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PubMed2002

Decoding of a motor command vector from distributed activity in superior colliculus.

Several alternative methods for decoding the desired motor command vector from neural networks containing distributed, place-coded information have been suggested. The two most widely discussed candidate mechanisms are vector summation (VS) and a center-of-mass (CM) computation. The latter mechanism has also been called vector averaging. The present paper compares the operation of these two methods in a model of an experimentally well-studied neural structure, the superior colliculus (SC). The SC is one structure that has been shown to be responsible for generating saccadic command vectors in the form of distributed neural activity that is topologically arranged across its surface. It has been suggested that the pattern of eye-movement errors obtained following the placement of a collicular lesion can distinguish between these two mechanisms. As a result of this suggestion, the pattern of saccadic errors produced by lesions in the SC have been widely cited to support the CM hypothesis. In the present paper the placement of a discrete lesion is simulated in a recurrent (dynamic) neural network model of the SC. These dynamic connections in the model SC network produce a systematic shift of the locus of distributed activity away from the site of the lesion. The spatiotemporal shift in the location of SC activity then produces a pattern of saccadic errors that appear to support the CM hypothesis, even though ensemble activity in our model colliculus is decoded by VS. This result demonstrates that, when ensemble activity on the SC motor map is dynamically modulated over space and time by intrinsic collicular circuitry, an explicit CM computation is not needed to reproduce the pattern of physiological results that follow focal SC lesions.

Animals↗
PubMed1987

[The regulation system of brain aromatase activity; distribution and changes with age of the aromatase activity of the rat brain].

Sexual differentiation of brain structure and function is dependent on the hormonal environment during perinatal life. Recently, some studies have found the greatest aromatase activity in brain areas associated with sexual differentiation and sexual behavior, namely the hypothalamic and limbic structures. We have characterized the developmental and anatomical patterns of aromatase of aromatase activity in brains of fetal, neonatal, infantile and adult rats of both sexes. Aromatase activities in slices of brain were assayed by measuring the amount of 3H2O formed during the conversion of [1 beta-3H] androstenedione to estrogen. We have demonstrated major changes of the aromatase activity in the brain with age. Aromatase activities of both sexes reached peak values in the hypothalamus-preoptic area (HPOA) at least 3 days before birth. Thereafter, the activities declined to 3 weeks after birth. We have found the greatest amount of aromatase activity in HPOA and amygdala of both sexes. Aromatase activities in HPOA and amygdala of neonatal male rat were higher than adult male rat. The hippocampus, thalamus, pituitary, cerebral cortex and cerebellum all contained negligible aromatase activity. And, we studied HPOA in detail, aromatase activities in preoptic area and anterior part of hypothalamus were twice higher than that in posterior part of hypothalamus. Aromatase activity reached peak values at the critical period of the sexual differentiation of the brain in HPOA and amygdala, associated with sexual behavior and sexual differentiation. We have reported that aromatase activity was regulated by androgen. We suggested that aromatization didn't occur effectively in female rat, owing to scarcity of androgen, which was activator and substrate of aromatase.(ABSTRACT TRUNCATED AT 250 WORDS)

Aging↗
PubMed1997

Mast cell distribution, activation, and phenotype in atherosclerotic lesions of human carotid arteries.

Immunohistochemical staining for mast cell tryptase and chymase was used to examine the distribution, activation, and tryptase/chymase phenotype of mast cells (MCs) in 250 samples of atherosclerotic lesions (type I to VI) of human carotid arteries. Dual immunolocalization and histochemical techniques were used to identify the associations of MCs with macrophages, smooth muscle cells, and extracellular matrix components. Whereas normal carotid arteries contained very few MCs within the intima, atherosclerotic lesions showed increased MC numbers with variable focal accumulations. MCs were identifiable from the earliest stages of atherosclerosis, and especially at the shoulder regions of the fully formed atheroma. They were observed in close association with macrophages (HAM56 positive) and extracellular lipid, as well as at sites of foam cell formation. MCs and diffuse tryptase staining were also evident within sites of new calcification and around small calcified deposits. Extensive MC activation/degranulation, as judged by diffuse extracellular tryptase staining, was a common feature of the advanced atherosclerotic plaques complicated by fissure, haemorrhage, and thrombus formation. Moreover, such sites of extracellular MC tryptase were often associated with localized oedema and disruption of the stromal matrix. MCs which contained both tryptase and chymase (the MCTC phenotype) represented approximately 80-95 per cent of all MCs. These studies are the first to demonstrate significant numbers and focal accumulations of MCs in all developmental stages of atherosclerotic carotid arteries. Since MCs contain or express a variety of potent mediators, their release could profoundly influence the development and pathological complications of atherosclerotic plaques.

