Modulating Expression of Endogenous Interleukin 1 Beta in the Acute Phase of the Pilocarpine Model of Epilepsy May Change Animal Survival.

The pilocarpine-induced (PILO) model has helped elucidate the electrophysiological and molecular aspects related to mesial temporal lobe epilepsy. It has been suggested that the extensive cell death and edema observed in the brains of these animals could be induced by increased inflammatory responses, such as the rapid release of the inflammatory cytokine interleukin 1 beta (Il1b). In this study, we investigate the role of endogenous Il1b in the acute phase of the PILO model. Our aim is twofold. First, we want to determine whether it is feasible to silence Il1b in the central nervous system using a non-invasive procedure. Second, we aim to investigate the effect of silencing endogenous Il1b and its antagonist, Il1rn.We used RNA interference applied non-invasively to knockdown Il1b and its endogenous antagonist Il1rn. We found that knocking down Il1b prior to pilocarpine injection increased the mortality rate of treated animals. Furthermore, we observed that, when exposing the animals to more Il1b by silencing its endogenous antagonist Il1rn, there was a better response to status epilepticus with decreased animal mortality in the acute phase of the PILO model. Thus, we show the feasibility of using a novel, less invasive approach to study genes involved in the inflammatory response in the central nervous system. Furthermore, our results provide suggestive evidence that modulating endogenous Il1b improves animal survival in the acute phase of the PILO model and may have effects that extend into the chronic phase.

Enhanced nonsynaptic epileptiform activity in the dentate gyrus after kainate-induced status epilepticus.

Understanding the mechanisms that influence brain excitability and synchronization provides hope that epileptic seizures can be controlled. In this scenario, non-synaptic mechanisms have a critical role in seizure activity. The contribution of ion transporters to the regulation of seizure-like activity has not been extensively studied. Here, we examined how non-synaptic epileptiform activity (NEA) in the CA1 and dentate gyrus (DG) regions of the hippocampal formation were affected by kainic acid (KA) administration. NEA enhancement in the DG and suppression in area CA1 were associated with increased NKCC1 expression in neurons and severe neuronal loss accompanied by marked glial proliferation, respectively. Twenty-four hours after KA, the DG exhibited intense microglial activation that was associated with reduced cell density in the infra-pyramidal lamina; however, cellular density recovered 7 days after KA. Intense Ki67 immunoreactivity was observed in the subgranular proliferative zone of the DG, which indicates new neuron incorporation into the granule layer. In addition, bumetanide, a selective inhibitor of neuronal Cl(-) uptake mediated by NKCC1, was used to confirm that the NKCC1 increase effectively contributed to NEA changes in the DG. Furthermore, 7 days after KA, prominent NKCC1 staining was identified in the axon initial segments of granule cells, at the exact site where action potentials are preferentially initiated, which endowed these neurons with increased excitability. Taken together, our data suggest a key role of NKCC1 in NEA in the DG.

Epilepsy-induced electrocardiographic alterations following cardiac ischemia and reperfusion in rats

The present study evaluated electrocardiographic alterations in rats with epilepsy submitted to an acute myocardial infarction (AMI) model induced by cardiac ischemia and reperfusion. Rats were randomly divided into two groups: control (n=12) and epilepsy (n=14). It was found that rats with epilepsy presented a significant reduction in atrioventricular block incidence following the ischemia and reperfusion procedure. In addition, significant alterations were observed in electrocardiogram intervals during the stabilization, ischemia, and reperfusion periods of rats with epilepsy compared to control rats. It was noted that rats with epilepsy presented a significant increase in the QRS interval during the stabilization period in relation to control rats (P<0.01). During the ischemia period, there was an increase in the QRS interval (P<0.05) and a reduction in the P wave and QT intervals (P<0.05 for both) in rats with epilepsy compared to control rats. During the reperfusion period, a significant reduction in the QT interval (P<0.01) was verified in the epilepsy group in relation to the control group. Our results indicate that rats submitted to an epilepsy model induced by pilocarpine presented electrical conductivity alterations of cardiac tissue, mainly during an AMI episode.

Epilepsy-induced electrocardiographic alterations following cardiac ischemia and reperfusion in rats.

