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PubMed1989

Effects of uniform and non-uniform synaptic 'activation-distributions' on the cable properties of modeled cortical pyramidal neurons.

Knowledge of the resting potential and input resistance reveal little about the electrotonic structure of nerve cells since that structure is governed by the background distribution of activated conductances. The background distribution of activated conductances (or 'activation-distribution') is commonly assumed to be uniform, but there is much evidence to suggest that the 'activation-distribution' of cortical pyramidal cells in non-uniform. We investigated effects of uniform and non-uniform activation-distributions with simulations employing passive cable models of an HRP-injected cortical pyramidal neuron. The consequences of 5 different activation-distributions on the effectiveness of synaptic inputs and the electrophysiological properties of the neuron were compared. With non-uniform activation-distributions, (i) the resting membrane potential was non-uniform (with difference of 10-15 mV or more found between soma and distal dendrites), (ii) the electrotonic distances to distal synapses were smaller than with a uniform distribution, and (iii) a two-fold range of variation was seen in the effectiveness of distal synaptic inputs. Differences in time constants, tau 0 and tau 1, obtained from an analysis of transients and in electrotonic length, L, were also found with different activation-distributions. These differences were difficult to assess due to the inherent difficulty in estimating tau 1 (as demonstrated here) and the inappropriateness of the usual formula for L for these cells. Reducing afferent activity (as might happen in tissue slice) increased the effectiveness of distal inputs and reduced the differences in resting potential seen in the neuron. It is concluded that the effectiveness of synaptic inputs and the electrophysiological properties of a neuron can be quite different when the activation-distribution is non-uniform rather than uniform.

Animals↗

PubMed1996

A Monte-Carlo program converting activity distributions to absorbed dose distributions in a radionuclide treatment planning system.

In systemic radiation therapy, the absorbed dose distribution must be calculated from the individual activity distribution. A computer code has been developed for the conversion of an arbitrary activity distribution to a 3-D absorbed dose distribution. The activity distribution can be described either analytically or as a voxel based distribution, which comes from a SPECT acquisition. Decay points are sampled according to the activity map, and particles (photons and electrons) from the decay are followed through the tissue until they either escape the patient or drop below a cut off energy. To verify the calculated results, the mathematically defined MIRD phantom and unity density spheres have been included in the code. Also other published dosimetry data were used for verification. Absorbed fractions and S-values were calculated. A comparison with simulated data from the code with MIRD data shows good agreement. The S values are within 10-20% of published MIRD S values for most organs. Absorbed fractions for photons and electrons in spheres (masses between 1 g and 200 kg) are within 10-15% of those published. Radial absorbed dose distributions in a necrotic tumor show good agreement with published data. The application of the code in a radionuclide therapy dose planning system, based on quantitative SPECT, is discussed.

Absorption↗

PubMedDate not supplied

Optimization of activity distribution in brachytherapy.

We investigated the problem of how to minimize the dose rate outside a spherical target volume for a given minimal dose rate inside the sphere for 1/r2 photon emitters. An integral equation for an activity distribution is derived from the demand that the dose rate is constant inside the sphere. The solution of this equation is given and it is proven that the resulting activity distribution gives the smallest dose rate at every point outside the target volume. Some other activity distributions are discussed; they are assessed by the required integral activity, which is proportional to the dose rate at some distance from the target volume. Compared with a single point source at the center of the sphere, one can save 50% of the total activity when using the optimal activity distribution. The benefit reduces to about 30% for the other continuous activity distributions and to a few % for symmetrical arrangements of a few point sources.

Brachytherapy↗

PubMed1991

Assessment of accuracy of PET utilizing a 3-D phantom to simulate the activity distribution of [18F]fluorodeoxyglucose uptake in the human brain.

A three-dimensional brain phantom has been developed to simulate the activity distributions found in human brain studies currently employed in positron emission tomography (PET). The phantom has a single contiguous chamber and utilizes thin layers of lucite to provide apparent relative concentrations of 5, 1, and 0 for gray matter, white matter, and CSF structures, respectively. The phantom and an ideal image set were created from the same set of data. Thus, the user has a basis for comparing measured images with an ideal set that allows a quantitative evaluation of errors in PET studies with an activity distribution similar to that found in patients. The phantom was employed in a study of the effect of deadtime and scatter on accuracy in quantitation on a current PET system. Deadtime correction factors were found to be significant (1.1-2.5) at count rates found in clinical studies. Deadtime correction techniques were found to be accurate to within 5%. Scatter in emission and attenuation correction data consistently caused 5-15% errors in quantitation, whereas correction for scatter in both types of data reduced errors in accuracy to less than 5%.

Brain↗

PubMedDate not supplied

Activity distribution of a cobalt-60 teletherapy source.

