Early volumetric changes of hippocampus and medial prefrontal cortex following medial temporal lobe resection.

Previous studies have shown that cognitive demands and physical exercise stimulate adult neurogenesis in the dentate gyrus and hippocampus. Recent observations in healthy humans and patients with mild cognitive impairment moreover suggest that training-induced increases in hippocampal volume may be associated with improved memory performance. The corresponding plasticity processes in hippocampal volume may occur on timescales of months to years. For patients with focal lesions in this region, previous functional imaging studies suggest that increased recruitment of the contralateral hippocampus and extratemporal regions may be an important part of the reorganization of episodic memory. However, it is currently unclear whether focal damage to the medial temporal lobe (MTL) induces gray matter (GM) volume changes in the intact contralateral hippocampus and in connected network regions on a shorter timescale. We therefore investigated whether unilateral resection of the MTL, including the hippocampus, induces measurable volumetric changes in the contralateral hippocampus and in the default mode network (DMN). We recruited 31 patients with unilateral left (N = 19) or right (N = 12) hippocampal sclerosis undergoing MTL resection for treatment of drug-resistant epilepsy. Structural MRI was acquired immediately before and 3 months after surgery. Longitudinal voxel-based morphometry (VBM) analysis revealed a significant increase of right hippocampal volume following resection of the left anterior MTL. Furthermore, this patient group showed GM volume increases in the DMN. These results demonstrate significant structural plasticity of the contralateral hippocampus, even in patients with a long-standing unilateral hippocampal dysfunction and structural reorganization processes extending to distant, but functionally connected brain regions.

Seizure outcome 1 year after temporal lobe epilepsy: an analysis of MR volumetric and clinical parameters.

BACKGROUND: The aim of this work was to determine predictors that may contribute to surgical success or failure. Relevant pre- and postoperative baseline data were analyzed, and temporal structures underwent a volumetric analysis. METHODS: A total of 207 patients (107 female) underwent complete evaluation for epilepsy surgery. Prospectively collected data used for this analysis included the clinical and demographic data. Classic prognostic factors (e.g., gender, age at operation, age at epilepsy manifestation, duration of epilepsy, education, side of pathology, intracranial EEG recordings, secondarily generalized tonic-clonic seizures, etiological factors, histology) and a volumetric analysis of 12 temporal lobe subregions were used in a regression analysis to identify possible prognostic factors in surgery for TLE. Primary outcome measure was seizure freedom at 1 year and during the full first year expressed as class I in the ILAE outcome scale. RESULTS: In the univariate analysis, we identified one negative predictor for a less favorable seizure outcome: intracranial EEG recordings (p = 0.010), hippocampal sclerosis as histological finding trended toward statistical significance (p = 0.054). No statistical outcome significance was found for preoperative temporal lobe compartment volume loss or postoperative lateral atrophy after mesial resection. CONCLUSIONS: Necessity for intracranial EEG recording is an independent factor of not optimal seizure control in the 1-year follow-up. Preoperative temporal lobe volume differences including smaller mesial subcompartments did not correlate with poorer seizure outcome.

Lesions affecting the right hippocampal formation differentially impair short-term memory of spatial and nonspatial associations.

Converging evidence from behavioral and imaging studies suggests that within the human medial temporal lobe (MTL) the hippocampal formation may be particularly involved in recognition memory of associative information. However, it is unclear whether the hippocampal formation processes all types of associations or whether there is a specialization for processing of associations involving spatial information. Here, we investigated this issue in six patients with postsurgical lesions of the right MTL affecting the hippocampal formation and in ten healthy controls. Subjects performed a battery of delayed match-to-sample tasks with two delays (900/5,000 ms) and three set sizes. Subjects were requested to remember either single features (colors, locations, shapes, letters) or feature associations (color-location, color-shape, color-letter). In the single-feature conditions, performance of patients did not differ from controls. In the association conditions, a significant delay-dependent deficit in memory of color-location associations was found. This deficit was largely independent of set size. By contrast, performance in the color-shape and color-letter conditions was normal. These findings support the hypothesis that a region within the right MTL, presumably the hippocampal formation, does not equally support all kinds of visual memory but rather has a bias for processing of associations involving spatial information. Recruitment of this region during memory tasks appears to depend both on processing type (associative/nonassociative) and to-be-remembered material (spatial/nonspatial).