The present study evaluated electrocardiographic alterations in rats with epilepsy submitted to an acute myocardial infarction (AMI) model induced by cardiac ischemia and reperfusion. Rats were randomly divided into two groups: control (n=12) and epilepsy (n=14). It was found that rats with epilepsy presented a significant reduction in atrioventricular block incidence following the ischemia and reperfusion procedure. In addition, significant alterations were observed in electrocardiogram intervals during the stabilization, ischemia, and reperfusion periods of rats with epilepsy compared to control rats. It was noted that rats with epilepsy presented a significant increase in the QRS interval during the stabilization period in relation to control rats (P<0.01). During the ischemia period, there was an increase in the QRS interval (P<0.05) and a reduction in the P wave and QT intervals (P<0.05 for both) in rats with epilepsy compared to control rats. During the reperfusion period, a significant reduction in the QT interval (P<0.01) was verified in the epilepsy group in relation to the control group. Our results indicate that rats submitted to an epilepsy model induced by pilocarpine presented electrical conductivity alterations of cardiac tissue, mainly during an AMI episode.

Lovastatin decreases the synthesis of inflammatory mediators during epileptogenesis in the hippocampus of rats submitted to pilocarpine-induced epilepsy.

Statins may act on inflammatory responses, decreasing oxidative stress and also reducing brain inflammation in several brain disorders. Epileptogenesis is a process in which a healthy brain becomes abnormal and predisposed to generating spontaneous seizures. We previously reported that lovastatin could prevent neuroinflammation in pilocarpine-induced status epilepticus (SE). In this context, this study investigated the long-lasting effects of lovastatin on mRNA expression of proinflammatory cytokines (interleukin-1ß, tumor necrosis factor α, interleukin-6) and the antiinflammatory cytokine IL-10 in the hippocampus during epileptogenesis by immunohistochemistry and real time polymerase chain reaction (RT-PCR) during the latent and chronic phases in the epilepsy model induced by pilocarpine in rats. For these purposes, four groups of rats were employed: saline (CONTROL), lovastatin (LOVA), pilocarpine (PILO), and pilocarpine plus lovastatin (PILO+LOVA). After pilocarpine injection (350mg/kg, i.p.), the rats were treated with 20mg/kg of lovastatin via an esophagic probe 2h after SE onset. All surviving rats were continuously treated during 15days, twice/day. The pilocarpine plus lovastatin group showed a significant decrease in the levels of IL-1ß, TNF-α, and IL-6 during the latent phase and a decreased expression of IL-1ß and TNF-α in the chronic phase when compared with the PILO group. Moreover, lovastatin treatment also induced an increased expression of the antiinflammatory cytokine, IL-10, in the PILO+LOVA group when compared with the PILO group in the chronic phase. Thus, our data suggest that lovastin may reduce excitotoxicity during epileptogenesis induced by pilocarpine by increasing the synthesis of IL-10 and decreasing proinflammatory cytokines in the hippocampus.

Beneficial influence of physical exercise following status epilepticus in the immature brain of rats.

Studies in adult animals have demonstrated a beneficial effect of physical exercise on epileptic insults. Although the effects of physical exercise on the mature nervous system are well documented, its influence on the developing nervous system subjected to injuries in childhood has been little explored. The purpose of our study was to investigate whether a physical exercise program applied during brain development could influence the hippocampal plasticity of rats submitted to status epilepticus (SE) induced by pilocarpine model at two different ages of the postnatal period. Male Wistar rats aged 18 (P18) and 28 (P28) days were randomly divided into four groups: Control (CTRL), Exercise (EX), SE (SE) and SE Exercise (SE/EX) (n=17 per group). After the aerobic exercise program, histological and behavioral (water maze) analyses were performed. Our results showed that only animals subjected to pilocarpine-induced SE at P28 presented spontaneous seizures during the observational period. A significant reduction in seizure frequency was observed in the SE/EX group compared to the SE group. In adulthood, animals submitted to early-life SE displayed impairment in long-term memory in the water maze task, while the exercise program reversed this deficit. Reduced mossy fiber sprouting in the dentate gyrus was noted in animals that presented spontaneous seizures (SE/EX vs SE). Exercise increased cell proliferation (Ki-67 staining) and anti-apoptotic response (bcl-2 staining) and reduced pro-apoptotic response (Bax staining) in animals of both ages of SE induction (P18/28). Exercise also modified the brain-derived neurotrophic factor (BDNF) levels in EX and SE/EX animals. Our findings indicate that in animals subjected to SE in the postnatal period a physical exercise program brings about beneficial effects on seizure frequency and hippocampal plasticity in later stages of life.

