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At least 1,207 records · Page 67Linked to original sources
PubMed2002

Fractional attachment of CD47 (IAP) to the erythrocyte cytoskeleton and visual colocalization with Rh protein complexes.

Interactions of CD47 and RhAG and the Rh proteins are visualized between one another and with the cytoskeleton of intact erythrocytes. In a first study, CD47 is labeled with a phycoerythrin (PhE)- tagged antibody, which generates discrete spots that reflect induced clusters of CD47. Rh and RhAG colocalize with each other and to these induced clusters, whereas Band 3 and glycophorin C remain more homogeneously dispersed on the cell periphery. In a second study, red cells are aspirated into a micropipette, and immunofluorescent maps of the surface gradients that develop for CD47 and RhAG determine cytoskeletal connectivity. CD47 and RhAG gradients on normal red cells prove to be nearly identical and also appear intermediate to those found for the fluid bilayer and network-linked glycophorin C. Similar gradients are obtained for CD47 on Rh(null) cells, suggesting that linkage of CD47 to the spectrin-actin skeleton is independent of Rh or RhAG and is not affected by CD47's reduced surface expression on these cells. The results show that CD47 colocalizes with Rh and RhAG but is fractionally attached to the red cell membrane skeleton independent of these and other major integral membrane proteins involved in cytoskeletal attachment. The results imply a homogeneous base distribution of CD47, restrained by cytoskeleton linkages, plus a smaller fraction of CD47, which is able to diffuse in the membrane.

Anion Exchange Protein 1, Erythrocyte↗
PubMed1999

[Recent advances in functional neuroimaging].

Positron emission tomography (PET) and functional magnetic resonance imaging (MRI) have been introduced into the field of brain science as an noninvasive approach to visualize brain function, focusing on the regional distribution of neuronal activity and its connectivity. Measurement of regional cerebral blood flow with PET has been established for mapping human brain function covering the whole brain with various task conditions. Recently introduced functional MRI technique can also detect the signal changes due to the local increase of blood flow by brain activation. Both PET and MRI provide similar activation patterns in cerebral cortical areas, and the study should be designed by considering the characteristics of each modality. Although PET continues to play a major role in imaging of the neurotransmission process, the efforts are now being made to apply this exciting technique to clinical diagnosis by means of single photon emission computed tomography (SPECT). Neuroreceptor imaging is now applied not only for differential diagnosis of neurological diseases but also for determination of optimal dose of appropriate therapeutic drugs in psychiatric patients. Combined use of activation studies with neurotransmission imaging will provide a new insight in understanding the brain mechanism of emotion and behavior.

Brain↗
PubMed2006

Contrast of directional influence upon motor overflow between submaximal and maximal static exertions.

This study investigated exertion-dependent motor overflow among healthy adults when they performed isometric tasks with contralateral joints in different task directions. Twenty healthy adults (10 males and 10 females, mean age = 26.2 yrs) were instructed to complete a set of isometric contractions of various force vectors with the shoulder, elbow, and wrist joints, in a total of ten motor tasks at submaximal and maximal intensities (50%, 100% maximal voluntary contractions). The electromyographical activities from eight muscles of the unexercised upper limb were recorded to characterize intensity of motor overflow during sustained isometric contraction. Both occurrence frequency and magnitude of motor overflow in terms of standardized net excitation (SNE) increased with exertion level for all joint movements (P < 0.001). Additionally, the motor overflow magnitude depended strongly on the task direction of maximal isometric contraction (P < 0.05). Motor overflow was particularly augmented by the contralateral isometric contractions where task directions were opposed to gravity. However, such a directional effect upon SNE was not evident during submaximal contraction (P > 0.05). The difference of the net excitation between maximal and submaximal contraction (DNE(100%-50%MVC) data) indicated that the pectoralis major and triceps brachii consistently exhibited a marked recruitment in reaction to change in task direction of isometric contraction. Patterned motor overflow may be physiologically relevant to topological mapping of the ipsilateral pathways and altered effectiveness of use-dependent interhemispherical connectivity. The current observations provide better insight into gain in muscle strength due to contralateral exercise.

Adult↗
PubMed1995

[The doctrine of brain localization and its development in the 20th century].

