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PubMed1985

Factors that determine the direction and magnitude of precordial ST-segment deviations during inferior wall acute myocardial infarction.

Sixty-one patients with inferior acute myocardial infarction (AMI) and no evidence of prior AMI were studied to determine which factors influence the magnitude of precordial ST-segment depression. In the total study group, there was a significant but weak correlation between the magnitude of precordial ST-segment depression and the magnitude of inferior ST-segment elevation (r = -0.46, p less than 0.001). In the 29 patients with evidence of concomitant right ventricular (RV) involvement, precordial ST-segment depression was significantly smaller both in absolute terms (-1.3 +/- 1.8 vs -2.8 +/- 1.9 mm, p less than 0.01) and relative to the magnitude of inferior ST-segment elevation (ratio of -0.2 +/- 1.0 vs -1.1 +/- 0.5, p less than 0.01), whereas in the 15 patients with lateral ST-segment elevation (greater than or equal to 1 mm in lead V6), precordial ST-segment depression was significantly greater both in absolute terms (-3.5 +/- 2.3 vs -1.6 +/- 1.7 mm, p less than 0.01) and relative to the magnitude of inferior ST-segment elevation (ratio of -1.1 +/- 0.8 vs -0.5 +/- 0.9, p less than 0.02). Consistent with these findings, the correlation between the magnitudes of precordial and inferior ST-segment deviations was considerably improved when only the 24 patients with neither evidence of RV involvement nor lateral ST-segment elevation were analyzed (r = 0.89, p less than 0.001, n = 24). These data suggest that in patients with inferior AMI, there is a reciprocal relation between precordial and inferior ST-segment deviations, which is distorted by concomitant RV involvement and by concomitant lateral left ventricular wall involvement.

Aged↗
PubMed1978

Effect of ischemia on axonal transport of choline acetyltransferase and acetylcholinesterase and on ultrastructural changes of isolated segments of rabbit nerves in situ.

Axonal transport of acetylcholinesterase (AChE) and choline acetyltransferase (ChAc) and ultrastructural degenerative changes were compared in isolated nerve segments of rabbit peroneal nerves kept in vivo for 22 h, either with preserved blood supply (control segments) or under conditions of ischemia (ischemic segments). Ischemia abolished the proximo-distal and disto-proximal axonal transport of AChE and the proximo-distal transport of ChAc which, in control segments, were revealed by accumulations of the enzymes at corresponding ends of the segments. Total activities of AChE and ChAc recovered in isolated segments with intact blood supply corresponded to the activities in normal nerves; in ischemic segments, 50% of ChAc activity was lost in 22 h, whereas all AChE activity was preserved. Ultrastructural changes were found in few fibres in control segments and in many fibres in ischemic segments 22 h after nerve interruption. The early changes in control segments correspond to those described in the literature for peripheral stump of severed nerves. The microtubules, neurofilaments and mitochondria were not affected. In ischemic segments, various stages of axoplasmic disintegration occurred in the myelinated and unmyelinated axons:flocculation and clumping of axoplasmic material, decomposition of neurofilaments and microtubules, swelling, formation of amorphous densities and breakdown of mitochondrial cristae. Swelling, amorphous densities, clumping of nuclear chromatin and necrotic mitochondrial changes appeared also in Schwann cells. It is concluded that ischemia blocks axonal transport and brings about, within 22 h, ultrastructural changes both in nerve fibres and in Schwann cells. Cytoplasmic ChAc is affected earlier by necrotic degeneration of the axons than membrane-bound AChE.

Acetylcholinesterase↗
PubMed1982

Permeability of gap junctions at the segmental border in insect epidermis.

