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PubMed1984

Neuromagnetic evidence of spatially distributed sources underlying epileptiform spikes in the human brain.

Neuromagnetic measurements were performed on 17 subjects with focal seizure disorders. In all of the subjects, the interictal spike in the scalp electroencephalogram was associated with an orderly extracranial magnetic field pattern. In eight of these subjects, multiple current sources underlay the magnetic spike complex. The multiple sources within a given subject displayed a fixed chronological sequence of discharge, demonstrating a high degree of spatial and temporal organization within the interictal focus.

Brain↗

PubMed1997

Spatial distribution of kainate receptor subunit mRNA in the mouse basal ganglia and ventral mesencephalon.

In an attempt to gain knowledge of the possible functions of kainate receptors, we have used in situ hybridization to examine the regional and cellular expression patterns of glutamate receptor subunits GluR5-7, KA1 and KA2 in the adult mouse basal ganglia, known to play a pivotal role in the translation of motivation into actions. Kainate receptor subunits were found to be differentially expressed in the circuitry forming the basal ganglia. They differ from each other in expression levels and their spatial localization. GluR6 appeared as the key subunit for the descending gamma-aminobutyric acid (GABA)ergic-glutamatergic pathways, with highest message levels in the caudate putamen, globus pallidus and subthalamic nucleus as well as in the nucleus accumbens and olfactory tubercle. GluR7 exhibited highest expression in the ascending nigrostriatal and mesolimbic dopaminergic neurons. GluR5 had a restricted distribution pattern, with high expression in the ventral pallidum, the islands of Calleja and pars compacta of the substantia nigra. KA2 was usually coexpressed with GluR6, although with a generally lower level of expression. Finally, KA1 mRNA was barely detectable in these neuronal circuits. These data suggest that kainate receptors in general may be involved in the functions associated with the basal ganglia, with a key role in the control of the central dopaminergic transmission. Thus, they might be implicated in the neurodegenerative and psychic disorders associated with an impairment of the basal ganglia.

Animals↗

PubMed1998

Phospholipid fatty acyl spatial distribution in bovine rod outer segment disk membranes.

The distribution of fatty acids within the phospholipid headgroup classes was investigated as a function of the age/spatial distribution of bovine rod outer segment disk membranes. The disks were separated into subpopulations based upon the cholesterol content in their membranes. Because disk membrane cholesterol content decreases as the disks are apically displaced in the rod outer segment, this separation yields disk subpopulations of different ages and from age-dependent spatial locations within the outer segment. The phospholipids, phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidylserine (PS) and phosphatidylinositol (PI), of each of these subpopulations were separated and the fatty acid composition of each was determined. These data indicated that while most of the fatty acids show little or no change with age/spatial location, some pronounced changes can be observed in certain classes. Within the PC class, 16:0 dramatically decreases with disk age while the 22:6 increases with disk age. While the PE class exhibits some fatty acid changes, they are small. The PS class exhibits no significant changes in fatty acid composition. The PI class which constitutes less than 2% of the total phospholipid exhibits age-related changes in each of the fatty acids which could be measured. Most notable of these is an increase in 20:4 as the disks are apically displaced. These changes indicate a remodeling of the disk membranes which may be related to the phototransduction process or to preparation for eventual disk phagocytosis.

Animals↗

PubMed2005

The evolution of a Müllerian mimic in a spatially distributed community.

