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PubMed1976

Comparison of electrical activity and behavioral correlates of neural networks in the cat and locust.

Extensive experimental data are available on the neural activity and behavioral correlates of specific networks in the locust and in the cat and rabbit. Two networks were selected for comparison, one involving visual movement detector interneurons in the locust and the second a hippocampal network in mammals. Both networks receive inputs correlated with motor activity. Each network was simulated using CSMP, a Continuous Systems Modeling program developed initially by IBM. Signals along the two simulated networks were calculated when similar inputs were applied. In addition, approaches toward relating behavior to neural activity were compared in the two networks.

Action Potentials↗
PubMed1992

Mammalian vitreous humor contains networks of hyaluronan molecules: electron microscopic analysis using the hyaluronan-binding region (G1) of aggrecan and link protein.

Vitreous humor from human, bovine, and chicken eyes was analyzed by rotary shadowing to characterize further the supramolecular organization of the gel-like matrix which forms this tissue. Extensive filamentous networks, distinct from collagen fibrils, were found in both human and bovine vitreous but not in chicken vitreous. The networks consisted of branching structures of various diameters, due to variable numbers of hyaluronan molecules being laterally associated with each other and apparently giving rise to a three-dimensional lattice. These networks could be decorated in a specific and regular manner by the hyaluronan-binding region called G1 purified from bovine nasal septum cartilage. The extent of decoration of hyaluronan was dependent on the relative concentration of G1. In the presence of an excess of G1 the networks were destabilized giving rise to individual unbranched hyaluronan chains of varying length that were saturated with G1. One or more globular proteins, as yet uncharacterized, were seen interacting with the hyaluronan networks, often at branch points. These proteins may serve to stabilize the three-dimensional structure of the matrix although highly ordered networks were also observed without globular proteins. Link protein, which also binds to hyaluronan, bound to the networks in a fashion clearly distinct from G1. Neither G1 nor link protein bound directly to human or bovine vitreous collagen fibrils. However, link protein did bind extensively to the glycosaminoglycan coat of chicken vitreous collagen fibrils described previously (D. W. Wright, and R. Mayne J. Ultrastruct. Mol. Struct. Res. 100, 224-234, 1988), while G1 did not. Digestion of the chicken vitreous collagen fibrils with Streptomyces hyaluronidase did not result in the removal of the glycosaminoglycan coat of the collagen fibrils nor did it affect the binding of G1 or link protein to the fibrils, indicating that hyaluronan is not a component of this structure. These studies demonstrate that proteins with specific binding properties can be used as probes to investigate the structure of the native vitreous humor gel from several species and suggest that this method potentially can be used for structural studies of other connective tissue matrices.

Aggrecans↗
PubMed1990

The effects of leukocytes on blood flow in a model skeletal muscle capillary network.

A model of blood flow in a skeletal muscle microvascular network, typical of a rat spinotrapezius muscle, was used to analyze the effects of white blood cells (WBCs) on network resistance and on the pathways followed by WBCs as they transit the network. This model incorporated plugging of vessel entrances by WBCs and the effects of vessel hematocrit, shear rate, and WBCs on blood apparent viscosity. Blood flow and HCT in each vessel and WBC positions were computed at discrete time steps. WBC introduction increased the network resistance 2.98% under normal conditions, and 14.4% above that of plasma alone when WBCs were considered to be suspended in plasma. This resistance increase was predominantly due to WBC plugging at vessel entrances. Comparison of resistance increases to the number of WBC plugs showed an exponential relationship once a threshold value of plugging was reached. Increased WBC plugging resulted from increases in either the feeding concentration of WBCs or the duration of individual plugs. Increased plug duration was the direct result of using alternate WBC deformation models and increasing WBC viscosity. A WBC viscosity range of 45 to 2400 P was used in the model, corresponding to the viscosities reported by various in vivo and in vitro studies. WBC plugging also significantly affected the pathways taken by WBCs. Under normal conditions, WBCs tended to flow through preferred pathways in the distal portions of the network. With increased plugging, WBC flow became more homogeneous. For significant increases in the network resistance to occur, it is essential that the WBC pathways be distributed throughout the network.

Blood Flow Velocity↗
PubMed1983

Response vs excitation in response-dependent and stimulus-dependent lateral inhibitory networks.

Response-dependent and stimulus-dependent lateral inhibitory networks may be distinguished by differences in their net response vs net excitation functions. It is shown that the net response of a stable, response-dependent network is a monotonically increasing function of the net excitation. By contrast, the response of a stimulus-dependent lateral inhibitory network can either increase, decrease or remain constant as the net excitation of the network is increased, depending on the relation of the inhibition to the excitation. These differences make it possible to determine that the inhibition produced by a lateral inhibitory network is stimulus-dependent if the net response of the network declines as the network excitation increases.

