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At least 991 records · Page 55Linked to original sources
PubMed1983

Fiber optic mapping of the Xenopus visual system: shift in the retinotectal projection during development.

Two new techniques for assaying the retina to tectum connections in the lower vertebrate visual system are presented. These techniques allow defined regions of the retina to be stimulated, thus circumventing some of the difficulties of the more conventional retinotectal mapping techniques. Applying these techniques to the Xenopus visual system demonstrates that the retina-to-tectum projection shifts during development. The central part of the retinotectal projection moves medially and caudally about 150 microns (10% of the size of the tectum) in two weeks. The presence of such plasticity in a normal developing animal indicates that the plasticity previously observed in experimentally altered animals probably reflects a normal developmental process.

Animals↗
PubMed1996

Topographically specific effects of ELF-1 on retinal axon guidance in vitro and retinal axon mapping in vivo.

Topographic maps, which maintain the spatial order of neurons in the order of their axonal connections, are found throughout the nervous system. In the visual retinotectal projection, ELF-1, a ligand in the tectum, and its receptors in the retina show complementary gradients in expression and binding, indicating they may be positional labels for map development. Here we show that ELF-1 acts as a repellent axon guidance factor in vitro. In vivo, when the tectal ELF-1 pattern is modified by retroviral overexpression, retinal axons avoid ectopic ELF-1 patches and map to abnormally anterior positions. All these effects were seen on axons from temporal but not nasal retina, indicating that ELF-1 could determine nasal versus temporal retinotectal specificity, and providing a direct demonstration of a cell recognition molecule with topographically specific effects on neural map development.

Animals↗
PubMed1998

The layout of orientation and ocular dominance domains in area 17 of strabismic cats.

In the primary visual cortex of strabismic cats, the elimination of correlated activity between the two eyes enhances the segregation of the geniculocortical afferents into alternating ocular dominance domains. In addition, both tangential intracortical fibres and neuronal synchronization are severely reduced between neurons activated by different eyes. Consequently, ocular dominance columns belonging to different eyes are functionally rather independent. We wondered whether this would also affect the organization of orientation preference maps. To this end, we visualized the functional architecture of area 17 of strabismic cats with both optical imaging based on intrinsic signals and double labelling of orientation and ocular dominance columns with [14C]2-deoxyglucose and [3H]proline. As expected, monocular iso-orientation domains had a patchy appearance and differed for the two eyes, leading to a clear segregation of the ocular dominance domains. Comparison of 'angle maps' revealed that orientation domains exhibit a pinwheel organization as in normally reared cats. Interestingly, the map of orientation preferences did not show any breaks at the borders between ocular dominance columns: iso-orientation domains were continuous across these borders. In addition, iso-orientation contours tended to cross the borders of adjacent ocular dominance columns at right angles. These data suggest that the basic relations between the layout of orientation maps and ocular dominance columns are not disturbed by artificial decorrelation of binocular input. Therefore in cat area 17, the orientation map does not seem to be modified by experience-dependent changes of thalamic input connections. This suggests the possibility that use-dependent rearrangement of geniculocortical afferents into ocular dominance columns is due to Hebbian modifications whereby postsynaptic responsivity is constrained by the scaffold of the orientation map.

Animals↗
PubMed2006

Modular neuropile organization in the Drosophila larval brain facilitates identification and mapping of central neurons.

Elucidating how neuronal networks process information requires identification of critical individual neurons and their connectivity patterns. For this purpose, we used the third-instar Drosophila larval brain and applied reverse-genetic tools, immunolabeling procedures, and 3D digital reconstruction software. Consistent topological definition of neuropile compartments in the larval brain can be obtained through simple fluorescence-immunolabeling methods. The modular neuropiles can be used as a fiducial framework for mapping the projection patterns of individual neurons labeled with green fluorescent protein (GFP). GFP-labeled neurons often exhibit dendrite-like arbors as well as clustered varicose terminals on neurite branches that innervate identifiable neuropile compartments. We identified candidate cholinergic interneurons in genetic mosaic brains that overlap with the larval optic nerve terminus. By using the neuropile framework, we demonstrate that the candidate visual interneurons are not a subset of the previously identified circadian pacemaker neurons that also contact the larval optic nerve terminus; they may represent parallel pathways in the processing of visual inputs. Thus, in the Drosophila larval brain, modular neuropiles can be used as a framework for systematically identifying, mapping, and classifying interneurons; understanding their roles in behavior can then be pursued further.

