81 research outputs found
Neural progenitor cell implants modulate vascular endothelial growth factor and brain-derived neurotrophic factor expression in rat axotomized neurons
Axotomy of central neurons leads to functional and structural alterations which largely revert when neural progenitor cells (NPCs) are implanted in the lesion site. The new microenvironment created by NPCs in the host tissue might modulate in the damaged neurons the expression of a high variety of molecules with relevant roles in the repair mechanisms, including neurotrophic factors. In the present work, we aimed to analyze changes in neurotrophic factor expression in axotomized neurons induced by NPC implants. For this purpose, we performed immunofluorescence followed by confocal microscopy analysis for the detection of vascular endothelial growth factor (VEGF), brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3) and nerve growth factor (NGF) on brainstem sections from rats with axotomy of abducens internuclear neurons that received NPC implants (implanted group) or vehicle injections (axotomized group) in the lesion site. Control abducens internuclear neurons were strongly immunoreactive to VEGF and BDNF but showed a weak staining for NT-3 and NGF. Comparisons between groups revealed that lesioned neurons from animals that received NPC implants showed a significant increase in VEGF content with respect to animals receiving vehicle injections. However, the immunoreactivity for BDNF, which was increased in the axotomized group as compared to control, was not modified in the implanted group. The modifications induced by NPC implants on VEGF and BDNF content were specific for the population of axotomized abducens internuclear neurons since the neighboring abducens motoneurons were not affected. Similar levels of NT-3 and NGF immunolabeling were obtained in injured neurons from axotomized and implanted animals. Among all the analyzed neurotrophic factors, only VEGF was expressed by the implanted cells in the lesion site. Our results point to a role of NPC implants in the modulation of neurotrophic factor expression by lesioned central neurons, which might contribute to the restorative effects of these implants
Agents’ interaction in virtual storytelling
In this paper we describe a fully implemented prototype for interactive storytelling using the Unreal engine. Using a sit-com like scenario as an example of how the dynamic interactions between agents and/or the user dramatise the emerging story. Hierarchical Task Networks (HTNs) are formalised using AND/OR graphs, which are used to describe the many possible variations of the story at a sub-goal level, and the set of all behaviours (from a narrative perspective) of the primary actors at a terminal action level. We introduc
Practitioner compression force variation in mammography : a 6 year study
The application of breast compression in mammography may be more heavily influenced by the practitioner
rather than the client. This could affect image quality and will affect client experience. This study builds on
previous research to establish if mammography practitioners vary in the compression force they apply over a six year period.
This longitudinal study assessed 3 consecutive analogue screens of 500 clients within one screening centre in
the UK. Recorded data included: practitioner code, applied pressure (daN), breast thickness (mm), BI-RADS®
density category and breast dose. Exclusion criteria included: previous breast surgery, previous/ongoing
assessment, breast implants. 344 met inclusion criteria. Data analysis: assessed variation of compression force
(daN) and breast thickness (mm) over 3 sequential screens to determine whether compression force and breast
thickness were affected by practitioner variations.
Compression force over the 3 screens varied significantly; variation was highly dependent upon the practitioner
who performed the mammogram. Significant thickness and compression force differences over the 3 screens
were noted for the same client (<0.0001). The amount of compression force applied was highly dependent upon
the practitioner. Practitioners fell into one of three practitioner compression groups by their compression force
mean values; high (mean 12.6daN), intermediate (mean 8.9daN) and low (mean 6.7daN).
For the same client, when the same practitioner performed the 3 screens, maximum compression force variations
were low and not significantly different (p>0.31). When practitioners from different compression force groups
performed 3 screens, maximum compression force variations were higher and significantly different (p<0.0001).
The amount of compression force used is highly dependent upon practitioner rather than client. This has
implications for radiation dose, patient experience and image quality consistency
Search for More Declarativity
Good tree search algorithms are a key requirement for inference
engines of rule languages. As Prolog exemplifies, inference engines
based on traditional uninformed search methods with their well-known
deficiencies are prone to compromise declarativity, the primary concern
of rule languages. The paper presents a new family of uninformed search
algorithms that combine the advantages of the traditional ones while
avoiding their shortcomings. Moreover, the paper introduces a formal
framework based on partial orderings, which allows precise and elegant
analysis of such algorithms
Analysis of the Karmarkar-Karp Differencing Algorithm
The Karmarkar-Karp differencing algorithm is the best known polynomial time
heuristic for the number partitioning problem, fundamental in both theoretical
computer science and statistical physics. We analyze the performance of the
differencing algorithm on random instances by mapping it to a nonlinear rate
equation. Our analysis reveals strong finite size effects that explain why the
precise asymptotics of the differencing solution is hard to establish by
simulations. The asymptotic series emerging from the rate equation satisfies
all known bounds on the Karmarkar-Karp algorithm and projects a scaling
, where . Our calculations reveal subtle
relations between the algorithm and Fibonacci-like sequences, and we establish
an explicit identity to that effect.Comment: 9 pages, 8 figures; minor change
Isolation of chromosome clusters from metaphase-arrested HeLa cells
We have developed a simplified approach for the isolation of metaphase chromosomes from HeLa cells. In this method, all the chromosomes from a cell remain together in a bundle which we call a “metaphase chromosome cluster”. Cells are arrested to 90–95% in metaphase, collected by centrifugation, extracted with non-ionic detergent in a low ionic strength buffer at neutral pH, and homogenised to strip away the cytoskeleton. The chromosome clusters which are released can then be isolated in a crude state by pelleting or they can be purified away from nearly all the interphase nuclei and cytoplasmic debris by banding in a Percoll TM density gradient. — This procedure has the advantages that it is quick and easy, metaphase chromatin is recovered in high yield, and Ca ++ is not needed to stabilise the chromosomes. Although the method does not yield individual chromosomes, it is nevertheless very useful for both structural and biochemical studies of mitotic chromatin. The chromosome clusters also make possible biochemical and structural studies of what holds the different chromosomes together. Such information could be useful in improving chromosome isolation procedures and for understanding suprachromosomal organisation of the nucleus.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/47359/1/412_2004_Article_BF00327351.pd
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