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Uwe Heinemann

Publications and source records attributed to Uwe Heinemann.

At least 37 records · Page 2Linked to original sources
PubMed2005

Mitochondrial calcium ion and membrane potential transients follow the pattern of epileptiform discharges in hippocampal slice cultures.

Emerging evidence suggests that mitochondrial dysfunction contributes to the pathophysiology of epilepsy. Recurrent mitochondrial Ca2+ ion load during seizures might act on mitochondrial membrane potential (DeltaPsim) and proton motive force. By using electrophysiology and confocal laser-scanning microscopy, we investigated the effects of epileptiform activity, as induced by low-Mg2+ ion perfusion in hippocampal slice cultures, on changes in DeltaPsim and in mitochondrial Ca2+ ion concentration ([Ca2+]m). The mitochondrial compartment was identified by monitoring DeltaPsim in the soma and dendrites of patched CA3 pyramidal cells using the mitochondria-specific voltage-sensitive dye rhodamine-123 (Rh-123). Interictal activity was accompanied by localized mitochondrial depolarization that was restricted to a few mitochondria in small dendrites. In contrast, robust Rh-123 release into the cytosol was observed during seizure-like events (SLEs), indicating simultaneous depolarization of mitochondria. This was critically dependent on Ca2+ ion uptake and extrusion, because inhibition of the mitochondrial Ca2+ ion uniporter by Ru360 and the mitochondrial Na+/Ca2+ ion exchanger by 7-chloro-5-(2-chlorophenyl)-1,5-dihydro-4,1-benzothiazepin-2(3H)-one but not the inhibitor of mitochondrial permeability transition pore, cyclosporin A, decreased the SLE-associated mitochondrial depolarization. The Ca2+ ion dependence of simultaneous mitochondrial depolarization suggested enhanced Ca2+ ion cycling across mitochondrial membranes during epileptiform activity. Indeed, [Ca2+]m fluctuated during interictal activity in single dendrites, and these fluctuations spread over the entire mitochondrial compartment during SLEs, as revealed using mitochondria-specific dyes (rhod-2 and rhod-ff) and spatial frequency-based image analysis. These findings strengthen the hypothesis that epileptic activity results in Ca2+ ion-dependent changes in mitochondrial function that might contribute to the neuronal injury during epilepsy.

Animals↗
PubMed2005

Cellular and network properties of the subiculum in the pilocarpine model of temporal lobe epilepsy.

The subiculum was recently shown to be crucially involved in the generation of interictal activity in human temporal lobe epilepsy. Using the pilocarpine model of epilepsy, this study examines the anatomical substrates for network hyperexcitability recorded in the subiculum. Regular- and burst-spiking subicular pyramidal cells were stained with fluorescence dyes and reconstructed to analyze seizure-induced alterations of the dendritic and axonal system. In control animals burst-spiking cells outnumbered regular-spiking cells by about two to one. Regular- and burst-spiking cells were characterized by extensive axonal branching and autapse-like contacts, suggesting a high intrinsic connectivity. In addition, subicular axons projecting to CA1 indicate a CA1-subiculum-CA1 circuit. In the subiculum of pilocarpine-treated rats we found an enhanced network excitability characterized by spontaneous rhythmic activity, polysynaptic responses, and all-or-none evoked bursts of action potentials. In pilocarpine-treated rats the subiculum showed cell loss of about 30%. The ratio of regular- and burst-spiking cells was practically inverse as compared to control preparations. A reduced arborization and spine density in the proximal part of the apical dendrites suggests a partial deafferentiation from CA1. In pilocarpine-treated rats no increased axonal outgrowth of pyramidal cells was observed. Hence, axonal sprouting of subicular pyramidal cells is not mandatory for the development of the pathological events. We suggest that pilocarpine-induced seizures cause an unmasking or strengthening of synaptic contacts within the recurrent subicular network.

Animals↗
PubMed2005

The metabotropic glutamate receptor mGluR3 is critically required for hippocampal long-term depression and modulates long-term potentiation in the dentate gyrus of freely moving rats.