Evaluating reference genes to normalize gene expression in human epileptogenic brain tissues.

Several reference genes have been used to quantify gene expression in human epilepsy surgery tissue. However, their reliability has not been validated in detail, although this is crucial in interpreting epilepsy-related changes of gene expression. We evaluated 12 potential reference genes in neocortical tissues resected from patients with temporal lobe epilepsy (TLE) with either few or many seizures (n=6 each) and post mortem controls (n=6) using geNorm and NormFinder algorithms. For all candidate reference genes threshold cycle (C(T)) values were measured. geNorm analysis revealed that the expression of e.g. glyceraldehyde-3-phosphate-dehydrogenase (GAPDH) and hypoxanthine phosphoribosyl-transferase (HPRT) is unstable, whereas synaptophysin (SYP) and neuron-specific enolase (NSE)/mitochondrial 39S ribosomal protein L28 (MRPL) are most stably expressed. The geometric mean of SYP, NSE and MRPL levels is recommended as normalization factor (NF). NormFinder analysis, in contrast, indicated HPRT as the most stable single gene and recommended the geometric mean of TATA-box binding protein (TBP) and NSE levels as NF. Different values of upregulation of glial fibrillary protein (GFAP) expression were found in TLE tissue compared to control tissue depending on the NF used: 4.5-fold (geNorm-NF), 4.7-fold (NormFinder-NF), 4.2-fold (vs. GAPDH) and 7.8-fold (vs. HPRT). The expression of GABA(A) receptor subunit α5 (GARα5) was unaltered in the TLE groups compared to controls (geNorm-NF, NormFinder-NF, vs. GAPDH). However, normalization to HPRT suggests an apparent increase of GARα5 expression. In conclusion, the geNorm-NF (SYP/NSE/MRPL) and the NormFinder-NF (TBP/NSE) are equally suitable for normalization of gene expression in the human epileptogenic neocortex. In contrast, normalization to single and probably less stably expressed genes may not deliver accurate results.

Hyperpolarization-activated cation currents in human epileptogenic neocortex.

PURPOSE: Hyperpolarization-activated cation currents (I(H)) play a pivotal role in the control of neuronal excitability. In animal models of epilepsy both increases and decreases of I(H) have been reported. We, therefore, characterized properties of I(H) in human epileptogenic neocortex. METHODS: Layer II/III neurons in slices from epilepsy surgery tissues and rat cortex were investigated with whole-cell patch-clamp recordings. RESULTS: A total of 484 neurons from 96 temporal lobe epilepsy (TLE) tissues and 32 neurons from 8 frontal lobe epilepsy (FLE) tissues were recorded. Voltage-clamp recordings revealed on hyperpolarizing command steps two time- and voltage-dependent inward currents, namely a fast, Ba(2+)-sensitive current (K(IR)) and a slowly activating current, namely consisting of two kinetically distinct components sensitive to the established I(H) blocker ZD7288. Only, the fast component (I(H)(fast)) of TLE neurons was on average smaller and activated more slowly (density 2.7 +/- 1.6 pA/pF; tau 38.4 +/- 34.0 ms) than in FLE neurons (4.7 +/- 2.3 pA/pF; 16.6 +/- 7.9 ms; p < 0.001 for both). Within the TLE tissues the I(H)(fast) density (averaged per patient) was smaller in cases with numerous annual grand mal seizures (GM; 2.2 +/- 0.6 pA/pF) compared to those with few GM (2.8 +/- 1.0 pA/pF; p = 0.0184). A similar difference was obtained in the case of complex partial seizures (CPS; many CPS 2.2 +/- 0.6 pA/pF; few CPS 2.9 +/- 1.0 pA/pF, p = 0.0037). DISCUSSION: The biophysical properties of I(H) in cortices from TLE, FLE, and rat tissue suggest a deficit of HCN1 subunits in the human epileptogenic neocortex, which in turn may increase excitability and probability of seizure activity.

