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Biomedical subjects

A A Lebedev

Publications and source records attributed to A A Lebedev.

At least 19 recordsLinked to original sources
PubMed2006

[Surgical treatment of patients with micro-cystitis of tuberculous and other etiology].

The urinary bladder was reconstructed by using different segments of the gastrointestinal tract in 45 patients aged 21 to 72 years. The indication for surgery was microcystis of tuberculous and other etiology in 28 (62.2%) and 17 (37.8%) patients, respectively. The overall post-operative mortality was 2.2% (1 patient). Early and late complications were observed in 17.8 and 30.4% patients, respectively. Analysis of the causes of complications has indicated that they are associated with the urine diversion method and with the scope of urinary bladder resection. Seven repeated operations were performed. Augmentation cystoplasty should follow subtotal microcystectomy. For correction of azotemia and for prevention of stricture in the early postoperative period, the neocystis should be continuously irrigated with antiseptic solutions in order to eliminate urine, mucus, and blood clots.

Adult↗
PubMed2005

Multifractal properties of the harmonic measure on Koch boundaries in two and three dimensions.

The multifractal properties of the harmonic measure on quadratic and cubic Koch boundaries are studied with the help of a new fast random walk algorithm adapted to these fractal geometries. The conjectural logarithmic development of local multifractal exponents is guessed for regular fractals and checked by extensive numerical simulations. This development allows one to compute the multifractal exponents of the harmonic measure with high accuracy, even with the first generations of the fractal. In particular, the information dimension in the case of the concave cubic Koch surface embedded in three dimensions is found to be slightly higher than its value D1 =2 for a smooth boundary.

Journal Article↗
PubMed2005

The effects of neurochemical lesioning of dopaminergic terminals in early ontogenesis on behavior in adult rats.

6-Hydroxydopamine, which induces selective degeneration of the dopaminergic system of the brain, was given intraamniotically to rats on days 13 and 17 of intrauterine development at a dose of 75 microg/fetus. Similar experiments were performed with 6-hydroxydopamine on days 4 and 10 of neonatal life. Rats were subsequently reared and motor and emotional (dopamine-dependent) types of behavior were studied in adulthood, addressing behavior in the open field test, rotatory behavior, anxiety in an elevated cross maze, a place-preference conditioned response, acquisition of the ability to differentiate new and old arms in a Y maze, aggressivity in the "foreigner-resident" test, and self-stimulation in a Skinner box. Prenatal exposure, to a lesser extent than postnatal exposure, initiated rotatory and stereotypical behavior, decreased the level of anxiety (fear) in the elevated maze, and reinforced the effects of phenamine in the conditioned place-preference test, impaired the differentiation of old and new Y-maze arms, impaired aggressivity in the "foreigner-resident" test, and impaired self-stimulation of the lateral hypothalamus. It is concluded that the early postnatal period of development is more sensitive to the action of this neurotoxin than the prenatal period. This is associated with the critical periods of the formation of the dopaminergic system during ontogenesis, which depend on synaptogenesis.

Age Factors↗
PubMed2004

The effects of substance P after central administration on the activity of the mesolimbic system of the rat brain as studied by microdialysis.

In vivo microdialysis was used to study the effects of substance P on dopamine, dihydroxyphenylacetic acid, and homovanillic acid levels in the nucleus accumbens in rats. Each animal received sequential injections of physiological saline, 0.1 microg of substance P, and 1 microg of substance P into the lateral ventricle over three days. Dialysates showed increases in dopamine levels in response to neuropeptide, by 41% for the 0.1 microg dose and 71% for the 1 microg dose. The dynamics of these changes also depended on the concentration of the agent. Administration of 1 microg of substance P gave a peak dopamine level at 50 min; the neurotransmitter level remained significantly elevated 75 min after dosage with substance P. The dopamine level was increased only at 75 min when the 0.1 microg dose of neuropeptide was used. Changes in metabolite levels were also dose-dependent. After the 1 microg dose, the dihydroxyphenylacetic acid level increased by 28%, while the 0.1 microg dose produced no significant change in the level of this metabolite. The homovanillic acid level did not respond to administration of substance P at either dose. These data support the suggestion that the influence of substance P on the internal compensation system is to a significant extent mediated by dopaminergic mechanisms and provides a possible explanation for the effects of the neuropeptide seen in a conditioned place preference reflex.