Group II metabotropic glutamate receptors (mGluRs) play an important role in the regulation of hippocampal synaptic plasticity in vivo: long-term potentiation (LTP) is inhibited and long-term depression (LTD) is enhanced by activation of these receptors. The contribution, in vivo, of the individual group II mGluR subtypes has not been characterized. We analysed the involvement of the subtype mGluR3 in LTD and LTP. Rats were implanted with electrodes to enable chronic measurement of evoked potentials from medial perforant path-dentate gyrus synapses. Neither the selective mGluR3 agonist, N-acetylaspartylglutamate (NAAG), nor the antagonist beta-NAAG, given intracerebrally, affected basal synaptic transmission. beta-NAAG significantly inhibited LTD expression. NAAG exhibited transient inhibitory effects on the intermediate phase of LTD. Whereas NAAG altered paired-pulse responses, beta-NAAG had no effect, suggesting that antagonism of mGluR3 prevents LTD via a postsynaptic mechanism, whereas agonist activation of mGluR3 modulates LTD at a presynaptic locus. NAAG impaired the expression of LTP, whereas beta-NAAG had no effect. NAAG effects on LTP were blocked by EGLU, a selective group II mGluR antagonist. Our data suggest an essential role for mGluR3 in LTD, and a modulatory role for mGluR3 in LTP, with effects being mediated by distinct pre- and post-synaptic loci.

Animals↗
PubMed2005

Persistent BBB disruption may underlie alpha interferon-induced seizures.

Generalized seizures during Interferon-alpha (IFN-alpha) therapy have been repeatedly described in about 1%-4% of patients. However, the mechanisms underlying IFN-alpha induced seizures are not known. We describe a patient who developed partial and secondary generalized seizures during IFN-alpha therapy while displaying a focal disruption of her blood-brain barrier (BBB) corresponding with pathological electroencephalography (EEG). To test our hypothesis that IFN-alpha induces seizure activity, we exposed rat somatosensory cortices to clinically relevant concentrations of IFN-alpha in the acute in-vitro slice preparation or in-vivo. While acute exposure did not induce epileptic activity, recordings from slices exposed to IFN-alpha in-vivo one week prior to recordings revealed pronounced epileptiform activity in > 80% of the slices. We propose that cortical exposure to IFN-alpha leads to the generation of an epileptic cortex, which explains the weeks of latency in patients from initial treatment to seizures, and stressing the importance of identifying possible BBB disruption among high-risk patients administered peripherally acting drugs.

Action Potentials↗
PubMed2005

Electrical and chemical long-term depression do not attenuate low-Mg2+-induced epileptiform activity in the entorhinal cortex.

PURPOSE: Low-frequency electrical and magnetic stimulation of cortical brain regions has been shown to reduce cortical excitability and to decrease the susceptibility to seizures in humans and in vivo models of epilepsy. The induction of long-term depression (LTD) or depotentiation of a seizure-related long-term potentiation has been proposed to be part of the underlying mechanism. With the low-Mg(2+)-model of epilepsy, this study investigated the effect of electrical LTD, chemical LTD, and depotentiation on the susceptibility of the entorhinal cortex to epileptiform activity. METHODS: The experiments were performed on isolated entorhinal cortex slices obtained from adult Wistar rats and mice. With extracellular recording techniques, we studied whether LTD induced by (a) three episodes of low-frequency paired-pulse stimulation (3 x 900 paired pulses at 1 Hz), and by (b) bath-applied N-methyl-D-aspartate (NMDA, 20 microM) changes time-to-onset, duration, and frequency of seizure-like events (SLEs) induced by omitting MgSO(4) from the artificial cerebrospinal fluid. Next we investigated the consequences of depotentiation on SLEs themselves by applying low-frequency stimulation after onset of low-Mg(2+)-induced epileptiform activity. RESULTS: LTD, induced either by low-frequency stimulation or by bath-applied NMDA, had no effect on time-to-onset, duration, and frequency of SLEs compared with unconditioned slices. Low-frequency stimulation after onset of SLEs did not suppress but induced SLEs that lasted for the time of stimulation and were associated with a simultaneous increase of the extracellular K(+) concentration. CONCLUSIONS: Our study demonstrates that neither conditioning LTD nor brief low-frequency stimulation decreases the susceptibility of the entorhinal cortex to low-Mg(2+)-induced epileptiform activity. The present study does not support the hypothesis that low-frequency brain stimulation exerts its anticonvulsant effect via the induction of LTD or depotentiation.

Animals↗
PubMed2005

Oxygen consumption and mitochondrial membrane potential indicate developmental adaptation in energy metabolism of rat cortical neurons.

