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Biomedical subjects

F Metzger

Publications and source records attributed to F Metzger.

At least 19 recordsLinked to original sources
PubMed2005

Therapeutic actions of insulin-like growth factor I on APP/PS2 mice with severe brain amyloidosis.

Transgenic mice expressing mutant forms of both amyloid-beta (Abeta) precursor protein (APP) and presenilin (PS) 2 develop severe brain amyloidosis and cognitive deficits, two pathological hallmarks of Alzheimer's disease (AD). One-year-old APP/PS2 mice with high brain levels of Abeta and abundant Abeta plaques show disturbances in spatial learning and memory. Treatment of these deteriorated mice with a systemic slow-release formulation of insulin-like growth factor I (IGF-I) significantly ameliorated AD-like disturbances. Thus, IGF-I enhanced cognitive performance, decreased brain Abeta load, increased the levels of synaptic proteins, and reduced astrogliosis associated to Abeta plaques. The beneficial effects of IGF-I were associated to a significant increase in brain Abeta complexed to protein carriers such as albumin, apolipoprotein J or transthyretin. Since levels of APP were not modified after IGF-I therapy, and in vitro data showed that IGF-I increases the transport of Abeta/carrier protein complexes through the choroid plexus barrier, it seems that IGF-I favors elimination of Abeta from the brain, supporting a therapeutic use of this growth factor in AD.

Amyloid beta-Peptides↗
PubMed2004

Purkinje cell dendritic tree development in the absence of excitatory neurotransmission and of brain-derived neurotrophic factor in organotypic slice cultures.

The development of the dendritic tree of a neuron is a complex process which is thought to be regulated strongly by signals from afferent fibers. In particular the synaptic activity of afferent fibers and activity-dependent signaling by neurotrophic factors are thought to affect dendritic growth. We have studied Purkinje cell dendritic arbor development in organotypic cultures under suppression of glutamate-mediated excitatory neurotransmission, achieved with multiple combinations of blockers of glutamate receptors. Despite the presence of either single receptor blockers or combinations of blockers predicted to fully suppress glutamate-mediated excitatory neurotransmission Purkinje cell dendritic arbors developed similar to those of control cultures. Furthermore, Purkinje cell dendritic arbors in organotypic cultures from brain-derived neurotrophic factor (BDNF) knockout mice or after pharmacological blockade of trk-receptors also developed in a way similar to control cultures. Our results demonstrate that during the stage of rapid dendritic arbor growth signals from afferent fibers are of minor importance for Purkinje cell dendritic development because a seemingly normal Purkinje cell dendritic tree developed in the absence of excitatory neurotransmission and BDNF signaling. Our results suggest that many aspects of Purkinje cell dendritic development can be achieved by an intrinsic growth program.

Afferent Pathways↗
PubMed2004

Corticotropin-releasing factor and urocortin differentially modulate rat Purkinje cell dendritic outgrowth and differentiation in vitro.

The precise outgrowth and arborization of dendrites is crucial for their function as integrators of signals relayed from axons and, hence, the functioning of the brain. Proper dendritic differentiation is particularly resonant for Purkinje cells as the intrinsic activity of this cell-type is governed by functionally distinct regions of its dendritic tree. Activity-dependent mechanisms, driven by electrical signaling and trophic factors, account for the most active period of dendritogenesis. An as yet unexplored trophic modulator of Purkinje cell dendritic development is corticotropin-releasing factor (CRF) and family member, urocortin, both of which are localized in climbing fibers. Here, we use rat organotypic cerebellar slice cultures to investigate the roles of CRF and urocortin on Purkinje cell dendritic development. Intermittent exposure (12 h per day for 10 days in vitro) of CRF and urocortin induced significantly more dendritic outgrowth (45% and 70%, respectively) and elongation (25% and 15%, respectively) compared with untreated cells. Conversely, constant exposure to CRF and urocortin significantly inhibited dendritic outgrowth. The trophic effects of CRF and urocortin are mediated by the protein kinase A and mitogen-activating protein kinase pathways. The study shows unequivocally that CRF and urocortin are potent regulators of dendritic development. However, their stimulatory or inhibitory effects are dependent upon the degree of expression of these peptides. Furthermore, the effects of CRF and urocortin on neuronal differentiation and re-modeling may provide a cellular basis for pathologies such as major depression, which show perturbations in the expression of these stress peptides.

