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Biomedical subjects

A G Bragin

Publications and source records attributed to A G Bragin.

At least 19 recordsLinked to original sources
PubMed1995

Integration of hippocampal suspension grafts with host neocortex.

The possibility of histological and functional integration of nervous tissue heterotopically grafted into the adult host brain was investigated. Suspensions of embryonic (E17-18) rat hippocampus with dentate fascia were placed into acute cavities in the barrel field of young adult rats (n = 25). Golgi-Cox silver impregnation and Cresyl Violet stain were used for histological analysis 3-4 months postgrafting. The surviving grafts were present in 80% of the grafted animals. Only three out of 20 surviving grafts were completely isolated from the surrounding host brain; other grafts had areas of direct confluence with the host neuropil. Extracellular recording of neuronal activity revealed normal spontaneous activity typical of the hippocampus in the majority of the grafts. Electrical stimulation of the posterior nucleus of the thalamus, homolateral motor neocortex, contralateral barrel field, and sensory stimulation of the host evoked responses in 50-60% of the grafted neurons. This did not differ significantly from the responsiveness of the similarly tested neurons of homotopic neocortical suspension grafts. The latencies of the responses in the hippocampal grafts were consistently longer (by about 10 ms) than in the neocortical ones. Comparison of the hippocampal suspension grafts with other types of hippocampal and neocortical grafts suggests that under certain conditions heterotopic tissue can be successfully integrated into the host brain. Development of the host-graft interconnections depends on topical proximity, the presence of denervated synaptic loci in both tissues, elimination of the intragraft neuronal targets and disruption of the intrinsic connections between them.

Animals↗
PubMed1992

Repeated changes of dendritic morphology in the hippocampus of ground squirrels in the course of hibernation.

Quantitative Golgi study of hippocampal pyramidal neurons of ground squirrels showed rapid and profound transformation of their apical dendrites in the course of hibernation. The dendrites were significantly shorter, less branched and had fewer dendritic spines in the middle of hibernation bout than in the active euthermic ground squirrels between bouts. After arousal from torpor, within 2 h dendrites completely restored their structure. During hibernation, season remodelling of the hippocampal dendrites occurs repeatedly during each torpor-activity cycle.

Animals↗
PubMed1991

[The comparative characteristics of the neuronal activity in surviving slices of transplanted and intact neocortex].

The background single unit activity and single or multiunit responses to electrical stimulation of the rat's embryonic cortex, grafted into the somatosensory cortex of adult rats were investigated in a slice preparation. The same characteristics of the intact cortex neurons were observed as a control. The percentage of neurons with background activity within grafts was higher, than that within intact neocortex slices (23% and 6%, respectively). However the percentage of neurons responding to electrical stimulation of the recipient neocortex was lower in grafts. The mean latency of multiunit responses of graft neurons was longer, than that of neurons of the intact neocortex recorded at the same distance from the stimulating electrode (19.4 +/- 5.0 and 5.8 +/- 1.1 ms, respectively). Duration of the evoked population discharges was approximately ten times longer in grafts. It is concluded that there are local functional connections between a graft and the host brain and that inhibitory processes within grafts are weak. Functional integration of grafts with the host brain of the recipients after cranial trauma is shown.

Animals↗
PubMed1990

Growth of the hippocampal grafts in the rat anterior eye chamber: effects of age and strain of the recipients.

Hippocampal tissue (1 mm3) was taken from embryonal (E17-18) rats of Wistar stock in population breeding and grafted into anterior eye chamber of the four groups of recipients: young (3 weeks) and old (18 months) males of the same stock and of inbred strain WAG. Morphometric analysis of the grafts developing up to 12 weeks in oculo showed rapid initial growth in both groups of the young hosts during the first three weeks, and limited increase of the graft volume during next three weeks. The start of growth was significantly retarded in the old hosts, but this was partly compensated by prolonged increase of the graft volume during the later stages. Both mean and maximal finite volume were much smaller in both WAG groups. The hippocampal grafts in these groups had rounded (not elongated, as in Wistar groups) shape and showed tendency to fragmentation and resorbtion at the late stages. Histological analysis revealed well organized layer of the pyramidal cells in the both Wistar groups and nearly complete absence of neuronal organization into layer in both WAG groups. Possible role of trophic and immune factors in development of intraocular grafts is discussed.

Aging↗
PubMed1989

[The nature of evoked potentials, recorded at neocortical transplants].