Carbamazepine inhibits angiotensin I-converting enzyme, linking it to the pathogenesis of temporal lobe epilepsy.

We find that a common mutation that increases angiotensin I-converting enzyme activity occurs with higher frequency in male patients suffering from refractory temporal lobe epilepsy. However, in their brains, the activity of the enzyme is downregulated. As an explanation, we surprisingly find that carbamazepine, commonly used to treat epilepsy, is an inhibitor of the enzyme, thus providing a direct link between epilepsy and the renin-angiotensin and kallikrein-kinin systems.

Morphological and electrophysiological properties of pyramidal-like neurons in the stratum oriens of Cornu ammonis 1 and Cornu ammonis 2 area of Proechimys.

Proechimys (Rodentia: Echimyidae) is a neotropical rodent of the Amazon region that has been successfully colonized in the laboratory and used for experimental medicine. Preliminary studies indicated that Proechimys (casiragua) rodents express an atypical resistance to developing a chronic epileptic condition in common models of temporal lobe epilepsy. Moreover, previous investigation of our laboratory described a remarkably different Proechimy's cytoarchitecture organization of the hippocampal CA2 subfield. In the present study, we investigated the intrinsic neuronal properties and morphological characteristics of the Proechimys's hippocampal pyramidal neurons of the CA1 and CA2 areas. A comparative approach was performed using neurons recorded in Wistar rats. A striking finding in Proechimys rodents was the presence of large pyramidal-like neurons throughout the stratum oriens from CA2 to CA1 area. In order to confirm such distinctive feature of the Proechimys's hippocampus, we performed Nissl staining and immunohistochemistry for neurofilament protein SM311. CA2 pyramidal neurons in the stratum pyramidale of Proechimys exhibited a significantly higher input resistance and lower time constant when compared to corresponding cell groups in the same area of the Wistar rat's. This newly identified population of pyramidal-shaped neurons in stratum oriens of Proechimys exhibited distinct electrophysiological and morphological properties. This included larger capacitance, lower input resistance, larger rheobase, long latency to first action potential and slower firing frequency. In addition, the apical dendrites of these neurons were oriented in parallel to apical dendrites of regular pyramidal neurons in stratum pyramidale. Moreover, these neurons were immunoreactive to SM311 as the majority of the neurons of the pyramidal layer. The functional role of these hippocampal neurons of the rodent Proechimys deserves further investigation.

Fish consumption, contaminants and sudden unexpected death in epilepsy: many more benefits than risks.

People with epilepsy have an increased risk of dying prematurely and the most common epilepsy-related category of death is sudden unexpected death in epilepsy (SUDEP). SUDEP is mainly a problem for patients with chronic uncontrolled epilepsy. The ultimate goal of research in SUDEP is to develop new methods to prevent it and actions other than medical and surgical therapies that could be very useful. Nutritional aspects, i.e., omega-3 fatty acids deficiency, could have an interesting role in this scenario. Some animal and clinical studies have suggested that omega-3 fatty acids could be useful in the prevention and treatment of epilepsy and hence SUDEP. It has been ascertained that the only foods that provide large amounts of omega-3 are seafood (fish and shellfish); however, some fish are contaminated with methylmercury, which may counteract the positive effects of omega-3 fatty acids. Our update review summarises the knowledge of the role of fish consumption on epilepsy research.

Fish consumption, contaminants and sudden unexpected death in epilepsy: many more benefits than risks / Consumo de peixe, contaminantes e morte súbita em epilepsia: mais benefícios do que riscos

People with epilepsy have an increased risk of dying prematurely and the most common epilepsy-related category of death is sudden unexpected death in epilepsy (SUDEP). SUDEP is mainly a problem for patients with chronic uncontrolled epilepsy. The ultimate goal of research in SUDEP is to develop new methods to prevent it and actions other than medical and surgical therapies that could be very useful. Nutritional aspects, i.e., omega-3 fatty acids deficiency, could have an interesting role in this scenario. Some animal and clinical studies have suggested that omega-3 fatty acids could be useful in the prevention and treatment of epilepsy and hence SUDEP. It has been ascertained that the only foods that provide large amounts of omega-3 are seafood (fish and shellfish); however, some fish are contaminated with methylmercury, which may counteract the positive effects of omega-3 fatty acids. Our update review summarises the knowledge of the role of fish consumption on epilepsy research.

