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Biomedical subjects

B Lössner

Publications and source records attributed to B Lössner.

At least 19 recordsLinked to original sources
PubMed1993

Glutamate binding to brain membranes is increased in pentylenetetrazole-kindled rats.

The specific binding of L-[3H]glutamate to its receptors was investigated on crude membrane preparations from different brain regions of pentylenetetrazole-kindled rats using a binding assay technique. Pentylenetetrazole kindling induced by 10 intraperitoneal applications of 45 mg/kg over a period of 20 days resulted in a significant increase of both the convulsive susceptibility of animals to the convulsant and the specific L-[3H]glutamate binding in hippocampus and in motor, frontal, and inferotemporal (acoustic) cortex tested with a L-[3H]glutamate concentration of 50 nM. No differences were observed in the other brain structures studied. Kinetic studies indicated that the enhanced L-[3H]glutamate binding to hippocampal membranes from kindled rats reflects changes in the density of the glutamate binding sites rather than an increase in receptor affinity. To study the effect of acute generalized convulsions on L-[3H]glutamate binding to synaptosomal membranes of hippocampus and visual cortex, rats were treated 24 h before the experiment with 60 mg/kg of pentylenetetrazole, i.p. Under these conditions, no differences between treated and control rats were observed. From these findings, it is concluded that the increase in glutamate receptor density demonstrated in hippocampus and several neocortical brain structures of pentylenetetrazole-kindled rats may be the expression of a specific enhancement of susceptibility of glutamatergic systems to this excitatory amino acid developing in the course of formation of pentylenetetrazole-induced kindling.

Animals↗
PubMed1993

[Valine and branched-chain amino acids in the treatment of hepatic encephalopathy].

We studied the effects of infusion of a liver adapted amino acid solution (Amino-Mel hepa: Group A) versus a liver adapted amino acid solution plus L-valine (Amino-Mel hepa + L-valine: Group B) in 30 patients with decompensated liver cirrhosis with coma. Each 15 patients were randomly allocated to the group A and B, respectively. Both regimens included the infusion of glucose and fat, further supplementation of vitamins and trace elements in addition to the amino acid solution. The results of this study show that in patients with advanced stage of hepatic coma a valine increased supply of branched chain amino acids neither influences the course of the disease nor the death rate. The prognosis of patients with this disease is mainly determined by liver function and accompanying complications.

Amino Acids, Branched-Chain↗
PubMed1991

Long-term potentiation induced changes in protein synthesis of hippocampal subfields of freely moving rats: time-course.

The incorporation of L-[U-14C]leucine into proteins of cytosolic (soluble proteins) and of the 100,000 x g pellet fraction from ipsilateral hippocampal subfields (CA1, CA3, CA4/area dentata) of rats was studied during and at various times after electrical tetanisation of the right perforant pathway using topical precursor applications and 1 h incorporation periods. Rates of protein synthesis were estimated calculating the relative specific radioactivity of proteins (RSA). The RSA-values of both protein fractions estimated in the ipsilateral CA4/area dentata were found to be about two times higher in tetanised rats compared to either passive or stimulated controls (p less than 0.05) when leucine was administered 5 min after tetanisation. Under these conditions, no differences between tetanised and control animals were observed in all other hippocampal subfields studied. No differences in RSA-values evaluated in CA4/area dentata between tetanised and passive controls were detected when leucine was administered immediately prior to tetanisation. From 2 h to 8 h after induction of LTP, protein synthesis in CA4/area dentata of tetanised rats appeared to be decreased (p less than 0.05) compared to passive controls. These results provide evidence for a transient LTP-induced augmentation of protein synthesis in the targets which might be an essential prerequisite for those structural changes realising the long-lasting enhanced efficacy of synaptic transmission at perforant path/granular cells connections.

Animals↗
PubMed1990

Posttetanic long-term potentiation in rat dentate area increases postsynaptic 411B immunoreactivity.

