PubMed Health⌕ Search

Biomedical subjects

R Dimova

Publications and source records attributed to R Dimova.

At least 19 recordsLinked to original sources
PubMed2005

Composition dependence of vesicle morphology and mixing properties in a bacterial model membrane system.

We have determined the mixing properties and lamellar organization of bacterial membrane mimetics composed of 1-palmitoyl-2-oleoyl-phosphatidylethanolamine (POPE) and -phosphatidylglycerol (POPG) at various molar ratios applying differential scanning calorimetry, small and wide-angle X-ray scattering, as well as optical phase contrast microscopy. Combining the experimental thermodynamic data with a simulation of the liquidus and solidus lines, we were able to construct a phase diagram. Using this approach, we find that the lipids mix in all phases non-ideally in the thermodynamic sense. As expected, pure POPE assembles into multilamellar and pure POPG into unilamellar vesicles, respectively, which are stable within the studied temperature range. In contrast, mixtures of the two components form oligolamellar vesicles consisting of about three to five bilayers. The layers within these oligolamellar liposomes are positionally correlated within the gel phase, but become uncorrelated within the fluid phase exhibiting freely fluctuating bilayers, while the vesicles as a whole remain intact and do not break up into unilamellar forms. X-ray, as well as DSC data, respectively, reveal a miscibility gap due to a lateral phase segregation at POPG concentrations above about 70 mol%, similar to previously reported data on mixtures composed of disaturated PEs and PGs. Hence, the existence of a region of immiscibility is a general feature of PE/PG mixtures and the mixing properties are dominated by PE/PG headgroup interactions, but are largely independent of the composition of the hydrocarbon chains. This is in accordance with a recent theoretical prediction.

Bacteria↗
PubMed2000

Pretransitional effects in dimyristoylphosphatidylcholine vesicle membranes: optical dynamometry study.

We used micron-sized latex spheres to probe the phase state and the viscoelastic properties of dimyristoylphosphatidylcholine (DMPC) bilayers as a function of temperature. One or two particles were manipulated and stuck to a DMPC giant vesicle by means of an optical trap. Above the fluid-gel main transition temperature, T(m) congruent with 23.4 degrees C, the particles could move on the surface of the vesicle, spontaneously (Brownian motion) or driven by an external force, either gravity or the laser beam's radiation pressure. From the analysis of the particle motions, we deduced the values of the membrane hydrodynamic shear viscosity, eta(s), and found that it would increase considerably near T(m). Below T(m), the long-distance motion of the particles was blocked. We performed experiments with two particles stuck on the membrane. By optical dynamometry, we measured the elastic resistance of the membrane to a variation in the interparticle distance and found that it would decrease considerably (down to zero) when the temperature was increased to T(m). We propose an interpretation relating the elastic response to the membrane curvature modulus, k(C). In this scheme, the two-bead dynamometry experiments provide a direct measurement of k(C) in the P'(beta) phase of lipid bilayers.

Biophysical Phenomena↗
PubMed1993

Ultrastructural features of the choline acetyltransferase-containing neurons and relationships with nigral dopaminergic and cortical afferent pathways in the rat striatum.

