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PubMed2002

[Spatial autocorrelation analysis on schistosomiasis cases and Oncomelania snails in three provinces of the lower reach of Yangtze River].

OBJECTIVE: To explore the spatial distribution of schistosomiasis cases and Oncomelania snails in the provinces of Jiangsu, Anhui and Jiangxi with the assistance of geographic information systems (GIS). METHODS: Epidemiological data of schistosomiasis in recent 20 years were collected, and the relevant GIS databases were established. The spatial autocorrelation analysis was carried out with ArcView 3. x, S-Plus, and Spatial Statistics software. RESULTS: Except for schistosomiasis cases in Jiangsu, the spatial distribution of schistosomiasis cases and Oncomelania snails in the three provinces were fitted to the spatial autocorrelation at a certain degree. Generally the autocorrelation coefficients (Moran's I) in Oncomelania snails were higher than that in schistosomiasis cases. CONCLUSION: Spatial autocorrelation analysis can be used to estimate the value of one variable in different spatial position, and it is a good way to find out the spatial cluster distribution in different stages.

Animals↗
PubMed1995

Regional distribution of rat electroolfactogram.

1. Electroolfactorgram (EOG) recordings were made from different regions of the rat olfactory epithelium to test for spatial distribution of odor responses. 2. The EOG recordings showed spatial distribution of the odor responses in the olfactory epithelium. While some odorants (amyl acetate, anisole, and ethyl butyrate) were more effective in evoking responses in the dorsal recess near the septum, other odorants (including limonene, cineole, cyclooctane, and hexane) were more effective in the lateral recesses among the turbinate bones. These differences were seen as statistically significant odorant-by-position interactions in analysis of variance. 3. Comparisons of recordings along the anteroposterior dimension of the epithelium produced smaller differences between the odor responses. These were not significant for 3-mm distances, but were statistically significant for 5- to 6-mm distances along the dorsomedial epithelium. 4. The latencies were significantly longer in the lateral recesses than in the medial region. This probably reflects a more tortuous air path along the turbinate bones to the lateral recesses. 5. The olfactory receptor cells were activated by antidromic stimulation via the nerve layer of the olfactory bulb. The population spikes evoked from the olfactory receptor cells could be suppressed by prior stimulation with odorants that evoked strong EOG responses. This collision of the antidromic action potentials with the odor-evoked action potentials indicates that the same population of receptor cells was activated in both cases. 6. The flow rate and duration of the artificial sniff were varied systematically in some experiments. The differential distribution of response sizes was present at all flow rates and sniff durations. Some odors (e.g., amyl acetate and anisole) produced increased responses in the epithelium of the lateral recesses when flow rates or sniff durations were high. We suggest that these changes may reflect the sorptive properties of the nasal membranes on these odors. The responses to other odors (e.g., hexane or limonene) were not greatly affected by flow rate or sniff duration. 7. Taken with existing anatomic data, the results indicate that the primary olfactory neurons that project axons to glomeruli in different parts of the olfactory bulb are responsive to different odors. The latency differences between responses at medial and lateral sites are large enough to be physiologically significant in the generation of the patterned responses of olfactory bulb neurons.

Animals↗
PubMed1990

Spatial aspects of population growth and migration in Constantine, Algeria.

"The objective of the paper is to depict the major changes brought about by demographic growth upon the internal structure of Constantine, the third largest Algerian city, and thus define the main types of settlement evolved, which in turn serves as background for the analysis of the spatial distribution of recent migrants within the different areas of Constantine. With regard to this distribution, the aim is to test whether there exist any spatial concentrations of migrants in particular areas according to their place of origin."

Africa↗
PubMed2005

Highly anisotropic distribution of iron nanoparticles within MCM-41 Mesoporous Silica.

Electron microscopy techniques are used to visualize the spatial distribution of iron nanoparticles inside a mesoporous MCM-41 molecular sieve. Direct observation of the iron oxide nanoparticles by STEM-HAADF imaging reveals a highly non-uniform spatial distribution inside the mesopores. These particles are retained in the pores after a reduction treatment unlike the behavior found in other similar systems. It is found that thermal treatments induce changes in its morphology, creating nanowires from particle strings.

