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Results for “Spatial pattern formation”

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PubMed2001

Discharge patterns of neurons in the medial pontobulbar reticular formation during fictive mastication in the rabbit.

In this study, we describe functional characteristics of neurons forming networks generating oral ingestive motor behaviours. Neurons in medial reticular nuclei on the right side of the brainstem between the trigeminal and hypoglossal motor nuclei were recorded in anaesthetized and paralysed rabbits during two types of masticatory-like motor patterns induced by electrical stimulation of the left (contralateral) or right (ipsilateral) cortical masticatory areas. Sixty-seven neurons in nucleus reticularis pontis caudalis (nPontc), nucleus reticularis parvocellularis (nParv), and nucleus reticularis gigantocellularis (Rgc) were studied. These were classified as phasic or tonic depending on their firing pattern during the fictive jaw movement cycle. Phasic neurons located in the dorsal part of nPontc were active during the jaw opening phase, whilst those in dorsal nParv tended to fire during the closing phase. In most neurons, burst duration and firing frequency changed between the two motor patterns, but there was little change in phase of firing. Tonic units were mainly recorded in the ventral half of nPontc, and at the junction between Rgc and caudal nParv. Cortical inputs with short latency from the contralateral masticatory area were more frequent in phasic (82%) than tonic (44%) neurons, whilst inputs from the ipsilateral cortex were equal in the two subgroups (57% and 56%). Phasic neurons had significantly shorter mean contralateral than ipsilateral cortical latencies, whilst there was no difference among tonic neurons. Intra- and perioral primary afferent inputs activated both types of neurons at oligo-synaptic latencies. Our results show that subpopulations of neurons in medial reticular nuclei extending from the caudal part of the trigeminal motor nucleus to the rostral third of the hypoglossal motor nucleus are active during the fictive masticatory motor behaviour. Unlike masticatory neurons in the lateral tegmentum, the medial subpopulations are spatially organized according to discharge pattern.

Action Potentials↗

PubMed2005

Dispersal patterns and clumping behaviors in the beetle Trichoton sordidum.

Although a significant number of behavioral studies of desert tenebrionids have been done, almost nothing is recorded of Trichoton sordidum (LeConte) (Coleoptera: Tenebrionidae), an inhabitant of the sunny, sparsely vegetated US/Mexican borderlands. For this small, flightless beetle successful predator evasion and adaptation to a desert environment has required development of complicated, quickly utilizable behavioral mechanisms for regulating exposure to extremes of heat, light, humidity, and habitat structure. In this study, T. sordidum was exposed to sudden changes in temperature, illumination, and habitat complexity, and some patterns representing its normal aggregation were recorded. Minimum Risk Distribution models (Floater 2001) predict changes in spatial distribution patterns of groups of individuals as they are exposed to environmental change. A successful species must have a large percentage of individuals adhering to changes with a set pattern of behaviors. All groups of T. sordidum tested demonstrated both rapid and cohesive dispersal patterns. They normally showed little tendency toward clustering, except clear adhesive aggregation patterns in cases of limited resources in a fragmented environment. Under conditions of extreme heat or light, aggregations in the form of clumping did occur. The formation of clumps from simple two-stacks to groups of up to ten is documented here. The sophistication, consistency of use, and rapid initiation of clumps suggest clumping might well be a highly evolved and successful mechanism for group threat evasion. The morphology of T. sordidum shows how clumping is achieved. An examination of the conditions leading to clumping gives clues to why clumps are formed.

Animals↗

PubMed2003

Brain nitric oxide synthase expression in the developing ferret lateral geniculate nucleus: analysis of time course, localization, and synaptic contacts.

Nitric oxide (NO) is a diffusible neurotransmitter that has been implicated in key developmental events, including the refinement of retinogeniculate axons into ON/OFF sublayers in the ferret lateral geniculate nucleus (LGN), and in the formation of eye-specific laminae in other species. To understand the role of NO in the LGN, it is critical to fully characterize the pattern of brain nitric oxide synthase (bNOS) expression within the nucleus, including the phenotype of the neural elements that express it. We have examined the temporal and spatial pattern of bNOS expression in the ferret LGN during the first 6 weeks of postnatal development, and in the adult, by detecting bNOS with a monoclonal antibody as well as beta-nicotinamide adenine dinucleotide phosphate-diaphorase histochemistry. We have found that bNOS is expressed in neurons in the A laminae of the LGN as early as postnatal day 7 (P7), a time coincident with eye-specific segregation of retinal axons. This expression continues through P35, with peak somatodendritic expression at P21. Fluorescent double labeling using antibodies to bNOS and glutamic acid decarboxylase indicate that bNOS is expressed in gamma-aminobutyric acid-ergic interneurons within the A laminae. Electron microscopic examination of bNOS-labeled cells showed synaptic contacts from terminals with two distinct morphologic profiles. Expression of bNOS within interneurons that receive contacts from multiple sources indicates that the synaptic circuitry associated with bNOS activation and the potential targets of NO may be more complex than originally thought and supports a potential new role for interneurons as cellular intermediaries in the refinement of pathways in the LGN. Our findings broaden the window of time that bNOS may be active within the developing LGN, suggesting an expanded role for NO during early postnatal development.

