Biomedical subjects

H Beck

Publications and source records attributed to H Beck.

At least 37 records · Page 2Linked to original sources

PubMed2000

Expression of connexin genes in hippocampus of kainate-treated and kindled rats under conditions of experimental epilepsy.

We have analyzed whether the expression of connexin genes is altered in the hippocampus of kindled and kainate-treated rats, i.e., animal models of human temporal lobe epilepsy. We have tested this hypothesis by analyzing mRNA, protein abundance and cellular location of connexins (Cx) 43, 36, 32 and 30. The expression of glial fibrillary acid protein and mRNA was also monitored both in kainate-treated and kindled rats, in order to take into account reactive gliosis under these conditions. We found significantly increased expression of GFAP mRNA (100%) and protein (178%) in kainate-treated rats 4 weeks after kainate application, whereas in kindled rats only moderate increases of GFAP mRNA and protein were detected 2-3 weeks (group 2) or 4-6 weeks (group 1) after the last stage 5 induced seizure. Under gliotic conditions, connexins 43 and 30 mRNA or protein expression in astrocytes of kainate-treated rats were nearly unaffected. Cx36 mRNA expression (presumably in neurons) was significantly reduced (44%), whereas abundance of Cx36 protein was only slightly reduced. In both groups of kindled rats, Cx30 and Cx43 mRNA or protein expression were either slightly decreased or unchanged. Again, Cx36 mRNA and protein expression were reduced by about half in group 2. Immunofluorescence analysis of Cx43, Cx36 and Cx30 expression revealed that 4 weeks after the last kainate administration or kindling, cellular localization of these connexins was indistinguishable from control animals.

Animals↗

PubMed2000

New method to improve treatment outcomes for radical prostatectomy.

Modifications in radical retropubic prostatectomy that use the deep dorsal vein ligator and either anterior urethropexy or puboprostatic ligament preservation were developed to reduce blood loss and improve continence results. Use of the deep dorsal vein ligator to secure the deep dorsal vein complex also improves visualization of the urethra for transection and the neurovascular bundle for nerve sparing and thereby may assist in laparoscopic radical retropubic prostatectomy.

Aged↗

PubMed2000

Synaptic plasticity in the human dentate gyrus.

Activity-dependent plasticity is a fundamental feature of most CNS synapses and is thought to be a synaptic correlate of memory in rodents. In humans, NMDA receptors have been linked to verbal memory processes, but it is unclear whether NMDA receptor-dependent synaptic plasticity can be recruited for information storage in the human CNS. Here we have for the first time analyzed different forms of synaptic plasticity in human hippocampus. In human subjects who show a morphologically intact hippocampus that is not the primary seizure focus, NMDA receptor-dependent long-term potentiation (LTP) and forskolin-induced long-lasting potentiation are readily induced at the perforant path-dentate gyrus synapse. In this group, long-term potentiation could be partially depotentiated by low-frequency stimulation. Because patients with a hippocampal seizure focus showed a marked reduction in verbal memory performance in previous studies, we asked whether synaptic plasticity is similarly affected by the presence of a hippocampal primary seizure focus. We found that the amount of potentiation induced by high-frequency stimulation or perfusion of forskolin is dramatically reduced in this patient group. In addition, low-frequency stimulation is not effective in inducing synaptic depression. In summary, we show that activity-dependent synaptic plasticity with properties similar to the rodent is available for information storage in the human hippocampus. Because both verbal memory processes and synaptic plasticity are impaired by a hippocampal seizure focus, we suggest that impaired synaptic plasticity may contribute to deficient declarative memory in human temporal lobe epilepsy.

1-Methyl-3-isobutylxanthine↗

PubMed2000

First-order transition in the ginzburg-landau model

The d-dimensional complex Ginzburg-Landau (GL) model is solved according to a variational method by separating phase and amplitude. The GL transition becomes first order for high superfluid density because of phase fluctuations. We discuss its origin with various arguments showing that, in particular for d = 3, the validity of our approach lies precisely in the first-order domain.

Journal Article↗

PubMed2000

Metaplasticity of mossy fiber synaptic transmission involves altered release probability.

