Biomedical subjects

M G Belekhova

Publications and source records attributed to M G Belekhova.

At least 19 recordsLinked to original sources

PubMed1998

Retinal and cortical afferents to the dorsal lateral geniculate nucleus of the turtle, Emys orbicularis: a combined axonal tracing, glutamate, and GABA immunocytochemical electron microscopic study.

The dorsal lateral geniculate nucleus (GLd) of the turtle Emys orbicularis has been analyzed with axonal tracing methods and immunocytochemical techniques for glutamate (GLU) and gamma-aminobutyric acid (GABA), in combination with a quantitative study of the morphologic characteristics, distribution, and synaptology of the retinofugal and corticofugal terminals. Ultrastructural observations show that the vast majority of retinal terminals (Rtr) have clear, rounded synaptic vesicles and account for 16% of all profiles containing synaptic vesicles (PCSV). Their synaptic index (0.5) is low, and they make three times more contacts with the dendrites of projection cells than with those of interneurons. A low proportion of retinal terminals of a second category contain pleomorphic synaptic vesicles and are highly GABA immunoreactive. Axon terminals, unlabeled after intraocular injection of the tracer (SR), smaller in size and with more rounded clear synaptic vesicles, longer synaptic differentiations, and higher synaptic index than Rtr terminals, account for 19.7% of all PCSV and make asymmetric synaptic contacts with large dendrites of projection cells and less with the dendrites of interneurons. Some SR have been unambiguously identified as corticofugal terminals (Cg), either after cortical injection of the tracer (16%) or cortical lesion (37%). Retinal and Cg/SR terminals are spatially segregated within the GLd. Both are highly GLU immunoreactive, with the highest density of labeling over synaptic vesicles, suggesting that these terminals may use GLU as neurotransmitter. The level of GLU immunoreactivity of GABA-positive profiles is half that of Rtr and Cg/SR terminals and is greatest over mitochondria, possibly reflecting the 'metabolic' pool of GLU that serves as a precursor in the formation of GABA.

Afferent Pathways↗

PubMed1995

Fine structure of the dorsal lateral geniculate nucleus of the turtle, Emys orbicularis: a Golgi, combined HRP tracing and GABA immunocytochemical study.

The afferent and efferent cortical projections of the dorsal lateral geniculate nucleus (GLD) of adult specimens of the turtle Emys orbicularis were investigated after intraocular or intracortical injections of horseradish peroxidase (HRP), and the distribution of gamma aminobutyric acid (GABA) immunoreactivity in the nucleus was carried out by immunocytochemical techniques, both techniques being combined with light and electron microscopy. In addition, some specimens were prepared for double-labeling of HRP and GABA immunoreactivity, and additional samples impregnated by a rapid Golgi technique. On purely morphological grounds, four types of neurons can be distinguished by light microscopy: two types of large cells in the cell plate which project to the cortex, and two types of smaller cells in the neuropil and optic tract which do not. The small cells are consistently GABA-immunoreactive, while the former are, with extremely rare exceptions, immunonegative for GABA. The supposition that the small neurons of the neuropil are interneurons is supported by electron microscopic observations; these strongly GABA-immunoreactive cells have large plicated nuclei surrounded by a thin layer of cytoplasm poorly endowed with organelles. The dendrites of these cells may contain pleomorphic synaptic vesicles (DCSVs) and appear to be presynaptic to other dendritic profiles. These DCSVs are occasionally contacted by GABA-immunoreactive axon terminals, and more frequently by retinal terminals consistently immunonegative for GABA. The latter, frequently organized in glomeruli, also make synaptic contacts with immunonegative dendrites arising from corticopetal neurons of the cell plate. Two major categories of GABA-immunoreactive axon terminals can be distinguished, and we are led to the conclusion that one of these represents an intrinsic GABAergic innervation of the GLD, while the second is tentatively interpreted as an extrinsic source of GABA to the nucleus, possibly from ventral thalamic structures. The fine structure of the dorsal lateral geniculate nucleus of Emys orbicularis thus shows many similarities with that of mammals.

Afferent Pathways↗

PubMed1992

[Distribution of GABA-immunoreactive elements in the reptile amygdaloid complex].