Animals↗
PubMed2002

Square spiral photonic crystals: robust architecture for microfabrication of materials with large three-dimensional photonic band gaps.

We provide a blueprint for microfabricating photonic crystals with very large and robust three-dimensional photonic band gaps (PBG's). These crystals are based on interleaving polygonal spiral posts and can be efficiently manufactured on a large scale in a one-step process using the recently introduced technique of glancing angle deposition. We classify various families of spiral photonic crystals based on (i) the parent three-dimensional (3D) point lattice to which they are most closely related, (ii) the crystallographic axis of the parent lattice around which the spiral posts wind, and (iii) the set of points of the parent lattice which the spiral arms connect or nearly connect. We obtain optimal geometries for the spiral photonic crystals by detailed mapping of the size and location of the PBG within a multidimensional parameter space which characterizes the shape of each spiral post. For the optimum PBG, the spiral arms and elbows may deviate significantly from the points of the original point lattice. The largest 3D PBG's are obtained for square spiral posts that wind around the [001] axis of diamond (or face centered cubic) lattice and in which the spiral arm segments approximately connect either the fifth or first nearest-neighbor points of the parent lattice. In the case of silicon posts (with a dielectric constant of 11.9) in an air background, whose arm segments nearly connect fifth nearest-neighbor point of the diamond lattice, the full PBG can be as large as 16% of the gap center frequency. For the corresponding air posts in a silicon background, the maximum PBG is 24% of the gap center frequency. We compute both the total electromagnetic density of states and the electromagnetic field distributions near the PBG. It is suggested the PBG in an optimized structure is highly tolerant to various forms of disorder that may arise during the manufacturing process.

Journal Article↗
PubMed2006

The development of cortical connections.

The cortex receives its major sensory input from the thalamus via thalamocortical axons, and cortical neurons are interconnected in complex networks by corticocortical and callosal axons. Our understanding of the mechanisms generating the circuitry that confers functional properties on cortical neurons and networks, although poor, has been advanced significantly by recent research on the molecular mechanisms of thalamocortical axonal guidance and ordering. Here we review recent advances in knowledge of how thalamocortical axons are guided and how they maintain order during that process. Several studies have shown the importance in this process of guidance molecules including Eph receptors and ephrins, members of the Wnt signalling pathway and members of a novel planar cell polarity pathway. Signalling molecules and transcription factors expressed with graded concentrations across the cortex are important in establishing cortical maps of the topography of sensory surfaces. Neural activity, both spontaneous and evoked, plays a role in refining thalamocortical connections but recent work has indicated that neural activity is less important than was previously thought for the development of some early maps. A strategy used widely in the development of corticocortical and callosal connections is the early overproduction of projections followed by selection after contact with the target structure. Here we discuss recent work in primates indicating that elimination of juvenile projections is not a major mechanism in the development of pathways feeding information forward to higher levels of cortical processing, although its use is common to developing feedback pathways.

Animals↗
PubMed2002

Mapping physiological states from microarray expression measurements.

MOTIVATION: The increasing use of DNA microarrays to probe cell physiology requires methods for visualizing different expression phenotypes and explicitly connecting individual genes to discriminating expression features. Such methods should be robust and maintain biological interpretability. RESULTS: We propose a method for the mapping of the physiological state of cells and tissues from multidimensional expression data such as those obtained with DNA microarrays. The method uses Fisher discriminant analysis to create a linear projection of gene expression measurements that maximizes the separation of different sample classes. Relative to other typical classification methods, this method provides insights into the discriminating characteristics of expression measurements in terms of the contribution of individual genes to the definition of distinct physiological states. This projection method also facilitates visualization of classification results in a reduced dimensional space. Examples from four different cases demonstrate the ability of the method to produce well-separated groups in the projection space and to identify important genes for defining physiological states. The method can be augmented to also include data from the proteomic and metabolic phenotypes and can be useful in disease diagnosis, drug screening and bioprocessing applications.

