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Biomedical subjects

U Heinemann

Publications and source records attributed to U Heinemann.

At least 181 records · Page 10Linked to original sources
PubMed1996

Electrophysiological properties of neurones in cultures from postnatal rat dentate gyrus.

Electrophysiological properties of neurofilament-positive neurones in dissociated cell cultures were prepared at postnatal days 4-5 from rat dentate gyrus and studied using the whole-cell patch-clamp technique. These cells expressed a fast-inactivating, 0.5 microM tetrodotoxin-sensitive Na+ current; a high-voltage-activated (HVA) Ca2+ current, which was 30 microM Cd(2+)- and partially 2 microM nicardipine-sensitive; and an inward rectifier current, which was sensitive to extracellularly applied 1 mM Cs+. The outward current pattern was composed of a delayed rectifier-like outward current sensitive to 20 mM tetraethylammonium (TEA) and a fast-inactivating, Ca(2+)-dependent outward current. This transient Ca(2+)-dependent K+ outward current was identified by a subtraction procedure. K+ currents recorded under conditions of blocked Ca2+ currents (after rundown of the HVA Ca2+ current or blocked by extracellularly applied Cd2+) were subtracted from control currents. By comparison with the current pattern of identified dentate granule cells, it is concluded that the investigated cell type originated from interneurones or projection neurones of the dentate hilus.

Animals↗
PubMed1996

Potassium currents in acutely isolated neurons from superficial and deep layers of the juvenile rat entorhinal cortex.

Using the whole-cell configuration of the patch-clamp technique, outward K+ currents were recorded from acutely isolated stellate cells from superficial layers, and pyramidal cells from deep layers, of the entorhinal cortex of juvenile rats. In both cell types a fast transient and a slowly inactivating outward K+ current were obtained. Whereas the fast transient current (IA) activated at potentials beyond -50 mV, the activation threshold of the slowly inactivating current (IK) was measured at -40 mV in stellate and pyramidal cells. In stellate cells a half-maximal inactivation was estimated for IA at -80.4 mV and for IK at -74.6 mV, and in pyramidal cells at -81.1 mV and -71.8 mV, respectively. IK of both cell types were reduced by tetraethylammonium (TEA) in a concentration-dependent manner. IC50 values were 0.8 mM TEA for stellate cells and 1.1 mM TEA for pyramidal cells. Superfusion of 4-aminopyridine resulted in a reduction of the amplitudes of IA and IK as well as in an acceleration of the inactivation time constants of IA. Extracellularly applied dendrotoxin did not have any effect on entorhinal cortex K+ currents. In summary, kinetic and pharmacological properties of IA as well as of IK are rather similar in superficial-layer stellate and deep-layer pyramidal cells acutely isolated from the entorhinal cortex of juvenile rats.

4-Aminopyridine↗
PubMed1996

Effects of gamma-aminobutyric acid (GABA) agonists and GABA uptake inhibitors on pharmacosensitive and pharmacoresistant epileptiform activity in vitro.

1. Lowering of the extracellular Mg(2+)-concentration induces various patterns of epileptiform activity in combined rat entorhinal cortex-hippocampal brain slices. After a prolonged period of exposure to Mg(2+)-free medium seizure-like events in the entorhinal cortex change to a state of late recurrent discharges which cannot be blocked by clinically available antiepileptic drugs. This late epileptiform activity thus represents a useful model to test the effects of new anticonvulsant substances. 2. A mechanism possibly underlying the development of sustained seizure-like activity is the loss of synaptically released gamma-aminobutyric acid (GABA). Drugs which increase the amount of GABA available in presynaptic endings might thus be useful in the treatment of these therapeutically complicated forms of epilepsy. 3. Therefore, we studied the effects of various substances increasing GABA-mediated inhibition on early and late forms of epileptiform activity. GABA and the GABAA receptor agonist muscimol blocked both the pharmacosensitive discharges in the hippocampus and entorhinal cortex as well as the late recurrent discharges in the medial entorhinal cortex. The GABAB receptor agonist baclofen blocked the recurrent short discharges very potently, but did not consistently block seizure-like events and late recurrent discharges in the entorhinal cortex. 4. GABA uptake blockers showed a differential potency to block the various discharge patterns. Whereas nipecotic acid and beta-alanine suppressed all forms of epileptiform activity albeit at high concentrations (1-5 mM), tiagabine was much more potent in blocking the hippocampal recurrent short discharges and the seizure-like events in the medial entorhinal cortex, but could not block the late recurrent discharges. 5. Our data support the idea that prolonged neuronal overactivity might result in a loss of synaptically available GABA. Selective block of uptake into glia cells or substitution of the transmitter may therefore be an efficient strategy for the treatment of severe prolonged epileptic discharges whereas block of neuronal GABA uptake fails to counteract synchronized discharges in this situation.

