Biomedical subjects

M G Belekhova

Publications and source records attributed to M G Belekhova.

At least 37 records · Page 2Linked to original sources

PubMed1980

[Tegmento-thalamic interrelationships in turtles].

In immobilized, weakly anesthetized with chloralose turtles Emys orbicularis the focus of evoked potentials and the largest number of single unit responses to the stimulation of the mesencephalic tegmentum were revealed in the ventral thalamic region (a heterosensory zone with dominating somatic modality). An incomplete separation of latero- and mediotegmental projections was observed in dorsal and ventral subdivisions of the ventral thalamic region, respectively. The tegmental stimulation coinciding or preceding the electrical stimulation of the limb skin or light flash produced mainly a suppressing effect on somatic reactions of single units, the influence on visual reactions being much less significant. A possibility to compare tegmento-thalamic systems in reptiles and mammals is discussed.

Afferent Pathways↗

PubMed1980

[Tegmento-telencephalic interactions in turtles].

Electrophysiological characteristics of tegmental projections in the forebrain were studied in immobilized slightly chloralose anesthetized turtles Emys orbicularis. The main zone of tegmental representation was found in the striatum where the most short-latent evoked potentials were recorded and the largest number of single units responding to tegmental stimulation was concentrated in comparison both with the dorsal ventricular ridge and general cortex. It is shown that laterotegmental projections have main target zone in the lateral part of the striatum, while mediotegmental projections--in the medial striatum part. Coinciding or preceding tegmental stimulation produced a suppressing effect on both somatic evoked responses and single unit reactions. An attempt to compare tegmento-thalamo-telencephalic systems in reptiles and mammals.

Animals↗

PubMed1977

[Transthalamic conduction of visual impulses into the cortex and subcortical portions of the turtle forebrain].

Thalamic structures relaying impulses originating from optic stimulation of the retina and electric stimulation of the tectum on the way to the general cortex, hyperstriatum dorsal ventricular ridge and striatum were studied in turtles Emys orbicularis. Anodal polarization of the n. rotundus temporarily, and the lesion of this nucleus irreversibly, suppressed the main negative component of responses evoked by tectal stimulation and light flashes in the dorsal ventricular ridge without affecting them in the general cortex. Polarization and lesions of the lateral thalamic region, including nucleus geniculatum lateralis produced an opposite effect. A conditioning single stimulation of the tectum or n. rotundus suppressed flash-evoked potentials in the hyperstriatum. However evoked potentials and single unit responses appeared following stimulation of the lateral thalamic region. They exhibited blocking interactions with the tectum-evoked responses. A conclusion is made that in the turtle the main pathways conducting visual information to the cortex and hyperstriatum are different: in the former case it is relayed in the lateral geniculatum region in the latter--in n. rotundus, although an overlap of the projections in dorsal ventricular ridge and striatum can be suggested.

Animals↗

PubMed1975

[Corticalization of 2 regions of the visual system in the evolution of vertebrates].

Data on the evolution of the visual system in the phylogenetic scale of vertebrates are reported. Visual projections in the telencephalon of cyclostomes (lampreys) and retinothalamo-telencephalic channel in elasmobranches (skates) are shown. In amphibians (frogs) and reptiles (turtles) the existence of two visual subsystems (retino-thalamo-telencephalic and retino-tecto-thalamo-telencephalic) is determined, both being overlapped partially at the level of n. geniculatus lateralis and totally in the telencephalon. In turtles earlier visual and tectal impulses towards the telencephalon proved to be relayed in n. geniculatus lateralis and later ones--in n. rotundus. In mammals (rats) visual tecto-cortical connections are shown to have one synaptic relay in thalamic structures since cortical potentials evoked by stimulation of the colliculus superior in rats posses a rather short latency. Significant latency shortening of tectal visual responses in monkeys, as compared with the latency of the respective potentials in turtles (chronic identical experiments), supports the idea of the progressive development of the tectal division of the visual system in the vertebrate phylogony. It is concluded that both divisions of the visual system--retino-thalamic and retino-tectal underwent corticalization at earlier evolutionary stages.

Animals↗

PubMed1975

[Comparative electrophysiologic characteristics of afferent representation in the cortical and striatal portions of the turtle forebrain].

Visual and somatic representations are established in the subcortical striatal sections of the forebrain (pallial thickening, dorsal ventricular ridge and putamen) of immobilized weakly anaesthetized turtles. According to electrophysiological characteristics they are similar to the corresponding sensory representations in the general cortex. The absence of reliable discrepancy between the latencies of potentials in the cortex and striatum evoked by light flash or by the electric stimulation of the dorsal thalamus indicates that visual projectional fibres ascending from the lateral geniculate nucleus terminate both in cortical and striatal structures. Differences in the latency distribution of single unit responses in the cortex and striatum to visual and thalamic stimulations can be due to the existence, besides the geniculo-telencephalic pathway, of a rotundo-telencephalic visual channel having direct connections with the striatum and polysynaptic ones with the general cortex. Significant differences in latency between the evoked potentials and neuronal responses in cortical and subcortical structures to electric stimulation of the skin shows that somatic projectional fibres on their way to the cortex are relayed in the striatum, thus indicating a lower corticolization degree of the somatosensory system as compared with that of the visual one.

Animals↗

PubMed1972