The discovery of the cerebral motor cortex in the last third of the 19th century has decisively influenced the doctrine of cerebral localization. It has dominated brain research from there on. Its considerable practical importance for focalized local diagnosis was recognized from the clinical point of view. As a consequence, interdisciplinary institutions for brain research developed in Europe and in the USA for the study of functional localization in the brain by means of cyto- and myeloarchitecture, electrical brain stimulation and lesion experiments in close connection with clinico-neurologic centers. From this research resulted the cerebral cortical maps with more or less numerous areas linked to either sensory, motor or 'higher' psychic functions. An intensive, emotional critique developed against the brain-localization theory from its onset. This article demonstrates that the arguments of the anti-localizationists gave rise in part to new knowledge about some principles of cerebral function. Some of these are the concept of 'diaschisis' (distant effects of acute lesions and functional recovery, von Monakow, 1902), the concept of 'motor equivalence' (Lashley, 1930) and of neuronal plasticity of the cerebral cortex (Cajal, 1911). Furthermore, modern imaging techniques (position emission tomography, functional nuclear spin resonance) show that complex functions in particular, such as the natural, targeted arm and grasp synergy, are not 'localized' within a small area of the cortex but do activate multiple neuronal networks interconnected dynamically and in alternating composition in the process of movement initiation and execution.

Brain↗
PubMed1996

The role of activity in the development of long-range horizontal connections in area 17 of the ferret.

Horizontal connections in area 17 of adult cats and ferrets link cells with similar preferred orientations by a patchy network of projections extending several millimeters across the cortex. The maturation of orientation selectivity in ferret area 17 has been demonstrated previously by quantitative single-unit recording and optical imaging to begin at approximately postnatal days (P) 32-P36. We therefore made restricted injections of cholera toxin B-subunit (CTB) or CTB-gold into ferret area 17 at a series of developmental ages and statistically quantified the degree of clustering in plots of retrogradely labeled cells in tangential sections through layer III for comparison to the published values for orientation tuning at each age. At P21, horizontal connections within area 17 lacked patchiness entirely, although clear patches of labeled cells were present in extrastriate areas. By P27, significant clustering of horizontal connections within area 17 was present. A second phase of cluster refinement was observed to occur at approximately P34-P36, coinciding with the emergence of mature orientation tuning and maps. Continuous silencing of cortical action potentials by chronic tetrodotoxin infusion from P21 resulted in a spatially random distribution of retrogradely labeled cells at P34. In contrast, bilateral enucleation from P21 did not prevent the initial development of clustered horizontal connections. We conclude, based on our findings and those of others, that the anatomical specificity of long-range horizontal connections results from an activity-dependent process that initially can use spontaneous activity in the cortical and thalamic networks to establish crude periodic connections and later uses visual cues to refine these connections.

Animals↗
PubMed2002

The structure of the archeabacterial flagellar filament of the extreme halophile Halobacterium salinarum R1M1 and its relation to eubacterial flagellar filaments and type IV pili.

Although the phenomenology and mechanics of swimming are very similar in eubacteria and archaeabacteria (e.g. reversible rotation, helical polymorphism of the filament and formation of bundles), the dynamic flagellar filaments seem completely unrelated in terms of morphogenesis, structure and amino acid composition. Archeabacterial flagellar filaments share important features with type IV pili, which are components of retractable linear motors involved in twitching motility and cell adhesion. The archeabacterial filament is unique in: (1) having a relatively smooth surface and a small diameter of approximately 100A as compared to approximately 240A of eubacterial filaments and approximately 50A of type IV pili; (2) being glycosylated and sulfated in a pattern similar to the S-layer; (3) being synthesized as pre-flagellin with a signal-peptide cleavable by membrane peptidases upon transport; and (4) having an N terminus highly hydrophobic and homologous with that of the olygomerization domain of pilin. The synthesis of archeabacterial flagellin monomers as pre-flagellin and their post-translational, extracellular glycosylation suggest a different mode of monomer transport and polymerization at the cell-proximal end of the filament, similar to pili rather than to eubacterial flagellar filaments. The polymerization mode and small diameter may indicate the absence of a central channel in the filament. Using low-electron-dose images of cryo-negative-stained filaments, we determined the unique symmetry of the flagellar filament of the extreme halophile Halobacterium salinarum strain R1M1 and calculated a three-dimensional density map to a resolution of 19A. The map is based on layer-lines of order n=0, +10, -7, +3, -4, +6, and -1. The cross-section of the density map has a triskelion shape and is dominated by seven outer densities clustered into three groups, which are connected by lower-density arms to a dense central core surrounded by a lower-density shell. There is no evidence for a central channel. On the basis of the homology with the oligomerization domain of type IV pilin and the density distribution of the filament map, we propose a structure for the central core.

Bacterial Proteins↗
PubMed1996

ERK6, a mitogen-activated protein kinase involved in C2C12 myoblast differentiation.

