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PubMed2001

Autoregressive spatial smoothing and temporal spline smoothing for mapping rates.

This article proposes generalized additive mixed models for the analysis of geographic and temporal variability of mortality rates. This class of models accommodates random spatial effects and fixed and random temporal components. Spatiotemporal models that use autoregressive local smoothing across the spatial dimension and B-spline smoothing over the temporal dimension are developed. The objective is the identification of temporal treads and the production of a series of smoothed maps from which spatial patterns of mortality risks can be monitored over time. Regions with consistently high rate estimates may be followed for further investigation. The methodology is illustrated by analysis of British Columbia infant mortality data.

Biometry↗
PubMed2006

Multiplex analysis of inflammatory signaling pathways using a high-content imaging system.

This chapter describes a robust high-content cellular screening assay to simultaneously analyze the spatiotemporal activation of three different kinase-associated signaling pathways involving NF-kappaB, JNK, and p38, all of which are closely implicated in proliferative and proinflammatory responses. Signal transduction is dependent on the translocation of NF-kappaB p65 and phosphorylated c-Jun and p38 from the cytosol to the nucleus, and fluorescent immunolabeling was used to monitor changes in their cellular distribution. Cellular screening, data acquisition, and data interpretation were conducted on the ArrayScan HCS Reader (Cellomics Inc., Pittsburgh, PA). Assay adaptation to various cellular systems is feasible when sufficient separation of the nuclear and cytosolic compartment can be achieved and if cell adhesion properties permit proper attachment to the culture plates. Substitution of NF-kappaB p65 and phosphorylated forms of c-Jun and p38 as targets to analyze other translocating components is possible and is limited primarily by antibody specificity and the risk of fluorescent bleed-through between emission channels. Because assay validity is particularly confounded by inadequate spectral separation of the detection dyes in multicolor labeling assays, means of eliminating or counterbalancing staining artifacts are illustrated. Also, protocol parameter settings important for imaging and image processing are described, including object identification, image exposure settings, separation of cytosolic and nuclear regions, number of cells sufficient for analysis, and the use of gating thresholds critical for cell sorting and subpopulation analysis. This assay is a useful tool to investigate the interplay between signaling pathways and the mode of action, potency, and selectivity of compound inhibition of specific target molecules in a cellular context.

Cell Nucleus↗
PubMed2000

Spatiotemporal properties of fast and slow neurons in the pretectal nucleus lentiformis mesencephali in pigeons.

Neurons in the pretectal nucleus lentiformis mesencephali (LM) are involved in the analysis of optic flow that results from self-motion. Previous studies have shown that LM neurons have large receptive fields in the contralateral eye, are excited in response to largefield stimuli moving in a particular (preferred) direction, and are inhibited in response to motion in the opposite (anti-preferred) direction. We investigated the responses of LM neurons to sine wave gratings of varying spatial and temporal frequency drifting in the preferred and anti-preferred directions. The LM neurons fell into two categories. "Fast" neurons were maximally excited by gratings of low spatial [0.03-0.25 cycles/ degrees (cpd)] and mid-high temporal frequencies (0.5-16 Hz). "Slow" neurons were maximally excited by gratings of high spatial (0.35-2 cpd) and low-mid temporal frequencies (0.125-2 Hz). Of the slow neurons, all but one preferred forward (temporal to nasal) motion. The fast group included neurons that preferred forward, backward, upward, and downward motion. For most cells (81%), the spatial and temporal frequency that elicited maximal excitation to motion in the preferred direction did not coincide with the spatial and temporal frequency that elicited maximal inhibition to gratings moving in the anti-preferred direction. With respect to motion in the anti-preferred direction, a substantial proportion of the LM neurons (32%) showed bi-directional responses. That is, the spatiotemporal plots contained domains of excitation in addition to the region of inhibition. Neurons tuned to stimulus velocity across different spatial frequency were rare (5%), but some neurons (39%) were tuned to temporal frequency. These results are discussed in relation to previous studies of the responses of neurons in the accessory optic system and pretectum to drifting gratings and other largefield stimuli.

Animals↗
PubMed2004

Blue-yellow signals are enhanced by spatiotemporal luminance contrast in macaque V1.

