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N M Chmykhova

Publications and source records attributed to N M Chmykhova.

At least 19 recordsLinked to original sources
PubMed2005

Comparative study of spinal motoneuron axon collaterals.

Numerous spinal motoneurons in mammals possess recurrent axon collaterals included in a feedback loop for controlling motoneuron activity. For nonmammalian vertebrates, the data concerning the existence of collaterals and their intraspinal branching are fragmentary and contradictory. We focused on axonal branching of motoneurons in lampreys, frogs, turtles and young rats, using light microscopic analysis of HRP- or neurobiotin-labeled motoneurons. In lampreys, only a restricted portion of spinal motoneurons, related to the dorsal fins, showed recurrent collaterals. In frogs, a great complexity and high total length of collateral branches as well as a great number of axon swellings were found. In turtles, axon collateralization of spinal motoneurons was much more restricted, and present in particular in lumbar motoneurons innervating proximal hindlimb muscles. Young rat spinal motoneurons have rather abundant recurrent axon collaterals. It is likely that the presence of axon collaterals from spinal motoneurons is related to the level of complexity of locomotion.

Animals↗
PubMed2004

[Modulation of miniature inhibitory potentials in motoneurons of the turtle spinal cord by group II metabotropic glutamate receptors].

The role of group II metabotropic glutamate receptors (mGluRs) in modulation of inhibitory synaptic activity was studied by intracellular recording of motoneuron miniature inhibitory spontaneous postsynaptic potentials (mIPSPs) in isolated lumbar segments of the turtle spinal cord in the medium containing TTX, CNQX, AP-5. The ratio of mIPSPs with fast and slow kinetics (83% vs 17%) is in accordance with the ratio shown for glycine- and GABA-mediated IPSP or IPSCs (Jones et al., 1988; Gao et al., 2001). In the majority of investigated motoneurons, the selective group II mGluRs antagonist EGLU (100-250 microM) increased the frequency of mIPSPs by 106.6 +/- 74.4% (n = 9) without affecting average amplitude, suggesting a presynaptic site of mGluRs action providing for the transmitter release reduction. The analysis of EGLU action on mIPSPs with different time courses (selection by half-width) showed that the frequency of inhancement of miniature inhibitory activity is caused by predominantly short-duration mIPSPs (ba 84.0 +/- 18.2%; n = 9), which are probably glycineergic. However, EGLU did not influence the mIPSPs frequency under condition of GABA-receptor blockade by bicuculline (20 microM). This fact suggest that group II mGluRs could modulate glycinergic transmission to the turtle spinal motoneurons on the necessary condition that GABergic system is active.

Animals↗
PubMed2003

[Recurrent axon collaterals of lumbar motor neurons in turtles].

A combined morphophysiological study was made of connections between motoneurons on the superfused isolated lumbar spinal cord of Testudo horsfieldi. Postsynaptic potentials of motoneurons, followed by antidromic stimulations of ventral root filaments (VR-PSPs), were recorded intracellularly. Depolarizing VP-PSPs had short latencies (1.0-1.5 mc) and amplitudes in the range of 0.3-3.0 mV. At the constant stimulus intensity, the fluctuations of amplitudes were recorded. In some motoneurons, hyperpolarizing VP-PSRs with the latencies 2.5-3.0 mc were observed. A possible structural basis of VR-PSPs was studied by the horseradish peroxidase (HRP) method. After HRP application on thin ventral root filaments the retrograde staining of motoneurons revealed recurrent axon collaterals of labeled motoneurons. Three-dimensional computer reconstructions showed one to three collaterals given off by motoneuron axons. There were up to 19 points of branching in a single collateral. In some cases the full length of collateral trees reached 4.0 mm. The collateral branches had up to 72 "en passant" and terminal axon swellings. The swellings (presumed contacting boutons) were distributed in the ventral and intermedial gray matter and in the ventromedial while matter and revealed on motoneurons and inerneurons. These data suggest the participation of the motor axon collaterals in the motoneuron--motoneuron communication in the turtle spinal cord whereas only dendro-dendritic contacts had been discussed earlier.

