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Biomedical subjects

E Popova

Publications and source records attributed to E Popova.

At least 19 recordsLinked to original sources
PubMed2004

Evaluation of the effect of the concentration of plasticizer di(2-ethylhexyl) phthalate on the quantity of residual monomer vinyl chloride in PVC chest drainage tubes.

The effect of amount of plasticizer di(2-ethylhexyl) phthalate (DEHP) amount on the amount of residual monomer vinyl chloride (VC) was determined in samples of plasticised polyvinyl chloride (PVC) with different concentration of plasticiser (22.32-33.05%), before and after sterilisation by a titrimetric method. The titrimetric method was used to determine the VC concentration in a KMnO4 solution where the samples were kept immersed under the same conditions for 2 h. The influence of PVC film extracts with different amounts of DEHP on mouse fibroblast cells L-929 in a culture medium was evaluated by using quantitative tests: the amount of cells (protein determination), viability (MTT test) and proliferation (incorporation of bromodeoxyuridine (BrDU). The amount of vinyl chloride before and after heat sterilisation at 120 degrees C for 30 min was found to be almost the same for all samples and without any dependence on the concentration of DEHP. The extracts of the PVC films which were tested have no toxic effect on cells in a culture medium.

Animals↗
PubMed2003

Participation of the GABAergic system in the action of 2-amino-4-phosphonobutyrate on the OFF responses of frog retinal ganglion cells.

Perfusion of dark adapted frog eyecups with the ON pathway blocker 2-amino-4-phosphonobutyrate (APB) not only abolished the ganglion cells (GCs)' ON responses and the ERG b-wave, but it markedly potentiated the OFF responses of all ON-OFF and phasic OFF GCs and the d-wave amplitude of a simultaneously recorded ERG as well. The blockade of GABA(A) and GABA(C) receptors by picrotoxin eliminated this potentiating effect in 24 out of 41 GCs, although in the rest of the cells it did not produce any change in the APB effect. On the other hand, the d-wave potentiation was preserved during the GABAergic blockade in all experiments. Our results indicate that GABAergic transmission is involved in the inhibition exerted by the ON upon the OFF channel in part of the ON-OFF and phasic OFF GCs in the frog retina. The tonic OFF GCs probably do not receive an inhibitory input from the ON channel, because their light responses were not altered either by APB alone or by APB during blockade of GABA(A) and GABA(C) receptors.

Aminobutyrates↗
PubMed2003

Effect of GABAergic blockade on light responses of frog retinal ganglion cells.

The effect of GABAergic blockade by picrotoxin on ganglion cells (GC) activity was investigated in perfused dark adapted eyecups of frog (Rana ridibunda). PT had diverse effects on the light responses of GC in contrast to its uniform potentiating effect on the amplitude of the ERG b- and d-wave. In some (n=32) of PT-sensitive ON-OFF GC the ON and OFF responses were changed in a similar manner (both responses were potentiated or both were inhibited), but in the other (n=10) the both responses were changed in a different manner. PT influenced differentially the activity of OFF GC (n=17) as well. It not only potentiated or inhibited their light responses, but changed also the temporal characteristics of the responses. Some tonic cells became phasic ones and in some phasic cells a late component appeared under the influence of PT. In some cases (n=4) the GABAergic blockade changed the apparent cell's type, because of appearance of a new type of response (ON or OFF) non-existing before the blockade. Our results indicate that the GABAergic interneurons are involved in different networks in the inner plexiform layer of frog retina.

Animals↗
PubMed2003

Effects of benzodiazepines on frog ERG.

Effect of flurazepam (water-soluble benzodiazepine) on the amplitude and time course of ERG waves was investigated in superfused frog eyecups (Rana ridibunda). Flurazepam (50 and 100 microM) had inhibitory effect on the b- and d-wave amplitude, which was not accompanied with significant changes in their implicit time. Flurazepam potentiated the depressant effect of GABA (2.5 and 5 mM) on the b- and d-wave amplitude. The inhibitory effect of flurazepam was not blocked by 50 microM bicuculline (BCC), (GABA(A) antagonist), although the blocker markedly potentiated the b- and d-wave amplitude. The suppressive effect of flurazepam on the b- but not d-wave amplitude was blocked by 100 microM BCC. Our results indicate existence of functional benzodiazepine regulatory sites on GABA(A) receptors in distal frog retina.

Animals↗
PubMed2002

Interlayer magnetic coupling interactions of two ferromagnetic layers by spin polarized tunneling.

