Grafting of striatal precursor cells into hippocampus shortly after status epilepticus restrains chronic temporal lobe epilepsy

Status epilepticus (SE) typically progresses into temporal lobe epilepsy (TLE) typified by complex partial seizures. Because sizable fraction of patients with TLE exhibit chronic seizures that are resistant to antiepileptic drugs, alternative therapies that are efficient for diminishing SE-induced chronic epilepsy have great significance. We hypothesize that bilateral grafting of appropriately treated striatal precursor cells into hippocampi shortly after SE is efficacious for diminishing SE-induced chronic epilepsy through long-term survival and differentiation into GABA-ergic neurons. We induced SE in adult rats via graded intraperitoneal injections of kainic acid, bilaterally placed grafts of striatal precursors (pre-treated with fibroblast growth factor-2 and caspase inhibitor) into hippocampi at 4 days post-SE, and examined long-term effects of grafting on spontaneous recurrent motor seizures (SRMS). Analyses at 9–12 months post-grafting revealed that, the overall frequency of SRMS was 67–89% less than that observed in SE-rats that underwent sham-grafting surgery and epilepsy-only controls. Graft cell survival was ~ 33% of injected cells and ~ 69% of surviving cells differentiated into GABA-ergic neurons, which comprised subclasses expressing calbindin, parvalbumin, calretinin and neuropeptide Y. Grafting considerably preserved hippocampal calbindin but had no effects on aberrant mossy fiber sprouting. The results provide novel evidence that bilateral grafting of appropriately treated striatal precursor cells into hippocampi shortly after SE is proficient for greatly reducing the frequency of SRMS on a long-term basis in the chronic epilepsy period. Presence of a large number of GABA-ergic neurons in grafts further suggests that strengthening of the inhibitory control in host hippocampi likely underlies the beneficial effects mediated by grafts.     

Chronic temporal lobe epilepsy is associated with severely declined dentate neurogenesis in the adult hippocampus

While it is clear that acute hippocampal injury or status epilepticus increases the production of new neurons in the adult dentate gyrus (DG), the effects of chronic epilepsy on dentate neurogenesis are unknown. We hypothesize that epileptogenic changes and spontaneous recurrent motor seizures (SRMS) that ensue after hippocampal injury or status epilepticus considerably decrease dentate neurogenesis. We addressed this issue by quantifying the number of cells that are positive for doublecortin (DCX, a marker of new neurons) in the DG of adult F344 rats at 16 days and 5 months after an intracerebroventricular kainic acid (ICV KA) administration or after graded intraperitoneal KA (IP KA) injections, models of temporal lobe epilepsy (TLE). At early post-KA administration, the injured hippocampus exhibited increased dentate neurogenesis in both models. Conversely, at 5 months post-KA administration, the chronically epileptic hippocampus demonstrated severely declined neurogenesis, which was associated with considerable SRMS in both KA models. Additionally, stem/progenitor cell proliferation factors, FGF-2 and IGF-1, were decreased in the chronically epileptic hippocampus. Interestingly, the overall decrease in neurogenesis and the extent of SRMS were greater in rats receiving IP KA than rats receiving ICV KA, suggesting that the extent of neurogenesis during chronic TLE exhibits an inverse relationship with SRMS. These results provide novel evidence that chronic TLE is associated with extremely declined dentate neurogenesis. As fraction of newly born neurons become GABA-ergic interneurons, declined neurogenesis may contribute to the increased seizure-susceptibility of the DG in chronic TLE. Likewise, the hippocampal-dependent learning and memory deficits observed in chronic TLE could be linked at least partially to the declined neurogenesis.     

Hippocampal neurodegeneration, spontaneous seizures, and mossy fiber sprouting in the F344 rat model of temporal lobe epilepsy