Animals↗
PubMed2001

Structural and physiological properties of connections between individual reticulospinal axons and lumbar motoneurons of the frog.

Although the direct, monosynaptic influence of brainstem projections onto motoneurons is well-known, detailed morphological studies on the synaptic contact systems and a correlation with their functional properties are largely lacking. In this work, 43 pairs, each formed by a reticulospinal fiber contacting a lumbar motoneuron, were identified and studied electrophysiologically. Four of these were successfully labeled intracellularly with horseradish peroxidase (HRP) or neurobiotin and reconstructed using a computer-assisted camera lucida with high resolution. The mean amplitude of excitatory post-synaptic potentials (EPSPs) recorded in these four pairs varied from 100 to 730 microV, spanning most of the range obtained for all pairs (70-1,200 microV; mean +/- SD: 400 +/- 250 microV). Between two and four collaterals of reticulospinal axons established 4-19 close appositions with a labeled motoneuron. Mean distance from the origin of each collateral to any bouton on that collateral was 566-817 microm. A presynaptic action potential must pass 11 branch points on average to reach it. Similarly, the boutons presumably contacting motoneurons were on average 558-624 microm (9-11 branch points) from the origin of the collateral. The distributions of diameters of all boutons and those making putative contacts with stained motoneurons were very similar. The dendritic surface of stained motoneurons was symmetrically distributed along the rostrocaudal axis with more than half the surface being more than 500 microm from the soma. However, the contacts from reticulospinal axons were concentrated ventromedially, 262-356 microm (range of average values for four connections) from the motoneuron soma, in some instances on very proximal dendritic segments. Thus, the location and size of putative contacts in relation to axonal collaterals was not distinguishable from location and size of other boutons, but they occupied specific positions on dendrites of lumbar motoneurons. The number of contacts formed by a reticulospinal axon on a motoneuron in a particular location could be described as the product of the available dendritic surface and the total number of presynaptic boutons in this region. Compartmental models of the reconstructed motoneurons were created, and currents with the time course of an alpha function were injected at the sites of these putative contacts. Despite the restricted volume occupied by contacts from a single fiber, a high variability of their contributions to somatic EPSPs owing to electrotonic attenuation was shown: The coefficient of variation of quantal responses was estimated to be between 60% and 120%, comparable to the variability of the path distance between contacts and soma (50-90%).

Animals↗
PubMed1995

Comparison of the topology and growth rules of motoneuronal dendrites.

The complexity, shape, and branching modes of the dendrites of spinal motoneurons were compared in cat, rat, and frog using topological analysis and growth models. The complexity of motoneuronal dendrites, measured as the mean number of terminal segments, varied significantly among samples and was related to contractile properties of innervated motor units. Despite this variation, all mature motoneurons having a mean number of terminal segments per dendrite greater than ten (up to 24.3) exhibited a narrow range of values of coefficients describing the symmetry of tree shapes (0.42-0.47). This implies low variability in the topological shape of motoneuronal dendrites of different animals. This similarity of tree shapes proved to be a result of the similarity of growth rules. The growth of the dendrites could be described to a first approximation by a two-parameter (Q and S) model called the QS model and by a multitype Markovian model. The estimation of parameters of the QS model, in which parameter Q is related to the probability of branching of intermediate segments, revealed that Q was equal or close to 0, implying that branching of dendrites is restricted to terminal segments. The estimates of the parameter S, which describes whether the probability of branching increases (S < 0) or decreases (S > 0) exponentially with segment order, were positive. This was in agreement with the results of estimation of probabilities of branching provided by the Markovian model, which showed that the branching probabilities decreased with segment order in an exponential manner in most of the neurons studied. The QS and Markovian models involve different assumptions about the sequence and timing of branching events, and selection of the best model can provide insight into details of dendritic outgrowth. Extensive simulation of tree outgrowth using a Markovian model revealed significant differences between stimulated trees and real dendrites, particularly with regard to variability of the number of terminals and to symmetry. In contrast, the QS model provided a good fit to the mean values and standard deviations of basic topological parameters. This model is adequate to describe the shape of mature motoneuronal dendrites. It implies that dendritic branches have many opportunities to bifurcate during the whole time of development and that bifurcating potency of a branch is a function of the number and position of other branches of that dendrite. Combined with analysis of metrical properties such as lengths of segments, the QS model can assist in a quantitative analysis of development and plasticity.