We measured the color tuning of a population of S-cone-driven V1 neurons in awake, fixating monkeys. Analysis of randomly chosen color stimuli that were effective in evoking action potentials showed that these neurons received opposite sign input from the S cones and a combination of L and M cones. Surprisingly, these cells also responded to LM cone contrast irrespective of polarity, a nonlinear sensitivity that was masked by conventional linear analysis methods. Taken together, these observations can be summarized in a nonlinear model that combines nonopponent and opponent signals such that luminance contrast enhances color processing. These findings indicate that important aspects of the cortical representation of color cannot be described by classical linear analysis, and reveal a possible neural correlate of perceptual color-luminance interactions.

Action Potentials↗
PubMed2003

Statistical mapping of scalp-recorded ictal EEG records using wavelet analysis.

PURPOSE: The wavelet transform (WT) is well suited for the analysis of signals whose characteristics vary rapidly over time. We devised a computerized method for objective scoring of scalp-recorded seizures that takes advantage of the WT. METHODS: Using wavelet coefficients as a metric, we devised a statistical scoring method aimed at detecting significant and sustained rhythmic buildup. The approach was used to create spatiotemporal significance maps for each seizure. Each seizure was also independently analyzed by computer and an expert reader not involved in the clinical workup or computer analysis of these patients. Hierarchical decision rules for determining seizure lateralization and localization were established from a training set of seizures and subsequently tested on those from an independent test set of seizures. The test dataset included a total of 57 scalp-recorded seizures from 18 patients, each with a > or =12-month seizure-free surgical outcome. RESULTS: Validation was determined by the site of surgical resection. Of the 57 seizure records in the test dataset, the computerized approach resulted in 48 correctly lateralized seizures as compared to 34 for the expert reader. Further, the computer correctly localized 41 seizures to the expert's 31. CONCLUSIONS: The method presented appears to provide an objective basis for the intrachannel scoring of ictal EEGs with minimal interference from artifacts and intermittent discharges. Although the approach has so far shown a substantial improvement over expert scoring in estimating the lateralization and locus of seizure onset, further testing is required to fully evaluate fully its diagnostic accuracy.

Brain Mapping↗
PubMed1997

Intra-operative localization of sensorimotor cortex by cortical somatosensory evoked potentials: from analysis of waveforms to dipole source modeling.

Intra-operative localization of sensorimotor cortex is of increasing importance as neurosurgical techniques allow safe and accurate removal of lesions around the central sulcus. Although direct cortical recordings of somatosensory evoked potentials (SEPs) are known to be helpful for cortical localization, source localization models can provide more precise estimates than subjective visual analysis. In addition to intra-operative analysis of waveforms and amplitudes of SEPs to median nerve stimulation in 20 neurosurgical patients, we used a spatiotemporal dipole model to determine the location of the equivalent dipoles consistent with the cortical distribution of the SEPs. The early cortical SEPs were modeled by 2 equivalent dipoles located in the postcentral gyrus. The first dipole was primarily tangentially oriented and explained N20 and P20 peaks. The second dipole was primarily radially oriented and explained P25 activity. We found consistent localization of the first dipole in the postcentral gyrus, which was always located within 8 mm of the central sulcus, with an average distance of 3 mm. This finding provides an objective basis for using the SEP phase reversal method for cortical localization. We conclude that dipole source modeling of the cortical SEPs can be considered as an objective way of localizing the cortical hand sensory area.

Adolescent↗
PubMed1999

Energy model for contrast detection: spatiotemporal characteristics of threshold vision.