The links among the extent of hippocampal neurodegeneration, the frequency of spontaneous recurrent motor seizures (SRMS), and the degree of aberrant mossy fiber sprouting (MFS) in temporal lobe epilepsy (TLE) are a subject of contention because of variable findings in different animal models and human studies. To understand these issues further, we quantified these parameters at 3-5 months after graded injections of low doses of kainic acid (KA) in adult F344 rats. KA was administered every 1 hr for 4 hr, for a cumulative dose of 10.5 mg/kg bw, to induce continuous stages III-V motor seizures for >3 hr. At 4 days post-KA, the majority of rats (77%) exhibited moderate bilateral neurodegeneration in different regions of the hippocampus; however, 23% of rats exhibited massive neurodegeneration in all hippocampal regions. All KA-treated rats displayed robust SRMS at 3 months post-KA, and the severity of SRMS increased over time. Analyses of surviving neurons at 5 months post-KA revealed two subgroups of rats, one with moderate hippocampal injury (HI; 55% of rats) and another with widespread HI (45%). Rats with widespread HI exhibited greater loss of CA3 pyramidal neurons and robust aberrant MFS than rats with moderate HI. However, the frequency of SRMS (approximately 3/hr) was comparable between rats with moderate and widespread HI. Thus, in comparison with TLE model using Sprague-Dawley rats (Hellier et al. [1998] Epilepsy Res. 31:73-84), a much lower cumulative dose of KA leads to robust chronic epilepsy in F344 rats. Furthermore, the occurrence of SRMS in this model is always associated with considerable bilateral hippocampal neurodegeneration and aberrant MFS. However, more extensive hippocampal CA3 cell loss and aberrant MFS do not appear to increase the frequency of SRMS. Because most of the features are consistent with mesial TLE in humans, the F344 model appears ideal for testing the efficacy of potential treatment strategies for mesial TLE.     

Role of cortical dysplasia in epileptogenesis following prolonged febrile seizure

Purpose: Hippocampal sclerosis, characterized by prominent neuronal loss and reactive gliosis, is the most common pathology in human temporal lobe epilepsy (TLE). Although prolonged febrile convulsion (FC) is a risk factor of TLE, it is not clear whether FC provokes hippocampal sclerosis and subsequent TLE. Given that underlying brain lesions, such as cortical dysplasia (CD), in the immature brain predispose patients to FC, CD may link FC and TLE. However, the role of CD in epileptogenesis after FC is also unclear. Here, we investigated whether inborn CD increases the risk of later epilepsy induced by prolonged FC using a rat model. Methods: Experimental CD was induced by in utero exposure of methylazoxymethanol (MAM). Rat pups from MAM‐treated or control rats were then subjected to prolonged FC. We examined morphologic changes in the hippocampi with respect to neuronal loss, reactive gliosis, and synaptogenesis, and evaluated spontaneous recurrent seizures (SRS) by long‐term video‐EEG (electroencephalography). Results: The MAM+FC group had a significantly lower hippocampal neuronal density in the CA1 and dentate hilus than other control groups. A robust increase in glial cells and synaptic reorganization was also detected in the MAM+FC groups. Furthermore, later SRS occurred in all rats in the MAM+FC group and in 50% and 25% of the rats in the FC‐only and MAM‐only group, respectively. The frequency and total duration of SRS was highest in the MAM+FC group. Discussion: Our results suggest that preexisting CD in the immature brain augments the proepileptogenic effects of prolonged FC, leading to TLE.     

Additive effects of caspase inhibitor and lazaroid on the survival of transplanted rat and human embryonic dopamine neurons

Major practical constraints on neural grafting in Parkinson's disease are the shortage of human donor tissue and the great loss of dopamine neurons during the grafting procedure. The vast majority of implanted embryonic dopamine neurons are believed to die within a few days of transplantation surgery, at least in part through apoptosis. We have previously found that survival of nigral grafts in rodents can be significantly augmented by pretreatment with the caspase inhibitor Ac-YVAD-cmk or by lazaroids (lipid peroxidation inhibitors). We now report that pretreatment with the caspase inhibitor Ac-DEVD-cmk, but not z-VAD-fmk, results in a significantly improved survival of transplanted dopamine neurons of similar magnitude to that achieved in this study using Ac-YVAD-cmk (both 220-230% of control). In addition, we found that treatment of the graft tissue with tirilazad mesylate (a lazaroid allowed for clinical use) almost doubled the survival of grafted dopamine neurons. When Ac-YVAD-cmk and tirilazad mesylate treatments were combined, the number of surviving dopamine neurons increased significantly further to 280% of control. Importantly, the same combination of neuroprotectants enhanced the survival of human dopamine neurons xenotransplanted to immunosuppressed rats (to 240% of control). In conclusion, these results suggest that combining treatments that counteract oxidative stress and caspase activation is a valuable strategy to enhance nigral graft survival that should be considered for clinical application.     

