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At least 1,189 records · Page 66Linked to original sources
PubMed1999

A marine snail neurotoxin shares with scorpion toxins a convergent mechanism of blockade on the pore of voltage-gated K channels.

kappa-Conotoxin-PVIIA (kappa-PVIIA) belongs to a family of peptides derived from a hunting marine snail that targets to a wide variety of ion channels and receptors. kappa-PVIIA is a small, structurally constrained, 27-residue peptide that inhibits voltage-gated K channels. Three disulfide bonds shape a characteristic four-loop folding. The spatial localization of positively charged residues in kappa-PVIIA exhibits strong structural mimicry to that of charybdotoxin, a scorpion toxin that occludes the pore of K channels. We studied the mechanism by which this peptide inhibits Shaker K channels expressed in Xenopus oocytes with the N-type inactivation removed. Chronically applied to whole oocytes or outside-out patches, kappa-PVIIA inhibition appears as a voltage-dependent relaxation in response to the depolarizing pulse used to activate the channels. At any applied voltage, the relaxation rate depended linearly on the toxin concentration, indicating a bimolecular stoichiometry. Time constants and voltage dependence of the current relaxation produced by chronic applications agreed with that of rapid applications to open channels. Effective valence of the voltage dependence, zdelta, is approximately 0.55 and resides primarily in the rate of dissociation from the channel, while the association rate is voltage independent with a magnitude of 10(7)-10(8) M-1 s-1, consistent with diffusion-limited binding. Compatible with a purely competitive interaction for a site in the external vestibule, tetraethylammonium, a well-known K-pore blocker, reduced kappa-PVIIA's association rate only. Removal of internal K+ reduced, but did not eliminate, the effective valence of the toxin dissociation rate to a value <0.3. This trans-pore effect suggests that: (a) as in the alpha-KTx, a positively charged side chain, possibly a Lys, interacts electrostatically with ions residing inside the Shaker pore, and (b) a part of the toxin occupies an externally accessible K+ binding site, decreasing the degree of pore occupancy by permeant ions. We conclude that, although evolutionarily distant to scorpion toxins, kappa-PVIIA shares with them a remarkably similar mechanism of inhibition of K channels.

Animals↗
PubMed2004

Porcupine feeding scars and climatic data show ecosystem effects of the solar cycle.

Using North American porcupine (Erethizon dorsatum) feeding scars on trees as an index of past porcupine abundance, we have found that porcupine populations have fluctuated regularly over the past 130 years in the Bas St. Laurent region of eastern Quebec, with superimposed periodicities of 11 and 22 years. Coherency and phase analyses showed that this porcupine population cycle has closely followed the 11- and 22-year solar activity cycles. Fluctuations in local precipitation and temperature were also cyclic and closely related to both the solar cycle and the porcupine cycle. Our results suggest that the solar cycle indirectly sets the rhythm of population fluctuations of the most abundant vertebrate herbivore in the ecosystem we studied. We hypothesize that the solar cycle has sufficiently important effects on the climate along the southern shore of the St. Lawrence estuary to locally influence terrestrial ecosystem functioning. This constitutes strong evidence for the possibility of a causal link between solar variability and terrestrial ecology at the decadal timescale and local spatial scale, which confirms results obtained at greater temporal and spatial scales.

Animals↗
PubMed1998

Acute ethanol administration reduces the cognitive deficits associated with traumatic brain injury in rats.

The present study was designed to determine whether a low dose of acute ethanol administration could attenuate cognitive deficits associated with traumatic brain injury. Adult male rats received oral administration of ethanol or drinking water 2 h prior to surgery to produce a blood ethanol concentration of 100 mg% and then received bilateral contusion injuries of the medial prefrontal cortex. Seven days after surgery, the rats began 10 days of testing for acquisition of spatial localization in the Morris water maze where they were required to find a hidden platform to escape from the water. The results indicate that the rats given ethanol at the time of injury later spent significantly less time searching for the hidden platform than their water-treated counterparts. On a memory probe test given on the final day of testing, in which the platform was removed from the pool, rats given the ethanol spent more time in the area where the platform had been located indicating that they learned its location better than the lesion/water controls. In addition, acute ethanol treatment reduced some of the histopathology that typically occurs following severe contusion of the medial frontal cortex but did not attenuate post-traumatic formation of edema. These results indicate that acute ethanol intoxication can reduce the severity of cognitive impairments caused by contusive traumatic brain injury and support the contention that there is a dose-response relationship of acute ethanol intoxication in the setting of traumatic brain injury.