Splice-specific roles of glycine receptor alpha3 in the hippocampus.

Glycine receptor (GlyR) alpha3 is involved in vision, and processing of acoustic and nociceptive signals, and RNA editing of GLRA3 transcripts was associated with hippocampal pathophysiology of mesial temporal lobe epilepsy (TLE). However, neither the role of GlyR alpha3 splicing in hippocampal neurons nor the expression of splice variants have yet been elucidated. We report here that the long (L) splice variant of GlyR alpha3 predominates in the brain of rodents. Cellular analysis using primary hippocampal neurons and hippocampus cryosections revealed preferential association of synaptic alpha3L clusters with glutamatergic nerve endings in strata granulare and pyramidale. In primary hippocampal neurons GlyR alpha3L clusters also preferred glutamatergic nerve endings while alpha3K was mainly in a diffuse state. Co-expression of GlyR beta subunit with alpha3L or alpha3K produced heteromeric receptor clusters and favoured their association with GABAergic terminals. However, heteromeric alpha3L was still more efficient than heteromeric alpha3K in associating with glutamatergic nerve endings. To give physiological relevance to these results we have finally analysed GlyR alpha3 splicing in human hippocampus obtained from patients with intractable TLE. As up-regulation of alpha3K occurred at the expense of alpha3L in TLE patients with a severe course of disease and a high degree of hippocampal damage, our results again involve post-transcriptional processing of GLRA3 transcripts in the pathophysiology of TLE.

Glutamine induces epileptiform discharges in superficial layers of the medial entorhinal cortex from pilocarpine-treated chronic epileptic rats in vitro.

PURPOSE: Glutamine (GLN) is a precursor for synthesis of glutamate and gamma-aminobutyric acid (GABA) and has been found in the cerebrospinal fluid (CSF) at mean concentrations of 0.6 mM. Experiments on slices are usually performed in artificial CSF (aCSF) kept free of amino acids. Therefore, the role of glutamine, particularly in tissue of epileptic animals, remains elusive. METHODS: Using extracellular recordings we studied effects of GLN on field potentials and stimulus-evoked field responses in the medial entorhinal cortex (MEC) of combined entorhinal cortex hippocampal slices from pilocarpine-treated chronic epileptic rats and age-matched saline-injected control rats. RESULTS: In presence of GLN (0.5 and 2 mM) recurrent epileptiform discharges (REDs) were observed in slices from epileptic rats (64% and 80%, respectively), but not in slices from control rats. REDs were restricted to the superficial MEC, suppressed by the alpha-Amino-3-hydroxy-5-methyl-4-isoxazol-propionate (AMPA)/kainate receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (30 microM), attenuated by the inhibitor of neuronal glutamine transporters methylamino-isobutyric acid (10 mM), and apparently augmented and prolonged by the GABA(A) receptor antagonist bicuculline-methiodide (5 microM). In contrast, amplitudes of stimulus evoked nonsynaptic and synaptic field responses increased in slices from control rats (+23% and +12% of the reference values) and insignificantly less or not in those of epileptic rats (+6.5% and -0.25%, respectively). Notably, stimulus-evoked slow negative transients confined to slices of epileptic animals were reduced in amplitude (-18%). DISCUSSION: In combined entorhinal hippocampal slices from chronic epileptic animals, GLN induces glutamatergic REDs via neuronal uptake in superficial layers of the MEC where inhibitory function seemed to be partially preserved.

Impaired function of GABA(B) receptors in tissues from pharmacoresistant epilepsy patients.

