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Biomedical subjects

Iu G Kratin

Publications and source records attributed to Iu G Kratin.

At least 19 recordsLinked to original sources
PubMed1987

[Mosaicism of excitatory and inhibitory processes in populations of cortical neurons during the brain activation response].

Comparative analysis of multiunit arousal response in the somatosensory I and the parietal associative brain areas of unanesthetized cats revealed the initial excitation of neuronal populations in both cortical areas to be independent of stimulus modality. The greatest firing rate was observed in the 1st period of the arousal response when the brain activation was maximal. Subsequent development of the multiunit response may be either tonic or phasic. The phasic responses are predominant in the somato-sensory neuronal populations (56-87%). The multiunit tonic responses (55-85%) occur mostly in the parietal associative area. The end of the inhibition phase coincided with the end of the arousal response. The relation of the response types to unspecific brain activation, is discussed.

Animals↗
PubMed1982

[Participation of the lateral geniculate body in the mechanisms of brain activation].

In chronic experiments on cats with intact LGB, electrical stimulation of the latter (120-190 microA) caused brain activation with the same threshold as the stimulation of the mesencephalic RF or of the thalamic CM with 50-80 microA. With all but the geniculo-cortical connections of the LGB disrupted, the threshold for brain activation increased to 220-400 microA. After LGB coagulation leaving intact all optical tract connections to the superior colliculi and to the brain stem, the adequate cortical activation was only possible with very strong light flashes (250-1000 l). This suggests that the LGB participates in unspecific brain mechanisms and can induce cortical activation regulated afterwards by the cortex itself.

Animals↗
PubMed1981

[Activation response to photic stimulation in normal cats and after transection of the afferent pathways of the mesencephalic reticular formation].

In chronic experiments on waking unrestrained cats with implanted electrodes the reaction of EEG activation to light stimulation was recorded in two sets of experiments in normal cats and in animals with transsection of brachia colliculi superioris that separated mesencephalic reticular system. The intensity of the activating reaction in the intact cats increased ith a rise in the light stimulus intensity. In the cats with brachia-colliculi superioris transsected there was no definite dependence on the stimuli intensity and the intensity of the activating reaction changed randomly. It is suggested that this irregularity is accounted for by blocking of the excitating afferent flow usually coming to the mesencephalic reticular formation through brachia and colliculi both from the visual pathways (ascending flow) and from the cortex (descending activation regulating flow).

Animals↗
PubMed1980

[Multicellular spiking of the cat somatosensory cortex at rest and during spontaneous EEG activation].

In chronical experiments on unanesthetized unrestrained cat multineuronal discharges and EEG were simultaneously recorded from the somatosensory cortex by the same semimi-croelectrode. The discharges were automaticaly separated into three amplitude levels. Three types of basic multineuronal discharge patterns were classified: continuous, bursting and grouped ones. During visually similar periods of spontaneous EEG activation the multineuronal discharges exhibited different and variable changes. The amplitude discrimination method revealed at different discharge levels parallel discharge frequency rise or fall or absence of changes in the average frequency. The kind of multineuronal discharge reorganization depended on the intensity of the EEG activation. The computer analysis showed the prevalence of the excitatory effects (55%), but inhibitory changes were also rather significant (21%). The experimental data suggest a complicated and highly dynamic functional structure of the spontaneous brain activation process at the level of neuronal populations.

Animals↗
PubMed1979

[Correlation between nonspecific and specific excitation in the cat somatosensory cortex during different modalities of stimulation].

Multiunit activity and EEG recorded with the same electrode from the somatosensory cortex in unrestrained cats, were compared. The obviously identical patterns of the EEG activation coincided with different multiunit patterns (acceleration or deceleration of frequency, modification of discharge order) depending on the stimulus modality (somatic, acoustic, direct RF stimulation) and on the foregoing background impulsation. This suggests that the EEG activation, although being basically unspecific, has specific features. The sensory information, apart from the known forms, seems to be coded in the form of diverse modes of functional activity of a neuronal population localized in a brain structure.

Acoustic Stimulation↗
PubMed1979

[Horseradish peroxidase labelled neurons of nonspecific thalamic nuclei projecting to the cat brain somatosensory zone I].

The morphology and topography of neurons whose axons form the thalamic nonspecific input to the primary somatosensory cortex were studied in the cat thalamus by the method of the retrograde transport of the horseradish peroxidase. The labelled cells were found in the dorsolateral part of the nucleus ventralis anterior, in the nucleus centralis lateralis, in the lateral part of the nucleus dorsalis medialis, in the dorsal part of the nucleus centrum medianum. A very small number of slightly stained cells were found in the nucleus paracentralis. The variety of the shape, size and intensity of labelling of the HRP-positive cells was observed in each thalamic structure. The results of the experiments indicate that not only the ventrobasal complex but also the nonspecific thalamic nuclei are projected to the primary somatosensory cortex. These data demonstrate the existence of multiple afferent thalamic inputs to the primary somatosensory cortex.

Afferent Pathways↗
PubMed1977

[Low-threshold mechanisms and pathways of corticofugal activation].

In chronic experiments of alert cats, moderate electrical stimulation of different points on the lateral cortical surface led to activation of different cerebral areas. Both the high-threshold and the low-threshold points were revealed in the sensorimotor cortex and in the Ep field of auditory area. The latter had as low a threshold of the activation response as the points within the mesencephalic RF and the thalamic CM, VPL and GM. In the morphological aspect, projections from the auditory Ep field to the thalamic intralaminar nuclei and to the brain stem RF, were revealed. Major projections spread from the dorsal part of the Ep field to the lateral tegmentum. The data obtained seem to provide better comprehending of the mechanisms for corticofugal activation. The functional role of the low-threshold loci in the cortex can involve triggering of unspecific apparatus of activation with a graduated volley which controls its excitation in accordance with biological significance of analysed signals.

Animals↗
PubMed1975

[Extinction of brain activation responses to direct electrical stimulation of its structures in normal awake cats].

In unrestrained cats, repeated electric stimulation of the mesencephalic reticular formation (MRF), center median (CM) of the thalamus, and different cortical areas: both the low--and the high--threshold points (in regard to the brain activation), with the threshold strength current evoked similar EEG reactions of activation which diminished and disappeared after 3--5 repetitions of the stimuli. The moderate strength current evoked, apart from the EEG activation, pseudoviolent movements (turning of the head, etc.) and changes in the breathing rate. All these reactions could be extinguidhed by sufficient number of repetitions of stimuli, the effector reactions disappearing first, the EEG changes--last. The essential difference of the stimulation effects emerged when the strong current stimulation was used. In this case, when stimulating the high-threshold cortical points, the EEG and effector reactions could be abolished during long enough repetition of the stimuli, but it was impossible when stimulating the low-threshold cortical points, the MRF or CM: all the reactions stayed intense and stable, the animals became highly irritated. The data obtained are discussed from the point of view of the authors' concept of the interaction between the activating and integrative analysing mechanisms of the brain.

Animals↗