Magnetic interactions involving ferromagnetic layers separated by an insulating barrier have been studied experimentally on a fully epitaxial hard-soft magnetic tunnel junction: Fe/MgO/Fe/Co. For a barrier thickness below 1 nm, a clear antiferromagnetic interaction is observed. Moreover, when reducing the MgO thickness from 1 to 0.5 nm, the coupling strength increases up to J=-0.26 erg.cm(-2). This behavior, well fitted by theoretical models, provides an unambiguous signature of the interlayer exchange coupling by spin-polarized quantum tunneling.

Journal Article↗
PubMed2001

Immunocytochemical and electrophysiological characterization of GABA receptors in the frog and turtle retina.

The expression of GABA receptors (GABARs) was studied in frog and turtle retinae. Using immunocytochemical methods, GABA(A)Rs and GABA(C)Rs were preferentially localized to the inner plexiform layer (IPL). Label in the IPL was punctate indicating a synaptic clustering of GABARs. Distinct, but weaker label was also present in the outer plexiform layer. GABA(A)R and GABA(C)R mediated effects were studied by recording electroretinograms (ERGs) and by the application of specific antagonists. Bicuculline, the GABA(A)R antagonist, produced a significant increase of the ERG. Picrotoxin, when co-applied with saturating doses of bicuculline, caused a further increase of the ERG due to blocking of GABA(C)Rs. The putative GABA(C)R antagonist Imidazole-4-acidic acid (I4AA) failed to antagonize GABA(C)R mediated inhibition and, in contrast, appeared rather as an agonist of GABARs.

Animals↗
PubMed2000

Effect of 2-amino-4-phosphonobutyrate on the OFF responses of frog retinal ganglion cells and local ERG after glycinergic blockade.

Perfusion with the ON channel blocker 2-amino-4-phosphonobutyrate (APB) of dark adapted frog eyecups not only abolished the ganglion cells' (GC) ON responses and the ERG b-wave, but markedly potentiated the OFF responses of ON-OFF and phasic OFF-GCs and the d-wave amplitude of simultaneously recorded local ERG. Glycinergic blockade by strychnine prevented this potentiating effect in 31 out of 69 GCs, but did not change it at all in the other cells. At the same time the d-wave potentiation was preserved during the glycinergic blockade in all eyecups. The results indicate that glycinergic transmission is involved in the inhibition exerted from ON upon OFF channel in some but not all frog retinal GCs.

Aminobutyrates↗
PubMed2000

Glycinergic and GABAergic control of intensity-response function of frog ERG waves under different conditions of light stimulation.

The effect of glycinergic blockade by strychnine and GABAergic blockade by picrotoxin on the intensity-response function and time course of ERG b- and d-wave was investigated in dark and light adapted frog eyecups as well as in chromatically adapted eyecups, in which the responses were predominantly mediated by one photoreceptor type. Both of the blockers markedly increased the maximal response amplitude and thus increased the contrast gain of the mechanisms generating ERG waves. Strychnine but not picrotoxin narrowed the dynamic range of the b-wave in all eyecups. The glycine and GABAergic control on retinal sensitivity however, depended on photoreceptor input. The b-wave sensitivity was increased to the greatest extent when green rods mediated the response; it was slightly increased when the response was mediated by red cones and was not changed at all when red rods mediated the b-wave. On the other hand the d-wave sensitivity was enhanced regardless of photoreceptor input so that it became equal (dark) or even greater (light adapted eyes) than that of the b-wave. Strychnine shortened but picrotoxin increased the implicit time of the b-wave and both the blockers markedly slowed the d-wave time course. Thus the blockers considerably diminished or fully eliminated the initial difference in time course between the ON and OFF response. The glycine- and GABAergic blockade did not principally alter the light adaptation process expressed in decreasing retinal sensitivity, narrowing the dynamic range and speeding the time course of the responses with increasing background illumination.

Animals↗
PubMed1999

Regulation of DLG localization at synapses by CaMKII-dependent phosphorylation.

Discs large (DLG) mediates the clustering of synaptic molecules. Here we demonstrate that synaptic localization of DLG itself is regulated by CaMKII. We show that DLG and CaMKII colocalize at synapses and exist in the same protein complex. Constitutively activated CaMKII phenocopied structural abnormalities of dlg mutant synapses and dramatically increased extrajunctional DLG. Decreased CaMKII activity caused opposite alterations. In vitro, CaMKII phosphorylated a DLG fragment with a stoichiometry close to one. Moreover, expression of site-directed dlg mutants that blocked or mimicked phosphorylation had effects similar to those observed upon inhibiting or constitutively activating CaMKII. We propose that CaMKII-dependent DLG phosphorylation regulates the association of DLG with the synaptic complex during development and plasticity, thus providing a link between synaptic activity and structure.

Animals↗
PubMed1999

The gene mod(mdg4) affects synapse specificity and structure in Drosophila.

