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PubMed1991

Gap-junctional permeability in early and cleavage-arrested ascidian embryos.

Using the whole-cell voltage clamp technique, we have studied junctional conductance (Gj), and Lucifer Yellow (LY) coupling in 2-cell and 32-cell ascidian embryos. Gj ranges from 17.5 to 35.3 nS in the 2-cell embryo where there is no passage of LY, and from 3.5 to 12.2 nS in the later embryo where LY dye spread is extensive. In both cases, Gj is independent of the transjunctional potential (Vj). Manually apposed 2-cell or 32-cell embryos established a junctional conductance of up to 10 nS within 30 min of contact. Furthermore, since we did not observe any significant number of cytoplasmic bridges at the EM and Gj is sensitive to octanol, it is probable that blastomeres in the 2-cell and 32-cell embryos are in communication by gap junctions. In order to compare Gj in the two stages and to circumvent problems of cell size, movement and spatial location, we used cytochalasin B to arrest cleavage. Gj in cleavage-arrested 2-cell embryos ranged from 25.0 to 38.0 nS and remained constant over a period of 2.5 h. LY injected into a blastomere of these arrested embryos did not spread to the neighbour cell until they attained the developmental age of a 32- to 64-cell control embryo. Our experiments indicate a change in selectivity of gap junctions at the 32-cell stage that is not reflected by a macroscopic change in ionic permeability.

Animals↗
PubMed1999

The nature of penumbral depolarizations following focal cerebral ischemia in the rat.

It has been previously suggested that the transient ischemic depolarizations (IDs), thought involved in the gradual expansion of ischemic injury in the first hours following middle cerebral artery occlusion (MCAo), are akin to spreading depression (SD). However, previous studies indicate that the characteristics of these events are heterogeneous (unlike those of SDs). We therefore sought to determine whether different types of IDs exist or not. Using four cortical microelectrodes, we compared the spatial and the temporal characteristics of IDs that occur following intraluminal MCAo in halothane-anesthetized rats to those of electrically induced SDs. An average 4.6+/-3.2 series of events, sequentially affecting the four electrodes, were recorded in 5 h following the induction of ischemia. The distribution of ID duration disclosed two types: short IDs (<7 min, 53% of all events) and long IDs (>7 min; 9% of all events). Most long IDs occurred within the first 30 min and as the initial electrophysiological event. Later on and often restricted to a single or reduced number of recording sites, intermittent IDs were of reduced amplitude or even replaced entirely by suppressed electrocorticographic activity (38% of all events). While the amplitude, duration and spreading characteristics were similar between short IDs and SDs provoked in the cortex of non-ischemic rats, those of long IDs were markedly different. Our results indicate that two types of IDs exist and confirm that most IDs (short ones) are similar in nature to SDs. Long IDs may represent a penumbral anoxic depolarization (AD), reversed by an improvement of perfusion, in the early stages of ischemia. Furthermore, we show that intermittent blockade of depolarization waves occurs and that its incidence increases with time. This blockade may reflect adaptive mechanisms which take place to prevent further depolarizations, the nature of which remains to be determined. The present description of electrophysiological abnormalities might have implications for anti-depolarization therapy in focal cerebral ischemia and to interpret the results of non-invasive techniques which enable the imaging of depolarized areas following stroke.

Animals↗
PubMed2004

Neural organisation in the first optic ganglion of the nocturnal bee Megalopta genalis.