Strong positive density-dependence should lead to a loss of diversity, but warning-colour and Müllerian mimicry systems show extraordinary levels of diversity. Here, we propose an analytical model to explore the dynamics of two forms of a Müllerian mimic in a heterogeneous environment with two alternative model species. Two connected populations of a dimorphic, chemically defended mimic are allowed to evolve and disperse. The proportions of the respective model species vary spatially. We use a nonlinear approximation of Müller's number-dependent equations to model a situation where the mortality for either form of the mimic decreases hyberbolically when its local density increases. A first non-spatial analysis confirms that the positive density-dependence makes coexistence of mimetic forms unstable in a single isolated patch, but shows that mimicry of the rarer model can be stable once established. The two-patch analysis shows that when models have different abundance in different places, local mimetic diversity in the mimic is maintained only if spatial heterogeneity is strong, or, more interestingly, if the mimic is not too strongly distasteful. Therefore, mildly toxic species can become polymorphic in a wider range of ecological settings. Spatial dynamics thus reveal a region of Müllerian polymorphism separating classical Batesian polymorphism and Müllerian monomorphism along the mimic's palatability spectrum. Such polymorphism-palatability relationship in a spatial environment provides a parsimonious hypothesis accounting for the observed Müllerian polymorphism that does not require quasi-Batesian dynamics. While the stability of coexistence depends on all factors, only the migration rate and strength of selection appear to affect the level of diversity at the polymorphic equilibrium. Local adaptation is predicted in most polymorphic cases. These results are in very good accordance with recent empirical findings on the polymorphic butterflies Heliconius numata and H. cydno.

Adaptation, Physiological↗

PubMed1986

On the spatial distribution of visual attention.

An implication of the data analysis and presentation of Podgorny and Shepard (1983) is that subjects are able to attend simultaneously to more than one square of a grid display when the squares are separated by unattended areas: Attention to such nonunitary areas produces similar benefits as attention to unitary areas. These benefits are reflected in reaction times (RTs), which were reported by Podgorny and Shepard (1983) as being related to a measure of spatial dispersion (compactness) of the attended areas, but this measure does not signify whether these areas are unitary or not. A reanalysis of part of Podgorny and Shepard's (1983) data shows that RTs to attended and unattended squares are almost identical when the attended areas are nonunitary. This reanalysis also shows that RTs are related to compactness for unitary attended areas but that this relation breaks down when attention is focused on nonunitary areas. In addition, Podgorny and Shepard's (1983) data are presented in a way that demonstrates the importance of the actual grid location of probes on RTs. The failure of compactness to reflect these aspects of the spatial nature of attention suggests that this metric is deficient when applied to the study of the spatial determinants of attention.

Attention↗

PubMed1975

Uganda kob (Adenota kob thomasi): territoriality and the spatial distributions of sexual and agonistic behaviors at a territorial ground).

Possible functions of territorial behavior were evaluated on the basis of observations of agonistic and reproductive activities of Uganda kob at a "territorial ground" (TG) in southwestern Uganda. We have found that male residents of a TG tend to occupy exclusive areas, and that agonistic interactions are concentrated along the boundaries separating adjacent occupied areas. Thus, we conclude that male kob do engage in the active defense of spatially exclusive territories at a TG.

Aggression↗

PubMed1979

The response of a spatially distributed neuron to white noise current injection.

The depolarization of passive nerve cylinder or dendritic tree in the equivalent cylinder representation is assumed to satisfy the cable equation. We consider in detail the effects of white noise current injection at a given location for the case of sealed end boundary conditions and for an initial resting state. The depolarization at a point is a Gaussian random process but is not Markovian. Expression (infinite series) are obtained for the expectation, variance, spatial and temporal covariances of the depolarization. We examine the steady state expectation and variance and investigate how these are approached in time over the whole neuronal surface. We consider the relative contributions of various terms in the series for the expectation and variance of the depolarization at x = 0 (soma, trigger zone, recording electrode) for various positions of the input process. It is found that different numbers of terms must be taken to obtain a reasonable approximation depending on whether the stimulus is at proximal, central or distal parts of the dendritic tree. We consider briefly the interspike time problem and see in an approximate way how spatial effects are important in determining the mean time between impulses.

Action Potentials↗

PubMed2006

Spatial distribution and temporal change of carbon storage in timber biomass of two different forest management units.

Forests make up large ecosystems and can play an important role in mitigating the emissions of CO2, the most important greenhouse gas. However, they are sources of atmospheric carbon when they are disturbed by human or natural causes. Storage of carbon through expansion and adaptive management of forest ecosystems can assist in reducing carbon concentrations in atmosphere. This study proposes a methodology to produce spatially explicit estimates of the carbon storages (aboveground plus belowground) depending on land use/cover changes in two different forest ecosystems during various periods. Carbon storages for each forest ecosystem were projected according to inventory data, and carbon storages were mapped in a geographic information system (GIS). Results showed that total carbon stored in above and belowground of both forest ecosystems increased from one period to other because of especially increase of productive forest areas and decline of degraded forest areas as well as protection of spruce forests subject to insect attacks.