Animals↗
PubMed1995

The topology of the kinetoplast DNA network.

Kinetoplast DNA (kDNA) of trypanosomatid parasites is a network of approximately 5000 catenated DNA minicircles and approximately 25 maxicircles. We developed the following strategy to deduce the topological linkage of the minicircles of the Crithidia fasciculata network. First, we used graph theory to provide precise models of possible network structures. Second, on the basis of these models, we predicted the frequencies of minicircle oligomers expected from random network breakage. Third, we determined the fragmentation pattern of kDNA networks as a function of the extent of digestion. Fourth, by comparison of the results with the predictions, we identified the model that best represents the network. We conclude that each minicircle is linked on average to three other minicircles. A honeycomb arrangement probably results, with each minicircle typically at the vertex of a hexagonal cell. This topology has implications for the assembly, structure, and function of kDNA networks.

Animals↗
PubMed1993

Stimulation of monolayer networks in culture through thin-film indium-tin oxide recording electrodes.

Monolayer networks, obtained from murine spinal cord tissue and grown on a matrix of 64 photo-etched, indium-tin oxide (ITO) microelectrodes, can be electrically stimulated through such thin-film recording electrodes. Multichannel coordinated network activity can be evoked and spontaneous network activity can be modified by generation of additional, multichannel bursting. Although single pulses through 1 electrode may trigger network responses, networks generally react best to short trains of pulses. Response thresholds approximate standard physiological strength/duration relationships. Repetitive stimulation trains often generate network activity patterns akin to epileptiform activity. The ITO conductors remain stable for recording under warm saline for long periods of time (maximum test period: 8 months). However, most electrodes show a reduction in impedance after several thousand stimulus pulses. Electrode breakdown in the form of ITO oxidation and loss of light transmittance occurs before hydrolysis is observed but requires a combination of voltage levels and pulse lengths beyond that needed for effective network stimulation.

Animals↗
PubMed1991

Structure of the basement membrane of corneal epithelium: quick-freeze, deep-etch comparative study of networks deposited in culture and during development.

The basement membranes elaborated by corneal epithelium in the chick embryo and in culture conditions have been studied by quick-freezing and deep-etching methods. Electron microscope observations of en face unidirectional platinum shadow castings revealed a polygonal network comparable to the type IV collagen network described in human amniotic basement membrane and EHS mouse tumor matrix. The material deposited in culture contained type type IV collagen, as demonstrated by immunofluorescence labeling using anti-type IV collagen antibodies and formed delicate networks. Fine filaments and granules composing this network were interpreted respectively as linear and globular NC1 domains of the type IV collagen molecule. These loose networks were considered as first steps in basement membrane assembly. Staggered superimposition of comparable networks could lead to the dense network organization as observed for basement membranes in situ. These observations showed that the basement membrane of the chick embryo corneal epithelium is also organized in a complex polygonal framework that is preserved even when secreted in culture conditions.

Animals↗
PubMed1990

The biocultural context of social networks and depression among the elderly.

The association between the size and structure of social networks and the prevalence of depressive symptoms was examined in a population-based study of 1615 men and women age 65 years and older. Age was significantly associated with marital status, social network index quartile, and the social relationship to the primary source of support. Women and men differed with respect to current marital status, number of close friends and relatives, frequency of face-to-face contact, and participation in voluntary associations and religious institutions. Regardless of their marital status, women were also less likely than men to point to a spouse as their primary source of support. Beck Depression Inventory mean scores and rates of depressive symptoms were inversely associated with social network index and participation in voluntary associations and religious institutions for both men and women. Individuals with no primary source of support or who depended on a relative had significantly higher than expected mean scores and rates of depressive symptoms. Both social network index and social distance to primary source of support were independently associated with depression after controlling for age, sex, and number of chronic conditions. Participation in voluntary associations, social distance from primary source of support, church membership, and number of close friends were also significant independent predictors of depressive symptoms. Results indicate that depressive symptoms are inversely associated with the size of social networks. The structure of these networks, in turn, is influenced by biological factors such as age, physical disability, and mortality of network members, and by culturally-determined rules that define the individuals and institutions available for support. However, these rules appear to differ for men and women.

Aged↗
PubMed1993

A comparison of social support and social networks of black parents and white parents with chronically ill children.

Characteristics of social networks and provision of support were examined for two groups of parents of chronically ill children, one group black and one group white. Black and white parents both reported similarities in the experience of parenting a child with a chronic illness. Both sets of parents relied primarily on family networks to provide much needed support. White networks were twice as large as black networks, although black parents perceived the individuals in their networks as being more supportive. For both groups, the networks were of long duration. Network members were geographically closer to blacks. White parents discussed support mostly in terms of affect. Black parents described support as instrumental actions. Differences in income levels between blacks and whites might account for differing descriptions of support. The experience of having a chronically ill child appears to override racism in the health care system. Black parents did not perceive any problems, based on race, that affected receiving medical care for their children.

