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Biomedical subjects

N Popov

Publications and source records attributed to N Popov.

At least 37 records · Page 2Linked to original sources
PubMed1988

A biochemical and immunohistological study of calmodulin in rat brain structures.

Calmodulin content and immunoreactivity in rat brain structures, believed to be essential site involved in plasticity events, were determined by using biochemical and immunohistochemical methods, respectively. The levels of cytosolic and membrane-bound calmodulin paralleled the overall distribution pattern of calmodulin immunoreactivity. Very intense immunoreactivity was observed in neuronal structures of hippocampus, striatum and mesencephalon. White matter structures and, especially, myelinated nerve fibres did not reveal calmodulin immunoreactivity. Thus, the present findings are consistent with data reported in the literature that calmodulin, unlike to other calcium-binding proteins, is primarily associated with neuronal elements. The present findings support the usefulness of calmodulin studies in elucidating of cellular mechanisms underlying neuronal plasticity.

Animals↗
PubMed1988

Alterations in calmodulin content of rat brain areas after chronic application of haloperidol and amphetamine.

The water-soluble (cytosolic) and Lubrol-soluble (membrane-bound) calmodulin contents were determined radioimmunologically in fractions of striatum, hippocampus and cerebellum of dopamine supersensitive rats. Development of supersensitivity was the sequel of 3-weeks treatment of the animals with 1 mg/kg haloperidol or 5 mg/kg amphetamine i.p. daily. In the dopamine-rich striatum, the membrane-bound calmodulin content was increased by both modes of treatment, consistent with data from the literature. The patterns suggest that additional calmodulin was synthesized under the conditions studied. The hippocampus, the region poor in dopamine while playing an essential role in learning and memory formation processes, revealed similar patterns after both modes of treatment. However, in this region a pronounced translocation was seen, i.e. a redistribution from the cytosolic into the membrane compartment, without signs evidencing enhanced synthesis. The third region under investigation, the cerebellum, did not show any alterations in calmodulin content. Differentiation between pre- and postsynaptic changes was not possible. The results are discussed in the light of the present knowledge about participation of dopaminergic systems in processes of neuronal plasticity.

Amphetamine↗
PubMed1985

Effects of D-galactosamine and D-glucosamine on retention performance of a brightness discrimination task in rats.

The glycoprotein and ganglioside precursors D-galactosamine and D-glucosamine were tested for effects on acquisition and retention of a brightness discrimination reaction in rats. Intraperitoneally (1.85 mmoles/kg) and intraventricularly (0.8 mumoles) applied D-galactosamine had no influence on acquisition, but improved the retention performance. Intraperitoneally (6.0 mmoles/kg) and intraventricularly (2.4 mumoles) applied D-glucosamine showed qualitatively identical results, i.e. improving effect on retention performance. The penetration abilities of [3H]D-glucosamine and [3H]N-acetyl-D-glucosamine to cross the blood-brain barrier were tested: D-glucosamine penetrated easily the blood-brain barrier (approximately 2:1 relation). However, after intravenous application of 200 mumoles 30 min before training both substances showed a positive effect on retention performance. The findings are discussed in the light that the retention-improving effects of the hexosamines under investigation are believed to be due to a direct, activating influence on glycoprotein and/or ganglioside syntheses in the brain.

Amino Sugars↗
PubMed1985

Effects of carbohydrate precursors of glycoproteins on retention performance of a brightness discrimination task in rats.

The influence of intraventricularly applied carbohydrate precursors of glycoproteins on acquisition and retention of a brightness discrimination task in rats was tested. The injection of 0.8 mumoles L-fucose/animal, N-acetylneuraminic acid or D-galactosamine as well as 2.4 mumoles/animal D-galactose or D-glucosamine 30 min before starting the behavioural experiments significantly improved the retention performance of the acquired behaviour. The intraventricular application of 2.4 mumoles D-mannose/animal had no influence on the behavioural parameters tested. The results are discussed in the light of an activation of glycoprotein formation in brain tissue mainly by carbohydrates which occupy terminal positions in the oligosaccharide chains.