Biomass↗

PubMed1994

Immunocytochemical characterization and spatial distribution of midget bipolar cells in the macaque monkey retina.

Midget bipolar cells form the first distinct step in the parvocellular (P-) pathway of the primate visual system, and are the major determinant of the receptive field properties of colour selective midget ganglion cells. This paper describes the sampling properties of the midget bipolar cell population and relates this to the processing of chromatic information in the P-pathway. Immunocytochemical markers were used to label midget bipolar cells so that their spatial density could be compared with that of cones and ganglion cells. Sections through macaque monkey retinae were immunostained with antibodies against cholecystokinin (CCK), and recoverin. In CCK-labelled sections, in addition to blue cone bipolar cells, numerous thin bipolar cell dendrites, which could be associated with individual cone pedicles are stained. CCK-immunoreactive midget bipolar cells are found throughout the retina. A different population of midget bipolar cells is revealed in recoverin-labelled sections. Based on a comparison with midget bipolar cells in Golgi-stained retinae we propose that ON-midget (invaginating) bipolars are immunoreactive for CCK and confirm that OFF-midget (flat) bipolar cells are immunoreactive for recoverin [Milam, Dacey and Dizhoor (1993) Visual Neuroscience, 10, 1-12]. The density of recoverin labelled midget bipolars matches the cone density to an eccentricity of about 10 mm; from there outwards it drops to 60% of the cone density. This suggests convergence of several cones to individual midget bipolar cells in peripheral retina. We conclude that midget bipolar cells are present throughout the entire primate retina, and could, in peripheral as well as in central retina, provide chromatically specific input to the P-pathway.

Animals↗

PubMed2005

Asymmetries in the spatial distributions of enhancing lesions and black holes in relapsing-remitting MS.

Magnetic resonance imaging (MRI) is the most important paraclinical test in the diagnosis of multiple sclerosis (MS) and for delineating its natural history. We investigate MRIs from a longitudinal study of 24 relapsing-remitting MS patients who had monthly MRI examinations for one year, and were not receiving active MS therapy during this period. We hypothesized that lesions occur randomly throughout the brain, and that patients are homogeneous with regard to spatial patterns of lesion presentation. We recorded the numbers and locations of enhancing lesions and hypointense lesions (black holes) in all scans, and found asymmetrical patterns of lesions about the mid-transaxial, mid-coronal, and mid-sagittal planes. Furthermore, in distinct subsets of patients, enhancing lesions and black holes tend to occur in the same locations. Clustering in lesion locations may be of functional significance, with consequent therapeutic implications.

Adult↗

PubMed2003

Nontyphoidal salmonellae in United Kingdom badgers: prevalence and spatial distribution.

Eighteen (72%) of 25 badger social groups were found to excrete Salmonella enterica serovar Ried, S. enterica serovar Binza, S. enterica serovar Agama, or S. enterica serovar Lomita. Each serovar was susceptible to a panel of antimicrobials. Based on results of pulsed-field gel electrophoresis, the S. enterica serovar Agama and S. enterica serovar Binza isolates were very similar, but two clones each of S. enterica serovar Lomita and S. enterica serovar Ried were found. Badgers excreting S. enterica serovar Agama were spatially clustered.

Animals↗

PubMed1988

Spatial distribution of cellular protein binding to retinoic acid in the chick limb bud.

Retinoic acid may be the natural morphogen used to generate digit pattern in the chick limb bud. It has been proposed that retinoic acid acts by binding to a cellular retinoic acid-binding protein (CRABP) and then entering the nucleus to alter the pattern of gene activity. High-affinity receptors that bind both retinoic acid and DNA and are analogous to the steroid receptors have been identified. But the concentration of endogenous retinoic acid in the limb and the binding coefficient of the nuclear receptors indicate that they are saturated throughout the limb. Here we investigate the CRABP distribution in the developing chick limb bud. We find CRABP in the area of intense morphogenetic activity at the tip, with a differential distribution across the anteroposterior axis, the high point being at the anterior margin. Retinoic acid also forms a concentration gradient across the limb bud, but is highest on the posterior side. We propose that CRABP could be reducing the effective concentration of retinoic acid reaching the nucleus to a level appropriate for the differential regulation of gene transcription, providing a spatially modulated morphogenetic gradient of information for digit formation.

