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E N Bezgina

Publications and source records attributed to E N Bezgina.

18 recordsLinked to original sources
PubMed2005

Distribution of calcium ions in the mixed synapses of Mauthner neurons in the goldfish in normal conditions, in exhaustion, and in conditions of adaptation to exhaustion.

The aim of this study was to investigate the structure of large myelinated club terminals of Mauthner neurons (MN) in the goldfish at different levels of functional activity and the distribution within these synapses of calcium ions as assessed using a modified pyroantimonate method. In intact preparations, calcium pyroantimonate precipitates were not seen in gap junctions (GJ) or desmosome-like contacts (DLC). Fibrillar bridges in DLC clefts were not contrasted. After natural stimulation, which induces long-term adaptation in MN, GJ showed electron-dense precipitates lining the whole cleft. Granules and clumps of precipitate were also seen in DLC clefts, with intense deposition on bridges. Increases in calcium ion concentrations to and above the levels detectable by the pyroantimonate method are known to block electrotonic transmission; filamentous actin is known to conduct the electrotonic signal as a cation current. The staining of DLC bridges with calcium pyroantimonate is therefore evidence for an association between calcium ions and actin molecules, as DLC bridges consist of actin, i.e., we have obtained evidence for the functioning of bridges as electrotonic transsynaptic shunts at the moment of fixation. These data lead to the conclusion that DLC in mixed synapses, apart from the known adhesive functions, also have a communication function. This appears in extreme conditions, allowing the synapse to maintain or change its conductivity according to ongoing need.

Acclimatization↗
PubMed2005

The structure of mixed synapses in Mauthner neurons during exposure to substances altering gap junction conductivity.

The aim of the present work was to study the effects of dopamine, ecdysone, and chlorpromazine, substances which alter the conductivity of gap junctions (GJ), on the ultrastructure of mixed synapses in goldfish Mauthner neurons. These studies showed that dopamine, which increased the electrical conductivity of mixed synapses, appeared to target desmosome-like contacts (DLC). Hypertrophy of DLC, along with increases in the numbers of bridges within their clefts, showed that the mechanism by which dopamine increased electrical conductivity involved neuronal actin. This was indicated by the transformation of isolated monomeric muscle actin into polymerized actin in the presence of dopamine. Conversely, GJ were degraded by dopamine. Ecdysone, which also increased GJ conductivity, altered GJ structure, increasing the numbers of GJ at the attachment zone and decreasing the sectional length. but had virtually no effect on DLC structure. Ecdysone also showed no interaction with DLC in in vitro conditions. The mechanism of action of ecdysone is thus associated primarily with GJ function. Chlorpromazine, which decreased GJ conductivity, partially or completely degraded the fibrillar juxtamembrane material of DLC, preventing actin polymerization, with corresponding in vitro effects, but produced no changes in GJ. The mechanism of its action therefore appears to be based on changes in the state of neuronal actin.

Animals↗
PubMed2005

Localization of calcium ions in mixed synapses of Mauthner neurons during exposure to substances altering the conductivity of gap junctions.

The pyroantimonate method was used to study the distribution of calcium ions in the mixed synapses of Mauthner neurons after exposure to substances altering the electrotonic conductivity of these synapses mediated by gap junctions (GJ). Ecdysone, an agent which increases GJ conductivity, produced precipitates of calcium pyroantimonate coating the whole postsynaptic surface of the GJ area, making them strongly asymmetrical. Precipitate granules were also seen to appear in the clefts of desmosome-like contacts (DLC). Chlorpromazine, which decreases GJ conductivity, produced precipitates in GJ clefts and on the pre- and postsynaptic membranes. No precipitate formed in DLC clefts. These results demonstrate that ecdysone acts as an agent selectively increasing GJ conductivity without affecting DLC function. Chlorpromazine had a double action, blocking conduction through both GJ and DLC. Thus, studies of agents altering GJ permeability require consideration of the possibility that they may interact with actin-containing structures also involved in the transport of the electrotonic signal.

Animals↗
PubMed2004

[Substances affecting gap junction conductivity and Mauthner neuron mixed synapses].

