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Biomedical subjects

M Krug

Publications and source records attributed to M Krug.

At least 91 records · Page 5Linked to original sources
PubMed1985

Degradation of phenolic compounds by the yeast Candida tropicalis HP 15. I. Physiology of growth and substrate utilization.

The yeast Candida tropicalis HP 15 was able to utilize phenol up to concentrations of 2.5 g/l as a sole carbon and energy source. Phenol was metabolized via the beta-ketoadipate pathway by an inducible enzyme system. Besides phenol, resorcinol, quinol, hydroxyquinol, catechol, and to a lesser extend 4-chlorocatechol, protocatechuate, p-cresol, m-chlorophenol, and p-chlorophenol were metabolized by the yeast. A total of 30 aromatic compounds were tested as substrates.

Adipates↗
PubMed1985

[The effect of the systemic and intraventricular application of orotic acid on monosynaptic evoked potentials in the dentate gyrus in free-moving rats].

In 20 freely moving Wistar rats the influence of systemically and intraventricularly applied orotic acid derivatives on monosynaptically evoked field potentials registered in the dentate gyrus on the stimulation of the medial entorhinal cortex was investigated. Both, methylglucamine-orotate and tris-orotate led to an increase of the amplitude of the population spike. The slope function of the field EPSP, however, remained unchanged. The effect has been observed to begin 2 h after application and had a duration of 6-10 h. The data obtained in a monosynaptic pathway targeting on a brain structure which is known to play a crucial role in memory formation support earlier findings of a transient effect of orotic acid on cerebral excitation processes. An influence on mechanisms of spike generation or other postsynaptic membrane processes might be assumed.

Animals↗
PubMed1984

Failure of translational repression in the phage f2 op3 mutant is not due to an altered coat protein-RNA interaction.

A secondary phenotype of the op3 mutant of RNA bacteriophage f2 is the absence of translational repression of the phage replicase gene by the phage coat protein. We have synthesized RNA fragments corresponding to the site of translational repression for both the wild type and the op3 mutant. Using a quantitative assay, we show that the affinity of the closely related R17 coat protein for the mutant and wild type RNA fragments is the same. In addition, we find that the op3 and R17 coat proteins bind to the wild type RNA fragment with essentially identical dissociation constants. Thus, the altered regulation of replicase protein synthesis in the op3 mutant does not appear to be due simply to a reduced affinity of the translational repressor for its target site.

Bacteriophages↗
PubMed1984

Anisomycin blocks the late phase of long-term potentiation in the dentate gyrus of freely moving rats.

Freely moving rats, chronically implanted with stimulation electrodes in the medial entorhinal cortex and recording electrodes in the dentate gyrus, received two 400 micrograms intraventricular injections of anisomycin during a tetanization procedure that induced a long-lasting potentiation (72 hours) of the monosynaptic field potential. Inhibition of protein synthesis during the tetanization procedure did not immediately influence the induction of long-term potentiation (LTP). However, 3-4 hours after the beginning of tetanization the potentiation effect decayed progressively and was abolished totally during the remaining 7 day observation period. In control experiments anisomycin did not affect the slope of field EPSP's and produced a reversible depression of the population spike amplitude. These data indicate a relatively specific effect of the protein synthesis inhibitor on mechanisms involved in a late phase of LTP stabilization.

Animals↗
PubMed1983

Aminergic blockade modulates long-term potentiation in the dentate gyrus of freely moving rats.

Long-term potentiation (LTP) was induced in the dentate gyrus of freely moving rats by tetanic stimulation of the medial entorhinal cortex under conditions of catecholamine depletion by 200 mg/kg alpha-Methyl-para-tyrosine (AMPT) or blockade of alleged dopamine receptors by 0.5 mg/kg haloperidol. Both substances did not change significantly the normal excitability of the glutamatergic perforant pathway, but affected the establishment of LTP. Whereas the potentiation effect on the EPSP component of the monosynaptic field potential was not changed by both substances when compared to the potentiation of controls, the potentiation of the population spike was prolonged and enhanced. These results point to an effect of catecholaminergic blockade on postsynaptic membranes of the target cells or on other components of the neuronal network but not to a specific influence on the homosynaptic mechanisms of LTP.

Animals↗
PubMed1982

Enzymatic synthesis of a 21-nucleotide coat protein binding fragment of R17 ribonucleic acid.

An oligoribonucleotide with a sequence identical with the bacteriophage R17 replicase initiator region has been synthesized. The sequence also encompasses the binding domain of R17 coat protein, which is known to act as a translational repressor at this site. The 21-nucleotide fragment was synthesized entirely by enzymatic methods, T4 RNA ligase being used to join shorter oligomers. The resulting fragment has a secondary structure with the expected thermal stability. Since the synthetic fragment binds R17 coat protein with the same affinity as a 59-nucleotide fragment isolated from R17 RNA, we conclude that it has full biological activity.