Each neural unit (cartridge) in the first optic ganglion (lamina) of the nocturnal bee Megalopta genalis contains nine receptor cell axons (6 short and 3 long visual fibres), and four different types of first-order interneurons, also known as L-fibres (L1 to L4) or lamina monopolar cells. The short visual fibres terminate within the lamina as three different types (svf 1, 2, 3). The three long visual fibres pass through the lamina without forming characteristic branching patterns and terminate in the second optic ganglion, the medulla. The lateral branching pattern of svf 2 into adjacent cartridges is unique for hymenopterans. In addition, all four types of L-fibres show dorso-ventrally arranged, wide, lateral branching in this nocturnal bee. This is in contrast to the diurnal bees Apis mellifera and Lasioglossum leucozonium, where only two out of four L-fibre types (L2 and L4) reach neighbouring cartridges. In M. genalis, L1 forms two sub-types, viz. L1-a and L1-b; L1-b in particular has the potential to contact several neighbouring cartridges. L2 and L4 in the nocturnal bee are similar to L2 and L4 in the diurnal bees but have dorso-ventral arborisations that are twice as wide. A new type of laterally spreading L3 has been discovered in the nocturnal bee. The extensive neural branching pattern of L-fibres in M. genalis indicates a potential role for these neurons in the spatial summation of photons from large groups of ommatidia. This specific adaptation in the nocturnal bee could significantly improve reliability of vision in dim light.

Animals↗
PubMed1993

Two different spatiotemporal patterns for Ca2+ oscillations in pancreatic acinar cells: evidence of a role for protein kinase C in Ins(1,4,5)P3-mediated Ca2+ signalling.

The oscillations in cytosolic Ca2+ evoked in pancreatic exocrine acinar cells by submaximal concentrations of the two phosphoinositidase-coupled agonists acetylcholine (ACh) and cholecystokinin octapeptide (CCK-8) have very different temporal patterns. In the present study we use digital video imaging of Fura-2 fluorescence to map the spatial distribution of Ca2+ during the oscillating responses to these two agonists. The spatial patterns induced are very different for each of these agonists. ACh oscillations are sinusoidal and initiated at the secretory pole of these morphologically and functionally polarized cells. As they spread across the cell, pronounced gradients in Ca2+ develop that persist throughout the oscillating response. CCK-8 induces a series of discrete Ca2+ transients of longer duration and lower frequency. These elevations in Ca2+ arise slowly, throughout the cells and without any detectable gradients in Ca2+. We consider that the different spatiotemporal patterns can be explained on the basis of a physiologically relevant interaction between Ins(1,4,5)P3 and protein kinase C in second messenger-mediated Ca2+ signalling.

Acetylcholine↗
PubMed1992

Modeling of the quantal release at interneuronal synapses: analysis of permissible values of model moments.

A theoretical study of effects of the different factors on fluctuation of post-synaptic potential (PSP) amplitudes was undertaken, using computation of regions of permissible values (RPV) of the ratio between the variance and the mean number of the quanta released (R1) and the ratio between the third moment and the variance (R2). The RPVs of these indexes for the binomial model were compared with regions determined for a number of models incorporating several factors. It has been shown that the involvement of temporal non-uniformity of transmitter release probability, decremental spreading of potentials along dendrites, and failure of spike propagation give the values of skewness index R2 less, compared to the binomial model. Simultaneously, a number of other factors, especially spatial non-uniformity of release probabilities in single release sites, would give amplitude histograms with high positive values of the index. The values of R1 and R2, calculated for 21 samples of sensorimotor EPSP amplitudes, were biased from RPV of these parameters constructed for the binomial model. The scattergram of R1 and R2 can be explained by the presence of two kinds of contacts which release quantum with different probabilities. The same was true for the beta-model based on the assumption that probabilities of quantal release are a sample of values of random variable that has beta-distribution. From analysis of the distribution of individual release probabilities, obtained from evaluation of beta-model parameters, is concluded that a greater part of boutons in the sensorimotor synapses release transmitter with very low probabilities, there being, however, a few boutons with probabilities close to 1.

Animals↗
PubMed2005

Optimization of sparse synthetic transmit aperture imaging with coded excitation and frequency division.