The aim of this work was to study the effect of dopamine, 20-hydroxyecdysone and chlorpromazine, drugs changing the conductance of gap junctions (GJs), on the ultrastructure of goldfish Mauthner neurons mixed synapses. It was shown that desmosome-like contacts (DLCs) were the presumable targets for dopamine, that increased the electrotonic conductance of mixed synapses. Their hypertrophy, as well as an increase in the number of bridges in their clefts suggests that neuronal actin is involved in the mechanism of dopamine-induced increase of electrotonic conductance. This assumption is further supported by the transformation of extracted monomeric muscular actin into polymeric actin in the presence of dopamine. On the contrary, GJs were shown to be damaged by dopamine treatment. Ecdysone, which is also known to increase the conductance of GJs, changed their structure, increasing their number in the zone of apposition and reducing the profile length, but practically not affecting the DLC structure. It also does not interact with isolated actin in vitro. Therefore, the mechanism of ecdysone action is mainly associated with GJ function. Chlorpromazine, which reduces the conductance of GJs, was shown to damage, partially or completely, DLC admembranous fibrillar material, thus preventing actin polymerization, as shown by in vitro experiments, but had no effect on GJs. Therefore, the mechanism of its action, appears to be based on the changes in the state of neuronal actin.

Actins↗
PubMed2004

[Calcium ions localization in mixed synapses of mauthner cells after exposure to substances changing the gap junction conductivity].

Using the pyroantimonate method, the distribution of calcium ions in Mauthner cell mixed synapses was studied following their treatment with substances changing gap junction (GJ) synapse electrotonic conductivity. Ecdyson, the drug known to increase GJ conductivity, induced the appearance of calcium pyroantimonate precipitates covering the whole postsynaptic area of GJs, making them highly asymmetric. Formation of precipitate grains was also observed in the cleft of desmosome-like contacts (DLCs). Chlorpromazine, substance that decreases GJ conductivity, induced the formation of precipitates in GJ cleft and on both pre- and postsynaptic sides of their surfaces. No precipitates were seen in DLC cleft. These results show that ecdyson acts as a substance selectively increasing the GJ conductivity with no effect on DLC function. Chlorpromazine has dual effect, by blocking the communication through both GJ and DLC. Thus, using chemicals that change GJ permeability, the possibility of their interaction with actin-containing structures which also participate in the electrotonic signal transfer, should be taken into consideration.

Animals↗
PubMed2003

[Morphofunctional features of microtubule ultrastructure and MAP2 protein phosphorylation in hippocampal neurons of rats with predisposition to audiogenic epilepsy].

It has been shown that modification of microtubule (MT) ultrastructure are accompanied by functional changes in microtubule-associated protein MAP2 in the hippocampus of Krushinsky--Molodkina rats (KM), which are prone to autogenic seizures. The morphogenetic analysis revealed that contrary to Wistar rats, which are insensitive to sound stimulation, in KM the middle length of microtubule fragments in the apical dendrites of pyramidal neurons in CA3 hippocampal area was reduced. Using immunoblot and autoradiography methods, we found that the level of MAP2 and the rate of its cAMP = and Ca(2+)-calmodulin-dependent phosphorylation were increased in hippocampus of KM, in comparison with Wistar rats. Daily repeated sound stimulation for 20 days (audiogenic kindling) induced a further decrease in length of MT fragments, and an increase of their density in the proximal part of apical dendrites of KM. Moreover, audiogenic kindling induced additional increase in MAP2 phosphorylation state, but did not change the level of MAP2 in KM hippocampus. We suppose that the obtained alteration of MAP2 phosphorylation state exerted influence on kinetic parameters of microtubule assembly, serving as part of genetically determined predisposition of KM to audiogenic epilepsy.

Animals↗
PubMed2003

[Calcium ions distribution in mixed synapses of the mauthner neurons of goldfish in the norm, fatigue, and adaptation state].