Analysis of Variance↗
PubMed2002

Altered dendritic development of cerebellar Purkinje cells in slice cultures from protein kinase Cgamma-deficient mice.

Protein kinase C (PKC) is a key molecule for the expression of long-term depression at the parallel fiber-Purkinje cell synapse in the cerebellum, a well known model for synaptic plasticity. We have recently shown that activity of PKC also profoundly affects the dendritic morphology of Purkinje cells in rat cerebellar slice cultures suggesting that synaptic efficacy and dendritic development may be controlled by similar intracellular signalling pathways. Here we have analyzed the role of the gamma-isoform of protein kinase C (PKCgamma), which is strongly and specifically expressed in Purkinje cells, during dendritic development. After pharmacological treatment with PKC modulators, phosphorylation of PKCgamma at serine 660 was altered in cerebellar slices suggesting that a change of PKCgamma activity by these treatments was taking place within the Purkinje cells. In PKCgamma-deficient mice, Purkinje cell dendritic trees were enlarged and had an increased number of branching points compared to wild-type mice indicating a role for the PKCgamma isoform as a negative regulator of dendritic growth and branching. Furthermore, the branching-stimulating effects of the PKC inhibitors 2-[1-(3-dimethylaminopropyl)indol-3-yl]-3-(indol-3-yl)maleimide and Gö6976 found in wild-type cultures were abolished in the absence of PKCgamma. In contrast, the strong inhibitory effect on dendritic growth by the PKC activator phorbol-12-myristate-13-acetate (PMA) did not require the presence of the PKCgamma isoform since it was still present in the cultures of PKCgamma-deficient mice. Our results clearly demonstrate an involvement of PKCgamma in Purkinje cell dendritic differentiation in cerebellar slice cultures.

Animals↗
PubMed2002

Morphological study of organotypic cerebellar cultures.

Organotypic cerebellar cultures from 8-days-old (P8) mouse pups were studied following 11 days of in vitro (I IDIV) culturing. The cerebellar cytoarchitectonic structure was maintained in most parasagittal cerebellar cortical slice cultures (also containing the deep cerebellar nuclei). The two main extrinsic excitatory inputs (the climbing and the mossy fibers) seem to be replaced by other axonal types: in the molecular layer mostly by parallel fibers (for climbing fibers) and in the granular layer by intrinsic mossy fiber collaterals of local excitatory interneurons, the unipolar brush cells. However, in a few organotypic cultures, which (although preserving the trilaminar cerebellar cortical structure) were "granuloprival" but also contained some of the deep cerebellar nuclei, the participation of extracortical axons from the deep cerebellar nuclei in the replacement of the missing afferents is suggested.

Afferent Pathways↗
PubMed2001

[Standardized findings in echocardiography using WWW: EchoBefundSystem].

As a non-invasive imaging system, ultrasound echocardiography has a very high impact on modern diagnosis and is widely used in clinical routine but without any structured and standardized documentation of the results. Thus, quality management (QM), statistics and comparison of the results are difficult. Therefore, a working group of the German Cardiac Society issued a consensus proposal. For evaluation and wide public distribution, we have developed the first internet-based application covering the full proposal: EchoBefundSystem. The EchoBefundSystem is a web based client-server application for standardized documentation of echocardiography results right at the workplace. The software leads the examiner by means of a user interface design and stored medical knowledge. The level of detail is scaled automatically to the ongoing examination. Every day clinical routine is performed on only two pages, one for general patient data and a second one covering the complete minimal data set called "minimum finding" in the standard. As the examiner discovers more and more special findings or might even enter a complete medical study, the interface offers more and more fields and checkboxes. One data set can contain up to 600 values and findings. The structured user interface reflects the organ structure as well as examination methods familiar to the examiner. Automatically calculated fields speed up the examination. Judgements, diagnoses, values and ranges are interrelated. If there is a difference between the entered data and the medical knowledge base, a warning will be issued but the doctor's decision is authoritative. Some values may be gathered by different methods and even different units are converted automatically. The final doctor's letter is generated automatically in clear text but still editable and can be given out to the patient right after the examination without any further delay. Beside the minimal data set, all abnormal findings will appear and findings will be summarized wherever possible. The report is intended for the referring general practitioner, your own documentation, expert witness as well as clinical studies. Interested examiners may test the full version online at http://echo.ma.uni-heidelberg.de

Computer Graphics↗
PubMed2000

[A standardized documentation structure for data documentation in echocardiography. Work Team on Standards and LV Function of the Work Group on Cardiovascular Ultrasound of the German Society of Cardiology, Heart and Circulation Research].