An effective aperture approach is used for optimization of a sparse synthetic transmit aperture (STA) imaging system with coded excitation and frequency division. A new two-stage algorithm is proposed for optimization of both the positions of the transmit elements and the weights of the receive elements. In order to increase the signal-to-noise ratio in a synthetic aperture system, temporal encoding of the excitation signals is employed. When comparing the excitation by linear frequency modulation (LFM) signals and phase shift key modulation (PSKM) signals, the analysis shows that chirps are better for excitation, since at the output of a compression filter the sidelobes generated are much smaller than those produced by the binary PSKM signals. Here, an implementation of a fast STA imaging is studied by spatial encoding with frequency division of the LFM signals. The proposed system employs a 64-element array with only four active elements used during transmit. The two-dimensional point spread function (PSF) produced by such a sparse STA system is compared to the PSF produced by an equivalent phased array system, using the Field II simulation program. The analysis demonstrates the superiority of the new sparse STA imaging system while using coded excitation and frequency division. Compared to a conventional phased array imaging system, this system acquires images of equivalent quality 60 times faster, when the transmit elements are fired in pairs consecutively and the power level used during transmit is very low. The fastest acquisition time is achieved when all transmit elements are fired simultaneously, which improves detectability, but at the cost of a slight degradation of the axial resolution. In real-time implementation, however, it must be borne in mind that the frame rate of a STA imaging system depends not only on the acquisition time of the data but also on the processing time needed for image reconstruction. Comparing to phased array imaging, a significant increase in the frame rate of a STA imaging system is possible if and only if an equivalent time efficient algorithm is used for image reconstruction.

Models, Theoretical↗
PubMed1999

Spatial and stochastic simulation to evaluate the impact of events and control measures on the 1997-1998 classical swine fever epidemic in The Netherlands. I. Description of simulation model.

The simulation model InterCSF was developed to simulate the Dutch Classical Swine Fever (CSF) epidemic of 1997-98 as closely as possible. InterCSF is a spatial, temporal and stochastic simulation model. The outcomes of the various replications give an estimate of the variation in size and duration of possible CSF-epidemics. InterCSF simulates disease spread from an infected farm to other farms through three contact types (animals, vehicles, persons) and through local spread up to a specified distance. The main disease-control mechanisms that influence the disease spread in InterCSF are diagnosis of the infected farms, depopulation of infected farms, movement-control areas, tracing, and pre-emptive slaughter. InterCSF was developed using InterSpread as the basis. InterSpread was developed for foot-and-mouth disease (FMD). This paper describes the process of modifying InterSpread into InterCSF. This involved changing the assumptions and mechanisms for disease spread from FMD to CSF. In addition, CSF-specific control measures based on the standard European Union (EU) regulations were included, as well as additional control measures that were applied during the Dutch epidemic. To adapt InterCSF as closely as possible to the Dutch 1997/98 epidemic, data from the real epidemic were analysed. Both disease spread and disease-control parameters were thus specifically based on the real epidemic. In general, InterSpread turned out to be a flexible tool that could be adapted to simulate another disease with relative ease. The most difficult were the modifications necessary to mimic the real epidemic as closely as possible. The model was well able to simulate an epidemic with a similar pattern over time for number of detected farms as the real outbreak; but the absolute numbers were (despite many relevant modifications) not exactly the same--but were within an acceptable range. Furthermore, the development of InterCSF provided the researchers with a better insight into the existing knowledge gaps. In part II (see the final paper in this issue), InterCSF was used to compare various control strategies as applied to this epidemic.

Animal Husbandry↗
PubMed1999

'Small worlds' and the evolution of virulence: infection occurs locally and at a distance.

Why are some discases more virulent than others? Vector-borne diseases such as malaria and water-borne diseases such as cholera are generally more virulent than diseases spread by direct contagion. One factor that characterizes both vector- and water-borne diseases is their ability to spread over long distances, thus causing infection of susceptible individuals distant from the infected individual. Here we show that this ability of the pathogen to infect distant individuals in a spatially structured host population leads to the evolution of a more virulent pathogen. We use a lattice model in which reproduction is local but infection can vary between completely local to completely global. With completely global infection the evolutionarily stable strategy (ESS) is the same as in mean-field models while a lower virulence is predicted as infection becomes more local. There is characteristically a period of relatively moderate increase in virulence followed by a more rapid rise with increasing proportions of global infection as we move beyond a 'critical connectivity'. In the light of recent work emphasizing the existence of 'small world' networks in human populations, our results suggests that if the world is getting 'smaller'--as populations become more connected--diseases may evolve higher virulence.

