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Biomedical subjects

J S Allen

Publications and source records attributed to J S Allen.

At least 55 records · Page 3Linked to original sources
PubMed1990

Schizophrenia, eye movements, and biocultural heterogeneity.

Smooth-pursuit eye-tracking dysfunction is a putative genetic trait marker for schizophrenia. In this study 88 Japanese schizophrenics from Kyushu and Okinawa were examined for the marker using precise high-resolution instrumentation: 76% of the schizophrenics from Kyushu and 89% of those from Okinawa had pursuit dysfunction. The presence of the culture-neutral smooth-pursuit marker for schizophrenia in Japan demonstrates that the etic concept "schizophrenia" is cross-culturally valid. Furthermore, the ubiquity of the marker in biologically and culturally diverse populations may indicate a limit on the extent of meaningful heterogeneity likely to be discovered within the condition.

Adult↗
PubMed1989

Site-directed mutagenesis of the catalytic residues Asp-52 and Glu-35 of chicken egg white lysozyme.

The roles of the catalytic active-site residues aspartic acid-52 and glutamic acid-35 of chicken lysozyme (EC 3.2.1.17) have been investigated by separate in vitro mutagenesis of each residue to its corresponding amide (denoted as D52N and E35Q, respectively). The mutant enzyme D52N exhibits approximately 5% of the wild-type lytic activity against Micrococcus luteus cell walls, while there is no measurable activity associated with E35Q (0.1% +/- 0.1%). The measured dissociation constants for the chitotriose-enzyme complexes were 4.1 microM (D52N) and 13.4 microM (E35Q) vs. 8.6 microM for wild type, indicating that the alterations in catalytic properties may be due in part to binding effects as well as to direct catalytic participation of these residues. The mutant lysozymes have been expressed in and secreted from yeast and obtained at a level of approximately 5 mg per liter of culture by high-salt elution from the cell walls.

Animals↗
PubMed1989

Effects of VDT resolution on visual fatigue and readability: an eye movement approach.

The effects of VDT resolution on visual fatigue and readability were studied. Two kinds of displays with different resolutions (1664 x 1200 pixels and 720 x 350 pixels) and fonts were used. In the first experiment, the subjects read from each display for 1 h to induce fatigue. Reading speed and blink rate while reading were measured. Eye movements during visual smooth pursuit tracking tasks were studied before and after reading; quantitative scoring of eye movement performance showed no significant changes. In the second experiment, readability tests with three different character sizes on both displays were conducted and resulting reading eye movements were analysed. For readability of sufficiently large characters, no significant difference between the high and the standard VDT could be detected. However, for very small characters, higher resolution improved readability.

Adult↗
PubMed1984

Ventrolateral medullary surface blood flow determined by hydrogen clearance.

The H2 clearance technique was used to determine the blood flow of the postulated respiratory chemosensitive areas near the ventrolateral surface of the medulla. In 12 pentobarbital sodium-anesthetized cats, flow (mean +/- SD) was measured from 25-micron Teflon-coated platinum wire electrodes implanted to a depth of 0.3-0.7 mm. Flow (in ml X min-1 X 100 g-1, n = 35) was 52.8 +/- 28.5 in hypocapnia [arterial CO2 partial pressure (PaCO2) = 21.8 +/- 1.6 Torr], 57.8 +/- 27.5 in normocapnia (PaCO2 = 31.9 +/- 2.2 Torr), and 75.0 +/- 31.7 in hypercapnia (PaCO2 = 44.5 +/- 3.0 Torr). Flow determined from 15 electrodes in adjacent pyramidal tracts (white matter) was less at all levels of CO2; 22.9 +/- 12.3 in hypocapnia, 29.1 +/- 15.9 in normocapnia, and 33.9 +/- 13.9 in hypercapnia. In hypoxia [arterial O2 partial pressure (PaO2) = 39.9 +/- 6.3 Torr] ventrolateral surface flow rose to 87.9 +/- 47.6, and adjacent white matter flow was 35.8 +/- 15.6. These results indicate that flow in the postulated central chemoreceptor areas exceeds that of white matter and is sensitive to variations in PaCO2 and PaO2.

