Epileptogenesis in the parahippocampal region. Parallels with the dentate gyrus

Extent of parahippocampal ablation is associated with seizure freedom after laser amygdalohippocampotomy

OBJECTIVE

The authors aimed to examine the relationship between mesial temporal subregion ablation volume and seizure outcome in a diverse cohort of patients who underwent stereotactic laser amygdalohippocampotomy (SLAH) for mesial temporal lobe epilepsy (MTLE).

METHODS

Seizure outcomes and pre- and postoperative images were retrospectively reviewed in patients with MTLE who underwent SLAH at a single institution. Mesial temporal subregions and the contrast-enhancing ablation volume were manually segmented. Pre- and postoperative MR images were coregistered to assess anatomical ablation. Postoperative MRI and ablation volumes were also spatially normalized, enabling the assessment of seizure outcome with heat maps.

RESULTS

Twenty-eight patients with MTLE underwent SLAH, 15 of whom had mesial temporal sclerosis (MTS). The rate of Engel class I outcome at 1 year after SLAH was 39% overall: 47% in patients with MTS and 31% in patients without MTS. The percentage of parahippocampal gyrus (PHG) ablated was higher in patients with an Engel class I outcome (40% vs 25%, p = 0.04). Subregion analysis revealed that extent of ablation in the parahippocampal cortex (35% vs 19%, p = 0.03) and angular bundle (64% vs 43%, p = 0.02) was positively associated with Engel class I outcome. The degree of amygdalohippocampal complex (AHC) ablated was not associated with seizure outcome (p = 0.30).

CONCLUSIONS

Although the AHC was the described target of SLAH, seizure outcome in this cohort was associated with degree of ablation for the PHG, not the AHC. Complete coverage of both the AHC and PHG is technically challenging, and more work is needed to optimize seizure outcome after SLAH.

HOP protein expression in the hippocampal dentate gyrus is acutely downregulated in a status epilepticus mouse model

Status epilepticus (SE) is a neurological emergency, and delayed management can lead to higher morbidity and mortality. It is thought that prolonged seizures stimulate stem cells in the hippocampus and that epileptogenesis may arise from aberrant connections formed by newly born cells, while others have suggested that the acute neuroinflammation and gliosis often seen in epileptic hippocampi contribute to hyperexcitability and epilepsy development. Previous studies have identified the expression of homeodomain-only protein (HOP) in the hippocampal dentate gyrus (HDG) and the heart. HOP was found to be a regulator of cell proliferation and differentiation during heart development, while it maintains the 'heart conduction system' in adulthood. However, little is known about HOP function in the adult HDG, particularly in the SE setting. Here, a HOP immunohistochemical profile in an SE mouse model was established. A total of 24 adult mice were analyzed 3-10 days following the SE episode, the 'acute phase'. Our findings demonstrate a significant downregulation of HOP and BLBP protein expression in the SE group following SE episodes, while HOP/Ki67 coexpression did not remarkably differ. Furthermore, coexpression of HOP/S100β and HOP/Prox1 was not observed, although we noticed insignificant HOP/DCX coexpression level. The findings of this study show no compelling evidence of proliferation, and newly added neurons were not identified during the acute phase following SE, although HOP protein expression was significantly decreased in the HDG. Similar to its counterpart in the adult heart, this suggests that HOP seems to play a key role in regulating signal conduction in adult hippocampus. Moreover, acute changes in HOP expression following SE could be part of an inflammatory response that could subsequently influence epileptogenicity.

Disruption of the sodium-dependent citrate transporter SLC13A5 in mice causes alterations in brain citrate levels and neuronal network excitability in the hippocampus

In addition to tissues such as liver, the plasma membrane sodium-dependent citrate transporter, NaCT (SLC13A5), is highly expressed in brain neurons, but its function is not understood. Loss-of-function mutations in the human SLC13A5 gene have been associated with severe neonatal encephalopathy and pharmacoresistant seizures. The molecular mechanisms of these neurological alterations are not clear. We performed a detailed examination of a Slc13a5 deletion mouse model including video-EEG monitoring, behavioral tests, and electrophysiologic, proteomic, and metabolomic analyses of brain and cerebrospinal fluid. The experiments revealed an increased propensity for epileptic seizures, proepileptogenic neuronal excitability changes in the hippocampus, and significant citrate alterations in the CSF and brain tissue of Slc13a5 deficient mice, which may underlie the neurological abnormalities. These data demonstrate that SLC13A5 is involved in brain citrate regulation and suggest that abnormalities in this regulation can induce seizures. The present study is the first to (i) establish the Slc13a5-knockout mouse model as a helpful tool to study the neuronal functions of NaCT and characterize the molecular mechanisms by which functional deficiency of this citrate transporter causes epilepsy and impairs neuronal function; (ii) evaluate all hypotheses that have previously been suggested on theoretical grounds to explain the neurological phenotype of SLC13A5 mutations; and (iii) indicate that alterations in brain citrate levels result in neuronal network excitability and increased seizure propensity.

