawal of drugs. Split sample validation suggested that the model was well calibrated. CONCLUSION--The model is currently the best available aid for counselling the many patients in the community with epilepsy currently in remission who seek advice about the risks of seizures recurring if they stop antiepileptic drug treatment. The model requires validation in a broad population of patients, and such studies are in progress.     

Effects of acute hypoxia on the development of corazol-induced seizures

Experiments on white random-bred rats showed that development of corazol seizures depend both on corazol dose and pO2 level in atmosphere. Latent period becomes short, the time of convulsive attack and the time of all seizures prolongs with increase of corazol dose. Acute hypoxia inhibits development of seizures: decreases the time of attack and the time of all seizures, prolongs latent period. The higher the hypoxia level is more massive its protective effect on corazol seizures. The anticonvulsant mechanisms of acute hypoxia are under discussion.     

The role of muscarinic acetylcholine receptor-mediated activation of extracellular signal-regulated kinase 1/2 in pilocarpine-induced seizures

Pilocarpine-induced seizures are mediated by the M(1) subtype of muscarinic acetylcholine receptor (mAChR), but little is known about the signaling mechanisms linking the receptor to seizures. The extracellular signal-regulated kinase (ERK) signaling cascade is activated by M(1) mAChR and is elevated during status epilepticus. Yet, the role of ERK activation prior to seizure has not been evaluated. Here, we examine the role of pilocarpine-induced ERK activation in the induction of seizures in mice by pharmacological and behavioral approaches. We show that pilocarpine induces ERK activation prior to the induction of seizures by both western blot and immunocytochemistry with an antibody to phosphorylated ERK. In addition, we show that the ERK pathway inhibitor SL327 effectively blocks the pilocarpine-induced ERK activation. However, SL327 pretreatment has no effect on the initiation of seizures. In fact, animals treated with SL327 had higher seizure-related mortality than vehicle-treated animals, suggesting activated ERK may serve a protective role during seizures. In addition, ERK inhibition had no effect on the development of the long-term sequelae of status epilepticus (SE), including mossy fiber sprouting, neuronal death and spontaneous recurrent seizures.     

The safety of evening primrose oil in epilepsy

The concern that evening primrose oil might cause epilepsy or seizures, or reduce the threshold for seizures, originated from two papers published in the early 1980s. These original reports are re-examined, and the association of evening primrose oil with seizures is shown to be spurious. Not only are linoleic acid and gamma-linolenic acid safe in epilepsy, with prolonged oral administration of linoleic acid and alpha-linolenic acid (in a 4:1 mixture) protecting rats from having seizures in four different epilepsy models, but the evening primrose oil-derived omega-6 fatty acid arachidonic acid inhibits sodium ion currents and synaptic transmission, while the evening primrose oil-derived eicosanoid prostaglandin E(1) appears to have anticonvulsant activity. In light of these findings, it is suggested that formularies should now remove seizures or epilepsy as a side-effect of evening primrose oil, and should remove a history of seizures or epilepsy as a contraindication to taking evening primrose oil.     

Influence of a new antiepileptic drug ORG 6370 on metrazol-induced seizures in rats during ontogenesis

The anticonvulsant action of a new antiepileptic drug ORG 6370 (Organon International B.V.) was studied in 217 male albino rats aged 7, 12, 18, 25 and 90 days. Epileptic phenomena induced by a subcutaneous injection of a 100 mg/kg dose of metrazol (isolated myoclonic jerk, minimal metrazol seizures and major, generalized tonic-clonic metrazol seizures) were used as a model. ORG 6370 did not influence myoclonic jerks or minimal metrazol seizures in those age groups where they were regularly elicited. In 12-day-old rats pretreatment with ORG 6370 led to the appearance of minimal metrazol seizures, a phenomenon rarely seen under control conditions. Major seizures were suppressed only in adult rats with a 20 mg/kg dose; on the other hand, ORG 6370 exhibited a selective action against the tonic phase of major seizures at all stages of development. The profile of action of ORG 6370 is almost the same as that of phenytoin.     