The mechanisms by which synapse assembly and maturation are orchestrated during development are largely unknown. We used P-element mutagenesis and a larval anatomical screen to isolate mutants in which synapse structure was altered. Here, we describe a mutation isolated with this screen, branch point disrupted (bpd), in which both synapse specificity and synapse morphology were altered. Synaptic terminals in bpd mutants developed abnormally, forming multiple branch points, overgrowing to inappropriate neighboring muscles, and establishing aberrant folding of postsynaptic membranes. Ultrastructural characterization of synaptic boutons in bpd demonstrated abnormal layering of the postsynaptic specialization or subsynaptic reticulum (SSR). Genetic and molecular analyses revealed that bpd is an allele of mod(mdg4), a gene coding for a protein with many similarities to transcription factors, which has been implicated in the regulation of chromatin insulation. Our results suggest that mod(mdg4) may regulate a gene(s) essential to normal synapse formation.

Alleles↗
PubMed1997

Influence of picrotoxin and strychnine on the spectral sensitivity of the turtle ERG b- and d-waves: II. Light adaptation.

The aim of the present work was to investigate the role of GABA and glycine, the two main inhibitory neurotransmitters in the retina, in the spectral sensitivity coding under conditions of light adaptation. To study this question, spectral sensitivity curves, based on the turtle ERG responses to stimuli of different wavelengths, were constructed. The spectral sensitivity curves. obtained before and during treatment with picrotoxin (PT), a GABAA antagonist, or with strychnine (ST), a glycine antagonist, were compared. Both PT and ST increased the b- and d-wave absolute sensitivity in a wavelength-dependent manner. PT significantly changed the shape of the b- and d-wave spectral sensitivity curves and the latter lost their peaks. It is concluded that, under conditions of light adaptation, GABA and glycine took part in the formation of the b- and d-wave spectral sensitivity curves, that both of them exerted an effect on the gain and that furthermore,GABA had a well pronounced effect on the tuning of the spectral sensitivity curves.

Adaptation, Ocular↗
PubMed1997

Influence of picrotoxin and strychnine on the spectral sensitivity of the turtle ERG b- and d-wave: I. Dark adaptation.

The ERG ON- (b-wave) and OFF-response (d-wave) to differently coloured stimuli was studied using a wide range of stimulus intensities in dark adapted turtle retina. The intensity-response curve of the b-wave showed saturation but that of the d-wave, decline in the high-intensity stimulus range. The curves of the relative spectral sensitivity of the ERG ON- and OFF-response were similar and showed a maximum in the longwave part of the spectrum. GABAergic blockade by 50 mumol L-1 picrotoxin caused an increase of the sensitivity, contrast sensitivity and the amplitude range of both ON- and OFF-responses without narrowing of the response dynamic range. In the range of lower stimulus intensities the ON-responses to blue stimuli and the OFF-responses to red stimuli were affected to a greater extent. An increased ERG b- and d-wave sensitivity was also observed during glycinergic blockade by 50 mumol L-1 strychnine. In the low intensity stimulus range the effect was maximal on the ON-response to blue stimuli and on the OFF-responses to 570 nm stimuli. It was concluded that the GABA- and glycinergic systems in the retina equalize rather than make different the relative spectral sensitivities of the ON- and OFF-responses.

Animals↗
PubMed1995

Effect of 2-amino-4-phosphonobutyrate on ERG OFF-response after glycinergic and GABAergic blockade.

Superfusion with 200 microM 2-amino-4-phosphonobutyrate (APB) of dark and chromatically adapted frog eyecups caused marked potentiation of the ERG OFF-response (d-wave). Blockade of the glycinergic synapses by strychnine did not change this effect at all. Blockade of the GABAergic synapses by picrotoxin slightly diminished the effect of APB in chromatically-adapted eyes with isolated cones' activity, and did not change it in dark-adapted eyes. The results indicate that the action of APB on ERG OFF-response does not depend significantly on GABAergic and glycinergic neurotransmission in frog retina.

Adaptation, Ocular↗
PubMed1995

ERG OFF response in frog retina: light adaptation and effect of 2-amino-4-phosphonobutyrate.

The intensity-response (V/log I) function of ERG OFF response (d-wave) in dark and light adapted superfused frog eyecups was investigated before and after blockade of the retinal ON channel by 2-amino-4-phosphonobutyrate (APB). The V/log I function of the dark adapted d-wave had two distinct components, each of them consisting of an ascendent and descendent part. In eyes adapted to mesopic or photopic background the V/log I function had only one component. It was shifted to the right along the intensity axis, had a steeper slope and a higher maximal response amplitude compared with the two components of the dark-adapted V/log I curve. Perfusion with 200 mumol APB markedly increased the d-wave amplitude at all stimulus intensities except for the threshold ones in both dark and light adapted eyes. The position of the V/log I curve was shifted slightly to the left along the intensity axis in dark adapted eyes, but was not changed in light adapted eyes. Thus the adaptational mechanism responsible for changes in the decremental sensitivity with increased background illumination was not altered by APB. The effect of APB was studied also in chromatically adapted eyes, in which the responses were predominantly mediated by one photoreceptor type. The results showed that the potentiating effect of APB on d-wave did not depend on photoreceptor input.

