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G Riedel

Publications and source records attributed to G Riedel.

At least 19 recordsLinked to original sources
PubMed1995

Aluminum impairs hippocampal long-term potentiation in rats in vitro and in vivo.

Although aluminum (Al) contributes to a variety of cognitive dysfunctions and mental diseases, the underlying mechanisms of Al interactions with the nervous system are still unknown. We have studied the action of Al on synaptic transmission and long-term potentiation (LTP) by performing electrophysiological recordings both in vivo, using freely moving animals, and in vitro, using hippocampal slices. In vivo recordings of the population spikes (PSs) of dentate gyrus granule cells in response to medial perforant path stimulation were performed on both acutely and chronically (Al each day for 5 days) intraventricularly injected animals. Acute Al-infusion (calculated brain concentrations of 0.27, 0.68, and 2.7 micrograms/ml) had no influence on baseline values. Al at 0.27 microgram/ml did not alter the induction and maintenance of LTP, but 0.68 and especially 2.7 micrograms/ml Al lead to a reduction in LTP, and the potentiation declined to baseline within 2 h. In chronic animals their neuronal responsiveness was reduced and in 30% of the rats the PS was completely lost. High-frequency tetanization failed to induce LTP. In slices, field potentials were evoked stimulating Schaffer collaterals and recording pyramidal cells of the CA1 region. Bath application of 0.68 microgram/ml Al increased the baseline amplitude of the PS slightly, whereas 2.7 micrograms/ml decreased the amplitude and concentrations > 5.4 micrograms/ml blocked the PS completely. Induction of LTP in the presence of 0.68 microgram/ml Al led to a smaller increase of the PS amplitude compared to controls, but the duration of LTP was not affected. In the presence of 2.7 micrograms/ml Al LTP was further reduced and declined to baseline levels within 60 min. Given that LTP is a form of synaptic plasticity underlying some forms of learning, our data suggest that both preparations are suitable models for investigating actions of Al-induced neurotoxicity.

Aluminum↗
PubMed1995

Block of spatial learning by mGluR agonist tADA in rats.

As demonstrated recently, mGluRs are involved in some forms of learning. We thus investigated the effect of tADA (trans-azetidine-2,4-dicarboxylic acid) applied intracerebroventricularly prior to learning a spatial alternation paradigm. Compared to controls, tADA treated animals were amnesic when tested for retention 24 hr after training. Effects of state-dependency were excluded. These data and our earlier work indicate that both mGluR agonists and antagonists can have memory-disrupting effects.

Animals↗
PubMed1995

Inhibition of long-term potentiation in the dentate gyrus of freely moving rats by the metabotropic glutamate receptor antagonist MCPG.

Metabotropic glutamate receptors (mGluRs) are critically involved in the maintenance of long-term potentiation (LTP) (Reymann and Matthies, 1989; Behnisch et al., 1991; Izumi et al., 1991; Bashir et al., 1993). In order to assess further the physiological role of MGluRs in LTP, we injected freely moving rats with the recently available, competitive mGluR antagonist (R,S)-alpha-methyl-4-carboxyphenylglycine (MCPG) intraventricularly and recorded extracellularly the population spike (PS) as well as the field excitatory postsynaptic potential (fEPSP) of the granule cells of the dentate gyrus in response to stimulation of fibers of the perforant path. MCPG was administered in two concentrations (A = 20 mM/5 microliters; B = 200 mM/5 microliters) either 30 min prior to or 5 min after LTP induction. Sodium chloride infusion served as a control. Normal synaptic transmission was not altered by MCPG. However, the mGluR antagonist inhibited LTP in a concentration-dependent manner. Concentration A did not influence the potentiation shortly after the tetanus. In the PS, short-term potentiation (STP), which is decremental in its time course, occurred normally, but in contrast to controls the potentiation declined back to baseline values after 2-3 hr. This dose also reduced the posttetanic increase in the slope function of the fEPSP, and led to a time course of potentiation similar to that for the PS. Concentration B completely abolished the tetanus-induced potentiation. This block was similar to that obtained for the NMDA antagonist 2-amino-5-phosphonopentanoate (AP5). Both MCPG concentrations had no influence on the time course of preestablished LTP. These effects seem to be due to the action of the (+)-isomer of MCPG, since intracerebroventricular application of the (-)-isomer was without effect on the duration and magnitude of LTP. In addition, we were interested in the mGluR subtypes involved in the blocking mechanism of MCPG. 1S,3R-aminocyclopentane-1,3-dicarboxic acid (ACPD)-activated PPI hydrolysis in hippocampal slices was competitively inhibited by MCPG at a concentration of 1 mM or higher. In contrast, this concentration of MCPG did not affect the reduction of forskolin-stimulated cAMP formation by ACPD. These results corroborate recent findings that mGluRs are required for the induction of LTP in CA1 and CA3 in vitro (Bashir et al., 1993; Sergueeva et al., 1993) and in vivo (Riedel and Reymann, 1993). The process of STP is found to be independent of mGluR activation.(ABSTRACT TRUNCATED AT 400 WORDS)

2-Amino-5-phosphonovalerate↗
PubMed1994

Computer-assisted shock-reinforced Y-maze training: a method for studying spatial alternation behaviour.

