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A Draguhn

Publications and source records attributed to A Draguhn.

At least 37 records · Page 2Linked to original sources
PubMed1998

Serotonin reduces synaptic excitation in the superficial medial entorhinal cortex of the rat via a presynaptic mechanism.

1. The superficial layers II and III of the entorhinal cortex, which form the main cortical input to the hippocampus, receive a large serotonergic projection from the raphe nuclei and express 5-HT receptors at high density. Here, we studied the effects of serotonin on the intrinsic properties and excitatory synaptic transmission of the superficial medial entorhinal cortex. 2. Intracellular and patch clamp recordings revealed that serotonin hyperpolarized only one-third of the cells, approximately, through a potassium conductance via a GTP-dependent process. 3. Serotonin depressed mixed as well as isolated alpha-amino-3-hydroxy-5-methyl-4-isoxazole- propionic acid receptor (AMPAR)- and N-methyl-D-aspartic acid receptor (NMDAR)-mediated excitatory postsynaptic potentials/currents (EPSPs/EPSCsapproximately 40 % reduction with 1 microM serotonin). 4. The effect of serotonin on EPSPs/EPSCs was similar in whole-cell versus intracellular recordings; it did not require intracellular GTP and was not visible in glutamate applications to excised patches. Miniature EPSCs recorded in the presence of tetrodotoxin and bicuculline were reduced in frequency, but not altered in amplitude. 5. The effects of serotonin on intrinsic properties and EPSPs were partially mimicked by 5-HT1A receptor agonists (+/-)-8-hydroxy-2-(di-n-propylamino)tetralin hydrobromide (8-OH-DPAT) and 5-carboxamido-tryptamine maleate (5-CT), and reduced by 5-HT1A receptor antagonists S-(-)-5-fluoro-8-hydroxy-DPAT hydrochloride (S-UH-301), 1-(2-methoxyphenyl)-4-[4-(2-phthalimido)butyl]piperazine hydrobromide (NAN-190) and spiperone. 6. We conclude that serotonin potently suppresses excitatory synaptic transmission via 5-HT1A receptors in layers II and III of the medial entorhinal cortex by a presynaptic mechanism.

8-Hydroxy-2-(di-n-propylamino)tetralin↗
PubMed1997

A simple hardware model for the direct observation of voltage-clamp performance under realistic conditions.

A new hardware cell model for electrophysiological recording has been constructed which allows for the assessment of voltage clamp accuracy in different recording situations. Each compartment consists of a capacitor in parallel with a variable resistor and can be connected to other compartments by a variable axial resistance. The simulated membrane resistance can be changed extrinsically by a command voltage input which is optically coupled to the cell without any direct galvanic contact. Each compartment possesses a buffer amplifier which reads out the potential at the simulated membrane element, (e.g. 'somatic' or 'dendritic' potential). The model allows for the direct observation of typical situations and problems arising in electrophysiological experiments. We used the model to monitor deviations between the 'intracellular' and the command voltage, e.g. due to series resistance errors. We also used the model to simulate synaptic currents which were generated by triangular membrane conductance changes. The results demonstrate the strong influence of synaptic location and series resistance on voltage clamp fidelity. The cell model is a new and easy-to-handle tool for the observation of voltage control under realistic experimental conditions.

Animals↗
PubMed1997

Large-conductance cation channels in the envelope of nuclei from rat cerebral cortex.

Eucaryotic nuclei are surrounded by a double-membrane system enclosing a central cisterna which is continuous with the endoplasmic reticulum and serves as a calcium store for intracellular signaling. The envelope regulates protein and nucleic acid traffic between the nucleus and the cytoplasm via nuclear pores. These protein tunnels cross through both nuclear membranes and are permeable for large molecules. Surprisingly, patch clamp recordings from isolated nuclei of different cell species have revealed a high resistance of the envelope, enabling tight seals and the resolution of single ion channel activity. Here we present for the first time single-channel recordings from nuclei prepared from neuronal tissue. Nuclei isolated from rat cerebral cortex displayed spontaneous long-lasting large conductances in the nucleus-attached mode as well as in excised patches. The open times are in the range of seconds and channel activity increases with depolarization. The single-channel conductance in symmetrical K+ is 166 pS. The channels are selective for cations with PK/PNa = 2. They are neither permeable to, nor gated by Ca2+. Thus, neuronal tissue nuclei contain a large conductance ion channel selective for monovalent cations which may contribute to ionic homeostasis in the complex compartments surrounding these organelles.

