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Biomedical subjects

I M Gelfand

Publications and source records attributed to I M Gelfand.

At least 55 records · Page 3Linked to original sources
PubMed1979

Upper surfaces of epithelial sheets and of fluid lipid films are nonadhesive for platelets.

Platelet-rich rabbit plasma was incubated with surfaces of two different types--sheets of cultured mouse kidney epithelium and films of different lipids. The upper surface of epithelial sheets was found to be nonadhesive for platelets; in the same cultures, the platelets attached easily to the glass surface not covered by epithelial cells. Platelets did not attach to the surface of lipids (egg lecthin and dioleoyllecithin) that were in the liquid-crystalline state at 23 degrees C. In contrast, the surface of the films made of lipids (dipalmitoyl- and distearoyllecithin) that were in the crystalline state at 23 degrees C was adhesive for platelets. It had been found previously that the surfaces of epithelial sheets and of liquid lipid films are nonadhesive for fibroblasts. Possible mechanisms responsible for the nonadhesiveness of these surfaces are discussed. It is stressed that the factors responsible for nonadhesiveness of epithelial surfaces may be similar to those responsible for nonadhesiveness of the luminal surface of endothelium in blood vessels.

Animals↗
PubMed1979

Hybrid resistance to parental bone marrow transplantation: adaptive modification of hemopoietic stem cell in a nonsyngeneic environment.

Defective growth of parental bone marrow in an F1 hybrid is associated with delay of the exponential growth phase of injected hemopoietic stem cells rather than with their rejection. This is demonstrated both by parental hemopoietic stem cell kinetics in the irradiated hybrid and by the increase in the number of spleen colonies with time after hemopoietic cell injection. After passage through an F1 hybrid the parental hemopoietic stem cells acquire ability for better growth in the same F1 host. This phenomenon, which we designated "adaptive modification of hemopoietic stem cells," is associated with the appearance, on their surface, of histocompatibility molecules carrying H-2 determinants of the recipient. Treatment of the modified cells with antiserum against the second parental strain abrogates the state of adaptive modification.

Animals↗
PubMed1978

Messages conveyed by descending tracts during scratching in the cat. I. Activity of vestibulospinal neurons.

(1) The activity of vestibulospinal (VS) neurons giving axons to the lumbosacral spinal cord was recorded during scratching in thalamic and decerebrate cats. The most part of the experiments was carried out on curarized cats, in which fictitious scratching13, i.e. rhythmical activity of motoneurons typical of actual scratching, was evoked. (2) During both actual and fictitious scratching, the discharge frequency of many VS neurons was rhythmically modulated in relation to the scratch cycle. Most modulated neurons were maximally active in the extensor phase of the cycle. (3) The firing pattern of VS neurons during fictitious scratching was similar to that during actual scratching. Therefore, rhythmical modulation of VS neurons is determined mainly by central mechanisms and not be a rhythmical sensory input. (4) In decerebellate cats, rhythmical modulation was not found during either actual or fictitious scratching. (5) Transection of the ventral spinocerebellar tract (VSCT) resulted in considerable reduction of rhythmical modulation of VS neurons during fictitious scratching, while transection of the spino-reticulocerebellar pathway (SRCP) resulted in just a small decrease of modulation. Therefore, of the two pathways (VSCT and SRCP) transmitting messages about intraspinal processes to the cerebellum during scratching6,7, the VSCT is of major importance for modulating VS neurons.

Animals↗
PubMed1978

Messages conveyed by spinocerebellar pathways during scratching in the cat. I. Activity of neurons of the lateral reticular nucleus.