Aged↗
PubMed1996

Poisson-distributed active fusion complexes underlie the control of the rate and extent of exocytosis by calcium.

We have investigated the consequences of having multiple fusion complexes on exocytotic granules, and have identified a new principle for interpreting the calcium dependence of calcium-triggered exocytosis. Strikingly different physiological responses to calcium are expected when active fusion complexes are distributed between granules in a deterministic or probabilistic manner. We have modeled these differences, and compared them with the calcium dependence of sea urchin egg cortical granule exocytosis. From the calcium dependence of cortical granule exocytosis, and from the exposure time and concentration dependence of N-ethylmaleimide inhibition, we determined that cortical granules do have spare active fusion complexes that are randomly distributed as a Poisson process among the population of granules. At high calcium concentrations, docking sites have on average nine active fusion complexes.

Animals↗
PubMedDate not supplied

Assessment of geometrical distortion and activity distribution after attenuation correction: A SPECT phantom study.

BACKGROUND: If single photon emission computed tomography (SPECT) images are reconstructed with filtered backprojection (FBP), not accounting for photon attenuation, artifacts can occur related to geometrical distortion and inaccurate estimation of regional distribution of radioactivity. By reconstructing the images with an iterative algorithm such as the maximum likelihood-expectation maximization (ML-EM) that incorporates the attenuation distribution information, it is possible to compensate for nonuniform attenuation. The aim of this study was to assess whether correction for nonuniform attenuation in SPECT can reduce the geometrical distortion and improve the activity quantitation. METHODS AND RESULTS: Three capillary sources containing the same amount of technetium 99m were imaged by a dual-headed SPECT system provided with two gadolinium 153 scanning transmission line sources, in nonuniform attenuation conditions. The images were reconstructed (1) with the use of FBP, (2) with the iterative ML-EM algorithm, and (3) with the iterative ML-EM algorithm incorporating attenuation maps. The geometrical distortion was estimated by comparing the spread that occurred in 2 orthogonal directions in the reconstructed transverse slices, expressed by full width at half maximum related to the x-axis and y-axis line spread functions. The accuracy of activity quantitation was analyzed by comparing the counts in regions of interest placed over the transverse slices of the 3 sources, located in different attenuating areas. The FBP-reconstructed slices showed a spread of image intensity toward the direction of minor attenuation; the source shape improved in the iterative ML-EM images, as well as in the iterative attenuation-corrected ML-EM images. The sources located deep in the phantom showed an apparent decrease in image intensity in both FBP and ML-EM images, which became less evident in the iterative attenuation-corrected ML-EM images. CONCLUSIONS: Image reconstruction with the iterative ML-EM algorithm, without the use of attenuation maps, can reduce geometrical distortion and eliminate streak artifacts, leading to an improvement in the object's shape and size, but does not reduce activity underestimation and inaccurate quantitation. In the iterative attenuation-corrected ML-EM images, there was a significant improvement in the accurate quantitation of activity distribution and a further reduction in geometrical distortion. In conclusion, nonisotropic attenuation correction with iterative ML-EM reduced the geometrical distortion of images and improved the accuracy of activity quantitation.

Abdomen↗
PubMed1994

Abnormalities in subset distribution, activation, and differentiation of T cells isolated from large intestine biopsies in HIV infection. The Berlin Diarrhoea/Wasting Syndrome Study Group.

Intestinal T cells have a unique state of activation and differentiation which might specifically affect or be affected by HIV infection. Lymphocyte subsets in the peripheral blood are well characterized, but our knowledge about intestinal lymphocytes in HIV infection is incomplete. We therefore analysed lymphocytes isolated from large intestine biopsies of AIDS patients and controls by three-colour cytofluorometry. In the large intestine of HIV-infected patients CD4 T cells were reduced and CD8 T cells were increased compared with controls. Most of the CD8 T cells in the colorectal mucosa of AIDS patients were of the cytotoxic phenotype. Activated and resting CD4 T cells were similarly reduced, the expression of CD25 and HLA-DR of CD8 T cells was unaltered and increased, respectively. In intestinal CD4 T cells the expression of CD29 was decreased, but the expression of CD45RO and HML-1 was normal. CD8 T cells had a decreased expression of all these differentiation markers. Our findings demonstrate substantial alterations in subset distribution, activation, and differentiation of large intestine T cells, which may contribute to the secondary infections and malignancies commonly observed in the gut of AIDS patients.