Blockade of 67-kDa Laminin Receptor Facilitates AQP4 Down-Regulation and BBB Disruption via ERK1/2-and p38 MAPK-Mediated PI3K/AKT Activations

Recently, we have reported that dysfunctions of 67-kDa laminin receptor (67LR) induced by status epilepticus (SE, a prolonged seizure activity) and 67LR neutralization are involved in vasogenic edema formation, accompanied by the reduced aquaporin 4 (AQP4, an astroglial specific water channel) expression in the rat piriform cortex (PC). In the present study, we found that the blockade of 67LR activated p38 mitogen-activated protein kinase (p38 MAPK) and extracellular signal-regulated kinase 1/2 (ERK1/2) signaling pathways, which enhanced phosphatidylinositol 3 kinase (PI3K)/AKT phosphorylations in endothelial cells and astrocytes, respectively. 67LR-p38 MAPK-PI3K-AKT activation in endothelial cells increased vascular permeability. In contrast, 67LR-ERK1/2-PI3K-AKT signaling pathways in astrocytes regulated astroglial viability and AQP4 expression. These findings indicate that PI3K/AKT may integrate p38 MAPK and ERK1/2 signaling pathways to regulate AQP4 expression when 67LR functionality is reduced. Thus, we suggest that 67LR-p38 MAPK/ERK1/2-PI3K-AKT-AQP4 signaling cascades may mediate serum extravasation and AQP4 expression in astroglio-vascular systems, which is one of the considerable therapeutic targets for vasogenic edema in various neurological diseases.

CDDO-Me Selectively Attenuates CA1 Neuronal Death Induced by Status Epilepticus via Facilitating Mitochondrial Fission Independent of LONP1

2-Cyano-3,12-dioxo-oleana-1,9(11)-dien-28-oic acid methyl ester (CDDO-Me) is a triterpenoid analogue of oleanolic acid that exhibits promising anti-cancer, anti-inflammatory, antioxidant and neuroprotective activities. In addition, CDDO-Me affects cellular differentiation and cell cycle arrest, and irreversibly inhibits Lon protease-1 (LONP1). In the present study, we evaluate the effects of CDDO-Me on mitochondrial dynamics and its downstream effectors in order to understand the underlying mechanism of the neuronal death following status epilepticus (SE, a prolonged seizure activity). CDDO-Me increased dynamin-related proteins 1 (DRP1)-serine 616 phosphorylation via activating extracellular-signal-regulated kinase 1/2 (ERK1/2) and c-Jun N-terminal kinase (JNK), but not protein kinase A (PKA) or protein phosphatases (PPs). In addition, CDDO-Me facilitated DRP1-mediated mitochondrial fissions, which selectively attenuated SE-induced CA1 neuronal death. Unlike CDDO-Me, LONP1 knockdown led to SE-induced massive degeneration of dentate granule cells, CA1 neurons and hilus interneurons without altering the expression and phosphorylation of DRP1, ERK1/2, JNK and PP2B. LONP1 knockdown could not inhibit SE-induced mitochondrial elongation in CA1 neurons. Co-treatment of CDDO-Me with LONP1 siRNA ameliorated only CA1 neuronal death, concomitant with abrogation of mitochondrial elongation induced by SE. Thus, our findings suggest that CDDO-Me may selectively attenuate SE-induced CA1 neuronal death by rescuing the abnormal mitochondrial machinery, independent of LONP1 activity.

Protein biomarkers of epileptogenicity after traumatic brain injury

Traumatic brain injury (TBI) is a major risk factor for acquired epilepsy. Post-traumatic epilepsy (PTE) develops over time in up to 50% of patients with severe TBI. PTE is mostly unresponsive to traditional anti-seizure treatments suggesting distinct, injury-induced pathomechanisms in the development of this condition. Moderate and severe TBIs cause significant tissue damage, bleeding, neuron and glia death, as well as axonal, vascular, and metabolic abnormalities. These changes trigger a complex biological response aimed at curtailing the physical damage and restoring homeostasis and functionality. Although a positive correlation exists between the type and severity of TBI and PTE, there is only an incomplete understanding of the time-dependent sequelae of TBI pathobiologies and their role in epileptogenesis. Determining the temporal profile of protein biomarkers in the blood (serum or plasma) and cerebrospinal fluid (CSF) can help to identify pathobiologies underlying the development of PTE, high-risk individuals, and disease modifying therapies. Here we review the pathobiological sequelae of TBI in the context of blood- and CSF-based protein biomarkers, their potential role in epileptogenesis, and discuss future directions aimed at improving the diagnosis and treatment of PTE.

Interactions Between Epilepsy and Plasticity

Undoubtedly, one of the most interesting topics in the field of neuroscience is the ability of the central nervous system to respond to different stimuli (normal or pathological) by modifying its structure and function, either transiently or permanently, by generating neural cells and new connections in a process known as neuroplasticity. According to the large amount of evidence reported in the literature, many stimuli, such as environmental pressures, changes in the internal dynamic steady state of the organism and even injuries or illnesses (e.g., epilepsy) may induce neuroplasticity. Epilepsy and neuroplasticity seem to be closely related, as the two processes could positively affect one another. Thus, in this review, we analysed some neuroplastic changes triggered in the hippocampus in response to seizure-induced neuronal damage and how these changes could lead to the establishment of temporal lobe epilepsy, the most common type of focal human epilepsy.

Commonalities in epileptogenic processes from different acute brain insults: Do they translate?