Animals↗
PubMed1996

Properties of a delayed rectifier potassium current in dentate granule cells isolated from the hippocampus of patients with chronic temporal lobe epilepsy.

PURPOSE: Properties of potassium outward currents were investigated in human hippocampal dentate gyrus granule cells from 11 hippocampal specimens obtained from patients with temporal lobe epilepsy (TLE) during resective surgery. METHODS: Dentate granule cells were isolated enzymatically and outward currents analyzed by using the whole-cell configuration of the patch-clamp method. Hippocampal specimens were classified neuropathologically with respect to severe segmental cell loss, gliosis, and axonal sprouting (Ammon's horn sclerosis, AHS), or the presence of a focal lesion in the adjacent temporal lobe. RESULTS: A delayed rectifier outward current (IK), but not an A-type potassium current (IA) or inwardly rectifying potassium currents, was observed in all cells. The average current density of IK, the time-dependent decay of IK, and the resting membrane characteristics were not significantly different between patients with and without AHS. The voltage of half-maximal activation V1/2(act) was 5.4 +/- 1.8 mV in AHS compared with -2.9 +/- 1.8 mV in lesion-associated epilepsy (NS). In contrast, V1/2(inact) was shifted in a hyperpolarizing direction in AHS (-67.7 +/- 0.6 mV) compared with that in hippocampi not showing AHS (-47.7 +/- 2.6 mV; p = 0.0017). CONCLUSIONS: The altered steady-state voltage-dependence of IK may result in abnormal excitability of dentate granule cells in AHS and exert a marked influence on input-output properties of the dentate gyrus.

Adult↗
PubMed1996

Different mechanisms regulate IPSC kinetics in early postnatal and juvenile hippocampal granule cells.

1. Monosynaptic inhibitory postsynaptic currents (IPSCs) were recorded from early postnatal and juvenile dentate granule cells in rat brain slices at room temperature. The focally evoked currents were mediated by gamma-aminobutyric acid-A (GABAA) receptors. 2. IPSCs were characterized by a steep rising phase and a slower, monoexponential decay time course. The decay time constant was potential dependent and average values ranged from 33 ms at a holding potential of -60 mV to 58 ms at a holding potential of +40 mV. 3. IPSCs were studied in tissue from animals between postnatal day (p) 3 and p25. All kinetic parameters as well as the mean current amplitude were unchanged during this ontogenetic period. 4. In juvenile granule cells from animals aged 13-16 days, addition of the GABA uptake blocker (R)-N-[4,4-bis (3-methyl-2-thienyl) but-3-en1-yl] nipecotic acid (tiagabine) (10 microM) prolonged the decaying phase of the IPSCs. The current decay remained monoexponential but the time constant increased to 250% of control values. Mean current amplitudes remained largely unchanged. 5. In contrast, tiagabine had no effect on IPSCs in early postnatal tissuĕ. The decay time constant remained unchanged in cells recorded from animals aged p4-p6. Other uptake blockers were also ineffective during the first postnatal week, whereas beta-alanine, NNC-711, and L-2,3-diaminoproprionic acid enhanced the decay time constant in the older tissue (p13-p16). 6. Hypoosmolaric extracellular solution was applied to restrict the extracellular space. In juvenile tissue (p13-p16), IPSCs were not affected by this treatment, whereas early postnatal granule cells (p4-p6) displayed clearly prolonged IPSC decay time constants (165% of control). 7. We conclude that the mechanism governing the kinetics of evoked IPSCs in granule cells changes during ontogenesis. Whereas in early postnatal tissue the transmitter leaves the postsynaptic site by diffusion, GABA uptake becomes time limiting after 2 wk of postnatal development.

Aging↗
PubMed1995

Serotonin and 8-OH-DPAT reduce excitatory transmission in rat hippocampal area CA1 via reduction in presumed presynaptic Ca2+ entry.

The effect of 5-HT and its 1A receptor agonist 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) on excitatory transmission in CA1 pyramidal cells was studied. Using concentrations of 5-HT within a range of 10-50 microM we observed no change in excitatory postsynaptic potentials (EPSPs) in CA1 cells evoked by Schaffer collateral stimulation. However, at higher concentrations, > or = 100 microM, 5-HT caused a significant decrease (30-40%) in EPSP/Cs, an effect that was also mimicked by 50 microM 8-OH-DPAT. A presumed presynaptic Ca2+ entry was measured in stratum radiatum following repetitive stimulation of the Schaffer collaterals with all excitatory synaptic transmission blocked. Both 5-HT and 8-OH-DPAT reduced this Ca2+ entry. These results suggest that 5-HT acts at presynaptic 5-HT1A receptors to reduce Ca2+ entry and thereby glutamatergic synaptic transmission.