Pessoas com epilepsia têm um risco aumentado de morrer de forma prematura e a causa mais comum de morte relacionada à epilepsia encontra-se na categoria de morte súbita inesperada em epilepsia (SUDEP). SUDEP é um problema significativo para pacientes com epilepsia crônica não controlada. O principal objetivo nas pesquisas em SUDEP é o desenvolvimento de métodos capazes de levar à sua prevenção e ações outras que não medicamentosas e cirúrgicas que podem ser úteis. Os aspectos nutricionais, como por exemplo, a deficiência do ácido graxo ômega-3 pode ter um papel interessante neste cenário. Alguns estudos animais e clínicos têm sugerido que os ácidos graxos ômega-3 podem ser úteis na prevenção e no tratamento da epilepsia e, consequentemente, na SUDEP. Os únicos alimentos que contêm grandes proporções de ômega-3 são os frutos do mar (peixes e mariscos). No entanto, alguns peixes podem estar contaminados com metilmercúrio, o que pode levar a um efeito contrário ao benefício trazido pelos ácidos graxos ômega-3. Aqui, resumimos o conhecimento do papel do consumo de peixe nas pesquisas em epilepsia.

Distinctive hippocampal CA2 subfield of the Amazon rodent Proechimys.

Previous data of our laboratory have shown that the Amazonian rodents Proechimys do not present spontaneous seizures in different models of epilepsy, suggesting endogenous inhibitory mechanisms. Here, we describe a remarkably different Proechimy's cytoarchitecture organization of the hippocampal cornu Ammonis 2 (CA2) subfield. We identified a very distinctive Proechimy's CA2 sector exhibiting disorganized cell presentation of the pyramidal layer and atypical dispersion of the pyramidal-like cells to the stratum oriens, strongly contrasting to the densely packed CA2 cells in the Wistar rats. Studies showed that CA2 is the only cornu ammonis (CA) subfield resistant to the extensive pyramidal neural loss in mesial temporal lobe epilepsy (MTLE) associated to hippocampal sclerosis. Thus, in order to investigate this region, we used Nissl and Timm staining, stereological approach to count neurons and immunohistochemistry to neuronal nuclei (NeuN), parvalbumin (PV), calbindin (CB) and calretinin (CR). We did not notice statistically significant differences in the total number of neurons of the CA2 region between Proechimys and Wistar. However, Proechimys rodents presented higher CA2 volume than Wistar rats. Furthermore, no significant difference in the optical density of parvalbumin-immunoreactivity was found between subject groups. On the other hand, Proechimys presented significant higher density of calbindin and calretinin-immunoreactivity when compared to Wistar rats. In this context, this unique CA2 subfield seen in Proechimys opens up a new set of possibilities to explore the contribution of CA2 neurons in normal and pathological brain circuits.

Could sudden death syndrome (SDS) in chickens (Gallus gallus) be a valid animal model for sudden unexpected death in epilepsy (SUDEP)?

Epilepsy is the most common serious neurological disorder and approximately 1% of the population worldwide has epilepsy. Moreover, sudden unexpected death in epilepsy (SUDEP) is the most important direct epilepsy-related cause of death. Information concerning risk factors for SUDEP is conflicting, but potential risk factors include: young age, early onset of epilepsy, duration of epilepsy, uncontrolled seizures, seizure frequency, AED number and winter temperatures. Additionally, the cause of SUDEP is still unknown; however, the most commonly suggested mechanisms are cardiac abnormalities during and between seizures. Similarly, sudden death syndrome (SDS) is a disease characterized by an acute death of well-nourished and seeming healthy Gallus gallus after abrupt and brief flapping of their wings and incidence of SDS these animals has recently increased worldwide. Moreover, the exactly cause of SDS in Gallus gallus is unknown, but is very probable that cardiac abnormalities play a potential role. Due the similarities between SUDEP and SDS and as Gallus gallus behavioral manifestation during SDS phenomenon is close of a tonic-clonic seizure, in this paper we suggest that epilepsy could be a new possible causal factor for SDS.

Effect of hormonal replacement therapy in the hippocampus of ovariectomized epileptic female rats using the pilocarpine experimental model.