Animals↗
PubMed1984

Protective effect of uridine on D-galactosamine-induced deficiency in brain uridine phosphates.

In the rat, 2 h after intraventricular application of 10 mumoles D-galactosamine as well as 10 and 20 mumoles uridine, opposite effects on brain content of UDP-glucose and uracil nucleotides were observed. While D-galactosamine caused a strong decrease in content of uridine phosphates, the brain content of the latter substances was markedly increased after uridine application. Furthermore, 20 mumoles uridine applied 10 min prior to D-galactosamine administration prevented the D-galactosamine-induced drop in brain uridine phosphates. The results are discussed in the light of behavioural findings in which D-galactosamine-induced impairment of retention performance of an acquired behaviour could be abolished by uridine pretreatment.

Animals↗
PubMed1983

Changes in activities of fucokinase and fucosyltransferase in rat hippocampus after acquisition of a brightness discrimination reaction.

Activities of enzymes involved in utilization of the glycoprotein precursor L-fucose (fucokinase and fucosyltransferase) were studied in rat hippocampal tissue after acquisition of a brightness discrimination reaction. Fucokinase activity was increased immediately after training, while fucosyltransferase revealed decreased values. However, 7 hr after training fucokinase activity showed normal values, while fucosyltransferase activity rose in trained animals over active and passive controls. The results are discussed in the light of a regulatory role that fucokinase and fucosyltransferase may play in fucose utilization under altered functional conditions.

Animals↗
PubMed1983

PAGE-autoradiography of fucose incorporation into rat hippocampal glycoproteins after acquisition of a brightness discrimination.

Male rats aged 8 weeks received intraventricular injections of 100 microCi (3.7 MBq) L-[1-3H] fucose each, 7 h after acquisition of a brightness discrimination task. Two, 8 and 24 h as well as 16, 29 and 60 days after injection of labelled fucose hippocampal tissue was prepared to obtain Tris-soluble, Triton-soluble and Triton-resistant fractions. Two and 8 h after application of [3H]fucose, the trained animals revealed an increased incorporation of fucose mainly into the Triton-soluble glycoproteins. However, it is considered that also material from the Tris-soluble fraction may be used as an additional precursor for Triton-soluble glycoproteins. Quantitative analysis of autoradiographic densitograms obtained after SDS-polyacrylamide gel electrophoresis showed the occurrence of a training-related increase in fucose incorporation predominantly into the slow-moving Triton-soluble glycoproteins. The latter exhibited a higher turnover rate than the faster-moving glycoproteins. For the longer incorporation times (days) after injection of labelled fucose, no differences were observed between trained animals and corresponding active and passive controls.

Animals↗
PubMed1982

Mechanisms of dopamine induced changes in hippocampal glycoprotein metabolism.

In rat hippocampal slices incubated in the presence of dopamine, a relatively strong correlation was observed between changes in the incorporation of 3H-fucose into total proteins and the formation of GDP-3H-fucose. However, in hippocampal homogenate the incorporation of 14C-fucose from GDP-14C-fucose was not stimulated by dopamine. In contrast, the incorporation of 3H-fucose was stimulated by dopamine to a similar extent observed in hippocampal slices. Furthermore, in hippocampal slices dopamine did not increase the activity of fucosyltransferase. These results, together with our previous findings, suggest that the increased incorporation of fucose induced by dopamine in the hippocampal slices may be due to a receptor-mediated cAMP-dependent regulation, which controls the rate of fucosylation of acceptor-glycoproteins either at the level of fucose phosphorylation or of formation of GDP-fucose rather than the activity of fucosyltransferase.

Animals↗
PubMed1982

Distribution of hippocampal glycoproteins as demonstrated in rats by lectin binding and autoradiography after intraventricular injections of labelled fucose, N-acetyl-glucosamine and mannose.