8-Hydroxy-2-(di-n-propylamino)tetralin↗
PubMed1995

Effects of losigamone on synaptic potentials and spike frequency habituation in rat entorhinal cortex and hippocampal CA1 neurones.

Losigamone is an anticonvulsant both in vivo and in vitro. We here studied possible mechanisms for such effects with conventional intracellular recordings from pyramidal cells of area CA1 and entorhinal cortex in combined hippocampal-entorhinal cortex slices. Losigamone reversibly reduced the number of action potentials elicited by 1 s long depolarising current injections. In addition, the drug moderately reduced EPSP amplitudes while monosynaptic fast and slow IPSPs were unaffected.

Action Potentials↗
PubMed1995

Constitutive activation of mitogen-activated protein kinase-activated protein kinase 2 by mutation of phosphorylation sites and an A-helix motif.

A recently described downstream target of mitogen-activated protein kinases (MAPKs) is the MAPK-activated protein (MAPKAP) kinase 2 which has been shown to be responsible for small heat shock protein phosphorylation. We have analyzed the mechanism of MAPKAP kinase 2 activation by MAPK phosphorylation using a recombinant MAPKAP kinase 2-fusion protein, p44MAPK and p38/40MAPK in vitro and using an epitope-tagged MAPKAP kinase 2 in heat-shocked NIH 3T3 cells. It is demonstrated that, in addition to the known phosphorylation of the threonine residue carboxyl-terminal to the catalytic domain, Thr-317, activation of MAPKAP kinase 2 in vitro and in vivo is dependent on phosphorylation of a second threonine residue, Thr-205, which is located within the catalytic domain and which is highly conserved in several protein kinases. Constitutive activation of MAPKAP kinase 2 is obtained by replacement of both of these threonine residues by glutamic acid. A constitutively active form of MAPKAP kinase 2 is also obtained by deletion of a carboxyl-terminal region containing Thr-317 and the A-helix motif or by replacing the conserved residues of the A-helix. These data suggest a dual mechanism of MAPKAP kinase 2 activation by phosphorylation of Thr-205 inside the catalytic domain and by phosphorylation of Thr-317 outside the catalytic domain involving an autoinhibitory A-helix motif.

3T3 Cells↗
PubMed1995

Crystal structure of Bacillus licheniformis 1,3-1,4-beta-D-glucan 4-glucanohydrolase at 1.8 A resolution.

The crystal structure of the 1,3-1,4-beta-D-glucan 4-glucanohydrolase from Bacillus licheniformis is solved at a resolution of 1.8 A and refined to R = 16.5%. The protein has a similar beta-sandwich structure as the homologous enzyme from Bacillus macerans and the hybrid H(A16-M). This demonstrates that the jellyroll fold of these proteins is remarkably rigid and only weakly influenced by crystal contacts. The crystal structure permits to extend mechanistic considerations derived for the B. licheniformis enzyme to the entire class of bacterial 1,3-1,4-beta-D-glucan 4-glucanohydrolases.

Bacillus↗
PubMed1995

Crystal and molecular structure at 0.16-nm resolution of the hybrid Bacillus endo-1,3-1,4-beta-D-glucan 4-glucanohydrolase H(A16-M).

H(A16-M) is a hybrid endo-1,3-1,4-beta-D-glucan 4-glucanohydrolase from Bacillus. Its crystal structure was refined using synchrotron X-ray diffraction data up to a maximal resolution of 0.16 nm. The R value of the resulting model is 14.3% against 21,032 reflections > 2 sigma. 93% of the amino acid residues are in the most favorable regions of the Ramachandran diagram, and geometrical parameters are in accordance with other proteins solved at high resolution. As shown earlier [Keitel, T., Simon, O., Borriss, R. & Heinemann, U. (1993) Proc. Natl Acad. Sci. USA 90, 5287-5291], the protein folds into a compact jellyroll-type beta-sheet structure. A systematic analysis of the secondary structure reveals the presence of two major antiparallel beta-sheets and a three-stranded minor mixed sheet. Amino acid residues involved in catalysis and substrate binding are located inside a deep channel spanning the surface of the protein. To investigate the stereochemical cause of the observed specificity of endo-1,3-1,4-beta-D-glucan 4-glucanohydrolases towards beta-1,4 glycosyl bonds adjacent to beta-1,3 bonds, the high-resolution crystal structure has been used to model an enzyme-substrate complex. It is proposed that productive substrate binding to the subsites p1, p2 and p3 of H(A16-M) requires a beta-1,3 linkage between glucose units bound to p1 and p2.