Acquired Immunodeficiency Syndrome↗
PubMed1998

Influence of the phosphate balance on the activity distribution of 99mTc-hydroxy-methylene diphosphonate. Experimental studies in the mouse.

OBJECTIVE: The purpose was to determine whether changes in the phosphate balance have an influence on the distribution of bone-seeking radiopharmaceuticals. MATERIAL AND METHODS: The biodistribution of 99mTc-HDP in mice, intravenously administered under varying conditions, was assessed by removing different organs and estimating their activity in a scintillation counter. Some experiments were also performed with 99mTc-MDP and 99mTc-DPD. RESULTS: After 1 h and 18 h on phosphate-enriched drinking water, the mice showed a strongly increased uptake in all organs/tissues representing background activity and a decrease in the bone uptake. This pattern changed with time. After 6-8 days of phosphate load, we saw a more favourable distribution with a reduction of the background and whole-body activity. Administration of hPTH 1-34 gave rise to an activity distribution similar to that after 6-8 days on phosphate-enriched water. Changing the phosphate balance had less obvious effects on the distribution of 99mTc-MDP and 99mTc-DPD. CONCLUSION: The activity distribution of bone-seeking radiopharmaceuticals in the mouse is affected by the phosphate balance. The mechanism behind this finding is unknown but it may be partially mediated by PTH. It is possible that changes in the phosphate balance, induced by pharmaceuticals or by dietary changes, may affect the image quality at bone scintigraphy.

Animals↗
PubMed1990

Batch tests to determine activity distribution and kinetic parameters for acetate utilization in expanded-bed anaerobic reactors.

Batch tests to measure maximum acetate utilization rates were used to determine the distribution of acetate utilizers in expanded-bed sand and expanded-bed granular activated carbon (GAC) reactors. The reactors were fed a mixture of acetate and 3-ethylphenol, and they contained the same predominant aceticlastic methanogen, Methanothrix sp. Batch tests were performed both on the entire reactor contents and with media removed from the reactors. Results indicated that activity was evenly distributed within the GAC reactors, whereas in the sand reactor a sludge blanket on top of the sand bed contained approximately 50% of the activity. The Monod half-velocity constant (K(s)) for the acetate-utilizing methanogens in two expanded-bed GAC reactors was searched for by combining steady-state results with batch test data. All parameters necessary to develop a model with Monod kinetics were experimentally determined except for K(s). However, K(s) was a function of the effluent 3-ethylphenol concentration, and batch test results demonstrated that maximum acetate utilization rates were not a function of the effluent 3-ethylphenol concentration. Addition of a competitive inhibition term into the Monod expression predicted the dependence of K(s) on the effluent 3-ethylphenol concentration. A two-parameter search determined a K(s) of 8.99 mg of acetate per liter and a K(i) of 2.41 mg of 3-ethylphenol per liter. Model predictions were in agreement with experimental observations for all effluent 3-ethylphenol concentrations. Batch tests measured the activity for a specific substrate and determined the distribution of activity in the reactor. The use of steady-state data in conjunction with batch test results reduced the number of unknown kinetic parameters and thereby reduced the uncertainty in the results and the assumptions made.

Journal Article↗
PubMed1991

The perinatal development of glucose-6-phosphatase activity distribution pattern in rat liver. A microdensitometrical study.

The ontogenetic development of the intralobular distribution pattern of glucose-6-phosphatase activity in the rat liver is described in terms of histochemical changes determined with microdensitometry. A newly developed cerium-lead technique was employed and compared with the common lead technique optimized by Teutsch (1978a). The cerium technique has advantages, meets the prerequisites for quantitative determinations and yields results comparable to biochemically obtained data from microdissected tissue. The first signs of a heterogeneous distribution pattern of glucose-6-phosphatase activity are observed on the 3rd d after birth, and differences between periportal and centrolobular areas are largest around 10th and 15th d. At 30th d after birth, the adult pattern is complete with a centrolobular glucose-6-phosphatase activity of 67% of the periportal value.

Aging↗
PubMed1994

Analysis of disease distribution, activity and complications in the patient with inflammatory bowel disease.