Neuronal energy needs are mainly covered via mitochondrial oxidative phosphorylation. Even if the energy supply appears identical in immature and adult brain, nevertheless quantitative differences exist. The present study focuses on the adaptations in cellular energy metabolism caused by the neuronal maturation. As main parameters of oxidative phosphorylation, cellular oxygen consumption and mitochondrial membrane potential were measured in isolated rat cortical cells using a Clark-type oxygen electrode and microfluorometric techniques. In four age groups (E18-P2, P8-P12, P16-P20, > or = P28), unstimulated neurons showed a significant age-dependent increase in basal oxygen consumption (6.1 up to 10.2 nM/min/10(7) cells). The excitatory neurotransmitter glutamate induced a further, but age- and concentration-independent, elevation of oxygen consumption to a plateau > or = 14 nM/min/10(7) cells and a complete depolarization of mitochondrial membrane in neurons > or = P8. Stimulation using K+ (5-50 mM) effected a concentration- and age-dependent increase in oxygen consumption, but a similar nearby complete depolarization of mitochondrial membrane in all tested age groups. Furthermore, uncoupling mitochondrial membrane function followed by a complete depolarization of mitochondrial membrane showed a maximal oxygen consumption (14-15 nM/min/10(7) cells) only in neurons > or = P8. These data suggest that developing and adult cortical neurons cover their increased need of energy following stimulation by an efficiency improvement of mitochondrial oxidative phosphorylation. The age-independent limited capacity of mitochondrial oxidative phosphorylation, however, causes a reduction in cellular energy disposal in mature neurons and therefore may play a critical role in the increased sensitivity of adult neurons against excitotoxicity and ischaemia.

Animals↗
PubMed2005

The subiculum: a potential site of ictogenesis in human temporal lobe epilepsy.

PURPOSE: This study determines synaptic and intrinsic alterations of subicular pyramidal cells that are associated with activity recorded in patients suffering from temporal lobe epilepsy. METHODS: Electroencephalograms with sphenoidal electrodes were correlated with in vitro single cell recordings of subicular pyramidal cells from the corresponding resected epileptic tissue. We determined alterations of synaptic and intrinsic properties of subicular pyramidal cells that accompany spontaneous rhythmic activity in human sclerotic and nonsclerotic epileptic tissue. RESULTS: We found that in sclerotic, but also in nonsclerotic hippocampal tissue, the subiculum showed cellular and synaptic changes that were associated with spontaneous rhythmic activity correlated to the occurrence and frequency of interictal discharges recorded in the electroencephalograms of the corresponding patients. CONCLUSIONS: Even though Ammon's horn sclerosis (AHS) in resected hippocampi from patients suffering from temporal lobe epilepsy has important prognostic implications for freedom from seizures postoperatively, we report here that both synaptic and intrinsic alterations enhance seizure susceptibility of the subiculum also in the absence of classical AHS.

Adult↗
PubMed2004

Glutamate transporters and metabotropic receptors regulate excitatory neurotransmission in the medial entorhinal cortex of the rat.

In layer III of the medial entorhinal cortex (mEC), a region that is especially prone to cell damage in Alzheimer's disease, schizophrenia and epilepsy, effects of blocking glutamate uptake on excitatory synaptic transmission were studied. Two competitive glutamate transporter antagonists, TBOA and tPDC, reduced the amplitude of pharmacologically isolated AMPAR and NMDAR mediated EPSPs/EPSCs without changing the time course of the events. This effect was mimicked by tACPD, an agonist of groups I and II metabotropic glutamate receptors (mGluRs). The competitive groups I and II mGluR antagonist MCPG blocked the depression of the EPSC amplitude induced by tACPD and also prevented the effect of either TBOA or tPDC. Furthermore, EGLU, which selectively antagonizes group II mGluRs, blocked the effect of tPDC and LY3414965, a specific group I mGluR antagonist, abolished the reduction of amplitude caused by TBOA. Additionally, application of TBOA increased the paired-pulse index, suggesting a presynaptic mechanism for the depression of EPSP/EPSC amplitude. The present data suggest that glutamate transporters and group I/II mGluRs regulate excitatory synaptic transmission in the mEC. Presynaptic mGluRs may limit excessive glutamate accumulation if uptake becomes compromised.

Amino Acid Transport System X-AG↗
PubMed2004

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.

Adult↗
PubMed2004

Differential involvement of oriens/pyramidale interneurones in hippocampal network oscillations in vitro.