The most common forms of acquired epilepsies arise following acute brain insults such as traumatic brain injury, stroke, or central nervous system infections. Treatment is effective for only 60%-70% of patients and remains symptomatic despite decades of effort to develop epilepsy prevention therapies. Recent preclinical efforts are focused on likely primary drivers of epileptogenesis, namely inflammation, neuron loss, plasticity, and circuit reorganization. This review suggests a path to identify neuronal and molecular targets for clinical testing of specific hypotheses about epileptogenesis and its prevention or modification. Acquired human epilepsies with different etiologies share some features with animal models. We identify these commonalities and discuss their relevance to the development of successful epilepsy prevention or disease modification strategies. Risk factors for developing epilepsy that appear common to multiple acute injury etiologies include intracranial bleeding, disruption of the blood-brain barrier, more severe injury, and early seizures within 1 week of injury. In diverse human epilepsies and animal models, seizures appear to propagate within a limbic or thalamocortical/corticocortical network. Common histopathologic features of epilepsy of diverse and mostly focal origin are microglial activation and astrogliosis, heterotopic neurons in the white matter, loss of neurons, and the presence of inflammatory cellular infiltrates. Astrocytes exhibit smaller K+ conductances and lose gap junction coupling in many animal models as well as in sclerotic hippocampi from temporal lobe epilepsy patients. There is increasing evidence that epilepsy can be prevented or aborted in preclinical animal models of acquired epilepsy by interfering with processes that appear common to multiple acute injury etiologies, for example, in post-status epilepticus models of focal epilepsy by transient treatment with a trkB/PLCγ1 inhibitor, isoflurane, or HMGB1 antibodies and by topical administration of adenosine, in the cortical fluid percussion injury model by focal cooling, and in the albumin posttraumatic epilepsy model by losartan. Preclinical studies further highlight the roles of mTOR1 pathways, JAK-STAT3, IL-1R/TLR4 signaling, and other inflammatory pathways in the genesis or modulation of epilepsy after brain injury. The wealth of commonalities, diversity of molecular targets identified preclinically, and likely multidimensional nature of epileptogenesis argue for a combinatorial strategy in prevention therapy. Going forward, the identification of impending epilepsy biomarkers to allow better patient selection, together with better alignment with multisite preclinical trials in animal models, should guide the clinical testing of new hypotheses for epileptogenesis and its prevention.

Effect of fasudil on cognitive function following status convulsion in rats

Fasudil has been demonstrated to possess a protective effect in neural injury; however, its protective effect on convulsive brain injury remains to be assessed. The aim of the present study was to investigate the latent mechanism and effect of fasudil on cognitive function following status convulsion (SC) in rats. Initially, to determine the effects of SC, the expression levels of Ras homolog gene family, member A (RhoA)/Rho-associated protein kinase (ROCK) signaling pathway-associated proteins were measured by western blot analysis in 16 rats. To investigate the effects of fasudil on cognitive function in SC rats, a further 40 rats were assigned to four groups: Group I (healthy untreated rats), group II (healthy rats treated with fasudil), group III (SC rats) and group IV (SC rats treated with fasudil). An object-in-place memory task and the Morris Water Maze test were subsequently performed. Histopathological alterations in brain tissue and SC latency were additionally analyzed. Following SC, protein expression levels of myelin-associated glycoprotein, myelin oligodendrocyte glycoprotein and leucine rich repeat and immunoglobulin-like domain-containing protein 1 were significantly increased (P<0.05) and levels of neurite outgrowth inhibitor protein A were significantly decreased (P<0.01). SC had no effect on RhoA level (P=0.921); however, it significantly increased the levels of phosphorylated RhoA (P<0.01). Cognitive function was significantly decreased following SC and significantly increased following fasudil intervention. Fasudil intervention improved CA1 structure, which was lost following SC. SC severely impaired cognitive function and affected the expression of neurite growth inhibitory factors. Fasudil treatment improved cognitive function and central nervous system (CNS) injury, and decreased SC susceptibility in rats. Fasudil and SC may regulate the CNS by affecting the expression of neurite growth inhibitory factors in the RhoA/ROCK signaling pathway.

The Contradictory Effects of Neuronal Hyperexcitation on Adult Hippocampal Neurogenesis

Adult hippocampal neurogenesis is a highly plastic process that responds swiftly to neuronal activity. Adult hippocampal neurogenesis can be regulated at the level of neural stem cell recruitment and activation, progenitor proliferation, as well as newborn cell survival and differentiation. An "excitation-neurogenesis" rule was proposed after the demonstration of the capability of cultured neural stem and progenitor cells to intrinsically sense neuronal excitatory activity. In vivo, this property has remained elusive although recently the direct response of neural stem cells to GABA in the hippocampus via GABAA receptors has evidenced a mechanism for a direct talk between neurons and neural stem cells. As it is pro-neurogenic, the effect of excitatory neuronal activity has been generally considered beneficial. But what happens in situations of neuronal hyperactivity in which neurogenesis can be dramatically boosted? In animal models, electroconvulsive shock markedly increases neurogenesis. On the contrary, in epilepsy rodent models, seizures induce the generation of misplaced neurons with abnormal morphological and electrophysiological properties, namely aberrant neurogenesis. We will herein discuss what is known about the mechanisms of influence of neurons on neural stem cells, as well as the severe effects of neuronal hyperexcitation on hippocampal neurogenesis.