Presently, there are no well-defined standards for documentation of echocardiographic studies. Nevertheless, standards are essential to provide comparability of data and to realize electronic communication, both essential for quality management in echocardiography. Therefore, the working group "Standards and LV function" of the German Society of Cardiology developed a consensus for documentation of echocardiographic studies. In the present paper this consensus is presented and illustrated by typical clinical examples. Additionally, a prototype of a user-oriented software based on this data set is presented. The complete data set for transesophageal and transthoracic echocardiography and the software prototype can be downloaded at http:@echo.ma.uni-heidelberg.de.

Aortic Valve Stenosis↗
PubMed2000

Protein kinase C activity modulates dendritic differentiation of rat Purkinje cells in cerebellar slice cultures.

The molecular mechanisms underlying dendritic differentiation in neurons are currently poorly understood. We used slice cultures from rat cerebellum of postnatal day 8 to investigate the effect of protein kinase C (PKC) activity on dendritic development of Purkinje cells. After 12 days in culture under control conditions, Purkinje cells had developed a typical dendritic tree consisting of a few long primary dendrites with shorter side branches. Following treatment with the PKC agonist, phorbol-12-myristate-13-acetate (PMA), the dendritic tree area was strongly reduced to 32% of control and primary dendrites were short with only a few side branches. Delayed addition of PMA after 6 days resulted in a retraction of existing dendrites, whereas discontinuation of PMA treatment after 6 days resulted in a recovery of the dendritic tree to almost control values. In the presence of the PKC inhibitor, 2-[1-(3-dimethylaminopropyl)indol-3-yl]-3-(indol-3-yl)maleimide (GF109203X), the dendritic tree area was increased to 158% of control with much more ramified branches after 12 days. The overall morphology of the cultures and the survival of Purkinje cells were unaffected by PKC modulators. Our data show that increased activity of PKC inhibits, and reduced activity of PKC promotes dendritic growth. This suggests that PKC activity is a critical regulator of dendritic growth and differentiation in cerebellar Purkinje cells.

Animals↗
PubMed2000

Contribution of Ca(2+)-permeable AMPA/KA receptors to glutamate-induced Ca(2+) rise in embryonic lumbar motoneurons in situ.

Intracellular Ca(2+) ([Ca(2+)](i)) was fluorometrically measured with fura-2 in lumbar motoneurons of acutely isolated spinal cord slices from embryonic rats. In ester-loaded cells, bath-applied glutamate (3 microM to 1 mM) evoked a [Ca(2+)](i) increase by up to 250 nM that was abolished by 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) plus 2-amino-5-phosphonovalerate (APV). CNQX or APV alone reduced the response by 82 and 25%, respectively. The glutamatergic agonists kainate (KA), quisqualate (QUI), and S-alpha-amino-3-hydroxy-5-methyl-4-isoxalone (S-AMPA) evoked a similar [Ca(2+)](i) transient as glutamate. N-methyl-D-aspartate (NMDA) was only effective to increase [Ca(2+)](i) in Mg(2+)-free saline, whereas [1S,3R]-1-aminocyclopentane-1,3-dicarboxylic acid ([1S,3R]-ACPD) had no effect. The glutamate-induced [Ca(2+)](i) rise was suppressed in Ca(2+)-free superfusate. Depletion of Ca(2+) stores with cyclopiazonic acid (CPA) did not affect the response. Thirty-six percent of the [Ca(2+)](i) increase in response to membrane depolarization induced by a 50 mM K(+) solution persisted on combined application of the voltage-gated Ca(2+) channel blockers nifedipine, omega-conotoxin-GVIA and omega-agatoxin-IVA. In fura-2 dialyzed motoneurons, the glutamate-induced [Ca(2+)](i) increase was attenuated by approximately 70% after changing from current to voltage clamp. Forty percent of the remaining [Ca(2+)](i) transient and 20% of the concomitant inward current of 0.3 nA were blocked by Joro spider toxin-3 (JSTX). The results show that voltage-gated Ca(2+) channels, including a major portion of R-type channels, constitute the predominant component of glutamate-induced [Ca(2+)](i) rises. NMDA and Ca(2+)-permeable KA/AMPA receptors contribute about equally to the remaining component of the Ca(2+) rise. The results substantiate previous assumptions that Ca(2+) influx through JSTX-sensitive KA/AMPA receptors is involved in (trophic) signaling in developing motoneurons.