411B is a monoclonal antibody raised to chick forebrain postsynaptic densities (PSDs) which also recognises an antigen in brain tissue from adult Wistar rats but not liver, heart, or lung. This antigen is enriched in the PSD fraction and appears to be a useful biochemical marker for plastic changes of postsynaptic structures in the rat brain. The aim of this study was to investigate whether 411B immunoreactivity is changed in various hippocampal subregions by post-tetanic long-term potentiation (LTP). LTP was elicited in freely moving rats by applying four trains of 300 square-wave pulses (frequency 200 Hz, pulse duration 0.2 ms, and intensity 300 mA) into the right perforant path; this included an increase in transmission efficacy at the ipsilateral perforant path-granular cell synapse of the dentate gyrus lasting several days. Eight hours after tetanisation, antigens recognised by monoclonal 411B and a polyclonal anti-actin antiserum were assayed in lysed homogenates of ipsi- and contralateral CA1. CA3, and CA4/dentate area hippocampal subfields as well as in visual cortex, cerebellum, and olfactory bulb dissected from LTP rats, and compared to passive controls. Under these experimental conditions, tetanisation of the perforant path resulted in a significant increase in the titre of 411B in the ipsilateral CA4/dentate area subfield (+34.0%; p less than 0.001) compared with passive controls, whereas in all other brain regions studied no differences between experimental and control rats were observed. In no region were anti-actin titres significantly different from controls.(ABSTRACT TRUNCATED AT 250 WORDS)

Actins↗
PubMed1990

Posttetanic long-term potentiation in the dentate gyrus of freely moving rats is accompanied by an increase in protein synthesis.

In rats, the incorporation of L-[U-14C]leucine into proteins of cytosolic (soluble proteins) and of the 100,000 x g pellet fraction from ipsilateral hippocampus subregions (CA1, CA3 and CA4/area dentata) and visual cortex was studied from 5 min to 65 min after electrical tetanization of the right perforant path. The rates of protein synthesis were estimated calculating the relative specific radioactivity of proteins (RSA). The stimulation parameters used were identical to those of previous experiments inducing post-tetanic long-term potentiation (LTP) of both the amplitude of population spike and the slope function of the excitatory post-synaptic potential (EPSP) in the area dentata. Under these conditions, RSA-values of both fractions evaluated in the CA4/area dentata were found to be about two times higher in tetanized rats compared to either stimulated or passive controls (p less than 0.05). In all the other brain regions studied, no differences between tetanized and control animals were observed. These results provided evidence for an LTP-induced augmentation of protein synthesis in the ipsilateral dentate area which might be an essential prerequisite for those structural changes realizing the long-lasting enhanced efficacy of synaptic transmission at the perforant path-granular cell connections within this hippocampus subfield.

Animals↗
PubMed1989

Correlations between zinc, amino acids and ammonia in liver cirrhosis.

In view of the universal metabolic importance of zinc in the organism, it was the purpose of the present work to determine the concentrations of zinc in serum, of amino acids and ammonia in plasma of patients with liver cirrhosis, and investigate that correlations might exist between these substances. The study involved 18 patients with decompensated liver cirrhosis without coma and eleven with coma. The subjects with normal livers were used as controls. While confirming known data (reduced zinc levels, imbalance of plasma amino acids, hyperammonaemia in chronic liver diseases) the findings also revealed correlations between the above substances. A negative correlations existed between zinc and ammonia. Decreases in zinc serum levels were accompanied by increases in plasma ammonia concentrations in hepatic coma (p less than 0.05). Plasma levels of amino acids did not correlate with serum zinc concentrations.

Amino Acids↗
PubMed1988

Methylglucamine orotate does not affect dopamine-stimulated fucosylation of rat hippocampal proteins.