Adult↗
PubMed1995

Changes in mobility of synaptic vesicles with assembly and disassembly of actin network.

In a presynaptic terminal, neurotransmitters are stored in synaptic vesicles and secreted into the synaptic cleft as a final step of cell signal transduction. At a static state, the vesicles are retained in the highly dense actin network. Prior to exocytosis, the dense actin network must disassemble or largely be organized. Actin networks are formed in vitro which retain synaptic vesicles prepared from rat cerebral cortex. Dynamic behaviors of synaptic vesicles are measured by the dynamic light scattering method. The D(app) values of synaptic vesicles confined in actin network became less than 1/4 those of free vesicles. The motions of synaptic vesicles are substantially restricted. This means that synaptic vesicles which are liberated from the actin network by detachment of synapsin 1 molecules are still trapped in the cage-like space of actin filaments. The actin network is disassembled by the actin severing protein, gelsolin, which is activated in the presence of microM level free Ca2+ ions. The D(app)(v) values of synaptic vesicles after severing the actin network return to those of free vesicles in the presence of short actin fragments. A molecular model for exocytosis in the synaptic terminal is constructed on the basis of these results.

Actin Cytoskeleton↗
PubMed1996

Ultrafast networks (ATM): first clinical experiences.

Ultrafast networks using asynchronous transfer mode (ATM) technology can provide the bandwidth and throughput that may be sufficient to satisfy the medical imaging community. Several trials are underway to assess the effect of ATM network capabilities on the clinical practice of radiology, by providing immediate interactive radiology consultations between subspecialists and general radiologists at affiliated academic institutions. The hardware to build such networks is now commercially available and its cost is decreasing steadily, but the monthly charges for ATM bandwidth use are still high. Nevertheless, given the tremendous increase in communication capability and data transfer rates possible with ATM networks, cost alone should not be the determining factor for selecting this technology. The ATM concept in general is first reviewed, followed by a description of early clinical ATM network installation in four medical environments worldwide. These medical clusters include: the UCLA affiliated hospitals (UCLA Medical Center, West LA VAMC and Olive-View UCLA Medical Center), the UCSF affiliated hospitals, Duke University Hospitals and a cluster of medical centers in Berlin which have all been connected via ATM networks. The use of ATM technology in these realistic clinical environments is discussed and evaluated for its potential impact on patient care and clinical teaching within radiology departments. From this preliminary study it is concluded that image communications over a regional PACS using an ATM network can allow interactive consultations between different subspecialist and general radiologists or other specialized radiologists spread over different medical centers.

Computer Systems↗
PubMed1992

Social networks as predictors of ischemic heart disease, cancer, stroke and hypertension: incidence, survival and mortality.

Three social network measures were obtained from a randomly sampled cohort of 2603 HMO members in 1970-71. Mortality and first incidence of ischemic heart disease, cancer, stroke, and hypertension were assessed over the next 15 years. Outcome data were adjusted for age, sex, smoking, SES, and baseline health status. Persons with histories of a given morbidity at or prior to baseline were excluded from the analyses of that morbidity. Social network measures, particularly network scope (a measure of the number of different domains in which a person has social contacts), were powerful predictors of 15-year mortality hazard, but weak predictors of incident disease. Only network scope predicted IHD incidence, and none of the other morbidities was predicted by the social network measures. However, social network measures were strong predictors of both cause-specific and all-cause mortality among persons who had incident cases of IHD, cancer, and stroke. These data suggest that social networks may be more effective in supporting recovery after illness has occurred than in preventing the incidence of new disease.

Adult↗
PubMedDate not supplied

Actin cytoskeletal network in aging and cancer.

The cytoskeleton is being recognized as an important modulator of metabolic functions of the cell. The actin cytoskeletal network, in particular, is involved in events regulating cell proliferation and differentiation. The state of actin in a variety of cell types is regulated by signals arising from the cell surface through a wide spectrum of interactions. In this review, we explore the role of actin cytoskeletal network in a series of events which are known to influence cell proliferation and differentiation. These include interaction of actin network with extracellular matrix proteins, cell surface membranes, second messengers, cytoplasmic enzymes and the nucleus. Because of the involvement of the actin network in such diverse interactions, we propose that alterations in the actin cytoskeletal function may be an important aspect of generalized decrease in cellular functions associated with aging. Preliminary data indicate that alterations in the cytoskeletal network do occur in cells obtained from older individuals. Alterations in actin state are also reported during malignant transformation of cells in culture, and in naturally occurring tumors. Taken together, the existing data seem to suggest that changes in the actin cytoskeletal network may be a part of the aging process as well as malignant transformation. Therefore, the study of the actin cytoskeletal network and its regulation has the potential to yield important information regarding cellular senescence and neoplastic transformation.