PURPOSE: Effects of pre- and postsynaptic γ-aminobutyric acid B (GABA(B)) receptor activation were characterized in human tissue from epilepsy surgery. METHODS: Slices of human cortical tissue were investigated in a submerged-type chamber with intracellular recordings in layers II/III. Parallel experiments were performed in rat neocortical slices with identical methods. Synaptic responses were elicited with single or paired stimulations of incrementing intervals. RESULTS: Neurons in human epileptogenic tissue exhibited usually small inhibitory postsynaptic potentials (IPSP) mediated by GABA(B) receptor, verified by the sensitivity to the selective antagonist CGP 55845A. The IPSP(B) conductance averaged 5.8 nS in neurons from epileptogenic tissues and 15.9 nS in neurons from nonepileptogenic tissues (p < 0.0001). Application of baclofen caused small conductance increases in human neurons, which were linearly related to IPSP(B) conductances. Paired-pulse stimulation revealed constant synaptic responses in human temporal lobe epilepsy (TLE) slices at all interstimulus intervals (ISIs). Pharmacologically isolated IPSP(A) in the human tissue exhibited a small paired-pulse depression (average 10% at 500 ms ISI). Bicuculline-induced paroxysmal depolarization shifts (PDSs) were transiently depressed by 24% in human TLE tissue; and by 74% in rat neocortical slices (200 ms ISI; p = 0.015). The depressions of bicuculline-induced PDSs were antagonized by CGP 55845A in both species. Staining for GABA(B) receptors revealed significantly smaller numbers of immunopositive dots in human epileptogenic neurons versus human control neurons. DISCUSSION: The small IPSP(B), baclofen-conductances, and paired-pulse depression of PDSs and IPSPs in human TLE tissue indicate a reduced density of post- and presynaptic GABA(B) receptors. The reduced efficacy of presynaptic GABA(B) receptors facilitates the occurrence of repetitive synaptic activity.

Reorganization of associative memory in humans with long-standing hippocampal damage.

Conflicting theories have been advanced to explain why hippocampal lesions affect distinct memory domains and spare others. Recent findings in monkeys suggest that lesion-induced plasticity may contribute to the seeming preservation of some of these domains. We tested this hypothesis by investigating visuo-spatial associative memory in two patient groups with similar surgical lesions to the right medial temporal lobe, but different preoperative disease courses (benign brain tumours, mean: 1.8 +/- 0.6 years, n = 5, age: 28.2 +/- 4.0 years; hippocampal sclerosis, mean: 16.8 +/- 1.9 years, n = 9, age: 38.9 +/- 4.1 years). Compared to controls (n = 14), tumour patients showed a significant delay-dependent deficit in memory of colour-location associations. No such deficit was observed in hippocampal sclerosis patients, which appeared to benefit from a compensatory mechanism that was inefficient in tumour patients. These results indicate that long-standing hippocampal damage can yield significant functional reorganization of the neural substrate underlying memory in the human brain. We suppose that this process accounts for some of the discrepancies between results from previous lesion studies of the human medial temporal lobe.

Shrinkage of the hippocampal remnant after surgery for temporal lobe epilepsy: impact on seizure and neuropsychological outcomes.

The aim of this study was to investigate the influence of the postoperative hippocampal remnant on postoperative seizure and neuropsychological outcome in temporal lobe epilepsy (TLE). Postoperative volumetric MRI measurements of 53 patients surgically treated for TLE revealed a postoperative volume loss of the hippocampal remnant compared with the respective preoperative segment in all patients. Extent of preoperative hippocampal pathology, remnant shrinkage, resection volume, and postoperative volume of the hippocampal remnant did not correlate with seizure outcome 1 year after surgery. With respect to neuropsychological outcome, performance on tasks assessing verbal memory and language-related functions was impaired in patients with left-sided pathology after surgery. Performance of patients with right-sided pathology (n=26) demonstrated no significant correlation with hippocampal measures or with neuropsychological data. Degree of hippocampal remnant shrinkage seems to be associated with decreased verbal memory performance in patients with left-sided TLE.

Nitric oxide modulates spreading depolarization threshold in the human and rodent cortex.