The present paper is concerned with the question whether dopamine-stimulated fucosylation of glycoproteins of the rat hippocampus in vitro is augmented by treating animals with methylglucamine orotate (MGO). Dopamine (DA) in concentrations between 0.1-0.5 mM resulted in a dose-dependent increase in L-fucose incorporation of up to about 130%. Neither the acute intraperitoneal application of 225 mg MGO/kg body mass nor the daily treatment of rats with 225 mg MGO/kg body mass over a 10-day period changed this dose-dependent relationship significantly. Even the in vitro substitution of nucleotides (1 mM) such as uridine 5'-monophosphate, cytidine 5'-monophosphate, guanosine 5'-monophosphate, and adenosine 5'-monophosphate did not alter dopamine-stimulated fucosylation of rat hippocampal proteins. These findings suggest that DA-stimulated fucosylation of brain proteins is not limited by the supply of nucleotides.

Animals↗
PubMed1988

Metabolism of D-proline beta-casomorphin derivatives in the rat brain.

The aim of the present study was to evaluate the metabolic breakdown of two biologically active derivatives of beta-casomorphin (beta CM)-i.e. D-proline4-beta CM (D-Pro4-beta CM) and des-tyrosine 1-D-proline4-beta CM (DT-D-Pro4-beta CM)- in the rat brain. After intracerebroventricular (icv.) administration of 0.78 nmoles of both [3H]D-Pro4-beta CM and [3H]DT-D-Pro4-beta CM, the concentration of the intact peptides and their metabolites was estimated in brain stem and corpus striatum. Both peptides were degraded in brain tissue forming a common metabolite. Phe-D-Pro-Gly. The metabolic half-lives of DT-D-Pro4-beta CM in brain stem and c. striatum were 22.6 min and 28.6 min, whereas those of D-Pro4-beta CM were 7.8 min and 8.2 min, respectively. According to both half-lives of the intact peptide and the kinetics of the formation of the stable metabolite Phe-D-Pro-Gly. DT-D-Pro4-beta CM seemed to be more resistant to biological degradation in brain tissue than D-Pro4-beta CM. In the case of D-Pro4-beta CM, the dipeptidylpeptidase IV (DP IV) (EC 3.4.14.-) is presumed to be the cardinal enzyme for the breakdown. Since the degradation of these peptides in brain tissue results in the unique metabolite Phe-D-Pro-Gly, the differences in the pattern of biological activities between D-Pro4-beta CM and DT-D-Pro4-beta CM may be due to the action of the corresponding intact peptide.

Animals↗
PubMed1987

Metabolism of beta-casomorphin and its derivatives in rat brain and liver homogenates.

Derivatives of opiate-like acting beta-casomorphin (beta-CM), (Tyr-Pro-Phe-Pro-Gly), were prepared by substitution of D-amino acids. The metabolism of these analogs was studied in brain and liver homogenates. Their half-lives and the metabolites resulting from their biological degradation were determined by means of the HPLC-technique. Resistance to biological degradation, which was considerably enhanced in some derivatives, was shown to depend on the position of the D-amino acids. The following substances proved to be particularly stable: D-Pro2-beta-CM, Des-Tyr-D-Pro2-beta-CM, Des-Tyr-D-Phe3-beta-CM. The resulting metabolites suggest that the activity of proline-specific peptidases is predominant in the catabolic process. The degradation pattern of beta-CM-pentapeptides produced by peptidases in the brain and liver is completely different from that of the enkephalin-pentapeptides, which are likewise protected by substitution of D-stereoisomers for certain L-amino acids. The different degradation kinetics of beta-CM-pentapeptides in neuronal and non-neuronal tissue homogenates (liver) reflect the variation in activity of certain peptidases. Considering the half-lives that we have estimated, we suggest which of the peptides tested has a high resistance against biological degradation in vivo.

Amino Acid Sequence↗
PubMed1986

Degradation of beta-casomorphin in the rat brain in vivo.