We have examined cell-cell communication between epidermal cells of fifth-instar larvae of the milkweed bug Oncopeltus fasciatus and those of maggots of the blowfly Calliphora erythrocephala. Ionic coupling and the transfer of injected Lucifer Yellow (molecular weight 450) and lead-EDTA (molecular weight 374) were used to map the pattern of communication. All epidermal cells, regardless of their position with respect to the segmental border, were ionically coupled. In both species Lucifer yellow was transferred freely between cells lying in the same segment--that is, in the same developmental compartment as defined by cell lineage. Dye injections close to the segmental border showed that Lucifer Yellow was not transferred between cells in adjacent segments--that is, across the compartmental border. In Calliphora failure of Lucifer Yellow transfer at the segmental border was always observed; in Oncopeltus Lucifer Yellow was not transferred in 90% of preparations examined. Injections of PbEDTA2- in Calliphora showed that this anion was transferred freely from cell to cell and did not respect the segmental boundary. Previous studies of the distribution of gap junctions at and away from the segmental border make it unlikely that the failure of Lucifer Yellow to cross from segment to segment is due to reduced number of gap-junctional channels at the border. We conclude that gap junctions at the segmental borders may have different permeability properties from those between cells in the same segment.

Animals↗
PubMed1994

Structure and genomic organization of VH gene segments in the channel catfish: members of different VH gene families are interspersed and closely linked.

To determine the structure and organization of germline VH gene segments in the channel catfish, genomic lambda libraries were screened with cDNA probes representing different catfish VH gene families. Thirty-six VH positive genomic clones were isolated and four of these were characterized by restriction mapping and Southern blot analysis with probes specific for each known VH gene family. The four clones, representing about 65 kb of DNA, contained 21 VH segments. The average distance between segments was about 3 kb and gene segments representing different VH gene families were interspersed with each other. Dot-blot hybridization analysis of all 36 genomic clones (average insert size 16-18 kb) indicated that the average clone contained gene segments representing four different VH families. In addition, these analyses indicated that VH segments representing each VH family could be found closely linked to gene segments representing each of the other VH families. Genomic restriction fragments containing a VH segment of each gene family were sequenced. These analyses showed that the general structure of VH segments is conserved in catfish. These structural features include the presence of a leader sequence split by a short intron, an uninterrupted open reading frame encoding readily identified framework and complementarity determining regions, and a downstream recombination signal sequence represented by a consensus heptamer, a 22-24 bp spacer, and an A-rich nonamer. Upstream of the VH segments was an octamer sequence. These analyses indicate that the organization and structure of VH segments typically associated with VH loci of higher vertebrates evolved early in phylogeny at the level of the bony fishes.

Amino Acid Sequence↗
PubMed1991

Segmental distribution of colonic neuropeptides in Hirschsprung's disease.

Despite continued research, the pathophysiologic mechanism responsible for functional obstruction in the aganglionic segment of bowel in Hirschsprung's disease remains controversial. Narrowing of the affected segment is thought by many investigators to be the result of loss of intrinsic inhibitory innervation. For this hypothesis to be consistent, inhibitory neuropeptides should be present in the dilating, transitional segment of bowel. In order to quantitate reported changes in peptidergic nerve staining in Hirschsprung's disease, we measured concentrations of five neuropeptides (vasoactive intestinal peptide, peptide histidine-methionine, met5-enkephalin, substance P and bombesin-like immunoreactivity) by radioimmunoassay in the affected segments of bowel from six patients with Hirschsprung's disease. Tissue extracts were prepared using gut obtained at surgery from the: (1) constricted, aganglionic segment, (2) dilating, aganglionic transitional segment and (3) dilated, proximal ganglionic segment. Concentrations of vasoactive intestinal peptide, peptide histidine-methionine, substance P and met5-enkephalin were significantly reduced in both the muscularis externa and the mucosal-submucosal layers from the constricted aganglionic segment. By contrast, concentrations of the candidate inhibitory neuropeptides, vasoactive intestinal peptide and peptide histidine-methionine, were minimally reduced in the dilating, aganglionic transitional segment. These results are consistent with the hypothesis that constriction of the aganglionic segment is due to loss of intrinsic inhibitory innervation. Concentrations of bombesin-like immunoreactivity were similar in the three segments of human gut, suggesting the presence of this immunoreactive neuropeptide in extrinsic nerve fibers.

Bombesin↗
PubMed1993

Image segmentation: methods and applications in diagnostic radiology and nuclear medicine.

