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PubMed2005

The Simon effect for vertical S-R relations: changing the mechanism by randomly varying the S-R mapping rule?

Recent findings indicate that the shape of the effect function of the Simon effect--derived by analysing the response time distribution for corresponding and non-corresponding trials--differs depending on the task. Specifically, decreasing effect functions have been reported for horizontal and stable rather increasing effect functions have been obtained for vertical stimulus-response (S-R) relations. Furthermore, it has been assumed that these differences reflect distinct mechanisms underlying the Simon effect. However, in two studies decreasing effect functions were reported for the vertical dimension. In order to investigate these contradictory findings four experiments were conducted. Since both studies--in which a decreasing effect function was obtained--used a modified version of the Simon task, that is, randomly varying S-R mapping rules, the Simon effect for fixed and random S-R mapping rules was investigated using vertical (Experiments 1, 2, and 4) and horizontal (Experiment 3) S-R relations. The results indicate that randomly varying S-R mapping rules affect the shape of the effect function for vertical but not for horizontal S-R relations. It was concluded that these findings indicate that the alternation of S-R mapping rules changes the information processing for the vertical dimension in a way, that the same mechanism as for horizontal S-R relations occurs.

Adult↗
PubMed2000

Correlation between Charge Contrast Imaging and the Distribution of Some Trace Level Impurities in Gibbsite.

Charge contrast images (CCI) of synthetic gibbsite obtained on an environmental scanning electron microscope gives information on the crystallization process. Furthermore, X-ray mapping of the same grains shows that impurities are localized during the initial stages of growth and that the resulting composition images have features similar to these observed in CCI. This suggests a possible correlation between impurity distributions and the emission detected during CCI. X-ray line profiles, simulating the spatial distribution of impurities derived from the Monte Carlo program CASINO, have been compared with experimental line profiles and give an estimate of the localization. The model suggests that a main impurity, Ca, is depleted from the solution within approximately 3-4 µm of growth.

Journal Article↗
PubMed1994

Photochemical labeling of membrane-associated and channel-forming domains of proteins directed by energy transfer.

Singlet-singlet energy transfer reactions from excited tryptophan residues to photoactivatable probes possessing a suitable chromophore, generate reactive species in the vicinity of the protein, leading to its covalent labeling. This delayed labeling process can be used to map the membrane-surrounded regions of proteins with improved efficiency when it is applied with appropriate photoactivatable phospholipids. The same principle could also be applied to the labeling of channel-forming transmembrane domains of ion channels, provided that suitable photoactivatable permeant ions were available. Both applications will be discussed with regard to their potential and feasibility.

Affinity Labels↗
PubMed1988

The carboxylmethylation of cerebral membrane-bound proteins increases with age.

Recently, we have characterized a membrane-bound (mb) component of brain protein carboxylmethyltransferase II (PCMT) which effectively carboxylmethylates endogenous mb methyl-accepting proteins (MAPs). (Neurochem. Int., 10 (1987) 155). We have also shown that exposing mb-MAPs to mild alkali leads to a marked increase in their recognition by PCMT. Since one of the likely consequences of the alkaline treatment appears to be the deamidation of selected protein-bound asparagines or aspartates, followed by the formation, in their place, of D-or L-isoaspartates, it is reasonable to assume that mb-MAPs constitute unique targets for the mb-PCMT because they contain such unnatural aspartate residues. Testing the relevance of this notion to the aging of cerebral mb-MAPs we focus in this report on age-related changes involving mb-MAPs. When two-or six-times washed (in 50 mM NaPO4 buffer, pH 6.5) 17,500 g, 30-min membranes or Percoll-gradient purified synaptic membranes were prepared from young (3-4 months) and old (11-12 months) rat brains and were incubated with 20 microM [3H]methyl S-adenosyl-L-methionine at pH 6.0, mb-MAP carboxyl[3H]methylation was significantly more intense in the old than in the young membranes, no additional increase being noted at 28-35 months. Mb-MAP carboxylmethylation increases were confirmed over a wide range of membrane protein concentrations and incubation times and are taken to reflect age-related modifications of the primary structure of susceptible mb-MAPs. To investigate these, we incubated young and old membranes, as well as their Lubrol-Px (1%) extracts (30 min, 0 degree C), with 0.05 M NH4OH for 90 min at 37 degrees C, a treatment which left PCMT activity largely unaffected. Our findings reveal that the effect of the NH4OH treatment on the generation of carboxylmethylatable sites was markedly smaller in "old" than in "young" proteins, suggesting that "new" carboxylmethylatable sites are generated in susceptible mb-MAPs in situ, by a process accompanying, or otherwise marking, the natural aging of neural membrane proteins.