Bacillus↗
PubMed1995

Electrophysiological and morphological evidence for a new projection of LMAN-neurones towards area X.

Neuronal connectivity of brain areas involved in song learning and song production was studied in the in vitro slice preparation of the zebra finch brain by electrophysiological intracellular recording techniques and by micro-injections of the fluorescent tracer tetramethyl-rhodamine-dextran-amine. While validating some of the known projections to be preserved in the in vitro slice preparation, we were also able to identify a new projection from neurones of the lateral portion of the magnocellular nucleus of the anterior neostriatum towards area X of the lobus parolfactorius.

Animals↗
PubMed1995

Synaptic transmission and paired-pulse behaviour of CA1 pyramidal cells in hippocampal slices from a hibernator at low temperature: importance of ionic environment.

To investigate the effects of ionic changes possibly associated with hibernation, hippocampal slices prepared from golden hamsters were studied in artificial cerebrospinal fluid (ACSF) of variable composition (K+ 3-5 mM, Ca2+ 2-4 mM, Mg2+ 2-4 mM, pH 7.0-7.7) at temperatures of 15-20 degrees C, just above the temperature below which synaptic transmission is blocked. Population action potentials (population spikes, PSs) of CA1 pyramidal cells were evoked by stimulation of the Schaffer collaterals/commissural fibers with paired pulses (interpulse interval 50 ms, interval between pairs 30 s). The responses evoked at given temperatures were investigated as a function of extracellular ion concentrations. In ACSF containing 3 mM K+, 2 mM Ca2+ and 2 mM Mg2+, PSs could be evoked at temperatures of > approximately 16 degrees C whereas at lower temperatures synaptic transmission was blocked. The threshold temperature was slightly higher for the first (PS1) than for the second PS (PS2) evoked by paired-pulse stimulation. The slices displayed paired-pulse facilitation (PPF) at all temperatures. Elevation of [K+]o from 3 to 5 mM depressed the amplitudes of both PS1 and PS2, with a stronger effect on PS2. PPF was reduced and, at near-threshold temperatures, turned into paired-pulse depression (PPD). Elevation of [Ca2+]o from 2 to 4 mM increased the amplitude of PS1. The amplitude of PS2, in contrast, was reduced at near-threshold temperatures. PPF turned into PPD. Elevation of [Mg2+]o from 2 to 4 mM reduced the amplitudes of both PS1 and PS2, with a stronger effect on PS1. Accordingly, PPF was increased. Acidification by 0.3 pH units strongly depressed the amplitudes of PS1 as well as PS2 and increased PPF. Alkalization by 0.4 pH units had only weak effects in the opposite direction. Changes in the ionic composition comparable to those investigated in the present study presumably occur in the brain interstitium of hamsters during entrance into hibernation. According to our results, such changes depress synaptic transmission at low temperatures in the hamster hippocampus in vitro. This modulation may be important for the regulation of neuronal activity during entrance into hibernation.

Action Potentials↗
PubMed1995

Decompaction of CNS myelin leads to a reduction of the conduction velocity of action potentials in optic nerve.

The conduction velocity of action potentials in nerve fibres is proportional to degree of myelination. Here we studied the influence of myelin ultrastructure on the compound action potential conduction velocity in optic nerves of the proteolipid protein (PLP)-deficient mouse model, which displays loose myelination in central fibres. We show that a myelin decompaction leads to a suboptimal conduction velocity. The significance of myelin ultrastructure for conduction of action potential in the optic nerve is discussed.

Action Potentials↗
PubMed1995

Properties of low Mg2+ induced epileptiform activity in rat hippocampal and entorhinal cortex slices during adolescence.