We review and discuss different classes of image segmentation methods. The usefulness of these methods is illustrated by a number of clinical cases. Segmentation is the process of assigning labels to pixels in 2D images or voxels in 3D images. Typically the effect is that the image is split up into segments, also called regions or areas. In medical imaging it is essential for quantification of outlined structures and for 3D visualization of relevant image data. Based on the level of implemented model knowledge we have classified these methods into (1) manual delineation, (2) low-level segmentation, and (3) model-based segmentation. Pure manual delineation of structures in a series of images is time-consuming and user-dependent and should therefore be restricted to quick experiments. Low-level segmentation analyzes the image locally at each pixel in the image and is practically limited to high-contrast images. Model-based segmentation uses knowledge of object structure such as global shape or semantic context. It typically requires an initialization, for example in the form of a rough approximation of the contour to be found. In practice it turns out that the use of high-level knowledge, e.g. anatomical knowledge, in the segmentation algorithm is quite complicated. Generally, the number of clinical applications decreases with the level and extent of prior knowledge needed by the segmentation algorithm. Most problems of segmentation inaccuracies can be overcome by human interaction. Promising segmentation methods for complex images are therefore user-guided and thus semi-automatic. They require manual intervention and guidance and consist of fast and accurate refinement techniques to assist the human operator.

Algorithms↗
PubMed1995

Extent of early ST segment elevation resolution: a strong predictor of outcome in patients with acute myocardial infarction and a sensitive measure to compare thrombolytic regimens. A substudy of the International Joint Efficacy Comparison of Thrombolytics (INJECT) trial.

OBJECTIVES: This study was undertaken to assess prospectively the prognostic power of early ST segment elevation resolution in a large cohort of patients with myocardial infarction and to test the value of differences in ST segment resolution as a surrogate end point. BACKGROUND: Previous studies revealed that the use of two cutoff points for three groups of ST segment resolution within 3 h after the start of thrombolysis is most effective in predicting outcome. METHODS: The International Joint Efficacy Comparison of Thrombolytics (INJECT) trial compared mortality in 6,010 patients randomized to receive either reteplase or streptokinase. The 1,909 German patients form the basis of this substudy. The three groups of ST segment resolution were defined as complete (> or = 70%), partial (70% to 30%) and no resolution (< 30% to > or = 0%). RESULTS: In 1,398 patients presenting < or = 6 h from onset of acute myocardial infarction, the 35-day mortality rate for complete, partial and no ST segment resolution was 2.5%, 4.3% and 17.5%, respectively (p < 0.0001). Peak creatine kinase levels (fraction of normal) were 9.8, 13.4 and 14.0, respectively (p < 0.0001). When baseline characteristics were included, ST segment resolution was the most powerful independent predictor of 35-day mortality. The proportion of patients with complete ST segment resolution was larger, and that with no ST segment resolution smaller, with reteplase than with streptokinase (p = 0.006). CONCLUSIONS: No ST segment resolution, indicating failed thrombolysis, predicts very high early mortality, whereas complete resolution is associated with a small infarct area and low mortality. Partial ST segment resolution also predicts larger infarct areas, but early mortality is relatively low. Different extents of ST segment resolution may serve as a sensitive surrogate end point in clinical trials.

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PubMed2004

Gender significance of ST-segment deviation detected by ambulatory (Holter) monitoring.

OBJECTIVE: To evaluate the gender influence in diagnostic and prognostic value of Holter-detected ST-segment deviation. METHODS: Two-hundred seventy-seven consecutive patients (196 men) who underwent coronary angiography for evaluation of chest pain were studied with 24-h Holter monitoring within 72 h of coronary angiography, and were followed up for 65+/-21 months. RESULTS: Men had a higher prevalence of coronary artery disease (169 of 196, 86%) compared to that of women (54 of 81, 67%), p<0.00025. Thirty-three (17%) men and 15 (19%) women had ST-segment deviation during 24-h recording. The sensitivity, specificity and positive predictive values of ST-segment deviation (elevation, depression, or both) for the detection of significant coronary artery disease were similar in men and women. The negative predictive values were significantly higher in women than men for ST-segment deviation (36% vs. 15%, p<0.001), ST-segment elevation (35% vs. 14%, p<0.001), and ST-segment depression (34% vs. 15%, p<0.001). Similarly, the diagnostic accuracies were significantly higher in women than men for ST-segment deviation (44% vs. 29%, p<0.025), ST-segment elevation (38% vs. 19%, p<0.001), and ST-segment depression (40% vs. 24%, p<0.025). There was no significant difference in composite end-point of events (mortality, nonfatal myocardial infarction, unstable angina, and coronary revascularization) in men versus women with ST-segment deviation (elevation, depression, or both). CONCLUSION: Holter-detected ST-segment deviation has a higher negative predictive value and diagnostic accuracy for detection of significant coronary artery disease in women than in men, although the prognostic values are not significantly different between men and women.