Management strategies in Crohn's disease and ulcerative colitis should be based on up-to-date information on disease distribution, extent, activity and complications. A system of structured analysis is suggested, with separate consideration of destructive ulceration, inflammatory activity and other factors. Direct investigation of gut immunity by using whole gut lavage fluid (WGLF) is a valuable new technique of clinical investigation in IBD and related disorders. Recent studies have shown that the concentrations of plasma-derived proteins in WGLF provide objective measures of disease activity; and that this activity is a separate phenomenon from destructive ulceration and fibrosis. Neutrophils in the lumen can be in- investigated by cytology, or by assay of neutrophil elastase in WGLF. Cytokines and other immuno-regulatory mediators can also be detected. These new techniques can provide a description of intestinal immunity and inflammation, based on a non-invasive test of 2-4 h duration. Work in progress shows that patients who respond clinically to elemental diet treatment have unusually high concentrations of soluble IL2 receptor in WGLF; cytokine profiles may facilitate the selection of patients suitable for other new treatment modalities.

Child↗
PubMedDate not supplied

Language activation distributions revealed by fMRI in post-operative epilepsy patients: differences between left- and right-sided resections.

OBJECTIVE: To reveal differences of cerebral activation related to language functions in post-operative temporal lobe epilepsy (TLE) patients. METHODS: Right (RTL) and left temporal lobe (LTL) resected patients, and healthy controls were studied using functional magnetic resonance imaging (fMRI). Only patients with complete left-hemispheric language dominance according to the intracarotid amytal procedure (IAP) were included. Language-related activations were evoked by performing word generation and text reading language tasks. Activation lateralization and temporo-frontal distribution effects were analysed. RESULTS: For word generation, only LTL patients showed reduced left lateralized activation compared to controls, due to a decrease in activation in the left prefrontal cortex and an increase in the right prefrontal cortex. For reading, the left-hemispheric lateralization in RTL patients increased because of enhanced activity in the left prefrontal cortex, whereas for LTL patients the activation became bilaterally distributed over the temporal lobes. Lateralization results between pre-operative IAP and post-operative fMRI were highly discordant. Significant temporo-frontal distribution changes manifested from the reading but not from the word generation task. CONCLUSION: The cerebral language representation in post-operative LTL epilepsy patients is more bi-hemispherically lateralized than in controls and RTL patients. Post-operative temporo-frontal and interhemispheric redistribution effects, involving contralateral homologous brain areas, are suggested to contribute to the cerebral reorganisation of language function.

Adult↗
PubMed1992

Activity distribution of seven digestive enzymes along small intestine in calves during development and weaning.

Ten groups of calves were used to study the changes in activity levels and distribution of seven hydrolases in the intestinal mucosa during development and weaning. The calves in the first group were sacrificed at birth while those in the remaining nine groups were either milk-fed until slaughter on days 2, 7, 28, 56, 70, and 119; or weaned between days 28 and 56 and then slaughtered on days 56, 70, and 119, respectively. The small intestine was immediately cut off and divided into five segments, ie, duodenum, proximal jejunum, median jejunum, distal jejunum, and ileum. In the milk-fed animals, the activity levels of aminopeptidases A and N, alkaline phosphatase, lactase, and isomaltase were maximum at 2 days of age, and then declined sharply between days 2 and 7 but did not change significantly thereafter. By contrast, the maltase activity increased between days 7 and 119, while no sucrase activity was detected. Weaning resulted in a decrease in the activity of lactase and an increase in that of aminopeptidase N, maltase, and isomaltase. The distribution of all these enzymes along the small intestine was slightly influenced by age but not at all by weaning.

Animals↗
PubMed1980

[Problems relating to the use of radioactively labelled bacteria in animal experiments. 3. Distribution of activities in mice, following parenteral administration of Pasteurella multocida labeled with various radionuclides].

When radioactively labelled fully developed Pasteurella (P.) multocida antigens were parenterally applied to mouse, through intravenous, intraperitoneal or subcutaneous routes, activity distribution was found to depend both the technique of application and the radionuclide used. This has given rise to the conclusion that activity distribution could be equated with whole-germ distribution only under certain conditions. Experimental antigen distribution, accordingly, reflected a complex process in which transport, location, and metabolism of bacteria had to be considered as being in conflict with the given host organism. Iodine labelled 125 was split off bacteria at relatively high rate and accumulated in the thyroid gland. When 59Fe was used, interpretation of distribution was rendered more difficult by propagation of iron through the organs of the host. Relatively favourable data were obtainable from the use of 3H or 14C which could be used in the form of nucleic acid precursors (orotic acid) in labelling Pasteurella. Intraperitoneal and intravenous forms of administration were found to be the same for intra-organic activity distribution. Retention of activity in liver, spleen, and lung was recordable and established from all the reviewed techniques for the application of P. multocida complete antigen. While maximum concentrations were measured between the first and third days, activities still were detectable after 14 days (period under review). Relatively high radioactivity was recordable from the digestive tract, within short time from the use of the parenteral procedures tested. This seemed to suggest passage of complete or incomplete P. multocida antigen through the mucous membranes of the gastro-intestinal tract.