In the course of quantifying the effect of radiation source size on the spatial resolution of portal images, a concentric ring structure in the activity distribution of a Cobalt-60 teletherapy source has been observed. The activity distribution was measured using a strip integral technique and confirmed independently by a contact radiograph of an identical but inactive source replica. These two techniques suggested that this concentric ring structure is due to the packing configuration of the small 60Co pellets that constitute the source. The source modulation transfer function (MTF) showed that this ring structure has a negligible influence on the spatial resolution of therapy images when compared to the effect of the large size of the 60Co source.

Cobalt Radioisotopes↗

PubMed1992

A quantitative autoradiographic study of the heterogeneous activity distribution of different indium-111-labeled radiopharmaceuticals in rat tissues.

In light of the increased interest in small scale dosimetry, this paper presents a quantitative autoradiographic method for evaluation of heterogeneous activity distribution in tissues. This was studied in rat tissues after administration of 111In-chloride, -oxine, -tropolone, 111In-labeled homologous blood cells and 111In-anti-CEA-F(ab')2, using quantitative whole-body autoradiography. Quantification was performed utilizing an image analyzing system designed for whole-body autoradiographs. Very heterogeneous activity distribution was found in several tissues including the liver, spleen, kidneys, bone marrow, lymph nodes and testes. Notable was the high 111In uptake in organs characterized as rapidly proliferating, and known to have numerous transferrin receptors. In the gastrointestinal tract, all activity was associated with the intestinal walls. The heterogeneous tissue distribution shown in this investigation accentuates the necessity for performing detailed studies of the tissue distribution of radiopharmaceuticals. This is especially important for the radiation dosimetry of radionuclides emitting beta-particles or low energy electrons. We suggest whole-body autoradiography as an excellent implement to determine local activity concentrations in organs and tissues necessary for accurate absorbed dose calculations.

Animals↗

PubMed1997

The effect of three dimensional activity distribution on the dose planning of radioimmunotherapy for patients with advanced intraperitoneal pseudomyxoma.

BACKGROUND: Six patients with histologically proven peritoneal carcinomatous pseudomyxomas were treated with radioimmunotherapy. METHODS: All the patients received a tracer dose of iodine-131 (131I) labeled B72.3 anti-TAG-72 monoclonal antibody (MoAb) to test the in vivo affinity. After informed consent was obtained the therapeutic dose (>3.7 gigabecquerels [GBq], 100 mCi) of the 131I labeled B72.3 anti-TAG-72 MoAb was infused within 60 minutes intraperitoneally using 2 catheters on both sides of the abdomen. The patients were imaged with single photon emission computed tomography (SPECT) at 3, 10, and 24 days after the therapeutic infusion. Treatment-planning software has been developed in which functional information obtained from SPECT is integrated with anatomic information obtained from computed tomography (CT). The activity distribution from SPECT images is converted to absorbed dose distributions using a point source kernel convolution dose calculation. The absorbed dose calculation requires a radionuclide specific dose kernel. The activity map is divided into equally sized source voxels from which the distribution is calculated for the target voxels that cover the patient volume. The resulting three dimensional (3D) absorbed dose distribution is viewed as isodose contours superimposed on the CT images or as 3D isodose surfaces. RESULTS: The measured activity distribution shows that the cumulated activity and biologic half-life vary in the patient's body. The developed planning system provides a method for calculating patient specific absorbed dose distributions. CONCLUSIONS: The variation of biologic clearance indicates that a 3D dose calculation method incorporating measured activity distributions is needed to quantify absorbed dose distribution.

Humans↗

PubMed1997

Shifting attention in visual space: tests of moving-spotlight models versus an activity-distribution model.

Participants were induced to concentrate preparatory attention at a central location, to identify a letter there, to identify a 2nd letter to the extreme left or right of a central horizontal range of 5 locations, and then to identify a 3rd letter at 1 of the central 5 locations. Analog and discrete versions of the moving-spotlight model predict that response times to the 3rd letter will be most rapid at the location of the 2nd letter, whereas an activity-distribution model predicts that the most rapid responses to the 3rd letter will be at the central location, where preparatory attention is strongest. The data from 3 experiments, taken together, are inconsistent with the moving-spotlight models and are consistent with the activity-distribution model.

Adult↗

PubMed1974

The distribution, activity, and function of the cilia in the frog brain.

1. The distribution, activity, and function of the cilia in the brain was studied using in vitro preparations of the frog choroid plexuses and ependyma.2. Scanning electron microscopy revealed that twenty to forty cilia, about 20 mum long, project from the cells of the choroidal epithelium and ependyma into the ventricular system of the brain.3. These cilia beat at a constant frequency which ranged from 5 to 20 c/s. Ciliary activity was enhanced by ATP, cyclic AMP, theophylline, and acetylcholine, and was depressed by DNP, IAA, Ni(2+), La(3+), and Co(2+).4. Ciliary motion produced a flow of c.s.f. over the surface of the cells lining the ventricles, and in the choroid plexus this flow reduced the effective thickness of the unstirred layer adjacent to the epithelium by about 100 mum.5. These results are discussed in relation to the factors that control the frequency of ciliary beating, and the role of the cilia in the circulation of the c.s.f.