Animals↗

PubMed2006

Generation of cell diversity and segmental pattern in the embryonic central nervous system of Drosophila.

Development of the central nervous system (CNS) involves the transformation of a two-dimensional epithelial sheet of uniform ectodermal cells, the neuroectoderm, into a highly complex three-dimensional structure consisting of a huge variety of different neural cell types. Characteristic numbers of each cell type become arranged in reproducible spatial patterns, which is a prerequisite for the establishment of specific functional contacts. The fruitfly Drosophila is a suitable model to approach the mechanisms controlling the generation of cell diversity and pattern in the developing CNS, as it allows linking of gene function to individually identifiable cells. This review addresses aspects of the formation and specification of neural stem cells (neuroblasts) in Drosophila in the light of recent studies on their segmental diversification.

Animals↗

PubMed1996

Temporal and spatial expression patterns of two G-protein coupled receptors in Drosophila melanogaster.

Temporal and spatial expression patterns of a muscarinic acetylcholine receptor (Acr60C) and an octopamine/tyramine receptor (Octyr) were determined in Drosophila melanogaster using quantitative Northern analysis and in situ hybridization to tissue sections. Expression of mRNA encoding both of these G-protein coupled receptors peaks initially in 18 to 21 hour embryos following the formation of the mature larval nervous system. Levels of mRNA then decline during larval stages, rising to a second peak in 3 to 4-day-old pupae after a period of major nervous system reorganization. The muscarinic acetylcholine receptor mRNA is expressed throughout the cortical regions of the central nervous system in adults and embryos. Particularly high levels of expression of Acr60C are observed in cell bodies adjacent to the antennal lobes, suggesting a major role for this muscarinic receptor in the processing of olfactory information. In contrast, the octopamine/tyramine receptor mRNA is distributed diffusely throughout the adult brain, with patches of signal concentrated in the cortex of the dorsal protocerebrum near the mushroom bodies. These patches may represent individual cells expressing Octyr receptors.

Animals↗

PubMed1998

The Eph family receptors and ligands.

The Eph family is the largest of all known tyrosine kinase receptor-ligand systems. They are expressed in distinct, but overlapping, spatial and temporal patterns during embryonic development and postnatal life, and function in a variety of morphogenic events. The best known function is their role in the guidance of migration of axons and cells in the nervous system through repulsive interactions. They may also play a role in angiogenesis, tissue patterning, and tumor formation.

Amino Acid Sequence↗

PubMed1996

Cell-cell interactions during neural development: multiple types of lateral inhibitions involved in Drosophila eye development.

Inhibitory signals of cellular differentiation from differentiating cells play an important role in regulating the number and spatial distribution of distinctive types of cells in developing tissues. Several types of inhibitory mechanisms of cellular differentiation have been identified by making full use of the developmental genetics of Drosophila compound eyes. These inhibitory mechanisms are distinct from each other in their signal transduction cascades and/or their role in the pattern formation of the developing Drosophila eye. The following events occur: firstly a diffusible protein, Scabrous (Sca), is required to confer regular spacings of the founder cells, R8 cells, or preommatidial clusters in the developing eye disc via an unknown signal transduction cascade, secondly the Notch-signalling is at least required for the single-out of the R8 cells within the pre-ommatidial cluster possibly by preventing other cells in the equivalent groups from adapting fates as R8 cells. Notch-signalling activates a simple signal cascade mediating communication between the plasma membrane and nucleus not via protein phosphorylation. In contrast, a novel diffusible ligand, Argos, was likely to be required subsequently to the selection of R8 cells. Argos was shown to inhibit the activation of a receptor tyrosine kinase, DER, and the subsequent signal transduction in the Ras/MAPK cascade (the third inhibitory mechanism). We proposed that the role of Argos is to regulate the number of differentiated cells by controlling cellular differentiation and subsequent programmed cell death. The distinct roles of these inhibitory signals in the developing Drosophila eye are discussed in detail.