ERK6, a mitogen-activated protein (MAP) kinase-related serine/threonine kinase, is highly expressed in human skeletal muscle and appears to function as a signal transducer during differentiation of myoblasts to myotubes. In transfected 293 cells, activation of the 45-kDa enzyme results in tyrosine-phosphorylated 46- and 56-kDa forms, which phosphorylate myelin basic protein. Overexpression of wild-type ERK6 or the inactive mutant Y185F has no effect on fibroblast and myoblast proliferation, but it enhances or inhibits C2C12 cell differentiation to myotubes, respectively. Our findings suggest ERK6 to be a tissue-specific, differentiation signal-transducing factor that is connected to phosphotyrosine-mediated signaling pathways distinct from those activating other members of the MAP kinase family such as LRK1 and ERK2.

3T3 Cells↗
PubMed2004

ViTO: tool for refinement of protein sequence-structure alignments.

UNLABELLED: ViTO is a graphical application, including an editor, of multiple sequence alignment and a three-dimensional (3D) structure viewer. It is possible to manipulate alignments containing hundreds of sequences and to display a dozen structures. ViTO can handle so-called 'multiparts' alignments to allow the visualization of complex structures (multi-chain proteins and/or small molecules and DNA) and the editing of the corresponding alignment. The 3D viewer and the alignment editor are connected together allowing rapid refinement of sequence-structure alignment by taking advantage of the immediate visualization of resulting insertions/deletions and strict conservations in their structural context. More generally, it allows the mapping of informations about the sequence conservation extracted from the alignment onto the 3D structures in a dynamic way. ViTO is also connected to two comparative modelling programs, SCWRL and MODELLER. These features make ViTO a powerful tool to characterize protein families and to optimize the alignments for comparative modelling. AVAILABILITY: http://bioserv.cbs.cnrs.fr/VITO/DOC/. SUPPLEMENTARY INFORMATION: http://bioserv.cbs.cnrs.fr/VITO/DOC/index.html.

Amino Acid Sequence↗
PubMed1989

N-methyl-D-aspartate antagonists prevent interaction of binocular maps in Xenopus tectum.

Glutamate receptors appear to play a key role in several forms of experience-dependent modification of both the strength of synapses and synaptic connectivity. In developing Xenopus frogs, the connections made by isthmotectal axons relaying visual input from the eye to the ipsilateral tectum are markedly influenced by the visual activity of contralateral retinotectal axons, and normal binocular visual input is necessary in order for the ipsilateral visuotectal map to come into register with the contralateral map. We have tested whether NMDA receptors play a role in establishment of the topographic matching of binocular maps during development. We have examined the effects of chronic treatment of tectum with either the receptor agonist NMDA or the antagonists APV or CPP applied throughout early postmetamorphic life using subpial implants of drug-impregnated elvax. Both antagonists blocked the matching of the ipsilateral map to the contralateral map, while NMDA permitted such matching. Our data therefore indicate that NMDA receptors are involved in the experience-dependent establishment of matching binocular maps during development.

2-Amino-5-phosphonovalerate↗
PubMed1982

Efferent projections of the posterior lateral line lobe in gymnotiform fish.

The posterior lateral line lobe (PLLL) of gymnotoid fish has efferent projections to two midbrain regions: the nucleus praeeminentialis dorsalis (n.P.d.) and the torus semicircularis dorsalis (T.Sd.). Both ipsilateral and contralateral connections are present; the n.P. d. receives nearly equal input from both sides while the T.Sd. receives a stronger contralateral input. The PLLL projection to n.P.d. merely maps medial PLLL to ventral n.P.d. and lateral PLLL to dorsal n.P.d., thus preserving the separate topography and relative orientation of the four electrosensory maps found in the PLLL. Only PLLL pyramidal cells (basilar and nonbasilar pyramids) contribute to this projection. The four PLLL electrosensory maps converge onto T.Sd. so that they map the dorsal body surface onto medial T.Sd. and the ventral body surface onto lateral T.Sd. Pyramidal cells, spherical cells, and multipolar cells contribute to this projection. A small commissural connection links homologous segments of the PLLL; these fibers arise from polymorphic cells of the PLLL.

Animals↗
PubMed2000

High-resolution EEG mappings: a spherical harmonic spectra theory and simulation results.

