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Biomedical subjects

G N Akoev

Publications and source records attributed to G N Akoev.

At least 19 recordsLinked to original sources
PubMed1995

On the relationship between the number of negative slope regions in the voltage-current curve of the Hodgkin-Huxley model and its parameter values.

We consider the problem of the existence of a negative slope region (NSR) in the voltage-current curve of the neuronal membrane and the relationship between this phenomenon and the membrane parameters. For the Hodgkin-Huxley model it is proposed to determine the dependence of the number of NSR on the values of the maximal sodium (gNa) and potassium (gk) conductances. The method is suggested for constructing the boundaries on the (gNa, gk) plane, in passing through which the number of NSR changes to 1. Using the method we partition the (gNa, gk) plane into the regions corresponding to the curves with the different number of NSR. This number can be changed from 0 to 2 in changing the values of gNa and gk over the physiologically possible range.

Animals↗
PubMed1995

Electroreceptors: involvement of excitatory amino acids in synaptic transmission.

Electroreceptors are present in the skin of fish, amphibia and lower mammals, e.g. platypus. Animals use these receptors for detecting weak electric and magnetic fields. Electroreceptors of fish and amphibia belong to the secondary receptors in which the primary transduction is carried out by neuroepithelial hair cells that transmit synaptically to the afferent nerve fibers. The role of excitatory amino acids in synaptic transmission in electroreceptors is the subject of this review.

Amphibians↗
PubMed1995

Reception of low-intensity millimeter-wave electromagnetic radiation by the electroreceptors in skates.

Low intensity millimeter-wave electromagnetic radiation of less than 10 mW cm-2 power intensity has a nonthermal effect on the body and it is widely used in medical practice for treatment of various diseases. Nevertheless, the effect of EMR on biological tissues is not understood. The skin and its sensory receptors are considered to be responsible for EMR reception, but this has yet to be confirmed. The present experiments were designed to study the effect of millimeter-wave electromagnetic radiation on the ampullae of Lorenzini in skates, which are very sensitive to weak electrical stimuli at low frequency. Reception of low-intensity millimeter-wave electromagnetic radiation at 37-55 GHz by the electroreceptors (ampullae of Lorenzini) in the skate has been shown. At a power intensity of 1-5 mW cm-2 irradiating the duct opening at 1-20 mm distance caused a transient increase in the firing rate of a single afferent unit. When the power intensity was increased inhibitory responses were also observed. Some receptors responded with a prolonged excitatory activity lasting up to 30 min to the irradiation of the duct opening. Direct irradiation of the sensory cells produced only an inhibition, probably due to a rise in temperature. It is proposed that millimeter-wave electromagnetic radiation generates a d.c. potential at the vicinity of duct opening which can be detected by the electroreceptors.

Animals↗
PubMed1994

Changes in sensitivities of amplitude and frequency curves of the Hodgkin-Huxley system produced by variations of maximal conductances.

The question of sensitivity of amplitude and frequency curves of the Hodgkin-Huxley system to variations of maximal values of sodium (gNa) and potassium (gK) conductances is considered. Changes in the sensitivity produced by simultaneous changes in gNa and gK values are examined. It has been shown that simultaneous increase of the values of gNa and gK is accompanied by decrease of the sensitivity and, therefore, by improvement of quality of nerve fiber functioning.

Algorithms↗
PubMed1993

Analysis of L-[3H]-glutamate radioligand binding to plasma membranes of the ampullae of Lorenzini of skates.

Radioligand binding analysis of L-[3H]-glutamate to plasma membranes of the ampullae of Lorenzini in the skate revealed one type of binding site with KD = 286 nM and Bmax = 2.1 pmol mg-1 protein. It was revealed that Na+, K+, Ca2+ and Mg2+ inhibited the L-[3H]-glutamate binding, while Cl- had no effect. The glutamate agonists kainate, quisqualate and N-methyl-D-aspartate (NMDA) were shown to inhibit glutamate binding in a dose-dependent manner. The results obtained confirm the electrophysiological observations suggesting the existence of three types of glutamate receptor at afferent synapses of the ampullae of Lorenzini of skates.