Algorithms↗
PubMed1980

Sensory maps in the claustrum of the cat.

The claustrum is a telencephalic cell group (Fig. 1A, B) possessing widespread reciprocal connections with the neocortex. In this regard, it bears a unique and striking resemblance to the thalamus. We have now examined the anatomical ordering of pathways linking the claustrum with sensory areas of the cat neocortex and, in parallel electrophysiological experiments, have studied the functional organization of claustral sensory zones so identified. Our findings indicate that there are discrete visual and somatosensory subdivisions in the claustrum interconnected with the corresponding primary sensory areas of the neocortex and that the respective zones contain orderly retinotopic and somatotopic maps. A third claustral region receiving fibre projections from the auditory cortex in or near area Ep was found to contain neurones responsive to auditory stimulation. We conclude that loops connecting sensory areas of the neocortex with satellite zones in the claustrum contribute to the early processing of exteroceptive information by the forebrain.

Animals↗
PubMed1985

Cytoskeletal architecture and immunocytochemical localization of microtubule-associated proteins in regions of axons associated with rapid axonal transport: the beta,beta'-iminodipropionitrile-intoxicated axon as a model system.

Axons from rats treated with the neurotoxic agent beta,beta'-iminodipropionitrile (IDPN) were examined by quick-freeze, deep-etch electron microscopy. Microtubules formed bundles in the central region of the axons, whereas neurofilaments were segregated to the periphery. Most membrane-bounded organelles, presumably including those involved in rapid axonal transport, were associated with the microtubule domain. The high resolution provided by quick-freeze, deep-etch electron microscopy revealed that the microtubules were coated with an extensive network of fine strands that served both to cross-link the microtubules and to interconnect them with the membrane-bounded organelles. The strands were decorated with granular materials and were irregular in dimension. They appeared either singly or as an extensive anastomosing network in fresh axons. The microtubule-associated strands were observed in fresh, saponin-extracted, or aldehyde-fixed tissue. To explore further the identity of the microtubule-associated strands, microtubules purified from brain tissue and containing the high molecular weight microtubule-associated proteins MAP 1 and MAP 2 were examined by quick-freeze, deep-etch electron microscopy. The purified microtubules were connected by a network of strands quite similar in appearance to those observed in the IDPN axons. Control microtubule preparations consisting only of tubulin and lacking the MAPs were devoid of associated strands. To learn which of the MAPs were present in the microtubule bundles in the axon, sections of axons from IDPN-treated rats were examined by immunofluorescence microscopy using antibodies to MAP 1A, MAP 1B, MAP 2, and tubulin. Anti-MAP 2 staining was only marginally detectable in the IDPN-treated axons, consistent with earlier observations. Anti-MAP 1A and anti-MAP 1B brightly stained the IDPN-treated axons, with the staining exclusively limited to the microtubule domains. Furthermore, thin section-immunoelectron microscopy using colloidal gold-labeled second antibodies revealed that both anti-MAP 1A and anti-MAP 1B stained fuzzy filamentous structures between microtubules. In view of earlier work indicating that rapid transport is associated with the microtubule domain in the IDPN-treated axon, it now appears that MAP 1A and MAP 1B may play a role in this process. We believe that MAP 1A and MAP 1B are major components of the microtubule-associated fibrillar matrix in the axon.

Animals↗
PubMed2002

Relationship of acupuncture points and meridians to connective tissue planes.

Acupuncture meridians traditionally are believed to constitute channels connecting the surface of the body to internal organs. We hypothesize that the network of acupuncture points and meridians can be viewed as a representation of the network formed by interstitial connective tissue. This hypothesis is supported by ultrasound images showing connective tissue cleavage planes at acupuncture points in normal human subjects. To test this hypothesis, we mapped acupuncture points in serial gross anatomical sections through the human arm. We found an 80% correspondence between the sites of acupuncture points and the location of intermuscular or intramuscular connective tissue planes in postmortem tissue sections. We propose that the anatomical relationship of acupuncture points and meridians to connective tissue planes is relevant to acupuncture's mechanism of action and suggests a potentially important integrative role for interstitial connective tissue.