Shown first is the equivalence between the multiple expansion (ME) of the brain electrical generator and the spherical harmonic spectra (SHS) of the potential generated by the electrical generator in an infinite volume conductor. Based on the equivalence, the SHS and the spatial filters which connect the SHS with the ME are deduced, in a concentric 3 sphere conductor and for the 5 EEG source mappings. They are cortical potential mapping (CPM), scalp Laplacian mapping (LM), pseudo-cortical potential mapping (PCPM), equivalent dipole layer mapping (EDM) and equivalent charge layer mapping (ECM). The theoretical simulation study of the spatial filters and mappings indicate that all 5 mappings provide higher resolution imaging maps of brain electrical activity than the scalp potential map. In the inverse problem, a spherical spline fit algorithm is provided to reconstruct the SHS of the scalp recording potential, and then the SHS and maps of the 5 mappings are reconstructed by utilizing the spatial filters and the SHS of the scalp potential. The results indicate that the correlativity order between a reconstructed map and the actual cortical potential map is CPM > or = EDM > PCPM > LM > ECM. An empirical VEP data study shows that any one of the 5 mappings also provides higher spatial resolution than the scalp potential map.

Brain↗
PubMed2003

C-Fos immunoreactivity mapping of the auditory system after electrical stimulation of the cochlear nerve in rats.

The aim of this study was to establish the use of c-Fos immunoreactivity as a marker for functional mapping in the auditory system in response to direct electrical stimulation of the cochlear nerve in the cerebellopontine angle. In rats the cochlear nerve was electrically stimulated with a biphasic current (120-250 microA, 5 Hz) for 30 min using a bipolar concentric Tungsten electrode. Bilateral cochlectomy was performed in a control group in order to investigate basal expression of c-Fos in the auditory brainstem nuclei. The response of auditory brainstem nuclei to electrical stimulation and the completeness of cochlear ablations were electrophysiologically verified. After the experiments, the animals were prepared for cryotomy and c-Fos immunohistochemistry. The results were morphologically analyzed and statistically compared among groups. In anesthetized animals with unilateral electrical stimulation of the cochlear nerve increased expression of c-Fos was detected in the ipsilateral ventral (VCN) and bilateral dorsal cochlear nucleus (DCN), whereas the VCN of the contralateral side revealed only few immunoreactive cells. In animals with bilateral cochlear ablation the number of c-Fos reactive cell nuclei representing basal expression was generally low in the VCN and DCN of both sides. Our data show that electrical stimulation of the cochlear nerve leads to increased expression of c-Fos in the cochlear nucleus. It also confirms bilateral connections between the cochlear nuclei. These experimental results suggest that c-Fos immunoreactivity mapping provides a powerful tool for functional investigations on the cellular level after direct electrical stimulation of the cochlear nerve. Future functional studies analyzing the effect of electrical stimulation of the central auditory system as performed by auditory brainstem implants could be investigated in detail by mapping c-Fos expression on cellular level.

Animals↗
PubMed2005

Radiofrequency catheter ablation of a coronary sinus-ventricular accessory connection in dextrocardia with complete situs inversus and an anomalous inferior vena cava.

An anomalous inferior vena cava (IVC) is often associated with patients with dextrocardia. However, radiofrequency catheter ablation in such a case with that combination has not been reported. We encountered a case of Wolff-Parkinson-White syndrome with dextrocardia associated with complete situs inversus and an azygos continuation of the IVC. A steep angulation at the junction of the azygos vein and superior vena cava precluded the precise mapping of the anatomical right cavity with a femoral vein approach. Successful catheter ablation of an accessory connection between the coronary sinus and left ventricle could be achieved with a right cubital vein approach.

Catheter Ablation↗
PubMed2005

Attention-gated reinforcement learning of internal representations for classification.

Animal learning is associated with changes in the efficacy of connections between neurons. The rules that govern this plasticity can be tested in neural networks. Rules that train neural networks to map stimuli onto outputs are given by supervised learning and reinforcement learning theories. Supervised learning is efficient but biologically implausible. In contrast, reinforcement learning is biologically plausible but comparatively inefficient. It lacks a mechanism that can identify units at early processing levels that play a decisive role in the stimulus-response mapping. Here we show that this so-called credit assignment problem can be solved by a new role for attention in learning. There are two factors in our new learning scheme that determine synaptic plasticity: (1) a reinforcement signal that is homogeneous across the network and depends on the amount of reward obtained after a trial, and (2) an attentional feedback signal from the output layer that limits plasticity to those units at earlier processing levels that are crucial for the stimulus-response mapping. The new scheme is called attention-gated reinforcement learning (AGREL). We show that it is as efficient as supervised learning in classification tasks. AGREL is biologically realistic and integrates the role of feedback connections, attention effects, synaptic plasticity, and reinforcement learning signals into a coherent framework.

Animals↗
PubMed1999

Sensory experience and the formation of a computational map of auditory space in the brain.