3,4-Dihydroxyphenylacetic Acid↗
PubMed2003

Role of the dopaminergic system of the brain in the effects of glucocorticoid hormones.

The conditioned reinforcement properties of the synthetic glucocorticoid dexamethasone and the possible mechanisms of its action were studied using a conditioned place preference response. On test day 1, male Wistar rats were placed in a two-chamber apparatus and the time spent in each sector was measured for 10 min. Over the next six days, combinations of one of the chambers with administration of agents (reinforcement) were presented using injections of dexamethasone in one sector and injections of physiological saline in the other sector on alternate days. After combinations of dexamethasone (0.25-0.77 mg/kg, i.p.) with the non-preferred sector, rats showed dose-dependent place preference on test day 2; however, when dexamethasone was combined with the initially preferred sector, animals given dexamethasone at a dose of 0.75 mg/kg showed only a slight level of place avoidance. Subthreshold doses of phenamine (0.25 mg/kg) given alone had no effect; however, when given on a background of dexamethasone (0.25 mg/kg), phenamine evoked a place preference response in rats lacking an initial place preference for one sector. Administration of dexamethasone alone (0.25 mg/kg) in these conditions did not induce place preference. Administration of the dopamine D2 receptor antagonist sulpiride (20 mg/kg) 30 min before combinations of dexamethasone (0.25 mg/kg) with the non-preferred sector completely prevented the acquisition of place preference. Administration of the D1 dopamine receptor antagonist SCH23390 (0.05 mg/kg) had no effect on the acquisition of conditioned preference. These results provide evidence for the involvement of D2 receptors in conditioned place preference induced by dexamethasone.

Amphetamine↗
PubMed2003

Mechanisms of the influences of the central administration of substance P on ethanol consumption in chronically alcoholic rats.

The effects of central administration of substance P (SP) on alcohol consumption and dopamine metabolism in the projections of the mesocorticolimbic and nigrostriatal systems of the brain were studied in chronically alcoholic rats. Rats received 15% ethanol solution for 6 months without choice. Intraventricular administration of SP (1 microg/rat) decreased consumption of 10% ethanol solution by 41% compared with controls in an alcohol free choice test lasting one day. After chronic alcoholism, there was a decrease in the ratio of dihydroxyphenylacetic acid (DOPA) and homovanillic acid (HVA) to dopamine in the nucleus accumbens and striatum in rats subjected to alcoholism, as compared with intact controls. Chronically alcoholic rats treated with SP showed increases in DOPA, HVA, and the DOPA:dopamine and HVA:dopamine ratios in the nucleus accumbens as compared with animals given physiological saline, by 17%, 23%, 9% and 19% respectively. The only increases in the striatum were in the absolute levels of DOPA and HVA, by 28% and 29%, while the ratios of these metabolites to dopamine remained unchanged. Thus, central administration of SP decreased the voluntary consumption of ethanol in the ethanol free choice test and enhanced dopamine metabolism in structures of the mesolimbic and nigrostriatal systems in chronically alcoholic rats.

3,4-Dihydroxyphenylacetic Acid↗
PubMed2003

[Effect of centrally administrated substance P on the brain mesolimbic system activity in rats as measured by microdialysis].