Increased expression of caspase 2 in experimental and human temporal lobe epilepsy

Temporal lobe epilepsy (TLE) is often caused by a neurodegenerative brain insult that triggers epileptogenesis, and eventually results in spontaneous seizures, i.e., epilepsy. Understanding the mechanisms of cell death is a key for designing new drug therapies for preventing the neurodegeneration associated with TLE. Here, we investigated the expression of caspase 2, a protein involved in programmed cell death, during the course of epilepsy. We investigated caspase 2 expression in hippocampal samples derived from patients operated on for drug refractory TLE. To understand the evolution of altered-caspase 2 expression during the epileptic process, we also examined caspase 2 expression and activity in the rat hippocampus after status epilepticus-induced acute damage, during epileptogenesis, and after the onset of epilepsy. Caspase 2 expression was enhanced in the hippocampal neurons in chronic TLE patients. In rats, status epilepticus-induced caspase 2 labeling paralleled the progression of neurodegeneration. Proteolytic activation and cleavage of caspase 2 was also detected in the rat brain undergoing epileptogenesis. Our data suggest that caspase 2-mediated programmed cell death participates in the seizure-induced degenerative process in experimental and human TLE. The work was supported by The Academy of Finland, The Kuopio University Foundation, The Neurology Foundation, The North-Savo Regional Fund of the Finnish Cultural Foundation, Sigrid Juselius Foundation, and The Vaajasalo Foundation.     

Diurnal variations in depression-like behavior of Wistar and spontaneously hypertensive rats in the kainate model of temporal lobe epilepsy

The purpose of this study was to explore whether the kainate (KA) model of temporal lobe epilepsy (TLE) can be used as a model of comorbid epilepsy and depression to study diurnal behavioral variations in rats. Development of chronic epilepsy was confirmed by the detection of spontaneous motor seizures (SMS) with video monitoring (24 hours/3-5 months after status epilepticus [SE]). KA-treated spontaneously hypertensive rats (SHRs) exhibited higher seizure frequency than Wistar rats during the light phase in the fourth and fifth months after SE. Although epileptic Wistar rats showed depression-like behavior and reduced anxiety mostly during the light phase, there were no diurnal variations in depression-like patterns in SHRs. Anxiety levels of control and epileptic SHRs were similar. Decreases in serotonin, tryptophan, and dopamine concentrations in the hippocampus were detected in epileptic Wistar rats compared with naive controls. However, monoamine levels of epileptic SHRs were close to those of their controls. Wistar rats and SHRs develop stable depression-like behavior during the chronic epileptic phase with strain-dependent diurnal differences.     

Implications of decreased hippocampal neurogenesis in chronic temporal lobe epilepsy

Temporal lobe epilepsy (TLE), characterized by spontaneous recurrent motor seizures (SRMS), learning and memory impairments, and depression, is associated with neurodegeneration, abnormal reorganization of the circuitry, and loss of functional inhibition in the hippocampal and extrahippocampal regions. Over the last decade, abnormal neurogenesis in the dentate gyrus (DG) has emerged as another hallmark of TLE. Increased DG neurogenesis and recruitment of newly born neurons into the epileptogenic hippocampal circuitry is a characteristic phenomenon occurring during the early phase after the initial precipitating injury such as status epilepticus. However, the chronic phase of the disease displays substantially declined DG neurogenesis, which is associated with SRMS, learning and memory impairments, and depression. This review focuses on DG neurogenesis in the chronic phase of TLE and first confers the extent and mechanisms of declined DG neurogenesis in chronic TLE. The available data on production, survival and neuronal fate choice decision of newly born cells, stability of hippocampal stem cell numbers, and changes in the hippocampal microenvironment in chronic TLE are considered. The next section discusses the possible contribution of declined DG neurogenesis to the pathophysiology of chronic TLE, which includes its potential effects on spontaneous recurrent seizures, cognitive dysfunction, and depression. The subsequent section considers strategies that may be useful for augmenting DG neurogenesis in chronic TLE, which encompass stem cell grafting, administration of distinct neurotrophic factors, physical exercise, exposure to enriched environment, and antidepressant therapy. The final section suggests possible ramifications of increasing the DG neurogenesis in chronic epilepsy.     

