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Biomedical subjects

A I Ivanov

Publications and source records attributed to A I Ivanov.

At least 19 recordsLinked to original sources
PubMed2005

Force field inside the void in complex plasmas under microgravity conditions.

Observations of complex plasmas under microgravity conditions onboard the International Space Station performed with the Plasma-Kristall experiment-Nefedov facility are reported. A weak instability of the boundary between the central void (region free of microparticles) and the microparticle cloud is observed at low gas pressures. The instability leads to periodic injections of a relatively small number of particles into the void region (by analogy this effect is called the "trampoline effect"). The trajectories of injected particles are analyzed providing information on the force field inside the void. The experimental results are compared with theory which assumes that the most important forces inside the void are the electric and the ion drag forces. Good agreement is found clearly indicating that under conditions investigated the void formation is caused by the ion drag force.

Journal Article↗
PubMed2005

Integral encounter theory of strong electron transfer.

The integral encounter theory (IET) has been extended to the reactions limited by diffusion along the reaction coordinate to the level crossing points where either thermal or hot electron transfer occurs. IET describes the bimolecular ionization of the instantaneously excited electron donor D* followed by the hot geminate backward transfer which precedes the ion pair equilibration and its subsequent thermal recombination. We demonstrate that the fraction of ion pairs which avoids the hot recombination is much smaller than their initial number when the electron tunneling is strong.

Journal Article↗
PubMed2004

Electrostatic modes in collisional complex plasmas under microgravity conditions.

A linear dispersion relation in a highly collisional complex plasma, including ion drift, was derived in the light of recent PKE-Nefedov wave experiment performed under microgravity conditions onboard the International Space Station. Two modifications of dust density waves with wave frequencies larger than the dust-neutral collision frequency were obtained. The relevance to the space observations was analyzed and a comparison of theory and observations was made for two different complex plasma domains formed by small and large microparticles. Good qualitative agreement is found between the measurements and the theoretical dispersion relations. This allows a determination of the basic complex plasma parameters.

Journal Article↗
PubMed2003

Decharging of complex plasmas: first kinetic observations.

The first experiment on the decharging of a complex plasma in microgravity conditions was conducted. After switching off the rf power, in the afterglow plasma, ions and electrons rapidly recombine and leave a cloud of charged microparticles. Because of microgravity, the particles remain suspended in the experimental chamber for a sufficiently long time, allowing precise measurements of the rest particle charge. A simple theoretical model for the decharging is proposed which agrees quite well with the experiment results and predicts the rest charge at lower gas pressures.

Journal Article↗
PubMed2003

Cell-based therapy of chronic degenerative diseases of the central nervous system.

The traditional methods of pharmacotherapy of the degenerative diseases of the central nervous system do not frequently allow one to achieve the desired clinical effect. The fundamentally new approach for the treatment of severe neurological diseases is provided by the methods of biological medicine, in particular, transplantation of a complex of fetal tissues. Cell-based therapy was used to treat patients with multiple sclerosis; ante-, intra- and postnatal lesions; consequences of hemorrhagic and ischemic apoplexies; neuritis of facial nerve; sclerosis; Parkinson's disease; Alzheimer's disease; epilepsy and other types of pathologic process. The source material for obtaining a suspension of cells was the fetuses of allogenic origin. The suspension of brain cells in amounts of up to 1.5 x 10(8) cells and vitality not less than 40% was administered to the patients into liquor spaces using the method of endolumbar puncture. The total number of transplantations was 1900. Practically in all the cases FT was tolerated well. Positive clinical and immunologic changes were observed in the majority of the patients, thus, remission induction (in the patients with the progressive course of multiple sclerosis) for a period over 12 months was registered in 87.5% of the cases. Noteworthy that considerable changes were observed in immunograms: depression of antibody levels to brain-specific proteins, native and denatured DNA; quantitative and qualitative improvement of lymphocyte subpopulation indices, positive changes in the immunoregulatory index. Clinically, in 69% of the cases there was an improvement in more than one neurological defect and a change in the values of the Kurtzke scale towards a decrease by 2-3 points. The conduct of cell therapy with the MS patients under the acute process conditions after liquorosorption allowed the arresting of clinical manifestations and the creation of preconditions for further restoration. The retrobulbar transplantations provided a quick arrest of the retrobulbar neuritis clinical symptoms and in one case an almost complete restoration of vision in the patient with amaurosis (blindness). The remission duration has a marked direct dependence on the number of courses of endolumbar transplantations. Thus, the method of cell therapy with the use of human tissue transplantations is safe and can be used for different neurodegenerative lesions of the central nervous system. The high efficacy of the method suggests the possibility and necessity of using this method as an alternative of classical pharmacological therapy. An important element of cell therapy is the control after the state of the patient's immunity system.

