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At least 775 records · Page 43Linked to original sources
PubMed2002

Linkage analysis of quantitative trait loci in multiple line crosses.

Simple line crosses, for example, backcross and F2, are commonly used in mapping quantitative trait loci (QTL). However, these simple crosses are rarely used alone in commercial plant breeding; rather, crosses involving multiple inbred lines or several simple crosses but connected by shared inbred lines may be common in plant breeding. Mapping QTL using crosses of multiple lines is more relevant to plant breeding. Unfortunately, current statistical methods and computer programs of QTL mapping are all designed for simple line crosses or multiple line crosses but under a regular mating system. It is not straightforward to extend the existing methods to handle multiple line crosses under irregular and complicated mating designs. The major hurdle comes from irregular inbreeding, multiple generations, and multiple alleles. In this study, we develop a Bayesian method implemented via the Markov chain Monte Carlo (MCMC) algorithm for mapping QTL using complicated multiple line crosses. With the MCMC algorithm, we are able to draw a complete path of the gene flow from founder alleles to their descendents via a recursive process. This has greatly simplified the problem caused by irregular mating and inbreeding in the mapping population. Adopting the reversible jump MCMC algorithm, we are able to simultaneously search for multiple QTL along the genome. We can even infer the posterior distribution of the number of QTL, one of the most important parameters in QTL study. Application of the new MCMC based QTL mapping procedure is demonstrated using two different mating designs. Design I involves two inbred lines and their derived F1, F2, and BC populations. Design II is a half-diallel cross involving three inbred lines. The two designs appear different, but can be handled with the same robust computer program.

Algorithms↗
PubMed1978

Connections of the visual cortex in the hedgehog (Paraechinus hypomelas). II. Corticocortical projections.

Cortical subdivisions based on cytoarchitectural and myeloarchitectural observations of normal tissue were correlated with the topography of corticocortical connections in the visual system of the Pakistani hedgehog. Large subpial aspiration lesions were made in both visual and non-visual cortical regions to determine the areal limits of the corticocortical connections of the visual cortex. Subsequently, discrete electrolytic lesions were placed within the visual cortex. After appropriate survival periods, the brains were processed and stained with the Fink-Heimer technique. The results of these studies show that the visual cortex may be subdivided into four distinct regions from lateral to medial; the lateral parastriate cortex, the lateral and medial part of striate cortex, and the medial parastriate cortex. Within these regions, interhemispheric connections between visual cortices arise mainly in the lateral striate and lateral parastriate regions and terminate in a single band within the lateral portion of the cytoarchitecturally defined striate cortex. These corticocortical projections, therefore, substantially overlap with the geniculostriate projections. Lateral striate cortex and lateral parastriate cortex project in a reciprocal fashion that correlates well with the physiologically defined mirror image representation of two retinotopic maps of the binocular visual field on cortex. These connections are reflected about a line that is closely correlated with the medial edge of the band of commissural axon terminals that is located within the lateral striate cortex, instead of corresponding exactly with the striate-parastriate border as they do in other mammals. Medial striate cortex projects to medial parastriate cortex, indicating that the monocular portion of V I is related to a separate secondary area of cortex on the medial wall of the hemisphere.

Animals↗
PubMed1998

Functional impact of cerebral projection systems.

Typically, anatomical connections have been traced by injecting pathway-tracing chemicals into restricted portions of the brain. After a few days, the brains are fixed and the transported chemicals identified in histological sections. Orthograde tracers move forward along axons from cell body to axon terminals and retrograde tracers move backwards along axons from terminals to parent cell body. The use of both types of tracers has revealed origins and terminations of pathways and a massively complex network of connections between numerous functionally and anatomically distinct cerebral and subcortical regions. In the monkey visual system alone more than 300 connections have been described between the 32 visual cortical areas. Even so, in the network descriptions neither anatomical strengths nor functional impacts of individual connections are identified. Yet, there is no doubt that knowledge about both aspects of connectivity is essential for developing accurate descriptions of network operations. We describe a new combination of a metabolic mapping and a reversible deactivation technique in an animal model to assess the functional impact of cerebral connections.

Animals↗
PubMedDate not supplied

Learning by selection in the trion model of cortical organization.