BACKGROUND AND PURPOSE: Recent clinical data have suggested that prolonged cortical spreading depolarizations (CSDs) contribute to the pathogenesis of delayed ischemic neurologic deficits after subarachnoid hemorrhage. Elevated extracellular potassium concentrations and lowered nitric oxide (NO) levels have been detected in experimental and clinical subarachnoid hemorrhage. We investigated whether a similar extracellular composition renders the brain more susceptible to CSDs. METHODS: Electrophysiologic and blood flow changes were studied in vivo in rats. Intrinsic optical signals, alterations of NO level, and electrophysiologic changes were investigated in rodent and human brain slices. RESULTS: Elevation of subarachnoid extracellular potassium in rats in vivo triggered CSDs. Using NO-sensitive dyes, we found that CSDs induce NO synthesis in neurons and endothelial cells. When we blocked NO synthesis in vivo, CSDs occurred at a significantly lower threshold and propagated with a wave of ischemia. This increased susceptibility for CSDs by a low NO level was confirmed in rat and human neocortical slices and depended on P/Q-type calcium channels and N-methyl-D-aspartate receptors, but not on guanylate cyclase. Mice deficient in endothelial NO synthase, in contrast to mice deficient in neuronal NO synthase, had an inherently lower threshold. CONCLUSIONS: Basal NO production determined CSD threshold. The threshold effect depended predominantly on endothelial NO synthase. Reduced NO levels, as in patients with subarachnoid hemorrhage, may render the brain more susceptible to CSDs. Because CSDs have been linked to the pathogenesis of delayed ischemic neurologic deficits, raising its threshold by increasing NO availability may prove therapeutically beneficial in patients with subarachnoid hemorrhage.

The human hippocampal formation mediates short-term memory of colour-location associations.

The medial temporal lobe (MTL) has long been considered essential for declarative long-term memory, whereas the fronto-parietal cortex is generally seen as the anatomical substrate of short-term memory. This traditional dichotomy is questioned by recent studies suggesting a possible role of the MTL for short-term memory. In addition, there is no consensus on a possible specialization of MTL sub-regions for memory of associative information. Here, we investigated short-term memory for single features and feature associations in three humans with post-surgical lesions affecting the right hippocampal formation and in 10 healthy controls. We used three delayed-match-to-sample tasks with two delays (900/5000 ms) and three set sizes (2/4/6 items). Subjects were instructed to remember either colours, locations or colour-location associations. In colour-only and location-only conditions, performance of patients did not differ from controls. By contrast, a significant group difference was found in the association condition at 5000 ms delay. This difference was largely independent of set size, thus suggesting that it cannot be explained by the increased complexity of the association condition. These findings show that the hippocampal formation plays a significant role for short-term memory of simple visuo-spatial associations, and suggest a specialization of MTL sub-regions for associative memory.

Delayed ischaemic neurological deficits after subarachnoid haemorrhage are associated with clusters of spreading depolarizations.

Progressive ischaemic damage in animals is associated with spreading mass depolarizations of neurons and astrocytes, detected as spreading negative slow voltage variations. Speculation on whether spreading depolarizations occur in human ischaemic stroke has continued for the past 60 years. Therefore, we performed a prospective multicentre study assessing incidence and timing of spreading depolarizations and delayed ischaemic neurological deficit (DIND) in patients with major subarachnoid haemorrhage (SAH) requiring aneurysm surgery. Spreading depolarizations were recorded by electrocorticography with a subdural electrode strip placed on cerebral cortex for up to 10 days. A total of 2110 h recording time was analysed. The clinical state was monitored every 6 h. Delayed infarcts after SAH were verified by serial CT scans and/or MRI. Electrocorticography revealed 298 spreading depolarizations in 13 of the 18 patients (72%). A clinical DIND was observed in seven patients 7.8 days (7.3, 8.2) after SAH. DIND was time-locked to a sequence of recurrent spreading depolarizations in every single case (positive and negative predictive values: 86 and 100%, respectively). In four patients delayed infarcts developed in the recording area. As in the ischaemic penumbra of animals, delayed infarction was preceded by progressive prolongation of the electrocorticographic depression periods associated with spreading depolarizations to >60 min in each case. This study demonstrates that spreading depolarizations have a high incidence in major SAH and occur in ischaemic stroke. Repeated spreading depolarizations with prolonged depression periods are an early indicator of delayed ischaemic brain damage after SAH. In view of experimental evidence and the present clinical results, we suggest that spreading depolarizations with prolonged depressions are a promising target for treatment development in SAH and ischaemic stroke.