Cell Transplantation↗
PubMed2003

[Impact of the helmet display on head movements against the flying G-loads].

Purpose of the study was to evaluate impacts of the mass added by the display mounted onto the helmet on head movements during 30-s flying +Gz from 2 to 6 units growing at the rate of 0.6 u/s. Increase in the total helmet mass and asymmetric placement of the display had a negative effect on g-tolerance and distorted head movements. G-tolerance (attested by the feeling of discomfort) was found to correlate with display asymmetry the extreme magnitude of which can be determined from a pre-set g-load value.

Acceleration↗
PubMed2002

Fluorescent probing of the ligand-binding ability of blood plasma in the acute-phase response.

The acute-phase response alters the composition of carrier proteins in plasma, which may affect the blood deposition and transport of biomediators and drugs. The effect of the acute-phase response on the ligand binding ability of plasma was studied in leukemic children with and without systemic inflammation (sepsis and septic shock). To target different transport proteins, differentially charged fluorescent dyes were used: anionic ANS (8-anilinonaphthalene-1-sulfonate), uncharged Nile red, and cationic Quinaldine red. Human serum albumin was a principal carrier for ANS and competed for Nile red binding with lipoproteins. The synchro-scan fluorescence spectra of Nile red in plasma distinguished two species of the dye bound to serum albumin and to low-density and/or very low-density lipoproteins. The binding of Quinaldine red did not correlate with albumin and lipoprotein levels, and was probably determined by alpha(1)-acid glycoprotein. Compared with the control group, leukemia increased Quinaldine red binding by 65% and did not significantly affect the binding of other probes. Sepsis and septic shock did not change the binding of Quinaldine red, but progressively decreased ANS binding, finally by about 33%, and shifted Nile red distribution from serum albumin toward lipoproteins. These changes reflected a modified composition of the three principal transport proteins in plasma in the acute-phase response. Simple and rapid fluorescent tests developed in this study can be used to evaluate the acute-phase response and to optimize drug administration protocols in clinical practice.

Acute-Phase Reaction↗
PubMed2002

[The effect of mobility of the information field of the helmet-mounted indicator on pilot's efficiency].

Results of an experimental investigation of pilot's efficiency with the use of a helmet-mounted indicator (HMI) are reported. Displacement of the HMI information field in consequence of head movements in search for external objects and target acquisition was shown to impact reliability of spatial orientation and cause difficulties during construction and realization of aircraft control movements. These difficulties are ascribed to impairment of functioning of the human "body scheme" (internal systems of coordinates) and modification of the geometric relations of the true and HMI displayed horizon. The conclusion is that to improve efficiency of pilots using HMI designed should be a device which will align the HMI information field with the longitudinal cabin axis after each head movement.

Aircraft↗
PubMed2001

Does obesity affect febrile responsiveness?

BACKGROUND AND OBJECTIVE: A decreased resistance to infection and impairments of immunity are common in obese humans and in rodents with hereditary obesity. Since brown fat thermogenesis is also suppressed in obese rodents, we hypothesized that obesity leads to a decreased febrile responsiveness. METHODS: We compared the fever responses to intravenous E. coli lipopolysaccharide (10 microg/kg) between Zucker fa/fa (obese due to a defective leptin receptor) and Fa/? (lean) rats and between Otsuka Long-Evans Tokushima Fatty (OLETF; obese due to the lacking cholecystokinin-A receptor) and Long-Evans Tokushima Otsuka (lean) rats. Obesity of Zucker fa/fa and OLETF rats was verified by increased body mass and fat content, hypertriglyceridemia and hypercholesterolemia. RESULTS: Neither fa/fa nor OLETF animals exhibited a decreased febrile responsiveness; if anything, their fevers tended to be higher than those in their lean counterparts. CONCLUSION: Obesity per se does not lead to antipyresis.

Adipose Tissue, Brown↗
PubMed2000

Multiple neural mechanisms of fever.