Properties of low Mg2+ induced epileptiform activity were studied in isolated rat hippocampal slices or in combined slices containing the entorhinal cortex and hippocampus. Slices were prepared from rats which were 1, 2, 3 or more weeks of age. Field potentials and often also changes in [K+]0, [Ca2+]0 and [Mg2+]0 were recorded with appropriate ion selective microelectrodes. In isolated hippocampal and entorhinal cortex/hippocampal combined slices the latency to onset of epileptiform activity upon lowering of extracellular Mg2+ was shortest in the youngest age group and approached adult levels at about the fourth postnatal week. Washout kinetics of Mg2+ were fastest in slices from 1-week-old rats. The onset of low Mg2+ induced epileptiform activity occurred at higher Mg2+ levels in slices from young compared with those from adult animals. In isolated hippocampal slices the epileptiform discharges varied in appearance during development. Short discharges lasting for 40 to 80 ms were observed in hippocampal slices prepared from 1-week-old and adult animals. Seizure-like events (SLE's) characterized by slow negative potential shifts and characteristic elevations in [K +]0 and decreases in [Ca2+]0 lasting for up to 30 s were observed in a proportion of hippocampal slices prepared after the first, second and third postnatal week. In slices from week 2 and 3 seizure-like events often progressed into spreading depressions (SD's). In entorhinal cortex/hippocampal combined slices seizure-like events were observed in all age groups. The seizure-like events spread readily into dentate gyrus (DG), area CA3 and CA1 after week 1.(ABSTRACT TRUNCATED AT 250 WORDS)

Aging↗
PubMed1995

Electrophysiology and morphology of a new type of cell within layer II of the rat lateral entorhinal cortex in vitro.

Using a combination of intracellular recording and morphological techniques, we describe the properties of a new cell type within layer II of the lateral entorhinal cortex. A thick and bifurcating apical dendrite and thinner basal dendrites extended from the pyramidal shaped cell body. The axon ramified within all superficial layers of the lateral entorhinal cortex. These pyramidal-like cells exhibited 2 pronounced electrophysiological features; a high threshold for spike generation, and their prominent excitatory synaptic potentials with little inhibition following lateral entorhinal cortex stimulation. The electrophysiological properties and the axonal morphology suggest that this cell type has a local information processing role within the lateral entorhinal cortex.

2-Amino-5-phosphonovalerate↗
PubMed1995

Crystal structure of an RNA dodecamer containing the Escherichia coli Shine-Dalgarno sequence.

The synthetic dodecameric RNA fragment rUAAGGAGGUGAU resembles a region upstream of the initiation site in prokaryotic mRNAs whereas the pyrimidine-rich complementary strand is identical to the last 12 nucleotides of Escherichia coli 16 S rRNA. The complex thus serves as a model for the Shine-Dalgarno interaction which is required for proper initiation of translation. The crystal structure of rUAAGGAGGUGUA.rAUCACCUCCUUA has been determined at 2.6 A resolution and refined against 2957 1 sigma(F) structure amplitudes to an R-value of 0.195. The unit cell of the triclinic crystals contains two double-stranded RNA molecules. The conformation of the two duplexes is similar, with a root-mean-square deviation of 0.683 A between equivalent atoms, and resembles calf thymus A-DNA as determined by X-ray fiber diffraction methods. Both molecules from continuous helices that penetrate the entire crystal, but the dinucleotide step in between dodecameric duplexes has an unusual geometry with a negative twist angle. The long helices cross over each other in a characteristic manner by inserting the backbone of one molecule into the minor groove of another. These contacts are stabilized by several direct intermolecular hydrogen bonds most of which are mediated by 2'-hydroxyl groups of the ribose sugars suggesting a general mode for the interaction between RNA molecules which is different from DNA-DNA interactions.

Base Sequence↗
PubMed1995

The perforant path projection to hippocampal area CA1 in the rat hippocampal-entorhinal cortex combined slice.

1. The perforant path projection from layer III of the entorhinal cortex to CA1 of the hippocampus was studied within a hippocampal-entorhinal combined slice preparation. We prevented contamination from the other main hippocampal pathways by removal of CA3 and the dentate gyrus. 2. Initially the projection was mapped using field potential recordings that suggested an excitatory sink in stratum lacunosum moleculare with an associated source in stratum pyramidale. 3. However, recording intracellularly from CA1 cells, stimulation of the perforant path produced prominent fast GABAA and slow GABAB IPSPs often preceded by small EPSPs. In a small number of cells we observed EPSPs only. 4. CNQX blocked excitatory and inhibitory responses. This indicated the presence of an intervening excitatory synapse between the inhibitory interneurone and the pyramidal cell. 5. Focal bicuculline applications revealed that the major site of GABAA inhibitory input was to stratum radiatum of CA1. 6. The inhibition activated by the perforant path was very effective at reducing simultaneously activated Schaffer collateral mediated EPSPs and suprathreshold-stimulated action potentials. 7. Blockade of fast inhibition increased excitability and enhanced slow inhibition. Both increases relied upon the activation of NMDA receptors. 8. Perforant path inputs activated prominent and effective disynaptic inhibition of CA1 cells. This has significance for the output of hippocampal processing during normal behaviour and also under pathological conditions.

2-Amino-5-phosphonovalerate↗