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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

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

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

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

[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

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

[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

[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

[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

[Skin mechanoreceptor functioning in the white rat during transcranial electrostimulation].

Functional properties of skin afferents were studied by the method of registration of spike activity from single nerve fibres, innervated non-hairy skin in white rats. It was found that mechanoreceptor units varied by the threshold intensity of applied stimulus. These units were divided to three functional groups: low-, medium- and high-threshold units. Transcranial electrical stimulation (TES) strongly affected on the functional characteristics of skin afferents. Full suppression of responses was observed in 18-20 min. irrespective of the category of units. A local intracutaneous injection of naloxon eliminated the effect of TES. It is supposed that endogenous opioid peptides regulate an afferent discharge on the level of sensory endings during TES.

Animals

[The effect of transcranial electrostimulation of the opioid structures of the brain on peripheral nerve regeneration in the rat].

Transcranial electrical stimulation of opioid brain structures was studied for its effect on the sciatic nerve of rat after transection and microsurgical restoration of the nerve. It was shown that electrical stimulation accelerated regeneration of sensory and motor fibres of the sciatic nerve. Participation of endogenous opioid peptides in the regeneration of peripheral nerves is discussed.

Animals

[Changes in the excitability of the skin mechanoreceptors in the rat against a background of transcranial electrostimulation].

Alterations in excitability of low-, medium- and high-threshold single mechanoreceptors (SMRs) of hairless hind paw skin elicited by transcranial electrical stimulation (TES) in analgesic regime were studied in anesthetized rats. Evoked impulsations of low- and medium-threshold SMRs were blocked by TES that lasted for about 1 and 5 min, respectively. TES for 18-20 min in duration abolished the reactions of high threshold SMRs activated only by nociceptive stimuli. Inhibitory effects of TES on all SMR types under study were eliminated by preliminary intraperitoneal or local intracutaneous (near SMRs location) injection of naloxone. Possible mechanisms of analgesic TES effects are discussed. An assumption is made that alterations of the SMR function are connected with an increase of the output of endogenous opioid peptides from the brain during TES.

Animals

[Substantiation of the use of terrilytin in the treatment of spinal cord disorders in tuberculous spondylitis].

Experiments on mice and studies with organotype cultures of the spinal ganglion showed that terrilytin, a proteolytic enzyme had neurite stimulating activity and promoted regeneration of the spinal marrow tissue after affection (squeeze). On the basis of this property and a previously observed favourable effect of the enzyme on microcirculation, the capacity for more rapid rarefaction and elimination of caseous masses and prevention of excessive fibrosis, it was recommended for use in treatment of cerebrospinal disorders in tuberculous spondylitis. A procedure for the treatment was developed. The clinical trials with 46 patients (22 in the main group and 24 in the control group) showed high efficiency of the procedure.

Amylases

[Analysis of the effect of quisqualate, N-methyl-D- aspartate and several blockers of amino acid receptors on synaptic transmission in the ampullae of Lorenzini].

Effects of bath-application of quisqualate (Q), N-methyl-D-aspartate (NMDA) and antagonists of NMDA-receptors: D-amino-adipate (AA), 2-amino-4-phosphonobutyrate (APB), 2-amino-5-phosphonovalerate (APV) and Mg2+ as well as acidic amino acid antagonist: D-glutamylglycine (DGG) on the synapse between the electroreceptor cells and afferent fibres were studied in the ampullae of Lorenzini. Q (threshold concentration 10(-8) M) and NMDA (threshold concentration 10(-5) M) strongly excited afferent fibres. Neither AA nor APB influenced the resting and evoked activities. APV blocked the synaptic transmission. Mg2+ (30-50 mM) blocked the responses to NMDA, while Q-induced responses were not affected, APV preferentially blocked NMDA-induced responses and in lesser degree--L-aspartate (L-ASP)-induced responses. DGG blocked the synaptic transmission. It is supposed that the synaptic receptor could represent a homogeneous receptor with different binding sites to the known agonists.

2-Amino-5-phosphonovalerate