The aim of this investigation was to study the structure of giant myelinated club-shaped terminals (afferent mixed synapses) of goldfish Mauthner (M-) cells in different functional states and to demonstrate calcium ion localization in them using modified pyroantimonate method. It was shown that in intact preparations calcium pyroantimonate precipitate was detected neither in gap junctions (GJ) nor in desmosome-like junctions (DLJ). The fibrillar bridges within DLJ cleft were not contrasted. After natural stimulation, which elaborated a long-term adaptation of M-cells, electron dense precipitate was found in GJ, lining all the cleft. Simultaneously fine granules and aggregates of precipitate appeared in DLJ gap and were intensely deposited over the bridges. It is known that the increase of calcium ion concentration up to and above the level demonstrable by pyroantimonate method blocks the electrotonic coupling and that filamentous actin is able to conduct electrotonic signal as a cationic current. Therefore calcium pyroantimonate staining of DLJ bridges, which were earlier shown to contain actin, indicates the association of calcium ions with filamentous actin, i.e. the functioning of bridges as transsynaptic electrotonic shunts at a moment of fixation. The data obtained allow to make a conclusion that DLJ in mixed synapses have not only a known adhesive function, but also a communicative one. The latter is manifested in extreme conditions, thus permitting synapse to maintain or change their conductivity in accordance with environmental demands.

Adaptation, Physiological↗
PubMed2001

[Primary culture of epithelial secretory cells from venom gland of the common adder Vipera berus].

A primary culture of epithelial secretory cells from the venom gland of Vipera berus was obtained. The cells adhered to collagen 1 and to a mixture of adhesion proteins (Matrigel), proliferated and retained the features of differentiation. Electron microscopy demonstrated the presence of all ultrastructures typical of these cells in vivo, a full complex of intercellular junctions, and cellular membrane polarity. The immunohistochemistry confirmed the capacity of secretory cells to synthesize venom in culture. We have studied the role of carbochole, an agonist of M-cholinoreceptor, in the initiation of the secretory cycle in cells in vitro. We propose that M-cholinoreceptors may play an important role in the initiation of the secretory cycle in vivo.

Animals↗
PubMed2000

[The reaction of endoplasmic reticulum of Mauthner cells of Xenopus laevis tadpoles in response to the partial denervation].

The structure of the Mauthner cells in Xenopus laevis tadpole was investigated by light- and electron microscopy in norm and after early unilateral enucleation. It was found that enucleation at early stages caused a delay in morphological development of the contralateral neurons during embryogenesis. We observed a decrease in size of the soma and nucleus and in the number of dendrites, a marked structural underdevelopment of the majority of cell organoids, as well as proliferation and hypertrophy of transversal cisternae in the contralateral Mauthner cells. The ipsilateral neurostructure remained normal in embryogenesis. The data obtained suggest the availability of some unknown powerful afferent contralateral input to Mauthner cells from the optical analyzer.

Animals↗
PubMed1999

[Morphogenesis of Mauthner neurons of Xenopus laevis tadpoles following early unilateral eye enucleation].

The connection between Mauthner neuron (CMN) and visual analyzer in Xenopus laevis tadpoles was studied using these neurons capacity to change their morphogenesis during the development in case of interruption of their connections with afferent fibres. In phase 31 of development tadpoles were subjected to unilateral enucleation of eye. Morphogenesis of contralateral (experimental) and ipsilateral (control) MN with respect to the operated eye was followed up. Comparison with intact Mauthner neuron of the tadpole of the same age who were not exposed to operation was conducted. Contralateral MN were found to be delayed in development phases 47 and 50. This was associated with 1.5-3.3 fold difference in neuron body central section area and 2-3 fold differences in nuclear section area. Three-dimensional reconstruction revealed lower number of cell processes in contralateral MN as well as decline in their length and diameter. Control and intact MN showed no difference similar to experimental and control ones in phase 41. The data obtained indicate that MN of Xenopus laevis tadpole possess powerful ipsilateral connections originating from the side of visual analyzer and contralateral ones from the side of the eye. This affects MN development and in contrast to octavolateral system (including vestibular apparatus and organs of lateral line) controls the contralateral neuron.

Animals↗
PubMed1997

[The ultrastructure of the neuromuscular synaptic terminal in the frog after denervation].