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PubMed2004

Intracranial vessel segmentation from time-of-flight MRA using pre-processing of the MIP Z-buffer: accuracy of the ZBS algorithm.

We evaluate the accuracy of a vascular segmentation algorithm which uses continuity in the maximum intensity projection (MIP) depth Z-buffer as a pre-processing step to generate a list of 3D seed points for further segmentation. We refer to the algorithm as Z-buffer segmentation (ZBS). The pre-processing of the MIP Z-buffer is based on smoothness measured using the minimum chi-square value of a least square fit. Points in the Z-buffer with chi-square values below a selected threshold are used as seed points for 3D region growing. The ZBS algorithm couples spatial continuity information with intensity information to create a simple yet accurate segmentation algorithm. We examine the dependence of the segmentation on various parameters of the algorithm. Performance is assessed in terms of the inclusion/exclusion of vessel/background voxels in the segmentation of intracranial time-of-flight MRA images. The evaluation is based on 490,256 voxels from 14 patients which were classified by an observer. ZBS performance was compared to simple thresholding and to segmentation based on vessel enhancement filtering. The ZBS segmentation was only weakly dependent on the parameters of the initial MIP image generation, indicating the robustness of this approach. Region growing based on Z-buffer generated seeds was advantageous compared to simple thresholding. The ZBS algorithm provided segmentation accuracies similar to that obtained with the vessel enhancement filter. The ZBS performance was notably better than the filter based segmentation for aneurysms where the assumptions of the filter were violated. As currently implemented the algorithm slightly under-segments the intracranial vasculature.

Algorithms↗
PubMed2005

A hybrid framework for 3D medical image segmentation.

In this paper we propose a novel hybrid 3D segmentation framework which combines Gibbs models, marching cubes and deformable models. In the framework, first we construct a new Gibbs model whose energy function is defined on a high order clique system. The new model includes both region and boundary information during segmentation. Next we improve the original marching cubes method to construct 3D meshes from Gibbs models' output. The 3D mesh serves as the initial geometry of the deformable model. Then we deform the deformable model using external image forces so that the model converges to the object surface. We run the Gibbs model and the deformable model recursively by updating the Gibbs model's parameters using the region and boundary information in the deformable model segmentation result. In our approach, the hybrid combination of region-based methods and boundary-based methods results in improved segmentations of complex structures. The benefit of the methodology is that it produces high quality segmentations of 3D structures using little prior information and minimal user intervention. The modules in this segmentation methodology are developed within the context of the Insight ToolKit (ITK). We present experimental segmentation results of brain tumors and evaluate our method by comparing experimental results with expert manual segmentations. The evaluation results show that the methodology achieves high quality segmentation results with computational efficiency. We also present segmentation results of other clinical objects to illustrate the strength of the methodology as a generic segmentation framework.

Algorithms↗
PubMed2006

Origin of segmentation in the human structure.