Animals↗

PubMed2001

Heat shock protein 27 shows a distinctive widespread spatial and temporal pattern of induction in CNS glial and neuronal cells compared to heat shock protein 70 and caspase 3 following kainate administration.

Kainate-induced status epilepticus is associated with both apoptotic and necrotic cell death and induction of heat shock proteins (HSPs) in hippocampal and cortical regions of the rodent brain. In the present study we have examined the temporal, spatial and cellular expression patterns of mRNAs for the highly inducible HSPs, HSP70 and HSP27, together with the apoptotic marker, caspase 3 (CPP32) in rat brain after systemic administration of kainate. HSP70 mRNA was transiently induced in the forebrain by kainate, principally in the CA1, CA3 and hilar cells of the hippocampal formation, in piriform cortex and discrete thalamic nuclei. Maximal expression was seen at 8 h after kainate which then declined to background levels by 7 days. Labelling was predominantly neuronal. In contrast, HSP27 mRNA expression was more widespread. Intense labelling was observed in CA1, CA3 and the hilar region at 8 h after kainate but the expression profile for HSP27 mRNA expanded considerably with intense signals seen in corpus callosum, cortex and thalamus at 24 h post kainate. Emulsion autoradiographs indicated a predominantly glial localisation for HSP27 mRNA. In the hilus, a distinct subpopulation of interneurones were found to express HSP27 mRNA. CPP32 mRNA was upregulated in CA1, CA3 and hilus of the hippocampal formation and in piriform cortex. CPP32 mRNA expression was more restricted and similar in distribution to HSP70 mRNA being localised to neurones. The present study demonstrates the unique early expression of HSP27 mRNA by glial cells and distinct populations of neurones which extends beyond those in which HSP70 and CPP32 induction occurs with subsequent cell loss.

Animals↗

PubMed2003

Molecular characterization and spatial expression of the sunflower ABP1 gene.

We have used RT-PCR and low-stringency cDNA library screening to isolate the coding sequence of the sunflower auxin-binding protein (ABP1). All the clones analysed contained the same nucleotide sequence, suggesting that ABP1 is encoded by a single-copy gene in sunflower. The deduced amino acid sequence shows a high degree of similarity with ABP1 proteins from other plant species. Most remarkably, the sunflower protein lacks two cysteine residues present in all other plant ABPs known to date and shown to be involved in a disulfide bridge in the maize protein. Genomic Southern hybridization data support the existence of a single copy of the ABP1 gene in the sunflower genome. Northern hybridization corroborated earlier observations indicating that the steady-state level of ABP1 transcript is higher in actively dividing and growing organs than in the rest of the plant: it is more abundant in the shoot apex, floral buds and immature embryos than in mature leaves, stem, roots and ray flowers. To characterize the tissular ABP1 transcript distribution in sunflower, various organ sections were analysed upon in situ hybridization. Localized accumulation of the ABP1 transcript suggests that its spatial expression is highly regulated at the tissue level. In addition, the transcript preferentially accumulates in tissues having a high rate of cellular division, such as shoot and root apical meristems, leaf primordia and pro-vascular tissues. The ABP1 expression pattern was also studied at a temporal scale during lateral root formation. Real time PCR showed an elevation of the steady state level of the ABP1 transcript in root axes after 36 h of seed germination. In situ hybridization revealed that this global increase is the result of local accumulation of the ABP1 transcript in lateral root primordia, which are known to develop under auxin action. The possibility that a high ABP1 expression level correlates with a high cellular sensitivity to auxin is discussed.

Amino Acid Sequence↗

PubMed2004

Early motor activity drives spindle bursts in the developing somatosensory cortex.

Sensorimotor coordination emerges early in development. The maturation period is characterized by the establishment of somatotopic cortical maps, the emergence of long-range cortical connections, heightened experience-dependent plasticity and spontaneous uncoordinated skeletal movement. How these various processes cooperate to allow the somatosensory system to form a three-dimensional representation of the body is not known. In the visual system, interactions between spontaneous network patterns and afferent activity have been suggested to be vital for normal development. Although several intrinsic cortical patterns of correlated neuronal activity have been described in developing somatosensory cortex in vitro, the in vivo patterns in the critical developmental period and the influence of physiological sensory inputs on these patterns remain unknown. We report here that in the intact somatosensory cortex of the newborn rat in vivo, spatially confined spindle bursts represent the first and only organized network pattern. The localized spindles are selectively triggered in a somatotopic manner by spontaneous muscle twitches, motor patterns analogous to human fetal movements. We suggest that the interaction between movement-triggered sensory feedback signals and self-organized spindle oscillations shapes the formation of cortical connections required for sensorimotor coordination.

Aging↗

PubMed2004

Spike-timing dynamics of neuronal groups.