Image Processing, Computer-Assisted↗
PubMed2004

Effects of electrode-to-fiber distance on temporal neural response with electrical stimulation.

This paper presents an analysis of the effects of the electrode-to-fiber distance on the temporal response properties of an auditory nerve fiber stimulated by electric current pulses. This analysis was based upon results from a computational model of a mammalian auditory nerve fiber axon having 50 nodes of Ranvier, each consisting of 130 stochastic sodium channels and 50 stochastic potassium channels, making it possible to represent the temporal fluctuations of action potential initiation and conduction. A monopolar stimulus electrode was located above a central (26th) node at electrode-to-fiber distances of 1, 4, and 7 mm, while the recording electrode was located at the 36th node. Action potentials (spikes) were generated by the biophysical model using the Crank-Nicholson method to solve a diffusive partial differential equation. By observing the occurrence times of spikes in response to 2000 cathodic monophasic stimulus pulses, temporal jitter (i.e., the standard deviation of spike times) was calculated and the poststimulus time (PST) histogram was generated as well. Furthermore, by computing the PST histogram for each initiation node as functions of space (node number) and time (PST), it was shown that spike initiation was distributed not only spatially but also temporally for stimulus levels producing firing efficiencies (FEs) near 0.5. However, at levels producing FEs near 0.99, while temporal variations approached zero, the spatial distribution of initiating nodes was comparable to that observed for the FE near 0.5. As temporal fluctuations are important for speech coding in cochlear implants, we conclude that spatial characteristics of the electrode-auditory nerve fiber interface may play a significant role in influencing these stochastic temporal processes.

Action Potentials↗
PubMed1994

Spatial and temporal distribution of insulin-like growth factors I and II during development of rat lung.

Insulin-like growth factors (IGF) I and II genes are expressed in developing lung tissue, but the details of distribution during different stages of lung development have not been delineated. To define the role of IGFs in lung development, the expression of IGF-I and IGF-II mRNAs and peptides was examined in rat lungs from 16-day gestation through adulthood. The expression of stable IGF mRNAs was investigated by Northern analysis, IGF mRNAs were localized by in situ hybridization histochemistry, and IGF peptides were localized by immunohistochemistry. Four IGF-II transcripts (3.5, 2.2, 1.8, and 1.0 kb) were identified; IGF-II mRNA levels were highest early in fetal life (day 16-18) and decreased gradually until 28 days postnatal. Four IGF-I transcripts (7.8, 4.4, 2.1, and 0.6 kb) were detected but were of low abundance. IGF-II mRNA was localized mainly in mesenchymal cells but was also identified in the airway epithelium, with peak expression in the perinatal lung. IGF-II peptide was prominent in late fetal life and for 5 days after birth and was identified in both mesenchymal and epithelial cells. In contrast, there was little evidence of IGF-I mRNA and peptide until after birth: IGF-I was most easily identified between 5 and 14 days postnatal (the height of alveolar multiplication and formation), when both mRNA and peptide were localized to mesenchymal and epithelial cells. Our studies demonstrate that IGF-I and IGF-II are synthesized and distributed in spatially and temporally different patterns in the developing lung. IGF-I and IGF-II peptides are more widely identified than their respective mRNAs, suggesting a paracrine distribution in the developing lung.

Aging↗
PubMed2004

Immunocytochemical distribution of somatotrophs in porcine anterior pituitary.

The objective of this immunohistochemical study was to identify the spatial distribution patterns of growth hormone (GH) secreting cells (somatotrophs) in the newborn and prepubertal porcine pituitary. No differences were observed among the total somatotrophs per unit area across the three ages. There were, however, changes in spatial distribution of somatotrophs in porcine pituitary with developmental age. Distinctive characteristics of the pattern included a high population of somatotrophs (44 +/- 1.2; mean +/- standard error of the mean per 30,495 microm(2)) in regions 1 and 5 and a low population (22 +/- 1.4) in regions 2 and 4 at each level (P < 0.05). Somatotrophs increased 55% in region 3 from proximal to distal levels at all ages. With increasing age, however, somatotrophs in region 3 at the proximal level decreased 33%. From these results, we suggest that there may be regional specificity of cellular differentiation and transformation to facilitate GH secretion to meet the need for endocrine regulation as the animal ages.

