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N R Tiras

Publications and source records attributed to N R Tiras.

At least 19 recordsLinked to original sources
PubMed2000

[Desmosome-like contacts of Mauthner neurons as targets of scorpion venom].

Desmosome-like contacts (DLC) in afferent chemical synapses of the Mauthner cells (MC) were investigated after application of low and high molecular mass peptide fractions 6 and 9, correspondingly, from the Central Asiatic black scorpion Orthochirus scrobiculosus. Besides, the DLC were examined in condition of a training induced morpho-functional stability of the MC (adaptation) mediated by transformation of actin monomers into polymers. In addition, the structure of DLC was studied after cytochalasin application which disrupts F-actin. Fraction 6 was shown to increase the length of DLC and osmiophily of fibrous material. Similar changes in DLC were caused by adaptation. Fraction 9 decreased the osmiophily of the fibrous material, made DLC asymmetric, but did not influence their length. Similar changes in DLC were seen also after cytochalasin D application. Taking into account our previous data on the role of F-actin in the MC functioning, which were obtained following specific pharmacological treatments, the similarity of ultrastructural changes in DLC after both adaptation and fraction 6 application, on the one hand, and after both cytochalasin D and fraction 9 application, on the other one, enabled us to suggest that these fractions may contain peptides able to exert influence of the actin cytoskeleton.

Animals↗
PubMed1999

Ultrastructure of Mauthner cells in fish adapted to long-duration vestibular stimulation and the effect of ethanol.

Adaptation or resistance of fish Mauthner cells (M-cells) to long duration (2 h) vestibular stimulation (LDS) was produced by daily brief and gradually increasing vestibular stimulation (training). The LDS resistance was accompanied by an increase in the number of desmosome-like junctions in the afferent axosomatic synapses. F-actin, the main component of desmosome-like contacts, has been suggested to be responsible for the increased resistance of M-cells to LDS. The purpose of the present study was to investigate the capacity of M-cells to adapt to LDS under the influence of ethanol, which alters the content of F-actin in cells. The experiments were carried out in goldfish fry. Vestibular stimulation (training and LDS) was performed in special drums that were rotated in two planes. The training time was increased from 1 min on day 1 to 30 min on day 30. For ethanol exposure, fish were immersed daily in a 2% ethanol solution for 20 min. To assess the level of resistance to LDS, motor activity indicating the functional state of M-cells was evaluated before and after LDS. The results show that exposure to ethanol reduces the resistance to LDS in both untrained and trained fish. Electron microscopic data demonstrated some structural changes in the synaptic endings located on M-cell soma in ethanol-exposed fish. Wrapping of boutons by cytoplasmic outgrowths and myelin-like structures was observed. Morphometric analysis revealed that exposure to ethanol without training decreases the number of desmosome-like contacts, probably due to ethanol-induced depolymerization of cytoskeletal actin. Ethanol exposure also partly suppressed the increase in the number of desmosome-like contacts that occurs as a result of training. In ethanol-treated trained fish, however, a concomitant increase in the length of desmosome-like contacts was observed. As training alone leads to the formation of additional desmosome-like contacts of standard length, it is possible that although a sufficient amount of such structures cannot be formed in the M-cells of ethanol-exposed trained fish, the existing contacts can be elongated. Thus, possibly changes of the actin state are involved in the adaptation of M-cells to LDS.

Actins↗
PubMed1998

In vitro long-term potentiation of electrotonic responses of goldfish mauthner cells is accompanied by ultrastructural changes at afferent mixed synapses.

The potentiated afferent mixed synapses of the Mauthner cells of fry and adult goldfish in stumps of the medulla oblongata incubated long-term in vitro were studied by electrophysiological and electron microscopic methods. It was shown that brief high-frequency stimulation of posterior branches of the eighth nerve induced a long-term potentiation of electrotonic transmission at large and small mixed club endings. It was about 135% upon subthreshold stimulation and about 200% upon suprathreshold stimulation. The ultrastructural analysis of ultrathin sections of potentiated mixed synaptic endings revealed an increase in the dimensions of desmosome-like contacts which was proportional to the degree of potentiation, about 135% or 200%, depending on the type of stimulation. The dimensions of gap junctions remained unchanged. The dimensions of active zones at potentiated synapses were reduced two-fold as compared with their unpotentiated counterparts, irrespective of the type of stimulation. Considering that desmosome-like contacts consist predominantly of F-actin, a molecule which possesses electroconductivity, it can be assumed that this cytoskeletal protein is involved in the process of potentiation. The increase in the synapse electrical conductivity can be mediated either directly, by shunting the synaptic junction with polymer actin filaments in the region of desmosome-like contacts, or indirectly, via the interaction of actin with gap junction connections situated nearby.

Animals↗
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↗
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↗
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

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↗
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

[Differences in the cytoskeleton in inhibitory and excitatory synapses].

The cytoskeleton of afferent chemical synapses, with various ultrastructure of contact zones, was examined in the Mauthner cells of the goldfish. The synapses with combined active zones and desmosome-like specialized contacts possessed a well developed cytoskeleton consisting of filaments and microtubules oriented towards the synaptic apposition. Regular arrays of synaptic vesicles oriented in the same direction were observed beyond and near the active zones. The cytoskeleton of the synapses lacking desmosome-like formations was diffusely organized throughout the boutons. The distribution of vesicles in the vicinity of active zones was also not ordered. The role of cytoskeleton in organization of the two morphologically distinct synapses is discussed. A special function of cytoskeleton as an intermediary between synaptoplasm and membrane is regarded as a necessary basis for plasticity of excitatory rather than inhibitory synapses.

Animals↗