Epileptogenic networks and drug-resistant epilepsy: Present and future perspectives of epilepsy research-Utility for the epileptologist and the epilepsy surgeon

A multidisciplinary approach is required to understand the complex intricacies of drug-resistant epilepsy (DRE). A challenge that neurosurgeons across the world face is accurate localization of epileptogenic zone. A significant number of patients who have undergone resective brain surgery for epilepsy still continue to have seizures. The reason behind this therapy resistance still eludes us. Thus to develop a cure for the difficult to treat epilepsy, we need to comprehensively study epileptogenesis. Till date, most of the studies on DRE is focused on undermining the abnormal functioning of receptors involved in synaptic transmission and reduced levels of antiepileptic drugs around there targets. But recent advances in imaging and electrophysiological techniques have suggested the role epileptogenic networks in the process of epileptogenesis. According to this hypothesis, the local neurons recruit distant neurons through complex oscillatory circuits, which further recruit more distant neurons, thereby generating a hypersynchronus neuronal activity. The epileptogenic networks may be confined to the lesion or could propagate to distant focus. The success of surgery depends on the precision by which the epileptogenic network is determined while planning a surgical intervention. Here, we summarize various modalities of electrophysiological and imaging techniques to determine the functionally active epileptogenic networks. We also review evidence pertaining to the proposed role of epileptogenic network in abnormal synaptic transmission which is one of the major causes of epileptiform activity. Elucidation of current concepts in regulation of synaptic transmission by networks will help develop therapies for epilepsy cases that cannot be managed pharmacologically.

Anticonvulsant activity of bone marrow cells in electroconvulsive seizures in mice

Background

Bone marrow is an accessible source of progenitor cells, which have been investigated as treatment for neurological diseases in a number of clinical trials. Here we evaluated the potential benefit of bone marrow cells in protecting against convulsive seizures induced by maximum electroconvulsive shock (MES), a widely used model for screening of anti-epileptic drugs. Behavioral and inflammatory responses were measured after MES induction in order to verify the effects promoted by transplantation of bone marrow cells. To assess the anticonvulsant effects of bone marrow cell transplantation, we measured the frequency and duration of tonic seizure, the mortality rate, the microglial expression and the blood levels of cytokine IL-1, IL-6, IL-10 and TNF-α after MES induction. We hypothesized that these behavioral and inflammatory responses to a strong stimulus such as a convulsive seizure could be modified by the transplantation of bone marrow cells.

Results

Bone marrow transplanted cells altered the convulsive threshold and showed anticonvulsant effect by protecting from tonic seizures. Bone marrow cells modified the microglial expression in the analyzed brain areas, increased the IL-10 and attenuate IL-6 levels.

Conclusions

Bone marrow cells exert protective effects by blocking the course of electroconvulsive seizures. Additionally, electroconvulsive seizures induced acute inflammatory responses by altering the pattern of microglia expression, as well as in IL-6 and IL-10 levels. Our findings also indicated that the anticonvulsant effects of these cells can be tested with the MES model following the same paradigm used for drug testing in pharmacological screening. Studies on the inflammatory reaction in response to acute seizures in the presence of transplanted bone marrow cells might open a wide range of discussions on the mechanisms relevant to the pathophysiology of epilepsies.

Seizure control by ketogenic diet-associated medium chain fatty acids

The medium chain triglyceride (MCT) ketogenic diet is used extensively for treating refractory childhood epilepsy. This diet increases the plasma levels of medium straight chain fatty acids. A role for these and related fatty acids in seizure control has not been established. We compared the potency of an established epilepsy treatment, Valproate (VPA), with a range of MCT diet-associated fatty acids (and related branched compounds), using in vitro seizure and in vivo epilepsy models, and assessed side effect potential in vitro for one aspect of teratogenicity, for liver toxicology and in vivo for sedation, and for a neuroprotective effect. We identify specific medium chain fatty acids (both prescribed in the MCT diet, and related compounds branched on the fourth carbon) that provide significantly enhanced in vitro seizure control compared to VPA. The activity of these compounds on seizure control is independent of histone deacetylase inhibitory activity (associated with the teratogenicity of VPA), and does not correlate with liver cell toxicity. In vivo, these compounds were more potent in epilepsy control (perforant pathway stimulation induced status epilepticus), showed less sedation and enhanced neuroprotection compared to VPA. Our data therefore implicates medium chain fatty acids in the mechanism of the MCT ketogenic diet, and highlights a related new family of compounds that are more potent than VPA in seizure control with a reduced potential for side effects.

This article is part of the Special Issue entitled ‘New Targets and Approaches to the Treatment of Epilepsy’.

Alzheimer's disease and epilepsy: insight from animal models

Alzheimer's disease (AD) and epilepsy are separated in the medical community, but seizures occur in some patients with AD, and AD is a risk factor for epilepsy. Furthermore, memory impairment is common in patients with epilepsy. The relationship between AD and epilepsy remains an important question because ideas for therapeutic approaches could be shared between AD and epilepsy research laboratories if AD and epilepsy were related. Here we focus on one of the many types of epilepsy, temporal lobe epilepsy (TLE), because patients with TLE often exhibit memory impairment, depression and other comorbidities that occur in AD. Moreover, the seizures that occur in patients with AD may be nonconvulsive, which occur in patients with TLE. Here we first compare neuropathology in TLE and AD with an emphasis on the hippocampus, which is central to both AD and TLE research. Then we compare animal models of AD pathology with animal models of TLE. Although many aspects of the comparisons are still controversial, there is one conclusion that we suggest is clear: some animal models of TLE could be used to help address questions in AD research, and some animal models of AD pathology are bona fide animal models of epilepsy.