Epileptogenic actions of GABA and fast oscillations in the developing hippocampus

GABA excites immature neurons and inhibits adult ones, but whether this contributes to seizures in the developing brain is not known. We now report that in the developing, but not the adult, hippocampus, seizures beget seizures only if GABAergic synapses are functional. In the immature hippocampus, seizures generated with functional GABAergic synapses include fast oscillations that are required to transform a naive network to an epileptic one: blocking GABA receptors prevents the long-lasting sequels of seizures. In contrast, in adult neurons, full blockade of GABA(A) receptors generates epileptogenic high-frequency seizures. Therefore, purely glutamatergic seizures are not epileptogenic in the developing hippocampus. We suggest that the density of glutamatergic synapses is not sufficient for epileptogenesis in immature neurons; excitatory GABAergic synapses are required for that purpose. We suggest that the synergistic actions of GABA and NMDA receptors trigger the cascades involved in epileptogenesis in the developing hippocampus.     

Complicated relationship between autism with regression and epilepsy

We retrospectively evaluated a set of 205 children with autism and compared it to the partial sub-set of 71 (34.6%) children with a history of regression. From 71 children with regression, signs of epileptic processes were present in 43 (60.6%), 28 (65.12%) suffered clinical epileptic seizures, and 15 (34.9%) just had an epileptiform abnormality on the EEG. In our analysis, autistic regression is substantially more associated with epileptic process symptoms than in children with autism and no history of regression. More than 90% of children with a history of regression also show IQ < 70 and reduced functionality. Functionality and IQ further worsens with the occurrence of epileptic seizures (98% of children with regression and epilepsy have IQ < 70). We proved that low IQ and reduced functionality significantly correlate rather with epileptic seizures than just sub-clinical epileptiform abnormality on EEG. Clinical epileptic seizures associated with regression significantly influence the age of regression and its clinical type. The age of regression is higher compared to children with regression without epileptic seizures (in median: 35 months of age in patients with seizures while only 24 months in other patients). Patients with seizures revealed regression after 24th months of age in 68% of cases, while patients without seizures only in 27%. However, coincidence with epilepsy also increased the occurrence of regression before the 18th month of age (23% of patients), while only 4% of patients without epilepsy revealed regression before the 18th month. Epileptic seizures are significantly associated especially with behaviour regression rather than speech regression or regression in both behaviour and speech. Also epileptic seizures diagnosed before correct diagnosis of autism were significantly associated with delayed regression (both behavioural and speech regression).     

基于二阶C0复杂度的癫痫发作预测

癫痫发作的预测是近年来在临床医学和神经系统科学研究领域中备受关注的问题。如果癫痫发作能够被可靠地预测,则可以提前采取有效的临床预防措施,从而能较大程度地改善癫痫患者的生活质量。文章提出了一种基于二阶C0复杂度的预测算法用于预测癫痫发作。该算法通过分析癫痫患者颅内脑电信号的二阶C0复杂度,利用发作前期复杂度曲线的变化特征预测癫痫发作。作者运用该算法对21组癫痫病人87次发作的临床颅内脑电数据和4组大鼠4次发作的颅内脑电数据进行分析计算,预测准确率分别为94.3%和100%。实验结果表明该算法可以有效地预测癫痫发作,具有潜在的重要临床应用价值。     

Substance P Causes Seizures in Neurocysticercosis

Neurocysticercosis (NCC), a helminth infection of the brain, is a major cause of seizures. The mediators responsible for seizures in NCC are unknown, and their management remains controversial. Substance P (SP) is a neuropeptide produced by neurons, endothelial cells and immunocytes. The current studies examined the hypothesis that SP mediates seizures in NCC. We demonstrated by immunostaining that 5 of 5 brain biopsies from NCC patients contained substance P (SP)-positive (+) cells adjacent to but not distant from degenerating worms; no SP+ cells were detected in uninfected brains. In a rodent model of NCC, seizures were induced after intrahippocampal injection of SP alone or after injection of extracts of cysticercosis granuloma obtained from infected wild type (WT), but not from infected SP precursor-deficient mice. Seizure activity correlated with SP levels within WT granuloma extracts and was prevented by intrahippocampal pre-injection of SP receptor antagonist. Furthermore, extracts of granulomas from WT mice caused seizures when injected into the hippocampus of WT mice, but not when injected into SP receptor (NK1R) deficient mice. These findings indicate that SP causes seizures in NCC, and, suggests that seizures in NCC in humans may be prevented and/or treated with SP-receptor antagonists.     