Ultrastructure of certain myoneural terminals were studied on serial sections on day 3, 5 and 8 after denervation. Ultrastructure of the terminal proximal and distal regions and Schwann cell were studied by means of morphometry and reconstruction of single terminals. On day 3 after denervation Schwann cell is activated in terminal proximal regions more rapidly than in distal ones with contractility in the terminal proximal region being more significant than in distal. On day 5 after denervation changes cover both initial and terminal regions and on day 8 almost all the regions where terminal were placed earlier were occupied with Schwann cell. A suggestion is made that structural changes in the Schwann cell-terminal system are the major contributors to decrease of synaptic discharge in early stages of denervation and appearance of Schwann cell potentials in more late ones.

Animals↗
PubMed1996

[The ultrastructure of the neuromuscular synapses at different stages in the development of the embryos and tadpoles of the clawed toad].

Myoneural synapses were studied in embryos and tadpole of Xenopus laevis on different stages of development using light and electron microscopy. On embryonal stages, during hatching and on stages of tadpole myoneural synapses vary in in appearance, number of organelles and extent of formation of different synaptic specialisations. During the process of myoneural contacts forming in the development of amphibians, terminal is the first to form, followed by the Schwann cell, that covers it, and postsynaptic plication forms in the last turn. When the embryo of Xenopus laevis becomes a tadpole some of its terminals contain significant number of large synaptic vesicles united into clusters both in cytoplasm and near to active zones (together with small ones). This heterogeneity was not found on earlier stages. A suggestion is made on possible participation of two different axons in the innervation of myotomic muscular fibres of tadpole of Xenopus laevis.

Animals↗
PubMed1989

[The ultrastructure of the individual nerve endings of the tonic fibers in the frog].

A regular diminution of specific areas of synaptic contacts and active zones (AZs) along the terminals towards the distal parts has been first shown. The discontinuity was found in the terminal nerve branch apposition to the muscle fiber as a result of periodic intercalation of the Schwann cell and its processes into the synaptic gap. A significant variability in shapes of active zones lengthways the terminal is revealed. It is suggested that all these structural features may reflect the functional properties of synapses on the tonic muscle fibres.

Animals↗
PubMed1988

[Nonuniformity of the fine structure of various portions of the nerve terminal in frog somatic muscles as the basis for the variation in its efficiency].

The ultrastructure of serially sectioned single terminals of two neuromuscular synapses differing in efficacy in frog sartorius and cutaneous pectoris muscles was investigated. Their central (CP) and distal (DP) parts were studied morphometrically, and the data on the terminal ultrastructure in different muscles were compared. The areas of active zones (AZ) in CP of terminals in both the muscles were significantly larger than in DP. At the same time the number of AZ in CP specific terminal length of sartorius muscle exceeded that in DP, whereas at terminal of cutaneous pectoris muscle the AZ were arranged more uniformly along the whole terminal length. Some other structural features of these terminals were revealed exerting their influence on the efficacy of transmitter release. We suggest that changes of AZ dimensions may closely correspond to the efficacy both in different parts of the same terminal and in two different terminals.

Animals↗
PubMed1988

[Synapses with a different synaptic contact structure in the cerebellar cortex].

The ultrastructure of cerebellar axosomatic (inhibitory) and axo-dendritic (excitatory) synapses were studied on the Purkinje cells and in the lower molecular layer of guinea-pigs and rats, respectively. It was shown that synaptic contacts of excitatory and inhibitory synapses differed in the existence of desmosome-like structures near the active zones. The classification of synaptic functions according to the ultrastructure of specialized contacts, earlier developed to identify neurons of lower vertebrates, is supposed to be applicable to the nervous system of higher vertebrates.

Animals↗
PubMed1987

[The single nerve ending of the frog sartorius muscle: its ultrastructural characteristics and mediator secretion].

Electron microscopy and extracellular recordings were used for the investigation of structural and functional peculiarities of single frog sartorius muscle nerve terminal. It has been found that the diameter, length of the synaptic contact and quantity of synaptic vesicles decreased from proximal to distal parts of the nerve terminal. A number of varicosities, separated from each other by schwann cells, have been revealed along the course of the nerve terminal. This indicates the existence of an interrupted synaptic contact. Both the evoked and spontaneous transmitter release decreased from the initial to the end parts of the nerve terminal. The data obtained suggest that there is a correlation between structural heterogeneity and the differences in the transmitter release.

Animals↗