2-Amino-5-phosphonovalerate↗
PubMed1999

Mechanical and excitotoxic lesion of motoneurons: effects of neurotrophins and ciliary neurotrophic factor on survival and regeneration.

Mechanical lesion of peripheral nerves leads to extensive death of corresponding motoneurons in newborn rodents. The extent of cell death can be significantly reduced by neurotrophic factors. These molecules are produced by glial and neuronal cells and play an important role in supporting survival and regeneration of various neuronal populations in the central nervous system, in particular after mechanical, excitotoxic and ischemic insults. In addition, factors such as ciliary neurotrophic factor and neurotrophin-3 influence glial cell proliferation and survival. We have investigated the role of neurotrophic factors on motoneurons, both in cell culture and after axotomy in vivo. Moreover, the role of excitatory neurotransmission in modulating dendritic architecture of these cells was analyzed. Our data suggest that motoneurons are a suitable model for investigating the complex functional and morphological changes after brain lesion and for the identification of new therapeutic strategies to influence survival and functional recovery under such circumstances.

Animals↗
PubMed1999

The role of p75NTR in modulating neurotrophin survival effects in developing motoneurons.

Neurotrophins exert their biological functions on neuronal cells through two types of receptors, the trk tyrosine kinases and the low-affinity neurotrophin receptor (p75NTR), which can bind all neurotrophins with similar affinity. The p75NTR is highly expressed in developing motoneurons and in adult motoneurons after axotomy, suggestive of a physiological role in mediating neurotrophin responses under such conditions. In order to characterize this specific function of p75NTR, we have tested the effects of nerve growth factor (NGF) on embryonic motoneurons from control and p75NTR-deficient mice. NGF antagonizes brain-derived neurotrophic factor (BDNF)- and neurotrophin-3 (NT-3)-mediated survival in control but not p75NTR-deficient motoneurons. Survival of cultured motoneurons in the presence of 0.5 ng/mL of either ciliary neurotrophic factor (CNTF) or glial-derived neurotrophic factor (GDNF) was not reduced by 20 ng/mL NGF. Dose-response investigations revealed that five times higher concentrations of BDNF are required for half-maximal survival of p75NTR-deficient motoneurons in comparison to motoneurons from wild-type controls. After facial nerve lesion in newborn wild-type mice, local administration of NGF reduced survival of corresponding motoneurons to less than 2% compared to the unlesioned control side. In p75NTR-deficient mice, the same treatment did not enhance facial motoneuron death on the lesioned side. In the facial nucleus of 1-week-old p75NTR -/- mice, a significant reduction of motoneurons was observed at the unlesioned side in comparison to p75NTR +/+ mice. The observation that motoneuron cell numbers are reduced in the facial nucleus of newborn p75NTR-deficient mice suggests that p75NTR might not function as a physiological cell death receptor in developing motoneurons.

Animals↗
PubMed1998

Effect of glutamate on dendritic growth in embryonic rat motoneurons.

Glutamate is a major excitatory neurotransmitter for spinal motoneurons. We have investigated its effect on survival and neurite formation in cultures of highly enriched motoneurons from 15-d-old rat embryos. Whereas the survival of these neurons was not reduced by this treatment, a distinct and specific effect on dendrite outgrowth could be observed. Axon outgrowth was not affected by glutamate. Our data suggest that calcium influx via ionotropic AMPA/kainate (AMPA/KA) receptors is responsible for the regulation of dendrite outgrowth by excitatory neurotransmission. This was shown by the use of specific inhibitors for the different classes of glutamate receptors. The effect was reduced by continuous depolarization at 35 mM KCl and by treatment with joro spider toxin (JSTX-3, 3 microM), a blocker of Ca2+-conducting AMPA receptors. Removal of glutamate after 5 d of culture led to increased dendrite growth during the following culture period, and delayed addition resulted in a reduction in the length of already existing dendrites. Our observation that the effect is dose-dependent and reversible reflects a potential physiological function of excitatory neurotransmission on dendrite growth and morphology during a developmental period when synaptic contacts from afferent neurons to motoneurons are made in the spinal cord.