Activity-dependent synaptic plasticity is a fundamental feature of CNS synapses. Intriguingly, the capacity of synapses to express plastic changes is itself subject to considerable activity-dependent variation, or metaplasticity. These forms of higher order plasticity are important because they may be crucial to maintain synapses within a dynamic functional range. In this study, we asked whether neuronal activity induced in vivo by application of kainate can induce lasting changes in mossy fiber short- and long-term plasticity. Several weeks after kainate-induced status epilepticus, the mossy fiber, but not the associational-commissural pathway, exhibits a marked loss of paired-pulse facilitation, augmentation, and long-term potentiation (LTP). Because the adenylyl cyclase-protein kinase A cascade is involved in mossy fiber LTP induction, we have tested the integrity of this key pathway by pharmacological activation of either adenylyl cyclase or protein kinase A. These treatments resulted in LTP in control, but not in kainate-treated animals, indicating that status-induced changes occur downstream of protein kinase A. To test whether altered neurotransmitter release might account for these changes, we measured the size of the releasable pool of glutamate in mossy fiber terminals. We find that the size of the releasable pool of glutamate was significantly increased in kainate-treated rats, indicating an increased release probability at the mossy fiber-CA3 synapse. Therefore, we suggest that lasting changes in neurotransmitter release probability caused by neuronal activity may be a powerful mechanism for metaplasticity that modulates both short- and long-term plasticity in the mossy fiber-CA3 synapse after status epilepticus.

Animals↗

PubMed2000

High regio-, chemo-, and stereoselectivity via low-temperature 4 + 3 cycloadditions. Convergent synthesis of multifunctionalized vinylmetals (M = Si, Sn) and S-vinyl benzenecarbothioates

A series of enantiomerically pure 8-oxabicyclo[3.2.1]oct-6-en-3-ones functionalized in the unsaturated two-carbon bridge has been prepared by the title reaction. Carbocation reactivity has been fined-tuned at -95 degrees C and adjusted to diene nucleophilicity. Conventional electrophilic substitution of 3-silylated and 3-stannylated furan is suppressed in favor of the rapid 4 + 3 cycloaddition mode. In the case of cycloadduct 13A, stereoselectivity (17:1) is perfectly matched to regioselectivity (17:1). High stereoselection as well as unprecedented regioselection and chemoselection is attributed to the low-temperature cycloaddition protocol and the design of chiral auxiliary and tether.

Journal Article↗

PubMed2000

Surviving granule cells of the sclerotic human hippocampus have reduced Ca(2+) influx because of a loss of calbindin-D(28k) in temporal lobe epilepsy.

In mesial temporal lobe epilepsy (mTLE), the predominant form of epilepsy in adults, and in animal models of the disease, there is a conspicuous loss of the intracellular Ca(2+)-binding protein calbindin-D(28k) (CB) from granule cells (GCs) of the dentate gyrus. The role of this protein in nerve cell function is controversial, but here we provide evidence for its role in controlling Ca(2+) influx into human neurons. In patients with Ammon's horn sclerosis (AHS), the loss of CB from GCs markedly increased the Ca(2+)-dependent inactivation of voltage-dependent Ca(2+) currents (I(Ca)), thereby diminishing Ca(2+) influx during repetitive neuronal firing. Introducing purified CB into GCs restored Ca(2+) current inactivation to levels observed in cells with normal CB content harvested from mTLE patients without AHS. Our data are consistent with the possibility of neuroprotection secondary to the CB loss. By limiting Ca(2+) influx through an enhanced Ca(2+)-dependent inactivation of voltage-dependent Ca(2+) channels during prolonged neuronal discharges, the loss of CB may contribute to the resistance of surviving human granule cells in AHS.

Action Potentials↗

PubMed2000

Expression of angiopoietin-1, angiopoietin-2, and tie receptors after middle cerebral artery occlusion in the rat.