Animals↗
PubMed2006

Spatiotemporal pattern of macrophage recruitment after chronic nerve compression injury.

The contribution of macrophages to the pathogenesis of chronic nerve compression (CNC) injuries is presently unclear. We examined the time course and spatial localization of macrophage invasion from 24 hours to 28 days post-CNC injury with immunohistochemistry (IHC) and electron microscopy (EM). To clarify the differences in macrophage activity between different peripheral nerve injuries, we compared CNC injury to a nerve crush (CR) injury at similar time points. Entire counts of macrophages with ED1-immunoreactivity (IR) showed a slow, gradual increase in macrophage number from 24 hours to 28 days post-operatively in compressed sections. ED1-IR was greatest at the site of compression and in distal nerve segments with minimal immunostaining in proximal and normal sections. Quantitative analysis of ED1-IR after crush injury demonstrated a rapid time course of macrophage recruitment with ED1-IR peaking at 48 hours and declining to normal values as early as 21 days post-CR injury. Ultrastructural analysis with EM 14 days post-CNC injury revealed greater macrophage localization in the inner one-third region of normal nerves relative to the outer region. Differences in macrophage localization within inner and outer regions of compressed sections were negligible, as macrophages were found diffusely throughout the endoneurium by day 14. Our findings suggest that macrophage recruitment is dependent upon proximity to neural vasculature with relative macrophage density highest specifically around endoneurial blood vessels in both normal and compressed sections. Taken together, our results detail the unique spatiotemporal dynamics of macrophage recruitment early after CNC injury as distinct from a crush injury.

Animals↗
PubMed2002

Vav regulates activation of Rac but not Cdc42 during FcgammaR-mediated phagocytosis.

Phagocytosis is the process whereby cells direct the spatially localized, receptor-driven engulfment of particulate materials. It proceeds via remodeling of the actin cytoskeleton and shares many of the core cytoskeletal components involved in adhesion and migration. Small GTPases of the Rho family have been widely implicated in coordinating actin dynamics in response to extracellular signals and during diverse cellular processes, including phagocytosis, yet the mechanisms controlling their recruitment and activation are not known. We show herein that in response to ligation of Fc receptors for IgG (FcgammaR), the guanine nucleotide exchange factor Vav translocates to nascent phagosomes and catalyzes GTP loading on Rac, but not Cdc42. The Vav-induced Rac activation proceeds independently of Cdc42 function, suggesting distinct roles for each GTPase during engulfment. Moreover, inhibition of Vav exchange activity or of Cdc42 activity does not prevent Rac recruitment to sites of particle attachment. We conclude that Rac is recruited to Fcgamma membrane receptors in its inactive, GDP-bound state and that Vav regulates phagocytosis through subsequent catalysis of GDP/GTP exchange on Rac.

Animals↗
PubMed1997

A ubiquitin-conjugating enzyme is essential for developmental transitions in Dictyostelium.

We have identified a developmentally essential gene, UbcB, by insertional mutagenesis. The encoded protein (UBC1) shows very high amino acid sequence identity to ubiquitin-conjugating enzymes from other organisms, suggesting that UBC1 is involved in protein ubiquitination and possibly degradation during Dictyostelium development. Consistent with the homology of the UBC1 protein to UBCs, the developmental pattern of protein ubiquitination is altered in ubcB-null cells. ubcB-null cells are blocked in the ability to properly execute the developmental transition that occurs between the induction of postaggregative gene expression during mound formation and the induction of cell-type differentiation and subsequent morphogenesis. ubcB-null cells plated on agar form mounds with normal kinetics; however, they remain at this stage for approximately 10 h before forming multiple tips and fingers that then arrest. Under other conditions, some of the fingers form migrating slugs, but no culmination is observed. In ubcB-null cells, postaggregative gene transcripts accumulate to very high levels and do not decrease significantly with time as they do in wild-type cells. Expression of cell-type-specific genes is very delayed, with the level of prespore-specific gene expression being significantly reduced compared with that in wild-type cells. lacZ reporter studies using developmentally regulated and cell-type-specific promoters suggest that ubcB-null cells show an unusually elevated level of staining of lacZ reporters expressed in anterior-like cells, a regulatory cell population found scattered throughout the aggregate, and reduced staining of a prespore reporter. ubcB-null cells in a chimeric organism containing predominantly wild-type cells are able to undergo terminal differentiation but show altered spatial localization. In contrast, in chimeras containing only a small fraction of wild-type cells, the mature fruiting body is very small and composed almost exclusively of wild-type cells, with the ubcB-null cells being present as a mass of cells located in extreme posterior of the developing organism. The amino acid sequence analysis of the UbcB open reading frame (ORF) and the analysis of the developmental phenotypes suggest that tip formation and subsequent development requires specific protein ubiquitination, and possibly degradation.