A neuronal network inspired by the anatomy of the cerebral cortex was simulated to study the self-organization of spiking neurons into neuronal groups. The network consisted of 100 000 reentrantly interconnected neurons exhibiting known types of cortical firing patterns, receptor kinetics, short-term plasticity and long-term spike-timing-dependent plasticity (STDP), as well as a distribution of axonal conduction delays. The dynamics of the network allowed us to study the fine temporal structure of emerging firing patterns with millisecond resolution. We found that the interplay between STDP and conduction delays gave rise to the spontaneous formation of neuronal groups--sets of strongly connected neurons capable of firing time-locked, although not necessarily synchronous, spikes. Despite the noise present in the model, such groups repeatedly generated patterns of activity with millisecond spike-timing precision. Exploration of the model allowed us to characterize various group properties, including spatial distribution, size, growth, rate of birth, lifespan, and persistence in the presence of synaptic turnover. Localized coherent input resulted in shifts of receptive and projective fields in the model similar to those observed in vivo.

Action Potentials↗

PubMed2004

Ribosomal crystallography: initiation, peptide bond formation, and amino acid polymerization are hampered by antibiotics.

High-resolution structures of ribosomal complexes revealed that minute amounts of clinically relevant antibiotics hamper protein biosynthesis by limiting ribosomal mobility or perturbing its elaborate architecture, designed for navigating and controlling peptide bond formation and continuous amino acid polymerization. To accomplish this, the ribosome contributes positional rather than chemical catalysis, provides remote interactions governing accurate substrate alignment within the flexible peptidyl-transferase center (PTC) pocket, and ensures nascent-protein chirality through spatial limitations. Peptide bond formation is concurrent with aminoacylated-tRNA 3' end translocation and is performed by a rotatory motion around the axis of a sizable ribosomal symmetry-related region, which is located around the PTC in all known crystal structures. Guided by ribosomal-RNA scaffold along an exact pattern, the rotatory motion results in stereochemistry that is optimal for peptide bond formation and for nascent protein entrance into the exit tunnel, the main target of antibiotics targeting ribosomes. By connecting the PTC, the decoding center, and the tRNA entrance and exit regions, the symmetry-related region can transfer intraribosomal signals, guaranteeing smooth processivity of amino acid polymerization.

Amino Acids↗

PubMed2002

Dissociated retinal neurons form periodically active synaptic circuits.

Throughout the developing nervous system, immature circuits generate rhythmic activity patterns that influence the formation of adult networks. The cellular mechanisms underlying this spontaneous, correlated activity can be studied in dissociated neuronal cultures. Using calcium imaging and whole cell recording, we showed that cultured dissociated mammalian retinal neurons form networks that produce spontaneous, correlated, highly periodic activity. As the culture matures, the spatial correlations of the periodic calcium transients evolve from being highly synchronized across neighboring cells to propagating across the culture in a wavelike manner reminiscent of retinal waves recorded in vivo. Spontaneous calcium transients and synaptic currents were blocked either by cadmium, tetrodotoxin, or the glutamate receptor antagonist 6,7-dinitroquinoxaline, indicating that the periodic activity was driven primarily by synaptic transmission between retinal ganglion cells. Evoked responses between pairs of ganglion cells exhibited paired-pulse synaptic depression, and the time constant of recovery from this depression was similar to the interval between periodic events. These results suggest that synaptic depression may regulate the frequency of network activity. Together, these findings provide insight into how networks containing primarily excitatory connections generate highly correlated activity.

Amacrine Cells↗

PubMed1997

Induction of Drosophila eye development by decapentaplegic.

The Drosophila decapentaplegic (dpp) gene, encoding a secreted protein of the transforming growth factor-beta (TGF-beta) superfamily, controls proliferation and patterning in diverse tissues, including the eye imaginal disc. Pattern formation in this tissue is initiated at the posterior edge and moves anteriorly as a wave; the front of this wave is called the morphogenetic furrow (MF). Dpp is required for proliferation and initiation of pattern formation at the posterior edge of the eye disc. It has also been suggested that Dpp is the principal mediator of Hedgehog function in driving progression of the MF across the disc. In this paper, ectopic Dpp expression is shown to be sufficient to induce a duplicated eye disc with normal shape, MF progression, neuronal cluster formation and direction of axon outgrowth. Induction of ectopic eye development occurs preferentially along the anterior margin of the eye disc. Ectopic Dpp clones situated away from the margins induce neither proliferation nor patterning. The Dpp signalling pathway is shown to be under tight transcriptional and post-transcriptional control within different spatial domains in the developing eye disc. In addition, Dpp positively controls its own expression and suppresses wingless transcription. In contrast to the wing disc, Dpp does not appear to be the principal mediator of Hedgehog function in the eye.

