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B I Shiriaev

Publications and source records attributed to B I Shiriaev.

At least 19 recordsLinked to original sources
PubMed1986

Synaptic organization of dorsal root projections to lumbar motoneurons in the clawed toad (Xenopus laevis).

Synaptic connexions between dorsal root primary afferents and lumbar motoneurons have been investigated in the isolated spinal cord of the clawed toad. The study of monosynaptic actions evoked in motoneurons by 9th or 10th dorsal root stimulation or by impulses in single primary afferents provided evidence for both electrical and chemical junctional transmission at the sensory-motor synapses. The anterograde filling of the 9th and 10th dorsal roots with horseradish peroxidase (HRP) shows that afferents do project to the motoneuron field of the segments IX and X. Some of the fibres not only reach the dorsally located motoneurons, but also cross the lateral motor column (LMC) and terminate in the marginal zone of ventral horn gray matter. The projections of the 9th and 10th dorsal root fibres are most numerous in the caudal part of segment X. Simultaneous HRP labeling of single motoneurons and the whole 10th dorsal root has revealed that afferent fibres make contacts not only on the distal dendrites of the motor cells, but also on the proximal ones. This latter finding is in a good agreement with the electrophysiological data.

Animals↗
PubMed1984

Synaptic connexions between primary afferents and thoracic motoneurones in the frog.

Synaptic actions were evoked in thoracic motoneurones of the isolated frog spinal cord by 6th or 7th dorsal root volleys or impulses in single primary afferents. In a few cases the impaled motoneurones or the whole dorsal root were filled with horseradish peroxidase. Although HRP labelling has revealed that motoneurones have extensive dendritic arborizations extending into the dorsal horn, the zone in which thoracic dorsal root afferents terminate, there is no positive evidence for a direct link between them. Synaptic actions produced in thoracic motoneurones by dorsal root stimulation are mediated via interneurones and do not involve direct sensorimotor synapses. This conclusion is in agreement with results of simultaneous intracellular recording from motoneurones and individual dorsal root fibres afferent to them.

Afferent Pathways↗
PubMed1984

Tracing of frog sensory-motor synapses by intracellular injection of horseradish peroxidase.

Monosynaptically connected primary afferent fibres and motoneurones of the isolated spinal cord of the frog were injected with horseradish peroxidase (HRP). Six labelled afferent fibre-motoneurone pairs were reconstructed and subjected to detailed analysis. Frog motoneurones possess eight to twelve dendritic arrays displaying some dorso-ventral asymmetry. Dorsal dendrites exhibit a rostro-caudal extent of 1.7-2.6 mm (average 2.2 mm). Primary afferent fibres bifurcate in the dorsal funiculus. First-order collaterals emanate from the main ascending and descending branches, at an average distance of 407 micron. The average number of boutons per collateral is 670. To reach a contacting bouton the presynaptic spike must pass on average five bifurcations and then zero to twelve boutons en passant, attached to a single terminal collateral branch. The structural equivalent of the axon cylinder of the collateral tree roughly preserves cross-sectional area. The branch power ranged between 1.15 and 3.35 (average 2.06). Primary afferent fibres usually form clusters of contacting boutons (contact regions). Connexions between an afferent fibre and a motoneurone comprise from five to twenty-three contact regions (average 12.5). Each contact region contains one to twelve contacting boutons (average 3.3). In two of three experiments contacting boutons were found to be significantly larger than non-contacting boutons. The average diameter of the former was 2.6 micron (range 1.2-4.0). In five out of six cases more than one collateral belonging to the same fibre participated in the connexion with a given motoneurone. The average number of contacting boutons per motoneurone and collateral is 19.1. It was estimated that each collateral could supply not more than thirty-five motoneurones. This would be less than 8.5% of the motoneurones with their dendrites which cross the termination space of a single collateral. The average number of contacting boutons forming one primary motoneurone connexion was 41.5 (range 21-72).

Action Potentials↗
PubMed1984

Relation between structural and release parameters at the frog sensory-motor synapse.

The sensory-motor synaptic connexions in the frog lumbar cord have been used to examine the relationship between the statistical characteristics of the unitary excitatory post-synaptic potential (e.p.s.p.) and the number and organization of synaptic contacts determined when the primary afferent fibre used in evoking the e.p.s.p., and a motoneurone in which it was recorded, were both labelled with horseradish peroxidase (HRP). A significant correlation is found between the number of contacting boutons and the amplitude of the chemical component of the unitary e.p.s.p.s generated at the same connexions. The amplitude fluctuation patterns of the single-fibre e.p.s.p.s could be fitted by both Poisson and binomial distribution. The number of presumed Poisson release sites as estimated from the ratio Vmax/v (where Vmax is the maximal amplitude of the chemical component of e.p.s.p. and v is quantal size) is always less than or equal to the total number of boutons observed histologically. In three connexions there was a close correspondence between the number of binomial release units, n, and the number of contact regions formed by the tight clusters of contacting boutons. The unit potential amplitude estimated from the Poisson distribution is found to be two to three times smaller than the quantal size calculated from binomial distribution. A similar numerical relationship was found between the number of contacting boutons and the number of contact regions. It is suggested that at a single bouton, transmission results in release of a single quantum of transmitter, whereas the binomial quantum probably reflects the multi-quantal release occurring simultaneously at boutons comprising a contact region. A significant correlation is found between the mean quantum content estimated either from Poisson or binomial distribution and the number of contacting boutons and contact regions respectively, indicating the dependence of quantal release on the magnitude of synaptic surface. No correlation is found between the motoneuronal soma diameter and the quantal size, although the former is significantly correlated with the number of contacting boutons.