In rats, fevers induced by moderate-to-high doses of intravenous lipopolysaccharide consist of three phases (phases 1, 2 and 3) with body temperature peaks at approximately 1, 2, and 5 h postinjection, respectively. In this study, the effects of bilateral truncal subdiaphragmatic vagotomy and intraperitoneal capsaicin desensitization on febrile phases 1-3 were assessed in adult Wistar rats. Surgical vagotomy was performed approximately 30 d before the experiment; this procedure interrupts both afferent and efferent vagal fibers. Capsaicin was administered intraperitoneally in two consecutive injections (2 and 3 mg/kg, 3 h apart) 1 week prior to the experiment; this procedure desensitizes afferent fibers, primarily within the abdominal cavity, and does not lead to the known thermal effects of systemic capsaicin desensitization. At a neutral ambient temperature, the rats were given Escherichia coli lipopolysaccharide (10 microg/kg) through a preimplanted jugular catheter, and their colonic temperature wes measured by thermocouples for 7 h. The control rats exhibited the typical triphasic febrile responses. Confirming our earlier studies, subdiaphragmatic vagotomy did not affect phases 1 and 2; it did, however, result in a 2.5-fold reduction of phase 3. Capsaicin desensitization modified the febrile response differently: phases 2 and 3 were unaffected, but phase 1 disappeared. We suggest that neural afferent fibers (nonvagal but perhaps vagal as well) play an important role in the early febrile response (phase 1) by transducing peripheral pyrogenic signals to the brain. We also suggest that vagal efferent fibers are likely to participate in the later febrile response (phase 3) via an unknown mechanism.

Animals↗
PubMed2000

Does the formation of lipopolysaccharide tolerance require intact vagal innervation of the liver?

The study was designed to test whether intact vagal innervation of the liver is required for the formation of tolerance to lipopolysaccharide (LPS). Wistar rats were subjected to either denervation of the liver (transection of the hepatic and both celiac branches of the abdominal vagus) or sham surgery. Two weeks later, each rat had an osmotic pump implanted subcutaneously. The pump was filled with either a suspension of Escherichia coli LPS (18 mg/ml) in saline or saline alone. Via a catheter, the pump delivered its content into the right jugular vein at a rate of approximately 0.72 microl/kg/h (approximately 13 microg/kg/h of LPS) over 28 d. On day 25 of the infusion, each animal had another catheter implanted into the left jugular vein. Three days later, each rat was injected with a lethal bolus dose of LPS (15 mg/kg) and had its colonic temperature recorded. The saline-infused sham-operated rats responded to the bolus injection of LPS with hypothermia followed by a fever (mean response magnitude 1.0+/-0.2 degrees C); 91% of the animals died within 24 h. The LPS-primed shams developed marked tolerance: When challenged with a lethal dose of LPS, they exhibited a significantly smaller thermal response (magnitude 0.5 +/- 0.2 degrees C) and none died. No group of the vagotomized animals, whether LPS- or saline-primed, became tolerant: Both groups exhibited similar hypothermic responses to the bolus LPS injection and a substantial mortality rate (40 and 100%, respectively). The study shows that prolonged infusion of low doses of LPS leads to the formation of tolerance and that vagal denervation of the liver by hepato-celiac vagotomy suppresses this process. The mechanisms of vagal control of the formation of LPS tolerance remain speculative.

Animals↗
PubMed2000

Lipopolysaccharide transport from the peritoneal cavity to the blood: is it controlled by the vagus nerve?

Vagotomy suppresses fever and hyperalgesia caused by intraperitoneal lipopolysaccharide (LPS) but has little effect on the febrile response to intravenous or intramuscular LPS. This suggests that some vagus-mediated mechanisms are recruited only when LPS is administered via the intraperitoneal route. We hypothesized that such mechanisms are associated with LPS transport from the peritoneal cavity to the circulation. Adult Wistar rats underwent total subdiaphragmatic, bilateral selective celiac, or sham vagotomy. On day 28-32 after surgery, they were injected IP with Escherichia coli LPS (5, 20, or 100 microg/kg) or saline and decapitated 90 min thereafter. Their plasma levels of LPS and their plasma interleukin-6, adrenocorticotropin, and corticosterone responses to LPS were measured. Success of intraperitoneal administration of LPS was verified by increased interleukin-1beta and interleukin-6 concentrations in the peritoneal lavage fluid. Effectiveness of vagotomies was confirmed by increased stomach mass (food retention) and pancreas mass (hypertrophy). In the shams, LPS caused a dose-dependent endotoxemia and increased plasma levels of interleukin-6, adrenocorticotropin, and corticosterone. Neither celiac nor total vagotomy affected any of these responses. LPS escapes from the peritoneal cavity by two primary routes, viz., the hematogenous (via the portal vein) and lymphogenous (via the lymphatic system). The design of the present study did not allow for evaluating the rapid, hematogenous transport. The results obtained suggest that the abdominal vagus does not control the slow. lymphogenous escape of LPS from the peritoneal cavity.

Adrenocorticotropic Hormone↗
PubMed2000

Intracellular Ca2+ dynamics during spontaneous and evoked activity of leech heart interneurons: low-threshold Ca currents and graded synaptic transmission.