Using whole-cell patch-clamp recordings in conjunction with post hoc anatomy we investigated the physiological properties of hippocampal stratum oriens and stratum pyramidale inhibitory interneurones, before and following the induction of pharmacologically evoked gamma frequency network oscillations. Prior to kainate-induced transient epochs of gamma activity, two distinct classes of oriens interneurones, oriens lacunosum-moleculare (O-LM) and trilaminar cells, showed prominent differences in their membrane and firing properties, as well as in the amplitude and kinetics of their excitatory postsynaptic events. In the active network both types of neurone received a phasic barrage of gamma frequency excitatory inputs but, due to their differential functional integration, showed clear differences in their output patterns. While O-LM cells fired intermittently at theta frequency, trilaminar interneurones discharged on every gamma cycle and showed a propensity to fire spike doublets. Two other classes of fast spiking interneurones, perisomatic targeting basket and bistratified cells, in the active network discharged predominantly single action potentials on every gamma cycle. Thus, within a locally excited network, O-LM cells are likely to provide a theta-frequency patterned output to distal dendritic segments, whereas basket and bistratified cells are involved in the generation of locally synchronous gamma band oscillations. The anatomy and output profile of trilaminar cells suggest they are involved in the projection of locally generated gamma rhythms to distal sites. Therefore a division of labour appears to exist whereby different frequencies and spatiotemporal properties of hippocampal rhythms are mediated by different interneurone subtypes.

Animals↗
PubMed2004

Expression analysis of members of the neuronal calcium sensor protein family: combining bioinformatics and Western blot analysis.

We have used in silico mining of public databases (NCBI UniGene and NCI SAGE Anatomic Viewer) as a tool to obtain the tissue distribution pattern of three members of the neuronal calcium sensor protein family, namely VILIP-1, hippocalcin, and NCS-1 in humans. The theoretical human mRNA expression profile of the calcium sensor proteins derived from expressed sequence tag (EST) and serial analysis of gene expression (SAGE) data was compared with expression data from human tissues obtained by Western blot analysis. Since the EST databank searches do not yet give comparable results for rat which is often used as model animal, we have also analyzed the protein expression in rat tissues. Similar to the human expression profile in rat tissues calcium sensor proteins are mainly detected in the nervous system, but the data consistently implicated the additional expression in peripheral tissues with remarkable differences between the calcium sensor proteins.

Animals↗
PubMed2004

Lasting blood-brain barrier disruption induces epileptic focus in the rat somatosensory cortex.

Perturbations in the integrity of the blood-brain barrier have been reported in both humans and animals under numerous pathological conditions. Although the blood-brain barrier prevents the penetration of many blood constituents into the brain extracellular space, the effect of such perturbations on the brain function and their roles in the pathogenesis of cortical diseases are unknown. In this study we established a model for focal disruption of the blood-brain barrier in the rat cortex by direct application of bile salts. Exposure of the cerebral cortex in vivo to bile salts resulted in long-lasting extravasation of serum albumin to the brain extracellular space and was associated with a prominent activation of astrocytes with no inflammatory response or marked cell loss. Using electrophysiological recordings in brain slices we found that a focus of epileptiform discharges developed within 4-7 d after treatment and could be recorded up to 49 d postoperatively in >60% of slices from treated animals but only rarely (10%) in sham-operated controls. Epileptiform activity involved both glutamatergic and GABAergic neurotransmission. Epileptiform activity was also induced by direct cortical application of native serum, denatured serum, or albumin-containing solution. In contrast, perfusion with serum-adapted electrolyte solution did not induce abnormal activity, thereby suggesting that the exposure of the serum-devoid brain environment to serum proteins underlies epileptogenesis in the blood-brain barrier-disrupted cortex. Although many neuropathologies entail a compromised blood-brain barrier, this is the first direct evidence that it may have a role in the pathogenesis of focal cortical epilepsy, a common neurological disease.

2-Amino-5-phosphonovalerate↗
PubMed2004

Subthreshold resonance explains the frequency-dependent integration of periodic as well as random stimuli in the entorhinal cortex.