A selective role for ARMS/Kidins220 scaffold protein in spatial memory and trophic support of entorhinal and frontal cortical neurons

Progressive cortical pathology is common to several neurodegenerative and psychiatric disorders. The entorhinal cortex (EC) and frontal cortex (FC) are particularly vulnerable, and neurotrophins have been implicated because they appear to be protective. A downstream signal transducer of neurotrophins, the ankyrin repeat-rich membrane spanning scaffold protein/Kidins 220 (ARMS) is expressed in the cortex, where it could play an important role in trophic support. To test this hypothesis, we evaluated mice with a heterozygous deletion of ARMS (ARMS(+/-) mice). Remarkably, the EC and FC were the regions that demonstrated the greatest defects. Many EC and FC neurons became pyknotic in ARMS(+/-) mice, so that large areas of the EC and FC were affected by 12 months of age. Areas with pyknosis in the EC and FC of ARMS(+/-) mice were also characterized by a loss of immunoreactivity to a neuronal antigen, NeuN, which has been reported after insult or injury to cortical neurons. Electron microscopy showed that there were defects in mitochondria, myelination, and multilamellar bodies in the EC and FC of ARMS(+/-) mice. Although primarily restricted to the EC and FC, pathology appeared to be sufficient to cause functional impairments, because ARMS(+/-) mice performed worse than wild-type on the Morris water maze. Comparisons of males and females showed that female mice were the affected sex in all comparisons. Taken together, the results suggest that the expression of a prominent neurotrophin receptor substrate normally protects the EC and FC, and that ARMS may be particularly important in females.

Glial cell activation in response to electroconvulsive seizures

Electroconvulsive therapy (ECT) is a very efficient treatment for severe depression. However, cognitive side effects have raised concern to whether ECT can cause cellular damage in vulnerable brain regions. A few recent animal studies have reported limited hippocampal cell loss, while a number of other studies have failed to find any signs of cellular damage and some even report that electroconvulsive seizures (ECS; the animal counterpart of ECT) has neuroprotective effects. We previously have described gliogenesis in response to ECS. Loss of glial cells is seen in depression and de novo formation of glial cells may thus have an important therapeutic role. Glial cell proliferation and activation is however also seen in response to neuronal damage. The aim of the present study was to further characterize glial cell activation in response to ECS. Two groups of rats were treated with 10 ECS using different sets of stimulus parameters. ECS-induced changes in the morphology and expression of markers typical for reactive microglia, astrocytes and NG2+ glial cells were analyzed immunohistochemically in prefrontal cortex, hippocampus, amygdala, hypothalamus, piriform cortex and entorhinal cortex. We observed changes in glial cell morphology and an enhanced expression of activation markers 2 h following ECS treatment, regardless of the stimulus parameters used. Four weeks later, few activated glial cells persisted. In conclusion, ECS treatment induced transient glial cell activation in several brain areas. Whether similar processes play a role in the therapeutic effect of clinically administered ECT or contribute to its side effects will require further investigations.

Metabolic changes in temporal lobe structures measured by HR-MAS NMR at early stage of electrogenic rat epilepsy

The purpose of this study was to determine cerebral metabolic profile changes in response to electric stimulation to the right dorsal hippocampus (HPC) for the establishment of an epileptic rat model. Electroencephalogram measurements and behavioral results indicated that the experimental rats were in an early stage of epilepsy. Metabolites were determined by high-resolution magic-angle-spinning nuclear magnetic resonance (HR-MAS NMR) spectroscopy of the following intact brain tissue: bilateral hippocampi, entorhinal cortices (ECs), and temporal lobes (TLs). The NMR data was statistically analyzed using principal component analysis (PCA). Results demonstrated that metabolic profiles were significantly different between the experimental and sham rats in the bilateral hippocampi and the ipsilateral EC. Significant increases in total creatine in the ipsilateral HPC and alanine in the ipsilateral TL were measured (p<0.05). Some metabolite levels were disturbed in the bilateral HPC-EC loops. In the sham group, glutamate and choline concentrations were significantly higher or lower in the ipsilateral EC than bilateral hippocampi, respectively (p<0.01). However, such differences were not observed in the experimental group. In addition, N-acetylaspartate levels in the experimental group were significantly less in the ipsilateral HPC than in bilateral ECs (p<0.05). The level of myo-inositol in the ipsilateral EC significantly increased in the experimental group, compared to the contralateral EC (p<0.05). These results may provide metabolic information about temporal lobe structures to provide more knowledge about epileptic abnormalities at the early stage.

A substance in broad beans (Vicia faba) is protective against experimentally induced convulsions in mice

Vicia faba (VF, broad beans) constitutes a major food item for the River Nile populations. Contrary to tropical Africa, the prevalence rate of epilepsy (0.9-1 per 1000) among schoolchildren of Khartoum Province, Sudan, is lower compared with the rates in Europe and North America. To explore whether broad beans contain any anticonvulsant that can explain this observation, Balb/c mice were either treated with VF extract (0.01 mL/g) or kept as a control. Various doses of strychnine and picrotoxin were used to explore the effect of VF extract on strychnine-sensitive glycine receptors and GABA(A) receptors. Diazepam (DIZ) was used as anticonvulsant. Thin-layer chromatography was run for the extract against phenobarbital, DIZ, and/or glycine. VF extract demonstrated a clear protective effect against strychnine-induced convulsions and death in Balb/c mice. Diazepam (20 mg/kg, intraperitoneally), administered 20 minutes prior to strychnine (0.112 mg/kg, intraperitoneally), increased the survival rate to 66.7% and, when given with VF extract (0.01 mL/g), to 100%. Various doses of DIZ protected against picrotoxin-induced convulsions (40 mg/kg, intraperitoneally) and deaths. Pretreatment of mice with VF extract was not protective. On chromatography, VF extract separated in a manner similar to the glycine spot, and revealed one peak coinciding with, but not identical to that of glycine. The extract of broad beans (VF) protects against convulsions probably through the inhibitory glycine receptors, and may contain a substance that is intimately related to glycine. Further research is needed to substantiate this by directly assessing the binding of the VF extract to the glycine receptors or a change in receptor physiology.