Action Potentials↗
PubMed1984

[Synaptic interaction of individual motor neurons of the isolated frog spinal cord].

The mode of synaptic transmission between single lumbar motoneurons in isolated spinal cord of frog was investigated by means of parallel penetration of two separate microelectrodes in two neighbouring motoneurons. The synaptic transmission between them was electrically mediated in 82 of 89 cases studied, which was indicated by the lack or very short latency of unitary intermotoneuronal EPSPs and by its amplitude persistence in Ca2+-free, Mn2+-containing solution. Effective electrotonic spread in either direction was demonstrated: both depo- and hyperpolarizing currents passed through an electrode in one motoneuron produced corresponding potentials in coupled motoneuron. The rise and decay of these potentials have much longer time constant as compared to time constant of both coupled motoneurons. The blockade of SD-component of an action potential in "trigger" motoneuron produced a decrease in the EPSP amplitude in the coupled motoneuron. Electrotonic synapses between motoneurons revealed no rectification. In four cases unitary intermotoneuronal EPSPs were chemically mediated as was indicated by their latencies (1.3-3.3 ms) and by their full blockade in CA2+-free, Mn2+-containing solution. The amplitude of this group of EPSPs fluctuated in accordance with binomial or Poisson statistics. In three cases double-component unitary intermotoneuronal EPSPs were recorded, first and second components of which were electrically and chemically mediated, respectively. Morphological structures which could be responsible for the generation of these three groups of unitary EPSPs are considered.

Animals↗
PubMed1983

Differential sensitivity of individual primary afferents to glutamic and gamma-aminobutyric acids in the amphibian spinal cord in vitro.

In the isolated amphibian spinal cord the responses to glutamate and GABA recorded intracellularly from individual primary afferents differed considerably according to the fibre type. Muscle afferents giving rise to direct sensory-motor synapses were strongly depolarized by glutamate, whereas GABA produced smaller and inconsistent depolarization. In contrast, fibres both of muscle and cutaneous origin establishing polysynaptic connections with motoneurones were relatively insensitive to glutamate but very sensitive to GABA. These observations suggest that the effects of glutamate on fibres synapsing with motoneurones are probably mediated via the depolarization of motoneurones electrically coupled with them and do not result from direct activation of presynaptic terminals by glutamate.

Afferent Pathways↗
PubMed1983

Tracing of motoneurones and primary afferent projections after intracellular staining with Lucifer Yellow: dye-coupling.

Intracellular injection of the fluorescent dye Lucifer Yellow CH into single motoneurones of the isolated perfused frog spinal cord resulted in backfilling of presynaptic fibres originating from dorsal roots and ventrolateral funiculi. The dye transfer from primary sensory fibres into motoneurones was observed following application of Lucifer Yellow to the central end of the cut dorsal root. The dye-coupling coincides with electrical coupling at sensory-motor synapses presumably through gap junctions. The fluorescent primary afferent fibres were traced from the dorsal roots to the motor nucleus where they terminate the chains of swellings. Most swellings are located in dorsal horn and in the intermediate zone approximately 100-100 micrometers from the somata of motoneurones. A few varicosities are located ion the cell bodies of the motoneurones.

Afferent Pathways↗
PubMed1983

[Synaptic effects evoked in the spinal cord motor neurons of the frog by adequate stimulation of muscle spindles].

Monosynaptic EPSPs in motoneurones of isolated spinal cord of the frog Rana ridibunda elicited by stretch of the m. sartorius occurred when the involvement of tendon and leaf-like receptors had been excluded. These EPSPs consisted of two components, the first of which persisted in Ca2+-free, Mn2+ or Mg2+-containing media whereas the second one was completely blocked. These observations are in agreement with electrical nature of the first component and chemical nature of the second one.

Animals↗
PubMed1982

Combined morphological and electrophysiological description of connections between single primary afferent fibres and individual motoneurons in the frog spinal cord.

In experiments on the isolated frog spinal cord the relationship between the statistical properties of the unitary EPSP and the number of synaptic contacts was determined when the primary afferent fibre used in evoking the EPSP and the motoneuron in which it was recorded were both stained with HRP. The size of the chemical component of the EPSP corresponds to the number of presynaptic boutons. Less obvious numerical correlation exists between the number of contact zones and the number of binomial units.