The basic issue of whether mammalian learning in cortex proceeds via a selection principle, as stressed by Edelman, versus an instructional one is of major importance. We present here a realization of selection learning in the trion model, which is based on the Mountcastle columnar organizational principle of cortex. We suggest that mammalian cortex starts out with an a priori connectivity between minicolumns that is highly structured in time and in space, competing between excitation and inhibition. This provides a "naive" repertoire of spatial-temporal firing patterns that stimuli and internal processing map onto. These patterns can be learned with small modifications to the connectivity strengths determined by a Hebbian learning rule. As various patterns are learned, the repertoire changes somewhat in order to respond properly to various stimuli, but the majority of all possible stimuli still map onto spatial-temporal firing patterns of the original repertoire. In order to show that the example presented here is showing true selectivity and is not an artifact of more stimuli evolving into the learned pattern, we develop a selectivity measure. We suggest that some form of instructional learning (in which connectivities are finely tuned) is present for difficult tasks requiring many trials, whereas very rapid learning involves selectional learning. Both types of learning must be considered to understand behavior.

Animals↗
PubMedDate not supplied

Nanoporous carbon allotropes by septupling map operations.

Spongy carbon nanostructures, also called schwarzites, have been synthesized. They consist of highly connected covalent networks, periodic in the three dimensions of Euclidean space. The intimate structure of schwarzites has a topology of triply periodic minimal surfaces. They can be tessellated by some geometric operations on maps, including the newly proposed septupling operations. Formulas for calculating the lattice parameters of iteratively transformed maps are presented. Examples are given for both finite/closed cages and infinite/open all-sp2 carbon structures. Strain energy calculations for structures, consisting of thousands of atoms, show that such carbon allotropes are very relaxed and approach to the non-strained graphite sheet.

Journal Article↗
PubMed2001

Neuronal connections of the paratrigeminal nucleus: a topographic analysis of neurons projecting to bulbar, pontine and thalamic nuclei related to cardiovascular, respiratory and sensory functions.

The paratrigeminal nucleus, which receives sensory input from trigeminal, glossopharyngeal and vagus nerves, has efferent projections to bulbar, pontine and possibly to thalamic structures associated with nociception, thermoregulation and cardiovascular control. Anterograde neuronal tracers were used to study paratrigeminal efferent connections. Labeled terminal fibers, evidencing bilateral efferent paratrigeminal projections were observed in the medial and caudal solitary tract (sol), lateral reticular nucleus (LRt), ambiguus nucleus (Amb), rostroventrolateral reticular nucleus (RVL), while ipsilateral projections were found in the parabrachial (PB) nuclei and ventral portion of the ventral posteromedial thalamic nucleus (VPM). This extends other findings that describe paratrigeminal projections. Retrograde neuronal transport tracers, microinjected in the defined projection areas were used to map distribution of the paratrigeminal neurons originating different efferent connections. Microinjection of latex microspheres containing fluorescein or rhodamine and Fluoro-gold in the ventral VPM, PB, RVL, Amb, LRt and NTS revealed sets of labeled paratrigeminal nucleus neurons respectively organised in a rostral-caudal sequence. The largest extent of the paratrigeminal nucleus (medial portion) contained neurons projecting to the RVL/Amb, structures associated with cardiovascular regulation. The data show a segmented topographical organization of the nucleus, with different sets of neurons within delimited segments, projecting to neuronal structures associated with different functions. This points to a complex and extensive role for the paratrigeminal nucleus in the integration of somatosensory reflexes related to cardiovascular, respiratory and pain mechanisms. The nucleus may act as a medullary relay interposed between sensory afferents and different structures related to homoeostatic functions.

Animals↗
PubMed2000

Regeneration as an application of gastropod neural plasticity.

Gastropod research is providing many insights into mechanisms of neural regeneration. These observations were made possible by the pioneering work of individuals who described the nervous systems of gastropods, mapped prominent neurons and determined their roles and connections, and developed the techniques for culturing them. This information has allowed questions about injury responses, target selection, and pathway cues to be explored at the level of individually identified neurons. Because of gastropod studies, more is known about axon sealing, growth cone formation and behavior, signals that travel from the site of axotomy to the soma, and the second messengers that are activated there. The responses in neurons and non-neuronal cells during neural development and injury are coordinated by chemical messenger systems that are highly conserved, including neurotransmitters, cytokines, and neurotrophins. The nervous system is modified in learning paradigms by some of the same messenger systems activated by injury, because learning and injury both challenge neurons to change. The conservation of basic mechanisms that coordinate neuronal plasticity allows us to approach basic questions in relatively simple nervous systems with reasonable confidence that the findings will be relevant for other nervous systems, including possible applications to the mammalian nervous system.