Crystallographic analysis of biological and non-biological minerals does not reveal any significant differences between the two, which is indicative of common crystallization processes. It can be supposed that the human organism is a biocrystalloid in a sense that it is regarded both at the level of the whole organism and individual cells as a composite entity consisting of a crystal-like structure and pericrystalline medium. A similarity can be found between the growing layer of a crystal in the crystal-forming medium and a cell structure with liquid washing it. A mineral organism therefore can be regarded as the active superficial part of a crystal taken together with pericrystalline crystal-forming medium which controls crystal growth and modifies the system depending on the structure of the growing system. Aggregation is one of the fundamental features of minerals as they are found primarily not only as separate objects but also as aggregates, i.e. regular cohesive masses or synmineralogical systems. Ability to aggregation in an orderly way is expressed as self-organization. This feature is inherent not only to compound molecules but also to associates of a higher order. The cell biology has shown that when similar cells touch each other they tend to cohere forming aggregates characteristic of the given cell population. Similar live systems and their components that perform the same function have an ability to integrate and form firstly a conglomerate (colony) and then an organism. Integration explains association of multi-segmented entities into a single organism and the resulting structure would consists of the two groups of segments, i.e. appearance of an organism consisting of two different but of the same type specimens, each of which had different number of segments. Phylogenetically, an early precursor of the man evolved from a simple cell into an integrated multi-segment organism through several stages--initially a simple cell, then a cell colony, then a single-segment organism, then an organism like a concave ball, then a colony of one-segment multicellular organisms and finally a multi-segment multicellular organism. Integration of five- and eight-segment organisms resulted in the formation of a 13-segment precursor organism of man. Segmentation is nothing else but traces of boundaries left following integration of separate multicellular non-segmented specimens with gradual fading of their differences and formation of a new entity in compliance with formation laws.

Biological Evolution↗
PubMed2005

Jalpha-gene segment usage and the CDR3 diversity of porcine TCRalpha-chain cDNA clones from the PBL of a five-month-old pig and the thymus of a one-month-old pig.

Porcine T-cell receptor alpha (TCRalpha)-chain cDNA clones were isolated from libraries made from two different sources, the thymus of a 1-month-old LW strain pig and the peripheral blood lymphocytes (PBL) of a 5-month-old Clawn strain pig. Among 109 cDNA clones with the Jalpha-gene segment, 44 different Jalpha-gene segments were found out of the 61 Jalpha-gene segments previously identified in the porcine germline sequence. Among the 103 complete TCRalpha-chain cDNA clones with the rearranged Valpha- and Jalpha-gene segments, 33 different Valpha-gene segments were identified, which randomly rearranged to Jalpha-gene segments indicating lack of any specific combinations between Valpha- and Jalpha-gene segments with only one exception of the same set of Jalpha-gene segments in duplicate clones. Among the cDNA clones from PBL of an individual 5-month-old Clawn strain pig, a broad distribution of the Jalpha-gene segment usage was observed over the entire Jalpha-gene cluster. The Jalpha-gene segment usage in an individual 1-month-old thymus from a LW strain pig also gave a pattern consistent with the 5-month-old pig. These distributions of the Jalpha-gene segment usage were similar to the previously reported patterns for human T-cells and those of adult murine T-cells. Among the porcine cDNA clones isolated, TCRalpha-chain CDR3 length ranged from 4 to 14 amino acids with the average being 9.35 amino acids. Present report provides groundwork for further studies on porcine TCRalpha-chain expression.

Amino Acid Sequence↗
PubMed2004

Gene expression suggests decoupled dorsal and ventral segmentation in the millipede Glomeris marginata (Myriapoda: Diplopoda).

Diplopods (millipedes) are known for their irregular body segmentation. Most importantly, the number of dorsal segmental cuticular plates (tergites) does not match the number of ventral structures (e.g., sternites). Controversial theories exist to explain the origin of this so-called diplosegmentation. We have studied the embryology of a representative diplopod, Glomeris marginata, and have analyzed the segmentation genes engrailed (en), hedgehog (hh), cubitus-interruptus (ci), and wingless (wg). We show that dorsal segments can be distinguished from ventral segments. They differ not only in number and developmental history, but also in gene expression patterns. engrailed, hedgehog, and cubitus-interruptus are expressed in both ventral and dorsal segments, but at different intrasegmental locations, whereas wingless is expressed only in the ventral segments, but not in the dorsal segments. Ventrally, the patterns are similar to what has been described from Drosophila and other arthropods, consistent with a conserved role of these genes in establishing parasegment boundaries. On the dorsal side, however, the gene expression patterns are different and inconsistent with a role in boundary formation between segments, but they suggest that these genes might function to establish the tergite borders. Our data suggest a profound and rather complete decoupling of dorsal and ventral segmentation leading to the dorsoventral discrepancies in the number of segmental elements. Based on gene expression, we propose a model that may resolve the hitherto controversial issue of the correlation between dorsal tergites and ventral leg pairs in basal diplopods (e.g., Glomeris) and is suggestive also for derived, ring-forming diplopods (e.g., Juliformia).