Selective changes in inhibition as determinants for limited hyperexcitability in the insular cortex of epileptic rats

The insular cortex (IC) is involved in the generalization of epileptic discharges in temporal lobe epilepsy (TLE), whereas seizures originating in the IC can mimic the epileptic phenotype seen in some patients with TLE. However, few studies have addressed the changes occurring in the IC in TLE animal models. Here, we analyzed the immunohistochemical and electrophysiological properties of IC networks in non‐epileptic control and pilocarpine‐treated epileptic rats. Neurons identified with a neuron‐specific nuclear protein antibody showed similar counts in the two types of tissue but parvalbumin‐ and neuropeptide Y‐positive interneurons were significantly decreased (parvalbumin, approximately ?35%; neuropeptide Y, approximately ?38%; P < 0.01) in the epileptic IC. Non‐adapting neurons were seen more frequently in the epileptic IC during intracellular injection of depolarizing current pulses. In addition, single‐shock electrical stimuli elicited network‐driven epileptiform responses in 87% of epileptic and 22% of non‐epileptic control neurons (P < 0.01) but spontaneous postsynaptic potentials had similar amplitude, duration and intervals of occurrence in the two groups. Finally, pharmacologically isolated, GABA_A receptor‐mediated inhibitory postsynaptic potentials had more negative reversal potential (P < 0.01) and higher peak conductance (P < 0.05) in epileptic tissue. These data reveal moderate increased network excitability in the IC of pilocarpine‐treated epileptic rats. We propose that this limited degree of hyperexcitability originates from the loss of parvalbumin‐ and neuropeptide Y‐positive interneurons that is compensated by an increased drive for GABA_A receptor‐mediated inhibition.     

Downregulation of gephyrin in temporal lobe epilepsy neurons in humans and a rat model

Gephyrin, which is a postsynaptic scaffolding protein participated in clustering GABA(A) receptors at inhibitory synapses, has been reported to be involved in temporal lobe epilepsy (TLE) recently. Here, we investigate gephyrin protein expression in the temporal lobe epileptic foci in epileptic patients and experimental animals in order to explore the probable relationship between gephyrin expression and TLE. Using immunohistochemistry, immunofluorescence, and western blot analysis, gephyrin expression was examined in 30 human temporal neocortex samples from patients who underwent surgery to treat drug-refractory TLE and 10 histological normal temporal neocortex from the controls. Meanwhile, we investigated the gephyrin expression in the hippocampus and adjacent neocortex from experimental rats on 24 h, 48 h, 1 week, 2 weeks, 1 month, and 2 months postseizure and from control rats. Gephyrin protein was mainly expressed in the membrane and cytoplasm of neurons in temporal lobe epileptic foci in humans and experimental rats. Gephyrin expression was significantly lower in the temporal neocortex of TLE patients compared to the controls. In experimental rats, the expression of gephyrin in temporal lobe was downregulated in epileptic groups compared to the control group. Gephyrin expression gradually decreased during the acute period and the latent period, but then began to increase below the levels seen in controls during the chronic phase. Our findings suggest that gephyrin may be involved in the development of TLE.     

Caspase inhibitors are functionally neuroprotective against oxygen glucose deprivation induced CA1 death in rat organotypic hippocampal slices

We have explored the neuroprotective efficacy of the cell penetrant caspase inhibitor, Ac-YVAD-cmk, in a hippocampal slice model of neuronal cell death induced by oxygen and glucose deprivation. Organotypic hippocampal slice cultures were prepared from 8 to 10-day-old rats and maintained for 10 to 12 days in vitro. Pre-treatment with Ac-YVAD-cmk prior to 45 min oxygen and glucose deprivation was neuroprotective as measured by propidium iodide uptake, with an EC(50) between 1 and 10 micromol/l. Ac-YVAD-cmk was also able to preserve synaptic function in the organotypic hippocampal slice cultures 24 h after oxygen and glucose deprivation. Ac-YVAD-cmk prevented the increase in histone-associated DNA fragmentation induced by oxygen and glucose deprivation. Interleukin-1beta did not reverse the protective effect of Ac-YVAD-cmk, and interleukin-1 receptor antagonist alone was not protective. These results show that caspase inhibitors are neuroprotective in a hippocampal slice culture system, using structural, biochemical and electrophysiological endpoints, and that this effect is not a result of inhibition of interleukin-1beta production.     