Animals↗

PubMed2000

Spatial distribution and characteristics of voltage-gated calcium signals within visual interneurons.

Most of our knowledge about insect calcium currents is derived from studies on cultured or dissociated somata. So far, only little data on calcium currents are available for neurons including their dendritic and presynaptic structures. Here we combined the switched-electrode voltage-clamp technique with optical recording using calcium-sensitive dyes in identified fly visual interneurons in vivo to characterize the voltage dependence and dynamics of calcium currents quantitatively and in a spatially resolved way. For all three cell types considered, i.e., centrifugal horizontal (CH), horizontal system (HS), and vertical system (VS) cells, the activation curve is rather flat and covers a voltage range from -60 to -20 mV in dendritic as well as presynaptic areas of the cells. The calcium increase is fastest for CH cells with a time constant of approximately 70 ms. In HS and VS cells, the time constant amounts to 400-700 ms. The calcium dynamics as determined in different regions of the cells are similar except for a small segment between the axon and the dendrite in HS and VS cells, where the calcium increase is significantly faster. In summary, the results show the existence of a low-voltage-activated calcium current with little or no inactivation in dendritic as well as presynaptic regions of fly lobula plate tangential cells.

Animals↗

PubMed1991

The temporal and spatial distribution pattern of maternal exuperantia protein: evidence for a role in establishment but not maintenance of bicoid mRNA localization.

The exuperantia (exu) gene of Drosophila melanogaster plays a fundamental role in the establishment of polarity of the oocyte and early embryo by ensuring the proper localization of the mRNA of the bicoid (bcd) gene to anterior regions of the oocyte. We have isolated and sequenced the exu gene, sequenced its female-specific transcript and a mutant allele of exu that affects primarily exu's female germline function, and determined the temporal and spatial pattern of exu protein expression during oogenesis. The exu protein is basic, with at least one basic residue being identified as necessary for exu function in the female germline, and is present transiently during oogenesis. Our results suggest that exu is not required for the maintenance of bcd mRNA localization during late stages of oogenesis and early embryogenesis, but rather for the establishment of bcd mRNA localization in the developing oocyte. We propose that the exu protein may serve to modify a component that binds bcd mRNA or to modify the bcd message itself, or may perform a role in docking the bcd mRNA at its site of localization in the developing oocyte.

Amino Acid Sequence↗

PubMed2001

Spatial distribution of selected genetic loci in nuclei of human leukemia cells after irradiation.

Fluorescence in situ hybridization (FISH) combined with high-resolution cytometry was used to determine the topographic characteristics of the centromeric heterochromatin (of the chromosomes 6, 8, 9, 17) and the tumor suppressor gene TP53 (which is located on chromosome 17) in cells of the human leukemia cell lines ML-1 and U937. Analysis was performed on cells that were either untreated or irradiated with gamma rays and incubated for different intervals after exposure. Compared to untreated cells, homologous centromeres and the TP53 genes were found closer to each other and also closer to the nuclear center 2 h after irradiation. The spatial relationship between genetic elements returned to that of the unirradiated controls during the next 2-3 h. Statistical evaluation of our experimental results shows that homologous centromeres and the homologous genes are positioned closer to each other 2 h after irradiation because they are localized closer to the center of the nucleus (probably due to more pronounced decondensation of the chromatin related to repair). This radial movement of genetic loci, however, is not connected with repair of DSBs by processes involving homologous recombination, because the angular distribution of homologous sequences remains random after irradiation.

Cell Nucleus↗

PubMed1996

Is the spatial distribution of tuberculous possums influenced by den quality?

This study aimed to test whether den sites in a single small area containing a cluster of tuberculous brushtail possums were more exposed to adverse environmental conditions than those in a nearby area where no tuberculous possums had been found. No significant differences were found in the visually assessed quality of dens between the two areas. This suggests either that den quality is relatively unimportant in the epidemiology of bovine tuberculosis in possums, or that the differences in den quality are not large enough or are too spatially localised to be detected with the methods used.