Action of substance P on the contents of dopamine, dihydroxyphenylacetic acid and homovanillic acid in the nucleus accumbens of rats was investigated with microdialysis procedure. During 3 days, each animal daily received i.v. the saline (the 1st day), 0.1 mcg of substance P (the 2nd day), 1 mcg of substance P (the 3rd day). Elevation of accumbal dopamine was observed amounting up to 41% and 71% for 0.1 mcg and 1 mcg of substance P, resp. Rates and duration of these changes also depended on neuropeptide concentration. 1 mcg of substance P produced the dopamine elevation with a peak by the 50th min. Moreover, in 75 min. after infusion of the neuropeptide, the levels of dopamine still remained increased. Response of metabolites also proved to be dose-related. With 1 mcg of substance P, the contents of dihydroxyphenylacetic acid increased by 28%, while with 0.1 mcg of substance P, this parameter did not change. Contents of homovanillie acid was unaffected by central substance P at the above doses. The data obtained corroborate the assumption of influence of the substance P on the reward system arising from its dopaminergic properties and provide a possible explanation of the neuropeptide effects observed in the conditioned place preference paradigm.

3,4-Dihydroxyphenylacetic Acid↗
PubMed2003

[The effect of neurochemical damage of dopaminergic terminals in early ontogenesis on the behavior of adult rats].

6-Hydroxydopamine (75 mkg), producing selective degeneration of dopaminergic neurons in the brain, was injected intraamniotically to every rat fetus on 13th or 17th day of mother pregnancy. The other experiment was performed, when 6-hydroxydopamine administered i.p. to newborn rats on 4th or 10th day of life. All rats were growing, and several dopamine-dependent behaviors were investigated in adult animals: open field, rotation behavior, anxiety in elevated plus maze, conditioned placed preference, differentiation of novel and known alleys of Y-maze, aggressive behavior in intruder-resident test, selfs-stimulation of lateral hypothalamus. Prenatal administration of 6-hydroxydopamine initiated rotations and stereotypy, decreased anxiety in elevated maze, reduced reinforcing properties of amphetamine in place preference test, disturbed differentiation of novel and known alley in Y-maze, high aggression and decreased self-stimulation in less degree that postnatal injection of neurotoxin. Therefore, the early postnatal period is more sensitive to neurotoxin action than prenatal period of development. This phenomenon is connected with critical periods of development of dopaminergic system in ontogeny.

Animals↗
PubMed2002

The structure of substrate-free microbial ribonuclease binase and of its complexes with 3'GMP and sulfate ions.

The structures of Bacillus intermedius ribonuclease (binase), an extracellular 109-residue enzyme, and its complexes with 3'GMP and sulfate ions were solved at 1.65 and 2.0 A, respectively. The structures were refined using REFMAC. The crystal of free binase belongs to the space group C2, whereas the crystals of complexes belong to the space group P2(1)2(1)2(1). In both crystal lattices the asymmetric unit contains two molecules which form an identical dimer. The structure of the dimer is such that only one of its subunits can bind the nucleotide in the 3'GMP-binase complex, where the guanyl base is located in the recognition loop of the enzyme. In both binase complex structures the phosphate group of 3'GMP or one of the sulfate ions make an electrostatic interaction with the binase molecule at the catalytic site. A second phosphate-binding site was found in the structures of the complexes at the cleft formed by the loop 34-39, the main chain of Arg82 and the side chain of Trp34. Comparison of the complex and unliganded enzyme crystal structures shows that there are some small but distinct differences in the specificity loop (56-62) and in the loops 34-39 and 99-104 associated with the binding of the nucleotide and sulfate ions.

Bacillus↗
PubMed2002

[The influence of substance P central administration on ethanol intake in rats chronically exposed to alcohol].

The influence of central substance P (SP) administration on alcohol intake and brain dopamine metabolism within mesocortico-limbic and nigrostiatal systems of rats exposed to ethanol, was studied. During 6 months, the rats consumed 15% ethanol solution instead of water. Central administration of SP (3 mcg/kg) decreased alcohol consumption by 41% in alcohol-preference animals. After long-term ethanol exposure ratios DOPAC/DA and HVA/DA were reduced in striatum and accumbens. SP in dose 3 mcg/kg increased content of DOPAC by 17% and HVA by 23% as well as DOPAC/DA by 9%, HVA/DA by 19% in accumbens. Whereas in striatum only increased DOPAC (28%) and HVA (29%) were observed as compared with saline-treated rats.

3,4-Dihydroxyphenylacetic Acid↗
PubMed2001

[Participation of the dopaminergic brain system in effects of glucocorticoid hormones].