GABA-immunoreactive (GABA-I) elements (neuronal somata and neuropile) are detected in turtle Emys orbicularis and lizard Ophysaurus spodus in all structures of ventral and dorsal parts of amygdaloid complex (AC) considered as phylogenetic more ancient and younger, respectively by means of the immunohistochemical method. Their maximal quantity in the ventral section of AC is found in the lateral region, lesser--in the ventral, central and medial regions. Besides in lizards a specialized laminar distribution of GABA-I elements in n. sphaericus is observed. GABA-I neurons are also detected in structures of dorsal part in turtles and lizards against the background of the immunopositive neuropile of a moderate density. It is supposed that GABA-ergic innervation of AC is liable to considerable variations in connection with taxonomic, ecological and other factors.

Amygdala↗

PubMed1991

Geniculo- and subthalamohypothalamic connections in the lizard: HRP study.

Reciprocal connections of the hypothalamus with the ventral nucleus of the lateral geniculate body and ventrolateral (subthalamic) nucleus were demonstrated in the lizard Ophisaurus apodus using the retrograde and anterograde axonal tracing method following local HRP injection into the mamillary complex.

Animals↗

PubMed1990

[The connections of the mammillary complex and the hypothalamotegmental section with the stem in the lizard brain].

Hypothalamic connections with the brain stem in lizard (Ophisaurus apodus) were studied by means of local injection of HRP and WGA-HRP into the mamillary complex and massive injections into the hypothalamotegmental area. Reciprocal direct connections were shown between the mamillary complex nuclei and hypothalamotegmental structures, on the one hand, and following structures in the brain stem, on the other hand: griseum centrale, n. parabrachialis, n. lemnisci lateralis, n. raphae and reticular formation of caudal mesencephalic tegmentum, pons and medulla oblongata. It was concluded that direct reciprocal hypothalamo-brainstem connections, as a basis for autonomic-emotional and probably nociceptive and antinociceptive reactions in mammals were formed already in reptiles.

Animals↗

PubMed1988

[Neural connections in the septum of lizards studied by the method of horseradish peroxidase axonal transport].

Septal connections in lizards (Ophisaurus apodus) were studied by means of the massive iontophoretic HRP injection into the septum. Reciprocal connections between the septum and both dorsal and mediodorsal cortex, projections of the nucleus of Broca diagonal band and anterior thalamic nuclei (mainly dorsolateral) to the septum were revealed. Reciprocal connections of the septum with the preoptic area, periventricular hypothalamic structures containing dopaminergic neurons, as well as with the nuclei of the mammillary complex were shown to be the most massive. HRP injection into the mammillary complex revealed mainly anterolateral location of neurons projecting to the mammillary nuclei and dorsolateral terminal field of mammillo-septal projections. Some peculiarities and common features in hodological organization of the septum in reptiles and mammals are considered.

Animals↗

PubMed1987

[Connections between the anterior thalamic nuclei in turtles (data of the peroxidase method)].

It turtles, Testudo horsfieldi (Gray) connections of anterior dorsomedial and dorsolateral thalamic nuclei have been investigated by means of horseradish peroxidase, injected ionophoretically. Retrogradely labelled neurons are predominantly revealed ipsilaterally in the cerebral structures belonging to the limbic system: in the forebrain--basal parts of the hemisphere, septum, adjoining nucleus, nuclei of the anterior and hippocampal commissures, hippocampal cortex, preoptic area; in the diencephalon--in the subthalamus (suprapeduncular nucleus), in some hypothalamic structures (para- and periventricular nuclei, posterior nucleus, lateral hypothalamic area, mamillary complex); in the brain stem--ventral tegmental area, superior nucleus of the suture. Less vast connections are with nonlimbic cerebral formations: projections to the striatum, afferents from the laminar nucleus of the acoustic torus, nuclei of the posterior commissure. Similarity and difference of the nuclei investigated in the turtles with the thalamic anterior nuclei in lizards, with the anterior and intralaminar nuclei in Mammalia are discussed. An idea is suggested on functional heterogeneity of the anterior nuclei in reptiles and on their role for ensuring limbic functions at the thalamic level.

Animals↗

PubMed1987

[Study of the connections of supposed diencephalic connections of the limbic system of the lizard using the technic of axonal transport of horseradish peroxidase].