Animals↗
PubMed1973

Receptive field organization of bipolar and amacrine cells in the goldfish retina.

1. Intracellular recordings were made from bipolar and amacrine cells in the isolated goldfish retina. Cells were identified mainly from their response patterns to a spot and an annulus in reference to the knowledge obtained from the previous work of intracellular Procion Yellow injection. Using white light and monochromatic lights receptive field organization of recorded cells were analysed.2. All bipolar cells had a centre-surround organization in their receptive fields. The field centre was estimated to be 100-200 mum in diameter, and the surround 1-1.5 mm.3. Bipolar cells were classified into two types according to the response properties to monochromatic lights. Opponent colour cells received inputs from red and green cones, responding with red on-centre, red and green off-surround or vice versa. Cells without colour coding received input from red cones both in the field centre and the surround. In these cells the centre and the surround were well balanced.4. Amacrine cells were also classified into two types, a sustained type and a transient type. The sustained type amacrine cells responded with a steady potential change and were colour coded. They were hyperpolarized by red and depolarized by green light. The transient type amacrine cells responded with transient depolarization at on and off of light flashes. They received input chiefly from red cones and were not colour coded. Both types of amacrine cells showed a large spatial summation in an area over 2.5 mm; centre-surround antagonism was not seen.5. Comparing the size of the receptive field with anatomy, especially with the size of dendritic spread, the field centre of bipolar cells agreed in size with their dendritic spread. Bipolar cell surround clearly exceeded its dendritic field. Since the response properties of the bipolar cell surround was mimicked most closely by the receptive field of external horizontal cells, the input to the bipolar cell surround is thought to be mediated by external horizontal cells.6. By comparing receptive field properties of various retinal cells it is suggested that both the opponent colour bipolar cells and the colour coded amacrine cells converge on to the double opponent ganglion cells.

Animals↗
PubMed1998

Localization of metastable atom beams with optical standing waves: nanolithography at the heisenberg limit

The spatially dependent de-excitation of a beam of metastable argon atoms, traveling through an optical standing wave, produced a periodic array of localized metastable atoms with position and momentum spreads approaching the limit stated by the Heisenberg uncertainty principle. Silicon and silicon dioxide substrates placed in the path of the atom beam were patterned by the metastable atoms. The de-excitation of metastable atoms upon collision with the surface promoted the deposition of a carbonaceous film from a vapor-phase hydrocarbon precursor. The resulting patterns were imaged both directly and after chemical etching. Thus, quantum-mechanical steady-state atom distributions can be used for sub-0.1-micrometer lithography.

Journal Article↗
PubMed2001

Sensitive nonradioactive detection of mRNA in tissue sections: novel application of the whole-mount in situ hybridization protocol.

The relative insensitivity of nonradioactive mRNA detection in tissue sections compared to the sensitive nonradioactive detection of single-copy DNA sequences in chromosome spreads, or of mRNA sequences in whole-mount samples, has remained a puzzling issue. Because of the biological significance of sensitive in situ mRNA detection in conjunction with high spatial resolution, we developed a nonradioactive in situ hybridization (ISH) protocol for detection of mRNA sequences in sections. The procedure is essentially based on the whole-mount ISH procedure and is at least equally sensitive. Increase of the hybridization temperature to 70C while maintaining stringency of hybridization by adaptation of the salt concentration significantly improved the sensitivity and made the procedure more sensitive than the conventional radioactive procedure. Thicker sections, which were no improvement using conventional radioactive ISH protocols, further enhanced signal. Higher hybridization temperatures apparently permit better tissue penetration of the probe. Application of this highly reliable protocol permitted the identification and localization of the cells in the developing heart that express low-abundance mRNAs of different members of the Iroquois homeobox gene family that are supposedly involved in cardiac patterning. The radioactive ISH procedure scarcely permitted detection of these sequences, underscoring the value of this novel method.

Animals↗
PubMed1994

A simulation of the transmission of HIV and AIDS in regional populations within the United Kingdom.