Cell-type specific modulation of intrinsic firing properties and subthreshold membrane oscillations by the M(Kv7)-current in neurons of the entorhinal cortex

The M-current (current through Kv7 channels) is a low-threshold noninactivating potassium current that is suppressed by muscarinic agonists. Recent studies have shown its role in spike burst generation and intrinsic subthreshold theta resonance, both of which are important for memory function. However, little is known about its role in principal cells of the entorhinal cortex (EC). In this study, using whole cell patch recording techniques in a rat EC slice preparation, we have examined the effects of the M-current blockers linopirdine and XE991 on the membrane dynamics of principal cells in the EC. When the M-current was blocked, layer II nonstellate cells (non-SCs) and layer III cells switched from tonic discharge to intermittent firing mode, during which layer II non-SCs showed high-frequency short-duration spike bursts due to increased fast spike afterdepolarization (ADP). When three spikes were elicited at 50 Hz, these two types of cells reacted with a slow ADP that drove delayed firing. In contrast, layer II stellate cells (SCs) and layer V cells never displayed intermittent firing, bursting behavior, or delayed firing. Under the M-current block, intrinsic excitability increased significantly in layer III and layer V cells but not in layer II SCs and non-SCs. The M-current block also had contrasting effects on the subthreshold excitability, greatly suppressing the subthreshold membrane potential oscillations in layer V cells but not in layer II SCs. Modulation of the M-current thus shifts the firing behavior, intrinsic excitability, and subthreshold membrane potential oscillations of EC principal cells in a cell-type-dependent manner.

Opioid receptor binding in parahippocampus of patients with temporal lobe epilepsy: its association with the antiepileptic effects of subacute electrical stimulation

Opioid receptor binding was evaluated in parahippocampal cortex (PHC) obtained from patients with intractable mesial temporal lobe epilepsy (MTLE) with and without subacute high frequency electrical stimulation (HFS) in this brain area. Mu, delta and nociceptin receptor binding was determined by autoradiography in PHC of five patients (ESAE group) with MTLE history of 14.8 +/- 2.5 years and seizure frequency of 11 +/- 2.9 per month, two of them (40%) with mesial sclerosis. This group demonstrated antiepileptic effects following subacute HFS (130 Hz, 450 micros, 200-400 microA), applied continuously during 16-20 days in PHC. Values were compared with those obtained from patients with severe MTLE (history of 21.7 +/- 2.8 years and seizure frequency of 28.2 +/- 14 per month) in whom electrical stimulation did not induce antiepileptic effects (ESWAE group, n = 4), patients with MTLE in whom no electrical stimulation was applied (MTLE group, n = 4) and autopsy material acquired from subjects without epilepsy (n = 4 obtained from three subjects). Enhanced 3H-DAMGO (MTLE, 755%; ESAE, 375%; ESWAE, 693%), 3H-DPDPE (MTLE, 242%; ESAE, 80%; ESWAE, 346%) and 3H-nociceptin (MTLE, 424%; ESAE, 217%; ESWAE, 451%) binding was detected in the PHC of all epileptic groups. However, tissue obtained from ESAE group demonstrated lower opioid receptor binding (3H-DAMGO, 44.5%, p < 0.05; 3H-DPDPE, 47%, p < 0.05; 3H-nociceptin, 39.3%, p < 0.5) when compared with MTLE group. The present results indicate that a high effectiveness to the antiepileptic effects induced by HFS is associated with reduced opioid peptide binding.

Status epilepticus-induced somatostatinergic hilar interneuron degeneration is regulated by striatal enriched protein tyrosine phosphatase

Excitotoxic cell death is one of the precipitating events in the development of temporal lobe epilepsy. Of particular prominence is the loss of GABAergic hilar neurons. Although the molecular mechanisms responsible for the selective vulnerability of these cells are not well understood, activation of the extracellular signal-regulated kinase/mitogen-activated protein kinase (ERK/MAPK) pathway has been implicated in neuroprotective responses to excitotoxicity in other neuronal populations. Here, we report that high levels of the striatal-enriched protein tyrosine phosphatase (STEP), a key regulator of ERK/MAPK signaling, are found in vulnerable somatostatin-immunoreactive hilar interneurons. Under both control conditions and after pilocarpine-induced status epilepticus (SE), ERK/MAPK activation was repressed in STEP-immunoreactive hilar neurons. This contrasts with robust SE-induced ERK/MAPK activation in the granule cell layer of the dentate gyrus, a cell region that does not express STEP. During pilocarpine-induced SE, in vivo disruption of STEP activity allowed activation of the MAPK pathway, leading to immediate-early gene expression and significant rescue from cell death. Thus, STEP increases the sensitivity of neurons to SE-induced excitotoxicity by specifically blocking a latent neuroprotective response initiated by the MAPK pathway. These findings identify a key set of signaling events that render somatostatinergic hilar interneurons vulnerable to SE-induced cell death.

Computer simulation of epilepsy: implications for seizure spread and behavioral dysfunction

Hippocampal area CA3 has been one of the most intensively studied brain regions for computer models of epileptiform activity. As physiological studies begin to extend outward to other hippocampal and parahippocampal areas, we must extend these models to understand more complex circuitry containing diverse elements. Study of subiculum is of particular interest in this context, as it is a structure of intermediate complexity, with an inchoate columnar and laminar organization. In addition to helping us understand seizures, modeling of these structures will also help us understand the genesis of physiological activity patterns that are below threshold for seizure generation. Such modeling can also serve as a basis for speculation regarding the nonictal behavioral consequences of epilepsy.