Amino Acid Sequence↗
PubMed1999

ST-segment deviation during 24-hour ambulatory electrocardiographic monitoring and exercise stress test in healthy male subjects 51 to 75 years of age: the Copenhagen City Heart Study.

BACKGROUND: Although ST-segment deviation has been evaluated and used during many years both on continuous electrocardiographic Holter monitoring and during exercise stress testing, considerable controversy still remains concerning the prevalence and diagnostic significance of fortuitously discovered ST-segment deviation in asymptomatic healthy persons. METHODS AND RESULTS: The occurrence of ST-segment deviation was studied in a population of 63 clinically healthy male subjects 51 to 75 years of age, with the use of 24-hour Holter monitoring and exercise stress testing. The subjects were recruited from the Copenhagen City Heart Study and were without cardiovascular risk factors, chronic diseases, or medication and without cardiovascular events during 5 to 12 years before and 3 to 5 years after admission. The specificity, that is, the probability of displaying a negative test result in healthy subjects without disease, was 1.0 when using as criterion for significant ST-segment deviation a horizontal or descending ST-segment depression of >0.20 mV or ST-segment elevation >/=0.15 mV during Holter monitoring, and acceptable, for example, 0.95, when using as criterion a horizontal or descending ST-segment depression of >/=0.15 mV during Holter monitoring or at the exercise test, respectively. Furthermore, the specificity was 0.95 when a horizontal or downsloping ST-segment depression of 0.1 mV was displayed in both the Holter and exercise electrocardiographic recording system. CONCLUSIONS: Thus in asymptomatic persons, the usual criterion for significant ST-segment depression of 0.1 mV can be applied when occurring in both electrocardiographic recording systems. However, if one test alone is used, the criterion of significant ST-segment depression should be 0.15 mV. Absence of ST-segment deviation during Holter monitoring and exercise stress testing, indicated with a specificity of 1.0 or 0.95 according to choice of criterion, implies that the person is in a healthy state.

Aged↗
PubMed1999

Effects of inhibitors and specific ion-free salines on segmental fluid secretion by the Malpighian tubules of the black field cricket Teleogryllus oceanicus.

The effects of inhibitors and specific ion-free salines on fluid secretion rates in the distal and main segments showed that there were major differences in secretory mechanisms in the two segments. Both main and distal segments of the Malpighian tubules were sensitive to DIDs, SITS and acetazolamide but in different ways. The evidence suggests that the main segment does not contain a Cl(-)/HCO(3)(-) exchanger in the basal membrane, whereas the distal segment may do so. Secretion in both segments was K(+) dependent. Ba(2+) markedly reduced fluid secretion by the main segment and K(+) entry into the cells of the main segment is suggested to be predominantly via K(+) channels. Entry of K(+) may be primarily by other routes, such as Na K ATPase, in the distal segment. In the distal segment secretion was highly Mg(2+) dependent. Both segments were sensitive to amiloride analogs suggesting the presence of apical cation/H(+) exchangers.

Journal Article↗
PubMed1998

Contractile responses of proximal and distal trachea segments isolated from rats subjected to immunological stimulation: role of connective tissue mast cells.

1. Anaphylaxis-induced contractions of proximal and distal tracheal segments isolated from 14-day ovalbumin (OA)-sensitized rats were studied. 2. OA-induced contractions in distal segments were significantly greater than those observed in proximal segments. 3. Pretreatment of the rats with compound 48/80 or with sodium cromoglycate (SCG) aerosolization significantly reduced OA-induced contractions of trachea distal segments, whereas the contractions of proximal segments were reduced only by compound 48/80. 4. Mepacrine reduced and indomethacin increased the OA-induced contractions in all tracheal segments. Nor-dihydroguaiaretic acid increased the OA-induced contractions in distal tracheal segments, whereas dazoxiben inhibited the contractions in these same segments; neither of these drugs had any effect on the contractions in proximal tracheal segments. 5. The depletion of connective tissue mast cells and subsequent in vitro treatment with indomethacin increased the OA-induced contractions in both segments. 6. We conclude that the contractions of tracheal muscle from OA-sensitized rats depends on the topographic and anatomical origin of the airway tissue. 7. Mediators released by connective tissue mast cells in proximal and distal segments play a pivotal role in this response and may account for variations in the intensity of contraction seen after the addition of OA.