The interaction between early life epilepsy and autistic-like behavioral consequences: a role for the mammalian target of rapamycin (mTOR) pathway

Early life seizures can result in chronic epilepsy, cognitive deficits and behavioral changes such as autism, and conversely epilepsy is common in autistic children. We hypothesized that during early brain development, seizures could alter regulators of synaptic development and underlie the interaction between epilepsy and autism. The mammalian Target of Rapamycin (mTOR) modulates protein translation and is dysregulated in Tuberous Sclerosis Complex, a disorder characterized by epilepsy and autism. We used a rodent model of acute hypoxia-induced neonatal seizures that results in long term increases in neuronal excitability, seizure susceptibility, and spontaneous seizures, to determine how seizures alter mTOR Complex 1 (mTORC1) signaling. We hypothesized that seizures occurring at a developmental stage coinciding with a critical period of synaptogenesis will activate mTORC1, contributing to epileptic networks and autistic-like behavior in later life. Here we show that in the rat, baseline mTORC1 activation peaks during the first three postnatal weeks, and induction of seizures at postnatal day 10 results in further transient activation of its downstream targets phospho-4E-BP1 (Thr37/46), phospho-p70S6K (Thr389) and phospho-S6 (Ser235/236), as well as rapid induction of activity-dependent upstream signaling molecules, including BDNF, phospho-Akt (Thr308) and phospho-ERK (Thr202/Tyr204). Furthermore, treatment with the mTORC1 inhibitor rapamycin immediately before and after seizures reversed early increases in glutamatergic neurotransmission and seizure susceptibility and attenuated later life epilepsy and autistic-like behavior. Together, these findings suggest that in the developing brain the mTORC1 signaling pathway is involved in epileptogenesis and altered social behavior, and that it may be a target for development of novel therapies that eliminate the progressive effects of neonatal seizures.     

Models of epileptic seizures in immature rats

Models of basic types of epileptic seizures are elaborated not only in adult but also in immature rodents. It is important because at least half of human epilepsies starts during infancy and childhood. This paper presents a review of chemically and electrically induced models of generalized convulsive and nonconvulsive (absence) seizures as well as models of partial simple (neocortical) and complex (limbic) seizures in immature rats. These models can also serve as a tool for study the development of central nervous system and motor abilities because the level of maturation is reflected in seizure semiology. Age-dependent models of epileptic seizures (absences and flexion seizures) are discussed. Models of seizures in immature animals should be used for testing of potential antiepileptic drugs.     

Mechanisms underlying modifications in the severity of audiogenic convulsions

Catecholamine levels were selectively decreased in peripheral sites or in brain of mice by intravenous or intraventricular injections of 6-hydroxydopamine. Brain dopamine alone was decreased by administering i.p. desmethylimipramine prior to 6 hydroxydopamine injections. A brain noradrenaline decrease does not induce mortality in a tonic strain of mice but can transform clonic audiogenic seizures into tonic seizures in a clonic mouse strain, while a dopamine depletion alone has no effect. However, a noradrenaline decrease at peripheral sites increases the number of lethal seizures in a tonic strain without modifying clonic seizures in a clonic strain. Catecholamine metabolism is neither involved in the onset of seizures in a non-sensitive strain nor involved in the change of clonus into tonus in unilaterally deafened tonic strain animals, which in this case present only clonic seizures.     