Amino Acid Sequence↗
PubMed2002

Characterization of human alpha-dystrobrevin isoforms in HL-60 human promyelocytic leukemia cells undergoing granulocytic differentiation.

The biochemical properties and spatial localization of the protein alpha-dystrobrevin and other isoforms were investigated in cells of the human promyelocytic leukemia line HL-60 granulocytic differentiation as induced by retinoic acid (RA). Alpha-dystrobrevin was detected both in the cytosol and the nuclei of these cells, and a short isoform (gamma-dystrobrevin) was modified by tyrosine phosphorylation soon after the onset of the RA-triggered differentiation. Varying patterns of distribution of alpha-dystrobrevin and its isoforms could be discerned in HL-60 promyelocytes, RA-differentiated mature granulocytes, and human neutrophils. Moreover, the gamma-dystrobrevin isoform was found in association with actin and myosin light chain. The results provide new information about potential involvement of alpha-dystrobrevin and its splice isoforms in signal transduction in myeloid cells during induction of granulocytic differentiation and/or at the commitment stage of differentiation or phagocytic cells.

Actins↗
PubMed2003

Receptor-mediated regulation of PI3Ks confines PI(3,4,5)P3 to the leading edge of chemotaxing cells.

Recent studies have demonstrated that PH domains specific for PI(3,4,5)P3 accumulate at the leading edge of a number of migrating cells and that PI3Ks and PTEN associate with the membrane at the front and back, respectively, of chemotaxing Dictyostelium discoideum cells. However, the dependence of chemoattractant induced changes in PI(3,4,5)P3 on PI3K and PTEN activities have not been defined. We find that bulk PI(3,4,5)P3 levels increase transiently upon chemoattractant stimulation, and the changes are greater and more prolonged in pten- cells. PI3K activation increases within 5 s of chemoattractant addition and then declines to a low level of activity identically in wild-type and pten- cells. Reconstitution of the PI3K activation profile can be achieved by mixing membranes from stimulated pi3k1-/pi3k2- cells with cytosolic PI3Ks from unstimulated cells. These studies show that significant control of chemotaxis occurs upstream of the PI3Ks and that regulation of the PI3Ks and PTEN cooperate to shape the temporal and spatial localization of PI(3,4,5)P3.

Animals↗
PubMed2006

Dynamics of Aerenchyma distribution in the cortex of sulfate-deprived adventitious roots of maize.

BACKGROUND AND AIMS: Aerenchyma formation in maize adventitious roots is induced in nutrient solution by the deprivation of sulfate (S) under well-oxygenated conditions. The aim of this research was to examine the extent of aerenchyma formation in the cortex of sulfate-deprived adventitious roots along the root axis, in correlation with the presence of reactive oxygen species (ROS), calcium levels and pH of cortex cells and root lignification. METHODS: The morphometry of the second whorl of adventitious (W2) roots, subject to S-deprivation conditions throughout development, was recorded in terms of root length and lateral root length and distribution. W2 roots divided into sectors according to the mean length of lateral roots, and cross-sections of each were examined for aerenchyma. In-situ detection of alterations in ROS presence, calcium levels and pH were performed by means of fluorescence microscopy using H(2)DCF-DA, fluo-3AM and BCECF, respectively. Lignification was detected using the Wiesner test. KEY RESULTS: S-deprivation reduced shoot growth and enhanced root proliferation. Aerenchyma was found in the cortex of 77 % of the root length, particularly in the region of emerging or developing lateral roots. The basal and apical sectors had no aerenchyma and no aerenchyma connection was found with the shoot. S-deprivation resulted in alterations of ROS, calcium levels and pH in aerenchymatous sectors compared with the basal non-aerenchymatous region. Lignified epidermal layers were located at the basal and the proximal sectors. S-deprivation resulted in shorter lateral roots in the upper sectors and in a limited extension of the lignified layers towards the next lateral root carrying sector. CONCLUSIONS: Lateral root proliferation is accompanied by spatially localized induced cell death in the cortex of developing young maize adventitious roots during S-deprivation.

Calcium↗
PubMedDate not supplied

Functional segregation of color and motion processing in the human visual cortex: clinical evidence.