Actins↗
PubMed1995

Interactions among neural networks for behavior.

In recent years, as our understanding of the pattern-generating networks responsible for a variety of behaviors has increased, the interactions of multiple neural networks have been examined in a number of systems. These studies have shown that functionally related pattern generators can interact extensively, and that the extent to which two or more of these networks interact is not fixed, but can be altered by neuromodulators. Furthermore, a number of studies have begun to elucidate the mechanisms responsible for those interactions. In the crustacean stomatogastric system, for example, neurons can switch between different pattern generators, and whole networks can fuse into single patterns. In addition, several networks can be dismantled, and their components used to generate a new network. The mechanisms responsible for these changes are the same as those involved in other circuit re-configurations, namely alterations of both intrinsic membrane properties of component neurons and alterations in the strength of synapses within the networks.

Animals↗
PubMed2006

Direct visualization of actin nematic network formation and dynamics.

Various actin assemblies within the cell regulate many cellular processes such as cell shape and motility. The mechanical properties of these networks are challenging to measure in vivo. They have been studied in solution by indirect observation methods, such as multiple ball tracking. However, little is known about the behavior of such networks near the crowded cell membrane. Here we used in vitro TIRF microscopy to directly probe the formation of actin networks in real-time near a hydrophilic surface in the presence of crowding agents. We find that under these conditions actin does not form a mesh like network, but either textured nematic liquid crystals or a bundled network. We are directly able to follow the thermal fluctuations of actin filaments within these networks. Prearranged parallel networks of actin filaments near the crowded cell membrane could play a role in the rapid formation of stress fibers or microvilli.

Actin Cytoskeleton↗
PubMedDate not supplied

Oscillatory network with self-organized dynamical connections for synchronization-based image segmentation.

An oscillatory network of columnar architecture located in 3D spatial lattice was recently designed by the authors as oscillatory model of the brain visual cortex. Single network oscillator is a relaxational neural oscillator with internal dynamics tunable by visual image characteristics - local brightness and elementary bar orientation. It is able to demonstrate either activity state (stable undamped oscillations) or "silence" (quickly damped oscillations). Self-organized nonlocal dynamical connections of oscillators depend on oscillator activity levels and orientations of cortical receptive fields. Network performance consists in transfer into a state of clusterized synchronization. At current stage grey-level image segmentation tasks are carried out by 2D oscillatory network, obtained as a limit version of the source model. Due to supplemented network coupling strength control the 2D reduced network provides synchronization-based image segmentation. New results on segmentation of brightness and texture images presented in the paper demonstrate accurate network performance and informative visualization of segmentation results, inherent in the model.

Animals↗
PubMed2006

Dissociated cortical networks show spontaneously correlated activity patterns during in vitro development.

In vitro cultured neuronal networks coupled to microelectrode arrays (MEAs) constitute a valuable experimental model for studying changes in the neuronal dynamics at different stages of development. After a few days in culture, neurons start to connect each other with functionally active synapses, forming a random network and displaying spontaneous electrophysiological activity. The patterns of collective rhythmic activity change in time spontaneously during in vitro development. Such activity-dependent modifications play a key role in the maturation of the network and reflect changes in the synaptic efficacy, fact widely recognized as a cellular basis of learning, memory and developmental plasticity. Getting advantage from the possibilities offered by the MEAs, the aim of our study is to analyze and characterize the natural changes in dynamics of the electrophysiological activity at different ages of the culture, identifying peculiar steps of the spontaneous evolution of the network. The main finding is that between the second and the third week of culture, the network completely changes its electrophysiological patterns, both in terms of spiking and bursting activity and in terms of cross-correlation between pairs of active channels. Then the maturation process can be characterized by two main phases: modulation and shaping in the synaptic functional connectivity of the network (within the first and second week) and general moderate correlated activity, spread over the entire network, with connections properly formed and stabilized (within the fourth and fifth week).

Action Potentials↗
PubMed2004

Social network correlates of self-reported non-fatal overdose.

The leading cause of death among heroin users is drug overdose. The present study examined the relationship between history of self-reported drug overdoses and social network characteristics among cocaine and opiate users. Data were from cross-sectional surveys administered from March 2001 through February 2003 as part of follow-up of an experimental network oriented HIV prevention intervention. A total of 838 participants with histories of cocaine and opiate use completed the survey. Several social network variables were found to be significantly associated with drug overdose in the prior 2 years, including larger number of network members who were injection drug users and a larger number of conflictual ties among the network members. Even after controlling for age, gender, frequency of injection drug and alcohol use, and health status, network variables continued to have a strong association with history of recent overdose. These data suggest that large drug networks should be targeted for drug overdose prevention interventions.

Adult↗