A model for contrast detection of spatiotemporal stimuli is proposed which consists of a spatiotemporal linear filter, an energy device and a threshold device. Assuming the existence of independent intrinsic noise, the probability of stimulus detection was approximated by a Weibull function of the response energy. With this assumption, the stimulus energy is a constant at fixed detection probability. This energy model for contrast detection satisfactorily accounted for the elliptical threshold contours of line pairs at stimulus separations within the range 2-30 min and at stimulus onset asynchronies within the range 20-140 ms. The threshold contour at a large stimulus onset asynchrony (300 ms) was in the form of a rounded square. This finding was explained by assuming that the probability of seeing the line pair was determined by the joint probability that at least one stimulus had been detected. With the energy model, the temporal and spatial autocorrelation functions of the response to a flashed line were evaluated. The autocorrelation functions thus determined were used to predict the temporal contrast sensitivity function to a flickering line stimulus and the spatial contrast sensitivity function to flashed gratings, which were in agreement with the experimental data. The data obtained were fitted adequately by an impulse response approximated by a spatiotemporal Gabor-like function.

Contrast Sensitivity↗
PubMed2005

Electrochemical imaging of fusion pore openings by electrochemical detector arrays.

Opening of individual exocytotic fusion pores in chromaffin cells was imaged electrochemically with high time resolution. Electrochemical detector arrays that consist of four platinum microelectrodes were microfabricated on a glass coverslip. Exocytosis of single vesicles containing catecholamines from a cell positioned on top of the array is detected by the individual electrodes as a time-resolved oxidation current, reflecting the time course of arrival of catecholamine molecules at the electrode surfaces. The signals exhibit low noise and reveal foot signals indicating fusion pore formation and expansion. The position of individual release events is determined from the fraction of catecholamines recorded by the individual electrodes. Simultaneous fluorescence imaging of release of acridine orange from individual vesicles confirmed the electrochemical position assignments. This electrochemical camera provides very high time resolution, spatiotemporal localization of individual fusion pore openings and quantitative data on the flux of transmitter from individual vesicles. Analysis of the amperometric currents employing random walk simulations indicates that the time course of amperometric spikes measured near the cell surface is due to a low apparent diffusion coefficient of catecholamines near the cell surface and not due to slow dissociation from the granular matrix.

Acridine Orange↗
PubMed1996

Activation of brain-type cannabinoid receptors interferes with preimplantation mouse embryo development.

The recent identification and cloning of guanine nucleotide regulatory protein-coupled brain-type and spleen-type cannabinoid receptors (CB1-R and CB2-R, respectively) provide evidence that many of the effects of cannabinoids are mediated via these receptors. Our recent observation of expression of both CB1-R and CB2-R genes in the preimplantation mouse embryo suggests that it could also be a target for cannabinoids. Indeed, cannabinoid agonists interfered with preimplantation embryo development in vitro. To examine whether cannabinoid effects on preimplantation embryos are mediated via CB1-R, we developed rabbit antipeptide antibodies against the N-terminal region of CB1-R and examined the receptor protein in the blastocyst by Western blotting and its spatiotemporal distribution in preimplantation mouse embryos by immunohistochemistry. Cannabinoid binding sites in the blastocyst were examined by Scatchard analysis, while the reversibility of cannabinoid-induced embryonic arrest in vitro was monitored using a specific antagonist to CB1-R, SR141716A. Western blot analysis detected a major band of approximately 59 kDa and a minor band of approximately 54 kDa in the blastocyst. Immunocytochemistry detected this receptor protein from the 2-cell through the blastocyst stages. Scatchard analysis using 3H-anandamide (an endogenous ligand) showed a single class of binding sites in Day 4 blastocysts with an apparent Kd of 1.0 nM and Bmax of 0.09 fmol/blastocyst. Considering the total number of cells (approximately 50) and total protein content (approximately 20 ng) of a blastocyst, it is apparent that the mouse blastocyst has many more high-affinity receptors than those in the mouse brain (Kd: 1.8 nM and Bmax: 18.8 pmol/mg membrane protein). Cannabinoid agonists and the CB1-R antagonist SR141716A effectively competed for anandamide binding in the blastocyst. To determine whether cannabinoid inhibition of embryonic development could be reversed by SR141716A, 2-cell embryos were cultured in the presence of cannabinoid agonists with or without SR141716A for 72 h. Most of the 2-cell embryos cultured in the absence of the agonists developed into blastocysts (approximately 90%). In contrast, the addition of cannabinoid agonists anandamide, Win 55212-2, or CP 55,940 in the culture medium severely compromised embryonic development: more than 60% of the 2-cell embryos failed to develop to blastocysts. A reduction in trophectoderm cell numbers was noted in those blastocysts that escaped the developmental arrest in the presence of cannabinoid agonists. However, this reduction was corrected when embryos were cultured simultaneously with an agonist and SR141716A. Furthermore, embryonic arrest was reversed when embryos were cultured simultaneously in the presence of an agonist and SR141716A. The addition of SR141716A alone in the culture medium apparently had no effects on embryonic development: more than 90% of the embryos developed into blastocysts. The results suggest that the CB1 receptors in preimplantation mouse embryos are biologically active and cannabinoid effects on them are primarily mediated by these receptors.