Connections of the anterior thalamic (n. dorsolateralis anterior, n. dorsomedialis) and habenular nuclei in lizards Ophisaurus apodus were studied by means of HRP administration into these nuclei. It was shown that all nuclei have overlapping locations of afferent sources (basotelencephalic structures, nuclei of anterior and hippocampal commissures, lateral area of the hypothalamus, superior raphe nucleus) and overlapping projectional zones (mammillary complex, ventral tegmental area). Besides common connections, specific ones for separate nuclei were revealed: for n. dorsolateralis anterior-reciprocal connection with dorsolateral hypothalamic nucleus, for habenular nuclei-projection to the interpeduncular nucleus, for n. dorsomedialis-projection to the dorsal hypothalamic area. No mammillary afferents were found for the anterior thalamic nuclei. All the nuclei studied are considered as diencephalic relay links of pathways which can be compared with dorsal (for habenular nuclei) and ventral (for anterior thalamic nuclei) pathways of the limbic system in mammals.

Animals↗

PubMed1986

[Characteristics of representations of the auditory and somatosensory systems in the thalamus of the turtle: electrophysiologic study].

Experiments with unanesthetized tubocurarine-immobilized turtles show that the auditory representation is localized in the n. reuniens which contains monomodal (auditory) and bimodal (auditory and somatosensory) units. The somatosensory system is represented wider, overlapping the auditory system projections in the lateral parts of n. reuniens. The focus of the somatosensory representation is localized in the n. ventralis where monomodal somatic units were recorded. A predominance of contralateral somatic projections is revealed as well. A range of optimal frequencies was 200-400 Hz. It is shown that the thalamic neurons have both wide and limited receptive fields to auditory and somatosensory stimulations.

Afferent Pathways↗

PubMed1985

An underestimated visual pathway in reptiles.

Field potentials evoked in the turtle general cortex by electric stimulation of the optic tectum were analyzed. Cathodal polarization and subtotal lesions of n. rotundus led to either facilitation or depression of later components of the cortical potential. On the contrary, cathodal polarization and lesions of n.geniculatus lateralis dorsalis similarly affected the initial component. After 21-23 months following eye enucleation or optic nerve section, the conduction of fast tectal volleys to the general cortex via n. geniculatus lateralis dorsalis was blocked, though the conduction of tectal impulses to the dorsal ventricular ridge via n.rotundus survived. It is concluded that in turtles one more visual channel, i.e., retino-tecto-geniculo-cortical, is functioning, in addition to well-known retino-tecto-rotundo-telencephalic and retino-geniculo-cortical channels.

Animals↗

PubMed1985

Connections of the mesencephalic, thalamic and telencephalic auditory centers in turtles. Some structural bases for audiosomatic interrelations.

The organization of auditory projections at the mesencephalic, thalamic and telencephalic brain levels was studied utilizing the method of horseradish peroxidase (HRP) transport in two species of the turtle--Emys orbicularis and Testudo horsfieldi. It was shown that the torus semicircularis receives bilateral afferents from the brain stem auditory centers. They arise predominantly from the contralateral cochlear nuclei, the ipsilateral superior olive, the dorsal and ventral nuclei of the lateral lemniscus and from the symmetrical torus semicircularis. These connections appear to be reciprocal. After the enzyme injections correspondingly into the torus semicircularis and n. reuniens anterograde and retrograde HRP transports show that the central nucleus of the torus semicircularis projects to n. reuniens throughout its rostro-caudal extent mainly ipsilaterally. In turn, n. reuniens projects to the medioventral part of the dorsal ventricular ridge. A following common principle of the organization of the auditory system was revealed at the three brain levels explored. Auditory relay centers occupy the most medial positions at every level (n. centralis of the torus semicircularis, n. reuniens, the medioventral part of the dorsal ventricular ridge). Immediately lateral to them are somatic centers (correspondingly, n. intercollicularis, n. ventralis, the central part of the dorsal ventricular ridge). These together with the auditory centers form united functional complexes at every level. In these complexes auditory and somatic projections overlap, thus constituting a basis for the interaction between auditory and somatic afferent inputs. Mesencephalic and thalamic auditory centers were shown to receive direct somatic (cervical spinal) projections and non-direct from the underlying somatic center as well as from the adjacent somatic center at the same level (n. intercollicularis in the mesencephalon, n. ventralis in the thalamus). Somatic centers in the complexes described get no direct auditory projections. Auditory impulses however can enter them via two pathways: along neuron axons from the neighbouring auditory center reaching the adjacent somatic center and along somatic neuron dendrites which pass into the adjacent auditory center. The morphological basis for the auditory-somatic interactions primarily in the auditory center and also in the somatic center was demonstrated in Golgi-like HRP labeled and Golgi-impregnated neurons of these centers. The organization of the auditory-somatic projections at the three brain levels in turtles in to a degree comparable to the auditory system in mammals which is structured according to the core-belt principle.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1985

[Study of cerebellar connections in the turtle using the technic of axonal transport of horseradish peroxidase].

