Biomedical subjects
Publications and source records attributed to M N Zhadin.
The possible mechanism of action of weak electric and magnetic fields of extremely low frequency on biomolecules is discussed in terms of the resonance effects on the precession of the ion orbits in a static magnetic field. The proposed model retains the principal merits of the familiar model of Liboff, but is free from the basic shortcomings of the latter.
Various forms of electropgraphic display of monoaminergic neurotransmitter system effect upon the cerebral cortex are discussed. Comparison of theoretical and experimental results suggests a modulating role of serotoninergic and noradrenergic systems.
Background neuronal discharges were recorded extracellularly in guinea-pig cerebral cortex slices maintained in vitro. Six types of activity were classified: 1--regular single discharges (38.5%), 2--irregular spikes (6.5%), 3--bursts (6.5%), 4--burst-single discharge (mixed) activity (26.5%), 5--group discharges (2.5%), 6--multineuronal volleys (18.5%). Characteristic distributions of interspike intervals and autocorrelograms corresponded to each of these types of activity. Regular pacemaker-type discharges were most peculiar under conditions of small volumes of the grey matter and lack of afferentation. Such regular activity was never observed in normal or isolated neocortex.
A differential equation describing the electroencephalogram (EEG) is deduced based on the data on the structure of the brain cortex and the conceptions about a recurrent inhibition. This equation allows the study of a number of essential electrophysiological phenomena: the philogenetic differences in the frequency composition of the EEG, the shift of the EEG spectrum to higher frequencies upon excitation of the cortex, the lowering of the EEG rhythms and changes in cell reaction on deafferentation of the cortex, the identity in the spectra of a spontaneous EEG and evoked responses. A possible mechanism for the onset of epileptic activity is proposed.
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Spontaneous unit activity in alert unrestrained rabbits was recorded simultaneously with two microelectrodes from the visual and sensorimotor cortex. The correlation analysis revealed that activity of majority of the neurons had no regular rhythm. But spectral analysis of the average correlograms showed existence of oscillations in the delta- and theta-ranges. The synergic type of interaction between cortical neurons was prevalent. Analysis of structure of the distant interaction showed the reduced probability of synergic spikes with periods 150-200 msec and less and the increased one with periods within 200-500 msec.
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Activity of single units in the visual and sensomotor cortex of an uncurarized, unanesthetized rabbit was recorded by means of two independent microelectrodes during photic stimulation at different frequencies. Trace effects characterized by repetition of the temporal structure of afferent stimulation and by an increase in the level of intercellular correlation were discovered mainly on analysis of distant interneuronal relations after stimulation with frequencies of 2 and Hz. Stimulation at a frequency of 8 Hz did not evoke trace effects.
Consideration is given to a possible mechanism of reinforcement during training mediated through the monoaminergic systems in the brain that modulate the effectiveness of intracortical synapses. Various forms of electroencephalographic manifestations of the effect of these systems on the cerebral cortex are discussed. A comparison of the theoretical and experimental results favors the modulating role of the serotoninergic and noradrenergic systems.
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Neuronal isolation of the rabbit cerebral hemisphere shifts the EEG spectrum in the direction of slower processes. Application of acetylcholine to the cortex brings about EEG activation and appearance of the theta rhythm. Initially serotonin application is accompanied by the appearance of theta rhythm periods; during subsequent administration of the drug these periods are gradually substituted by slow delta waves. Combined application of serotonin and acetylcholine to the isolated cortex brings about bursts of high amplitude activity, abruptly substituted by "silent" phases. In contrast to the intact cortex, where serotonin brought about prolonged and rhythmic alternation on the EEG of phases of high amplitude activity and of silent periods, in the isolated cortex the bursts of activity of about 1 min duration appeared only after application of acetylcholine to the serotonin-saturated cortex. Repeated phases of activation were either absent or of short duration and were rapidly extinguished.
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