Amado and Cavalheiro [Amado, D., Cavalheiro, E.A., 1998. Hormonal and gestational parameters in female rats submitted to the pilocarpine model of epilepsy. Epilepsy Res. 32, 266-274], studying the establishment of the pilocarpine epilepsy model in female rats observed that the estrous cycle was dramatically altered during the three periods of this experimental model. This work was delineated to study the function of sexual hormones in the development of the epilepsy model induced by pilocarpine in ovariectomized rats. Experimental groups were: (a) control animals during estrus phase of the estrous cycle (E) and ovariectomized female rats (OVX) treated with saline instead of pilocarpine in the same volume, (b) experimental animals, that developed status epilepticus (SE) and were studied during the chronic phase of this model: intact chronic rats (CHRON) and ovariectomized chronic rats (OVX+CHRON) and (c) ovariectomized chronic rats, that were submitted to hormonal replacement therapy treated with: medroxyprogesterone (OVX+CHRON+MPA); 17beta-estradiol (OVX+CHRON+E2), or both (OVX+CHRON+E2+MPA). All ovariectomized animals showed genital atrophy 4 days after the surgical procedure. Moreover, all animals that developed SE and survived showed spontaneous recurrent seizures during the chronic phase. Concerning to seizure frequency, animals receiving medroxyprogesterone associated with 17beta-estradiol showed decreased seizures' number. However, animals that received only medroxyprogesterone therapy also showed reduction in the number of seizures. In addition, hormonal treatment was also able to stabilize the mossy fibers sprouting process, showing the importance of these hormones in the development of the epilepsy in female rats.

Kinin B1 receptors facilitate the development of temporal lobe epilepsy in mice.

Kinins may play a relevant role in epilepsy. In the present study, we evaluated the hippocampal expression of the remaining kinin receptor in B1 (B1KO) and B2 (B2KO) knockout mice strains during the development of pilocarpine epilepsy model. After pilocarpine injection, animals had their behavior parameters monitored to determine different phases of temporal lobe epilepsy (TLE) progression. Hippocampal mRNA expression was evaluated using specific primers for kinin receptors by Real Time-PCR. B1KO hippocampus from acute, silent and chronic phases showed no differences in B2 receptor mRNA expression when compared to control. An increased B1 receptor mRNA expression in treated B2KO hippocampus (0.97+/-0.12, acute; 0.86+/-0.09, silent; and 0.94+/-0.11, chronic phase; p<0,001) when compared to control (0.12+/-0.03) was observed. Behavioral and neurochemistry parameters suggest that kinin B1 receptor is fundamental to development of epilepsy on pilocarpine-induced model.

Cerebrospinal fluid GABA levels in chronic migraine with and without depression.

Psychiatric comorbidity is one of the key elements in chronic migraine (CM) management. Depression is particularly common in these patients, occurring in up to 85%. Preclinical studies have suggested that gamma-aminobutyric acid (GABA) levels may be decreased in animal models of depression. Also, clinical studies have reported low level in mood disorder patients for both plasma and cerebrospinal fluid (CSF) GABA. We hypothesized that low GABA levels in the brain might be related to the depression associated with CM. We studied 14 chronic migraine patients, with or without depression, compared to age-and sex-matched controls. CSF GABA levels were measured by HPLC. CSF GABA levels showed significant lower levels in depressed patients than those without depression. No difference was found when comparing patients versus controls. A GABA deficiency may be the underlying mechanism of depression in CM. Hence, preventive therapies modulating GABA neurotransmission could be used in CM associated with depression.

Seizure occurrence in patients with chronic renal insufficiency in regular hemodialysis program

Hemodialysis-associated seizure is a complication of hemodialysis. This report describes the occurrence of seizures in patients with end stage renal disease on dialysis therapy at the Nephrology Institute of Mogi das Cruzes, São Paulo State, Brazil. A retrospective medical history of 189 patients was reviewed to investigate the occurrence of convulsive seizures during dialytic program. Seven patients with history of seizures were selected but five of them were included in our study. Three patients presented generalized tonic-clonic seizures, one had partial seizure with secondary generalization, and one presented unclassified seizure. Three patients presented seizure just during the dialysis (unique seizure) and one of them presented convulsive status epilepticus. The two other patients had already presented seizures prior the beginning of dialysis. We conclude that seizures in renal failure could be considered as occasional events that do not usually become chronic.