Carbamazepine-resistance in the epileptic dentate gyrus of human hippocampal slices.

Overexpression of drug efflux pumps at the blood brain barrier (BBB) has been suggested to be one important factor contributing to drug resistance in epilepsy. This would imply that resected brain tissue of drug-resistant patients is drug-sensitive in absence of the BBB. Here we studied the effects of carbamazepine (CBZ) at therapeutically relevant concentration on epileptiform activity electrophysiologically recorded in acute hippocampal slices of patients with mesial temporal lobe epilepsy (MTLE; 28 patients, 49 slices) or extra-hippocampal tumours (tumour; 6 patients, 11 slices). Epileptiform activity was induced by hilar stimulation (0.067 Hz) during elevation of extracellular potassium concentration ([K(+)](o)) and remained self-sustained in presence of 10-12 mM [K(+)](o). Quantitative analysis of data revealed that epileptiform activity in tissue of tumour-patients was predominantly suppressed by CBZ, indicating that the 'epilepsy model' used is CBZ-sensitive. In contrast, epileptiform activity in tissue of drug-resistant MTLE patients was resistant to CBZ in 82% of patients, partially suppressed in 11% and completely suppressed in 7%. The effects of CBZ in tissue of MTLE patients did not depend on the type of activity, hippocampal pathology, excitability of the tissue, or equilibration time of the drug. Considering that CBZ has direct access to all compartments of the slice, our results suggest that CBZ-resistance mechanisms are located within the parenchyma of the dentate gyrus and contribute to drug resistance in the majority of MTLE patients. BBB-located drug-resistance mechanisms per se may play a minor role in this region, because CBZ-sensitivity was only observed in 7% of CBZ-resistant patients.

Perioperative fluctuations of lamotrigine serum levels in patients undergoing epilepsy surgery.

UNLABELLED: Some patients undergoing epilepsy surgery suffer from early postoperative seizures which may have a negative impact on later outcome. Factors contributing to these seizures have not to date been examined systematically. We hypothesized that reduction of postoperative serum levels of antiepileptic drugs (AED) may be one risk factor for early postoperative seizures. METHODS: We retrospectively reviewed medical records from 20 patients treated with lamotrigine (LTG) who underwent epilepsy surgery between January 1997 and February 2004. Demographic data, anaesthesiological and surgical procedures, co-medication, and pre- as well as one or more postoperative LTG serum levels were evaluated. RESULTS: We found a significant decrease in LTG serum levels, amounting to more than 20% (mean 46%, range 21.9-69.1%), in 16 of 20 patients (80%). Six patients (30%) suffered from seizures in the first 2 weeks after surgery. In three patients, postoperative seizures occurred isochronically with the LTG serum level nadir. The magnitude of the reduction in serum levels was not influenced by age, sex, duration of the operation, the type of anaesthetic drugs or the postoperative co-medication. DISCUSSION: Reductions in LTG serum levels are a relevant contributing factor for early postoperative seizures. Postoperative alteration of the gastrointestinal motility and transient time leading to delayed absorption and reduced bioavailability of AED may be a major risk factor. Therefore, close monitoring of postoperative LTG serum levels is necessary and should lead to a temporary dose augmentation and/or anticonvulsant co-medication with benzodiazepines in case of a pronounced reduction of serum levels.

Metabolic dysfunction during neuronal activation in the ex vivo hippocampus from chronic epileptic rats and humans.