Upregulation of dysbindin in temporal lobe epileptic foci of human and experimental animals

The gene encoding dystrobrevin-binding-protein-1 (dysbindin) is expressed in many areas of the central nervous system and plays a role in intracellular vesicle trafficking, synaptic vesicle trafficking, and neurotransmitter release. At a cellular level, dysbindin is thought to mediate presynaptic glutamatergic transmission. Using Western blotting and immunofluorescence, we investigated dysbindin expression in brain tissues of the patients with temporal lobe epilepsy (TLE) and rats with TLE (lithium chloride pilocarpine model) to explore its possible role in epileptogenesis. Twenty-five samples of temporal neocortex from patients undergoing surgery for drug-refractory TLE epilepsy and 10 histologically normal temporal lobes tissues from control subjects were used in our study. We also examined dysbindin expression in the hippocampus and adjacent cortex from experimental Sprague-Dawley rats. Dysbindin was expressed in the cytoplasm of neurons from epileptic specimens, and levels of dysbindin proteins were significantly increased in patients with TLE. Dysbindin was also expressed in the neurons of the hippocampus and adjacent cortex from experimental and control rats. Western blotting of rat brain tissue showed that dysbindin was upregulated gradually from 6 h after kindling. Maximal expression was seen around 2 months in chronic epileptic phase. These results demonstrated that the increased expression of dysbindin might play a role in the pathogenesis of drug-refractory TLE.     

Right hippocampal sclerosis is more common than left after febrile seizures

Temporal lobe epilepsy (TLE) is frequently associated with hippocampal sclerosis (HS) and a history of febrile convulsions (HFC). The authors investigated 292 patients with TLE due to HS. Left HS occurred more frequently (57%) than right HS (43%, p = 0.01). Forty-seven percent of the patients had HFC. In patients with right HS, HFC occurred in 59.6%, whereas in patients with left HS, HFC was present in 37.5%, showing a highly significant lateralization difference.     

Association Between the Density of Mossy Fiber Sprouting and Seizure Frequency in Experimental and Human Temporal Lobe Epilepsy

Summary: Purpose : If the sprouting of granule cell axons or mossy fibers in the dentate gyrus is critical for the generation of spontaneous seizures in temporal lobe epilepsy (TLE), one could hypothesize that epileptic animals or humans with increased sprouting would have more frequent seizures. This hypothesis was tested by analyzing the data gathered from experimental and human epilepsy.
Methods : In experiment I (rats with "newly diagnosed" TLE), self-sustained status epilepticus was induced in rats by electrically stimulating the amygdala. Thereafter, the appearance of spontaneous seizures was monitored by continuous video-electroencephalography (EEG) until the animal developed two spontaneous seizures and for 11 d thereafter. Rats were perfused for histology, and mossy fibers were stained using the Timm method. In experiment II (rats with "recently diagnosed" TLE), status epilepticus was induced in rats and the development of seizures was monitored by video-EEG for 24 h/d every other day for 60 days. All animals were then perfused for histology. In experiment III (rats with "chronic" TLE), animals were monitored by video-EEG for 24 h/d every other day for 6 months before histologic analysis. To assess mossy fiber sprouting in human TLE, hippocampal sections from 31 patients who had undergone surgery for drug-refractory TLE were stained with an antibody raised against dynorphin.
Results and Conclusions : Our data indicate that the density of mossy fiber sprouting is not associated with the total number of lifetime seizures or the seizure frequency in experimental or human TLE.     

Bcl‐2/Bax ratio increase does not prevent apoptosis of glia and granular neurons in patients with temporal lobe epilepsy

Temporal lobe epilepsy (TLE) is usually associated with hippocampal sclerosis (HS), characterized by gliosis and neuronal loss, mainly in the cornus ammonis (CA). Regardless the type of HS, gliosis is associated with neuronal loss. Indeed, glial reactivation seems to induce both neuronal and glial apoptosis. Anti‐apoptotic mechanisms are also activated in order to contain the cell death in chronic epilepsy. However, the role of the intrinsic apoptosis pathway in human TLE is unclear, mainly in relation to glial death. The purpose of this study was to evaluate the reactive gliosis areas in parallel with Bcl‐2/Bax ratio and active caspase 3 immunoreactivity in hippocampi of TLE patients in comparison with control hippocampi. We also sought to investigate whether the levels of these markers were correlated with TLE clinical parameters. Paraffin‐embedded sclerotic and control hippocampi were collected for immunohistochemical analyses of glial fibrillary acidic protein (GFAP), human leucocyte antigen DR (HLA‐DR), neuronal nuclei protein (NeuN), Bax, Bcl‐2 and active caspase 3. Sclerotic hippocampi presented higher immunoreactivity areas of GFAP and HLA‐DR than controls, with similar values in HS types 1 and 2. Bcl‐2 protein expression was increased in epileptic hippocampi, while Bax expression was similar to controls. Despite Bcl2/Bax ratio increase, granular neurons and glia exhibited active caspase 3 expression in TLE hippocampi, while controls did not show staining for the same marker. In conclusion, glial and neuronal death is increased in sclerotic hippocampi, independently of HS type, and co‐localized with gliosis. Furthermore, Bcl‐2/Bax ratio increase does not prevent expression of active caspase 3 by glia and granular neurons in TLE.     