Aging↗
PubMedDate not supplied

Analysis of second-order kernel response components of multifocal electroretinograms elicited from normal subjects.

PURPOSE: It has been reported that the second-order kernel response components of multifocal electroretinograms (mERGs) reflect the electrical activity of the inner retinal layers. In this study, we have investigated whether the amplitudes of the second-order kernel response components correlate with the spatial distribution of human retinal ganglion cells. METHODS: Multifocal electroretinograms were recorded using the Veris III system from 5 healthy subjects with different stimulus and recording parameters. The mERGs were analyzed using the Veris Science software programs. The stimuli consisted of densely arranged arrays of 103, 61, 37 or 19 hexagonal elements. Four minutes were required to record one set of mERG responses using 8 sessions, and 8 minutes using 16 sessions. The second-order kernel response components were extracted and analyzed using the Veris Science program. RESULTS: The signal-to-noise ratio of the first-order kernel response components was improved considerably by the summation of the nine reproducible responses from the same subject but the second-order kernel response components were not. The summation of the nine reproducible responses was insufficient to identify an array of the second-order kernel response components. Both the first- and second-order kernel response components were larger when fewer hexagonal elements were used. There was no significant difference in the individual responses between the 4-minute and the 8-minute recordings. A response density analysis revealed a weak correlation between the amplitude distribution of the second-order kernel response components and the spatial distribution of human retinal ganglion cells. CONCLUSIONS: The distribution of the amplitudes of the second-order kernel response components of the mERGs elicited from normal subjects did not correlate with the distribution of human ganglion cells. This suggests that the theory that second-order kernel response components arise from the activity of retinal ganglion cells should be reconsidered.

Adult↗
PubMed2001

Growth hormone as a neuronal rescue factor during recovery from CNS injury.

There is growing evidence to suggest that growth hormone plays a role in the growth and development of the CNS. Specifically, growth hormone has been implicated in promoting brain growth, myelination, neuronal arborisation, glial differentiation and cognitive function. Here we investigate if growth hormone has a role in the recovery from an unilateral hypoxic-ischaemic brain injury. Using moderate (15 min hypoxia) and severe (60 min hypoxia) models of hypoxic-ischaemia in juvenile rats and standard immunohistochemical techniques, we found intense growth hormone-like immunoreactivity present within regions of cell loss by 3 days (P<0.05). Growth hormone-like immunoreactivity was observed on injured neurones, myelinated axons, glial cells within and surrounding infarcted tissue and on the choroid plexus plus ependymal cells within the injured hemisphere. The pattern of immunoreactivity suggests that (a) growth hormone (or a growth hormone-like substance) is transported via the cerebrospinal fluid and (b) that growth hormone (or a growth hormone-like substance) is acting in a neurotrophic manner specifically targeted to injured neurones and glia. To test this hypothesis we treated a moderate hypoxic-ischaemic brain injury with 20 microg of rat growth hormone by intracerebroventricular infusion starting 2 h after injury (n=12/group). After 3 days the animals were killed and the extent of neuronal loss quantified. Growth hormone treatment reduced neuronal loss in the frontoparietal cortex (P<0.001), hippocampus (P<0.01) and dorsolateral thalamus (P<0.01) but not in the striatum. This spatial distribution of the neuroprotection conveyed by growth hormone correlates with the spatial distribution of the constitutive neural growth hormone receptor, but not with the neuroprotection offered by insulin-like growth factor-I treatment in this model. These results suggest that some of the neuroprotective effects of growth hormone are mediated directly through the growth hormone receptor and do not involve insulin-like growth factor-I induction.In summary, we have found that a growth hormone-like factor increased in the brain in the days after injury. In addition, treatment with growth hormone soon after an hypoxic-ischaemic injury reduced the extent of neuronal loss. These results further suggest that a neural growth hormone axis is activated during recovery from injury and that this may act to restrict the extent of neuronal death.

Animals↗
PubMed2004

Direct time-resolved and spatially resolved monitoring of molecular transport in a crystalline nanochannel system.