Evoked potentials (EP) recorded from a barrelfield of adult rats were compared with those recorded from neocortical embryonal grafts 4-6 month after their transplantation into the barrelfield of adult rats. EPs at the surface of the intact barrelfield started with a positive component followed by a negative wave. EPs reversed their polarity at a depth of 0.4-1.0 mm from the cortical surface. EPs registered from the surface of grafts has the same latency as those in the intact barrelfield, but consisted exclusively of a negative component. It is concluded that though the simultaneously activated grafted neurons can generate local field potentials, their detection during EP recording is prevented as a result of diffuse neuronal organization of the grafts and they can be masked by passive current spreading from the adjacent intact areas of the host brain.

Animals↗
PubMed1988

Transplants of the embryonal rat somatosensory neocortex in the barrel field of the adult rat: responses of the grafted neurons to sensory stimulation.

The degree of participation of grafted neurons in sensory analysis was investigated in embryonal rat somatosensory neocortex transplanted into the cavity at the place of the barrel field in the neocortex (SI) of adult rats. The neurons were investigated extracellularly 3 to 6 months after grafting. In the majority of grafts the neurons had normal levels and patterns of spontaneous activity. Many of them (65%) responded to displacement of the whiskers with latencies insignificantly different (18 +/- 0.8 ms) from those for reactions in the intact barrel field (16 +/- 0.5 ms). The receptive fields of the grafted neurons were very large. None of the neurons responded to stimulation of a single vibrissa, as in intact cortex. As a rule, the same neuron responded to isolated deflections of several (up to 10-20) vibrissae. Many of them were responsive to stimulation of the small anterior vibrissae and tactile stimulation of nose, limbs and body surface. Nevertheless, there was some spatial gradient in the effectiveness of stimulation of the body surface at various distances from the vibrissal pad; among effective vibrissae, usually several adjacent ones (2-4) produced larger responses with shorter latencies than the other ones. All units responded to painful stimuli irrespective of their location. The data show that the grafted neurons receive and may transmit sensory signals. The grafts which were proved histologically to be isolated from the host's brain did not respond to sensory stimulation and were characterized by the presence of aperiodic hypersynchronous bursts in their background activity. Electrophysiological criteria may be used for intravital diagnosis on the degree of the graft morphofunctional integration.

Animals↗
PubMed1987

Behavioural, biochemical and histochemical effects of locus coeruleus transplantation in rats with neurotoxic lesions of the catecholaminergic system.

Exploratory activity in the open field and noradrenaline concentration in the neocortex and brain stem were investigated in intact rats (n = 10) and in the following groups of rats with early postnatal neurotoxic (6-hydroxydopamine) lesion of the catecholaminergic system: (i) rats with embryonal locus coeruleus grafts in the frontal neocortex (n = 5); (ii) rats with the same grafts in lateral ventricles (n = 4); (iii) a control group with intracortical hippocampal tissue grafts (n = 3); (iv) sham-operated rats (n = 3). Experiments were performed by four independent groups of investigators using a double-blind method. In sham-operated rats as well as in rats with hippocampal grafts, and with locus coeruleus grafts in the ventricles, both exploratory activity and noradrenaline content of the forebrain were significantly lowered. In the rats with intracortical locus coeruleus grafts the level of exploratory activity was much higher (almost as in intact controls). This improvement of exploratory behaviour correlated highly with increased noradrenaline concentration in the forebrain. In all animals with locus coeruleus in lateral ventricles a significant increase in noradrenaline level of the brain stem was present, but no change of exploratory behaviour was observed. The grafts with the 3-mm-thick slabs of the adjacent tissue were dissected from the brain and used for histological analysis. The presence of typical locus coeruleus cells was shown in neocortex of all animals which received the grafts of corresponding tissue. The data show the possibility of stable compensation of the forebrain noradrenaline level and exploratory behaviour by embryonic noradrenergic neurons grafted into the neocortex, but not into lateral ventricles.

Animals↗
PubMed1987

[Electrophysiological indices of the degree of functional integration of a cortical transplant with the brain of the recipient].