Animals↗
PubMed2004

Genetic signatures of pre-expansion bottleneck in the Choctaw population of Oklahoma.

Previous research showed that the Choctaw Indians of Oklahoma exhibit considerable linkage disequilibria (LD) in a number of regions of the genome that has allowed genetic fine mapping for potential susceptibility genes for the autoimmune connective tissue disease scleroderma, or systemic sclerosis (SSc). In principle, such enhanced background LD in the Choctaws could be caused by population bottleneck event(s) followed by recent population expansion. This investigation utilizes genome-scan data on 175 dinucleotide loci from 76 Choctaw individuals to seek genetic evidence of the demographic history of the Choctaw Nation. Of the 175 loci examined, 105 are in Hardy-Weinberg equilibrium. The average unbiased homozygosity over the 105 loci for the Choctaws (29.3%) is significantly higher than that in the European descent group (20.9%); and when adjusted for sample-size differences, the Choctaw also exhibit a significantly smaller number of segregating alleles (6.65 vs. 8.14) at these loci. Both of these observations are consistent with the trend expected in an isolated population. Comparison of the allele size variance and gene diversity yields an imbalance index (lnbeta) of 0.811 in the Choctaw. Of the 105 loci examined, 93 exhibit excess expected homozygosity in comparison to the expectations of a stepwise mutation model in a population of constant size. Taken together, these observations are consistent with a signature of the recent population size expansion of the Choctaws, preceded by bottleneck event(s).

Female↗
PubMedDate not supplied

A genetic study of the human low-voltage electroencephalogram.

The studied phenotype, the low-voltage electroencephalogram (LVEEG), is characterized by the absence of an alpha rhythm from the resting EEG. In previous studies, evidence was found for a simple autosomal-dominant mode of inheritance of the LVEEG. Such a polymorphism in brain function can be used as a research model for the stepwise elucidation of the molecular mechanism involved in those aspects of neuronal activity that are reflected in the EEG. Linkage with the variable number of tandem repeats (VNTR) marker CMM6 (D20S19) and localization of an LVEEG (EEGV1) gene on 20q have previously been reported, and genetic heterogeneity has been demonstrated. This latter result has been corroborated by studying new marker (MS214). The phenotype of the LVEEG is described here in greater detail. Its main characteristic is the absence of rhythmic alpha activity, especially in occipital leads, whereas other wave forms such as beta or theta waves may be present. Analysis of 17 new families (some of them large), together with 60 previously described nuclear families, supports the genetic hypothesis of an autosomal-dominant mode of inheritance. Problems connected with the analysis of linkage heterogeneity, exclusion mapping, and the study of multipoint linkage are discussed. A possible explanation of the localization of LVEEG in the close vicinity of another gene influencing synchronization of the normal EEG, the gene for benign neonatal epilepsie, is given.

Aging↗
PubMed1992

Evidence for excitatory amino acid neurotransmitters in the geniculo-cortical pathway and local projections within rat primary visual cortex.

To examine the organization of axon collaterals of neurons that selectively take up and transport excitatory amino acids, we have used retrograde tracing with D-[3H]Aspartate after injections into different layers of rat primary visual cortex. The results show cells in the lateral geniculate nucleus retrogradely labeled from the cortex. Additional topographically precise input to the thalamic recipient layer 4 originates from neurons in the visual cortex lying in layers 2/3, 5 and 6. These inputs are reciprocated by point-to-point projections from layer 4. Layer 2/3 cells project to layers 5 and 6 in columnar fashion. Putative excitatory input to layer 2/3 originates from a vertical column of cells in layer 5 and the middle of layer 6. In addition layer 2/3 receives input via horizontal collaterals of topographically distant upper layer neurons, from more widespread projections in lower layer 6, and from very widespread projections of cells at the layer 5/6 border. Cells in the depth of layer 5 also distribute collaterals within layers 5 and 6. Our findings provide anatomical evidence that the geniculo-cortical pathway in the mammalian visual system may use excitatory amino acid transmitters. In addition, the results support the notion that most long range connections that link distant points of the topographic map are excitatory.