The aim of this study was first to specify the morphology and neuronal environment of the large cholinergic neurons, and second to determine the distribution and mode of termination of the corticostriatal and dopaminergic inputs on these neurons in the rat striatum. Immunocytochemical procedures with a monoclonal antibody against choline acetyltransferase, Golgi staining and standard electron microscopic techniques were used to specify the ultrastructural features of the putatively cholinergic classical large neurons. The large/choline acetyltransferase-positive neurons are characterized by a voluminous, eccentric, and deeply indented nucleus leaving a large cytoplasmic area, and by the presence of an abundant granular endoplasmic reticulum and of many polysomes and free ribosomes. Serial ultrathin sectioning further indicated the presence of nematosomes or nucleolus-like bodies within the nucleus and the cytoplasm of the large neurons. In addition, these neurons were found to be in direct apposition with up to four surrounding neurons showing features typical of medium-sized spiny neurons. These data support the view that the putatively cholinergic neurons may have an intense metabolic activity and may be involved in striatal clusters. When choline acetyltransferase immunostaining was coupled with the identification of degenerating corticostriatal afferents after lesion of the cerebral cortex, degenerating terminals were seen to form synapses of an asymmetrical type on distal labelled dendrites, but these contacts were very rare. On the other hand, nigrostriatal dopaminergic axons, identified by means of either the degeneration method or tyrosine hydroxylase immunostaining, were often found to run directly for long distances around the choline acetyltransferase-positive cell bodies. Occasionally, dopaminergic terminals formed possible symmetrical synapses on choline acetyltransferase-positive cell bodies or proximal dendrites. These data provide evidence that the putatively cholinergic neurons are directly contacted by corticostriatal and dopaminergic nigrostriatal afferents. The respective positions and nature of the two types of contacts further provide morphological support for the hypothesis that postsynaptic interactions may occur between the corticostriatal and dopaminergic nigrostriatal afferents at the level of the cholinergic neurons.

Afferent Pathways↗
PubMed1992

Ultrastructural relationships between choline acetyltransferase- and neuropeptide y-containing neurons in the rat striatum.

The relationships between cholinergic and neuropeptide Y-containing neuronal systems in the rat striatum were examined using a dual immunoperoxidase labelling method. These neurons were identified by their immunoreactivity to choline acetyltransferase and neuropeptide Y, respectively, and were visualized on the same sections using 3,3'-diaminobenzidine and benzidine dihydrochloride as distinct chromogens under two conditions: (i) neuropeptide Y detection by the 3,3'-diaminobenzidine diffuse brown reaction product and choline acetyltransferase detection by the benzidine dihydrochloride blue, granular reaction product; (ii) choline acetyltransferase detection by 3,3'-diaminobenzidine and neuropeptide Y detection by benzidine dihydrochloride. Although both neuropeptide Y- and choline acetyltransferase-immunoreactive cell bodies were simultaneously detected and were easily distinguishable whatever the conditions used, neuropeptide Y- and choline acetyltransferase-immunoreactive dendrites and axons could not be visualized on the same sections, since only the diaminobenzidine-labelled processes were detectable. Light microscopic observations on sections dual labelled with either method confirmed that choline acetyltransferase and neuropeptide Y immunoreactivities were localized in morphologically different populations of striatal neurons scattered throughout the striatum, choline acetyltransferase immunoreactivity being associated with large neurons and neuropeptide Y immunoreactivity with medium-sized neurons. In addition, the choline acetyltransferase-immunoreactive neurons were found to be more numerous than the neuropeptide Y-immunoreactive neurons and to be prevalent in the dorsolateral areas of the striatum, whereas neuropeptide Y-immunoreactive neurons were preferentially found in the ventromedial areas of this structure. Electron microscopic observations on sections processed under either condition revealed that choline acetyltransferase-positive terminals form synaptic contacts of the symmetrical type with neuropeptide Y-positive somata and proximal dendrites and that choline acetyltransferase-positive neurons are contacted by neuropeptide Y-positive terminals. These data show that the striatal neuropeptide Y- and choline acetyltransferase-containing neuronal systems have reciprocal synaptic interactions and provide morphological support for the hypothesis that striatal cholinergic and neuropeptide Y interneuron activities may be functionally linked.

3,3'-Diaminobenzidine↗
PubMed1989

[Lennert's lymphoma].

The epithelioid cell Lennert's lymphoma is a rare form of malignant lymphomas. The authors present the cases of 4 patients, aged 50-71 years, 3 men and 2 women, with histologically proved Lennert's lymphoma. In two of the patients the diagnosis was proved at post mortem, too. The cases were characterized by a great variety of the clinico-hematologic data, the course of the disease and the therapeutic response. In all patients the disease was expressed in the III stage and in three of the patients it progressed to the IV stage. The therapeutic conduct is discussed because an early occurrence of cytopenia was found.

Aged↗
PubMed1989

[15 patients with myelodysplastic syndrome].