Analgesics↗
PubMed2006

NG2 colocalizes with axons and is expressed by a mixed cell population in spinal cord lesions.

The NG2 proteoglycan is of general interest after spinal cord injury because it is expressed by oligodendrocyte progenitors (OPCs), which contribute to central nervous system remyelination; however, NG2 may inhibit axon regeneration. We and others have examined the spatiotemporal expression of NG2 after spinal cord injury (SCI). Here, we extend those observations and provide a comprehensive analysis of the distribution, phenotype, and colocalization of NG2 cells with axons in a clinically relevant model of spinal contusion. Because contusion models mimic the majority of human SCI, this information is important for understanding endogenous processes that promote and/or prevent repair. The data demonstrate that NG2 levels rise significantly between 3 and 7 days postinjury (dpi) and remain elevated chronically throughout the lesions. NG2 within the lesions could be derived from an array of infiltrating cells; thus, a panel of antibodies was used to investigate NG2 cell phenotypes. First, platelet-derived growth factor-alpha receptor (PDGFalphaR) colocalization was examined because OPCs normally express both markers. PDGFalphaR cells were present in lesions at all times examined. However, only 37% of NG2 cells coexpressed PDGFalphaR at 14 dpi, which dropped to <1% by 70 dpi. This contrasts with the nearly complete overlap in spared tissue surrounding the lesion. In contrast, 40% to 60% of NG2 cells expressed p75 and approximately 84% expressed Sox10, suggesting that many NG2 cells were nonmyelinating Schwann cells. Despite rising levels of NG2, we noted robust and sustained axon growth into the lesions, many of which were located along NG2 profiles. Thus, spinal contusion produces an NG2-rich environment into which axons grow and in which the source of NG2 appears considerably different from that in surrounding spared tissue.

Animals↗
PubMed2006

Inference of cowpox virus transmission rates between wild rodent host classes using space-time interaction.

There have been virtually no studies of 'who acquires infection from whom' in wildlife populations, but patterns of transmission within and between different classes of host are likely to be reflected in the spatiotemporal distribution of infection among those host classes. Here, we use a modified form of K-function analysis to test for space-time interaction among bank voles and wood mice infectious with cowpox virus. There was no evidence for transmission between the two host species, supporting previous evidence that they act as separate reservoirs for cowpox. Among wood mice, results suggested that transmission took place primarily between individuals of the opposite sex, raising the possibility that cowpox is sexually transmitted in this species. Results for bank voles indicated that infected females might be a more important source of infection to either sex than are males. The suggestion of different modes of transmission in the two species is itself consistent with the apparent absence of transmission between species.

Animals↗
PubMed2002

Possible neural coding with interevent intervals of synchronous firing.

Neural networks composed of excitable neurons with noise generate rich nonlinear dynamics with spatiotemporal structures of neuronal spikes. Among various spatiotemporal patterns of spikes, synchronous firing has been studied most extensively both with physiological experimentation and with theoretical analysis. In this paper, we consider nonlinear neurodynamics in terms of synchronous firing and possibility of neural coding with such synchronous firing, which may be used in the "noisy brain." In particular, reconstruction of a chaotic attractor modeling a dynamical environment is explored with interevent intervals of synchronous firing from the perspective of nonlinear time series analysis and stochastic resonance.

Journal Article↗
PubMed2000

Recurrent patterns of atrial depolarization during atrial fibrillation assessed by recurrence plot quantification.