Neurons integrate subthreshold inputs in a frequency-dependent manner. For sinusoidal stimuli, response amplitudes thus vary with stimulus frequency. Neurons in entorhinal cortex show two types of such resonance behavior: stellate cells in layer II exhibit a prominent peak in the resonance profile at stimulus frequencies of 5-16 Hz. Pyramidal cells in layer III show only a small impedance peak at low frequencies (1-5 Hz) or a maximum at 0 Hz followed by a monotonic decrease of the impedance. Whether the specific frequency selectivity for periodic stimuli also governs the integration of non-periodic stimuli has been questioned recently. Using frozen-noise stimuli with different distributions of power over frequencies, we provide experimental evidence that the integration of non-periodic subthreshold stimuli is determined by the same subthreshold frequency selectivity as that of periodic stimuli. Differences between the integration of noise stimuli in stellate and pyramidal cells can be fully explained by the resonance properties of each cell type. Response power thus reflects stimulus power in a frequency-selective way. Theoretical predictions based on linear system's theory as well as on conductance-based model neurons support this finding. We also show that the frequency selectivity in the subthreshold range extends to suprathreshold responses in terms of firing rate. Cells in entorhinal cortex are representative examples of cells with resonant or low-pass filter impedance profiles. It is therefore likely that neurons with similar frequency selectivity will process input signals according to the same simple principles.

Action Potentials↗
PubMed2004

Effects of phencyclidines on signal transfer from the entorhinal cortex to the hippocampus in rats.

The information transfer from the superficial layers of the entorhinal cortex (EC) to the hippocampus is regulated in a frequency dependent manner. Phencyclidine and related compounds such as MK-801 produce psychotic symptoms that closely resemble schizophrenia. We studied the effects of systemic administration of MK-801 on the signal transfer from the EC layer III to the hippocampal area CA1. High frequency (above 10 Hz) activation of the bi-synaptic entorhinal input in control animals results in a strong suppression of the field potentials in the stratum lacunosum-moleculare of the area CA1. In contrast, in MK-801 pretreated rats the field response was less reduced. The field potential responses evoked in these two groups of animals by high-frequency activation of the monosynaptic input were similar suggesting selective alterations in layer III of the medial EC. We suggest, that MK-801 causes disinhibition of layer III projection cells and, therefore, may cause strong, pathological activation of direct layer III-CA1 pathway.

Action Potentials↗
PubMed2004

Hyperoxia is not an essential condition for status epilepticus induced cell death in organotypic hippocampal slice cultures.

The low Mg2+ model of epilepsy in organotypic hippocampal slice cultures is used to elucidate the mechanism underlying neuronal cell death following sustained epileptiform activity. However, the high oxygen tension of 95% widely used in this model is capable of inducing neuronal cell death by itself. Here we demonstrate that even under normoxic conditions 1h of epileptiform activity induced neuronal cell death as assessed by Propidium Iodide uptake. We conclude that hyperoxia is not essential for status epilepticus induced neuronal cell death in this model.

Animals↗
PubMed2004

Basic mechanisms of partial epilepsies.

PURPOSE OF REVIEW: Partial epilepsies are characterized by cell loss with consequences for neuronal organization, excitability, mnestic and cognitive functions and present with pharmaco-resistance and difficulties in clinical management. While mesial temporal lobe epilepsies present frequently with cell loss and neuronal reorganization, neocortical epilepsies frequently involve developmental alterations. RECENT FINDINGS: There is increasing evidence that nerve cells in epileptic tissue become more vulnerable to excitotoxic cell death due to impairment of mitochondrial functions and that free radical formation is critically involved in these processes. Whether and to what extent such alterations contribute to pharmaco-resistance is unclear. However, at least three mechanisms may contribute to pharmaco-resistance: changes in target molecules for antiepileptic drugs, upregulation of drug transporters, and potentially reorganization processes in inhibitory networks. Upregulation of drug transporters also seems to be involved in pharmaco-resistance of developmental alterations underlying focal epilepsies. Recent data from the literature suggest that transgenic models for disturbances of cortical development may be useful models for the study of these variable forms of partial epilepsies. SUMMARY: The data suggest that improvement of therapy could result from free radical scavenging and from manipulation of drug transport into the affected tissue. New models of developmental epilepsies may help us to understand mechanisms underlying increased vulnerability to seizures as well as improving strategies for treatment.

Anticonvulsants↗
PubMed2004

Characterization of the inhibitory glycine receptor on entorhinal cortex neurons.

In addition to the well-established functional description of the glycine receptor (GlyR) in the spinal cord, GlyR expression has recently been found in higher brain regions, such as the striatum or hippocampus. In this study we have investigated the electrophysiological response of glycine in the rat entorhinal cortex slice. In all recorded cells we found significant current responses to glycine with an EC(50) value of about 100 micro m. Most importantly, we detected a cross-inhibition of glycine responses by GABA but not vice versa. These findings are in line with recent published data of cross-talks between GABA(A)R and GlyR but indicate a novel type of cross-inhibition of these receptors in the entorhinal cortex.

Animals↗