Animals↗
PubMed1985

Acetylcholinesterase (AChE) and pseudocholinesterase (BuChE) activity distribution pattern in early developing chick limbs.

The distribution of acetylcholinesterase (AChE) and pseudocholinesterase (BuChE) activities was studied by histochemical, quantitative and electrophoretical methods during the early development of chick limbs, from stage 16 to stage 32 H.H. (Hamburger & Hamilton, 1951). By quantitative methods, true AChE activity was found, and increased about threefold during the developmental period, together with a smaller amount of BuChE which increased more rapidly in comparison with the AChE activity from stage 25 to 32 H.H. Cholinesterase activity was histochemically localized mainly in interacting tissues, such as the ectoderm (including the apical ectodermal ridge) and the underlying mesenchyme. True AChE was histochemically localized around the nuclei and on the plasma membrane of ectodermal (including AER) and mesenchymal cells, and at the plasma membrane of mesenchymal cell processes reaching the basal lamina between the ectoderm and the mesenchyme. AChE together with BuChE activity was found in the basal lamina between the ectoderm and the mesenchyme, in underlying mesenchymal cells and in deeper mesenchymal cells, especially during their transformation into unexpressed chondrocytes. During limb morphogenesis, the cellular and regional localization of the enzyme activities showed variations depending on the stage of development and on the occurrence of interactions. The possibility of morphogenetic functions of the enzyme id discussed.

Acetylcholinesterase↗
PubMedDate not supplied

Serum alanine aminotransferase in blood donors: activity distribution and effect of phenotype.

Alanine aminotransferase (ALT) phenotype and serum activities were determined in 200 random volunteer blood donors. Serum enzyme activities were not significantly affected by the ALT phenotype (p greater than 0.1). Studies on 500 random volunteer blood donors showed significant differences in serum ALT levels between male and female donors (p less than 0.001). Elevated serum ALT levels were more commonly found in male donors; the frequency of male donors with levels of 45 IU/l or higher was 2.5 percent compared with 0.9 percent in female donors. The frequency of donors with serum ALT levels of 80 IU/l or higher was 0.6 percent of the total donor population sampled.

Alanine Transaminase↗
PubMed1999

The effect of surgical stress and endotoxin-induced sepsis on the NK-cell activity, distribution and pulmonary clearance of YAC-1 and melanoma cells.

Following surgery the activity of natural killer (NK) cells is decreased in the blood. It is possible that sepsis with release of endotoxin will further decrease the NK-cell activity. The purpose of the present study was to investigate the NK-cell cytotoxicity, the clearance in the lungs of YAC-1 and melanoma cells, as well as the distribution of NK-cells in the liver, following abdominal surgery and intraperitoneally (i.p.) administered endotoxin. Ten mice in each group were allocated to abdominal surgery, i.p. endotoxin or anaesthesia alone. Following abdominal surgery, the cytotoxicity of NK-cells isolated from the spleen was decreased and 4 h after injection the clearance of YAC-1 cells from the lungs was only 79.5+/-6.1% compared to 99.5+/-0.3% in the control group. The number of NK-cells in the liver was also significantly reduced following abdominal surgery. In contrast, i.p. endotoxin increased the activity of NK-cells by 28.5% compared to 11.8% in the control group and 8.1% in the surgery group, lowered the number of melanoma metastases in extrapulmonary organs and significantly increased the number of NK-cells in the liver. Following abdominal surgery, activity of NK-cells, pulmonary clearance and number of NK-cells in the liver were decreased. The number of NK-cells in the liver correlated with the NK-cell activity throughout the study. The increased NK-cell cytotoxicity and the increased number of NK-cells in the liver following i.p. administered endotoxin might initially be an appropriate measure against intra-abdominal infection.

Animals↗
PubMed2003

Designing a knowledge management system for distributed activities: a human centered approach.

In this study we use the principles of distributed cognition and the methodology of human-centered distributed information design to analyze a complex distributed human-computer system, identify its problems, and generate design requirements and implementation specifications of a replacement prototype for effective organizational memory and knowledge management. We argue that a distributed human-computer information system has unique properties, structures and processes that are best described in the language of distributed cognition. Distributed cognition provides researchers a richer theoretical understanding of human-computer interactions and enables re-searchers to capture the phenomenon that emerges in social interactions as well as the interactions between people and structures in their environment.

Artificial Intelligence↗