The aim of this study was to determine the presence of organization of atrial activation processes during atrial fibrillation (AF) by assessing whether the activation sequences are wholly random or are governed by deterministic mechanisms. We performed both linear and nonlinear analyses based on the cross correlation function (CCF) and recurrence plot quantification (RPQ), respectively. Recurrence plots were quantified by three variables: percent recurrence (PR), percent determinism (PD), and entropy of recurrences (ER). We recorded bipolar intra-atrial electrograms in two atrial sites during chronic AF in 19 informed subjects, following two protocols. In one, both recording sites were in the right atrium; in the other protocol, one site was in the right atrium, the other one in the left atrium. We extracted 19 episodes of type I AF (Wells' classification). RPQ detected transient recurrent patterns in all the episodes, while CCF was significant only in ten episodes. Surrogate data analysis, based on a cross-phase randomization procedure, decreased PR, PD, and ER values. The detection of spatiotemporal recurrent patterns together with the surrogate data results indicate that during AF a certain degree of local organization exists, likely caused by deterministic mechanisms of activation.

Adult↗
PubMed2001

Growth characteristics of glioblastoma spheroids.

Cell spheroids have been proposed as models of early tumor growth from which a better understanding of tumor cell heterogeneity and its effects on treatment response might be gained. Results of experiments performed to understand the underlying dynamics of cell growth within a spheroid formed by SNB19, a high-grade glioblastoma cell line, are presented. We discuss the spatiotemporal distribution of the cells and their cell cycle status based on physical measurements, immunohistochemistry, and flow cytometry analysis. The size of the spheroids and their growth rates were dependent on the initial cell number, the proliferation was mostly limited to the outermost region as the spheroids grew in size, and the number of dead cells increased with age and size as well. Interestingly, though the population of the proliferating cells became localized to the outer rim as spheroids grew, the fraction of proliferating cells did not change drastically. Also, our data reveal that the calculated density varied with respect to age of the spheroid as well as position within the spheroid. We show that a simple exponential model is not adequate for modelling the growth characteristics that have been seen by these experiments. In contradiction to available studies, we report that an acellular (necrotic) center appeared and then disappeared during the period of investigation. Furthermore, after the acellular region disappeared, a few proliferative cells appeared in the center area, raising many questions about the growth-related dynamics of the spheroids formed by this particular cell type.

Antigens, Neoplasm↗
PubMed2003

Expression analysis of a tyrosinase promoter sequence in zebrafish.

Sequence comparisons and functional analysis of the 5' upstream regions of tyrosinase genes have revealed the importance of cis-regulatory elements acting to control the spatiotemporal expression of tyrosinase in the melanocytes and retinal pigmented epithelium of developing embryos. To date there are no reports addressing the control of tyrosinase gene transcription in zebrafish, a vertebrate model organism of increasing importance. To exploit the tyrosinase gene as a marker in zebrafish we set out to clone its promoter and analyse its regulation during embryogenesis. Amplification of a zebrafish tyrosinase complementary DNA fragment by reverse transcriptase polymerase chain reaction allowed us to isolate and sequence a 1041 nt genomic DNA fragment that includes a transcription initiation site and 73 nt of the open reading frame. Bioinformatic analysis of this genomic sequence revealed five E-box motifs, including one CATGTG type E-box present in a putative initiation region. These are conserved positive regulatory elements in vertebrate tyrosinase promoters. We show that a region of 814 nt upstream from the translation start site of the zebrafish tyrosinase gene can drive expression in retinal pigmented epithelium in transiently transgenic zebrafish embryos but that its activity is not restricted to melanin-producing cells. This region is unable to drive transcription in human melanoma cell lines. Ectopic expression from this zebrafish tyrosinase promoter fragment is probably due to the absence of positive and negative cis-regulatory elements, such as a tyrosinase distal element, which is known to function as a pigment cell-specific enhancer.

Animals↗
PubMed2001

A multi-channel whisker stimulator for producing spatiotemporally complex tactile stimuli.

