Search PubMed⌕ Search

Biomedical subjects

D A Moshkov

Publications and source records attributed to D A Moshkov.

At least 55 records · Page 3Linked to original sources
PubMed1998

[Ultrastructural changes in afferent mixed synapses in long-term potentiation of electrotonic responses in Mauthner neurons of goldfish medulla oblongata].

Ultrastructural synaptic features of long-term potentiation (double increase of amplitude) of electrotonic responses of the goldfish Mauthner neurons (MN) in conditions of prolonged in vitro incubation of medulla oblongata fragments were studied. Potentiation was induced by tetanization of the 8th nerve posterior roots, axonal terminals of which end on distal segments of MN lateral dendrite as piniform mixed synapses and increase their electrotonic conductivity. It was established that potentiated synapses vary from control ones in 1) greater length of synaptic contact; 20 greater (30% higher) ratio of desmosome like structures (DLS); 3) greater area of the DLS individual and total sections (two-fold increase); 4) two-fold decrease of total active zone square. Gap junction (GJ) parameters did not change. Taking an account of the proven actin origin of DLS, reports on actin filaments electron conductivity, close localization of DLS and GJ in the synaptic contact and correlative increase of synapse electric conductivity and DLS parameters. DLS contribution to electrotonic transmission is suggested, direct or mediated by actin interaction with nearby localized GJ connexons.

Afferent Pathways↗
PubMed1998

[Central Asiatic black scorpion venom protect Mauthner neurons from the damaging action of prolonged stimulation].

The effect of long-term natural stimulation resulting in prolonged fatigue and structural disorders as well as the black scorpion poison influence on these processes were studied in gold fish Mauthner neurons (MN). The poison previously applied to MN significantly protects their function and structure from the stimulatory effect and subsequently allows the neurons to recover more fast. Appearance of numerous desmosome-like (actin-containing) contacts and proliferation of subsurface cisterns, the accumulators of calcium ions was noted immediately after the poison action and stimulation and one day later in afferent synapse ultrastructure. The poison interaction with neuronal actin, mediated by alteration of calcium-accumulating systems is probably one of the mechanisms of its protective effect.

Animals↗
PubMed1998

[Experimentally induced actin depolymerization disrupts the adaptive state of a neuron].

The state of filament actin in Mauthner neuron (MN) of gold-fish adapted to long-term natural stimulation was investigated after introduction of actin-depolymerizing cytochalasin D. Cytochalasin was demonstrated to cause almost complete disappearance of long actin bundles that were characteristic for the cytoplasm of adapted fish and were absent from MN of intact fish. Polymeric actin supporting the cytoskeleton integrity was suggested to be involved in mechanisms underlying the increase of MN resistance extreme loads.

Actins↗
PubMed1998

[Changes in the ratio of granular and agranular endoplasmic reticulum of the Mauthner neurons in fishes as an index of the compensatory processes during sensory stimulation].

Endoplasmic reticulum structure was studied on Mauthner neurons of adult fish and fry. Two-fold decrease of extension of rough endoplasmic reticulum components and similar increase of extension of smooth endoplasmic reticulum components were found to occur following long-term stimulation of Mauthner neurons. The significance of transformation of rough endoplasmic reticulum into smooth one as a result of neuronal compensatory response was discussed.

Adaptation, Physiological↗
PubMed1997

[The cultivation of fragments of the parotid venom-secreting gland in the common adder (Vipera berus)].

The primary culture of the Vipera berus poison-secretory parotid gland has been obtained. The morphology of the intact secretory epithelium and epithelial cells cultured in different conditions has been examined by light and electron microscopy. The secretory epithelium cells were able to survive in the cultural medium and to adapt to in vitro conditions maintaining their nearly normal ultrastructure corresponding to the stage of active poison secretion commonly observed in epithelial cells of the native gland.

Animals↗
PubMed1996

[The ultrastructure of Mauthner's neurons in the surviving medulla oblongata of goldfish].

Ultrastructure of Mauthner neurons (MN) was studied in fragments of myelencephalon incubated for 0.5-1.5 hours obtained from immature gold fish. Incubation terms increase along with destruction extent and reorganization of cytoplasmic organelles and nucleus with structure of MN afferent synaptic apparatus less disturbed. Specialized synaptic contacts-active zones, cleft contacts and desmosome-like structure are well retained. The data obtained indicate MN viability during the incubation terms studied, which allows to use surviving grafts with MN as a model for studying ultrastructural bases of certain functional changes of neurons and other neurobiological problems.

Animals↗
PubMed1996

[An ultrastructural study of the hippocampal neurons in mice subjected to heat exposure].

The ultrastructure of hippocampal neurons in mice subjected to heat treatment for 40 min at 42 degrees C was studied. Such a treatment has been shown to result in significant changes in the structure of pyramidal neurons. An increased chromatin condensation in the nuclei was found in addition to deep invagination of their envelopes and reduction or fragmentation of the reticulum cisterns. These changes were accompanied by mitochondrial swelling and increased number of clathrine vesicles around the Golgi complex. The heat exposure followed by feeding on vitamins and beta-carotin appeared to diminish chromatin condensation and kept the cisterns invariable.

