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At least 433 records · Page 24Linked to original sources
PubMed2004

Altered representation of the spatial code for odors after olfactory classical conditioning; memory trace formation by synaptic recruitment.

In the olfactory bulb of vertebrates or the homologous antennal lobe of insects, odor quality is represented by stereotyped patterns of neuronal activity that are reproducible within and between individuals. Using optical imaging to monitor synaptic activity in the Drosophila antennal lobe, we show here that classical conditioning rapidly alters the neural code representing the learned odor by recruiting new synapses into that code. Pairing of an odor-conditioned stimulus with an electric shock-unconditioned stimulus causes new projection neuron synapses to respond to the odor along with those normally activated prior to conditioning. Different odors recruit different groups of projection neurons into the spatial code. The change in odor representation after conditioning appears to be intrinsic to projection neurons. The rapid recruitment by conditioning of new synapses into the representation of sensory information may be a general mechanism underlying many forms of short-term memory.

Animals↗
PubMed2000

Segmentation and somitogenesis derived from phase dynamics in growing oscillatory media.

The formation of spatially repetitive structures along the growth axis of a developing embryo is a common theme in developmental biology. Here we apply the novel flow-distributed oscillator (FDO) mechanism of wave pattern formation to the problem of axial segmentation in general and to somitogenesis in particular. We argue that the conditions for formation of FDO waves are satisfied during somitogenesis in the chick and mouse and that the waves of gene expression observed in these species arise from phase dynamics in a growing oscillatory medium. We substantiate this claim by showing that the FDO mechanism allows the waves to be mimicked by an inorganic experiment and that it predicts a wavelength that coincides with that observed experimentally. To see whether the FDO mechanism is compatible with other aspects of somitogenesis, we construct an FDO-based model of somitogenesis and successfully test it against a number of experimental observations, including the effect of heat shock. Our analysis provides a rigorous physical basis for the hypothesis that the phase dynamics of a segmental clock controls important stages of segmentation during somitogenesis in the chick and mouse as well as in other organisms that undergo segmentation during their axial growth.

Animals↗
PubMed2002

In situ analysis of enzymes involved in sucrose to hexose-phosphate conversion during stolon-to-tuber transition of potato.

An in situ study of enzymes involved in sucrose to hexose-phosphate conversion during in vitro stolon-to-tuber transition of potato (Solanum tuberosum L. cv. Bintje) was employed to follow developmental changes in spatial patterns. In situ activity of the respective enzymes was visualized by specific activity-staining techniques and they revealed distinct spatially and developmentally regulated patterns. Two of the enzymes studied were also subject to in situ investigations at the transcriptional level. During the stages of stolon formation high hexokinase (EC 2.7.1.1) and acid (cell wall-bound) invertase (EC 3.2.1.26) activities were restricted to the mitotically active (sub)apical region, suggesting a possible importance of these enzymes for cell division. At the onset of tuberization sucrose synthase (EC 2.4.1.13) and fructokinase (EC 2.7.1.4) were strongly induced (visualized at transcriptional and translational level) and the acid invertase activities disappeared from the swelling subapical region as expected. The high degree of similarity in the spatial pattern and the temporal induction of sucrose synthase and fructokinase suggests a tightly co-ordinated coarse (up)regulation, which may be subject to a sugar-modulated mechanism(s) by which genes involved in the metabolic sucrose-starch converting potential are co-ordinately regulated during tuber growth. The overall activity of uridine-5-diphosphoglucose pyrophosphorylase (EC 2.7.7.9) was present in all tissues during stolon and tuber development, implying that its coarse control is not subject to (in)direct developmental regulation.

Journal Article↗
PubMed2005

A cell cycle arrest is necessary for bottle cell formation in the early Xenopus gastrula: integrating cell shape change, local mitotic control and mesodermal patterning.