Animals↗
PubMed1975

Regulation of bacterial cell division: temperature-sensitive mutants of Escherichia coli that are defective in septum formation.

Mutations ts2158 and ts1882, which confer temperature sensitivity of septum formation, map near leu in the region of min 2.0 to 2.1 on the Escherichia coli chromosome. These mutants stop division abruptly and grow as filaments at 42 C; when returned to 28 C, division resumes after about 30 min to produce short cells. The product of the gene defined by these mutations probably is required during all stages of septum formation rather than specifically for initiation of septation. Filaments that formed at 42 C contained incomplete constrictiions (septa). When actively dividing filaments (i.e., those incubated at 28 C until division resumed) were shifted to 42 C a second time, division again stopped abruptly and incomplete constrictions persisted during the incubation at 42 C. Filaments that were subjected to 28 C incubation for a brief time (10, 20, or 30 min) before being shifted again to 42 C did not resume division as would be expected of a strain defective in initiating septation. Mutations ts 1882 and ts2158 and recessive to the ts+ allele, which is consistent with the interpretation that these mutations cause the loss of a function. They did not complement each other and presumably represent one cistron. Mutants carrying ts1882 and ts2158 mutations were compared with a mutant defective in the ftA allele, also known to map near leu.

Cell Division↗
PubMed1974

Regulation of bacterial cell division: genetic and phenotypic analysis of temperature-sensitive, multinucleate, filament-forming mutants of Escherichia.

Three mutants of Escherichia coli K-12 which form filaments during 42 C incubation have been characterized. The mutant strains AX621, AX629, and AX655 continued to grow and to synthesize deoxyribonucleic acid at 42 C for 150 to 180 min, after which time growth ceased. When cultures of the mutants were transferred from 42 to 28 C, septation of the filaments began after a 25- to 30-min period and continued at a greater than normal rate until no filaments remained. Addition of chloramphenicol at the time of transfer from 42 to 28 C prevented cell division in strain AX655 and caused lysis of strains AX621 and AX629. The temperature sensitivity mutation in each strain mapped near leu. For strain AX621, the mutation was specifically located between leu and nadC by P1 transduction. Properties of these strains are compared with those of other cell division mutants.

Azides↗
PubMed1974

Bacterial cell division regulation: characterization of the dnaH locus of Escherichia coli.

The dnaH locus is the fourth gene to be identified as required for deoxyribonucleic acid polymerization in Escherichia coli. A temperature-sensitive mutant defective in this gene exhibited an abrupt decrease in rate of deoxyribonucleic acid synthesis when shifted to 42 C. The locus mapped in the proC-purE region of the chromosome by conjugation and was co-transducible with purE. dnaH(+) is carried on the F'(13) episome and is dominant over the dnaH(-) mutation.

Cell Division↗
PubMed1973

Bacterial cell division regulation: lysogenization of conditional cell division lon - mutants of Escherichia coli by bacteriophage.

The lon(-) mutants of Escherichia coli grow apparently normally except that, after temporary periods of inhibition of deoxyribonucleic acid synthesis, septum formation is specifically inhibited. Under these conditions, long, multinucleate, nonseptate filaments result. The lon(-) mutation also creates a defect such that wild-type bacteriophage lambda fails to lysogenize lon(-) mutants efficiently and consequently forms clear plaques on a lon(-) host. Two lines of evidence suggest that this failure probably results from interference with expression of the lambdacI gene, which codes for repressor, or with repressor action:-(i) when a lon(-) mutant was infected with a lambdacII, cIII, or c Y mutant, there was an additive effect between the lon(-) mutation and the lambdac mutations upon reduction of lysogenization frequency; and (ii) lon(-) mutants permitted the growth of the lambdacro(-) mutant under conditions in which the repressor was active. The isolation of lambda mutants (lambdatp) which gained the ability to form turbid plaques on lon(-) cells is also reported.

Cell Division↗