Aging↗
PubMed1994

Functional magnetic resonance imaging (FMRI) of the human brain.

Functional magnetic resonance imaging (FMRI) can provide detailed images of human brain that reflect localized changes in cerebral blood flow and oxygenation induced by sensory, motor, or cognitive tasks. This review presents methods for gradient-recalled echo-planar functional magnetic resonance imaging (FMRI). Also included is a discussion of the hypothesized basis of FMRI, imaging hardware, a unique visual stimulation apparatus, image post-processing and statistical analysis. Retinotopic mapping of striate and extrastriate visual cortex is discussed as an example application. The described echo-planar technique permitted acquisition of an image in 40 ms with a repetition rate of up to 2 per second. However, FMRI responses are slow compared to changes in neural activity. Onset of a visual checkerboard test pattern evoked a response that was delayed by 1-2 s and reached 90% of peak in 5 s. Return to baseline following stimulation was slightly slower. Alternating control (blank) and test (checkerboard) patterns every 20 s induced a cyclic response that was detected in the presence of noise using a cross-correlation technique that was verified by parametric statistics. FMRI revealed retinotopically organized patterns of visually evoked activity in response to annular stimuli that increased in visual field eccentricity. Retinotopy was also observed with test patterns rotated around the fixation point (center of gaze). Results from repeated tests 1 week apart were highly similar. Compared to passive viewing, an active visual discrimination task enhanced responses from extrastriate association cortex.

Brain↗
PubMed1992

Mapping of the region predominantly recognized by antibodies to the Plasmodium falciparum merozoite surface antigen MSA 1.

The locations of the epitopes of a panel of mouse monoclonal antibodies directed against the Plasmodium falciparum merozoite surface antigen MSA 1 were mapped by using naturally occurring processed fragments, by chemical cleavage of the protein and by comparison of the isolate-specificity of binding with known sequence variation. By these criteria, the most antigenic region occurs in the cysteine-rich, invariant 19-kDa carboxyl terminal domain with 12/19 monoclonal antibodies (mAbs) binding to this region. One of these mAbs recognized an epitope near the C-terminal putative glycosylphosphatidylinositol anchor site. This was the only mAb which significantly inhibited parasite growth in vitro. The other mAbs recognized conformational epitopes involving the cysteine residues located throughout this fragment. This study has identified further naturally occurring processing sites and a consensus processing site sequence is now emerging.

Amino Acid Sequence↗
PubMed1993

Regional distribution of serotonin and substance P co-existing in nerve fibers and terminals in the brainstem of the rat.

Two-color fluorescence immunohistochemistry was used to identify and map the distribution of nerve processes immunoreactive for both serotonin and substance P in the rat brainstem. Doubly labeled fibers were observed throughout the brainstem, but tended to be densest in cranial nerve motor nuclei and in reticular regions of the ventral medulla. In the trigeminal motor nucleus, the facial nucleus and the spinal accessory nucleus, the majority of serotonergic varicosities also appeared to contain substance P; in the occulomotor nucleus and the hypoglossal nucleus the numbers of double-labeled and single-labeled serotonergic varicosities were roughly equal. Thus, co-existence of substance P with serotonin was common in many cell groups innervating skeletal muscle. The proportion of double-labeled varicosities was significantly lower in the nucleus of the solitary tract, wherein single-labeled varicosities were much more common. Double-labeled fibers and varicosities were also significantly less common in the spinal trigeminal nucleus. In addition, double-labeling appeared to be uncommon in regions involved in the processing of special sensory information (e.g. auditory, vestibular and visual pathways). These results demonstrate a subpopulation of serotonergic fibers immunoreactive for substance P in the brainstem of the rat. The consistently high density of double-labeled processes in cranial nerve motor nuclei suggests that, as may be the case in the spinal cord, neurons containing serotonin and substance P regulate the activity of motoneurons that innervate skeletal muscle. In addition, they may be involved in other aspects of the function of the brainstem.

Animals↗
PubMed1991

The chicken gene encoding the alpha isoform of tropomyosin of fast-twitch muscle fibers: organization, expression and identification of the major proteins synthesized.