Animals↗
PubMed1993

Structure of recurrent axon collaterals of frog lumbar motoneurons as revealed by intracellular HRP labelling.

Iontophoretical injection of horseradish peroxidase (HRP) into lumbar motoneurons of the isolated and perfused frog spinal cord allowed to reveal recurrent axon collaterals of motoneurons and to study their structural organization. The axons of about 50% of stained motoneurons gave rise to recurrent collaterals. Motoneurons emitted usually one and in a few cases two recurrent axon collaterals. Recurrent collaterals exhibited a complex ramification pattern with numerous swellings presumably corresponding to synaptic boutons both en passant and terminaux. Swellings of recurrent axon collaterals were observed exclusively in the gray matter. Most of the boutons were located in the neuropil, while some of them were found in close apposition to the soma of ventral horn neurons, in particular, motoneurons. The present data provide direct evidence for structural basis involved in recurrent actions of motoneuronal activity in the amphibian spinal cord.

Animals↗
PubMed1991

Sensorimotor connections in the lumbar spinal cord of the young rat: a morphological study.

A morphological investigation of sensorimotor connections was performed on the isolated lumbar spinal cord of 8-15-day-old rats using horseradish peroxidase labelling techniques. Horseradish peroxidase was applied to the filaments of dorsal and ventral roots and injected intracellularly into motoneurons. The labelled afferent fibres and their contacts on motoneurons were examined under a light microscope. Numerous afferent collaterals entered the lateral motor nuclei. In the medial motor nuclei a few afferent collaterals were found. Some fibres were visible passing through the ventral commissure. The number of boutons per afferent collateral in the motor nuclei was 40-60. A single terminal branch contained one to five boutons (average 1.5). Predominating axodendritic and apparent axosomatic contacts were found between afferent fibres and motoneurons belonging to the lateral motor nuclei. The contacting boutons were both terminaux and en passant. As a rule, the sensorimotor connection involved dorsally and rostrocaudally directed dendrites of the first to sixth orders.

Animals↗
PubMed1991

Relation between structural and release parameters at the young rat sensorimotor connection.

The present work was carried out on isolated spinal cords of young rats. The aim of this study was the combined morphological and electrophysiological investigation of sensorimotor connections labelled with horseradish peroxidase and the evaluation of the relationship between their structural and functional properties. Sensorimotor contacts were widely distributed along the postsynaptic cell: from the soma and juxtasomatic dendrites to distal dendrites. The number of contacting boutons in the connection of a single afferent fibre and an individual motoneuron was about 10. The amplitude fluctuation patterns of the unitary and the minimal excitatory postsynaptic potentials of the motoneurons fitted with predictions based on a binomial model. A close correspondence was found between the estimated number of binomial release sites, n, and the number of contacting boutons. The calculated size of the quantal potential was about 100 microV. The difference in the organization of sensorimotor connections of the young rat and the frog is discussed.

Afferent Pathways↗
PubMed1989

[Morphologic and quantum characteristics of sensomotor neuron synapses in isolated rat spinal cord].

The structural-functional relationships of sensorimotor connections were studied in isolated lumbar cord segments of 7-14 day-old rats. Individual motoneurons were found to have synaptic contacts only with a single collateral of the afferent fibre. The number of contacting boutons gained 10. The n parameter of the binomial model was established to reflect the number of contacts at the sensorimotor connection. The analysis of sensorimotor EPSPs by convolution with two binomial distributions has shown that sites of the transmitter release were different in their probability (efficiency) of response to nerve impulse.

Animals↗
PubMed1988

[Morphological bases of motor neuron interaction in the isolated spinal cord of rat pups studied with horseradish peroxidase].