(1) Signals transmitted to the cerebellum by the spino-reticulocerebellar pathway (SRCP) during scratching were studied. For this purpose, the activity of neurons of the lateral reticular nucleus (LRN), which are the last-order neurons of the SRCP, was recorded during scratching in thalamic cats. Scratching was evoked by stimulation of the pinna. LRN neurons were identified antidromically by stimulation of the hindlimb area in the cerebellar anterior lobe. In most experiments, animals were immobilized with Flaxedil, and stimulation of the pinna resulted in fictitious scratching, i.e., in periodical reciprocal activity of flexor and extensor motoneurons typical of actual scratching. (2) During both actual and fictitious scratching, the discharge frequency of LRN neurons was rhythmically modulated in relation with the scratch cycle. Most LRN neurons fired in short high-frequency bursts of spikes which coincided (completely or partly) with the extensor phase of the cycle. In this respect the SRCP differs from the ventral spinocerebellar tract (VSCT) which is maximally active in the flexor phase of the cycle. (3) The firing pattern of LRN neurons during fictitious scratching was similar to that during actual scratching. Therefore, the rhythmical burst firing of LRN neurons is determined mainly by the central mechanisms and not by the rhythmical sensory input. (4) Rhythmical modulation of LRN neurons disappeared after transection of the ipsilateral lateral funiculus of the spinal cord in which spinoreticular fibers are located. On the other hand, considerable reduction of rhythmical activity in descending brainstem-spinal pathways after contralateral hemisection of the spinal cord did not affect the discharge pattern of LRN neurons. These two facts indicate that the SRCP conveys mainly messages about activity of the central spinal mechanisms, and that influences of supraspinal motor centers.on LRN neurons and on spinoreticular neurons are of minor importance. (5) Axonal terminations of LRN neurons are distributed rather evenly over the hindlimb area in the anterior lobe of the cerebellum. Therefore, messages about the events, which happen within the spinal cord in the vicinity of the extensor phase of the cycle, arrive at every point of the hindlimb area.

Animals↗
PubMed1978

Messages conveyed by spinocerebellar pathways during scratching in the cat. II. Activity of neurons of the ventral spinocerebellar tract.

(1) The activity of neurons of the ventral spinocerebellar tract (VSCT) during scratching was studied in thalamic and decapitate cats. The neurons were identified antidromically either by stimulation of the hindlimb area in the anterior lobe of the cerebellum (in thalamic cats) or by stimulation of the contralateral ventrolateral funiculus of the spinal cord (in decapitate cats). The scratch reflex was elicited by stimulation of either the pinna (in thalamic cats) or the cervical spinal cord (in decapitate cats). In most experiments, animals were immobilized and the activity of VSCT neurons was recorded during fictitious scratching. (2) During both actual and fictitious scratching, the discharge of VSCT neurons was rhythmically modulated in relation with the scratch cycle: neurons fired in bursts separated with periods of silence. Phases of activity of different neurons were unevenly distributed over the scratch cycle: most neurons fired within the limits of the flexor phase of the cycle. (3) The firing pattern of VSCT neurons during fictitious scratching was similar to that during actual scratching. Therefore, rhythmical burst firing of VSCT neurons is determined mainly by central mechanisms and not by a rhythmical sensory input. (4) The firing pattern of VSCT neurons in decapitate cats was similar to that in thalamic cats. Therefore, rhythmical burst firing of VSCT neurons is determined mainly by the central spinal mechanism and not by supraspinal motor centers. (5) The VSCT neurons which fired in long bursts during the greater part of the flexor phase were usually activated during the latent period of scratching, while those firing later in the cycle were usually either inhibited or not affected during this period. (6) The antidromic response in most VSCT neurons could be evoked from a large number of points in the hindlimb area of the cerebellar anterior lobe, both in the vermis and in the pars intermedia. Due to such extensive branching of axons, each point of the cortex receives signals from neurons firing in different phases of the cycle. But axons of VSCT neurons firing in long bursts during the greater part of the flexor phase terminate more extensively in the pars intermedia, while axons of neurons firing later in the cycle terminate more extensively in the vermis. (7) The functioning of the VSCT is essentially similar to that of the spino-reticulocerebellar pathway (SRCP). Both pathways convey messages about activity of the central spinal mechanism generating the motor output pattern of scratching, but the VSCT is active mainly in the flexor phase of the scratch cycle and the SRCP in the extensor one. A hypothesis is advanced that these pathways monitor activity of different groups of spinal interneurons.

Animals↗
PubMed1978

Microtubular system in cultured mouse epithelial cells.

Previous observations had shown that colcemid does not affect locomotion of epithelial cells. Nevertheless, cultured mouse kidney cells forming epithelial sheets were found to contain a well-developed microtubular system sensitive to colcemid. The orientation of microtubules in the epithelial cells was not correlated with the stable or active state of the cell edges. It is suggested that microtubular system of the epithelial cells forming coherent sheets, in contrast to that of individually moving fibroblasts, is not essential for stabilization of the lateral cell edges.