During development cell proliferation and morphogenetic movements are tightly intermingled. Both processes depend on the same cytoskeletal elements. Therefore, precise regulation of local mitotic activity seems to be basic for proper embryogenesis. Here, I report on bottle cells as an early non-mitotic cell population in the Xenopus gastrula. Endogenous and activin/BVg1-induced ectopic bottle cells do not proliferate. Overexpression of the mitosis-promoting phosphatase cdc25C increases the proliferation rate and interferes with bottle cell formation whereas the phosphatase-dead mutant cdc25C(C457A) does not. Cdc25C also affects other gastrulation processes such as epiboly, vegetal rotation or tissue separation as inferred from histological inspection of early gastrulae. Double stainings of gsc/Xbra transcripts and mitotic nuclei in ectopic and endogenous lips demonstrated that non-mitotic cells occur in the bottle cell region and, to a lesser extent, in the gsc domain which both are indicative of high TGF-beta signalling. In contrast, the Xbra-region and the remainder of the animal cap appear to be permissive for higher rates of cell proliferation. These data suggest inhibition of cell proliferation by high levels of activin-type signals and a close link of mesodermal and mitotic patterning. Finally, coexpression of eFGF together with activin/BVg1 interferes with TGF-beta-induced bottle cell formation. This inhibitory effect correlates with increased cell proliferation as compared to embryos injected with activin/BVg1 alone. Taken together, these data suggest that TGF-beta and FGF signals play antagonistic roles in bottle cell formation and the spatial control of the cell cycle in early Xenopus gastrulae.

Activins↗
PubMed1992

The Drosophila spitz gene encodes a putative EGF-like growth factor involved in dorsal-ventral axis formation and neurogenesis.

We describe the molecular characterization of the Drosophila gene spitz (spi), which encodes a putative 26-kD, EGF-like transmembrane protein that is structurally similar to TGF-alpha. Temporal and spatial expression patterns of spi transcripts indicate that spi is expressed throughout the embryo. Examination of mutant embryos reveals that spi is involved in a number of unrelated developmental choices, for example, dorsal-ventral axis formation, glial migration, sensory organ determination, and muscle development. We propose that spi may act as a ligand for cell-specific receptors, possibly rhomboid and/or the Drosophila EGF receptor homolog.

Amino Acid Sequence↗
PubMed1975

The characteristics of EEG activity and the subjective estimation of time during dreams of different structure.

During dreams evoked by stimuli of a certain duration, the EEF was studied in healthy subjects and in patients with implanted electrodes (EEG, ESCoG (electrosubcorticogram), unit activity). Estimation of the temporal structure of the dream was made from the verbal account of the subject. In the case of an unformed dream the duration of the dream was shown to be adequately estimated, the EEF and ESCoG patterns to be rather variable, and correlation between the bioelectric activities of different structures to be nearly absent. Apparently, in these cases, only some of the structures participate in the formation of dreams, which accounts for their unstructure, with no disorder of temporal and spatial relationships, is accompanied by certain orderly rhythms, similar EEG and ESCoG patterns, and a high correlation between bioelectric processes occurring in the structures under study. Dreams with a complex structure, with simultaneous action in different aspects and with major overestimation of their duration, are accompanied by polymorphous EEG and ESCoG patterns. Almost no correlation is observed between bioelectric processes in different structures. Apparently these dreams are associated with independent activities in different structures and, in the verbal account, the subject tends to place the events in a certain temporal order which creates the effect of considerable acceleration of the time flow.

Alpha Rhythm↗
PubMed2004

Allocentric spatial memory in humans with hippocampal lesions.

An immersive virtual reality (IVR) system was used to investigate allocentric spatial memory in a patient (PR) who had selective hippocampal damage, and also in patients who had undergone unilateral temporal lobectomies (17 right TL and 19 left TL), their performance compared against normal control groups. A human analogue of the Olton [Olton (1979). Hippocampus, space, and memory. Behavioural Brain Science, 2, 315] spatial maze was developed, consisting of a virtual room, a central virtual circular table and an array of radially arranged up-turned 'shells.' The participant had to search these shells in turn in order to find a blue 'cube' that would then 'move' to another location and so on, until all the shells had been target locations. Within-search errors could be made when the participants returned to a previously visited location during a search, and between-search errors when they revisited previously successful, but now incorrect locations. PR made significantly more between-search errors than his control group, but showed no increase in within-search errors. The right TL group showed a similar pattern of impairment, but the left TL group showed no impairment. This finding implicates the right hippocampal formation in spatial memory functioning in a scenario in which the visual environment was controlled so as to eliminate extraneous visual cues.

Adult↗
PubMed1996

From gradients to stripes in Drosophila embryogenesis: filling in the gaps.

Pattern formation along the anterior-posterior axis of the Drosophila embryo is organized by asymmetrically distributed maternal transcription factors. They initiate a cascade of spatially restricted and interacting zygotic gene activities that provide a molecular blueprint of the larval body at blastoderm stage. The key players in the pattern forming process have been identified. Recent progress has begun to reveal the mechanisms by which coherent positional information of maternal origin becomes transferred into serially repeated zygotic gene expression domains reflecting the metameric body plan of the larva.

