Biomedical subjects

N P Tiras

Publications and source records attributed to N P Tiras.

3 recordsLinked to original sources

PubMed2005

[Correlation of the sizes of Mauthner neurons with the preference in the goldfish to turn rightwards or leftwards].

Using the three-dimensional computer reconstruction from serial histological sections, the morphology of right and left Mauthner cells (MC) was examined in the goldfish fry which demonstrated clearly pronounced preference to turn to the right or to the left in a narrow water channel or which did not show any asymmetry in choosing the side of turning. Visually, the goldfish with left-sided motor asymmetry seemed to possess larger right MC, while in the goldfish with right-sided motor asymmetry left MC were larger. In fish with symmetric proportion of right or left turnings, the sizes of MC did not differ. Quantitative evaluation of MC in fish showing the preference of turning side has revealed significant differences in the sizes of cell bodies, axon hillock and axons of MC, located contralaterally in medulla oblongata. Analysis of a statistic relations between functional (motor) and morphological asymmetry of MC cell body in the same fish indicated the existence of a stable correlation (0,69) between them. Taking into consideration that MC initiate unilateral body turn during free swimming of fish, it may be concluded that the larger size of neuron predetermines its more frequent natural activation in comparison with the contrlateral neuron, that has smaller size.

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↗

PubMed2002

[Morpho-functional changes in mauthner neurons of goldfish adapted to prolonged orthodromic stimulation of acoustic nerve in vitro].

In newly-hatched goldfish the adapted state was developed using repeated short-term stimulation of the vestibular apparatus. It differed from the non-adapted state by the absence of fatigue during the turns of fishes produced by unilateral tail fin flicks in ring channel. Electrophysiological study of Mauthner neurons (MN) in adapted goldfish using the slices of medulla oblongata incubated in vitro, has shown the preservation of the amplitude of the extracellular responses after prolonged orthodromic electric stimulation of acoustic nerve, which suppressed the responses of non-adapted MN. Thus, the resistance against fatigue has developed also at the level of MN. Using electron microscopy it was demonstrated that adapted MN following the prolonged electric stimulation in vitro were characterized by the resistance of specialized desmosome-like contacts, similar to what was earlier observed in these neurons in vivo. The data obtained suggest that indirect evaluation of MN functional state in goldfish by counting the number of turns performed by it in narrow ring channel, corresponds to the direct morpho-functional assessment of MN state. This form of innate behavior of freely moving fish seems to be the result of MN excitation.

Adaptation, Physiological↗