Confocal Raman microspectrometry has been applied successfully as an in situ probe of the transport of guest molecules through the one-dimensional channel system in a crystalline inclusion compound, yielding insights into the spatial distribution of guest molecules and, in particular, the variation in the spatial distribution of the guest molecules as a function of time during the transport process.

Journal Article↗
PubMed1975

Extracellular potassium activity, intracellular and extracellular potential responses in the spinal cord.

1. Microcapillary electrode assemblies of two or three channels were used to record extracellular and intracellular potentials together with the extracellular activity of potassium ions, from essentially single locations within the substance of the decapitate spinal cord of cats. A liquid ion exchanger filled the tip of the potassium sensing microprobe. Activity was evoked by electrical stimulation of afferent peripheral nerves (ventral roots were cut). 2. Within the substance of the spinal grey matter increments of extracellular potassium activity evoked by repetitive afferent volleys were precisely correlated with magnitudes of sustained shifts of extracellular electric potential. Raising [K+]o from 3 to 4 mM was associated with a negative shift of potential of 2-5 +/- 0-5 mV, regardless of the position of the electrode in the tissue, and regardless of treatment by convulsant or depressant drugs. 3. The spatial distribution of the responses of potassium activity was mapped by the spatial distribution of the negative sustained potential shifts. 4. Depolarization shifts of potential recorded from within neuroglia cells ran parallel with changes of extracellular potassium potential. Even though the magnitude of extracellular sustained potential shifts was precisely correlated with the responses of both extracellular potassium and intracellular glial potentials, the trajectory of sustained potential shifts did not exactly mirror the two other variables. Onset and offset of sustained potential shifts were faster than those of glial potentials or of extracellular potassium. 5. The responses of the true transmembrane potential (intracellular less extracellular potential shifts) of neuroglia cells in the spinal grey matter can fully be described by the Nernst equation. 6. Membrane potentials of neurones, potentials recorded from dorsal root filaments, or from white matter, appeared unrelated to the activity of potassium ions in extracellular fluid. 7. The results are compatible with the suggestions that changes of the membrane potential of spinal neuroglia cells are fully determined by the change of the activity of extracellular potassium, and that glia cells supply most of the current which generates sustained shifts of the extracellular potential of spinal grey matter. The results are hard to reconcile with suggestions that under conditions of moderate excitation (i.e. in the absence of convulsive neuronal activity) changes of extracellular potassium would significantly influence the membrane potential of spinal neurones, or of primary afferent nerve fibres.

Action Potentials↗
PubMed2003

Developmental regulation of plasticity in the forepaw representation of ferret somatosensory cortex.

This study characterized the spatiotemporal responses in ferret somatosensory cortex after sensory deprivation at different phases of cortical development. We hypothesized that cortical responses to stimulation of intact superficial radial nerve in adults will vary systematically according to maturation of thalamocortical relationships at the time of an ulnar nerve transection. Depending on the age of the animal at the time of the lesion, we found differential effects on the spatial distribution of the short- and long-latency components of the cortical response. In animals lesioned at postnatal days 5-7, when thalamic projections are not yet stabilized and layer 4 is not yet formed, we found that initial (short-latency) cortical responses are widespread and fragmented. Ulnar nerve transections performed at postnatal day 20 or 21, when thalamocortical afferents are more stabilized and layer 4 is clearly identifiable, yield moderate expansions in the distribution of short- and long-latency components of the cortical response. Nerve lesions in adults lead to a wider distribution of long-latency cortical activity. Neonatal lesions broaden the spatial distribution and increase the latency of the initial cortical response; interruption of nerve input in older juveniles alters both the early and later components; and nerve lesions in adult animals expand the distribution of later cortical activity only. These findings demonstrate correlation between developmental phase at the time sensory input is interrupted and the latency of affected components of the cortical response. This supports the hypothesis that differential response changes are regulated by functional reorganization of thalamocortical connections after neonatal lesions and alteration of corticocortical dynamics after adult lesions.

Age Factors↗
PubMed1984

Non-random distribution of intraepithelial lymphoid cells in follicle-associated epithelium of Peyer's patches in mice.