Animals↗
PubMed1978

Generation of scratching. I. Activity of spinal interneurons during scratching.

1. In decerebrate, curarized cats, stimulation of the cervical spinal cord evoked fictitious scratching (9), i.e., periodical activity of the hindlimb motoneurons with a discharge pattern typical of actual scratching (cycle duration about 250 ms, flexor phase about 200 ms, extensor phase about 50 ms). During fictitious scratching, extra-cellular records were obtained from 182 spinal neurons located in different regions of the gray matter cross section (except for the motor nuclei), from segments L4 and L5. 2. The firing rate of 73% of neurons was rhythmically modulated in relation with the scratch cycle. Most of the modulated neurons fired in bursts and were silent between bursts. They were located mainly in Rexed's (22) layer VII. 3. Burst onsets ("switchings on" of the neurons) were distributed rather evenly throughout the scratch cycle except for a small maximum at the very beginning of the cycle (the cycle was assumed to start with the termination of the extensor phase). Burst terminations ("switchings off") in the overwhelming majority of the neurons were distributed over the last-third part of the cycle. As a result, those neurons which began to fire earlier in the cycle usually had longer bursts, compared to the neurons which began to fire later. Besides, since there were very few switchings off in the first half of the cycle, the number of simultaneously active neurons increased during the first half of the cycle, reached the maximum somewhat later than the middle of the cycle, and considerably decreased by the end of the cycle. 4. With more intensive scratching, the firing rate in the bursts considerably increased in all neurons tested, while the duration of the scratch cycle changed only slightly. 5. A correlation between the burst position in the cycle and the behavior during the latent period of scratching (when stimulation of the cervical spinal cord had already been started but rhythmical oscillations had not yet appeared) was found in many neurons. Most of the neurons which began to fire at the beginning of the scratch cycle and had long bursts were tonically activated during the latent period. On the contrary, most of the neurons which fired in short bursts at the end of the cycle were either inhibited or not affected during this period. 6. A correlation betwen the burst position in the cycle and the frequency pattern was found in many neurons. In most of the neurons which began to fire in the first half of the cycle (except for the very beginning), the discharge rate increased in the course of the burst. In the remaining neurons, the discharge rate changed only slightly during the burst. 7. Hypotheses concerning organization of the spinal mechanism of scratching are discussed.

Animals↗
PubMed1978

Generation of scratching. II. Nonregular regimes of generation.

1. The activity of muscle nerves and that of spinal interneurons from the L4 and L5 segments was recorded during fictitious scratching (5), which was evoked in decerebrate curarized cats by stimulation of the cervical spinal cord. In some experiments, rhythmical generation was disturbed by stimulation of the fifth lumbar dorsal root (DL5). 2. Excluding the very beginning of scratching, rhythmical generation was usually rather regular: fluctuations of the cycle duration were less than +/-5%. But changes in the stimulation strength, in the stimulating electrode position, and in the hindlimb position led to changes of the generation regime. In different regimes, the mean value of the cycle duration could differ by 20-30%. No correlation was found between mean durations of flexor and extensor phases for different regimes. 3. Rhythmical generation was possible only if the hindlimb was put to "scratch posture," i.e., deflected forward. Generation immediately stopped when the limb was deflected backward, and immediately started when it was returned to scratch posture. 4. In some experiments, stimulation of the cervical spinal cord first resulted in generation of slow oscillations with the temporal pattern typical of stepping (cycle duration about 500 ms, flexor and extensor phases being almost equal to each other). Then, during 5-20 cycles, gradual transition to a normal scratch cycle (about 250 ms) occurred mainly due to considerable shortening (5-10 times) of the extensor phase. In some experiments, considerable spontaneous variations of the flexor phase were observed, while the extensor phase was constant. 5. A single stimulus applied to DL5 considerably affected the cycle duration. Repetitive DL5 stimulation,with a rhythm close to that of scratching, resulted in synchronization of the spinal generator by the stimuli. 6. Spinal interneurons recorded during transition from slow oscillations to a normal scratch cycle only slightly changed phases of their activity in relation to the activity of motoneurons. 7. A hypothesis is advanced that generation of different kinds of limb movements is produced by one and the same central spinal mechanism which can operate in different regimes. The role of sensory input for operation of this mechanism is discussed.