Animals↗
PubMed1993

Functional states of an excitable membrane and their dependence on its parameter values.

The property of an excitable membrane of a nerve cell to change the type of electrical activity has been examined with the change of the value of applied current (I). The dependence of this property on the values of the membrane parameters is determined. Two different functional states depending on the values of the membrane parameters are considered. For one of the states a change in the value of I is accompanied by a change in the type of activity (damped periodic oscillations jump to undamped periodic oscillations or vice versa). For the other state the type of activity remains phasic (damped periodic oscillations) for each value of I. For the mathematical model of a membrane we have considered the problem of obtaining the boundary, partitioning the parameter space into the regions to which these functional states correspond. We suggest a mathematical set of this problem and give its algorithm. These boundaries have been constructed for two different variable parameters of the model. A good agreement between the boundaries and the experimental values of sodium and potassium conductances for different excitable membranes has been obtained.

Algorithms↗
PubMed1992

Partition of the Hodgkin-Huxley type model parameter space into the regions of qualitatively different solutions.

We have examined the problem of obtaining relationships between the type of stable solutions of the Hodgkin-Huxley type system, the values of its parameters and a constant applied current (I). As variable parameters of the system the maximal Na+(-gNa), K+(-gK) conductances and shifts (Gm, Gh, Gn) of the voltage-dependences have been chosen. To solve this problem it is sufficient to find points belonging to the boundary, partitioning the parameter space of the system into the regions of the qualitatively different types of stable solutions (steady states and stable periodic oscillations). Almost all over the physiological range of I, a type of stable solution is determined by the type of steady state (stable or unstable). Using this fact, the approximate solution of this problem could be obtained by analyzing the spectrum of eigenvalues of the Jacobian matrix for the linearized system. The families of the plan sections of the boundary have been constructed in the three-parameter spaces (I, -gNa, -gK), (I, Gm, Gh), (I, Gm, Gn).

Algorithms↗
PubMed1992

L-serine-O-phosphate blocks NMDA-evoked responses in the ampullae of Lorenzini of skates.

In the present study, we have shown by single afferent unit recording in the organs of Lorenzini that L-serine-O-phosphate (L-SOP) decreases the resting discharge frequency as well as electrically evoked responses. L-SOP in a concentration of 0.1-100 microM antagonizes responses induced by L-glutamate (L-GLU) and N-methyl-D-aspartate (NMDA) and has no effect on the responses to application of kainate (KA) and quisqualate (Q). The results obtained confirm previous observations about the existence of NMDA receptors in the afferent synapse of the ampullae of Lorenzini.

Amino Acids↗
PubMed1992

Brain neurite-stimulating protein promotes formation of mechanosensory endings in sensory neuron.

In the present study we have shown that in the organotypic culture of dorsal root ganglia (DRG) of 10-11 day-old chick embryos, the neurite-stimulating protein (NSP) from bovine brain promotes the development of branching mechanosensory endings. The light and electron microscopic observation revealed that the morphological features of these sensory endings are similar to those in vivo. A mechanical stimulation of these endings elicited bursts of impulses in the sensory neurons.

Animals↗
PubMed1992

[Extra-organ sources of parasympathetic innervation of small intestine in the region of ligament of Treitz].

Localization sites of neurons in the dorsal motor nucleus of cat vagus innervating the duodenal-jejunal region and upper part of the jejunum were investigated using the technique of the retrograde axonal transport of horseradish peroxidase. Most part of the neurons was located within the ventrolateral area of the nucleus from +1.0 to +2.7 mm (according to obex). Morphological features of the ganglion nodosum neurons which organize afferent innervation of the intestine were analyzed. It has been shown that the maximal amount of such neurons is concentrated in the medium and caudal parts of the ganglion.

Afferent Pathways↗
PubMed1991

Effects of excitatory amino acid antagonists on synaptic transmission in the ampullae of Lorenzini of the skate Raja clavata.