Base Sequence↗
PubMed1982

Reversal of T4 RNA ligase.

Unexpected products detected in oligoribonucleotide synthesis reactions catalyzed by T4 RNA ligase are shown to be a result of a partial reversal of the enzyme reaction. A transfer assay for the reversal of the third step in the RNA ligase reaction mechanism and an exchange assay for the reversal of both the second and third steps are described. Reversal is confirmed by the formation of the expected covalent intermediates, adenylylated donor and adenylyl ligase, from a reaction containing 5'-AMP, unadenylylated ligase, and the tetranucleotide (Ap)3Cp. In the reverse reaction, RNA ligase shows a strong preference for hydrolysis of the 3'-terminal phosphodiester bonds of oligoribonucleotides which terminate in a 3'-phosphate. Several strategies are discussed to minimize the effects of reversal in the enzymatic synthesis of oligoribonucleotides.

Adenosine Monophosphate↗
PubMed1981

Identical responses of the two hippocampal theta generators to physiological and pharmacological activation.

The possible existence of two separate RSA generators in the dorsal hippocampus raises questions as to the degree of coupling or independence of both. In order to answer these questions bipolar EEG recording were made in the CA1 and dentate gyrus of freely moving rats during conditions of RSA generation by different manipulations. The quantitative EEG parameters of simultaneous records were compared and cross correlation functions were calculated. Results indicate that even under different conditions of inducing RSA (physiological activation or injection of arecoline and nicotine) yielding RSA with different frequency characteristics, the quantitative EEG parameters were similar in both recordings. In addition, a high degree of concordance of both EEG was evidenced in the cross correlation function. These observations are discussed in terms of a high degree of coupling between both RS generators.

Animals↗
PubMed1980

The septo-hippocampal pathway: electrophysiological observations.

In 40 rats immobilized with gallamine evoked field potentials were elicited in the dorsal hippocampus by stimulation of the septal nuclei. Latency of the septohippocampal evoked potential (SHEP) elicited by stimulation of the medial septal nuclei, the variations of latencies and amplitudes with increasing stimulus intensities as well as the occurrence of frequency potentiation and post-tetanic potentiation allow the conclusion that the SHEP registered in the stratum granulare of dentate gyrus is mainly monosynaptically elicited. Nevertheless some data discussed in the paper point to the existence of a more complicated and not exclusively monosynaptic activation of granular cells caused by septal stimulation.

Action Potentials↗
PubMed1980

Hemodialysis without heparin infusion using Cordis Dow 3500 hollow fiber.

1) Hemodialysis for 3-4 hrs with C-3500 without heparin infusion is possible. 2) Hemodialysis without heparin with C-3500 may be preferred for patients with active or potential bleeding. 3) Excessive clotting may occur when blood flow is less than 250 ml/min, blood transfusion is used during dialysis or dialysis is longer than 3.5-4 hrs.

Blood Coagulation↗
PubMed1980

The influence of cholinergic drugs on evoked field potentials in the gyrus dentatus of immobilized rats.

We reported previously the elicitation of presumably monosynaptic evoked field potentials in the dentate gyrus of immobilized rats by stimulation of the medial septal nuclei. The septo-hippocampal pathway mediating this evoked potential (SHEP) is widely assumed to be cholinergic in nature. In order to further verify this assumption we studied the effects of muscarinic drugs on the SHEPs. Scopolamine as muscarinic cholinolytic and arecoline as muscarinic cholinergic agent influenced the SHEP in the expected manner. We conclude that the SHEP is elicited by cholinergic muscarinic activation.

Animals↗
PubMed1977

Effects of orotic acid and pirazetam on cortical bioelectrical activity in rabbits.

In order to obtain further evidence of the pharmacological effects of retention-facilitating substances, the influence of sodium-orotate, methylglucamine orotate, and pirazetam on the bioelectrical activity of central nervous system structures were studied. Sodium orotate showed no influence on the cortical and hippocampal spontaneous EEGs of conscious nonimmobilized rabbits. The amplitude of the first surface-positive wave of the cortical evoked potential that was elicited by stimulation of tooth pulp was, however, significantly increased in long-lasting terms by both pirazetam and the two salts of orotic acid. Similarly, the three substances also influenced the changes in excitability induced by PTP of tooth pulp. The findings suggest that these chemicals facilitate in nonspecific manner responses to externally applied stimuli through central structures. The relationships between the altered stimulus response and the retention-facilitating action of these substances are discussed.

Animals↗