Following the conditioning with dexamethasone, a dose-dependent place preference in non-preferred compartment was observed on the second test day in male Wistar rats. Amphetamine in subthreshold dose exerted no effect if administered alone and induced a place preference in an unbiased paradigm after pre-treatment with dexamethasone. Administration of D2-dopamine receptors' antagonist sulpiride 30 min prior to dexamethasone conditioning completely blocked the acquisition of the place preference. The D1-dopamine receptors' antagonist SCH23390 exerted no effect on the place conditioning. The findings suggest that the D2-dopamine receptors take part in conditioned place preference with dexamethasone.

Animals↗
PubMed2001

[Characteristics of the rat behavior following single and multiple exposures of the hypoglycemic insulin doses].

Rats behaviour in the "open field" changed in 2 hrs after a single episode of hypoglycaemia was abolished with glucose whereas no changes occurred in their stereotyped behaviour and intraspecies interaction. In 24 hrs quantitative parameters of the "open field" behaviour normalised although the behaviour still had an altered structure. At the same time, amphetamine-induced stereotyped behaviour's indices became reduced. These and other findings suggest some deeper behavioural changes in rats during their recovery from repeated hypoglycaemic episodes and absence of synchronisation of the insulin effects.

Aggression↗
PubMed2000

Crystal structure of decameric 2-Cys peroxiredoxin from human erythrocytes at 1.7 A resolution.

BACKGROUND: The peroxiredoxins (Prxs) are an emerging family of multifunctional enzymes that exhibit peroxidase activity in vitro, and in vivo participate in a range of cellular processes known to be sensitive to reactive oxygen species. Thioredoxin peroxidase B (TPx-B), a 2-Cys type II Prx from erythrocytes, promotes potassium efflux and down-regulates apoptosis and the recruitment of monocytes by endothelial tissue. RESULTS: The crystal structure of human decameric TPx-B purified from erythrocytes has been determined to 1.7 [corrected)] A resolution. The structure is a toroid comprising five dimers linked end-on through predominantly hydrophobic interactions, and is proposed to represent an intermediate in the in vivo reaction cycle. In the crystal structure, Cys51, the site of peroxide reduction, is oxidised to cysteine sulphinic acid. The residue Cys172, lies approximately 10 A away from Cys51 [corrected]. CONCLUSIONS: The oxidation of Cys51 appears to have trapped the structure into a stable decamer, as confirmed by sedimentation analysis. A comparison with two previously reported dimeric Prx structures reveals that the catalytic cycle of 2-Cys Prx requires significant conformational changes that include the unwinding of the active-site helix and the movement of four loops. It is proposed that the stable decamer forms in vivo under conditions of oxidative stress. Similar decameric structures of TPx-B have been observed by electron microscopy, which show the protein associated with the erythrocyte membrane.

Catalytic Domain↗
PubMed2000

[Neurochemical organization of the brain reinforcing systems].

Modern concepts of neurophysiological mechanisms of the brain reinforcing systems are reviewed from A.A. Ukhtomsky's concept of dominanta. The brain mesocorticolimbic system was shown to play a key role in functioning of the brain reinforcing systems. Morphological and neurochemical organisation of this system determining the emotional sphere, was studied. The dopamine system was found to be the main neurochemical tool of the mesocorticolimbic system. Other transmitters, neuromodulators, and hormones play a regulatory role in the latter. The data obtained corroborate the authors' concept of fluctuating emotional gradient.

Animals↗
PubMed1999

[Paracellular ion transfer in kidney and tissues and its pharmacological regulation].

The paper deals with the basic mechanisms underlying the channel reabsorption of sodium and chlorine. The process involves two mechanisms: active transcellular transport of ions and intercellular transport of ions and H2O. Intercellular ion transport directly requires no energy expenditure; nevertheless, it ensures selective ion transport to a certain degree. The hypothesis of fixed entry charges of intercellular compounds (the mechanism which is involved in the treatment of primary urine when the latter passes along the renal tubules) is discussed. Evidence for the existence of this mechanism is given.

Animals↗