Adaptation, Physiological↗
PubMed1996

[The reaction of the cytoskeleton and smooth endoplasmic reticulum of Mauthner's neurons in goldfish to partial denervation and prolonged sensory stimulation].

Structure of smooth endoplasmic reticulum and cytoskeleton of goldfish Mauthner neurons were studied together with the behavior of fish after partial deafferentation of one of the dendrites with following long-term natural stimulation of another one and soma. Strong disturbance of cytoskeleton and proliferation of smooth endoplasmic reticulum especially of its transversely localised component accompanies exhaustion of Mauthner neurons caused by stimulation in normal absolute afferentation. On behavioral level it is manifests in significant suppression of fish motor activity. Similar stimulation of partly deafferentated Mauthner neurons turns to be more sparing both for fish behaviour and Mauthner neurons structure. Proliferation of endoplasmic reticulum was not in fact observed and in the cytoskeleton bundles of filaments were detected which implies improvement of its physico-chemical characteristics and increase of resistance to external factors. Probably, this relative resistance of partly deafferentated Mauthner neurons of fish to long-term natural stimulation is conditioned predominantly by postsynaptic mechanisms and is likely linked with reorganization in cytoskeleton, caused by preliminary change of Mauthner neurons innervation.

Animals↗
PubMed1995

Distribution of calcium pyroantimonate precipitates in Xenotoca Mauthner cells at normal and increased functional activity.

The pyroantimonate method was used for the ultrastructural localization of calcium ions (Ca2+) in Xenotoca Mauthner cells under normal conditions and after prolonged natural stimulation. In normal state, the highest concentration of these ions was observed as compact electron-dense precipitates inside the synaptic cleft exactly at the synaptic active zones. Some amount of dotted precipitates was revealed in the synaptic boutons. In the extracellular space and in the cytoplasm the precipitates are seen mainly as single membrane-bound dots. After prolonged stimulation significant redistribution of the precipitates was observed. They were entirely absent in the presynaptic areas, became diffuse and discontinuous or disappeared completely at the synaptic active zones. On the contrary, in the cytoplasmic organelles (subsynaptic cisternae, vacuoles, smooth reticulum, mitochondria) the precipitates were aggregated into continuous dense clusters inside the membranous compartments or on their surfaces. Also, large amounts of granules, not associated with membranes, were localized inside the cytoplasm directly at the cytoskeletal elements. It is suggested that membrane subsynaptic organelles are the primary structures which sequestrate, accumulate and retain Ca2+. Thus, these elements, together with deeper elements of smooth cytoplasmic reticulum, may control the cytoplasmic activity of Ca2+ and, as a consequence, control many physiologically significant reactions of the neurons.

Animals↗
PubMed1995

[The functional-structural characteristics of the neurons in cultured explants of the cerebral cortex of rats subjected to immobilization-cold exposure in the prenatal developmental period].

A tissue culture was obtained from the sensorimotor cortex of rat embryos after keeping pregnant animals under immobilization-cold stress. The functional state of culture was determined by RNA synthesis intensity. On analysing the tissue morphology, much attention was paid to the pattern of cytoskeleton (microtubules and microfilaments) of neuronal processes. For both periods of cultivation (7 and 14 days), the levels of RNA synthesis in culture of stressed animals were weaker than in the control one by 44 and 34%, resp. After 2 weeks of incubation the density of microtubules, i.e. the number of microtubules per process width, was reduced by 26% in profiles of dendrites. No changes in the number of microfilaments were detected. Besides, destruction of the neuron cytoplasm, redistribution of microtubules within dendrites, and reduction in the number of synaptic endings were noticed. All these alterations seem to be caused by lowering the capability of neurons to form their processes.

Animals↗
PubMed1992

[The structure of the reticulum of Mauthner's neurons in tadpoles of the clawed toad grown under increased gravitational force].

The ultrastructure of the Mauthner cells (M-cells) and the behaviour of Xenopus laevis tadpoles, reared from eggs under increased gravity (2.9 g) which changes the activity of an afferent vestibular input, were investigated. Besides, a study was made of tadpoles after the hindbrain ablation at earlier embryonal stages which significantly altered the microenvironment of M-cells. It is shown that experimental treatments enhance the proliferation of endoplasmic reticulum and its derivatives, so called subsurface cisterns, in the subsynaptic areas. Some structural changes of the synaptic active zones and the cytoskeleton of M-cells were also noticed. It is assumed that the development of the endoplasmic reticulum promotes an intense removal of calcium ions from subsynaptic areas. The plasticity of the endoplasmic reticulum together with other ultrastructural changes apparently stipulate the adaptation of neurons to changed conditions of functioning.

Animals↗
PubMed1991

[The cytoskeleton of the Mauthner neurons in the guppy after returning from an orbital flight].