Actins↗

PubMed2000

Computer simulation and geometric design of endarterectomized carotid artery bifurcations.

The main goal of this computational study is to establish surgical guidelines for optimal geometries of carotid endarterectomy reconstructions that may measurably reduce postoperative complications, that is, thrombosis, stroke, and/or restenosis. The underlying hypotheses are that nonuniform hemodynamics, or "disturbed flows," are linked to arterial diseases and consequently that minimization of "disturbed flow" indicators leads to geometric bifurcation designs that lower postoperative complication rates. Considering transient 3-D laminar blood flow in partially occluded, in-plane, rigid-wall carotid artery bifurcations, the results presented include time-averaged indicators of "disturbed flow", such as the wall shear stress, spatial wall shear stress gradient, and wall shear stress angle deviation. In addition, trajectories and deposition patterns of critical blood particles (i.e., monocytes) are shown and evaluated. Within given physiological constraints, the vessel geometry was then changed in order to reduce the magnitudes of key indicators associated with thrombosis (i.e., blood clot formation) or restenosis (e.g., renewed atherosclerosis and/or hyperplasia). The quantitative results and knowledge base generated will be crucial for future clinical trials.

Blood Flow Velocity↗

PubMed2006

Spatial and temporal patterns of herd somatic cell score in france.

Spatial and temporal patterns of annual milk somatic cell score (ASCS) were explored in French dairy herds between 1996 and 2000 to detect regional singularities for risk of mastitis. A new cluster detection method was used, which was adapted to continuous variables and which allowed ASCS variation factors to be taken into account. The statistical unit was the herd-year. A linear regression model for each year allowed adjustment for breed, mean parity, number of calvings for each season, herd size, and farm altitude. Cluster detection was performed on raw data and on residuals of the model through a method based on the Hellinger distance between spatial distributions. The Hellinger distance between farm distributions was computed at different levels of ASCS (or residuals). Temporal ASCS patterns were explored using a computation of correlations and comparisons between spatial structures of the different years. The general ASCS trend over the study period was a decrease. The global Hellinger distance, which was higher than what could have been randomly expected for each of the 5 yr, indicated a significant spatial cluster formation. Cluster mapping over the 5 yr identified several areas, which sometimes differed between detection using raw data and that using ASCS residuals. Temporal correlations between ASCS residuals for each year were positive and decreasing, and 1996 and 2000 appeared spatially different from the other years. The more affected areas were regions that were not specialized in dairy production. During the study period, 2 progressive movements were detected, corresponding to a disappearance of clusters in the northwest and an increase of clusters in the southwest. Cluster detection could aid in the identification of new risk factors that are relevant at different spatial scales, and could help local organizations to supervise the risk of mastitis, and improve udder health management.

Animals↗

PubMed2001

The Spemann-Mangold organizer: the control of fate specification and morphogenetic rearrangements during gastrulation in Xenopus.

Vertebrate embryonic development is controlled by sequentially operating signalling centres that organize spatial pattern by inductive interactions. The embryonic body plan is established during gastrulation through the action of the Spemann-Mangold or gastrula organizer, a signalling source discovered 75 years ago by Hans Spemann and Hilde Mangold. Transplantation of the organizer to a heterotopic location in a recipient embryo results in the formation of a secondary embryonic body axis, in which several tissue types, most notably somites and the neural tube, are derived from ventral host cells. Because of these non-cell autonomous recruiting or inducing activities the organizer has become a paradigm for studying intercellular communication in the vertebrate embryo. Here, I review some of the recent advances in understanding 1) the initiation of the Spemann-Mangold organizer, 2) its function in pattern formation along the dorsal-ventral and anterior-posterior axes and 3) the integration of cell fate specification events and downstream execution of morphogenetic movements during gastrulation in Xenopus laevis.

Animals↗

PubMed1993

Transsexualism and sex-related differences in hemispheric asymmetry.

Sex differences in human brain lateralization are documented by studies on normal subjects, patients with the unilateral brain damage, and individuals with atypical level of hormones. However, there is no agreement as to the specific role of gender in the development of hemispheric asymmetry. This experiment was designed to examine whether gender identity plays an important role in the formation of brain lateralization, as some recent data seem to suggest. A group of subjects showing gender dysphoria (transsexuals) and two groups of control male and female subjects were presented with verbal and visual-spatial tasks. Results show that neither biological sex nor gender identity are sufficient factors to determine the pattern of hemispheric asymmetry.

Adolescent↗