Animals↗
PubMed1997

Losigamone decreases spontaneous synaptic activity in cultured hippocampal neurons.

Losigamone is a new antiepileptic drug with an unknown mechanism of action. Here we report on the effects of losigamone on the synaptic activity in a network of cultured rat hippocampal neurons. Losigamone dose dependently reduced the frequency of spontaneous synaptic events without affecting the mean current amplitude. The drug affected equally the isolated inhibitory as well as excitatory postsynaptic currents. Miniature postsynaptic currents were not altered by losigamone, suggesting that the mechanism of action depends on functional Na+ channels. Consistent with these findings, the drug decreased the frequency of spontaneous action potentials and suppressed repetitive firing of neurons. Thus, losigamone generally depresses synaptic activity in a neuronal network without selectively modulating a specific postsynaptic receptor type. We conclude that losigamone acts via a presynaptic mechanism reducing neuronal excitability.

Action Potentials↗
PubMed1997

Ischemia changes the coexpression of somatostatin and neuropeptide Y in hippocampal interneurons.

Transient cerebral ischemia causes extensive cell death in hippocampal CA1 pyramidal cells and selective loss of interneurons in the dentate hilus. Many hippocampal interneurons can be classified by their contents of somatostatin (SS) and/or neuropeptide Y (NPY). Following ischemia in the rat, most of the NPY immunoreactivity is permanently lost in hippocampus. Furthermore, SS interneurons in the dentate hilus die, whereas CA1 interneurons survive and their expression of SS mRNA and peptide returns to preischemic levels within 16 days after ischemia. We have addressed the following questions: (1) Does the loss of NPY involve a specific downregulation in surviving CA1 interneurons that pre-ischemically expressed both SS and NPY? (2) Can the subpopulation of dying interneurons in hilus be identified from their preischemic coexpression of SS and NPY? We investigated the coexpression of SS mRNA and NPY peptide using combined in situ hybridization and immunocytochemistry. Cells containing one or both markers were counted in control sections and sections taken 2-16 days after ischemia from the hippocampal formation. In CA1, a decrease in the number of neurons containing NPY alone as well as a decrease in the number of neurons coexpressing NPY and SS was observed, whereas the number of neurons containing SS alone increased 16 days after ischemia. We conclude that neurons coexpressing SS and NPY before ischemia added to the number of neurons containing SS alone after ischemia, because NPY expression was selectively down regulated in the coexpressing population. In hilus, we demonstrated both survival and ischemic cell death of neurons expressing either SS, NPY or both, indicating that hilar interneurons dying from ischemia cannot unequivocally be identified from their preischemic colocalization of SS and NPY.

Animals↗
PubMed1996

Dendritic shrinkage and dye-coupling between rat hippocampal CA1 pyramidal cells in the tetanus toxin model of epilepsy.

A small dose of tetanus toxin injected into the rat hippocampus produces a chronic model of temporal lobe epilepsy. We have examined whether morphological changes occur in hippocampal CA1 pyramidal cells in this model by using intracellular injections of biocytin. Eight weeks after the injection of tetanus toxin, significantly more "dye-coupled' cells were found in this group than in the buffer (control) injected group (63% compared with 7%). Half of these coupled cells appeared to be linked at the soma, and the other half by dendrodendritic contacts. Analysis of the dendritic trees revealed that the tetanus toxin group showed a decrease in complexity around the proximal to mid-apical dendritic regions and around the mid- to distal basal dendritic regions. The dye-coupling indicates that electrotonic interaction is induced or strengthened between hippocampal neurones, possibly as a result of the epilepsy-induced dendritic damage.

Animals↗
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

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

Co-localization of somatostatin mRNA and parvalbumin in the dorsal rat hippocampus after cerebral ischemia.