Metabolic dysfunction has been implicated in the pathogenesis of temporal lobe epilepsy (TLE), but its manifestation during neuronal activation in the ex vivo hippocampus from TLE patients has not been shown. We characterized metabolic and mitochondrial functions in acute hippocampal slices from pilocarpine-treated, chronic epileptic rats and from pharmaco-resistant TLE patients. Recordings of NAD(P)H fluorescence indicated the status of cellular energy metabolism, and simultaneous monitoring of extracellular potassium concentration ([K+]o) allowed us to control the induction of neuronal activation. In control rats, electrical stimulation elicited biphasic NAD(P)H fluorescence transients that were characterized by a brief initial 'drop' and a subsequent prolonged 'overshoot' correlating to enhanced NAD(P)+ reduction. In chronic epileptic rats, overshoots were significantly smaller in area CA1, but not in the subiculum as compared to controls. In TLE patients, who were histopathologically classified in groups with and without Ammon's horn sclerosis (AHS, non-AHS), large drops and very small overshoots of NAD(P)H transients were observed in dentate gyrus, CA3, CA1 and subiculum. Nevertheless, monitoring mitochondrial membrane potential (DeltaPsi(m)) by mitochondria-specific, voltage-sensitive dye (rhodamine-123) revealed similar mitochondrial responses during neuronal activation with glutamate and protonophore application in area CA1 of control and chronic-epileptic rats. Applying confocal laser scanning microscopy, these findings were confirmed in individual neurons of AHS tissue, indicating a negative DeltaPsi(m) and activation-dependent mitochondrial depolarization. Our data demonstrate severe metabolic dysfunction during neuronal activation in the hippocampus from chronic epileptic rats and humans, although mitochondria maintain negative DeltaPsi(m). Thus, our findings provide a cellular correlate for 'hypometabolism' as described for epilepsy patients and suggest mitochondrial enzyme defects in TLE.

Stimulus and potassium-induced epileptiform activity in the human dentate gyrus from patients with and without hippocampal sclerosis.

Hippocampal specimens resected to cure medically intractable temporal lobe epilepsy (TLE) provide a unique possibility to study functional consequences of morphological alterations. One intriguing alteration predominantly observed in cases of hippocampal sclerosis is an uncommon network of granule cells monosynaptically interconnected via aberrant supragranular mossy fibers. We investigated whether granule cell populations in slices from sclerotic and nonsclerotic hippocampi would develop ictaform activity when challenged by low-frequency hilar stimulation in the presence of elevated extracellular potassium concentration (10 and 12 mm) and whether the experimental activity differs according to the presence of aberrant mossy fibers. We found that ictaform activity could be evoked in slices from sclerotic and nonsclerotic hippocampi (27 of 40 slices, 14 of 20 patients; and 11 of 22 slices, 6 of 12 patients, respectively). However, the two patient groups differed with respect to the pattern of ictaform discharges and the potassium concentration mandatory for its induction. Seizure-like events were already induced with 10 mm K+. They exclusively occurred in slices from sclerotic hippocampi, of which 80% displayed stimulus-induced oscillatory population responses (250-300 Hz). In slices from nonsclerotic hippocampi, atypical negative field potential shifts were predominantly evoked with 12 mm K+. In both groups, the ictaform activity was sensitive to ionotropic glutamate receptor antagonists and lowering of [Ca2+]o. Our results show that, in granule cell populations of hippocampal slices from TLE patients, high K+-induced seizure-like activity and ictal spiking coincide with basic electrophysiological abnormalities, hippocampal sclerosis, and mossy fiber sprouting, suggesting that network reorganization could play a crucial role in determining type and threshold of such activity.

Increased extracellular K+ concentration reduces the efficacy of N-methyl-D-aspartate receptor antagonists to block spreading depression-like depolarizations and spreading ischemia.