Quantitative Neuropathology of the Entorhinal Cortex Region in Patients with Hippocampal Sclerosis and Temporal Lobe Epilepsy

PURPOSE

Clinical, radiologic, and experimental evidence indicates that the entorhinal cortex (EC) region may be linked to the pathophysiology of hippocampal sclerosis (HS) in patients with temporal lobe epilepsy. Few neuropathologic studies of this region have been undertaken in patients with HS undergoing surgery, some suggesting preferential loss of layer III neurones.

METHODS

We carried out a quantitative analysis in 26 patients with HS, nine patients with lesional temporal lobe epilepsy (LTLE), and eight postmortem controls. We measured neuronal densities in EC by using a three-dimensional cell-counting technique on NeuN immunostained and Nissl-stained sections. We also quantified the density of calretinin-positive interneurones in this region and the density of neurones in adjacent subiculum and CA1 subfields. We also assessed the patterns of gliosis in the EC in the patient groups and the presence of any neocortical neurone loss.

RESULTS

No significant difference was found in the mean neuronal densities in the EC region between HS and LTLE groups or postmortem controls. Laminar gliosis in midcortical layers was seen in a proportion of HS cases but also in the LTLE group. No significant difference was seen in the density of calretinin interneurones and no correlation between the presence of neocortical neuronal loss and EC neuronal densities.

CONCLUSIONS

A stereotypical pattern of neuronal loss and gliosis in the EC region in patients with HS is not confirmed that distinguishes this pathologic process from that in patients with lesional TLE.

Evaluation of GABA system and cell damage in parahippocampus of patients with temporal lobe epilepsy showing antiepileptic effects after subacute electrical stimulation

PURPOSE

The gamma-aminobutyric acid (GABA) system and neuronal loss were evaluated in the parahippocampal cortex (PHC) of patients with intractable mesial temporal lobe epilepsy (MTLE) who received subacute electrical stimulation and showed antiepileptic effects.

METHODS

GABA tissue content, GABA(A) and benzodiazepine (BZD) receptor levels, as well as neuronal density were determined in PHC of five patients (ESAE group) with an MTLE history of 14.8 +/- 2.5 years and seizure frequency of 11 +/- 2.9 per month, two (40%) of them with mesial sclerosis. This group demonstrated antiepileptic effects after subacute electrical stimulation (130 Hz, 450 micros, 200-400 microA), applied continuously during 16 to 20 days in PHC. Values were compared with those obtained from patients with severe MTLE (history of 21.7 +/- 2.8 years and seizure frequency of 28.2 +/- 14 per month) in whom electrical stimulation did not induce antiepileptic effects (ESWAE group, n = 4), patients with MTLE in whom no electrical stimulation was applied (MTLE group, n = 4), and autopsy material acquired from subjects without epilepsy (n = 4 obtained from three subjects).

RESULTS

The ESAE group demonstrated high GABA tissue levels (219%), as well as a significantly higher cell count (58.5%) when compared with the MTLE group. The ESWAE group showed enhanced BZD-receptor levels (38%), whereas their values for GABA tissue levels and GABA(A) receptor were similar to those obtained from the MTLE group.

CONCLUSIONS

It is suggested that subacute electrical stimulation of PHC is more effective in patients with less severe epilepsy, an effect associated with a high GABA tissue content and a low rate of cell loss.

Input and output stations of the entorhinal cortex: superficial vs. deep layers or lateral vs. medial divisions?

Based on the results of recent electrophysiological and anatomical studies, we argue that the classical division of the entorhinal cortex (EC) into a superficial layer input station and deep layer output station is no longer tenable. We point out that the anatomical data suggest that the medial and lateral divisions of EC are separate, and recent studies of the propagation of signals originating in the lateral olfactory tract and perirhinal cortex to the EC [J. Neurophysiol. 83 (2000) 1924-1931; Biella and de Curtis, 2000) indicate that the lateral division is the input station, and the medial division the output station for information processed in the hippocampus and subiculum.

Strychnine-sensitive glycine receptors depress hyperexcitability in rat dentate gyrus

Previously we have shown that strychnine-sensitive glycine-gated chloride channels (GlyRs) are functionally expressed by CA1 pyramidal cells and GABAergic interneurons in mature rat hippocampal slices. We now report that glycine application to dentate granule cells and hilar interneurons recorded in acute slices from adolescent rats elicits a strychnine-sensitive current similar to glycine-mediated currents recorded in area CA1, indicating that GlyRs are also present on neurons in the dentate gyrus. This finding suggests that GlyRs have a widespread distribution in the hippocampal region. The physiological role of GlyRs in forebrain is unclear, but it is possible that these receptors mediate neuronal inhibition, similar to gamma-aminobutyric acid-A (GABA(A)) receptors and thus could be a novel target for antiepileptic therapy. Therefore we tested the hypothesis that activation of inhibitory GlyRs could suppress neuronal hyperexcitability in dentate, a brain region vulnerable to epileptic activity. In whole-cell current-clamp recordings of granule cells, we observed a membrane potential hyperpolarization followed by cessation of the action potential firing pattern in hyperexcitable slices induced by elevated extracellular K(+) or by blocking GABA(A) receptors with bicuculline. The GlyR antagonist, strychnine, prevented the antiepileptic effect of glycine. These results demonstrate that glycine, acting at GlyRs, elicits neuronal inhibition in dentate. Further, our findings suggest the possibility that these receptors could be a therapeutic target for the treatment of epilepsy.