"The spread of HIV-1 in the United Kingdom is simulated by a model which integrates behavioural and epidemiological processes within a multi-regional population projection framework and represents the spatial heterogeneities in the distribution of HIV which have significant effects on transmission patterns. Analyses determine the significance of different parameters in contributing to prediction uncertainty and highlight the importance of behavioural change and international population movements."

Acquired Immunodeficiency Syndrome↗
PubMed2002

Thalamocortical bursts trigger recurrent activity in neocortical networks: layer 4 as a frequency-dependent gate.

Sensory information reaches the cortex via thalamocortical (TC) synapses in layer 4. Thalamic relay neurons that mediate information flow to cortex operate in two distinct modes, tonic and burst firing. Burst firing has been implicated in enhancing reliability of information flow between individual neurons. However, little is known about how local networks of neocortical neurons respond to different temporal patterns of TC activity. We studied cortical activity patterns evoked by stimulating TC afferents at different frequencies, using a combination of electrophysiology and calcium imaging in TC slices that allowed for the reconstruction of spatiotemporal activity with single-cell resolution. Stimulation of TC axons at low frequencies triggered action potentials in only a small number of layer 4 neurons. In contrast, brief high-frequency stimulus trains triggered widespread recurrent activity in populations of neurons in layer 4 and then spread into adjacent layers 2/3 and 5. Recurrent activity had a clear threshold, typically lasted 300 msec, and could be evoked repetitively at frequencies up to 0.5 Hz. Moreover, the spatial extent of recurrent activity was controlled by the TC pattern of activity. Recurrent activity triggered within the highly interconnected networks of layer 4 might act to selectively amplify and redistribute transient high-frequency TC inputs, filter out low-frequency inputs, and temporarily preserve a record of past sensory activity.

Action Potentials↗
PubMed1991

[Value of computerized tomography and nuclear magnetic resonance tomography in diagnosis of tumorous processes of the bronchial system].

In the evaluation of the local and regional spread of tumors of the bronchi, CT and MR provide similar information. CT seems to be the method of choice for the routine work-up, because of the higher spatial resolution, the better availability, and the lower costs. MR should be used if an infiltration of the heart is suspected. MR can used if the relationship of the tumor to the neighboring structures should be visualized other than in the transverse plane preoperatively.

Carcinoma, Bronchogenic↗
PubMed1984

[Epizootiological evaluation of intestinal yersiniasis in Sakhalin Province].

The work presents the data obtained as the result of the study of intestinal yersiniosis in the synanthropic and natural foci of the Sakhalin region. The circle of Yersinia carriers spreading this infection in the household and natural biocenoses has been established. For the first time the data on the water-type natural focus of yersiniosis with its specific spatial structure, detected on the Tyuleny Island, are published.

Animals↗
PubMed2006

A multipinhole small animal SPECT system with submillimeter spatial resolution.

Single photon emission computed tomography (SPECT) is an important technology for molecular imaging studies of small animals. In this arena, there is an increasing demand for high performance imaging systems that offer improved spatial resolution and detection efficiency. We have designed a multipinhole small animal imaging system based on position sensitive avalanche photodiode (PSAPD) detectors with the goal of submillimeter spatial resolution and high detection efficiency, which will allow us to minimize the radiation dose to the animal and to shorten the time needed for the imaging study. Our design will use 8 x 24 mm2 PSAPD detector modules coupled to thallium-doped cesium iodide [CsI(Tl)] scintillators, which can achieve an intrinsic spatial resolution of 0.5 mm at 140 keV. These detectors will be arranged in rings of 24 modules each; the animal is positioned in the center of the 9 stationary detector rings which capture projection data from the animal with a cylindrical tungsten multipinhole collimator. The animal is supported on a bed which can be rocked about the central axis to increase angular sampling of the object. In contrast to conventional SPECT pinhole systems, in our design each pinhole views only a portion of the object. However, the ensemble of projection data from all of the multipinhole detectors provide angular sampling that is sufficient to reconstruct tomographic data from the object. The performance of this multipinhole PSAPD imaging system was simulated using a ray tracing program that models the appropriate point spread functions and then was compared against the performance of a dual-headed pinhole SPECT system. The detection efficiency of both systems was simulated and projection data of a hot rod phantom were generated and reconstructed to assess spatial resolution. Appropriate Poisson noise was added to the data to simulate an acquisition time of 15 min and an activity of 18.5 MBq distributed in the phantom. Both sets of data were reconstructed with an ML-EM reconstruction algorithm. In addition, the imaging performance of both systems was evaluated with a uniformity phantom and a realistic digital mouse phantom. Simulations show that our proposed system produces a spatial resolution of 0.8 mm and an average detection efficiency of 630 cps/MBq. In contrast, simulations of the dual-headed pinhole SPECT system produce a spatial resolution of 1.1 mm and an average detection efficiency of 53 cps/MBq. These results suggest that our novel design will achieve high spatial resolution and will improve the detection efficiency by more than an order of magnitude compared to a dual-headed pinhole SPECT system. We expect that this system can perform SPECT with submillimeter spatial resolution, high throughput, and low radiation dose suitable for in vivo imaging of small animals.