The chicken gene alpha fTM encoding the alpha-tropomyosin of fast-twitch muscle fibers (alpha fTM) covers 20 kb and consists of 15 exons. From this gene, three types of mature transcripts (1.3 kb, 2 kb and 2.8 kb) are expressed through the use of alternative promoters, alternatively spliced exons and multiple 3' end processing. Northern analysis and S1 mapping have shown that the 1.3-kb transcript (exons 1a, 2b, 3, 4, 5, 6b, 7, 8, 9a-9b) is expressed in fast-twitch skeletal muscles and that 2-kb transcripts are expressed in smooth muscle (exons 1a, 2a, 3, 4, 5, 6b, 7, 8, 9d) and in fibroblasts (exons 1a, 2b, 3, 4, 5, 6a or 6b, 7, 8, 9d). These 2-kb transcripts encode distinct proteins which we have identified by two-dimensional (2D) gel electrophoresis. The 2.8-kb transcript which has not been so far characterized in birds is expressed in brain (exons 1b, 3, 4, 5, 6b, 7, 8, 9c-9d). This transcript has been characterized by a cDNA polymerase chain reaction assay and by S1 nuclease mapping. It produces a major TM isoform of chick brain which we have identified by 2D gels.

Amino Acid Sequence↗
PubMed2004

Discovering genes: the use of microarrays and laser capture microdissection in pain research.

The DNA microarray is a powerful, high throughput technique for assessing gene expression on a system-wide genomic scale. It has great potential in pain research for determining the network of gene regulation in different pain conditions, and also for producing detailed gene expression maps in anatomical areas that process nociceptive stimuli. However, for the potential of this high throughput technology to be realised in pain research, microarrays need to be combined with other technologies. Laser capture microdissection is capable of isolating small populations of homogenous cells, allowing distinct areas involved in nociceptive processing to be examined. In combination with sophisticated PCR-based amplification protocols this technique provides sufficient amounts of messenger RNA (mRNA) for application to microarrays. Aside from the technological issues, a difficult task in any microarray study is the analysis of the resulting enormous data set to reveal the key genes, whose regulation is central to the phenotypic changes observed. For this to be achieved, the methods of data analysis, pattern searching and feature recognition, and bioinformatics have to be properly deployed all within the context of an appropriate statistical design. These issues are especially relevant to pain research where interindividual and interpopulation variation is likely to be high, and where polymorphisms can greatly affect nociceptive sensitivity and susceptibility to pain conditions. Methods for assessing the function of new candidate genes identified in microarray screening experiments are also discussed.

Animals↗
PubMed1998

Multiple crystal types reveal photosystem II to be a dimer.

Three types of photosystem II (PS II) crystals have been produced using a variety of detergents. Intermediate stages of crystal formation were examined and it was determined that each crystal probably originates from a single grana membrane. Each crystal type was examined by electron microscopy and image processing, providing three different projection maps. The highest resolution results came from type 1 and type 2 crystals. Projection maps from these crystals were examined for two-fold symmetry via difference maps between the unsymmetrized averages and their 180 degrees rotation. A comparison of the final maps shows a high degree of two-fold symmetry, with only slight differences noted in the low density regions of the two halves of the structure. The interpretation is that PS II is a dimer, with the further suggestion that the two reaction center cores may have slightly different complements of antennae polypeptides.

Crystallization↗
PubMed2002

The role of proofreading in signal transduction specificity.

Many intracellular signaling proteins such as MAP kinases and transcription factors require multiple covalent modifications before activating downstream targets. This property suggests that signaling pathways are organized to facilitate proofreading, which expends energy to enhance the specificity of the pathway for the appropriate effector. Focusing on MAP kinases, we show that each phosphorylation of the kinase can act as an independent specificity test for that kinase. This is independent of whether MAP kinase activation is distributive, processive, or confined to a protein scaffold. We also highlight the importance of phosphatases in developing and maintaining specificity. Support for our proposals can be drawn from the existing literature.

Biophysical Phenomena↗
PubMed2002

A method to obtain reference images for evaluation of ultrasonic tissue characterization techniques.