The degradation of beta-casomorphin 1-5 (Tyr-Pro-Phe-Pro-Gly (beta CM]--an opiate-like acting pentapeptide--was investigated in brain stem and corpus striatum of male Wistar rats during the first 20 min after an intracerebroventricular (i.c.v.) application of 166 nmol [3H]Phe3-beta CM. Dependent on the time after [3H]Phe3-beta CM injection, the radioactivity carried by beta CM and its metabolites was estimated in the HCl-soluble tissue fraction of these brain structures. The separation of the intact pentapeptide from its metabolites was performed using HPLC-technique. In both brain regions a rapid decrease in the concentration of beta CM was observed during the first 10 min after [3H]Phe3-beta CM application (1st phase). 10 to 20 min after injection, the decrease in beta CM concentration was found to be considerably smaller (2nd phase). Moreover, beta CM is rapidly degraded forming phenylalanine and tyrosine as the main metabolites. Furthermore, at any time, small amounts of Phe-Pro-Gly, Phe-Pro, Pro-Phe-Pro-Gly and Tyr-Pro-Phe-Pro were estimated. From these results, the analgesic effect by i.c.v. application of 166 nmol beta CM is assumed to be caused rather by the intact pentapeptide molecule than by one of its metabolites.

Animals↗
PubMed1985

Inhibition of brain protein fucosylation by sulfated sugar molecules.

Brain fucosyltransferase reaction (GDP-fucose: glycoprotein fucosyltransferase, EC 2.4.1.68) was found to be inhibited by heparin. Also a variety of other sulfated polysaccharides led to a decrease in the fucosyltransferase reaction comparable to that induced by heparin. This action seems not to be related to the structural and functional integrity of the glucosaminoglycan since the same effect of the enzyme reaction was seen using its breakdown products obtained by hydrolysis or ultrasonics. In contrast, unsulfated polysaccharides and constituents of heparin, respectively, did not influence the enzyme reaction at all. The same was true for phosphorylated monosaccharides. Therefore, it seems likely that the inhibitory effect of appropriate polysaccharides or their breakdown products is related to the action of sulfated sugar units. Moreover, investigating the influence of a heparin hydrolysate on the incorporation of [3H]fucose into the glycoproteins of hippocampal slices, also an inhibition of the sugar incorporation was found. Thus, the inhibitory influence of sulfated sugar units on brain fucosyltransferase reaction seems to be effective under both conditions, in the assay system of the enzyme in vitro as well as in intact cells of the hippocampal structure.

Animals↗
PubMed1985

Dopamine-stimulated fucosylation of brain proteins in vitro is not inhibited by puromycin.

In slices of rat hippocampus, the influence of puromycin (0.5 mM) on dopamine (0.5 mM)-stimulated L-fucose incorporation into glycoproteins was studied. Puromycin (15 min, 2 h and 4 h pretreatment) inhibited protein synthesis by some -70% (estimated by the in vitro incorporation rate of L-leucine), whilst L-fucose incorporation into rat hippocampal glycoproteins was only inhibited about -20% (4 h pretreatment) compared to control values (100%). Under these experimental conditions, the dopamine-induced increase in both the L-fucose incorporation into glycoproteins and the activity of fucokinase was not affected by puromycin. These data suggest that these short-lasting dopamine actions do not depend on protein synthesis.

Animals↗
PubMed1985

Dopamine stimulated fucosylation of rat hippocampal proteins in vitro. A histoautoradiographic study.

The aim of the present investigation was to provide evidence for the topographic localization of dopamine (0.5 mM) stimulated L-[3H]fucose incorporation into rat hippocampal proteins in vitro. For this purpose, radiochemical estimations of fucosylation of hippocampal proteins were paralleled by histoautoradiography. The data of the radiochemical study showed a dopamine induced increase in L-[3H]fucose incorporation into hippocampal proteins by about + 120% compared to control values. Hippocampus slices from the same animals were processed for histoautoradiography. Under the influence of dopamine, L-[3H]fucose incorporation (estimated as silver grains either per cell or per square) was found to be significantly elevated in pericarya of granular cells as well as in the neuropil and in the glial cells of the stratum moleculare of the exposed blade of dentate area. This increase was most pronounced in the pericarya of granular cells, i.e. by about 200% over control level. With exception of fibres in the stratum lacunosum-moleculare of CA 1, the trends of increase in neurons, glial cells and fibre layers of other hippocampus subfields were not significant. The results may suggest that in rat hippocampus slices, dopamine induced increases in L-fucose incorporation are particularly localized in neurons of the exposed blade of dentate area.