Anatomical and physiological investigations indicate two major distinct functional streams within the extrastriate visual cortex of the macaque monkey, and behavioral observations suggest that the ventral (occipitotemporal) pathway is the cornerstone for object recognition whereas the dorsal (occipitoparietal) pathway is primarily involved in visuospatial perception and visuomotor performance. In the context of this dichotomy we conducted a psychophysical and neuropsychological study of visual perceptual abilities in two stroke patients, each with lesions involving several extrastriate areas. Magnetic resonance imaging demonstrated bilateral lesions; in one patient (E.W.) the lesion involves the ventral medial portions of the occipital and temporal lobes, and in the other (A.F.) the lesion involves dorsally the occipital-parietal area, including the region of the temporal-parietal-occipital junction. E.W. suffers from achromatopsia of central origin, prosopagnosia, visual agnosia, and alexia without agraphia. His depth and motion perception, including recognition of moving objects, are normal. He has superior visual field loss bilaterally, and slightly impaired acuity, and complains that the world appears in a deep twilight even on a sunny day. In contrast, A.F. shows specific deficits of stereopsis, spatial localization, and several aspects of motion perception. He is also impaired at recognizing objects presented from unconventional views, but recognition of prototypical views of objects, and color and form discrimination are normal, as is his ability to recognize faces. The anatomical characteristics of the lesions of these two patients permit a direct experimental comparison of the effects of lesions confined to the parietal or temporal pathways. E.W.'s and A.F.'s performance on the psychophysical and neuropsychological tasks discussed here supports the functional distinction between a dorsal and a ventral extrastriate system but additionally suggests the existence of a pathway involved in identification-from-motion that is separate from both the dorsal early motion/spatial analysis pathway and the ventral color/static-form pathway.

Cerebrovascular Disorders↗
PubMed2005

Temporal characterization of the neural correlates of perceptual decision making in the human brain.

Single and multi-unit recordings in primates have identified spatially localized neuronal activity correlating with an animal's behavioral performance. Due to the invasive nature of these experiments, it has been difficult to identify such correlates in humans. We report the first non-invasive neural measurements of perceptual decision making, via single-trial EEG analysis, that lead to neurometric functions predictive of psychophysical performance for a face versus car categorization task. We identified two major discriminating components. The earliest correlating with psychophysical performance was consistent with the well-known face-selective N170. The second component, which was a better match to the psychometric function, did not occur until at least 130 ms later. As evidence for faces versus cars decreased, onset of the later, but not the earlier, component systematically shifted forward in time. In addition, a choice probability analysis indicated strong correlation between the neural responses of the later component and our subjects' behavioral judgements. These findings demonstrate a temporal evolution of component activity indicative of an evidence accumulation process which begins after early visual perception and has a processing time that depends on the strength of the evidence.

Adult↗
PubMed1997

Olfactory receptor database (ORDB): a resource for sharing and analyzing published and unpublished data.

An olfactory receptor database (ORDB) is being developed to facilitate analysis of this large gene family. ORDB currently contains over 400 olfactory receptor sequences and related information, and is available via the World Wide Web. We plan to incorporate functional data, structural models, spatial localization and other categories of information, toward an integrated model of olfactory receptor function.

Amino Acid Sequence↗
PubMed1999

Identification of a phosphoinositide binding motif that mediates activation of mammalian and yeast phospholipase D isoenzymes.

Phosphoinositides are both substrates for second messenger-generating enzymes and spatially localized membrane signals that mediate vital steps in signal transduction, cytoskeletal regulation and membrane trafficking. Phosphatidylcholine-specific phospholipase D (PLD) activity is stimulated by phosphoinositides, but the mechanism and physiological requirement for such stimulation to promote PLD-dependent cellular processes is not known. To address these issues, we have identified a site at which phosphoinositides interact with PLD and have assessed the role of this region in PLD function. This interacting motif contains critical basic amino acid residues that are required for stimulation of PLD activity by phosphoinositides. Although PLD alleles mutated at this site fail to bind to phosphoinositides in vitro, they are membrane-associated and properly localized within the cell but are inactive against cellular lipid substrates. Analogous mutations of this site in yeast PLD, Spo14p, result in enzymes that localize normally, but with catalytic activity that has dramatically reduced responsiveness to phosphoinositides. The level of responsiveness to phosphoinositides in vitro correlated with the ability of PLD to function in vivo. Taken together, these results provide the first evidence that phosphoinositide regulation of PLD activity observed in vitro is physiologically important in cellular processes in vivo including membrane trafficking and secretion.

Amino Acid Sequence↗
PubMed1996

Behavioral slowing with age: boundary conditions of the generalized slowing model.