The spatial distribution of intraepithelial lymphoid cells in follicle-associated and villus epithelium within Peyer's patches was studied quantitatively in Balb/C and CFW/L1 mice. The results were essentially the same for both strains. The distribution of the number of lymphoid cells per segmental length (equal to an average width of an epithelial cell) of dome epithelium was found to be non-random, since it deviated significantly from the theoretical Poisson distribution. Some segments of the dome epithelium, therefore, are lymphocyte-rich and some are lymphocyte-depleted, i.e. they contain either more, or less lymphoid cells than expected from the random distribution. This was in contrast to the distribution in the epithelial layer of the villi, in which the distribution of the number of lymphoid cells per segment followed the Poisson distribution. It was also demonstrated that segments rich in lymphocytes in the dome epithelium occurred in series or clusters. Lymphoid cell clustering was not observed in the villus epithelium. Possible mechanisms responsible for the non-random spatial distribution of lymphoid cells within the dome epithelium of the mouse Peyer's patches are discussed.

Animals↗
PubMedDate not supplied

Governments' perceptions and policies of population redistribution in East and South East Asia.

"This paper is based on the results of the Third Inquiry among Governments on Population and Development carried out in 1977 by the UN Secretariat. It reports on perceptions and policies concerning international migrations, spatial distribution of the national population, internal migration and settlement patterns in fourteen South East and East Asian countries. "It appears that nearly all countries under consideration were concerned with the spatial distribution of population both as a factor related to problems caused by excessive natural increase and as a problem on its own right. The majority of countries were prepared to pursue policies affecting basic trends in internal migration. Most governments declared their willingness to alter patterns of rural or both rural and urban settlement. Only two countries were interested in increasing emigration; the remaining ones were satisfied with the existing levels of international migration."

Asia↗
PubMed2005

Edges and bars: where do people see features in 1-D images?

There have been two main approaches to feature detection in human and computer vision--based either on the luminance distribution and its spatial derivatives, or on the spatial distribution of local contrast energy. Thus, bars and edges might arise from peaks of luminance and luminance gradient respectively, or bars and edges might be found at peaks of local energy, where local phases are aligned across spatial frequency. This basic issue of definition is important because it guides more detailed models and interpretations of early vision. Which approach better describes the perceived positions of features in images? We used the class of 1-D images defined by Morrone and Burr in which the amplitude spectrum is that of a (partially blurred) square-wave and all Fourier components have a common phase. Observers used a cursor to mark where bars and edges were seen for different test phases (Experiment 1) or judged the spatial alignment of contours that had different phases (e.g. 0 degrees and 45 degrees ; Experiment 2). The feature positions defined by both tasks shifted systematically to the left or right according to the sign of the phase offset, increasing with the degree of blur. These shifts were well predicted by the location of luminance peaks (bars) and gradient peaks (edges), but not by energy peaks which (by design) predicted no shift at all. These results encourage models based on a Gaussian-derivative framework, but do not support the idea that human vision uses points of phase alignment to find local, first-order features. Nevertheless, we argue that both approaches are presently incomplete and a better understanding of early vision may combine insights from both.

Contrast Sensitivity↗
PubMed1989

Distribution and spatial geometry of dopamine interplexiform cells in the rat retina: I. Developing retina.

The morphology and distribution of dopaminergic interplexiform cells were analyzed in 9-day-old rat retinas processed as wholemounts for tyrosine hydroxylase immunohistochemistry. The mean number of dopaminergic interplexiform cells was estimated as about half of the total number of dopaminergic neurons in the immature retina, with a higher density in the temporal retina. Four interplexiform cells were individually analyzed and reconstructed with a computer system. Their arborizations could be divided into three different regions based on both their morphological features and their position within the retinal layers: (1) an internal arborization, spreading at the margin between the inner nuclear layer and the inner plexiform layer, composed of long, thick, somatofugal dendrites branching at acute angles, (2) an external arborization in the middle of the inner nuclear layer, formed by short, thin, varicose, recurved, axon-like processes branching at right angles, (3) and one or more scleral process(es), originating either from the cell body or from the internal arborization, running toward the outermost cell row of the INL, some of which reached the outer plexiform layer. Finally, analysis of the arborization network by computer simulations based on the 4 digitalized cells was compared with a nearest-neighbour analysis of cell body distribution. It showed that cell bodies are almost randomly distributed--at least in the inferior retina--but that an adjustment of dendritic growth and orientation probably occurs to ensure a homogeneous coverage of the retina with a constant degree of overlap in the adult. This report represents the first three-dimensional computer reconstruction of chemically identified neurons in the retina.