Animals↗
PubMed1994

[Opioids, cerebral circulation and intracranial pressure].

The effects of the opioids alfentanil (A), fentanyl (F), and sufentanil (S) on cerebral blood flow (CBF) and intracranial pressure (ICP) have been discussed in several recent publications. The purpose of this review is to describe the results of studies in animals, healthy volunteers, and patients with and without intracranial diseases. Clinical relevance and mechanisms of the reported ICP and CBF increases are analysed. METHODS. Approximately 70 original articles and abstracts were retrieved by a systematic literature search using the key word list at the end of this abstract. The cited studies came from computerised database systems like Silver Platter and DIMDI, the SNACC reference list, and the bibliographies of pertinent articles and books. These studies were classified into three groups: significant increase of ICP and/or CBF; no significant or clinically relevant alterations; and significant decreases of ICP and/or CBF. RESULTS. The numerical relationship was 6:7:3 for A, 7:16:9 for F, and 5:11:8 for S. Increases of previously normal or only slightly elevated ICP were registered in some studies in connection with a decrease in mean arterial pressure (MAP). On the other hand, in patients with brain injury and elevated ICP opioids did not further increase ICP despite MAP decreases. In studies monitoring ICP and/or CBF continuously, transient and moderate increases of questionable clinical relevance became apparent a few minutes after bolus injection of opioids. Alterations of systemic and cerebral haemodynamics observed after bolus application were not registered during continuous infusion of A and S. DISCUSSION AND CONCLUSIONS. The cerebral effects of opioids are dependent on several factors, e.g., age, species, ventilation, anaesthesia before and during measurements, systemic haemodynamics, and underlying diseases. The probable mechanism of ICP increase during decreasing MAP is cerebral vasodilatation due to maintained autoregulation. With increasing severity of the cerebral lesion autoregulation is often disturbed. Therefore, ICP often remains unaltered despite MAP decreases. However, the resulting decrease in cerebral perfusion pressure makes such patients more susceptible to develop ischaemic neurological deficits. Induction of somatic rigidity or (with high doses) convulsions, exceeding the upper limit of autoregulation, histamine release, cerebral vasodilatation, increased cerebral oxygen consumption, or carbon dioxide accumulation during spontaneous breathing were discussed as mechanisms for transient ICP/CBF increases. It is concluded that opioids are often beneficial and not generally contraindicated for patients with cerebral diseases and compromised intracranial compliance. However, since negative side effects cannot be excluded, opioid effects and side effects should be monitored (MAP, ICP, cerebrovenous oxygen saturation, transcranial Doppler sonography) in patients at risk. It has to be stressed that opioids should be administered only to patients with stable haemodynamic situations and preferably in well-titrated, continuous infusions.

Alfentanil↗
PubMed2001

Stickler syndrome and vitreoretinal degeneration: correlation between locus mutation and vitreous phenotype. Apropos of a case.

BACKGROUND: Autosomal dominant vitreoretinopathies are characterized by genetic heterogeneity. Structural mutations in COL2A1 are the most frequent cause of Stickler syndrome with ocular involvement. The affected patients have a characteristic vitreous alteration, so-called membranous vitreous, or type 1 vitreous phenotype. Recently a novel mutation in the gene encoding the alpha 1 chain of type XI collagen (COL11A1) was reported in rare Stickler pedigrees, with a different, so-called beaded or type 2 vitreous phenotype. METHODS: Five patients of an Italian family affected by high myopia, high frequency of retinal detachment, and other systemic stigmata evocative of Stickler syndrome (flat midface, depressed nasal bridge, short nose, spondyloepiphyseal dysplasia and osteoarthritis) were studied. Genetic investigations were also performed, considering three candidate loci for Stickler syndrome and Wagner syndrome (COL2A1, COL11A1, WGN1). RESULTS: Segregation analysis was performed utilizing polymorphic markers. COL2A1 and WGN1 segregations were excluded; COL11A1 showed concordance with the disease. The vitreous phenotype of the family was a typical type 1 or "membranous" vitreous, although all the previously reported COL11A1-related Stickler syndromes had always shown the type 2 or "beaded" vitreous phenotype. CONCLUSIONS: The clear presence of the type 1 or "membranous" vitreous phenotype in our family, despite the probable mutation in the COL11A1 gene, suggests greater phenotypical heterogeneity and a more extensive mutation spectrum, even of the COL11A1 gene, than previously thought, explaining the basis for the different vitreous phenotypes seen in Stickler syndrome.