Afferent Pathways↗
PubMed1982

[Distribution of the terminals of primary afferent fibers polysynaptically connected to motoneurons in the spinal cord in the frog].

In experiments carried out on an isolated perfused frog spinal cord connected with the hindlimb nerves primary afferent fibres and motoneurons were studied by intracellular electrical stimulation and recording with subsequent injection of HRP. It is found that collaterals of fast-conducting fibres belonging to the cutaneous or muscle nerves and establishing polysynaptic connections with motoneurons terminate within the upper and middle portions of the dorsal horn. Terminal branching of these fibres are characterized by numerous collaterals originating at short distances from each other. In some cases HRP-positive interneurons with axons terminating in immediate proximity to injected fibres were found. It is suggested that HRP-positive interneurons make axo-axonal contacts with terminals of primary afferent fibres.

Animals↗
PubMed1982

[Intracellular horseradish peroxidase injection study of connections between primary afferents and spinal cord motor neurons in the frog].

Simultaneous intracellular penetration of a frog motoneuron and a single primary afferent fibre monosynaptically connected with it was used for potential recording followed by HRP injection. Subsequent histological reconstruction of labelled motoneurons and their afferents revealed numerous contacts between them. These contacts were found both on the motoneuronal soma and dendrites, being most numerous in the proximal parts of dendrites and in the second-third-order branches. Recurrent collaterals of motoneuron axons and their contacts with dendrites were found.

Animals↗
PubMed1980

Dual mode of junctional transmission at synapses between single primary afferent fibres and motoneurones in the amphibian.

1. The isolated hemisected frog spinal cord has been used to examine the effects of changes in ionic composition of perfusing medium on the intracellularly recorded e.p.s.p.s produced in single motoneurones by direct stimulation of individual dorsal root fibres through a separate intracellular micro-electrode.2. The monosynaptic single-fibre e.p.s.p.s usually reveal two distinct components, early and late. The early component is resistant to replacement of external Ca(2+) by Mn(2+) whereas the later is reversibly abolished. It is concluded that the junction between primary afferent fibre and motoneurone provides joint electrical and chemical transmission.3. The average amplitude of the unitary electrical e.p.s.p. varies at different junctions from 25 to 430 muV, mean 124 +/- 17 muV (n = 50). It is relatively stable and changes its amplitude only with changes in the height of presynaptic spike. The individual amplitudes observed in a given cell usually have a normal distribution suggesting that any variability in electrical response is entirely due to noise.4. The average amplitude of the single-fibre chemically mediated e.p.s.p. varies from less than 20 muV to 1.7 mV, mean 222 +/- 33 muV (n = 71). A positive correlation was found between the amplitudes of chemical and electrical e.p.s.p.s recorded from different motoneurones.5. Chemical e.p.s.p.s evoked by consecutive impulses in a single presynaptic fibre show statistical fluctuations in amplitude. The fluctuations occur in quantal steps in a manner described by binomial or Poisson statistics. Only in a few cases the deviation from stochastic distribution can be attributed to variable invasion of nerve impulses into the terminal region.6. The amplitude of the unit e.p.s.p. varies between 33 and 104 muV, mean 66.4 +/- 4.3 muV (n = 19). The mean quantum content (m) varies from less than 1 to more than 10. The m is reversibly reduced by Ca(2+) lack and by Mn(2+) until the chemically mediated response fluctuates according to a Poisson distribution with the unit e.p.s.p. equivalent to the single quantum of transmitter.7. When paired or repetitive stimuli are applied to the presynaptic fibre the facilitation of the chemically mediated unitary e.p.s.p. can be observed as well as the post-tetanic potentiation. The amplitude of the electrical e.p.s.p. remains unchanged during the period of post-tetanic potentiation, suggesting that the latter is attributable to some change restricted to the specific presynaptic mechanism responsible for the transmitter release but not to changes in presynaptic spike height.

Action Potentials↗
PubMed1980

[Electrical activity of motor neurons of the vascularly perfused spinal cord of kittens].

In 5--22-day kittens, using an original method of perfusion of the spinal cord and the hindlimb through arterial vessels, PSPs were intracellularly recorded from lumbar motoneurons of perfused cord during stimulation of dorsal roots, ventral columns or muscle nerves of the hindlimb. All synaptic actions were completely though reversibly abolished in Ca2+-free solution containing 1.5--2.0 mM Mn2+, indicating the chemical mode of transmission in these synapses. The addition of Mn2+ and removal of Ca2+ markedly reduced and eventually abolished the post--spike after--hyperpolarization of motoneurons without alteration of the spike height. In motoneurons the input resistance ranged from 1.3 to 15.1 Mom (5.9 Mon on the average).

Action Potentials↗