Journal Article↗

PubMed2006

Temporal and spatial distribution of immunoreactive PER1 and PER2 proteins in the suprachiasmatic nucleus and peri-suprachiasmatic region of the diurnal grass rat (Arvicanthis niloticus).

The suprachiasmatic nucleus (SCN) of the hypothalamus contains the primary circadian pacemaker in both diurnal and nocturnal mammals. The lower subparaventricular zone (LSPV) immediately dorsal to the SCN may also play an important role in the regulation of circadian rhythms. The SCN contains a multitude of oscillator cells that generate circadian rhythms through transcriptional/translational feedback loops involving a set of clock genes including per1 and per2. Little is known about the temporal and spatial features of the proteins encoded by these genes in day-active mammals. The first objective of this study was to characterize the expression of PER1 and PER2 in the SCN of a diurnal rodent, the unstriped Nile grass rat (Arvicanthis niloticus). The second objective was to evaluate the hypothesis that a molecular clock could exist in the LSPV, where endogenous rhythms in Fos expression are seen in grass rats but not in laboratory rats. Animals were kept on a 12:12 light/dark cycle and perfused at 4-h intervals, and their brains were processed for immunohistochemical detection of PER1 and PER2. Both proteins were seen in the SCN where they peaked early in the dark phase, providing further evidence that the differences between diurnal and nocturnal patterns of behavior emerge from mechanisms lying downstream from the pacemaker within the SCN. Rhythmic expression of PER1 and PER2 was also seen in the LSPV providing support for the hypothesis that this region might participate in circadian time keeping in the diurnal grass rat. In addition, rhythms were seen lateral to the LSPV and the SCN. Results of this study are discussed in light of similarities and differences in the circadian time-keeping systems of day- and night-active animals.

Analysis of Variance↗

PubMed1992

Effect of inhibition of abscisic Acid accumulation on the spatial distribution of elongation in the primary root and mesocotyl of maize at low water potentials.

Previous work showed that accumulation of endogenous abscisic acid (ABA) acts both to maintain primary root growth and inhibit shoot growth in maize seedlings at low water potentials (psi(w)) (IN Saab, RE Sharp, J Pritchard, GS Voetberg [1990] Plant Physiol 93: 1329-1336). In this study, we have characterized the growth responses of the primary root and mesocotyl of maize (Zea mays L. cv FR27 x FRMo 17) to manipulation of ABA levels at low psi(w) with a high degree of spatial resolution to provide the basis for studies of the mechanism(s) of ABA action. In seedlings growing at low psi(w) and treated with fluridone to inhibit carotenoid (and ABA) biosynthesis, ABA levels were decreased in all locations of the root and mesocotyl growing zones compared with untreated seedlings growing at the same psi(w). In the root, low psi(w) (-1.6 megapascals) caused a shortening of the growing zone, as reported previously. The fluridone treatment was associated with severe inhibition of root elongation rate, which resulted from further shortening of the growing zone. In the mesocotyl, low psi(w) (-0.3 megapascal) also resulted in a shortened growing zone. In contrast with the primary root, however, fluridone treatment prevented most of the inhibition of elongation and the shortening of the growing zone. Final cell length measurements indicated that the responses of both root and mesocotyl elongation to ABA manipulation at low psi(w) involve large effects on cell expansion. Measurements of the relative changes in root and shoot water contents and dry weights after transplanting to a psi(w) of -0.3 megapascal showed that the maintenance of shoot elongation in fluridone-treated seedlings was not attributable to increased water or seed-reserve availability resulting from inhibition of root growth. The results suggest a developmental gradient in tissue responsiveness to endogenous ABA in both the root and mesocotyl growing zones. In the root, the capacity for ABA to protect cell expansion at low psi(w) appears to decrease with increasing distance from the apex. In the mesocotyl, in contrast, the accumulation of ABA at low psi(w) appears to become increasingly inhibitory to expansion as cells are displaced away from the meristematic region.

Journal Article↗