Child↗
PubMed1988

Doppler flow velocity mapping in an in vitro model of the normal pulmonary artery.

Pulsed Doppler pulmonary artery velocity measurements are useful in evaluating a number of cardiac conditions including pulmonary hypertension, pulmonary stenosis and insufficiency, intracardiac shunts and other congenital abnormalities. However, variations in sample location relative to the arterial wall and valve have been thought to affect pulmonary artery velocity and acceleration measurements clinically. Therefore, pulsed Doppler and color flow mapping were performed in a pulsatile flow apparatus connected to a glass or Plexiglas model of the main pulmonary artery and its bifurcation, which contained a Hancock 29 mm pericardial tissue valve (5.35 cm2 orifice). Doppler sample volumes were placed at four sites: 1) at the pulmonary valve leaflet tips, centrally; 2) 2 cm distal to the leaflet tips, centrally; 3) 2 cm distal but laterally near the pulmonary artery wall; and 4) at the pulmonary artery bifurcation, centrally. Doppler peak flow velocity and acceleration time were measured. There was no difference between sites 1 and 2 in peak flow velocity or acceleration time. At site 3, peak flow velocity and acceleration time were both less than at site 1 (mean +/- SD, 85 +/- 44 versus 105 +/- 39 cm/s, p less than 0.005, and 162 +/- 65 versus 188 +/- 46 ms, p less than 0.03, respectively). Moreover, the pulmonary artery velocity contour at site 3 exhibited increased spectral dispersion and notching and increased variance on the color spectrum. At site 4, peak flow velocity was less than at site 1 (85 +/- 31 versus 105 +/- 39 cm/s, p less than 0.005), whereas pulmonary artery acceleration time was not significantly different. In this model, Doppler pulmonary artery flow velocity was best recorded within 2 cm of the valve and in the center of the vessel. Similar studies should be performed in the human pulmonary artery to standardize the recording technique and sample sites for Doppler measurements of velocity and acceleration.

Blood Flow Velocity↗
PubMed2006

Risk-maps informing land-use planning processes A survey on the Netherlands and the United Kingdom recent developments.

The definition of safety distances as required by Art 12 of the Seveso II Directive on dangerous substances (96/82/EC) is necessary to minimize the consequences of potential major accidents. As they affect the land-use destinations of involved areas, safety distances can be considered as risk tolerability criteria with a territorial reflection. Recent studies explored the suitability of using Geographical Information System technologies to support their elaboration and visual rendering. In particular, the elaboration of GIS "risk-maps" has been recognized as functional to two objectives: connecting spatial planners and safety experts during decision making processes and communicating risk to non-experts audiences. In order to elaborate on these findings and to verify their reflection on European practices, the article presents the result of a comparative study between the United Kingdom and the Netherlands recent developments. Their land-use planning practices for areas falling under Seveso II requirements are explored. The role of GIS risk-maps within decisional processes is analyzed and the reflection on the transparency and accessibility of risk-information is commented. Recommendations for further developments are given.

Accidents, Occupational↗
PubMed2006

Homeostatic synaptic scaling in self-organizing maps.

Various forms of the self-organizing map (SOM) have been proposed as models of cortical development [Choe Y., Miikkulainen R., (2004). Contour integration and segmentation with self-organized lateral connections. Biological Cybernetics, 90, 75-88; Kohonen T., (2001). Self-organizing maps (3rd ed.). Springer; Sirosh J., Miikkulainen R., (1997). Topographic receptive fields and patterned lateral interaction in a self-organizing model of the primary visual cortex. Neural Computation, 9(3), 577-594]. Typically, these models use weight normalization to contain the weight growth associated with Hebbian learning. A more plausible mechanism for controlling the Hebbian process has recently emerged. Turrigiano and Nelson [Turrigiano G.G., Nelson S.B., (2004). Homeostatic plasticity in the developing nervous system. Nature Reviews Neuroscience, 5, 97-107] have shown that neurons in the cortex actively maintain an average firing rate by scaling their incoming weights. In this work, it is shown that this type of homeostatic synaptic scaling can replace the common, but unsupported, standard weight normalization. Organized maps still form and the output neurons are able to maintain an unsaturated firing rate, even in the face of large-scale cell proliferation or die-off. In addition, it is shown that in some cases synaptic scaling leads to networks that more accurately reflect the probability distribution of the input data.