The structure of connections of the lumbar motoneurons was investigated in the isolated spinal cord of young rats by the HRP methods. HRP was applied to the ventral roots and injected intracellularly into the motoneurons. The light microscopic study has shown that dendrodendritic, dendrosomatic and somatosomatic contacts between motoneurons might be established. Recurrent collaterals of motor axons were revealed. They were found to form contacts on the motoneuron dendrites and perikarya. The course and terminal arborizations of the ventral root afferent fibre were also described. The obtained morphological data related to electrophysiological analysis of motoneuronal postsynaptic potentials evoked by ventral root stimulation are discussed.

Animals↗
PubMed1988

[Mechanisms of motor neuron interaction in the isolated spinal cord of rat pups].

Interactions between lumbar motoneurons were studied by intracellular recording of responses to stimulation of ventral roots and intracellular HRP injection in isolated spinal cord preparations of immature (9-14 days old) rats. Ventral root-evoked electrotonic potentials in individual motoneurons were due to interconnections with few other motoneurons and could not elicit spike potentials. Direct chemical excitatory interactions of motoneurons were also found which may occur via axon collaterals. Differences between individual motoneurons in the mode of responses to ventral root stimulation, probably, depend on their functional specialization.

Action Potentials↗
PubMed1987

Morphophysiological characteristics of connexions between single ventrolateral tract fibres and individual motoneurones in the frog spinal cord.

In experiments on the isolated frog spinal cord, simultaneous intracellular recordings were performed from synaptically connected individual ventrolateral tract fibres and lumbar motoneurones. Statistical parameters of amplitude fluctuations of unitary excitatory postsynaptic potentials evoked by direct activation of presynaptic axons were compared with the number of synaptic contacts at the same connexions revealed by staining both pre- and postsynaptic elements with horseradish peroxidase. Close correspondence between the number of contacting boutons and that of release elements (n) determined from binomial relations was observed.

Animals↗
PubMed1982

[Intracellular activity of potassium in frog spinal cord motor neurons].

Intracellular K activity (aik) in frog motoneurons of isolated spinal cord as measured by double-barrelled K+-selective microelectrodes revealed mean values as follows: 74.8 +/- 2.5 mM at the beginning of the recording and 51.6 +/- 2.9 mM afterwards (mean +/- SE). The average value of the resting potential of motoneurons (Em) was 54.1 +/- 1.2 mV. The difference between Ek (potassium equilibrium potential) and Em was 25.0 +/- 0.98 mV. Stimulation of ventral roots of spina-cord decreased aik both in normal and in Ca2+-free Ringer solution. No changes of aik occurred in synaptic stimulation without spike potentials.

Animals↗
PubMedDate not supplied

[Quantitative determination of potassium content of spinal motor neurons frogs by x-ray microanalysis].

X-ray microanalysis has been made of the potassium content of motoneurons in the frogs Rana ridibunda and R. temporaria. The tissue was frozen in isopentane up to-160 degrees, dried in vacuum at-50 degrees, embedded into epoxy resin and sectioned by ultramicrotome. The obtained mean value of intracellular potassium concentration-65 mM/kg of wet weight or 80 mM/l of intracellular water-is in a good agreement with the results of calculation of intracellular potassium from equilibrium potential of post-spike after-hyperpolarization.

Animals↗
PubMedDate not supplied

[A light microscopic study of the axonal collaterals of the lumbar motoneurons in the spinal cord of the frog Rana ridibunda].

By using intracellular injection of horseradish peroxidase into the lumbar motoneurones of the isolated spinal cord of the frog Rana ridibunda the structure of axon collaterals was studied. It was shown that about 50% of the HRP-stained cells had mainly one axon collateral of the 1st order. The subsequent branching patterns of the collaterals showed considerable variations. The number of swellings in various collaterals was from 10 up 100. The mean diameter of swellings varied from 0.8 up 10.0 microns. It is believed that the axon collateral swellings from contacts on the dendrites of the nerve cells mainly. Apparent axosomatic contacts were revealed on the motoneurons and small nerve cells. As in the cat, collateral swellings were found on the dendrites of the parent motoneuron. Obtained morphological data the structure of motor axon collaterals in the frog are compared with those in the cat. Functional significance of the axon collateral in the frog is discussed.

Animals↗