Drug resistance and hippocampal damage after delayed treatment of pilocarpine-induced epilepsy in the rat

Temporal lobe epilepsy (TLE) is the most common and pharmacoresistant form of epilepsy. Problems that cause pharmacoresistance may include delayed therapy due to late consultation, especially in developing countries. Our study aimed at unraveling consequences of delayed drug treatment using a rat model of TLE. Following pilocarpine-induced status epilepticus interrupted after 4h, rats were continuously videorecorded for onset and recurrence of spontaneous convulsive seizures. The animals were then treated for 50 days with carbamazepine (CBZ; first-line drug in TLE and effective also in rats), starting at seizure onset (27.22+/-3.38 days after status epilepticus) or 50 days later, and compared with epileptic untreated rats and non-epileptic CBZ-treated ones. Convulsive seizure frequency and duration, and hippocampal cell changes were evaluated. In particular, parvalbumin-containing hippocampal interneurons, astrocytes and microglia were characterized with immunohistochemistry and quantitative analyses. Prompt administration of CBZ suppressed seizures; delayed treatment only decreased frequency of convulsive seizures, which were also relatively prolonged. In hippocampal regions, histopathological damage, parvalbumin immunoreactivity loss, and glial activation were very marked after delayed treatment, and were reduced only slightly compared to untreated epilepsy, but enhanced compared to early treatment. The data on high frequency and duration of convulsive seizures in late-therapy rats indicate that delayed CBZ administration caused a high degree of drug resistance. This condition was subserved by severe damage in the hippocampus, presumably consequent to long-term seizure recurrence. Overall the data indicate that the paradigm of delayed treatment of limbic epilepsy could provide a model of drug-refractory TLE with hippocampal sclerosis.     

Decreased neuronal differentiation of newly generated cells underlies reduced hippocampal neurogenesis in chronic temporal lobe epilepsy

Hippocampal neurogenesis declines substantially in chronic temporal lobe epilepsy (TLE). However, it is unclear whether this decline is linked to altered production of new cells and/or diminished survival and neuronal fate‐choice decision of newly born cells. We quantified different components of hippocampal neurogenesis in rats exhibiting chronic TLE. Through intraperitoneal administration of 5′‐bromodeoxyuridine (BrdU) for 12 days, we measured numbers of newly born cells in the subgranular zone‐granule cell layer (SGZ‐GCL) at 24 h and 2.5 months post‐BrdU administration. Furthermore, the differentiation of newly added cells into neurons and glia was quantified via dual immunofluorescence for BrdU and various markers of neurons and glia. Addition of new cells to the SGZ‐GCL over 12 days was comparable between the chronically epileptic hippocampus and the age‐matched intact hippocampus. Furthermore, comparison of BrdU+ cells measured at 24 h and 2.5 months post‐BrdU administration revealed similar survival of newly born cells between the two groups. However, only 4–5% of newly born cells (i.e., BrdU+ cells) differentiated into neurons in the chronically epileptic hippocampus, in comparison to 73–80% of such cells exhibiting neuronal differentiation in the intact hippocampus. Moreover, differentiation of newly born cells into S‐100β+ astrocytes or NG2+ oligodendrocyte progenitors increased to ∼79% in the chronically epileptic hippocampus from ∼25% observed in the intact hippocampus. Interestingly, the extent of proliferation of astrocytes and microglia (identified through Ki‐67 and S‐100β and Ki‐67 and OX‐42 dual immunofluorescence) in the SGZ‐GCL was similar between the chronically epileptic hippocampus and the age‐matched intact hippocampus, implying that the proliferation of neural stem/progenitor cells in the SGZ‐GCL of the chronically epileptic hippocampus was not obscured by an increased division of glia. Thus, severely diminished DG neurogenesis in chronic TLE is not associated with either decreased production of new cells or reduced survival of newly born cells in the SGZ‐GCL. Rather, it is linked to a dramatic decline in the neuronal fate‐choice decision of newly generated cells. Overall, the differentiation of newly born cells turns mainly into glia with chronic TLE from predominantly neuronal differentiation seen in control conditions. © 2009 Wiley‐Liss, Inc.     