Animals↗
PubMedDate not supplied

Shaping of receptive fields in the visual cortex during retinal maturation.

We present a computational study of the formation of simple-cell receptive field patterns in the primary visual cortex. Based on the observation that the spatial frequency of the retinal filter increases postnatally, our results explain differences in the time course of the development of orientation selectivity in binocularly deprived and normally reared kittens. Development after eye-opening in normal animals is modelled by training with natural images, whereas in the case of binocular deprivation noise-like stimulation continues. Further, it is shown that different orientation selectivities are obtained for network models trained with natural images in contrast to random phase images of identical second order statistics. The latter finding suggests that higher-order statistics of the inputs influences development of primary visual cortex. Finally, we search for quantities that identify possible signatures of natural image statistics in order to specify the amount of constructiveness that visual experience has on the formation of receptive fields.

Aging↗
PubMed2006

Pattern formation in Taylor-Couette flow of dilute polymer solutions: dynamical simulations and mechanism.

We report spatiotemporal pattern formation in Taylor-Couette flow (i.e., flow between rotating cylinders) of viscoelastic dilute polymer solutions obtained for the first time from first-principles dynamical simulations. Solution structures with varying spatial and temporal symmetries, such as rotating standing waves, flames, disordered oscillations, and solitary vortex solutions which include diwhirls (stationary and axisymmetric) and oscillatory strips (axisymmetric or nonaxisymmetric), are observed, depending on the ratio of fluid relaxation time to the time period of inner cylinder rotation. The flow-microstructure coupling mechanisms underlying the pattern formation process are also discussed.

Journal Article↗
PubMed1998

Differential expression of lactoseries carbohydrate epitopes HNK-1, CD15, and NALA by olfactory receptor neurons in the developing chick.

The formation of the nasal lining with its sensory and its nonsensitive respiratory epithelium requires a spatially ordered pattern of cellular differentiation. Aiming at identifying cell recognition molecules that may be involved in cellular differentiation steps, we applied a panel of antibodies to terminal carbohydrate sequences of the lactoseries on the developing chick olfactory epithelium. This approach is based on the idea that these terminal sugar residues may be involved in certain steps of maturation. Restricted expression of three epitopes NALA, HNK-1, and CD15 was observed in olfactory receptor neurons. The first immature olfactory receptor neurons were observed by day 3 of incubation, expressing the HNK-1 epitope, whereas a total epithelial staining was observed for NALA. By day 9 of incubation high numbers of HNK-1 positive immature olfactory receptor neurons were observed. At the same time mature olfactory receptor neurons showed immunoreactivity for CD15, whereas NALA was still expressed throughout the whole epithelial cell population. However, there was a pronounced staining in the population of mature olfactory receptor neurons. Around hatching only CD15 was detectable in (mature) olfactory receptor neurons, whereas HNK-1 and NALA immunoreactivity have switched to glandular and sustentacular cells respectively. The differentiation-dependent expression patterns of these three cell surface molecules suggest them as suitable markers to explore mechanisms that determine embryonic olfactory receptor neurogenesis.

Animals↗
PubMed1994

Spatially controlled adhesion, spreading, and differentiation of endothelial cells on self-assembled molecular monolayers.

Chemically modified glass substrates were used to demonstrate differential adhesion, growth, and differentiation of endothelial cells. Endothelial cells were examined for adhesion and growth on glass, glass treated with N-(2-aminoethyl)-3-aminopropyl trimethoxysilane (EDA), or EDA with a subsequent treatment with physically adsorbed extracellular matrix components human fibronectin and heparin sulfate. EDA and EDA/human fibronectin showed similar abilities to support adhesion, spreading, and proliferation of endothelial cells. In contrast, heparin sulfate inhibited endothelial cell adhesion to EDA. Differentiation of endothelial cells resulting in precapillary cord formation was triggered by addition of basic fibroblast growth factor (bFGF). On EDA and EDA/human fibronectin bFGF causes confluent endothelial cell monolayers to differentiate and form cords, which resulted in a large-scale spatial redistribution of cells on the surface. Formation of organized neovascular assemblies was demonstrated on coplanar molecular patterns of EDA and a nonadhesive perfluorinated alkylsilane (tridecafluoro-1,1,2,2-tetrahydrooctyl)-1-dimethylchloros ilane (13F). Endothelial cells preferentially adhered to the EDA lines and after 24-48 hr, microfilaments aligned with the long axes of the patterned EDA region. Finally, endothelial cells that became confluent within the confines of the EDA region (bound by the nonadhesive, 13F domains) were observed to differentiate into neovascular cords in long-term culture (7-10 days) with bFGF.