Convulsões durante o tratamento dialítico podem constituir uma complicação da hemodiálise. Esse artigo descreve a ocorrência de crises em pacientes em estágio final de insuficiência renal crônica sob tratamento dialítico no Instituto de Nefrologia de Mogi das Cruzes, São Paulo, Brasil. Foram revistos os prontuários de 189 pacientes, com o objetivo de investigar a ocorrência de crises convulsivas durante o tratamento dialítico. Dos sete pacientes selecionados com história de crises, cinco concordaram em participar de nosso estudo. Três pacientes apresentaram crises generalizadas tônico-clônicas, um apresentou crise parcial com generalização subseqüente e um apresentou crise inclassificada. Três pacientes apresentaram crises apenas durante o processo dialítico (crise única) sendo que um deles apresentou status epilepticus convulsivo. Os outros dois pacientes já haviam apresentado crises antes do início do tratamento dialítico. Nós concluímos que as crises convulsivas que ocorrem em pacientes com falência renal podem ser consideradas como eventos ocasionais e que usualmente não se tornam crônicas.

Expression of nestin in the hippocampal formation of rats submitted to the pilocarpine model of epilepsy.

Nestin is an embryonic intermediate filament component protein, transiently expressed by the immediate precursor cells of neurons and glia, during brain development. We studied the nestin distribution in the hippocampal formation of rats submitted to pilocarpine model of epilepsy. Animals were studied during the acute, silent and chronic phases. Rats from control and acute groups presented absence of nestin-immunoreactivity (IR) in the hippocampal cells. In contrast, cells from this region presented strong nestin IR during the silent phase (3 and 7 days after status epilepticus (SE) onset), disappearing 14 days after SE. Nestin IR cells were scattered expressed in all hippocampal formation during the chronic phase. Almost all nestin IR cells exhibited glial fibrillary acidic protein (GFAP), which seems to revert to a more primitive glial form, as part of an adaptive response, transiently re-expressing phenotypic features typical of earlier stages of glial development. The re-expression of this developmental protein in the damaged cerebral tissue suggests that nestin may play an important role in the reconstruction of the glial cytoskeleton and/or remodeling events occurring in the pilocarpine model of epilepsy. Understanding how astrocytes influence network function in the injured hippocampus may, therefore, provide insight into epileptogenic mechanisms.

Expression of apoptosis inhibitor protein Mcl1 linked to neuroprotection in CNS neurons.

Mcl1 is a Bcl2-related antiapoptotic protein originally isolated from human myeloid leukemia cells. Unlike Bcl2, expression has not been reported in CNS neurons. We isolated Mcl1 in a direct screen for candidate modifier genes of neuronal vulnerability by differential display of mRNAs upregulated following prolonged seizures in two mouse strains with contrasting levels of hippocampal cell death. Mcl1 is widely expressed in neurons, and transcription is rapidly induced in both strains. In resistant C57Bl/6J mice, Mcl1 protein levels remain persistently elevated in hippocampal pyramidal neurons after seizures, but fall rapidly in C3H/HeJ hippocampus, coinciding with extensive neuronal apoptosis. DNA damage and caspase-mediated cell death were strikingly increased in Mcl1-deficient mice when compared to +/+ littermates after similar seizures. We identify Mcl1 as a neuronal gene responsive to excitotoxic insult in the brain, and link relative levels of Mcl1 expression to inherited differences in neuronal thresholds for apoptosis.

Succinate increases neuronal post-synaptic excitatory potentials in vitro and induces convulsive behavior through N-methyl-d-aspartate-mediated mechanisms.

Succinate is a dicarboxylic acid that accumulates due to succinate dehydrogenase inhibition by malonate and methylmalonate exposure. These neurotoxins cause increased excitability and excitotoxic damage, which can be prevented by administering high amounts of succinate. In the present study we investigated whether succinate alters hippocampal field excitatory post-synaptic potentials. Bath application of succinate at intermediate concentrations (0.3-1 mM) increased the slope of field excitatory post-synaptic potentials in hippocampal slices, and at high concentrations (above 1 mM) did not alter or decrease field excitatory post-synaptic potentials slope. Succinate-induced enhancement of field excitatory post-synaptic potentials slope was abolished by the addition of d-2-amino-5-phosphonovaleric acid (50 microM) to the perfusate, supporting the involvement of N-methyl-d-aspartate receptors in the excitatory effect of this organic acid. Accordingly, succinate (0.8-7.5 micromol) i.c.v. administration caused dose-dependent convulsive behavior in mice. The i.c.v. co-administration of MK-801 (7 nmol) fully prevented succinate-induced convulsions, further suggesting the involvement of N-methyl-d-aspartate receptors in the convulsant action of succinate. Our data indicate that accumulation of moderate amounts of succinate may contribute to the excitotoxicity induced by succinate dehydrogenase inhibitors, through the activation of N-methyl-d-aspartate receptors.