Quantitative analysis of benzodiazepine receptor in temporal lobe epilepsy: [(125)I]iomazenil autoradiographic study of surgically resected specimens

PURPOSE

To evaluate the changes of the inhibitory neurotransmitter receptor system related to epileptogenesis by measuring central benzodiazepine receptors (BZDRs) in surgically resected specimens of temporal lobe epilepsy by using [(125)I]iomazenil autoradiography.

METHODS

Surgically resected specimens were obtained from 66 temporal lobe epilepsy patients [51 with mesial temporal lobe epilepsy (MTLE) and 15 with non-MTLE] receiving no BZDs and seven MTLE patients receiving BZDs. BZDR densities in brain sections were measured by using [(125)I]iomazenil autoradiography. Cell densities were measured from cresyl violet-stained sections.

RESULTS

Compared with non-MTLE patients, non-BZD-treated MTLE patients showed remarkable reduction of BZDR density in the pyramidal cell region of cornu ammonis (CA) 1, CA3, and CA4, and a smaller but significant reduction in CA2 and the molecular and granule cell layers of dentate gyrus (mDG). In the MTLE group, the BZDR density in the mDG correlated with that in lateral cortex. Significant correlations between BZDR density and cell density were found in all hippocampal regions. A significant difference in BZDR density/cell-density ratio was observed in CA1 region between MTLE and non-MTLE. BZD-treated patients tended to have lower BZDR densities than did non-BZD-treated patients, although the differences did not reach significance. In all MTLE cases, [(123)I]iomazenil singlephoton emission computed tomography (SPECT) showed decreased BZDR binding in MTL.

CONCLUSIONS

In MTLE, BZDR densities decreased parallel to reduction in cell density in most hippocampal subfields, but BZDR density appeared to decrease in excess of neuron loss in CA1. [(125)I]iomazenil SPECT might be useful for detecting in vivo changes of BZDR density.

Intrinsic connectivity of the rat subiculum: II. Properties of synchronous spontaneous activity and a demonstration of multiple generator regions

Brain structures that can generate epileptiform activity possess excitatory interconnections among principal cells and a subset of these neurons that can be spontaneously active ("pacemaker" cells). We describe electrophysiological evidence for excitatory interactions among rat subicular neurons. Subiculum was isolated from presubiculum, CA1, and entorhinal cortex in ventral horizontal slices. Nominally zero magnesium perfusate, picrotoxin (100 microM), or NMDA (20 microM) was used to induce spontaneous firing in subicular neurons. Synchronous population activity and the spread of population events from one end of subiculum to the other in isolated subicular subslices indicate that subicular pyramidal neurons are coupled together by excitatory synapses. Both electrophysiological classes of subicular pyramidal cells (bursting and regular spiking) exhibited synchronous activity, indicating that both cell classes are targets of local excitatory inputs. Burst firing neurons were active in the absence of synchronous activity in field recordings, indicating that these cells may serve as pacemaker neurons for the generation of epileptiform activity in subiculum. Epileptiform events could originate at either proximal or distal segments of the subiculum from ventral horizontal slices. In some slices, events originated in both proximal and distal locations and propagated to the other location. Finally, propagation was supported over axonal paths through the cell layer and in the apical dendritic zone. We conclude that subicular burst firing and regular spiking neurons are coupled by means of glutamatergic synapses. These connections may serve to distribute activity driven by topographically organized inputs and to synchronize subicular cell activity.

Survival of dentate hilar mossy cells after pilocarpine-induced seizures and their synchronized burst discharges with area CA3 pyramidal cells

The clinical and basic literature suggest that hilar cells of the dentate gyrus are damaged after seizures, particularly prolonged and repetitive seizures. Of the cell types within the hilus, it appears that the mossy cell is one of the most vulnerable. Nevertheless, hilar neurons which resemble mossy cells appear in some published reports of animal models of epilepsy, and in some cases of human temporal lobe epilepsy. Therefore, mossy cells may not always be killed after severe, repeated seizures. However, mossy cell survival in these studies was not completely clear because the methods did allow discrimination between mossy cells and other hilar cell types. Furthermore, whether surviving mossy cells might have altered physiology after seizures was not examined. Therefore, intracellular recording and intracellular dye injection were used to characterize hilar cells in hippocampal slices from pilocarpine-treated rats that had status epilepticus and recurrent seizures ('epileptic' rats). For comparison, mossy cells were also recorded from age-matched, saline-injected controls, and pilocarpine-treated rats that failed to develop status epilepticus. Numerous hilar cells with the morphology, axon projection, and membrane properties of mossy cells were recorded in all three experimental groups. Thus, mossy cells can survive severe seizures, and those that survive retain many of their normal characteristics. However, mossy cells from epileptic tissue were distinct from mossy cells of control rats in that they generated spontaneous and evoked epileptiform burst discharges. Area CA3 pyramidal cells also exhibited spontaneous and evoked bursts. Simultaneous intracellular recordings from mossy cells and pyramidal cells demonstrated that their burst discharges were synchronized, with pyramidal cell discharges typically beginning first. From these data we suggest that hilar mossy cells can survive status epilepticus and chronic seizures. The fact that mossy cells have epileptiform bursts, and that they are synchronized with area CA3, suggest a previously unappreciated substrate for hyperexcitability in this animal model.