Vascular endothelial growth factor (VEGF), a key regulator of vasculogenesis and embryonic angiogenesis, was recently found to be up-regulated in an animal model of stroke. Unlike VEGF, angiopoietin (Ang)-1 and -2, their receptor tie-2, and the associated receptor tie-1 exert their functions at later stages of vascular development, i.e., during vascular remodeling and maturation. To assess the role of the angiopoietin/tie family in ischemia-triggered angiogenesis we analyzed their temporal and spatial expression pattern after middle cerebral artery occlusion (MCAO) using in situ hybridization and immunohistochemistry. Ang-1 mRNA was constitutively expressed in a subset of glial and neuronal cells with no apparent change in expression after MCAO. Ang-2 mRNA was up-regulated 6 hours after MCAO and was mainly observed in endothelial cell (EC) cord tips in the peri-infarct and infarct area. Up-regulation of both Ang-2 and VEGF coincided with EC proliferation. Interestingly, EC proliferation was preceded by a transient period of EC apoptosis, correlating with a change in VEGF/Ang-2 balance. Our observation of specific stages of vascular regression and growth after MCAO are in agreement with recent findings suggesting a dual role of Ang-2 in blood vessel formation, depending on the availability of VEGF.

Angiopoietin-1↗

PubMed2000

Temporal lobe epilepsy associated up-regulation of metabotropic glutamate receptors: correlated changes in mGluR1 mRNA and protein expression in experimental animals and human patients.

Aberrant axonal reorganization and altered distribution of neurotransmitter receptor subtypes have been proposed as major pathogenic mechanisms for hippocampal hyperexcitability in chronic temporal lobe epilepsies (TLE). Recent data point to excitatory class I metabotropic glutamate receptors (mGluR1 and mGluR5) as interesting candidates. Here, we have analyzed the hippocampal distribution and mRNA expression of mGluR1 and mGluR5 in two rat models of limbic seizures, i.e. electrical kindling and intraperitoneal kainate injections, as well as in human TLE. Quantitative RT-PCR analysis detected a significant increase of hippocampal mGluR1 gene transcript levels in kainate treated and kindled rats. In addition, microdissected hippocampal tissue samples localized this increase to the dentate gyrus. Using immunohistochemistry with mGluR1alpha subtype specific antibodies, increased labeling was observed within the dentate gyrus molecular layer (DG-ML). A similar pattern of increased mGluR1alpha neuropil staining was found within the DG-ML of epilepsy patients (n = 42) compared with peritumoral hippocampus specimens obtained from nonepileptic patients (biopsy controls, n = 3). This increase was detected in TLE patients with segmental hippocampal cell loss, as well as in TLE patients with focal lesions but no histopathological alterations of the hippocampus. In contrast, mGluR5 immunoreactivity and mRNA expression were not significantly altered in the DG-ML. Our data demonstrate a striking regional induction of mGluR1alpha in the hippocampal dentate gyrus of experimental animals with limbic seizures as well as in human patients with chronic, intractable TLE. This increase corresponds to functional alterations of class I mGluRs observed in seizure models and may significantly contribute to hippocampal hyperexcitability in focal human epilepsies.

Adult↗

PubMed2000

Modulation of calcium channels by group I and group II metabotropic glutamate receptors in dentate gyrus neurons from patients with temporal lobe epilepsy.

PURPOSE: Metabotropic glutamate receptors (mGluRs) might be promising new drug targets for the treatment of epilepsy because the expression of certain mGluRs is regulated in epilepsy and because activation of mGluRs results in distinctive anti- and proconvulsant effects. Therefore, we examined how mGluR activation modulates high-voltage-activated (HVA) Ca2+ channels. METHODS: Whole-cell patch-clamp recordings were obtained from granule cells and interneuron-like cells acutely isolated from the dentate gyrus of patients with pharmacoresistent temporal lobe epilepsy. RESULTS: Agonists selective for either group I or group II mGluRs rapidly and reversibly reduced HVA currents in most dentate gyrus cells. These modulatory effects were inhibited by the respective group I and group II mGluR antagonists. The specific Ca2+ channel antagonists nifedipine and omega-conotoxin GVIA potently occluded the effects of group I and II mGluR agonists, respectively, indicating that group I mGluRs acted on L-type channels and group II mGluRs affected N-type channels. About two thirds of the responsive neurons were sensitive either to group I or group II mGluRs, whereas a minority of cells showed effects to agonists of both groups, indicating a variable mGluR expression pattern. CONCLUSIONS: Group I and group II mGluRs are expressed in human dentate gyrus neurons and modulate L- and N-type HVA channels, respectively. The data shed light on the possible cellular sequelae of the mGluR1 upregulation observed in human epileptic dentate gyrus as well as on possible mGluR-mediated anticonvulsant mechanisms.