Acupuncture↗
PubMed1997

Optically imaged maps of orientation preference in primary visual cortex of cats and ferrets.

Feature maps in the cerebral cortex constitute orderly representations of response features created within the cortex; an example is the mapping of orientation-selective neurons in visual cortex. We have compared the properties of orientation maps in area 17 of cats and ferrets, obtained by optical imaging of intrinsic signals. Orientation maps in both species contain a quasi-periodic distribution of iso-orientation domains that are organized into a lattice of pinwheels. However, the spatial density of orientation domains and of pinwheels in ferret area 17 is nearly twice that in cat area 17. The ferret map also contains more discontinuities, or fractures, where orientation changes abruptly. The size of orientation domains scales with interdomain spacing, so that the ratio of the two is approximately the same in both species. Consistent with this finding, the orientation tuning width of individual pixels is similar in the two. The magnitude of orientation preference, however, is much lower in ferret compared to cat. The greater incidence of fractures in ferret appears to be due to proportionately greater overlap between domains of different orientations, particularly along fracture lines that link pinwheel centers. We hypothesize that a key determinant of orientation maps, the relationship between orientation domain size and spacing, expresses an anatomical link between sizes of thalamocortical arbors and horizontal intracortical connections in area 17.

Animals↗
PubMed1975

Afferents to prefrontal cortex from the thalamic mediodorsal nucleus in the rhesus monkey.

Thalamic afferents to Macaque prefrontal cortex from the mediodorsal nucleus were examined by techniques specific for anterograde degeneration and axoplasmic transport. The sampling procedure employed permits establishing the extent of topographic projections to cortex from subcortical foci for the same brain which was surveyed subsequently in tracing specific neuronal connections by electron microscopy. Topographic and general laminar distribution of thalamic terminals are presented in terms of 3 subareas of prefrontal cortex. The dorsolateral and ventral (orbital) surfaces of prefrontal cortex receive respectively projections from the lateral and medial subdivision of the mediodorsal nucleus. In addition, the medial wall of the frontal lobe, including the dorsomedial part of the lateral convexity, heretofore regarded as athalamic, receives input from the caudal-dorsomedial aspect of the mediodorsal nucleus. Preliminary evidence suggests that axons from the mediodorsal nucleus terminate in the head of caudate nucleus, as Sachs-81 described 65 years ago in the first orthograde study of thalamo-prefrontal cortex connections.

Animals↗
PubMed1996

Refolding, isolation and characterization of crystallizable human interferon-alpha 8 expression in Saccharomyces cerevisiae.

Human interferon-alpha 8 was expressed in Saccharomyces cerevisiae and found to accumulate intracellularly in an insoluble form. The protein could be solubilized and converted to a biologically active form with high yield by a denaturation-refolding procedure. The interferon-alpha 8 was further purified to apparent homogeneity by copper-chelate affinity chromatography and anion-exchange chromatography and fully characterized by sodium dodecylsulfate polyacrylamide gel electrophoresis (SDS-PAGE), N-terminal sequence analysis, mass spectrometry, circular-dichroism (CD) spectroscopy and specific activity. Secondary-structure predictions from CD spectroscopy indicate that the molecule is correctly folded. Peptide mapping supported the correct sequence and the expected disulfide-bridge connectivity. The purified protein elutes on reversed-phase high-pressure liquid chromatography (RP-HPLC) as two peaks. Electrospray mass spectrometry and N-terminal sequence analysis of the minor component indicated the existence of an N-terminal acetyl group for the later eluting HPLC-component. In anti-viral assays, the two IFN forms were equally active. Hexagonal crystals of this interferon preparation could be obtained. On the basis of the electrophoretic mobility, HPLC profile, and biological activity assay, the crystalline material was judged to be identical to the uncrystallized interferon. Interferon in crystallized form was found to be stable for up to 24 months and, therefore, could be used for long-term storage, particularly for material intended for clinical use.