BACKGROUND AND PURPOSE: Spreading depression (SD)-like depolarizations may augment neuronal damage in neurovascular disorders such as stroke and traumatic brain injury. Spreading ischemia (SI), a particularly malignant variant of SD-like depolarization, is characterized by inverse coupling between the spreading depolarization wave and cerebral blood flow. SI has been implicated in particular in the pathophysiology of subarachnoid hemorrhage. Under physiological conditions, SD is blocked by N-methyl-D-aspartate receptor (NMDAR) antagonists. However, because both SD-like depolarizations and SI occur in presence of an increased extracellular K+ concentration ([K+]o), we tested whether this increase in baseline [K+]o would reduce the efficacy of NMDAR antagonists. METHODS: Cranial window preparations, laser Doppler flowmetry, and K+-sensitive/reference microelectrodes were used to record SD, SD-like depolarizations, and SI in rats in vivo; microelectrodes and intrinsic optical signal measurements were used to record SD and SD-like depolarizations in human and rat brain slices. RESULTS: In vivo, the noncompetitive NMDAR antagonist dizocilpine (MK-801) blocked SD propagation under physiological conditions, but did not block SD-like depolarizations or SI under high baseline [K+]o. Similar results were found in human and rat neocortical slices with both MK-801 and the competitive NMDAR antagonist D-2-amino-5-phosphonovaleric acid. CONCLUSIONS: Our data suggest that elevated baseline [K+]o reduces the efficacy of NMDAR antagonists on SD-like depolarizations and SI. In conditions of moderate energy depletion, as in the ischemic penumbra, or after subarachnoid hemorrhage, NMDAR inhibition may not be sufficient to block these depolarizations.

Tumor-necrosis-factor-related apoptosis-inducing-ligand (TRAIL)-mediated death of neurons in living human brain tissue is inhibited by flupirtine-maleate.

Neuronal damage mediated by the TRAIL-system might be involved in the pathogenesis of neuroinflammatory diseases of the central nervous system. Here we used an investigator-independent approach to quantify TRAIL-mediated death of total CNS cells and neurons in a living human brain slice culture system, a model which is much closer to the in vivo situation than dissociated cell culture. We observed dose-dependent TRAIL-mediated death of both total human CNS cells and neurons, which was prevented by flupirtine-maleate, a centrally acting analgesic drug with proposed neuroprotective properties. Our data suggest flupirtine-maleate as an orally available neuroprotective approach in the course of neuroinflammation.

Drug resistance in cortical and hippocampal slices from resected tissue of epilepsy patients: no significant impact of p-glycoprotein and multidrug resistance-associated proteins.

Drug resistant patients undergoing epilepsy surgery have a good chance to become sensitive to anticonvulsant medication, suggesting that the resected brain tissue is responsible for drug resistance. Here, we address the question whether P-glycoprotein (Pgp) and multidrug resistance-associated proteins (MRPs) expressed in the resected tissue contribute to drug resistance in vitro. Effects of anti-epileptic drugs [carbamazepine (CBZ), sodium valproate, phenytoin] and two unspecific inhibitors of Pgp and MRPs [verapamil (VPM) and probenecid (PBN)] on seizure-like events (SLEs) induced in slices from 35 hippocampal and 35 temporal cortex specimens of altogether 51 patients (161 slices) were studied. Although in slice preparations the blood brain barrier is not functional, we found that SLEs predominantly persisted in the presence of anticonvulsant drugs (90%) and also in the presence of VPM and PBN (86%). Following subsequent co-administration of anti-epileptic drugs and drug transport inhibitors, SLEs continued in 63% of 143 slices. Drug sensitivity in slices was recognized either as transition to recurrent epileptiform transients (30%) or as suppression (7%), particularly by perfusion with CBZ in PBN containing solutions (43, 9%). Summarizing responses to co-administration from more than one slice per patient revealed that suppression of seizure-like activity in all slices was only observed in 7% of patients. Patients whose tissue was completely or partially sensitive (65%) presented with higher seizure frequencies than those with resistant tissue (35%). However, corresponding subgroups of patients do not differ with respect to expression rates of drug transporters. Our results imply that parenchymal MRPs and Pgp are not responsible for drug resistance in resected tissue.