Anaphylaxis↗
PubMed1999

Segmental and laminar distributions of nicotinamide adenine dinucleotide phosphate-diaphorase-expressing and neuronal nitric oxide synthase-immunoreactive neurons versus radioassay detection of catalytic nitric oxide synthase activity in the rabbit spinal cord.

The distributions of neuronal nitric oxide synthase-immunoreactive neurons and of nicotinamide adenine dinucleotide phosphate-diaphorase activity were studied in the C6, Th2, L1, L5, S2 and S3 segments and laminae in the rabbit spinal cord and compared with the catalytic nitric oxide synthase activity, determined by monitoring the conversion of [3H]arginine to [3H]citrulline in the same segments and laminae. Morphologically, a heterogeneous population of nicotinamide adenine dinucleotide phosphate-diaphorase-expressing and neuronal nitric oxide synthase-immunoreactive neurons was detected in the superficial and deep dorsal horn and the pericentral region in all segments studied, and in the intermediolateral cell column of the thoracic and lumbosacral segments. A disproportionate distribution of both neuronal categories which had a significantly higher number of nicotinamide adenine dinucleotide phosphate-diaphorase-expressing rather than neuronal nitric oxide synthase-immunoreactive cell bodies was found in all segments. The catalytic nitric oxide synthase activity was distributed unequally in the C6, Th2, L1, L5, S2 and S3 segments, with a comparatively low value in the Th2 segment (70 +/- 5.1 d.p.m./microg protein) in comparison with the S3 segment, where the highest level (140 +/- 5.5 d.p.m./microg protein) was found. A close correlation between the number of neuronal nitric oxide synthase-immunoreactive somata and catalytic nitric oxide synthase activity was revealed in the dorsal horn (laminae I-VI). Whereas a low number of neuronal nitric oxide synthase-immunoreactive somata in laminae VII-X was found in the L5, S2 and S3 segments, the values of catalytic nitric oxide synthase activity in the same laminae and segments were found to be exceedingly high. These findings indicate that the occurrence of many neuronal nitric oxide synthase-immunoreactive fibers (mainly axons), and dense, punctate, non-somatic neuronal nitric oxide synthase immunopositivity in the neuropil staining of the same laminae and segments, can substantially enhance catalytic nitric oxide synthase activity.

Animals↗
PubMed1987

Positron emission tomography detects tissue metabolic activity in myocardial segments with persistent thallium perfusion defects.

Positron emission tomography with 13N-ammonia and 18F-2-deoxyglucose was used to assess myocardial perfusion and glucose utilization in 51 myocardial segments with a stress thallium defect in 12 patients. Myocardial infarction was defined by a concordant reduction in segmental perfusion and glucose utilization, and myocardial ischemia was identified by preservation of glucose utilization in segments with rest hypoperfusion. Of the 51 segments studied, 36 had a fixed thallium defect, 11 had a partially reversible defect and 4 had a completely reversible defect. Only 15 (42%) of the 36 segments with a fixed defect and 4 (36%) of the 11 segments with a partially reversible defect exhibited myocardial infarction on study with positron tomography. In contrast, residual myocardial glucose utilization was identified in the majority of segments with a fixed (58%) or a partially reversible (64%) thallium defect. All of the segments with a completely reversible defect appeared normal on positron tomography. Apparent improvement in the thallium defect on delayed images did not distinguish segments with ischemia from infarction. Thus, positron emission tomography reveals evidence of persistent tissue metabolism in the majority of segments with a fixed or partially resolving stress thallium defect, implying that markers of perfusion alone may underestimate the extent of viable tissue in hypoperfused myocardial segments.

Aged↗