Afferent Pathways↗
PubMed1977

Effects of antitubulins on the redistribution of crosslinked receptors on the surface of fibroblasts and epithelial cells.

Substrate-attached normal mouse fibroblasts, transformed mouse fibroblasts (L strain), and epithelial cells (MPTR strain) were incubated with two ligands crosslinking different groups of the surface receptors: concanavalin A and cationic ferritin. Surface-attached ligands were revealed by an indirect immunofluorescence method. Incubation of control cells with these ligands induced the patching of corresponding surface receptors and the clearing of these receptors from the surface zones located on the lamellar cytoplasm near cell edges actively protruding pseudopodia. Effects of three antitubulins (microtubule-destroying drugs: Colcemid, colchicine, and vinblastine) on the ligand-induced redistribution of receptors were investigated and compared with the previously described effects of these drugs on the distribution of active cell edges. Incubation of normal and transformed fibroblasts with these antitubulins led to the disappearance of nonactive cell edges; the whole cell perimeter became active. Correspondingly, the clearing pattern of the surface receptors of fibroblasts was altered by antitubulins: the cleared area in antitubulin-treated cells formed a circular band along the whole peripheral cell edge. In epithelial cultures, in contrast to fibroblastic ones, antitubulins changed neither the distribution of the active sites of the surface nor the distribution of the areas cleared of crosslinked receptors. Thus, the specific ability of the surface areas located near the active cell edges to become cleared of crosslinked receptors is characteristic not only for the cells with intact microtubules, but also for the cells with microtubules destroyed with antitubulins.

Cell Line↗
PubMed1976

Serum dependence of expression of the transformed phenotype: experiments with subline of mouse L fibroblasts adapted to growth in serum-free medium.

Characteristics of LSF cells grown in serum-containing and serum-free medium were compared. LSF is a subline of the L-strain of mouse transformed fibroblasts adapted to continuous growth is serum-free medium. Proliferation of LSF cells in monolayer on solid substratum was almost similar in serum-containing and in serum-free media. However, several other characters were found to be altered by the addition of serum to the serum-free medium: ability of cells to form colonies in semi-solid medium increased considerably; agglutinability of cells by Concanavalin A increased; uptake of 2-deoxy-D-glucose by the cells increased considerably; ability of cells to metabolize benzo (a) pyrene was inhibited; cell morphology was altered and, in particular, the cells became less spread on the substratum and density of microvilli on the cell surface increased. All these changes induced by serum were reversed by transfer of the cells back into serum-free medium. Thus, addition of serum increased the expression of a number of cellular traits characteristic of transformed phenotype, while in serum-free medium partial phenotypic reversion of transformation was observed. A possible role of serum in the expression of the transformed phenotype is discussed. It is pointed out that cell lines adapted to growth in serum-free medium provide an experimental system convenient for analysis of the effects of different serum components on the cell phenotype.

Animals↗
PubMed1976

Active cell edge and movements of concanavalin A receptors of the surface of epithelial and fibroblastic cells.

Movements of the receptors of concanavalin A on various parts of the surfaces of substrate-attached cells were compared. Cultured mouse embryo cells of several types were used: epithelial kidney cells and normal and transformed fibroblasts. Initial distribution of receptors was random on the cells of all types. Binding of concanavalin A induced patching of its receptors on all the cell parts. In contrast, directional centripetal movement of receptors was observed only on the surface of certain cell parts, namely, only the surface of peripheral lamellar cytoplasm was cleared of the receptors. Clearing was always initiated in the zone of lamellar cytoplasm located near active cell edges. In epithelial sheets, clearing was not observed on the surface of central cells that had no lamellar cytoplasm. Concanavalin A receptors on the cleared areas of cell surface were gradually restored after the end of incubation. It is suggested that anchoring of the patches of membrane receptors by cortical microfilaments is possible only on the surface of pseudopods and of lamellar cytoplasm but not on the surface of other cell parts. Besides receptor movements, this hypothesis may be explain differences in the adhesive properties of various parts of the cell surface.