Decreased expression of synaptic vesicle protein 2A, the binding site for levetiracetam, during epileptogenesis and chronic epilepsy

Purpose:   We previously showed that gene expression of synaptic vesicle protein 2A (SV2A), the binding site for the antiepileptic drug levetiracetam, is reduced during epileptogenesis in the rat. Since absence of SV2A has been associated with increased epileptogenicity, changes in expression of SV2A could have consequences for the progression of epilepsy. Therefore we investigated hippocampal SV2A protein expression of temporal lobe epilepsy (TLE) patients and in rats during epileptogenesis and in the chronic epileptic phase.
Methods:   SV2A immunocytochemistry and Western blot analysis were performed on the hippocampus of autopsy controls, patients that died from status epilepticus (SE), and pharmacoresistant TLE patients. In addition, in epileptic rats, SV2A expression was determined after SE during the acute, latent, and chronic epileptic phase.
Results:   In control tissue, presynaptic SV2A was expressed in all hippocampal subfields, with strongest expression in mossy fiber terminals. SV2A positive puncta were distributed in a patchy pattern over the somata and dendrites of neurons. SV2A decreased throughout the hippocampus of TLE patients with hippocampal sclerosis (HS), compared to autopsy control, SE, and non-HS tissue. In most rats, SV2A was already decreased in the latent period especially in the inner molecular layer and stratum lucidum. Similarly as in humans, SV2A was also decreased throughout the hippocampus of chronic epileptic rats, specifically in rats with a progressive form of epilepsy.
Discussion:   These data support previous findings that reduced expression of SV2A could contribute to the increased epileptogenicity. Whether this affects the effectiveness of levetiracetam needs to be further investigated.     

Effects of chronic naloxone pretreatment on amygdaloid kindling in rats

Effects of chronic naloxone pretreatment (75 or 270, μg/h for 14 days) on the development of amygdaloid kindling in rats were evaluated. The acquisition of seizure activity was modified in the naloxone pretreated animals, depending on the nucleus stimulated: facilitation of stages IV and V occurred in 37%, variability of electrographic and behavioral responses to electrical stimulation during the kindling development in 33%, and facilitation of stages IV and V followed by long periods of seizure suppression in 29%. Enhancement of postictal seizure suppession during a recycling paradigm was observed in all the naloxone pretreated rats. It was concluded that the chronic administration of naloxone (known to induce opioid binding upregulation and supersensitivity), in association with the enduring changes in opioid mechanisms provoked by kindled seizures, were responsible for the facilitation and suppression of epileptic activity. These findings support bidirectional modulatory effects of opioid peptides on epileptic seizures as well as the view that epileptic seizures can induce enduring alterations in opioid mechanisms.     

Childhood febrile convulsions--which factors determine the subsequent epilepsy syndrome? A retrospective study

To analyze the spectrum of epilepsy syndromes which follow childhood febrile convulsions (FC) and to examine whether retrospective analysis of clinical features of the FC enables discrimination of patients who develop temporal lobe epilepsy (TLE) from those who develop generalized epilepsy (GE). One hundred and thirteen patients with epilepsy and antecedent FC were retrospectively analyzed. We inquired in detail about the clinical characteristics of FC (age, duration, number, focal symptoms) as well as family history, birth history, neurological status, and psychomotor development before onset of FC. Forty five (39.8%) patients had TLE, 41 (36.6%) GE, and 27 (23.9%) had extratemporal epilepsy (ETE). Patients with TLE had a significantly longer duration of FC (P≤0.001), more often focal features (P≤0.001), and febrile status epilepticus (P≤0.001) than patients with GE. Age at FC, Number of FC, family history, birth history and neurological status at FC did not differ between groups. A stepwise discriminant model allowed correct assignment after cross validation in 84.2% to TLE and in 100% to GE. A broad spectrum of epilepsy syndromes follow FC. We found a strong association of prolonged and focal FC with later development of TLE. Short generalized FC were associated with GE.