Y-mazes are widely used for discrimination learning and spatial alternation tasks. We present here a computer-assisted Y-maze model for spatial alternation learning via footshock reinforcement. No intramaze cues are provided and handling between trials is no longer required. Pretraining application of scopolamine (1 mg kg-1) and D-AP5 (2-amino-5-phosphonopentanoate; 0.016 mg) clearly impairs acquisition and retention (tested 24 h after acquisition) of spatial alternation. These effects are not due to state-dependent changes caused by drug treatment. Similar results were reported by others in food-motivated spatial alternation tasks as well as spontaneous alternation paradigms. The data support our model as a useful tool for studying spatial alternation in the Y-maze.

2-Amino-5-phosphonovalerate↗
PubMed1994

(R,S)-alpha-methyl-4-carboxyphenylglycine (MCPG) blocks spatial learning in rats and long-term potentiation in the dentate gyrus in vivo.

Recently, it was demonstrated by the use of the competitive and selective antagonist (R,S)-alpha-methyl-4-carboxyphenylglycine (MCPG) that metabotropic glutamate receptor (mGluR) activation is required to induce long-term potentiation (LTP) in the hippocampus. Accordingly, we investigated whether MCPG also inhibits spatial learning. Rats were trained on a spatial alternation task in a Y-maze with footshock reinforcement, and MCPG (0.0208 mg) was injected intracerebroventricularly prior to training and/or retention test. Animals injected pre-training are clearly impaired in retention, whereas preretention application was without effect. A state dependency could be excluded. Additionally, MCPG at the same concentration completely blocks a potentiation at perforant path/dentate gyrus synapses in vivo. These results strongly implicate a role of mGluRs in spatial learning and LTP.

Animals↗
PubMed1994

Hippocampal long-term potentiation in vivo induces translocation of protein kinase C gamma.

The possible involvement of the Ca(2+)-dependent protein kinase C (PKC) isoenzymes alpha/beta and gamma in mechanisms of long-term potentiation (LTP) was investigated after tetanic stimulation of the perforant path in vivo. Brief tetanic stimulation of the perforant path resulted in a 150% increase in population spike amplitude recorded from the dentate gyrus synapses in response to test stimuli 5 and 10 min after tetanization. Immunoblot analysis of PKC immunoreactivity in cytosolic and membrane fractions revealed a LTP-induced translocation of gamma PKC but not alpha/beta PKC into the cytosol in dentate gyrus but also in the other ipsilateral hippocampal regions. These data suggest different physiological roles of Ca(2+)-dependent PKC isoenzymes in activity-dependent synaptic plasticity.

Animals↗
PubMed1994

LTP in hippocampal CA1 of urethane-narcotized rats requires stronger tetanization parameters.

Rats with chronically implanted electrodes in the hippocampal CA1 region were tested in their capacity to express and maintain long-term potentiation (LTP) of the population spike (PS) or of the field excitatory postsynaptic potential (fEPSP). Two different states were compared: a) freely moving animals; b) urethane-anesthetized animals (1 g/kg, IP). We found that a short, high-frequency tetanus (six bursts of 15 pulses; 200 Hz; double-pulse width; interburst interval 10 s) increased PS amplitudes and fEPSP slopes up to 300% in response to test stimuli in double-pulse width; interburst interval 10 s) increased PS amplitudes and fEPSP slopes up to 300% in response to test stimuli in the awake rat. The PS amplitude slowly decreased in time, returning to baseline levels 4 h post-tetanically, whereas the fEPSP slope remained at higher values for 24 h. Urethane injection reduced the fEPSP slope and abolished the PS to normal test pulses. We thus increased the strength of the test stimuli until we again recorded magnitudes of PSs and fEPSPs comparable to those in the awake animal. In conjunction with these stronger stimuli, tetanus-induced LTP was elicited that for the PS was increased in magnitude and prolonged in duration compared to the untreated control group. Although, stronger tetanic stimuli were applied to the narcotized fEPSP group too, no difference was found compared to controls. These results suggest that urethane narcosis influences the sensitivity of CA1 neurons to express LTP. Stronger stimulation was required to induce and maintain a long-lasting potentiation of the fEPSP slope and PS amplitude.