Animals↗
PubMed1975

On the role of central program and afferent inflow in the control of scratching movements in the cat.

Rhythmical scratching movements of the hindlimb were evoked in decerebrate and decapitate cats by stimulation of C1-C2 segments of the spinal cord. Movements of the limb and electrical activity of its muscles were recorded. All muscles were divided into two groups according to their activity. Muscles of the first group supported the limb in a propriate position; they were active during most of the cycle and relaxed during small intervals when muscles of the second group contracted. A deafferented limb was also capable of rhythmical scratching movements with approximately the same cycle duration. However, after deafferentation, the mean position of the limb changed and the amplitude of oscillations increased. This is due mainly to decreased activity of the first group muscles. In curarized preparations, stimulation of C1-C2 segments evoked a rhythmical process within the lumbosacral spinal cord ('fictive' scratching) with a cycle duration nearly the same as in normal scratching. Electrical activity of the muscle nerves during 'fictive' scratching resembled that of corresponding muscles during normal movements. 'Fictive' scratching could be easily elicited provided that the limb was put in a position similar to that of normal scratching.

Animals↗
PubMed1975

Neoplastic fibroblasts sensitive to the growth inhibition by homologous cells but insensitive to inhibition by parent normal cells.

3H-thymidine labelling and autoradiography were used to compare density dependent inhibition of growth in the cultures of two transformed lines of hamster fibroblasts and in primary cultures of their parent normal cells. Similar manifestations of density dependent inhibition were found in the isolated cultures of normal and neoplastic cells: at saturation densities these cultures had low labelling indices; these indices considerably increased when the cells migrated into the wound from the dense sheet, prelabelled cells seeded on the dense sheets of unlabelled homologous cells did not proliferate. However, proliferation of neoplastic cells was not inhibited when they were seeded on the dense sheet of normal fibroblasts. Thus, neoplastic hamster fibroblasts of both lines retained sensitivity to the inhibiting effect of homologous neoplastic cells but completely lost sensitivity to the inhibiting effect of normal fibroblasts. The possible significance of this selective loss of the sensitivity to normal cells is discussed briefly.

Animals↗
PubMed1975

Contact inhibition of phagocytosis in epithelial sheets: alterations of cell surface properties induced by cell-cell contacts.

Contact inhibition of phagocytosis was found to be characteristic for epithelial sheets formed in cultures by several cell types: normal and transformed mouse kidney cells, and differentiated mouse hepatoma cells. In these sheets most central cells surrounded by other cells had very low phagocytic activity. In contrast, marginal cells having a free edge were able to perform an active phagocytosis. Contact inhibition of phagocytosis was absent in dense cultures of mouse embryo fibroblasts and in cultures of anaplastic mouse hepatoma 22a. The upper surface of epithelial sheets was nonadhesive for prelabeled epithelial cells and fibroblasts. In contrast, the upper surface of dense cultures of mouse fibroblasts was adhesive for these cells. These and other data strengthen the suggestion that contact inhibition of phagocytosis is a result of different adhesiveness of the upper cell surface and of the surfaces near the free edge. Agents inhibiting cell surface movements at the free edges of marginal epithelial cells (cytochalasin, azide, sorbitol, low temperature) prevented adhesion of particles to these edges. Possibly, the surface of actively moving cytoplasmic processes is the only cell part that has adhesive properties necessary for the formation of attachments with other cellular and noncellular surfaces. In epithelial sheets, in contrast to fibroblast cultures, Colcemid did not activate movements of immobile contacting cell edges. These results indicate that mechanisms of contact immobilization of cell surface may be different in epithelium and fibroblasts. Firm contacts formed between epithelial cells are sufficient for stable immobilization of the surface; additional stabilization of the surface by microtubules is not essential. Fibroblasts do not form firm contacts and the Colcemid-sensitive stabilization process is essential for maintenance of the immobile state of their surfaces. Differences in the stability of cell surface immobilization produced by cell-cell contacts may also explain different adhesiveness of the upper surfaces of dense fibroblastic and epithelial cultures.

Animals↗