Animals↗
PubMed1998

Mechanism of block by tedisamil of transient outward current in human ventricular subepicardial myocytes.

1. Tedisamil is a new antiarrhythmic drug with predominant class III action. The aim of the present study was to investigate the blocking pattern of the compound on the transient outward current (I(to)) in human subepicardial myocytes isolated from explanted left ventricles. Using the single electrode whole cell voltage clamp technique, I(to) was analysed after appropriate voltage inactivation of sodium current and block of calcium current. 2. Tedisamil reduced the amplitude of peak I(to), but did not affect the amplitude of non-inactivating outward current. The drug accelerated the apparent rate of I(to) inactivation. The reduction in time constant of I(to) inactivation depended on drug concentration, the apparent IC50 value was 4.4 microM. 3. Tedisamil affected I(to) amplitude in a use-dependent manner. After 2 min at -80 mV, maximum block of I(to) was reached after 4-5 clamp steps either at the frequency of 0.2 or 2 Hz, indicating that the block was not frequency-dependent in an experimentally relevant range. Recovery from block was very slow and proceeded with a time constant of 12.1+/-1.8 s. Also in the presence of drug, a fraction of channels recovered from inactivation with a similar time constant as in control myocytes (i.e. 81+/-40 ms and 51+/-8 ms, respectively, n.s.). 4. From the onset of fractional block of I(to) by tedisamil during the initial 60 ms of a clamp step, we calculated k1 = 9 x 10(6) mol(-1) s(-1) for the association rate constant, and k2 = 23 s(-1) for the dissociation rate constant. The resulting apparent KD was 2.6 microM and is similar to the IC50 value. 5. The effects of tedisamil on I(to) could be simulated by assuming a four state channel model where the drug binds to the channel in an open (activated) conformation. It is concluded that in human subepicardial myocytes tedisamil is an open channel blocker of I(to) and that this effect probably contributes to the antiarrhythmic potential of this drug.

Action Potentials↗
PubMed1997

Sulphonylurea binding in rat isolated glomeruli: pharmacological characterization and dependence on cell metabolism and cytoskeleton.

The kidney is endowed with ATP-sensitive K+ channels (KATP channels) both at the vascular and at the epithelial level. In this study we have characterized the binding of the sulphonylurea glibenclamide, the most widely used blocker of KATP channels, in rat isolated glomeruli. In metabolically intact glomeruli, 3H-glibenclamide labelled two different binding components with affinities of 47 +/- 12 nM and 10 +/- 1 microM and estimated binding capacities of 1.2 +/- 0.1 and 501 +/- 11 pmol/mg protein, respectively. 3H-glibenclamide binding was inhibited differentially by other sulphonylureas (tolbutamide, glibornuride, gliquidone and glipizide) and benzoic acid analogues such as meglitinide, AZ-DF 265 and UL-DF 9. Sulphonylureas interacted with the high affinity component and, in some cases, also with the low affinity component whereas the benzoic acid derivatives inhibited exclusively low affinity glibenclamide binding. Severe metabolic stress affected both components of glibenclamide binding by shifting high affinity binding to the right and reducing the capacity of the low affinity component. Disruption of the cytoskeletal actin filaments by cytochalasin B and D mimicked the effect of metabolic stress on the high affinity component but left the low affinity component unchanged. In crude membranes, the affinity of the first component was again reduced and a major loss of the low affinity sites was observed. The data show that the two binding components of glibenclamide binding in rat isolated glomeruli have very different properties. The high affinity component is not recognized by the benzoic acid derivatives; its affinity is modulated by cell metabolism and the actin component of the cytoskeleton. The low affinity sites are, in their majority, cytosolic. The function and cellular localization of the high affinity sites are under further study.