Anticonvulsants↗

PubMed2000

Up-regulation of the metabotropic glutamate receptor mGluR4 in hippocampal neurons with reduced seizure vulnerability.

Selective hippocampal cell loss and altered neurotransmitter receptor expression have been proposed as pathogenic mechanisms in the development of chronic mesial temporal lobe epilepsy (TLE). Studies in animal models point to metabotropic glutamate receptors (mGluRs) as modulators of hippocampal epileptogenesis. In addition, mGluRs may constitute specific targets for the development of novel anticonvulsive drugs. As mGluR4 represents an inhibitory class III mGluR associated with the reduction of intracellular cyclic AMP levels and calcium influx, we have analyzed the regional and cellular expression of mGluR4 in surgical hippocampal specimens obtained from patients with TLE by using immunohistochemistry and in situ hybridization. Although the hippocampi of control specimens (n = 11) were almost devoid of mGluR4 immunolabeling, all TLE specimens (n = 35) showed a striking up-regulation of mGluR4 immunoreactivity, in particular within the dentate gyrus. Immunoelectron microscopy localized the receptor protein to the periphery of presynaptic and postsynaptic membranes. In situ hybridization revealed increased transcript levels of mGluR4 in dentate granule cells and residual CA4 neurons of TLE specimens compared with controls. Our results suggest a potential role of mGluR4 in counteracting excitatory hippocampal activity and in modulating seizure-associated vulnerability of hippocampal neurons. These data may also provide a basis for pharmacological studies of mGluR4 agonists as potential novel drugs in the treatment of TLE.

Adult↗

PubMed2000

Mitochondrial complex I deficiency in the epileptic focus of patients with temporal lobe epilepsy.

Mitochondria are cellular organelles crucial for energy supply and calcium homeostasis in neuronal cells, and their dysfunction causes seizure activity in some rare human epilepsies. To directly test whether mitochondrial respiratory chain enzymes are abnormal in the most common form of chronic epilepsy, temporal lobe epilepsy (TLE), living human brain specimens from 57 epileptic patients and 2 nonepileptic controls were investigated. In TLE patients with a hippocampal epileptic focus, we demonstrated a specific deficiency of complex I of the mitochondrial respiratory chain in the hippocampal CA3 region. In contrast, TLE patients with a parahippocampal epileptic focus showed reduced complex I activity only in parahippocampal tissue. Inhibitor titrations of the maximal respiration rate of intact human brain slices revealed that the observed reduction in complex I activity is sufficient to affect the adenosine triphosphate production rate. The abnormal complex I activity in the hippocampal CA3 region was paralleled by increased succinate dehydrogenase staining of neurons and marked ultrastructural abnormalities of mitochondria. Therefore, mitochondrial dysfunction is suggested to be specific for the epileptic focus and may constitute a pathomechanism contributing to altered excitability and selective neuronal vulnerability in TLE.

Adolescent↗

PubMed1999

Evidence relating human verbal memory to hippocampal N-methyl-D-aspartate receptors.

Studies in rodents and nonhuman primates have linked the activity of N-methyl-D-aspartate (NMDA) receptors within the hippocampus to animals' performance on memory-related tasks. However, whether these receptors are similarly essential for human memory is still an open question. Here we present evidence suggesting that hippocampal NMDA receptors, most likely within the CA1 region, do participate in human verbal memory processes. Words elicit a negative event-related potential (ERP) peaking around 400 ms within the anterior mesial temporal lobe (AMTL-N400). Ketamine, an NMDA-receptor antagonist, reduces the amplitude of the AMTL-N400 (in contrast to other hippocampal potentials) on initial presentation, eliminates the typical AMTL-N400 amplitude reduction with repetition, and leads to significant memory impairment. Of the various hippocampal subfields, only the density of CA1 neurons correlates with the word-related ERPs that are reduced by ketamine. Altogether, our behavioral, anatomical, and electrophysiological results indicate that hippocampal NMDA receptors are involved in human memory.

Adult↗

PubMed1999

A rapid method to separate endosomes from lysosomal contents using differential centrifugation and hypotonic lysis of lysosomes.