15 patients (10 men and 5 women) with myelodysplastic syndrome, treated in a Hematologic Clinic during the last three years, are studied. The patients are classified in the following groups: with a refractory anemia (4 patients), with an acquired idiopathic sideroblast anemia (3 patients), with a refractory anemia with an excess of blast cells (8 patients). The diagnosis is proved by morphologic examinations, in some of the patients by isotopic examinations and in 5 patients a cytogenetic analysis is made. 7 patients died and in 5 of them the post mortem examination confirms the clinical diagnosis of myelodysplastic syndrome passed in acute leukosis. 4 patients are still alive and are under active observation. For the remaining 4 patients there are no data. The shortest survival is 6 months and the longest one is 9 years. The prognostic importance of the number of blast cells in the bone marrow is pointed out. The patients with refractory anemia with an excess of blast cells are treated with mercaptopurine or small doses of cytosine arabinoside in addition to the conventional blood-stimulating therapy applied in the other forms of myelodysplastic syndrome.

Adult↗
PubMed1988

[Long-term myelodysplastic syndrome transformed into blastic leukemia].

A very rare case of myelodysplastic syndrome of long duration transformed into acute leukemia is reported. The syndrome presented with refractory anemia with ring sideroblasts and after eight years of favourable course abruptly turned into acute myelomonoblastic leukemia with a rapid fatal outcome caused by gram-negative sepsis. The disappearance of the ring-sideroblasts from the bone marrow is pointed out as a bad prognostic sign. Treatment of the myelodysplastic syndrome with small doses of cytosine arabinoside is discussed as well as the nonobligatory passing through the stage of a gradual increase of the blast cells before the transformation into acute leukemia.

Adult↗
PubMed1985

[Electron microscopic detection of viruses in cervix papilloma].

The authors describe the electron microscope findings in a case of papilloma of the uterine cervix. In the nuclei of single koilocytes spherical inclusions measuring 47-56 nm were found. The ultrastructural pattern of the particles is entirely identical with one of the human papilloma virus particles.

Adult↗
PubMed1984

[So-called immunoglobulin-producing lymphoma with a case presentation and the production of monoclonal immunoglobulin M].

The authors discuss the B-cellular lymphomas, producing various kinds of monoclonal paraproteins as well as parts of them--light or heavy chains. A case of a patient with lymphoplasmocytic malignant lymphoma, producing monoclonal IgM in pentamer form mainly, as well as in Valdenström disease but without the symptoms characteristic for it--hyperviscosity and hemorrhagic diathesis, is described. The disease has been histologically, cytologically and electron microscopically diagnosed. Attention is paid to the long-term relatively benign course and subsequent malignant course with manifested laboratory changes as well as change in the objective state, requiring the monotherapy to be substituted for active complex treatment, though the effect was unsatisfactory, with a fatal outcome of the inflammatory complications and progressive anemia. The place of the case in Kiel classification of malignant lymphomas is discussed.

B-Lymphocytes↗
PubMed1984

[Blast stage in chronic myeloleukemia--diagnostic and therapeutic problems].

The data are reported from the study on 34 patients with chronic myeloleukosis (ChML), blast stage (BS). The early progress of BS is stressed upon--in 41% of the patients during the first year after making the diagnosis. A juxtaposition is made between some clinical and laboratory indices and the BS progress as well as with life span. Some criteria are presented that could aid the differentiation of BS from a recurrence of ChML. The unsatisfactory results from BS treatment are also stressed upon in spite of the achievements during the last several years. One of the patients was with twice overcome BS, with a duration of the second remission of 8 months.

Adult↗
PubMed1983

The axon of the giant neuron in the rat neostriatum.

The axon of the giant cells in the rat neostriatum was studied by serial sections on Golgi and electron microscopic preparations and with the combined Golgi-electron microscopic technique (Fairen, Peters and Saldanha, 1977). The ultrastructural characteristics of the initial part are given. It was established that the axon was coated with myelin and gives off myelinated collaterals. The present observations are discussed with regard to the problem of striato-cortical connections.

Animals↗