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 (1.19 +/- 0.1 mV) were recorded between 50 and 200 microns in depth and maximal delta[K+]0 (0.69 +/- 0.08 mM) between 100 and 350 microns. The changes of SPS and delta[K+]0 showed a close similarity in experiments with changes in voltage, pulse duration and frequency of stimuli within a train. The induced SPS had a duration of 28 +/- 1.54 s, the delta[K+]0 of 32 +/- 1.23 s. The flash stimulus induced an SPS and delta[K+]0 of maximal amplitudes between 50 and 200 microns in depth with values of 0.57 +/- 0.1 mV and 0.29 +/- 0.03 mM respectively. An additional wave with a latency of ca 1 s and a duration of ca 3 s arose on the background of the SPS to a flash stimulus, associated with an additional increase in [K+]0. It is considered that the accumulation of K+ in extracellular space, with neuronal activity, results in depolarization of radial processes of ependymal glia. This is reflected in the neuropil of the upper layers of the optic tectum as an SPS.

[I. S. Beritashvili and his school in the critical period of 1948-1953]. / I. S. Beritashvili i ego shkola v kriticheskii period 1948--1953 gg.

Cynically violating the principles of science, the organizers of the scientific session of the USSR Acad. Sci. and Acad. Med. Sci. in 1950 made an attempt to make null and void of the contributions of Academician I. S. Beritashvili and his associates to the physiological science. At the special sessions of the "Pavlovian Council" in April 1951, Beritashvili's concept on the psychonervous activity was qualified as anti-Pavlovian, idealistic. The hypothesis developed by him and his associated on the process of inhibition was rejected as dualistic; the use of the notion "spontaneous electrical activity" was qualified as the deviation from the principles of determinism. In the resolution adopted, "vicious aims" of I. S. Beritashvili were censured, and soon he was exempted from the post of Director of the Institute of Physiology. The campaign against I. S. Beritashvili and his School ceased in 1953; it proved to be a vivid example of the form of leadership pernicious for science.

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. Quantitative analysis showed that the basic part of the slow negativity is the glial component, whereas the neuronal component--inhibitory postsynaptic potential--plays a much lesser role. The negative shift of the potential on the cortical surface evoked by its high-frequency stimulation is similar in shape and time course to the depolarization shift of the membrane potential of the cortical glial cells (the mean value and standard error of time to peak for glial depolarization were 567.6 +/- 26.8 ms and 427 +/- 24 ms for negative shift of potential). (The results are based on recordings from 37 cells.) The negative shift decays much quicker; it is not similar in shape and time course to the hyperpolarization shift of the neuronal membrane potentials (the mean value and standard error of time to peak for inhibitory postsynaptic potential was 44.9 +/- 4.5 ms). According to the quantitative analysis, the negative shift of the potential reflects mainly the depolarization of the cortical glial cells. The contribution of the hyperpolarization of neurons to the surface-negative shift can be distinctly observed during the first 0.2-0.3 s of stimulation. It is supposed that accumulation of K+ ions in intercellular clefts results in depolarization of glial syncytium, which is reflected on the cortical surface as a slow negativity and a negative shift of the potential.

[Changes in the concentration of extracellular potassium in the cerebral cortex with different parameters of electrical stimulation]. / Izmeneniia kontsentratsii vnekletochnogo kaliia v kore mozga pri raznykh parametrakh ee élektricheskogo razdrazheniia.

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. Repetitive tetanic stimulation resulted in impairment of the effect also in the case when [K+]o following the preceding stimulus, reached the initial level. K-potential started to decay in the course of prolonged tetanic stimulation; impairment of the neuronal activity is supposed to underlie this event.

[Non-synaptic inhibition in the cortex of the cat]. / O nesinapticheskom tormozhenii v kore mozga koshki.

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. A strong stimulus applied through S1 elicited slow negativity (SN) and increase in [K+]o. At that time the dendritic potential (DP) evoked by stimulation through S2 was depressed. The depression of DP correlated with the voltage of SN and with the level of [K+]o. It is suggested that DP depression is caused by presynaptic action of K+ ions.

[Post-tetanic potentiation of the dendritic potentials of the cerebral cortex]. / O posttetanicheskoi potentsiatsii dendritnykh potentsialov kory mozga.

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. The PTP of dendritic potentials seems to be associated with metabolic processes in presynaptic fibers of the 1 layer which have synaptic contacts with apical dendrites.

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. If tetanic stimulations are applied at less than 2 min intervals they result in an attenuated K+ release. During tetanic stimulation of the cortex a depolarizing shift of the glial cell membrane potential develops at all strata of the cortex. It is known that conditioned reflex may be elaborated when the electrical stimulation of the motor cortex is used as unconditioned stimulus if the intertrial intervals are not too short. It is hypothesized that the effectiveness of the stimulation of the cortex in eliciting the K+ release and in promoting a conditioned reflex acquisition are interrelated. According to this hypothesis an increase in [K+]o is a signal for myelin formation, and myelination of the naked axonic terminals which convey conditioned signal is the basis for the conversion of the potential connections into the actual ones.

[Glial origin of negative shifts in the surface potential of the brain upon tetanic stimulation: microelectrode study and mathematical analysis]. / Glial'noe proiskhozhdenie otritsatel'nykh sdvigov potentsiala poverkhnosti kory mozga pri ee tatanicheskom razdrazhenii: mikroélektrodnoe issledovanie i matematicheskii analiz.

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.

[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]. / Izmeneniia kontsentratsii vnekletochnogo kaliia i medlennyi otritsatel'nyi potentsial v somatosensornoi oblasti kory pri razdrazhenii ventroposterolateral'nogo iadra talamusa koshki.

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.

[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]. / Izmeneniia kontsentratsii vnekletochnogo kaliia i fenomen ugneteniia dendritnogo potentsialav na fone medlennogo otritsatel'nogo potentsiala kore mozga koshki.

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. At this time the dendritic potential evoked by stimulation through S was depressed. The depression of the dendritic potential was found to correlate with [K+]0.

[Glial origin of the slow negative potential of the direct cortical response: microelectrode study and mathematical analysis]. / Glial'noe proiskhozhdenie medlennogo otritsatel'nogo potentsiala priamogo otveta kory: mikroélektrodnoe issledovanie i matematicheskii analiz.

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.

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. Thus Sechenov discovered some basic electrical manifestations of the activity of the CNS and initiated fundamental electrophysiological studies of the brain.

[Changes in the extracellular potassium concentration and the slow negative potential in the cerebral cortex]. / Izmeneniia kontsentratsii vnekletochnogo kaliia i medlennyi otritsatel'nyi potentsial v kore mozga.

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 0.1-1.5 mM. The time course of the K+ signal coincide with the course of the slow negativity. It is supposed that the slow negativity reflects glial depolarizaion arising under the action of K+ ions.