In oscillatory neuronal networks that pace rhythmic behavior, Ca(2+) entry through voltage-gated Ca channels often supports bursting activity and mediates graded transmitter release. We monitored simultaneously membrane potential and/or ionic currents and changes of Ca fluorescence (using the fluorescence indicator Ca Orange) in spontaneously active and experimentally manipulated oscillator heart interneurons in the leech. We show that changes in Ca fluorescence in these interneurons during spontaneous bursting and evoked activity reflect the slow wave of that activity and that these changes in Ca fluorescence are mediated by Ca(2+) entry primarily through low-threshold Ca channels. Spatial and temporal maps of changes in Ca fluorescence indicate that these channels are widely distributed over the neuritic tree of these neurons. We establish a correlation between the amount of transmitter released, as estimated by the integral of the postsynaptic current, and the change in Ca fluorescence. In experiments in which we were able to record presynaptic low-threshold Ca currents, associated IPSCs, and presynaptic changes in Ca fluorescence from fine neuritic branches of heart interneurons near their region of synaptic contact with their contralateral partner, there was a close association between the rise in Ca fluorescence and the rise of the postsynaptic conductance. The changes in Ca fluorescence that we record at the end of fine neuritic branches appear to reflect changes in [Ca(2+)](i) that mediate graded synaptic release in leech heart interneurons. These results indicate that widely distributed low-threshold Ca currents play an important role in generating rhythmic activity and in mediating graded transmitter release.

Animals↗
PubMed2000

Bathocuproine-assisted reduction of copper(II) by human albumin.

Human albumin (studied here as the recombinant protein rHA), a copper-binding protein in blood plasma, is shown to reduce Cu(II) to Cu(I) in the presence of a Cu(I) chelator, bathocuproinedisulfonate (BD). This reaction was accelerated at low pH, when there was little binding of Cu(II) to rHA. The addition of a competitive metal ion, Ni(II), or an increase in the concentration of BD, enhanced the reduction of Cu(II) to Cu(I). It was concluded that the oxidant was the Cu(II) complex of BD, which is likely to bind strongly to albumin. The free thiol at Cys34 was ruled out as the sole reducing agent, since Cys34-blocked albumin also gave rise to Cu(I) in the presence of BD. Reactions with amino acids and peptides suggested that Tyr and possibly His side-chains are potential reductants. BD and its homologues are frequently used as Cu(I)-specific chelators in biological experiments, but the strong oxidant activity of [Cu(II)(BD)2]2- and its ability to bind to biological macromolecules should not be overlooked, and may artificially trigger/accelerate Cu(II) reduction.

Albumins↗
PubMed2000

Neural route of pyrogen signaling to the brain.

In the pathogenesis of systemic inflammation and fever, peripheral inflammatory and pyrogenic signals gain access to the brain via humoral and neural routes. One of the neural routes is represented by chemosensitive afferent fibers of the abdominal vagus. We summarize our recent studies of the role of the abdominal vagus in fever. We conclude that capsaicin-sensitive fibers traveling within the hepatic vagal branch constitute a necessary component of the afferent mechanism of the febrile response to low, but not high, doses of circulating pyrogens. We speculate that this mechanism is triggered by blood-borne prostaglandins of the E series.

Afferent Pathways↗
PubMed1999

Blood-borne, albumin-bound prostaglandin E2 may be involved in fever.

Although the involvement of blood-borne PGE2 in fever has been hypothesized by several authors and has substantial experimental support, the current literature often rejects this hypothesis because several attempts to induce fever by a peripheral PGE2 failed. However, it is usually ignored that the amphipathic molecules of PGE2 are readily self-associating and that such an aggregation could have prevented the peripherally administered PGE2 (free form) from expressing its pyrogenic activity, thus leading to false negative results. To ensure disaggregation of PGE2, we prepared its complex within a carrier protein, human serum albumin (HSA). HSA was purified with activated charcoal and polymixin B-polyacrylamide gel and incubated with PGE2 for 1 h at 37 degrees C. Adult Chinchilla rabbits were injected intravenously with PGE2-HSA complex in either the higher (75 micrograms/kg PGE2:30 mg/kg HSA) or the lower (15 micrograms/kg:6 mg/kg) dose, and the rectal temperature (Tr) was measured. In the controls, either the ligand alone or the carrier alone was administered. At the higher dose, neither free PGE2 nor albumin alone was pyrogenic, whereas the PGE2-HSA complex produced a fever characterized by a short latency (<10 min) and a maximal Tr rise of 0.7 +/- 0.2 degrees C. At the lower dose, none of the substances affected the Tr. This study demonstrates a marked pyrogenic activity of the intravenous PGE2-HSA, but not of the free PGE2. Administration of a preformed complex may be more physiologically relevant than administration of the free ligand because of the ligand's disaggregation, protection from enzymatic degradation, and facilitated delivery to targets. Our study supports the hypothesis that peripheral PGE2 is involved in fever genesis.

Animals↗