Pieces of the embryonal rat neocortex were grafted into the cavity at the place of the barrel-field of adult rats. Neuronal discharges and slow activity were recorded in 11 grafts 3-8 months after the grafting. Neurons of nine grafts responded to vibrissae deflection, their background activity consisted of randomly distributed discharges as in the normal cortex. The similar slow activity was observed in the responding grafts and in the host's intact contralateral barrel-field. Neurons of two grafts did not respond to vibrissae deflection. Hypersynchronous discharges prevailed in their background activity as well as slow delta-waves and epileptiform sharp spikes and waves. Complexes predominated in slow activity of these grafts. Histology revealed a close contact between responding grafts and host brain tissue. Nonresponding grafts were separated from the host brain by a thick glial scar which apparently prevented the axonal exchange between them.

Acoustic Stimulation↗
PubMed1986

Serotonin and norepinephrine content in brain structures of rats with experimental and transplantation-compensated diabetes.

The development of alloxan-induced diabetes in rats is shown to be accompanied by a decrease in the norepinephrine (NE) and serotonin (5-OT) content in the neocortex and caudal segment of the brain stem. Simultaneously the intensity of 3H-leucine labelling of the brain tissue was decreased. The attempt to compensate the diabetic syndrome in rats by transplanting the embryonic pancreas (EP) into the anterior chamber of the eye (ACE) was successful. All the animals with the adapted transplant showed a return of the monoamine level to the normal, a decrease in urine glucose, as well as normalization of protein synthesis by the 14th-20th days.

Alloxan↗
PubMed1986

Organization of the nervous tissue (hippocampus and septum) developing in the anterior eye chamber. III. Axonal processes and their synaptic endings.

Embryonal tissue of rat's septum and hippocampus developing in the anterior eye chamber for three to four months was investigated. Electron microscopic analysis of axonal processes and synaptic boutons is presented in this paper. Dense neuropil of the grafts includes myelinated and unmyelinated fibers. Some of them have definite structural features of peripheral fibers; there are also some transitory forms, combining the traits of peripheral and central axons. Synapses of presumed monoaminergic nature and other unidentified synaptic contacts with the neurons are formed by peripheral fibers entering the grafts from the iris. The majority of axons belongs to the neuronal elements of the grafts themselves. Distribution of the synapses upon neuronal somata and dendritic trees seems to be quite normal. Synapses of symmetric type are present mainly upon neuronal bodies and dendritic shafts; synapses with dendritic and somatic spines are asymmetric. At the same time some unusual features are observed: the presence of the axonal growth cones, long ribbon-like axonal terminals, forming numerous serial synapses with elements of neuropil or neuronal bodies, pseudo-glomerular synaptic contacts encapsulated by glial processes. Increased pinocytotic and microphagocytotic activity between various elements of neuropil is present within the grafts. Spinular complexes, which are often encountered in interneuronal contacts, possibly also participate in processes of exocytosis-endocytosis. Some ultrastructural characteristics of the grafted tissue indicate to its incomplete maturation which may result from deficit of normal afferentation or from absence of some more general developmental factors in the intraocular grafts.

Animals↗
PubMed1986

[Responses of neurons of the embryonal neocortex transplanted into the vibrissa projection area of the somatosensory cortex of the adult rat].

Pieces of embryonic rat neocortex were grafted into the barrel-field of adult rats. Extracellular activity of the grafted neurons was registered 3-4 months later. The background neuronal activity in the grafts did not differ neither in pattern, nor in frequency (3.7 +/- 1.4 spikes per s) from that of the normally developing somatosensory cortex. About 57% of the grafted cells responded to deflexion of the contralateral vibrissae by on-effects, 30%-by phasic increase of discharge frequency and 13%-by initial suppression of spontaneous activity.

Action Potentials↗
PubMed1985

[Activity of septal and hippocampal neurons during isolated and combined growth in the anterior chamber of the eye in the rat].

Neuronal activity of the septal and hippocampal grafts, developing in the anterior eye chamber of the rat for 3-6 months was recorded extracellularly in curarized or cerveau isolé animals. While the units of isolated septum had background activity of regular, irregular and rhythmic burst type, the hippocampal units displayed no background discharges or produced very low-frequency population spikes. In the paired septal-hippocampal grafts neurons of the hippocampus possessed the same types of activity, as that of the septum. Spontaneous epileptiform phenomena were observed in many paired grafts; such phenomena were easily provoked by mild electrical stimulation of one of the grafts. Superfusion with low Ca2+, high Mg2+ medium abolished spontaneous activity in most of hippocampal units but not in septal units. Epileptic discharges were also partly suppressed.

Animals↗
PubMed1985

[Ultrastructure of the capillaries of nerve tissue transplants growing in the anterior chamber of the eye].