Following transient global ischemia most of the neurons containing somatostatin in the fascia dentata of the dorsal hippocampal formation die, while somatostatinergic neurons in the CA1 region survive. The neurons react to ischemia with a transiently reduced expression of somatostatin mRNA and peptide. We have tested the hypothesis that this selective vulnerability is solely related to those somatostatinergic neurons which do not express the calcium-binding protein parvalbumin. Postischemic changes were studied in rat dorsal hippocampus at 2 and 16 days after 10 min of global cerebral ischemia using a four-vessel occlusion model. We performed a double-staining visualizing the mRNA coding for somatostatin by non-radioactive in situ hybridization and parvalbumin protein by immunocytochemistry. Only 5% of the somatostatinergic cells in the fascia dentata contained parvalbumin. The number of somatostatinergic cells was permanently reduced following ischemia. Among surviving neurons we found cells with and without parvalbumin expression. Thus, expression of parvalbumin is not predictive for survival of somatostatinergic cells in the fascia dentata. In contrast, in CA1, 37% of the somatostatinergic cells contained parvalbumin. These cells were unaffected by the transient ischemic period. The somatostatinergic cells lacking parvalbumin showed transiently reduced mRNA levels at day 2, but recovered to control values at the 16th postischemic day. Thus, expression of the calcium-buffering protein parvalbumin coincides with resistance of somatostatinergic neurons in CA1 to transient effects of ischemia. We conclude that the calcium-buffering capacity of parvalbumin may partially contribute to the protection of somatostatinergic neurons from ischemia in the dorsal hippocampus. However, the survival of somatostatinergic cells without parvalbumin indicates the importance of other factors as well.

Animals↗
PubMed1994

Strategies for the development of drugs for pharmacoresistant epilepsies.

Presently, most strategies for development of antiepileptic drugs (AEDs) center around seizure models that are known to respond to presently marketed AEDs. These strategies do not take into account that epilepsy can be a progressive disease. Moreover, region-specific aspects of epileptogenesis are rarely considered when new AEDs are developed. Seizures in the temporal lobe are often difficult to treat. Animal studies on various seizure models in the hippocampus and the entorhinal cortex (EC) suggest that these structures do not a priori produce seizures that are difficult to treat. However, seizure-like events in the EC tend to progress to a state of status epilepticus-like activity that cannot be suppressed by presently marketed AEDs. Loss of gamma-aminobutyric acid (GABA)ergic neurotransmission and increased excitatory synaptic coupling seem to cooperate for induction of this state. Epilepsy induced alterations in the interaction between the EC and the hippocampus may lead to alterations that facilitate precipitation of seizures. Because of the recurrent interaction between the hippocampus and the EC, these seizures may reach an intensity that is no longer controllable by presently available AEDs. Ontogenetic alterations of the circuitry between the EC and the hippocampus, seizure-induced stabilization of synaptic connections overexpressed during ontogenesis, seizure-induced lesions and subsequent rearrangements of internal cell properties, and synaptic arrangements and kindling-like alterations of nerve cell and glial behavior may all be involved in the generation of a neuronal aggregate whose balance between inhibitory and excitatory processes becomes readily disturbed. Strategies for the development of AEDs treating such seizures should suppress hyperactivity and prevent progression of epileptogenesis. AEDs directed against seizures may be effective if they can be given in sufficient concentrations to suppress very intense local seizures.

Animals↗
PubMed1993

Properties of horizontal cells transiently appearing in the rat dentate gyrus during ontogenesis.

In an ontogenetic study, combining morphological analysis and patch clamp recordings, a transiently appearing horizontal cell type was identified in the dentate gyrus. The cells were exclusively located in the outer third of the stratum moleculare. They were present at postnatal day 2 (P2) and could be identified with fluorescent dyes until around P14. The morphology was bipolar, with a putative axonal and a dendritic process stretching out parallel to the pial surface without any preferential direction. Patch clamp studies in the current and voltage clamp mode were performed in hippocampal slices on visually identified horizontal cells, between P4 and P7, which were subsequently stained with lucifer yellow. The cells had a low resting membrane potential, around -55 mV. They were excitable, displaying broad action potentials (duration 3-20 ms) and, unlike mature dentate granule cells, they also expressed a strong delayed inward rectifier with properties reminiscent of the IQ current. Unlike granule cells, no postsynaptic signals could be observed during elevation of [K+]o or electrical stimulation, suggesting that the horizontal cells did not participate in functional hippocampal circuitry. We suggest that these cells represent migrating cells with subsequent differentiation to granule cells or inhibitory interneurons. Alternatively they may be part of the early radial glia or serve as transient target cells for afferent fibres between the entorhinal cortex and the dentate gyrus.