The present study demonstrates distinct distribution patterns of glycoproteins in rat hippocampus, with respect to synthesis from precursors (autoradiography) and endogenous contents (lectin binding). The autoradiographic analysis performed 1, 2, 8 and 24 h after intraventricular injections of tritium-labelled L-fucose. N-acetyl-D-glucosamine and D-mannose revealed that up to 2 h after application of any of the three precursors, radioactivity occurred in the pyramidal and granular cell layers. Afterwards, however, rapid migration of label proceeded from the cell bodies into the neuropil after application of fucose and acetylglucosamine, while after injection of mannose a considerable amount of radioactivity stayed in the cell body layers, even 24 h after administration of labelled precursor. These findings were consistent with the histochemical visualization of glycoprotein constituents by fluorescent wheat germ lectin (preferentially binding to glucosaminyl residues) and concanavalin A-horseradish peroxidase (preferentially binding to mannosyl residues). These showed a heavy staining predominantly in neuropil and somata, respectively, with concanavalin A-binding giving more distinct patterns than the application of labelled mannose. The usefulness of the three glycoprotein precursors as correlates with functional behavioural changes in discussed.

Acetylglucosamine↗
PubMed1980

Effect of L-fucose on brain protein metabolism and retention of a learned behavior in rats.

The intraperitoneal or intraventricular application of L-fucose (100 mg/kg or 75 microgram, respectively) prior to training in shuttle box avoidance as well as in shock-motivated brightness discrimination in rats significantly improved the retention of learned behavior 24 hr later. The application of D-fucose was without influence on retention. In naive animals, intraventricularly applied L-fucose (75-200 microgram) caused an increase in the rate of protein synthesis in the hippocampus, resulting in a significant increase in total proteins of this brain structure, mainly attributed to the Tris-insoluble protein fractions. The results are discussed in terms of an activation of glycoprotein formation by increasing supply with L-fucose.

Animals↗
PubMed1980

Inhibitory effect of intraventricularly applied D-galactosamine on incorporation of labelled precursors into RNA and protein of rat hippocampus.

Ten mumoles of intraventricularly injected D-galactosamine (GalN) inhibited the incorporation of [(3)H]-guanosine and [(3)H]-leucine into RNA and protein of the rat hippocampus, respectively. The inhibition of guanosine incorporation of appr. 80% occurred during the first 30 min after GalN treatment and lasted at least 4 h. The incorporation of leucine was inhibited by appr. 30% only; this effect occurred not earlier than 90 min after GalN injection. The results demonstrate a similar effect of GalN on brain macromolecular syntheses as already observed in the liver suggesting the same mechanism of action, namely trapping of uridine phosphates. The results are discussed with regard to the amnesic effect of GalN observed on the retention of a brightness discrimination in rats.

Animals↗
PubMed1980

Intraventricularly applied D-galactosamine inhibits the incorporation of [(3)H]-fucose into rat brain glycoproteins.

In the rat, intraventricularly applied D-galactosamine (GalN) (10 or 20 mumoles) inhibited [(3)H]-fucose incoporation into hippocampal and subcortical glycoproteins by appr. 50% of the controls. The inhibitory effect occurred within 40 min after GalN administration and did not reach normal values even 16 h upon GalN injection. During the first hours upon GalN administration the inhibition of fucose incorporation involved predominanatly water-soluble and Triton-soluble glycoproteins, whereas the Triton-resistant fraction showed a delayed suppression. The results suggest that GalN suppresses the formaton of membrane glycoproteins (because only 15% of fucose radioactivity remained in water-soluble fraction) which are believed to play an essential role in formation of long-term memory. Under these aspects, the amnesic effect of GalN on the retention of a brightness discrimination and the abolishment by uridine treatment, as observed in our laboratory, may be interpreted as a further support to the particular role of glycoproteins in the consolidation of a memory trace.

Animals↗