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Biomedical subjects

P Fletcher

Publications and source records attributed to P Fletcher.

103 records · Page 6Linked to original sources
PubMed1975

On the physiological functions of teichoic acids.

The choline-containing teichoic acids of pneumococci can be modified by biosynthetic replacement of the choline residues with certain structural analogues, such as ethanolamine (EA) or the N-monomethyl-(MEA) and N-dimethyl-(DEA) amino derivatives of ethanolamine. Cells containing such analogues in their teichoic acids develop pleiomorphic alterations in several physiological properties, which include resistance to detergent-induced lysis and inhibition of cell separation (chain formation). We report here the results of physiological studies on the mechanism of these two phenomena. Our results are summarized in the following: (a) Pneumococci grown on various amino alcohols produce cell walls of identical amino sugar and amino acid composition. (b) Both choline- and EA-containing teichoic acids seem to follow the same conservative pattern of segregation during growth and cell division.(c)Lysis sensitivity of pneumococci requires the juxtaposition oflysissensitive (choline-containing) cell walls and endogenous autolysin at the cell wall growth zone. (d) Upon readdition of choline to ethanolamine-containing cells, lysis sensitivity and catalytically active (C-type) autolysin reappear in the bacteria with the same kinetics. (e) The chains of EA-grown pneumococci contain fully compartmentalized cells and normal cross walls.

Amino Alcohols↗
PubMed1975

The effect of curare on the release of acetylcholine from mammalian motor nerve terminals and an estimate of quantum content.

Curarized and non-curarized rat hemidiaphragm muscles were indirectly stimulated in vitro. 2. The fluid bathing the active curarized muscles was eluted through a dextran gel (Sephadex G-10), effecting a complete separation of ACh from curare. The acetylcholine fraction was then assayed on an isometric leech muscle preparation. 3. Prostaglandin (PGE1) in a concentration fifteen times that estimated to be released from the skeletal muscle preparation did not affect the response of leech muscle to ACh. 4. The amount of ACh released by curarized muscles (4-9 X 10(-18) mole/impulse-junction) was not significantly different from that released by non-curarized muscles (4-6 X 10(-18) mole/impulse-junction). These quantities are similar to those obtained by previous workers. It is concluded that curare in a paralytic dose does not affect the output of ACh from motor nerve terminals stimulated at low frequencies. 5. Spontaneous release of ACh from non-curarized muscles was estimated at 0-45-0-65 p-mole/min. hemidiaphragm. It is calculated that only 2% of this amount could give rise to post-synaptic electrical events, the remainder having a non-synaptic source. 6. The number of molecules of 'quantal' ACh released by stimulated muscle is calculated as 2-5 X 10(6)/impulse-junction, taking account of the non-synaptic release. The number of ACh molecules in one quantum was estimated to be 6250, an amount that could be easily accommodated in one synaptic vesicle.

Acetylcholine↗
PubMedDate not supplied

Analytical applications of flow injection with chemiluminescence detection--a review.

This paper reviews the literature on analytical applications of flow injection (FI) techniques with chemiluminescence (CL) detection from 1995-1999. The focus is on the application of FI-CL to the quantitative determination of specific analytes in real sample matrices. Therefore, entries have been tabulated under the most appropriate application area, ie pharmaceutical, environmental, foods and beverages and biomedical, as defined by the matrix that has been analysed. Each table lists analytes alphabetically and gives details of the exact sample matrix, the limit of detection (as reported in the original paper) and comments on the CL reaction used.

Environmental Pollutants↗
PubMedDate not supplied

Lexical diversity and productivity in Cantonese-speaking children with specific language impairment.

Recent studies of lexical diversity in English-speaking children with specific language impairment (ESLI) have produced conflicting results. Differences between SLI and age-matched (AM) groups on verb types, and overall types have been reported, as have differences between SLI and language-matched (LM) groups on verb types and/or verb tokens, and noun types and noun tokens. At the same time there have been other claims that there is no difference between SLI and LM groups in terms of lexical diversity. This comparison of the lexical diversity of Cantonese-speaking children with SLI (CSLI) and their language-matched peers controlled the length of the samples and the number of tokens as the basis for comparison. There was no difference between the groups in use of verb tokens or types, but there were significant differences in noun tokens and types and 'other' open class tokens and types. Although there was no difference between the groups in the use of a specific grammatical marker (aspect markers), the way in which the CSLI children deployed these markers was severely restricted in comparison with their LM peers. A limited capacity model of language production is invoked to explain the findings.

Case-Control Studies↗
PubMedDate not supplied

Functional topography: multidimensional scaling and functional connectivity in the brain.

In neuroimaging, functional mapping usually implies mapping function into an anatomical space, for example, using statistical parametric mapping to identify activation foci, or the characterization of distributed changes with spatial modes (eigenimages or principal components) (Friston et al., 1993a). This article is about a complementary approach, namely, mapping anatomy into a functional space. We describe a simple variant of multidimensional scaling (principal coordinates analysis; Gower, 1966) that uses functional connectivity as its metric. The scaling transformation maps anatomy into a functional space. The topography, or proximity relationships, in this space embody the functional connectivity among brain regions. The higher the functional connectivity, the closer the regions. Functional connectivity is defined here as the correlation between remote neurophysiological events. The technique represents a descriptive characterization of anatomically distributed changes in the brain that reveals the structure of corticocortical interactions in terms of functional correlations. To illustrate the approach we have analyzed data from normal subjects and schizophrenic patients obtained with PET during the performance of word generation tasks. In particular, we focus on prefrontotemporal integration in normal subjects and show that, in schizophrenia, the left temporal regions and prefrontal cortex evidence abnormal functional connectivity.

Brain↗
PubMedDate not supplied

Research priorities in language and learning.

The paper reviews recent work in the area of linguistics applied to abnormal language development, specifically in the area of grammar. Particular attention is paid to the notion of linguistic profiling as a procedure for assessment and remediation, using information from normal language development research as a guide. It is suggested that in addition to the potential benefit of the continuing advance in knowledge of normal language acquisition for studies of language disorders, the study of the language of mothers to children could prove of considerable value to the speech and language pathologist.

Child↗
PubMedDate not supplied

Reality check.

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Attitude of Health Personnel↗