Amino Acid Sequence↗
PubMed1995

Working memory networks and the origin of language areas in the human brain.

Temporoparietal-prefrontal working memory networks are proposed as fundamental in the evolutionary origin of the language regions. Having a primordial capacity to name objects or situations, primitive hominids may have strongly benefited from the possibility to recall past events from memory, in order to refer to them through vocal communication. Working memory cortical networks are related to these types of tasks, and are arranged quite similarly to the language networks in the brain. It is possible that the language areas and their connections arose as a local specialization of these large-scale cortical networks, that developed as neural strategies to recall past events to be shared in community. The origin of syntax may have taken place after these networks were sufficiently stabilized, and (at least originally) may have been related to aspects of vocal motor control, involving the progressive differentiation of the anterior language areas and their connections.

Biological Evolution↗
PubMed1983

Geometry and orientation of neuronal processes in cat primary auditory cortex (AI) related to characteristic-frequency maps.

Microelectrode mapping and horseradish peroxidase oxidase histochemistry were combined to study the relationship between the characteristic-frequency representation and the intrinsic connectivity of the primary auditory cortex in the cat. Small extracellular iontophoretic injections of horseradish peroxidase within the characteristic-frequency map resulted in labeling of neuronal processes that, in the tangential plane, radiated out asymmetrically from the injection site over distances of several millimeters. The heaviest concentration of labeled fibers was along an axis parallel with the orientation of the isofrequency line within which the injection had been made. Thus, primary field neurons that have the same or a similar characteristic frequency have the potential of being preferentially interconnected.

Animals↗
PubMed2005

Inferring causality in brain images: a perturbation approach.

When engaged by a stimulus, different nodes of a neural circuit respond in a coordinated fashion. We often ask whether there is a cause and effect in such interregional interactions. This paper proposes that we can infer causality in functional connectivity by employing a 'perturb and measure' approach. In the human brain, this has been achieved by combining transcranial magnetic stimulation (TMS) with positron emission tomography (PET), functional magnetic resonance imaging or electroencephalography. Here, I will illustrate this approach by reviewing some of our TMS/PET work, and will conclude by discussing a few methodological and theoretical challenges facing those studying neural connectivity using a perturbation.

Brain Mapping↗
PubMed1990

Cryoablation of medically refractory nodoventricular tachycardia.

Paroxysmal wide QRS tachycardia, based on a nodoventricular accessory connection, is an uncommon arrhythmia. In this report, the endocardial and epicardial mapping and cryoablation of a nodoventricular fiber, documented to participate in medically refractory tachycardia in an 11-year-old boy, are described. Epicardial cryothermia, applied at the earliest site of right ventricular activation, resulted in the abrupt termination of tachycardia. Endocardial cryothermia was subsequently applied in the perinodal region, the presumed site of origin of the nodoventricular fiber. No tachyarrhythmias were inducible postoperatively, and no antiarrhythmic treatment has been required during 18 months of follow-up. Based on precise anatomic localization of the nodoventricular connection, a definitive cure of associated tachyarrhythmias may be possible utilizing cryothermia, without the requirement for extensive intraoperative dissection.

Bundle of His↗
PubMed2001

Plant MAP kinase pathways: how many and what for?

Mitogen activated protein kinases (MAPK) are important mediators in signal transmission, connecting the perception of external stimuli to cellular responses. MAPK cascades are involved in signalling various biotic and abiotic stresses, like wounding and pathogen infection, temperature stress or drought, but also some plant hormones, such as ethylene and auxin. Moreover, MAPKs have been implicated in cell cycle and developmental processes. In Arabidopsis mutant screens and in vivo assays several components of plant MAPK cascades have been identified. This review compares results obtained from functional analyses of MAPK cascades in plants with recent data obtained from searching the complete Arabidopsis genome. This analysis reveals that plants have an overall of 24 MAPK pathways of which only a small subset has been studied so far.

Arabidopsis↗