Animals↗
PubMed1993

An antagonist of the metabotropic glutamate receptor prevents LTP in the dentate gyrus of freely moving rats.

The effect of the competitive metabotropic glutamate receptor antagonist (RS)-alpha-methyl-4-carboxyphenylglycine (MCPG) on long-term potentiation (LTP) in the dentate gyrus was studied in freely moving rats. Intracerebroventricular infusion of MCPG (0.0208 mg) 30 min prior to tetanic stimulation reduced the duration of LTP of the population spike amplitude to 2-3 hr. MCPG itself was without effect on the basal responses evoked by test stimuli. These results provide the first evidence for the requirement of activation of metabotropic glutamate receptors for the induction and maintenance of LTP at perforant path/dentate gyrus synapses in freely moving animals.

Animals↗
PubMed1984

Efficient method for visualization and isolation of proteins resolved in polyacrylamide gels.

Polyacrylamide gel electrophoresis is a popular method used to purify proteins for reconstitution experiments, amino acid composition and sequence determinations. In this report we describe methods that will be of general use in the isolation and characterization of proteins and the benefits of substituting boric acid for glycine in the electrophoresis tray buffers. We also describe how proteins resolved in a variety of gel systems (including those containing sodium dodecyl sulfate) may be rapidly visualized with 8-anilino-1-naphthalene sulfonic acid and efficiently transferred to a second gel for two-dimensional gel analysis, or isolated by electroelution for subsequent characterization.

Anilino Naphthalenesulfonates↗
PubMed1984

Objective evaluation of dextromethorphan and glaucine as antitussive agents.

Twenty-four inpatients affected by chronic cough completed a single-dose double-blind cross-over study of placebo, glaucine 30 mg and dextromethorphan 30 mg. The study was carried out using a balanced incomplete block design, each patient receiving two of the three experimental treatments. Objective evaluation of cough was ensured by means of a writing cough recorder. Coughs after dextromethorphan and glaucine were fewer than coughs after placebo: however only glaucine was significantly different from placebo in reducing coughs. Treatments were well tolerated: clinical results included a reduction in pulse rate after both dextromethorphan and glaucine , and a large number of patients reporting side effects after dextromethorphan administration.

Adult↗
PubMed1980

A plasmid cloning vehicle allowing a positive selection for inserted fragments.

We describe a plasmid cloning vehicle, pTR262, which allows a strong positive selection (resistance to tetracycline) for transformants bearing plasmids which have DNA insertions. pTR262 is derived from plasmid pBR322 and contains the cI gene and adjacent regulator region oRpR or the bacteriophage lambda. The expression of the tetracycline resistance (tet-r) gene(s) in pTR262 requires transcription from pR and is repressed by the cI gene product, lambda repressor. Insertion of a DNA fragment into the HindIII or Bc/I sites in pTR262 inactivates the cI gene and allows expression of the tet-r gene(s) in the host bacterium. A 100-fold increase in the number of tetracycline-resistant transformants is obtained when HindIII- or Bc/I-generated fragments are added to a ligation mixture containing HindIII- or Bc/I-digested pTR 262 DNA.

DNA Restriction Enzymes↗
PubMed1979

The effects of salt concentration and H-1 depletion on the digestion of calf thymus chromatin by micrococcal nuclease.

We have removed histone H1 specifically from calf thymus nuclei by low pH treatment, and studied the digestion of such nuclei in comparison with undepleted nuclei. By a number of criteria the nuclei do not appear damaged. The DNA repeat-length in nuclear chromatin is found to be the same (192 +/- 4 bp) in the presence or absence of H1. These experiments demonstrate that the core histone complex of H2A, H2B, H3, and H4 can itself protect DNA sequences as long as 168 bp from nuclease. Our interpretation is that this represents an important structural element in chromatin, carrying two full turns of superhelical DNA. Depending on conditions of digestion this 168 bp fragment may be metastable and is normally rapidly converted by exonucleolytic trimming to the well-known "core-particle" containing 145 bp. Larger stable DNA fragments observed indigestion of H-1 depleted nuclei appear to arise from oligomers assembled from 168 bp cores in close contact exhibiting trimming of 0-20 bp at the ends. Electrophorograms of undepleted nuclear digests reveal oligomer bands in several size classes, each corresponding to one or more combinations of 168 bp particles, H1-protected spacers of about 20 bp length, and particles with ends trimmed to varying degrees.

Animals↗