Actin Cytoskeleton↗
PubMed2000

Roughness evolution of ion sputtered rotating InP surfaces: pattern formation and scaling laws.

The topography evolution of simultaneously rotated and Ar (+) ion sputtered InP surfaces was studied using scanning force microscopy. For certain sputter conditions, the formation of a highly regular hexagonal pattern of close-packed mounds was observed with a characteristic spatial wavelength which increases with sputter time t according to lambda approximately t(gamma) with gamma approximately 0.26. Based on the analysis of the dynamic scaling behavior of the surface roughness, the evolution of the surface topography will be discussed within the limits of existing models for surface erosion by ion sputtering.

Journal Article↗
PubMed2001

Perception of forbidden colors in retinally stabilized equiluminant images: an indication of softwired cortical color opponency?

In color theory and perceptual practice, two color naming combinations are forbidden-reddish greens and bluish yellows-however, when multicolored images are stabilized on the retina, their borders fade and filling-in mechanisms can create forbidden colors. The sole report of such events found that only some observers saw forbidden colors, while others saw illusory multicolored patterns. We found that when colors were equiluminant, subjects saw reddish greens, bluish yellows, or a multistable spatial color exchange (an entirely novel perceptual phenomena); when the colors were nonequiluminant, subjects saw spurious pattern formation. To make sense of color opponency violations, we created a soft-wired model of cortical color opponency (based on winner-take-all competition) whose opponency can be disabled.

Color Perception↗
PubMed1997

Dynamic, state-dependent thresholds for the perception of single-element apparent motion: bistability from local cooperativity.

Previous studies have indicated that the formation of coherent patterns for multielement motion displays depends on global cooperative interactions among large ensembles of spatially distributed motion detectors. These interactions enhance certain motion directions and suppress others. It is reported here that perceiving one element moving between two nearby locations likewise is subject to cooperative influences (possibly facilitating and inhibiting interactions within a local ensemble of overlapping detectors). Thresholds depending on luminance contrast were measured for a generalized single-element apparent-motion stimulus, and evidence for spontaneous switching and hysteresis effects indicated that motion perception near the 50% threshold was bistable. That is, for conditions in which motion and nonmotion were perceived half the time, the two percepts were distinct; when one was perceived, it clearly was discriminable from the other. These results indicated that (1) single-element apparent-motion thresholds depended on the immediately preceding state of the ensemble of motion detectors responding to the stimulus, and (2) the stimulus activation of individual motion detectors always might be influenced by recurrent, cooperative interactions resulting from the detectors' being embedded within interconnected ensembles.

Adult↗
PubMed1987

The sensory projections of Drosophila mutants which show abnormal wing formation or flying behavior.

The central projection pattern of sensory neurones from the wing of Drosophila melanogaster arise from a small number of differentiated cell types which are localized in a precise and reproducible spatial pattern. We report here the distribution of the nerve pathways revealed by filling with peroxidase and the structure and number of the wing sensory receptors, in flies which have wings but which nevertheless are flightless, including one which presents abnormal wing formation. Our results indicate that in dumpy and taxi mutants, there are no detectable modifications in the neural projections or in the number and morphology of sensory receptors. Vestigial mutants however, present several alterations including the absence of the ovoid projection, a fact consistent with the existence of very few marginal bristles. The projection of the large companiform sensilla branch profusely along the ventromedial tract and more sensory fibers cross the midline in the mesothorax. Wings of vestigial mutants show a decrease in the number of large campaniform sensilla, and more importantly some receptors present abnormally oriented trichomes in the neighboring cells.

Afferent Pathways↗
PubMed1981

Oxygen gradients cause pattern orientation in Dictyostelium cell clumps.

We have investigated the formation of the prestalk-prespore pattern in Dictyostelium discoideum. Pattern formation occurs in clumps of Dictyostelium cells embedded in agar under a 100% oxygen atmosphere. Agar embedding allows us to control spatially the environment surrounding the cell clumps. Our results suggest that the ambient oxygen concentration plays a role in controlling the size of the multicellular mass. Further, oxygen gradients established across clumps embedded in agar or held in holes in a plastic barrier cause orientation of the prestalk-prespore pattern such that the anterior prestalk region forms at the highest end of the gradient. The results also indicate that developing cells have the ability to migrate up a gradient of oxygen.

Agar↗