A system is described that delivers complex, biologically realistic, tactile stimuli to the rat's facial whisker pad by independently stimulating up to 16 individual facial whiskers in a flexible yet highly controlled and repeatable manner. The system is technically simple and inexpensive to construct. The system consists of an array of 16 miniature-solenoid driven actuators that are attached to 16 individual facial whiskers via very small (130 microm dia.) Teflon-coated stainless steel wires. When individual solenoids are energized, the wire is rapidly retracted, resulting in a deflection of individual whiskers. The rise time of deflection is approx. 1 mm/ms. Repeatable stimulation of individual whiskers can be achieved without touching adjacent whiskers, thereby allowing a very high density of stimulators to be attached within the spatially restricted region of the facial whisker pad. Complex patterns of whisker stimulation (designed to mimic biologically realistic stimuli) are delivered to the whisker pad by activating individual solenoid actuators in precisely controlled temporal patterns. These stimulations can be combined with multi-electrode single-unit ensemble recordings at multiple sites within the rat trigeminal somatosensory system. Analysis of neuronal population responses to these complex stimuli is intended to examine how the trigeminal somatosensory system encodes and processes spatiotemporally complex stimuli.

Animals↗
PubMed2005

Decreased glutathione transferase levels in rd1/rd1 mouse retina: replenishment protects photoreceptors in retinal explants.

Currently much attention is focused on glutathione S transferase (GST)-induced suppression of apoptosis. The objective of our studies was therefore to see if GST isoenzymes rescue photoreceptors in retinal explants from rd1/rd1 mice, in which photoreceptors degenerate rapidly. Eyes from C3H rd1/rd1 and +/+ mice were collected at various time points between postnatal day (PN) 2 and PN28. Localization and content of alpha-GST and mu-GST was investigated by immunofluorescence and semi-quantitative Western blot analysis, respectively. In addition, PN2 and PN7 retinal explants were cultured till PN28, during which they were treated with 10 ng/ml alpha-GST or mu-GST. The spatiotemporal expression of both GST isoforms was closely similar: early presence in ganglion cell layer after which staining became restricted to Muller cells (particularly in the endfeet) and horizontal cell fibers in both rd1/rd1 and +/+. Doublets of alpha-GST and mu-GST were detected by Western blot analysis. Densitometry of these bands indicated steady reduction of alpha-GST content in rd1/rd1 retina starting from the second postnatal week. When alpha-GST and mu-GST were added exogenously to rd1/rd1 explants, photoreceptor rescue was produced that was more prominent in PN2 than in PN7 explants and more effective by alpha-GST than mu-GST. We propose that alpha-GST neuroprotection is mediated by reduction of tissue oxidative stress.

Animals↗
PubMedDate not supplied

High-frequency periodic sources underlie ventricular fibrillation in the isolated rabbit heart.

The mechanism(s) underlying ventricular fibrillation (VF) remain unclear. We hypothesized that at least some forms of VF are not random and that high-frequency periodic sources of activity manifest themselves as spatiotemporal periodicities, which drive VF. Twenty-four VF episodes from 8 Langendorff-perfused rabbit hearts were studied using high-resolution video imaging in conjunction with ECG recordings and spectral analysis. Sequential wavefronts that activated the ventricles in a spatially and temporally periodic fashion were identified. In addition, we analyzed the lifespan and dynamics of wavelets in VF, using a new method of phase mapping that enables identification of phase singularity points (PSs), which flank individual wavelets. Spatiotemporal periodicity was found in 21 of 24 episodes. Complete reentry on the epicardial surface was observed in 3 of 24 episodes. The cycle length of discrete regions of spatiotemporal periodicity correlated highly with the dominant frequency of the optical pseudo-ECG (R(2)=0.75) and with the global bipolar electrogram (R(2)=0.79). The lifespan of PSs was short (14.7+/-14.4 ms); 98% of PSs existed for <1 rotation. The mean number of waves entering (6.50+/-0.69) exceeded the mean number of waves that exited our mapping field (4.25+/-0.56; P<0.05). These results strongly suggest that ongoing stable sources are responsible for the majority of the frequency content of VF and therefore play a role in its maintenance. In this model, multiple wavelets resulting from wavebreaks do not appear to be responsible for the sustenance of this arrhythmia, but are rather the consequence of breakup of high-frequency activation from a dominant reentrant source.

Animals↗