The basic wiring of the brain is first established before birth by using a variety of molecular guidance cues. These connections are then refined by patterns of neural activity, which are initially generated spontaneously and subsequently driven by sensory experience. In the superior colliculus, a midbrain nucleus involved in the control of orienting behaviour, visual, auditory, and tactile inputs converge to form superimposed maps of sensory space. Maps of visual space and of the body surface arise from spatially ordered projections from the retina and skin, respectively. In contrast, the map of auditory space is computed within the brain by tuning the neurons to different localization cues that result from the acoustical properties of the head and ears. Establishing and maintaining the registration of the maps in the face of individual differences in the size and relative positions of different sense organs is an activity-dependent process in which the synaptic circuits underlying the auditory representation are modified and calibrated under the influence of both auditory and visual experience. BioEssays 1999;21:900-911.

Animals↗
PubMed2000

Extraction of sensory parameters from a neural map by primary sensory interneurons.

We examine the anatomical basis for the representation of stimulus parameters within a neural map and examine the extraction of these parameters by sensory interneurons (INs) in the cricket cercal sensory system. The extraction of air current direction by these sensory interneurons can be understood largely in terms of the anatomy of the system. There are two critical anatomical constraints. (1) The arborizations of afferents with similar directional tuning properties are located near each other within the neural map. Therefore, a continuous variation in stimulus direction causes a continuous variation in the spatial pattern of activation. (2) The restriction of the synaptic connections of an interneuron to a unique set of afferents results from the unique anatomy of that interneuron: its dendritic arbors are located within restricted regions of the afferent map containing afferents with a limited subset of directional sensitivities. The functional organization of the set of four interneurons studied here is equivalent to a Cartesian coordinate system for computing the stimulus direction vector. For any air current stimulus direction, the firing rates of the active interneurons could be decoded as Cartesian coordinates by neurons at successive processing stages. The implications of this Cartesian coordinate system are discussed with respect to optimal coding strategies and developmental constraints on the cellular implementation of this coding scheme.

Afferent Pathways↗
PubMed1983

Activity sharpens the map during the regeneration of the retinotectal projection in goldfish.

In the regenerating retinotectal projection of goldfish, we have used intraocular injections of tetrodotoxin (TTX) to determine whether activity plays a role in organizing or refining the retinotopic map. Repeated injections produced a continuous 27-day block without producing extraocular effects or causing deleterious effects in the retinal ganglion cells. The retinotectal maps regenerated in the TTX fish were normally organized but the multiunit receptive fields were grossly enlarged. In control regenerates, 1-3 units (arbors of retinal ganglion cell axons) were simultaneously recorded at each penetration and their combined receptive field averaged 11-12 degrees, nearly the same as for single units. In TTX fish each penetration yielded at least 5-10 units whose receptive fields were clustered over a wider area averaging 27 degrees across. Individual ganglion cell receptive fields were assessed both by tectal and by intraretinal recording and were not enlarged. Many fish were recorded up to 4 months after the release from TTX block, but no further refinement of the maps occurred. If the nerve was recrushed and regenerated a second time without TTX, a normal map was formed, ruling out any permanent changes in the retinal ganglion cells or in the tectum. Blocks during various portions of the regeneration process showed that lack of activity during the process of axonal elongation (first 2 weeks) does not cause enlargement of the multiunit receptive fields, but lack of activity during the period of synapse formation and maturation (14-34 days) does. The results are discussed in terms of an activity-dependent stabilization of synapses. Neighboring retinal ganglion cells are known to fire in a statistically correlated fashion and this could help in their elimination of incorrect branches following an early period of diffuse connections.

Animals↗
PubMed1998

Functional topography of single cortical cells: an intracellular approach combined with optical imaging.

Pyramidal cells mediating long-range corticocortical connections have been assumed to play an important role in visual perceptual mechanisms [C.D. Gilbert, Horizontal integration and cortical dynamics, Neuron 9 (1992) 1-13]. However, no information is available as yet on the specificity of individual pyramidal cells with respect to functional maps, e.g., orientation map. Here, we show a combination of techniques with which the functional topography of single pyramidal neurons can be explored in utmost detail. To this end, we used optical imaging of intrinsic signals followed by intracellular recording and staining with biocytin in vivo. The axonal and dendritic trees of the labelled neurons were reconstructed in three dimensions and aligned with corresponding functional orientation maps. The results indicate that, contrary to the sharp orientation tuning of neurons shown by the recorded spike activity, the efferent connections (axon terminal distribution) of the same pyramidal cells were found to terminate at a much broader range of orientations.

Action Potentials↗