1. The effects of excitatory amino acid antagonists on synaptic transmission in the ampullae of Lorenzini of the skate Raja clavata were studied. 2. At concentrations of 10(-3) to 10(-6) M. L-glutamic acid diethylester (GDEE) and L-glutamic acid dimethylester (GDME) decreased the resting afferent discharge frequency as well as the electrically evoked activities and depressed the responses to application of excitatory amino acids. 3. D-alpha-Aminoadipic acid (AA) and 2-amino-4 phosphonobutyric acid (APB) had practically no effect either on resting afferent discharge or on evoked afferent activity. 4. 2-Amino-5-phosphonovaleric acid (APV) reduced the resting afferent discharge and electrically evoked activity in the afferent fibres. APV blocked N-methyl-D-aspartate (NMDA) induced responses at a lower concentration than those induced by aspartate,. 5. Responses caused by NMDA were Mg 1(2+)-dependent; those to quisqualate (Q) application depended to a lesser degree on the Mg2+ concentration. 6. Cis-2,-3-piperidinedicarboxylic acid (PDA) blocked both the resting afferent discharge and the electrically evoked activity; it also reversibly blocked the postsynaptic, amino acid-induced responses. The L-glutamate (L-GLU) response was more resistant to the blockade than the L-aspartate (L-ASP) response. 7. Both kynurenic acid (KEN) and gamma-D-glutamylglycine (DGG) reduced the resting and evoked activities in the afferent fibres. L-ASP was more resistant to blockade by KEN than L-GLU. 8. These observations suggest a prominent physiological role of quisqualate-, kainate- and NMDA-preferring receptors in the ampullae of Lorenzini of Raja clavata.

2-Amino-5-phosphonovalerate↗
PubMed1991

[The effect of L-serine-O-phosphate on synaptic transmission in the afferent synapses of the ampullae of Lorenzini in skates].

Effect of bath-application of L-serine-O-phosphate (SOP) on the resting and evoked activity as well as on responses elicited by L-glutamate (L-GLU), quisqualate (Q), kainate (KA) and N-methyl-D-aspartate (NMDA) were studied at the level of afferent synapses of the ampullae of Lorenzini. SOP blocked the synaptic transmission (threshold concentration 10(-7) mol/l) and inhibited responses elicited by application of L-GLU and NMDA, while Q- and KA-induced responses remained unchanged. The data obtained permit supposing that inhibitory effects of SOP in the afferent synapses of the ampullae of Lorenzini are associated with its action on membrane receptors of the NMDA type.

Afferent Pathways↗
PubMed1991

[A comparative analysis of the biological activity of an acid-extractable brain protein and fibroblast growth factors].

An acid-soluble protein was isolated from bovine brain tissue using a combination of 5% HClO4 acidic extraction, cation-exchange chromatography and heparin-Sepharose affinity chromatography. This preparation had a biological activity similar to that of the fibroblast growth factor (FGF). It has stimulated neurite outgrowth in organotypic culture of chicken embryo dorsal root ganglia and also has stimulated a proliferation of human embryonic fibroblasts in the culture. The biological activity of isolated preparation was totally inhibited by anti-bFGF antibodies, while anti-aFGF antibodies had no effect. The bFGF showed a neurite stimulating activity in the organotypic culture that was completely abolished by the anti-bFGF, IgG, while the aFGF was inactive. This data, as well as cationic properties of isolated protein and its heparin-binding ability, enable us to postulate a high degree of homology of the brain acid-soluble protein and the bFGF. At the same time the relations of the isolated growth factor and other brain-derived heparin-binding growth factors are yet to be established.

Animals↗
PubMed1991

[Structural-functional changes in the peripheral nerves after administration of several drugs].

Structural and functional changes in the sciatic nerve induced by some drugs were studied using morphological and electrophysiological methods. It was stated that the application of this drug on the nerve causes different degenerating changes. Electrophysiological data, using the regeneration of action potential, proved the presence of structural changes in the nerve after application of mentioned drugs and showed partly preserved conduction of the nerve trunks.

Action Potentials↗