Animals↗
PubMed1991

Argiotoxin636 inhibits NMDA-activated ion channels expressed in Xenopus oocytes.

Argiotoxin636, a component of the spider venom of argiope species, was chemically synthesized together with a number of derivatives in order to analyse their blocking activity on mammalian glutamate receptors. Xenopus laevis oocytes injected with rat brain mRNA served as assay system. The results showed that argiotoxin636 had a higher affinity for N-methyl-D-aspartate (NMDA) than for kainate receptors, blocking the corresponding ion channels in a voltage-dependent manner. Modifications of the polyamine tail or the terminal arginine residue strongly reduced the blocking potency. The iodinated monohydroxyl phenylderivatives, however, retained their NMDA-selective binding and could serve as non-competitive antagonists for radioligand binding assays aiding in the biochemical isolation of glutamate receptors.

Animals↗
PubMed1990

Structural and functional characterization of the gamma 1 subunit of GABAA/benzodiazepine receptors.

The GABAA receptor gamma 1 subunit of human, rat and bovine origin was molecularly cloned and compared with the gamma 2 subunit in structure and function. Both gamma subunit variants share 74% sequence similarity and are prominently synthesized in often distinct areas of the central nervous system as documented by in situ hybridization. When co-expressed with alpha and beta subunits in Xenopus oocytes and mammalian cells, the gamma variants mediate the potentiation of GABA evoked currents by benzodiazepines and help generate high-affinity binding sites for these drugs. However, these sites show disparate pharmacological properties which, for receptors assembled from alpha 1, beta 1 and gamma 1 subunits, are characterized by the conspicuous loss in affinity for neutral antagonists (e.g. flumazenil) and negative modulators (e.g. DMCM). These findings reveal a pronounced effect of gamma subunit variants on GABAA/benzodiazepine receptor pharmacology.

Amino Acid Sequence↗
PubMed1990

GABAA-receptors: structural requirements and sites of gene expression in mammalian brain.

GABAA-receptors, the major synaptic targets for the neurotransmitter GABA, are gated chloride channels. By their allosteric drug-induced modulation they serve as molecular control elements through which the levels of anxiety, vigilance, muscle tension and epileptiform activity can be regulated. Despite their functional prominence, the structural requirements of fully functional GABAA-receptors are still elusive. Expression of cDNAs coding for the alpha 1- beta 1-subunits of rat brain yielded GABA-gated chloride channels which were modulated by barbiturates but displayed only agonistic responses to ligands of the benzodiazepine receptor. GABAA-receptors with fully functional benzodiazepine receptor sites were formed when the alpha 1- and beta 1-subunits were co-expressed with the gamma 2-subunit of rat brain. These receptors, however, failed to show cooperativity of GABA in gating the channel. In order to determine the subunit repertoire available for receptor assembly in different neuronal populations in vivo, the sites of subunit gene expression were (alpha 1, alpha 2, alpha 3, alpha 5, alpha 6, beta 1, beta 2, beta 3, gamma 2) mapped by in situ hybridization histochemistry in brain sections. The mRNAs of the alpha 1-, beta 1- and gamma 2-subunits were co-localized e.g. in mitral cells of olfactory bulb, pyramidal cells of hippocampus as well as granule cells of dentate gyrus and cerebellum. The lack of colocalization in various other brain areas points to an extensive receptor heterogeneity. The presence of multiple GABAA-receptors in brain may contribute to synaptic plasticity, differential responsiveness of neurons to GABA and to variations in drug profiles.

Animals↗
PubMed1990

GABAA-receptor expressed from rat brain alpha- and beta-subunit cDNAs displays potentiation by benzodiazepine receptor ligands.