One hundred and twenty-two adults ranging in age from 20 to 83 years participated in this study of visual discrimination and recognition. The simultaneous-matching-to-sample (discrimination) and delayed-matching-to-sample (recognition) paradigms used identical stimuli for spatial frequency, luminance, spatial localization, orientation, pattern, trajectory, and velocity matching. Linear regression analyses indicated that increased age slowed reaction time on the simultaneous-matching tasks. This relationship was not found, however, when subjects were required to match the stimuli after a delay. When older adults' reaction times were regressed on those of adults in their 20s, very different patterns of age-related slowing emerged from the data as a function of task requirements. The results from the simultaneous-matching paradigm replicate previous reports of general slowing on nonlexical tasks, but this was not true for the results from the delayed-matching paradigm, which used similar stimuli but also involved short-term memory.

Adult↗
PubMed1988

An examination of three spatial disease clustering methodologies.

Patterns of disease in space are often analysed to determine whether a relationship exists between a disease outcome and environmental exposures. This report examines the performance of three cluster analytical methods when applied to a single data set. These methods, designed to assess the purely spatial variation of events, have been examined to assess their ability to detect clustering in an area where disease rates have previously been shown to be significantly elevated. The ability of these methods to detect spatial clustering was also examined using simulation techniques. All three methods were found to be poor at detecting spatially localized disease rates which were approximately three time the expected rate, as measured by the relative risk.

California↗
PubMed1999

Spatio-temporal dynamics of resident and immigrating populations of Carcinops pumilio (Coleoptera: Histeridae) in high-rise poultry facilities.

The histerid beetle Carcinops pumilio (Erichson) is an important natural predator of the house fly, Musca domestica L., in accumulated poultry house manure. We examined the spatio-temporal dynamics of establishing adult C. pumilio in high-rise poultry facilities using conventional and geostatistical approaches. The growth curves of resident and immigrating populations followed logistic and exponential equations, respectively, and their rates of establishment were statistically the same. Frequency distributions for both populations were strongly positively skewed, and approximately 53% of sampling intervals were significantly modeled by the negative binomial. Taylor's power law indicated both populations to be aggregated, and gave excellent least squares regression fits to both populations. Correlograms, a geostatistical tool, suggested little local spatial structure (e.g., 2nd order effects) for either population. The resident population was 'randomly' aggregated: beetles were clustered around randomly distributed aggregations of house fly immatures. The immigrating population exhibited significant spatial trends (e.g., 1st order effects) consistently seen at all sampling intervals. C. pumilio spatial structure was represented primarily by this spatial trend; thus, immigration of C. pumilio may have been either a singular event in time, or initiating at 1 or multiple times from a singular location.

Animal Husbandry↗
PubMed2006

Spectral restoration and energy resolution improvement of electron energy-loss spectra by Pixon reconstruction: II. Application to practical ELNES analysis of low SNR.

We applied Pixon deconvolution as introduced in Part I to several practical, examples of low signal-to-noise ratio (SNR), electron energy-loss spectra with a goal toward restoring their fine spectral features and/or improving the energy resolution. We demonstrate that by directly fitting the two-dimensional spectral data recorded on the CCD; the method enables us to reveal fine spectral structures. Consequently, Pixon reconstruction extends the ability to probe electronic states in very spatially localized areas, a capability currently unique to our method.

Algorithms↗
PubMed2001

Prolactin receptor gene expression and immunolocalization of the prolactin receptor in human luteinized granulosa cells.

Prolactin is mainly known for its role in breast development and lactation, but has been also implicated in other physiological functions such as immunoregulation and ovarian steroid production. Although prolactin and prolactin receptor (PRL-R) transcripts have been previously identified in the human ovary, the spatial localization of the receptor is unknown. To investigate the presence of PRL-R within the follicular apparatus, human luteinized granulosa cells were obtained at the time of follicular aspiration from women undergoing ovarian stimulation for IVF. RNA extracted from these cells was subjected to reverse transcriptase-polymerase chain reaction (RT-PCR) using specific primers for the PRL-R gene. In addition, paraffin sections of isolated granulosa cells and sections of premenopausal human ovaries were immunostained with a mouse anti-human PRL-R monoclonal antibody. PRL-R were immunolocalized to the cell membrane of isolated luteinized granulosa cells and PRL-R transcripts were detected in the extracted RNA. No detectable staining was noted in secondary and early antral follicles in archived paraffin sections. These findings confirm the presence of PRL-R in human luteinized granulosa cells and suggest a localized role for PRL within the mature follicle. The absence of PRL-R in the early follicle suggests that the effects of prolactin are exerted around the time of ovulation.

Adult↗