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Biomedical subjects

J A Nichols

Publications and source records attributed to J A Nichols.

9 recordsLinked to original sources
PubMed2001

Cyclin E and its associated cdk activity do not cycle during early embryogenesis of the sea Urchin.

Female sea urchins store their gametes as haploid eggs. The zygote enters S-phase 1 h after fertilization, initiating a series of cell cycles that lack gap phases. We have cloned cyclin E from the sea urchin Strongylocentrotus purpuratus. Cyclin E is synthesized during oogenesis, is present in the germinal vesicle, and is released into the egg cytoplasm at oocyte maturation. Cyclin E synthesis is activated at fertilization, although there is no increase in cyclin E protein levels due to continuous turnover of the protein. Cyclin E protein levels decline in morula embryos, while cyclin E mRNA levels remain high. After the blastula stage, cyclin E mRNA and protein levels are very low, and cyclin E expression is predominant only in cells that are actively dividing. These include cells in the left coelomic pouch, which forms the adult rudiment in the embryo. The cyclin E present in the egg is complexed with a protein kinase. Activity of the cyclin E/cdk2 changes little during the initial cell cycles. In particular, cyclin E-cdk2 levels remain high during both S-phase and mitosis. Our results suggest that progression through the early embryonic cell cycles in the sea urchin does not require fluctuations in cyclin E kinase activity.

Amino Acid Sequence↗
PubMed2000

Control of column temperature in reversed-phase liquid chromatography.

When separations by reversed-phase liquid chromatography (RP-LC) are carried out at temperatures other than ambient, resulting retention times and bandwidths can depend on the equipment used. As a result, an RP-LC separation that is adequate when carried out on one LC system may prove inadequate when the separation is repeated on a second system. In the present study, various temperature-related problems which can result in a failure of method transfer for non-ambient RP-LC methods were examined. Means for correcting for such effects and thereby ensuring method transferability are described.

Chromatography, Liquid↗
PubMed2000

Performance of experimental sample injectors for high-performance liquid chromatography microcolumns.

An experimental injector for HPLC microcolumns and a 3-nl conductivity detector connected directly to the injector outlet with a 19-nl tube were used to study injector dispersion, guide the design of improved injectors, and suggest appropriate injection techniques. With regard to the small injection volumes required when no on-column concentration technique is used, we show that in some circumstances: (i) there are two volumes to be considered, the sample volume (that which is intended to be injected) and the effective injection volume (that which contains all the sample after it has completely emerged from the injector). Due to dispersion, the latter is often many times the former. An injector performance factor is defined as the ratio of the two volumes. (ii) A smaller sample chamber volume in an injector does not necessarily produce a proportionately smaller effective injection volume, in which case there is a reduction of peak height that degrades sensitivity without a commensurate reduction in peak width that would improve resolution. (iii) Adjusting the geometry of the sample chamber and stator passage can significantly improve injector performance, as illustrated for sample volumes from 2 nl to 1 microl. (iv) In some cases, reducing the diameter of an injector passageway in an attempt to reduce dispersion actually causes performance to worsen.

Chromatography, High Pressure Liquid↗
PubMed1997

Assessing anxiety about retirement: the case of academicians.

One hundred and forty-four individuals, ninety-two of whom were active university faculty and fifty-two of whom were retired, completed a measure of anxiety about retirement as well as a battery of self-report scales assessing a number of personality, job-related, and retirement-specific constructs. Results suggested that the newly developed measure of retirement anxiety possessed high internal consistency as well as both discriminant and construct validity. Moreover, it is multidimensional in nature, and distinct in content from previous scales assessing anxiety about retirement. Its use for persons anticipating retirement is discussed in the context of the benefits of a proactive stance toward retirement preparation.

Aged↗
PubMed1984

Computer-assisted edge detection in two-dimensional echocardiography: comparison with anatomic data.

Four methods of computer-based edge detection were evaluated for identification of endocardial and epicardial borders on 2-dimensional echocardiograms of excised hearts. A method was also evaluated for observer identification of cardiac borders in the same hearts. The accuracy of computer-derived borders and of observer-derived borders were determined by comparison to anatomic borders measured from photographs of slices of the excised hearts. Echocardiographic borders were compared with anatomic borders by calculation of segmental cavity areas and wall thickness. Each of the methods tested (computer and observer) identified endocardial borders accurately, resulting in cavity segment areas that correlated well with the corresponding anatomic data (r = 0.90 to 0.92). Regional wall thicknesses correlated less well with anatomic data (r = 0.74 to 0.80), suggesting that endocardial borders were identified more accurately than were epicardial borders. Thus, the methods of computer-assisted echocardiographic border detection tested identified the endocardium and epicardium as accurately as a trained observer evaluating unprocessed echocardiograms. Computer-based methods of border detection may be useful in the automated analysis of clinical echocardiograms.

Animals↗
PubMed1978

An accurate data collection method for spatial motion using a sonic digitizer.

An accurate collecting method for spatial displacement data utilizing a sonic digitizer which works electronically and acoustically is described. The sequence of the operation of the digitizer system is explained. As an application, the study of elbow flexion-extension is presented. Finally, operational precautions for using this system are discussed.

Biomechanical Phenomena↗
PubMed1975

Revaccination against measles--a pilot study.

(1) During the first ten years after primary vaccination with live measles virus vaccine, a slow decline in the level of HAI antibody titres has been demonstrated. The decline after more attenuated vaccines was at the same gradient, but at lower titres.(2) During the same period after primary vaccination by inactivated (; killed ') followed by live - K + L - measles vaccine, a much steeper decline in the level of HAI antibody titres was demonstrated.(3) The GMT may not reach the lowest standard titres for over 40 years after the least attenuated vaccine, and 20-25 years after more attenuated vaccines. After K + L vaccine the GMT may be negative after 15 years or less, but this will depend on the frequency of natural boosting.(4) On revaccination after five to ten years, one out of 20 children (five per cent) who had received live vaccine alone for primary vaccination showed a fourfold or greater rise in titre of HAI antibody, whereas 17 out of 41 children (41%) who had received K + L vaccine showed a significant rise in titre.(5) With either regime, the age at primary vaccination did not appear to influence the rate of boosting after revaccination except perhaps in children under two years.(6) Among those who originally received K + L Vaccine, The Lower The Hai Antibody Titre Before Revaccination And The Longer The Time Since Primary Vaccination, The More Likely Was A Significant Rise In Titre To Occur After Revaccination. All Should Be Revaccinated Within 10-15 Years Of Primary Immunisation.(7) Children whose primary vaccination was by live ;further attenuated' vaccine before the age of two years may need to be revaccinated before they leave school, but this requires further study.(8) A case can be made for using a less attenuated strain of measles virus for revaccination than for primary vaccination.(9) The eventual need for and timing of revaccination against measles should be examined in a larger group of children.

Antibodies, Viral↗