Blood capillaries have been studied electron microscopically in the areas of grafts (rat embryonal hippocamp and septal cerebral parts transplanted to mature rats) containing mainly nervous, glial or connective tissue cells. Certain differences in the capillary wall structure have been revealed. In areas with a great concentration of nervous cells, the blood capillaries are characterized by a dense arrangement of cellular elements in their walls, a continuous layer of the glial end-feet, this is specific for the CNS capillaries providing the blood--brain barrier. In peripheral area of the grafts, where glial elements predominate, the capillaries have loose arrangement of the mural cellular elements, great endotheliocyte activity, thick connective tissue tunic, lack of a dense glial surrounding. These characteristics make dubious the statement whether these capillaries possess the blood--brain barrier function. In places where connective tissue cells make aggregates, the capillaries do not possess the barrier properties because of perforations and fenestrae in endothelium and interruptions of the basal membrane, absence of pericapillary glial elements. All types of the capillaries demonstrate certain signs of a high functional activity. Formation of the capillary structure depends on the surrounding tissue.

Animals↗
PubMed1985

[Surface structure of nerve tissue transplants growing in the anterior chamber of the rat eye (electron-microscopic study)].

Two different types of the glial envelope are demonstrated around the septal cerebral area grafts (SCAG) and the hippocampal grafts (HG) developing in the anterior eye chamber of the rat during 3-4 months. In the SCAG it is multilayered, consists mainly of modified oligodendrocytes. Processes of the nervous cells perforate the surface of the envelope. In the HG the unilayered glial envelope consists of bodies and processes of the fibrous astrocytes; it is impenetrable for the nervous processes. Since both types of the cellular elements making these envelopes have been described in the norm, it is possible that the differences in the surfaces described are specific for these structures.

Animals↗
PubMed1985

[Background and evoked activity of septal and hippocampal neurons transplanted into the neocortex of the rat].

Embryonic tissue of the septum and hippocampus was transplanted into a cavity made in parietal neocortex of adult rats. Extracellular recording 4-6 months after grafting revealed units with background spike activity in the grafted tissue. The activity (mean rate 3.6 +/- 0.4 spikes per s) had a random pattern without pathological features. About 90% of the graft cells responded to electrical stimulation of neighbouring cortical tissue with latencies 5-43 ms. The optimal frequencies for driving spike discharges were 5-10 Hz. Postactivatory suppression was observed in most units. The same proportion of the graft cells responded to tactile stimulation of the host animal. Phasic reactions of on-off type with latencies of 50-600 ms were observed. The normalization of the activity in intrabrain grafts as compared to intraocular ones and functional integration of graft units with the host brain are discussed.

Animals↗
PubMed1985

Organization of the nervous tissue (hippocampus and septum) developing in the anterior eye chamber. II. Neuronal perikarya and dendritic processes.

Rat's embryonal tissue of septum and hippocampus was transplanted into anterior eye chamber (AEC) of the adult rats. Ultrastructure of septal (SGs) and hippocampal (HGs) grafts was analyzed after three-four month of survival in AEC. Special attention was directed to deviations of ultrastructure of the grafted neurons from standard characteristics. Neuronal perikarya and dendritic processes basically had normal structure typical of highly differentiated, mature neurons. Organotypic features of neuronal ultrastructure were well preserved by the grafted tissue. At the same time certain anomalies were observed: presence of multilaminated bodies, vacuolization of some areas in mitochondria, cisternae of Golgi apparatus and of endoplasmic reticulum, slight increase of electron opacity of cytoplasm in some neurons. Dendrites had irregular contour due to abundance of various microprocess with and without postsynaptic specializations. Some dendritic spines with abnormal configurations were observed (with long, thin stalks, with arrow-shaped heads). The microprocesses and spines were present also upon the surface of perikarya. Extensive appositions of plasmalems of adjacent neurons with gap junctions were usual. Synaptic vesicles and disaggregation of microtubules were observed in some dendrites. The neurons and large dendritic processes covered by multilayer myelin-like sheaths were encountered in the grafted tissue. Active micropinocytosis and exchange by cytoplasmic fragments (phagocytosis) was observed between the neurons as well as between the nervous and glial cells. It is suggested that some unusual features of ultrastructure of the grafted tissue result of deficit of extrinsic afferentation, while others may be regarded as consequences of excessive excitability of the grafted tissue.

Animals↗