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V E Lopantsev

Publications and source records attributed to V E Lopantsev.

8 recordsLinked to original sources
PubMed1992

[Strychnine-induced changes of the membrane and postsynaptic potentials in neocortical neurons].

Intracellular responses of neurons of the suprasylvian gyrus to the intracortical stimulation (ICS) before and after superficial application of strychnine were investigated in experiments on immobilized and unanaesthetized cats. The normal cortex neurons reacted to ICS by monosynaptic EPSPs followed by IPSPs. Strychnine application triggered the epileptiform activity and appearance in neurons of paroxysmal depolarization shifts of the membrane potential (MP) which were replaced by hyperpolarization potentials. An increase and summation of the latter elicited the MP enlargement and either reduction or suppression of background spike activity. Intracellular injections of EGTA blocking the membrane calcium-dependent potassium conductivity (gK(Ca)) have eliminated the hyperpolarization potentials. Development of epileptiform activity was accompanied by depression of IPSPs and increase of the monosynaptic EPSPs. The contribution of gK(Ca) and of postsynaptic inhibition to the epileptogenesis is discussed.

Animals↗
PubMed1990

Paroxysmal afterpotentials and role of calcium-dependent potassium conductivity in neuronal activity of strychninized neocortex.

Reactions of cortical suprasylvian gyrus neurons were investigated intracellularly after supracortical strychnine application in immobilized and anaesthetized cats. It was shown that paroxysmal depolarizing shifts of membrane potential could be accompanied by de- and hyperpolarizing afterpotentials. When passing from epileptiform to normal physiological activity, short afterhyperpolarizations, 300-500 ms in duration, were converted into inhibitory postsynaptic potentials which were also accompanied by a decrease in membrane potential. When the frequency of paroxysmal discharge was less than 1 s, prolonged (1-2 s) afterhyperpolarizations were observed; at a higher frequency their summation led to tonic hyperpolarization of the membrane. The ictal discharges were accompanied by postictal hyperpolarizations of up to 30 s duration. The intracellular injection of EGTA blocking Ca2(+)-dependent potassium conductivity eliminated prolonged after- and postictal hyperpolarizations and produced depolarizing afterpotentials and a gradual depolarization of cell membranes. Our results indicate that the development of short hyperpolarizing afterpotentials could be determined by the inhibitory synaptic effects. The activation of Ca2(+)-dependent potassium conductivity caused by the development of prolonged afterhyperpolarizations and postictal polarizations, as well as maintained tonic hyperpolarization of cell membranes. Obviously, the depolarizing afterpotentials are of a non-synaptic origin and can be induced by inward calcium current.

Animals↗
PubMed1990

[The postsynaptic components of the paroxysmal reactions of the neurons in the strychninized neocortex].

Intracellular responses of neurons of cortical strychninized suprasylvian gyrus were investigated in experiments on immobilized and unanaesthetized cats. Paroxysmal depolarizing shifts (PDS) of the neuronal membrane potential were registered. They consisted of the burst discharge (BD) and slow depolarization wave. By means of intracellular stimulation it was shown that PDS could be summarized and were able to change their form and size. BD in PDS were triggered by large EPSPs which could be elicited from paroxysmal responses. Presumably, the intradendritic recordings have shown the presence of large EPSPs during generation of epileptiform discharges in the neocortex. In some neurons PDSs were accompanied by hyperpolarizing potentials which were apparently IPSPs because they were reversed at the intracellular Cl- injections. The contribution of excitatory and inhibitory synaptic influences to the neuronal paroxysmal responses is discussed.

Animals↗
PubMed1990

[Prolonged depolarizing potentials of the neurons in a strychninized isolated strip of the cat cerebral cortex].

Reactions of isolated cortical slab neurons to the supracortical application of strychnine were investigated with intracellular registration in experiments on unanaesthetized and immobilized cats. It was shown that some neurons demonstrated prolonged depolarizing potentials (PDP) spontaneously and as reactions to single intracortical electrical stimuli. The development of these potentials could be a result of transformation of the reaction of the "paroxysmal depolarizing shift (PDS)--hyperpolarization" type, where hyperpolarizations were replaced by depolarizing potentials. A gradual increase of depolarizing afterpotentials resulted in DDP generation. These transformations, as a rule, were accompanied by amplification of the summary epileptiform activity in an isolated cortical slab. The suggestion was made that the DDP generation was determined by an increase in the Ca(++)-conductance of the neuronal membrane in an isolated cortical slab with the intensification of paroxysmal reactions.

Animals↗
PubMed1990

[The cellular reactions of a strychninized isolated strip of the cat cerebral cortex].

Reactions of neuronal and glial cells of an isolated cortical slab to direct electrical stimulation after supracortical strychnine application were investigated in experiments on immobilized and unanaesthetized cats. Strychnine evoked single epileptiform discharges and afterdischarges in the isolated cortical slab and large paroxysmal depolarization shifts (PDS) of the membrane potential (MP) in the neurons. It was shown that spontaneous summary epileptiform discharges and cellular activity of neurons investigated were synchronized slightly. Electrical stimuli produced a generalized paroxysmal activity in the isolated slab. Neuronal PDSs were accompanied by refractory periods which development did not depend on the MP level. Strychnine enhanced a number of neurons with the background activity in which PDS were generated by rhythmic depolarizing MP oscillations of the nonsynaptic origin. It was shown also that epileptiform reactions of the strychninized isolated cortical slab to the single stimuli were accompanied by large depolarization shifts of the glial cells' MP. The suggestion is made that the paroxysmal excitation development in the strychninized isolated cortical slab was determined by non-synaptic factors and was strongly related to the changes of the extracellular potassium concentration.

Action Potentials↗
PubMed1989

[Responses of neurons of an isolated cortical strip in a state of convulsive excitation to single electrical stimuli].

Responses of isolated cortical slab neurons to single stimuli before, during and after the development of epileptiform state in a slab were investigated in experiments on immobilized and locally anaesthetized cats. It was shown that during the development of generalized seizure activity in an isolated cortical slab its neurons generate EPSP and paroxysmal depolarizing shifts (PDS) of the membrane potential (MP) accompanied by refractory periods. Refractory periods coincide with PDS plato and MP repolarizing shifts. During these shifts single electrical stimuli produce gradually transforming PDS. After cessation of the ictal activity neurons are still able to generate PDS to single stimuli for some time. It is suggested that the role of postsynaptic responses in genesis of the epileptiform activity is not the most important. Nonsynaptic factors are, probably, involved in its generation.

Animals↗
PubMed1988

[Electrical activity of the neurons in an epileptic focus created in an isolated strip of cerebral cortex by electrical stimulation].

The peculiarities of the activity of cortical isolated slab neurons were investigated in experiments on unanaesthetized and immobilized cats during the development of seizure spikes evoked by repetitive powerful stimulation. It was shown that in the investigated focus of epileptiform discharges the neurons were not differentiated by the degree of pathological alterations, since paroxysmal membrane potential shifts of all neurons were recorded intracellularly. All these neurons were characterized by a lack of the spike activity. At the same time bursting spike discharges of isolated slab neurons were recorded extracellularly and they did not propagate to the soma. Simultaneous extra- and intracellular recordings of the activity from the same neurons have shown that during the epileptiform activity action potentials were generated in some trigger zones without propagating to the cell bodies. Possible mechanisms of the origin of the spike activity in isolated slab neurons during the development of generalized epileptiform state are discussed.

Animals↗