Scalp EEG for the diagnosis of epilepsy and photosensitivity in the baboon

Spontaneous seizures have been observed in several baboon species housed at the Southwest National Primate Research Center (SNPRC), including Papio hamadryas anubis and cynocephalus/anubis, hamadryas/anubis, and papio/anubis hybrids. The goal of this study was to establish a noninvasive, reliable electroencephalographic technique to characterize epilepsy phenotypes and assess photosensitivity in these subspecies. Thirty baboons with witnessed seizures, and 15 asymptomatic baboons underwent scalp electroencephalograms (EEGs) with photic stimulation (PS). The sensitivity and specificity of surface EEG for identifying interictal epileptic discharges (IEDs) in baboons with witnessed seizures were examined. The morphology of IEDs, electroclinical features of seizures and responses to PS, reproducibility of EEG findings, and intrarater reliability were also evaluated. Twenty-three seizure baboons (77%) demonstrated IEDs, predominantly with frequencies of 4-6 Hz in 18 baboons and 2-3 Hz in six baboons. Two seizure animals had a mixture of 2-3-Hz and 4-6-Hz IEDs. All animals with 2-3-Hz IEDs were 3 years old or younger. Myoclonic seizures (MS) and generalized tonic-clonic seizures (GTCS) were recorded in 13 baboons (43%). PS activated IEDs in 15 baboons (50%) and seizures in nine baboons. The presence of IEDs or seizures was not associated with a particular gender or species (Fisher exact test, alpha=0.05). Seizures were more common in animals >3 years old, while PS-induced IEDs and seizures were more prevalent in P.h. anubis/cynocephalus crosses compared to P.h. anubis. In the asymptomatic controls, IEDs were recorded in five baboons (33%), and photoparoxysmal responses were observed in two (13%). Surface EEG is a sensitive and reliable instrument for characterizing the epilepsy encountered in Papio species. Electroclinically, the seizure animals had generalized epilepsy with photosensitivity. The variation in IED morphology may be age-related or it may reflect different epileptic phenotypes. Ketamine provoked IEDs and seizures in most seizure animals and only in a few asymptomatic baboons; therefore, it may enhance the sensitivity of surface EEG for detecting a predisposition to epilepsy.     

Antipentylenetetrazol action of clobazam in developing rats

Clobazam (0.5 to 7.5 mg/kg i.p.) was tested against motor seizures elicited by pentylenetetrazol in rats 7, 12, 18, 25 and 90 days old. Minimal, predominantly clonic seizures with preserved righting ability were reliably induced by pentylenetetrazol and suppressed by clobazam in rats aged 18 days or more. The incidence of minimal seizures after clobazam pretreatment was not increased in 7- and 12-day-old rat pups. Generalized tonic-clonic seizures were markedly suppressed by clobazam in all age groups. In 18-day-old and older animals clobazam doses suppressing generalized seizures were always lower than those necessary for exerting an effect on minimal seizures. The differences in clobazam action appearing at various levels of maturation are only quantitative.     

Lovastatin exacerbates atypical absence seizures with only minimal effects on brain sterols

AY-9944 (AY) exacerbates chronic recurrent seizures in rats that are analogous to atypical absence epilepsy in humans. The mechanism by which AY affects the slow spike-and-wave discharges associated with these seizures is not known, but is thought to involve inhibition of cholesterol synthesis. We tested the hypothesis that seizures seen with AY are due to significant reduction in brain cholesterol and/or elevated brain 7-dehydrocholesterol by assessing whether three other cholesterol synthesis inhibitors mimic AY seizures in rats. Effects of AY on brain sterols and spike-and-wave discharge duration were compared with those of two other late-stage cholesterol inhibitors [BM 15.766 (BM) and U18666A (UA)] and to an HMG-CoA reductase (early-stage cholesterol) inhibitor, lovastatin. With BM or UA, prolongation of seizure duration and brain sterol changes was similar to that caused by AY. AY effects on both brain sterols and seizure duration were dose-related. Lovastatin, with or without concurrent AY, mimicked AY seizures but reduced brain cholesterol by <10% and did not significantly change brain 7-dehydrocholesterol. Either lovastatin has a different mechanism of action than these late-stage cholesterol inhibitors or the brain sterol changes are not directly responsible for seizures in this model.