Animals↗
PubMed1985

[Dopamine-stimulated glycosylation of rat hippocampal proteins in vitro: structure-response relationship].

Dopamine, but also other catecholamines (noradrenaline, adrenaline and isoprenaline), as well as L-dopa and alpha-methyl-dopa increase the incorporation of L-[1-3H]fucose into proteins of rat hippocampal slices. Among all substances that have been tested, dopamine exhibited the highest activity. Other non- or monohydroxylated phenylethylamine-derivatives (tyramine, octopamine, beta-phenylethylamine, metamphetamine) and pyrogallol had no effect on the fucosylation of hippocampal proteins. alpha-Methyl-dopa was less active than L-dopa. However, under the influence of alpha-methyl-dopa, an inhibitor of the dopadecarboxylase (aromatic L-amino acid decarboxylase, EC 4.1.1.28) the stimulatory effect of L-dopa on protein fucosylation was attenuated. From these results it is concluded that the dopamine-stimulated glycosylation of hippocampal proteins is triggered by (at least) two mechanisms, i.e. (1) via an activation of adenylate cyclase coupled dopamine receptor sites, and (2) via a mechanism which appears to be not related to an activation of transmitter-receptor sites but linked to the 3,4-dihydroxy-phenylethylamine-structure.

Animals↗
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↗
PubMed1984

Dopamine stimulated glycosylation of brain proteins in vitro is inhibited only partially by dopamine receptor antagonists.

Dopaminergic agonists which act on adenylate cyclase-linked dopamine receptor sites (D1-type) (dopamine, apomorphine and ADTN) induced a dose-dependent increase in the incorporation of L-fucose and D-mannose into glycoproteins of hippocampal, striatal and cortical slices of rat and mouse brain, whilst in rat liver slices dopamine failed to elicit such alterations in protein glycosylation. Testing in slices of rat hippocampus dopaminergic agonists with selective affinity to D2-receptors (bromocriptine, ergometrine) no changes in sugar incorporation into glycoproteins of rat hippocampus were observed. Dopamine stimulated L-fucose incorporation into rat hippocampal glycoproteins was inhibited to a different degree, but almost incompletely by dopamine receptor antagonists like haloperidol, D-butaclamol, promazine and alpha-flupenthixol, whilst chloropromazine and the selective D2-receptor antagonist sulpiride were without any effects. Also serotonin receptor antagonists (cinanserine) and beta-adrenergic receptor blockers (pindolol, alprenolol, practolol) failed to interfere with this dopamine action. But D,L-propranolol enhanced dopamine stimulated glycosylation of rat hippocampal proteins in an additive synergistic manner. This effect appeared to be not related to the antagonistic action of propranolol on beta-adrenergic receptor sites. From our results it is concluded that interactions with dopamine receptor sites (D1-type) is only one part of the mechanism triggering dopamine stimulated glycosylation of brain proteins in vitro.

Adrenergic beta-Antagonists↗
PubMed1984

Dopamine stimulated L-fucose incorporation into brain proteins is related to an increase in fucokinase activity.

Fucokinase (E.C. 2.7.1.52) activity was estimated in supernatant of homogenate from hippocampal slices. After an incubation of the slices in the presence of 0.5 mM dopamine a significant increase in the enzyme activity was observed. Under these conditions also an increase in the incorporation of [3H]fucose into hippocampal glycoproteins was observed. Thereby, the dopamine elicited changes in both fucokinase activity and fucose incorporation are similar in their time dependence. Moreover, dibutyryl-cyclic AMP led also to an increase in both fucokinase activity and sugar incorporation in hippocampal slices whereas cyclic AMP was without effect when added to the incubation mixture of the enzyme. The observed changes in fucokinase activity and its regulation by Ca2+ are discussed in terms of possible mechanisms realizing the dopamine stimulated fucosylation of rat hippocampal glycoproteins.

Animals↗