Adenosine Triphosphate↗
PubMed1997

Binding and effects of KATP channel openers in the vascular smooth muscle cell line, A10.

1. The ATP-sensitive K+ channel (KATP channel) in A10 cells, a cell line derived from rat thoracic aorta, was characterized by binding studies with the tritiated KATP channel opener, [3H]-P1075, and by electrophysiological techniques. 2. Saturation binding experiments gave a KD value of 9.2 +/- 5.2 nM and a binding capacity (BMax) of 140 +/- 40 fmol mg-1 protein for [3H]-P1075 binding to A10 cells; from the BMax value a density of binding sites of 5-10 per microns2 plasmalemma was estimated. 3. KATP channel modulators such as the openers P1075, pinacidil, levcromakalim and minoxidil sulphate and the blocker glibenclamide inhibited [3H]-P1075 binding. The extent of inhibition at saturation depended on the compound, levcromakalim inhibiting specific [3H]-P1075 binding by 85%, minoxidil sulphate and glibenclamide by 70%. The inhibition constants were similar to those determined in strips of rat aorta. 4. Resting membrane potential, recorded with microelectrodes, was -51 +/- 1 mV. P1075 and levcromakalim produced a concentration-dependent hyperpolarization by up to -25 mV with EC50 values of 170 +/- 40 nM and 870 +/- 190 nM, respectively. The hyperpolarization induced by levcromakalim (3 microM) was completely reversed by glibenclamide with an IC50 value of 86 +/- 17 nM. 5. Voltage clamp experiments were performed in the whole cell configuration under a physiological K+ gradient. Levcromakalim (10 microM) induced a current which reversed around -80 mV; the current-voltage relationship showed considerable outward rectification. Glibenclamide (3 microM) abolished the effect of levcromakalim. 6. Analysis of the noise of the levcromakalim (10 microM)-induced current at -40 and -20 mV yielded estimates of the channel density, the single channel conductance and the probability of the channel to be open of 0.14 micron-2, 8.8 pS and 0.39, respectively. 7. The experiments showed that A10 cells are endowed with functional KATP channels which resemble those in vascular tissue; hence, these cells provide an easily accessible source of channels for biochemical and pharmacological studies. The density of binding sites for [3H]-P1075 was estimated to be one order of magnitude higher than the density of functional KATP channels; assuming a plasmalemmal localization of the binding sites this suggests a large receptor reserve for the openers in A10 cells.

Animals↗
PubMed1996

Differences between outward currents of human atrial and subepicardial ventricular myocytes.

1. Outward currents were studied in myocytes isolated from human atrial and subepicardial ventricular myocardium using the whole-cell voltage clamp technique at 22 degrees C. The Na+ current was inactivated with prepulses to -40 mV and the Ca2+ current was eliminated by both reducing extracellular [Ca2+] to 0.5 mM and addition of 100 microM CdCl2 to the bath solution. 2. In human myocytes, three different outward currents were observed. A slowly inactivating sustained outward current, I(so), was found in atrial but not ventricular myocytes. A rapidly inactivating outward current, I(to), of similar current density was observed in cells from the two tissues. An additional uncharacterized non-inactivating background current of similar size was observed in atrial and in ventricular myocytes. 3. I(to) and I(so) could be differentiated in atrial myocytes by their different kinetics and potential dependence of inactivation, and their different sensitivities to block by 4-amino-pyridine, suggesting that two individual channel types were involved. 4. In atrial cells, inactivation of I(to) was more rapid and steady-state inactivation occurred at more negative membrane potentials than in ventricular cells. Furthermore, the recovery of I(to) from inactivation was slower and without overshoot in atrial myocytes. In addition, 4-aminopyridine-induced block of I(to) was more efficient in atrial than in ventricular cells. These observations suggest that the channels responsible for atrial and ventricular I(to) were not identical. 5. We conclude that the differences in outward currents substantially contribute to the particular shapes of human atrial and ventricular action potentials. The existence of I(so) in atrial cells only provides a clinically interesting target for anti-arrhythmic drug action, since blockers of I(so) would selectively prolong the atrial refractory period, leaving ventricular refractoriness unaltered.

Action Potentials↗