A general problem when evaluating ultrasonic methods for tissue characterization is that "a golden standard" is seldom known. This paper describes a manual method to obtain a reference image, with the same geometry as the ultrasound image, indicating spatial location of the different tissue types present in the biological tissue scanned in vitro. A 30 x 10 x 2 mm3 piece of formalin fixed porcine tissue was molded into an agar block, which on the top surface, contained a set of fiducial markers, spaced 2.5 mm. The block was submerged into 20 degrees C water and a set of parallel 7.5 MHz spatial compound ultrasound images of tissue and fiducial markers were recorded each 0.5 mm. Guided by the fiducial markers, the agar block was subsequently cut into slices 2.5 mm thick, photographed and finally analyzed histologically identifying these tissues: collagen rich, collagen poor, micro vessels and muscle fibres. Due to: (1) the cutting procedure, (2) the finite size of the ultrasound beam and (3) the spatial variation in propagation velocity, the macroscopic photographs did not align completely with the ultrasound images. Likewise, the histological image is a geometrically distorted version of the macroscopic photograph, due to the histological preparation process. The histological information was "mapped back" into the format of the ultrasound images the following way: On the macroscopic images, outlines were drawn manually which defined the border of the tissue. These outlines were superimposed on the corresponding ultrasound images (identified via the fiducial markers) and modified to encompass what appeared to be tissue regions on the ultrasound images and subsequently re-applied to the macroscopic image. This modified macroscopic outline was used as guideline when drawing outlines identifying regions of the various tissue types. Specifically, the macroscopic image revealed the borders between the different tissues, while the histological image identified the four tissue types. A set of 12 reference images based on modified macroscopic outlines was created. The overlap between the ultrasound images and the macroscopic images--which are the geometrical basis for the final reference images--was between 77% and 93%. A set of 12 reference images spaced 2.5 mm, identifying spatial location of four different tissue types in porcine muscle has been created. With the reference images, it is possible to quantitatively compare different ultrasound based tissue classification techniques.

Animals↗
PubMed1998

Distribution of functional glutamate receptors in cultured embryonic Drosophila myotubes revealed using focal release of L-glutamate from caged compound by laser.

During the formation of neuromuscular junctions in Drosophila embryos, glutamate receptors undergo a drastic change in distribution. To study the underlying mechanism of this developmental process, it is desirable to map the distribution of functional receptors with accurate spatial resolution. Since glutamate receptors desensitize within several milliseconds, the agonist must be applied rapidly. To fulfil these requirements we used laser stimulation of a caged compound to release L-glutamate at a focal spot. Since the glutamate receptor channel is permeable to Ca2+, we assayed the change in internal Ca2+ concentration using a Ca2+ indicator, fluo-3. Using this approach, we mapped the distribution of functional glutamate receptors in cultured embryonic Drosophila myotubes and myoblasts. Consistent with previous immunofluorescence studies using an antibody against a glutamate receptor subunit, a large increase of internal Ca2+ concentration was observed when laser stimulation was located close to some nuclei in the myotube. No change was detected when the laser stimulus was applied over any regions of the myoblasts. No increase of the internal Ca2+ concentration in myotubes was observed when the external solution contained either glutamate at a desensitizing concentration (1 mM) or a glutamate receptor channel blocker, argiotoxin (1 microg/ml). These results indicate that a rise in intracellular Ca2+ concentration can be used to show the distribution of the functional receptor on the muscle surface membrane.

Animals↗
PubMed1999

Where the abstract feature maps of the brain might come from.

Three types of neuronal organization can be called 'brain maps': sets of feature-sensitive cells, ordered projections between neuronal layers and ordered maps of abstract features. The latter are most intriguing as they reflect the central properties of an organism's experiences and environment. It is proposed that such feature maps are learned in a process that involves parallel input to neurons in a brain area and adaptation of neurons in the neighborhood of the cells that respond most strongly to this input. This article presents a new mathematical formulation for such adaptation and relates it to physiological functions.

Algorithms↗
PubMed1997

Induction of nerve growth factor synthesis by sphingomyelinase and ceramide in primary astrocyte cultures.

Astrocytes synthesize nerve growth factor (NGF) in response to pro-inflammatory cytokines. To further study the signaling mechanism involved in this induction of NGF production, the sphingomyelin (SM) pathway was studied. Addition of exogenous neutral SMase (Staphylococcus aureus) or C2-ceramide to primary cultures of newborn rat cortical astrocytes elicited a dose-response increase of NGF synthesis, with maximal effect at 1 U/ml and 25 microM, respectively. Induction of NGF synthesis by SMase and ceramide was shown to be independent of classical PKC activity. Intracellular cAMP-raising agents, such as forskolin and 3-isobutyl-1-methylxanthine, partially prevented the SMase- and C2-ceramide-induced secretion of NGF to the cell supernatant. PD098059 and apigenin, inhibitors of the mitogen-activated protein (MAP) kinase pathway, produced a dose-response inhibition of the SMase- and C2-cer-induced release of NGF. This observation points to the possibility that regulation of NGF synthesis and secretion by the SMase pathway may be mediated downstream by the MAP kinase cascade. As a matter of fact, pre-treatment of astrocytes with SMase or C8-ceramide led to an increased phosphorylation of raf-1. Moreover, MAP kinase activity was enhanced in astrocytes treated with SMase or both ceramides. In conclusion, results suggest that the SMase pathway may control NGF synthesis in the central nervous system, and raise the possibility of an involvement of the MAP kinase cascade in this process.