Animals↗
PubMed2002

Neuronal changes during development and evolution (an overview).

This overview highlights the presentations made by several authors, with sidelights commentaries on the topics covered in this session. The Neurotropic hypothesis, formulated by Cajal more than one century ago, has been one of the fundamental tenets of modern Neuroscience. Research work is unveiling highly complex molecular mechanisms by means of which neuronal processes grow in the right direction leading to the formation of neural networks. Another interesting topic covered in this session pertains to the remarkably conserved similarity of most parts of the brain between reptiles, birds and mammals. The presence of the neocortex, which occurs in mammals, is discussed on the basis of different migratory behavior during development. The question of neuronal stability throughout the life cycle raises interesting aspects on the generation of new neurons. This is a particularly timely topic because recent evidence, denied by others, has shown the generation of new neocortical neurons in the adult. In another session, it was discussed the evidence showing that pyramidal cells and intrinsic cells of the neocortex have different developmental origins. Finally, several modern analyses show the role of different transcription factors in the formation of brain cortical maps before the arrival of their proper afferent connections.

Afferent Pathways↗
PubMed2000

Severe tortuosity and stenosis of the systemic, pulmonary and coronary vessels in 12 patients with similar phenotypic features: a new syndrome?

We describe what is, to the best of our knowledge, a previously unreported association in patients with similar facial features, skin and joint laxity, of lengthening and tortuosity of systemic, pulmonary and coronary vessels. We evaluated 12 patients with similar phenotypes, from eight different families. Detailed echocardiographic and angiographic evaluations were performed in all, and biopsies of the skin in seven. All patients have elongated facies, prominent ears, micrognathia and laxity of their joints. Angiographic pictures showed a varying degree of lengthening and tortuosity of systemic, pulmonary, and coronary arteries. Pulsatile carotid arteries formed cervical masses in 2 patients, and three had severe renal arterial stenoses. All showed varying degrees of branch and peripheral pulmonary arterial stenosis, necessitating placement of stents in six. Biopsy of the skin proved normal in all seven patients studied, thus excluding cutis laxa, Ehlers-Danlos and Marfan syndromes. The constellation of abnormalities suggests a genetic syndrome of connective tissue etiology. Further genetic studies, and gene mapping, are underway.

Adolescent↗
PubMed1986

Glutathione reductase from Escherichia coli: cloning and sequence analysis of the gene and relationship to other flavoprotein disulfide oxidoreductases.

A glutathione reductase negative strain of Escherichia coli K-12 was isolated as a thermoresistant survivor when a gor::MuctsAp lysogen was subjected to elevated temperature. It was found that in addition to being ampicillin sensitive this mutant was hypersensitive to arsenate, which may be connected with the fact that the gor gene maps between 77 and 78 min on the E. coli genome, close to the pit locus encoding the major arsenate transport system of E. coli. A derivative of this mutant was used as the recipient in a screen of the Clarke and Carbon hybrid plasmid bank of E. coli DNA. A plasmid, pGR, was isolated that encodes both an arsenate-resistance element and glutathione reductase. Restriction mapping of this plasmid showed that the insert DNA is approximately 10 kilobase pairs in length, and a fragment of the gor gene was identified that allowed the gor gene to be accurately mapped on pGR by a combination of restriction analysis and Southern blotting. The DNA sequence of the gor gene was determined and found to encode a protein of 450 amino acid residues. The glutathione reductase of E. coli is very homologous to the human enzyme and is also related (though less closely) to other flavoprotein disulfide oxidoreductases whose sequences are available. These enzymes have retained a common mechanism while evolving different specificities.

Amino Acid Sequence↗