Stimulus-evoked slow potential shifts and changes in [K+]0 of the frog optic tectum.

In 17 frogs (Rana esculenta var ridibunda) immobilised with succinyl choline the optic tectal surface was stimulated by trains of electrical pulses or by a flash to the contralateral eye. Sustained potential shifts (SPSs) and changes in extracellular potassium concentration (delta[K+]0) were simultaneously recorded. In response to electrical stimulation SPSs of maximal amplitudes (1.

Relationships between electrically induced slow negative potentials and changes in extracellular potassium concentrations in cerebral cortex of the cat.

Experiments were carried out on cats under deep nembutal anaesthesia. Local cortical stimulation evoked both a slow negative potential (SNP) and an increase in extracellular potassium ([K+]o) which were maximal in the upper cortical layers. The decline in the K(+)-potential in deeper layers was slower than in the upper ones so that with time [K+]o became equal in upper and deeper layers.

[I. S. Beritashvili and his school in the critical period of 1948-1953].

Cynically violating the principles of science, the organizers of the scientific session of the USSR Acad. Sci. and Acad.

Contribution of glia and neurons to the surface-negative potentials of the cerebral cortex during its electrical stimulation.

In 20 cats anaesthetized with pentobarbital the suprasylvian gyrus was stimulated by single stimuli or by trains of 50 s stimuli and the potentials from the cortical surface and the intracellular potentials from glial and nerve cells were recorded. Glial cells were identified according to conventional electrophysiological criteria: the absence of action potentials and postsynaptic potentials; slow depolarization in response to electrical stimulation. The slow negativity of direct response to a single stimulus is similar in shape and time course to the depolarization of the cortical glial cells and is unlike the hyperpolarization of the cortical neurons.

[Changes in the concentration of extracellular potassium in the cerebral cortex with different parameters of electrical stimulation].

In anesthetized cats, a recording macroelectrode, a K+-sensitive microelectrode and a stimulating electrode were placed on the surface of the suprasylvian gyrus. As the duration or intensity of stimulus increased, the amplitude of K+-potential reflecting the changes in the extracellular concentration of K+ ions (delta [K+]o) was augmented, while the half time of decay decreased. delta [K+]o also increased when the number of stimuli increased.

[Non-synaptic inhibition in the cortex of the cat].

Experiments were carried out on cats under pentobarbital anaesthesia. Two stimulating electrodes (S1 and S2), a recording macroelectrode and K+-selective microelectrode were placed on g. suprasylvius.

On the process of inhibition in the superficial neuropil of the cerebral cortex.

Experiments were carried out on cats under Nembutal anaesthesia. The electrodes were placed on the gyrus suprasylvius. The recording macroelectrode and the K+--sensitive microelectrode were placed between two stimulating electrodes (S1 and S2).

[Post-tetanic potentiation of the dendritic potentials of the cerebral cortex].

In acute experiments on anesthetized cats, the post-tetanic potentiation (PTP) of cortical dendritic potentials lasted for over 30 min. The PTP did not occur after cooling of the cortex below 31 degrees C or after ouabain application to the cortex. In presentation of paired stimuli during the PTP, mathematical analysis revealed an enhancement of relative depression of the dendritic potential at the second stimulus.

On the possible nature of the processes induced by unconditioned stimulation in the cerebral cortex.

Tetanic stimulation of the cortex elicits in some cortical neurons a hyperpolarizing change of the membrane potential and inhibition of impulse activity; after cessation of stimulation often an enhanced discharge occurs. Other neurons respond to stimulation with high-frequency discharges. At the site of stimulation [K+]o is increased more than by 2 mM.

[Changes in the concentration of intracellular potassium and the phenomenon of dendritic potential depression against a slow negative potential background in the cat cerebral cortex].

Two stimulating electrodes (S1 and S2), a recording macroelectrode and a K+-selective microelectrode were placed on g. suprasylvius of cat. A stimulus applied through S1 elicited slow negativity and an increase in [K+]0.

[Changes in the concentration of extracellular potassium and the slow negative potential in the somatosensory area of the cortex in response to stimulation of the ventroposterolateral nucleus of the thalamus in the cat].

A single electrical stimulus applied to the VPL nucleus with intensity, strong enough to elicit in gyrus sigmoideus posterior slow negativity following the primary response, caused a local increase in [K+]0 reaching 0.2 mM. On the basis of this finding it is supposed that the slow negativity reflects mainly depolarization.

[Glial origin of negative shifts in the surface potential of the brain upon tetanic stimulation: microelectrode study and mathematical analysis].

It is shown in experiments on anesthetized cats that negative shift of the cortical surface potential evoked by its tetanic stimulation is similar in form and time course to the depolarization of glial cells. On the contrary, hyperpolarizing shifts of neuronal membrane potential are dissimilar in form and time course to the negative shift of the cortical surface potential. A conclusion is made that the contribution of neuronal hyperpolarization to the surface-negative shift of the potential can distinctly be seen only at the beginning of tetanization--in the first 200-300 ms; negative shift of the cortical surface potential is mainly produced by depolarization of glial cells.

[Glial origin of the slow negative potential of the direct cortical response: microelectrode study and mathematical analysis].

Slow negative potential of a direct cortical response is similar in configuration, time-course and reaction to repeated stimuli to depolarization of the cortical glial cells and differs from IPSP of the cortical neurons. According to data of digital spectral (frequency) analysis, slow negative potential is based on the glial component formed by summing up the constituents, which coincide with glial depolarization within a constant factor. The neuronal component, whose contribution is comparatively much smaller, is an indirect result of IPSP.

[Changes in the extracellular potassium concentration and the slow negative potential in the cerebral cortex].

Changes of potassium concentration in the extracellular space ([K+]0) of the g. suprasylvius of cat cerebral cortex were recorded by means of K+ selective microelectrodes; the electrical field potential was recorded simultaneously. Under deep anesthesia a single electrical stimulus, applied to the cortical surface, at intensity enough to elicit the slow negativity, caused a local increase of [K+]0 reaching 0.

The importance of I. M. Sechenov's electrophysiological research.

In his electrophysiological studies I. M. Sechenov described for the first time the spontaneous electrical activity of the isolated brain, the physical electrotonus in the CNS, the amplifying action of anodic polarization on spontaneous and induced electrical activity, phenomena of inhibition of spontaneous and induced electrical oscillations of the brain upon tetanization of sensory nerves and negative shifts in the potential of the brain.

[Synapses with myelinated and unmyelinated preterminal portions of axons in cat cerebral cortex].

The electron microscopic study of the cat cerebral cortex revealed two kinds of preterminal axonal regions with synaptic boutons at the end: nonmyelinated and myelinated. In the first case their diameter was about 90 nm; in the second case it was considerably greater; the myelin could reach the bouton. The possible physiological meaning of these structural features is discussed.