Animals↗
PubMed1995

In vivo ultrasonic parametric imaging of carotid atherosclerotic plaque by videodensitometric technique.

Extensive experimental and clinical data show that the ultrasonic image conveys information on the biochemical composition of the atherosclerotic plaque, ie, the relative content of lipids (hypoechoic), fibrous tissue (hyperechoic), and calcific deposits (very echogenic with shadowing). A more dishomogeneous echo structure of the plaque is also more often associated with clinically complicated carotid plaques. To date, however, the assessment of plaque density and homogeneity by transcutaneous B-mode imaging remains subjective and qualitative. The aim of this study was to assess whether plaque echodensity and homogeneity might be established on a more objective and quantitative basis by description of the spatial distribution of echo amplitude (referred to as tissue texture) applied to digitized images, obtained with commercially available B-mode transcutaneous imaging systems. A total of 47 B-mode images derived from echotomographic studies in 10 patients were digitized off line. For each region of interest, a set of first-order (mean gray level, standard deviation, skewness, kurtosis: mathematical descriptors of the shape of the frequency distribution of gray-level histogram) and of second-order (entropy, angular moment: mathematical descriptors of the spatial distribution of gray levels within the region of interest) textural parameters were evaluated. The visual, concordant reading by two independent, experienced observers assigned the plaques on the basis of qualitatively assessed echodensity to three groups: "soft" (n = 18), "fibrotic" (n = 20), "calcific" (n = 9). Regarding spatial gray-level distribution, 46 plaques would be separated into "homogenous" (n = 17) and "dishomogeneous" (n = 29). On digitized images, the normalized mean gray level was the most effective first-order textural parameter for distinguishing soft (24.2 +/- 12.4 arbitrary units in a zero to 255 scale) from fibrotic (64.5 +/- 16.4) and calcific plaques (125.3 +/- 24.5), P < 0.01 for all intergroup differences. "Homogeneous" plaques were separated from "heterogeneous" ones on the basis of entropy (5 +/- 1 vs 7.9 +/- 9.7; P < 0.01), whereas the values of angular second moment overlapped (1.542E-3 + 1.334E-3 vs 5.181E-4 +/- 2.5615E-4, P = ns). In conclusion, quantitative texture analysis of ultrasonic images derived from transcutaneous, high-resolution, commercially available B-scan systems is feasible in man and provides a quantitative operator-independent assessment of plaque echodensity and homogeneity.

Arteriosclerosis↗
PubMed2004

[Population structure and distribution pattern of rare plant communities in Houhe Nature Reserve].

An investigation on the size structure and spatial pattern of 26 major tree species with a diameter at breast height (DBH) > or = 5 cm was made on a 1 hm2 fixed plot in the mixed evergreen and deciduous broad-leaved forest in Houhe National Nature Reserve of Central China. The results showed that 7 populations of the 26 species, i.e., Dipteronia sinensi, Aesculus wilsonii, Pterostyrax psilophyllus, Davidia involucrate, Euptelea pleiosperma, Tetracentron sinense and Cercidiphyllum japonicum, were rare endangered, species, and two of the 7 populations, T. sinense and C. japonicum, were very limited in numbers. The population structure of P. psilophyllus was in declining, and that of the rest was in growing. The spatial distribution pattern of P. psilophyllus, A. wilsonii and T. sinense was in random, and that of the others was clumped. Among the other 19 non-rare populations, the population structure of P. wilsonii was in declining, that of D. lotus, A. palmatum, A. wilsonii, A. franchetii, M. cuneifolia and H. dulcis was stable, and the rest was in growing. The spatial distribution pattern of D. lotus and H. dulcis was in random, and that of the others was clumped. On the whole, the growing populations were dominant, amounting to 61.54%, and the stable and declining populations accounted for 6.92% and 11.54%, respectively. The results of the two judging methods were consistent, showing that the distribution pattern of clumping (80.77%) was dominant, while the random and even distribution patterns were infrequent.

Aesculus↗