Here we describe a fast and efficient subcellular fractionation procedure that permits lysosomes to be separated from endosomes. Differential centrifugation is used to isolate a subcellular fraction containing both endosomes and lysosomes. Because lysosomes are sensitive to osmotic stress, hypotonic conditions destroy them, whereas endosomes, which are osmotically insensitive, stay intact. We demonstrate that hypotonic lysis of an endosome-lysosome-pool releases 85% of the lysosomes into the supernatant as measured by the activity of the lysosomal marker enzyme N-acetyl-beta-D-glucosaminidase (beta-AGA). The endosomal fraction is thoroughly characterised using a variety of subcellular markers. After pulsing cells with fluorescein isothiocyanate labelled transferrin (FITC-Tf), only about 12% of the marker is released under hypotonic conditions. A typical fractionation procedure takes about 1-2 h from initial cell homogenisation. The fractionation gives a pure lysosomal fraction (fraction L) containing high activities of lysosomal enzymes and an endosomal fraction (fraction E) reflecting different stages of endosomes.

Antigens, Differentiation, B-Lymphocyte↗

PubMed1999

Altered mitochondrial oxidative phosphorylation in hippocampal slices of kainate-treated rats.

Mitochondria provide the main neuronal energy supply and are important organelles for the sequestration of intracellular Ca2+. This indicates a possible important role for mitochondria in modulating neuronal excitability in normal function as well as in disease. Therefore, we have investigated mitochondrial oxidative phosphorylation in the kainate model of epilepsy. We measured the oxygen consumption of single 400-micron rat hippocampal slices applying high resolution respirometry and determined mitochondrial NAD(P)H autofluorescence signal changes in single slices by laser-excited fluorescence spectroscopy. We observed an about 2-fold higher (p<0.001) basal glucose oxidation rate in slices from kainate-treated animals. This increased endogenous energy consumption was found to be unrelated to spontaneous activity since it was not sensitive to the inhibitors of the sodium-potassium ATPase ouabain and of the mitochondrial adenine nucleotide translocator atractyloside. This finding suggested an increased mitochondrial energy turnover in kainate-induced epilepsy. Furthermore, the uncoupler-stimulated oxygen consumption of the slices was approximately 1.3-fold higher (p<0.01) in the kainate model. In accordance with the respirometric data, fluorescence spectroscopy showed decreased reduction levels of the mitochondrial NAD-system in glucose oxidizing slices from kainate-treated rats. The preincubation of epileptic hippocampal slices with either BAPTA AM, ruthenium red or TPP+ increased the atractyloside sensitivity of glucose oxidation to about 1.4-fold (p<0.01). These observations indicate that the increased mitochondrial energy turnover in hippocampal slices from kainate-treated rats is most possibly caused by futile Ca2+-cycling.

Animals↗

PubMed1999

Differential regulation of apoptosis-related genes in resistant and vulnerable subfields of the rat epileptic hippocampus.

Animals exposed to kainic acid (KA) induced status epilepticus display a striking pattern of selective neuronal vulnerability in the hippocampus. Neurons in the hilus/CA3 and CA1 subfields appear particularly sensitive whereas dentate gyrus (DG) granule cells are resistant. The molecular basis for this differential susceptibility remains largely unknown. Recently, an involvement of nitric oxide, c-Jun amino-terminal kinases (JNK) and interleukin-1 beta converting enzyme (ICE)-related proteases has been proposed in KA induced neuronal cell death. In the present study, we have determined the regional expression of transcripts for two modulating genes operating in these pathways, i.e., the endogenous protein inhibitor of neuronal nitric oxide synthase (PIN), and a cytoplasmic inhibitor of the JNK signal transduction pathway, designated JNK interacting protein-1 (JIP-1) and of the gene for the apoptosis-executing protease Caspase-3 in KA-treated animals. The expression of PIN and JIP-1 was found significantly upregulated in granule cells of the resistant DG. In contrast, an induction of the ICE-related protease Caspase-3 was observed in vulnerable hippocampal regions, i.e. CA1, CA3 and hilus. These results point towards PIN and JIP-1 as antiapoptotic factors contributing to selective resistance of granule cells, whereas Caspase-3 may be involved in cell death of hippocampal CA1, CA3 and hilar neurons in the kainate epilepsy model.