In mammalian brain, the activation of GABAA-receptors is associated with the opening of chloride channels, whose function can be allosterically modulated by drugs, in particular by ligands of the benzodiazepine receptor. Agonistic ligands potentiate while inverse agonists reduce the efficiency of GABA. We have cloned cDNAs encoding alpha 1- and beta 1-subunits of the GABAA-receptor from rat brain. When the corresponding RNAs were co-expressed in Xenopus oocytes. GABA-induced currents were recorded which were inhibited by bicuculline and potentiated by pentobarbital. GABA activated the channel in a weakly cooperative manner. Furthermore, the GABA-response was modulated by benzodiazepine receptor ligands. However, not only various agonists but also the antagonist flumazenil and the inverse agonist DMCM potentiated the GABA-response. Thus, alpha 1- and beta 1-subunits are sufficient to form GABAA-receptors which contain benzodiazepine binding sites, although in a functionally restricted form.

Amino Acid Sequence↗
PubMed1990

Reinnervation and recovery of mouse soleus muscle after long-term denervation.

Reinnervation and recovery of the mouse soleus muscle were studied 2-10 months after denervation periods of about 7 months. To maintain denervation the right sciatic nerve was frozen 14 times at 2-week intervals. Though initially intermittent muscle reinnervation occurred, contractile force of denervated muscles was reduced to less than 10% of the contralateral muscles by the fifth nerve freezing and further declined thereafter. Following reinnervation, recovery of soleus muscle force proceeded slowly to reach plateau values after 5-6 months. Tetanic muscle force reached on average 72% (range 58-86%, n = 12) of contralateral muscles after 5-10 months, (P less than 0.01, t-test for absolute values) and 87% of unoperated animals after 10 months (P less than 0.05, n = 5). Muscle fibre diameters were significantly reduced in reinnervated muscles, but frequency distributions were normal and similarly shaped in reinnervated and control muscles, suggesting complete muscle reinnervation and the absence of denervated fibres even at 2 months of reinnervation. Total numbers of muscle fibres were similar in reinnervated (842 +/- 73 S.D., n = 15), contralateral (854 +/- 104 S.D., n = 15) and control soleus muscles (853 +/- 77 S.D., n = 5). The number of myelinated axons in regenerating soleus nerves reached control values by 3 months after the last freezing, continued to increase till 6 months (150% of control), and declined thereafter (125% at 9-10 months). In the contralateral soleus nerves the number of myelinated axons remained constant during this period. Nerve fibre diameters remained abnormally small; even after 10 months of reinnervation fibre diameters were unimodally distributed with a mean diameter of 3.3 microns in contrast to the bimodal distribution in intact nerves (mean values 3.9 and 9.0 microns, respectively). Total fibre cross-section area per nerve increased with time but reached only 54% +/- 6 S.D., (n = 3) of contralateral nerves by 10 months. The relative thickness of the myelin sheath (g-ratio) returned to normal after 9-10 months. Anatomically, muscle reinnervation appeared to be complete by 7-8 weeks since unusually small muscle fibre profiles were absent.(ABSTRACT TRUNCATED AT 400 WORDS)

Acetylcholine↗
PubMed1990

Functional properties of recombinant rat GABAA receptors depend upon subunit composition.

GABA-gated chloride channels were expressed in human embryonic kidney cells following transfection of cDNAs encoding the alpha 1, beta 2, and gamma 2 subunits of the rat GABAA receptor (GABAR). Functional properties were determined using patch-clamp techniques in the whole-cell and outside-out configurations. Large whole-cell currents were observed in cells expressing the alpha 1 beta 2, alpha 1 gamma 2, and alpha 1 beta 2 gamma 2 subunit combinations. The unique characteristics of GABAR channels consisting of these subunit combinations depended upon the presence or absence of beta 2 and gamma 3 subunits. GABA-activated currents in cells expressing GABARs with the beta 2 subunit desensitized faster and showed greater outward rectification, and the channels had a shorter mean open time than GABARs composed of alpha 1 gamma 2 subunits. When the gamma 2 subunit was present the resulting GABAR channels had a larger conductance. The slope of the concentration-response curve was significantly steeper for GABARs composed of alpha 1 beta 2 gamma 2 subunits compared with GABARs consisting of alpha 1 beta 2 or alpha 1 gamma 2 subunit combinations.

Animals↗