Animals↗
PubMed1996

Application of molluscs for radioecological monitoring of the Chernobyl outburst.

Accumulation of radionuclides was studied in molluscs from the territories polluted by the Chernobyl outburst. In addition to radiochemical evaluation of (90)Sr, a simple method of beta-radiometry of shells was applied which allowed processing of extensive samples and mapping of contamination of large territories: the Dnieper drainage area and the Kiev administrative region. Pre-Hiroshima and pre-Chernobyl radioactivity was investigated in museum collections. Differences in (90)Sr accumulation in molluscs of different genera were demonstrated for freshwater and terrestrial snails, an especially high accumulation factor was found in Helix. Indices of relative accumulation were calculated treating Lymnaea stagnalis as a standard. All the measurements were recalculated to this standard in order to provide comparisons between sampling sites disregarding collected species and to reduce variance before mapping. Based on shell beta-activity measurements, the average accumulation factor for (90)Sr in Lymnaea compared to its concentration in the river water was about 5000, its transfer factor compared to the soil contamination was about 0.1 m(2) kg(-1), figures for (137)Cs were smaller by an order of magnitude. Inverse dependence between free calcium content in the environment and the transfer factor was demonstrated, as well as a difference in (90)Sr/(137)Cs ratio in molluscs collected on different tracks of Chernobyl pollution. Monitoring the biologically accessible and biologically active fraction of (90)Sr contamination, the shell beta-activity above 15 kBq kg(-1) indicates a dangerous level of contamination for the human population.

Journal Article↗
PubMed2001

Genetic rationale for microheterogeneity of human diphosphoinositol polyphosphate phosphohydrolase type 2.

Selective expression of enzymes that adjust the intensity of turnover of diphosphoinositolpolyphosphates may regulate vesicle trafficking and DNA repair. For example, the type 2 human diphosphoinositolpolyphosphate phosphohydrolases (hDIPP2alpha and 2beta) are distinguished by a solitary amino-acid residue; the type 2beta isoform contains Gln86 whereas the type 2alpha isoform does not, yet the latter has 2-5 fold more catalytic activity than its beta counterpart (J. Biol.Chem. (2000) 12730). We discovered that both alpha and beta-type mRNAs were co-expressed in clonal cell-lines. We sought a genetic explanation for this microheterogeneity. Two BACs containing distinct, but intronless, hDIPP2beta genes were cloned. Only one of these genes could potentially give rise to our previously characterized hDIPP2beta mRNA; the other gene has several sequence differences and, in any case, is likely a processed pseudogene. These BACS were mapped to 1q12-q21 and 1p12-p13 by FISH. No analogous intronless hDIPP2alpha gene was detected by analysis of 21 individual genomic DNAs. However, sequence analysis of a third hDIPP2 gene (at 12q21) places the Gln86 CAG codon within an AGCAG pentamer, offering adjacent, alternate intronic 3'-boundaries. Thus, 'intron boundary skidding' by spliceosomes provides a mechanism for yielding both hDIPP2alpha and hDIPP2beta mRNAs. Our studies expand the repertoire of molecular mechanisms regulating diphosphoinositolpolyphosphate metabolism and function.

Acid Anhydride Hydrolases↗
PubMed1997

Transcriptional analysis of mga, a regulatory gene in Streptococcus pyogenes: identification of monocistronic and bicistronic transcripts that phase vary.

Transcription of several surface virulence proteins of Streptococcus pyogenes is regulated by Mga, a protein that shows homology to response regulators of two-component signal-transducing systems. Two of these surface virulence proteins, M protein and C5a peptidase, undergo phase variation. To determine whether Mga itself undergoes phase variation and might allow the phasing switch to coordinate the activity of these genes, expression of the mga gene was analyzed. We show for the first time that there are two mga-specific transcripts: a 3.8-kb bicistronic message that includes both mga and emm12 genes and a monocistronic 1.6-kb mga message. Both transcripts phase vary and are present in higher amounts in M+ variants than in M- variants. Incubation of RNA with rifampicin indicates that the smaller 1.6-kb message is not a processed product. Two promoters were mapped upstream of mga: P1 at position 666 (-395) and P2 at position 978 (-83). In strain CS46 (delta mga), transcription initiation from the P1 promoter does not occur, and multiple start sites are found around the P2 promoter. Complementation experiments indicate that sequences upstream of the P2 promoter are required for activation of emm12 and scpA by Mga in trans.

Amino Acid Sequence↗