Adaptor Proteins, Signal Transducing↗

PubMed1999

An increase of hippocampal calretinin-immunoreactive neurons correlates with early febrile seizures in temporal lobe epilepsy.

Numerous studies indicate that initial precipitating injuries (IPI) such as febrile seizures during early childhood may play a pivotal role in the pathogenesis of temporal lobe epilepsy (TLE) and Ammon's horn sclerosis (AHS). Previous data demonstrate an increase of horizontally oriented neurons in molecular layers of hippocampal subfields, which are immunoreactive for calretinin (CR-ir) and resemble Cajal-Retzius-like cells. Cajal-Retzius cells are transiently expressed in the murine developing hippocampus and are critically involved in neuronal pattern formation. Here we investigated a potential relationship between the distribution of horizontally oriented calretinin-immunoreactive neurons and the clinical history of TLE patients with AHS. Horizontally oriented neurons in the molecular layer of the hippocampal formation have been visualized by antibodies against the calcium-binding proteins calretinin and calbindin D-28k. Cell counts derived from 27 epilepsy patients with AHS were compared with autopsy specimens from developing and adult normal human hippocampus (n = 26). During ontogeny, CR-ir cells showed a marked perinatal peak in the CA1 and dentate gyrus molecular layer (CA1-ML, DG-ML) followed by a gradual postnatal decline. In hippocampal specimens from TLE patients with AHS and seizure onset before the age of 4 years, significantly higher levels of CR-ir neurons in CA1-ML (P = 0.05) and DG-ML (P < 0.05) were encountered than in AHS patients without precipitating seizures or with an uneventful early medical history. However, all three groups had higher levels of CR-ir neurons compared to adult controls obtained at autopsy (P < 0.01). In addition, AHS specimens showed increased CR-ir neuropil staining throughout the DG-ML compared with the restricted distribution of CR-ir fibers within the superficial granule cell layer visible in controls. These findings suggest that a considerable number of TLE patients with AHS display signs of impaired hippocampal maturation and circuitry formation as indicated by increased numbers of Cajal-Retzius like cells. It remains to be elucidated, how these changes contribute to the pathogenesis of TLE.

Adolescent↗

PubMed1999

Distribution of voltage-dependent calcium channel beta subunits in the hippocampus of patients with temporal lobe epilepsy.

Voltage-dependent Ca2+ channels constitute a major class of plasma membrane channels through which a significant amount of extracellular Ca2+ enters neuronal cells. Their pore-forming alpha1 subunits are associated with cytoplasmic regulatory beta subunits, which modify the distinct biophysical and pharmacological properties of the alpha1 subunits. Studies in animal models indicate altered expression of alpha1 and/or beta subunits in epilepsy. We have focused on the regulatory beta subunits and have analysed the immunoreactivity patterns of the beta1, beta2, beta3 and beta4 subunits in the hippocampus of patients with temporal lobe epilepsy (n = 18) compared to control specimens (n = 2). Temporal lobe epilepsy specimens were classified as Ammon's horn sclerosis (n = 9) or focal lesions without alteration of hippocampal cytoarchitecture (n = 9). Immunoreactivity for the beta subunits was observed in neuronal cell bodies, dendrites and neuropil. The beta1, beta2 and beta3 subunits were found mainly in cell bodies while the beta4 subunit was primarily localized to dendrites. Compared to the control specimens, epilepsy specimens of the Ammon's horn sclerosis and of the lesion group showed a similar beta subunit distribution, except for beta1 and beta2 staining in the Ammon's horn sclerosis group: in the severely sclerotic hippocampal subfields of these specimens, beta1 and beta2 immunoreactivity was enhanced in some of the remaining neuronal cell bodies and, in addition, strongly marked dendrites. Thus, hippocampal neurons apparently express multiple classes of beta subunits which segregate into particular subcellular domains. In addition, the enhancement of beta1 and beta2 immunoreactivity in neuronal cell bodies and the additional shift of the beta1 and beta2 subunits into the dendritic compartment in severely sclerotic hippocampal regions indicate specific changes in Ammon's horn sclerosis. Altered expression of these beta subunits may lead to increased currents carried by voltage-dependent calcium channels and to enhanced synaptic excitability.

Adult↗