Adaptation, Ocular↗
PubMed1994

A Drosophila receptor tyrosine phosphatase expressed in the embryonic CNS and larval optic lobes is a member of the set of proteins bearing the "HRP" carbohydrate epitope.

Recent studies have defined several cell surface glycoproteins expressed in the developing nervous system of insect embryos that may be involved in axon outgrowth and guidance processes. These glycoproteins include the fasciclins and a group of receptor-linked protein tyrosine phosphatases (R-PTPs). In embryos, the fasciclins are localized to axonal subsets, while the R-PTPs appear to be expressed on most or all CNS axons. To identify other neuronal cell surface glycoproteins in the Drosophila embryo, we have taken a biochemical approach. This is based on the observation that antisera against horseradish peroxidase (HRP) recognize a carbohydrate epitope that is selectively expressed in the insect nervous system. A large number of neuronal glycoproteins (denoted "HRP proteins") apparently bear the HRP carbohydrate epitope. We have used polyclonal anti-HRP antibodies to purify these proteins from Drosophila embryos, and have obtained protein sequences from seven HRP protein bands. These data define three major HRP proteins as neurotactin, fasciclin I, and an R-PTP, DPTP69D. Western blotting data suggest that fasciclin II, neuroglian, DPTP10D, and DPTP99A are also HRP proteins. We show that DPTP69D, like the previously characterized R-PTPs, is localized to CNS axons in the embryo. In third instar larvae, DPTP69D expression is restricted to subsets of neuronal processes in the brain, ventral nerve cord, and eye disk. In the optic lobes, DPTP69D is localized to the neuropils of the lamina and medulla, and to an array of parallel thick bundles that may be the transmedullary fibers of the developing lobula complex.

Amino Acid Sequence↗
PubMed1993

Comparative investigation of retinal responses to brief light stimuli: 2-amino-4-phosphonobutyrate studies--I. Frog retina, Rana ridibunda.

1. Electroretinogram (ERG) and responses of single ganglion cells to 75 microseconds light flashes, applied at two different backgrounds, were studied. Additionally, a stimulation with long-lasting stimuli (ordinarily 5 sec ON-, 5 sec OFF-) was used. Both white and coloured light stimuli were presented. 2. 150 microM 2-amino-4-phosphonobutyrate (APB) was used to separate OFF- from ON- channels. 3. Before APB application, one or two components in the impulse activity in response to a flash were observed, depending on the type of ganglion cell (ON-, OFF- or ON-OFF). the latency of the first component was 60 msec and the latency of the second one was from 160 to 430 msec on average, at different background conditions. APB abolished the first component and enhanced the second one. 4. By means of APB, two components were shown to exist in the main positive wave of the flash ERG. APB abolished the first component and did not influence or enhance the second one. 5. The data obtained show that both ON- and OFF- channels take part in the generation of the frog retinal responses to brief stimuli.

Action Potentials↗
PubMed1993

Comparative investigation of retinal responses to brief light stimuli: 2-amino-4-phosphonobutyrate studies--II. Turtle retina (Emys orbicularis).

1. Electroretinogram (ERG) and responses of single ganglion cells to 75 microseconds light flashes, presented on two different backgrounds, were studied. Additionally, stimulation with long lasting stimuli (ordinarily 5 sec ON-, 15 sec OFF-) was used. 2. 2-amino-4-phosphonobutyrate (APB) at a concentration of 450 microM on average was used to separate OFF- from ON- channels. It is known, that in other species APB selectively blocks the activity of ON- channel only. 3. The existence of APB- sensitive membrane receptors was demonstrated in the turtle retina. As in other species, APB abolished the ERG b-wave and enhanced the d-wave, when long lasting stimulation was used. 4. By means of APB, two components were shown to exist in the ERG positive wave in response to a flash. APB abolished the first component and did not influence or enhanced the second one. 5. By means of APB, one or two components in the impulse activity in response to flash were demonstrated, depending on the type of ganglion cell (ON-, OFF- or ON-OFF). The latency of the first component was 70 msec and the latency of the second one 210 msec on average. APB abolished the first component, and enhanced the second one. 6. The data obtained show that both ON- and OFF- channels take part in the generation of the turtle retinal responses to brief stimuli. 7. Based on the results obtained, some peculiarities of the network organization of the ganglion cells' receptive fields are discussed.

Action Potentials↗