Acetylcholine↗

PubMed1995

Distribution, activation and tryptase/chymase phenotype of mast cells in the rheumatoid lesion.

OBJECTIVE: To determine the distribution, activation, and tryptase/chymase phenotype of mast cells (MCs) in the rheumatoid lesion. METHODS: MC tryptase and chymase were studied by immunohistochemistry using monoclonal antibodies and examination by brightfield, interference, and fluorescent microscopy. Thirty four specimens of cartilage-pannus junction and 26 specimens of rheumatoid synovium, all derived from knee surgery, were examined. RESULTS: MCs were identified in all specimens examined, but their distribution and local concentrations varied, both within and between specimens. As a proportion of total synovial cells, there were more MCs in fibrous synovial tissues than in those with active inflammatory cell infiltrations; MCs usually showed a peripheral distribution around lymphocytic/mononuclear cell infiltrations. Most cartilage-pannus specimens demonstrated local concentrations of MCs at, or close to, sites of cartilage erosion, a significant proportion of which showed extracellular tryptase indicative of MC degranulation. MC degranulation was often associated with localised oedema and disruption of the stromal matrix. Two MC phenotypes were identified: one population contained tryptase alone (MCT) whilst another contained both tryptase and chymase (MCTC). The ratio MCT:MCTC approximated 8:1. CONCLUSIONS: This histological study demonstrated that local concentrations of MCs and their activation/degranulation are commonly observed in the rheumatoid lesion, and especially at sites of cartilage erosion. Such observations add weight to the concept that MCs contribute to the processes of inflammation, matrix degradation and tissue remodelling.

Aged↗

PubMed1982

In vitro mass: activity distribution of lecithin--cholesterol acyltransferase among human plasma lipoproteins.

In order to compare the mass-activity distribution of lecithin-cholesterol acyltransferase (LCAT) among plasma lipoproteins separated by various ultracentrifugal or chromatographic procedures, we have quantified the enzyme by an electroimmunoassay technique using a specific antibody raised in the rabbit. This antibody, when added to whole serum, inhibited all of the enzyme activity present in it. The percent mass distribution of the enzyme among the lipoproteins isolated by rate-zonal ultracentrifugation (d 1.00-1.36 g/ml, SW 40 rotor, 37 000 rpm, 16 h) was as follows: very low density lipoproteins (VLDL), 0; low density lipoproteins (LDL), 6.2; HDL2, 6.5; HDL3, 12 and d greater than 1.21 g/ml fraction, 75. Measurement of LCAT activity of each lipoprotein fraction against mixed single bilayer lecithin-cholesterol vesicles (molar ratio, 4:1) containing apo A-I, indicated that VLDL, LDL and HDL2 were inactive or minimally active under the experimental conditions used, whereas HDL3 and the d greater than 1.21 g/ml fraction contained 17.5 and 79.9% of the total enzyme activity. Prolonged ultracentrifugation of the LCAT-containing lipoproteins resulted in the recovery of activity in the lipoprotein-free infranatant. In studies with lipoproteins linked to Sepharose 4B, LCAT was found to bind LDL, HDL2, and HDL3. It is concluded that LCAT is present in all the major lipoproteins except for VLDL. The activity appears to be dependent, at least in part, on the type of lipoproteins to which the enzyme is associated with.

Centrifugation, Isopycnic↗

PubMed1992

[Quantitative topographic characterization of the myoelectric activity distribution of the masseter muscle: mapping of spectral EMG parameters].

A new method for quantitative characterization of myoelectrical masseter activity distribution by mapping of spectral EMG-parameters is described. The surface electromyograms of M. masseter were monopolarly recorded (16 channels). On the basis of registered EMG intervals (512 ms) the spectral EMG power of several frequency bands was calculated (Fast Fourier Transformation). The spectral EMG parameters between the 16 electrode positions were estimated by linear interpolation (4-nearest neighbours algorithm). Afterwards the spectral EMG parameters were fitted in a grey-tone or colour scale with 10 intervals. The so obtained EMG activity maps ("EMG-Maps") permit a quantitative-topographic characterization of myoelectrical masseter activity during different functional load procedures. The frequency range which is to consider in masseter surface-EMG investigations encloses frequencies between 15 and 500 Hz. The topography of EMG activation pattern of M. masseter is only described in a comprehensive manner when the electrode array consists of 16 electrodes and more. During defined motor tasks like clenching with controlled forces the reproducibility of EMG-Maps which respect to the topography of EMG activity pattern is very high. The absolute values of spectral EMG power as well as power changes of selected band ranges during clenching correlate to the extent of chewing forces.

Adult↗

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↗

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↗

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↗