The ultrastructural investigations of the Mauthner neurons (M-cells) of P. reticulata were performed on the return of the fishes after a two weeks orbital flight, the M-cells of fishes from different control groups being simultaneously examined. The structure of M-cells from the experimental fishes was shown to be severely damaged. The changes involved the synaptic apparatus, postsynaptic areas, mitochondria and other organelles of the cytoplasm and the nucleus. Particular changes were seen in the neuronal cytoskeleton. While in the M-cells of intact fishes these were seen as evenly distributed microfilaments and neurofilaments, in the M-cells of experimental fishes the cytoskeleton looked as alternating bundles of condensed filaments. The first indications of cytoskeleton damage appeared in M-cells of the guppy from transport control group and strengthened in fishes from the group of synchronous control. Thus, the data obtained give us a possibility to suggest that the return on the Earth and following readaptation after a prolonged flight at conditions of microgravity and consequent disfunction of vestibular apparatus may result in the damage of central neurons receiving vestibular afferentation (such as M-cells). That, in turn, may be a cause of functional disorders of the central nervous system, including the nerve centres maintaining the organs of motion. These facts are necessary to take into consideration when more prolonged cosmic flights are planned.

Animals↗
PubMed1991

[The effect of prolonged hypothermia on the structure and function of the neurons of surviving slices of guinea pig and suslik hippocampus].

Hippocampi of the guinea pig and ground squirrel were used to examine the neuronal structure of CA1 and CA3 field in surviving slices incubated in warm chamber to rehabilitate the functional activity; then the slices were subjected to a prolonged cooling under zero temperatures. It was shown that the structure of the guinea pig hippocampal slices, first of all of the neuronal cytoskeleton, was disturbed at 1.5 h warm incubation. A further 1 h cooling in a refrigerator resulted in a significant swelling of synapses, dendrites and their organelles. In 24 h the structure was severely damaged. It was determined for the first time that the ground squirrel hippocampal slices revealed in the same conditions a high tolerance to both warming and long-term cooling. Even after 5 days in a refrigerator the neurons and dendrites could be clearly seen in slices, nearly intact ultrastructure of their cytoskeleton, synapses and organelles was preserved. A correlation was found between the structural integrity and the functional activity of hippocampal slices. It was suggested that the cytoskeleton may play a crucial role in maintaining the neuronal structure under conditions of both heating and cooling of the hippocampal slices. These data are useful to further elaborating appropriate methods for prolonging the term of incubation and to neurobiological investigation of surviving brain slices.

Animals↗
PubMed1991

Structural and chemical changes in the cytoskeleton of the goldfish Mauthner cells after vestibular stimulation.

The ultrastructure and protein content of goldfish Mauthner cells (M-cells) at different functional states induced by natural vestibular stimulations were studied. 2-h stimulation, usually causing a fatiguing of the fishes, was found to be accompanied by ultrastructural changes within M-cells and a decreased content of cytoskeletal proteins. After training by short stimulations resulting in a long-term adaptation of the fishes, the ultrastructure and protein content of M-cells could not be distinguished qualitatively and quantitatively from those of non-adapted fishes. When the adapted fishes were stimulated for 2 h the content of a 70-kDa protein was found to be increased. In addition, the content of a 42-kDa protein, obviously actin, was elevated in this case. Correspondingly, electron microscopic analysis demonstrated a significantly increased resistance of the cytoskeleton to fatiguing stimulation. The data obtained indicate that the neural cytoskeleton is a central target of fatiguing stimulation. We suppose that the 70-kDa protein is responsible for the adaptive properties of the cytoskeleton. This protein is assumed to be identical with one of the so-called heat-shock proteins of non-neural cells which have the same electrophoretic mobility and are also able to protect the cytoskeleton under stress conditions.

Acoustic Stimulation↗
PubMed1991

Alterations in the cytoskeleton of the goldfish Mauthner cells under various pharmacological treatments.

The ultrastructural changes in the cytoskeleton of the goldfish Mauthner cells (M-cells) at various functional states induced by intracerebral microinjections of biologically active substances were studied. Under the action of kainic acid, a structural analog of the excitatory neurotransmitter of glutamate, the density of the cytoplasmic matrix increased. Cytotoxin II from the cobra toxin, which blocks acetylcholine transmission, had an opposite effect upon the M-cell cytoskeleton. Simultaneously, in some areas of the neural cytoplasm strands of an electron-dense material of various shapes appeared. They had an unique structure which did not resemble any known cytoskeleton element. The molecular composition of the strands is unknown, but similar strands appeared after injections of phalloidin or cytochalasin B, both disturbing the microfilamental component of the cytoskeleton. Decoration with myosin subfragment-1 revealed actin in intact M-cells which was organized as crossing loose filaments and bundles of parallel fibers. The morphology of the fiber bundles resembles the helical part of the strands appearing after the treatment with phalloidin, cytochalasin B, or cytotoxin II. It is suggested that the cytoplasmic matrix of M-cells is a dynamic system which responds to the functional changes by thickening or loosening of its cytoskeletal elements or by formation of new structures.

Acoustic Stimulation↗