Cerebellar connections in turtles were studied after unilateral horseradish peroxidase administration both in the corpus and nuclei and in the mesencephalic tegmentum. Cells of origin of projections into cerebellum revealed in the caudal brain stem (vestibular nuclei, perihypoglossal complex, inferior reticular formation, oliva inferior) and in the spinal cord appeared to be more numerous than those in rostral structures (pretectum, tegmentum). Efferent cerebellar projections were observed in the medulla oblongata (vestibular nuclei, nuclei of dorsal columns of the spinal cord), in the mesencephalic tegmentum and scarce projections - in the hypothalamus and ventral thalamus. It is concluded that reptiles and mammals have the greatest similarity in afferent and efferent connections of the cerebellum with the spinal cord, caudal brainstem and mesencephalic structures, all of them being functionally united by participation in the regulation of muscle tonus and in the coordination of the locomotor activity.

Animals↗

PubMed1983

[Study of the connections of the hippocampal (mediodorsal) cortex of Ophisaurus apodus by means of horseradish peroxidase axonal transport].

Origin of afferent projections of the hippocampal (mediodorsal cortex in lizards (Ophisaurus apodus) cells was revealed by studying retrograde transport of horseradish peroxidase. Most labelled neurons were located in n. dorsolateralis anterior thalami, corpus mamillaris, n. raphe superior, ipsilateral dorsal cortex and contralateral hippocampal cortex. Less neurons projecting to the hippocampal cortex were observed in the ventromedial part of basal telencephalon (tuberculum olfactorium, n. accumbens, nucleus of diagonal Broca band), hypothalamic preoptic area, mesencephalic ventrotegmental area. Labelled terminals of hippocampal efferents were found in the septum, thalamus, hypothalamus (mainly ipsilaterally) and bilaterally in the hippocampal and dorsal cortex. Both afferent and efferent connections of the hippocampal cortex in lizards are similar to those in mammals.

Animals↗

PubMed1983

[Analysis of the conduction of visual, somatic and audiovibrational sensory information of the hippocampal cortex in the lizard].

Acute electrophysiological experiments on lizards Ophisaurus apodus show that stimulation of both thalamic n. dorsolateralis anterior and medial forebrain bundle elicited short latency responses in the hippocampal cortex resembling in topic and patterns responses evoked by sensory stimuli in the same structure. Ample lesion of n. dorsolateralis anterior and of medial forebrain bundle suppressed up to a complete block conduction of sensory (visual, somatic, audiovibratory) and tectal impulses to the hippocampal cortex. A conclusion is made that n. dorsolateralis anterior and medial forebrain bundle are the main, if not the only route for conducting these sensory impulses to the hippocampal cortex in lizards.

Animals↗

PubMed1983

[Connections of the thalamic and telencephalic centers of the auditory system in turtles].

In the turtles Emys orbicularis and Testudo horsfieldi connections of the thalamic (n. reuniens) and telencephalic (medio-ventral part of the dorsal ventricular edge--DVE) centers of the auditory system have been revealed by means of the retrograde and anterograde horseradish peroxidase (HP) transport method. At a local HP administration into the n. reuniens, the labelled neurons are detected bilaterally in the midbrain: in the auditory center (n. centralis of the torus) and predominantly in the somatic nucleus (n. intercollicularis); in the thalamus--ipsilaterally among the marked fibers of the dorsal peduncle of the forebrain lateral bundle, in the anterior and posterior parts of the suprapeduncular nucleus, in the nucleus of the ventral supraoptic chiasm. The HP anterograde transport is followed in the thalamic n. anterior and n. ventralis, in the forebrain lateral bundle as far as the medial part of the DVE. When HP is injected into the DVE auditory zone, retrogradely labelled neurons are revealed ipsilaterally along the whole pathway of the auditory center (n. reuniens), as well as in the n. anterior and n. ventralis, in the posterior part of the suprapeduncular nucleus, in the posterior commissure nucleus, in the caudal nucleus. Most of these thalamic nuclei are connected with the somatosensory system. The principle of the structural-functional organization of the auditory system in reptiles is discussed; it ensures the interaction between the auditory and somatic impulses making a necessary base for the audition-controlled behaviour.

Animals↗

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↗