Animals↗
PubMed2004

Spatially and temporally distinct expression of fibroblast connexins after sheep ventricular infarction.

OBJECTIVES: Myocardial infarction leads to extensive changes in the organization of cardiac myocytes and fibroblasts, and changes in gap junction protein expression. In the immediate period following ischemia, reperfusion causes hypercontraction, spreading the necrotic lesion. Further progressive infarction continues over several weeks. In reperfusion injury, the nonspecific gap junction channel uncoupler heptanol limits necrosis. We hypothesize that gap junction coupling and fibroblast invasion provide a substrate for progressive infarction via a gap junction mediated bystander effect. METHODS: A sheep coronary occlusion infarct model was used with samples collected at 12, 24 and 48 h, and 6, 12 and 30 d (days) post-infarction. Immunohistochemical labelling of gap junction connexins Cx40, Cx43, and Cx45 was combined with cell-specific markers for fibroblasts (anti-vimentin) and myocytes (anti-myomesin). Double and triple immunolabelling and confocal microscopy were used to follow changes in cardiac myocyte morphology, fibroblast content and gap junction expression after myocardial infarction. Gap junction protein levels and fibroblast numbers were quantified. RESULTS: Within 12 h of ischemia, myocyte viability is impaired within small islands in the ischemic region. These islands spread and fuse into larger infarct zones until 12 d post-infarction. Thereafter, surviving myocytes within the infarct and in the border-zone appear to become stabilized. Distant from the infarct, continuing myocyte disruption is regularly observed, even after 30 d. Cx43 becomes redistributed from intercalated discs to the lateral surface of structurally compromised myocytes within 12 d. Cx45 expressing fibroblasts infiltrate the damaged region within 24 h, becoming most numerous at 6-12 d post-infarction, with peak Cx45 levels at 6 d. Later, Cx43 expressing fibroblasts are observed, and the related Cx43 label increases over the 30 d observation period, even though fibroblast numbers decline after 12 d. Cx40 was only seen in vascular endothelium. CONCLUSIONS: Progressive infarction, identified by myocyte sarcomere disruption and subsequent cell loss, occurs in parallel with fibroblast invasion and gap junction remodeling. Two fibroblast phenotypes occur within infarcts, expressing either Cx43 or Cx45. Coupled fibroblasts may play a number of roles in tissue remodeling following myocardial infarction, including provision of a possible substrate for progressive infarction via a gap junction mediated bystander effect.

Animals↗
PubMed1997

Pixel independence: measuring spatial interactions on a CRT display.

The standard working assumption of careful CRT imaging is that each pixel is imaged independently, through a point nonlinearity (the monitor's gamma function, relating screen luminance to input voltage), and then blurred by the point-spread function of the beam spot on the phosphor. Unfortunately most monitors have inadequate video bandwidth, DC restoration, and high-voltage regulation to live up to this ideal model. Two tests are recommended for assessing a CRT's deviation from the pixel-independence model.

Computer Terminals↗