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Biomedical subjects

J T Walker

Publications and source records attributed to J T Walker.

At least 73 records · Page 4Linked to original sources
PubMed1981

Auditory-visual conflicts in the perceived duration of lights, tones and gaps.

The perceived duration of a short tone (1,000 or 1,500 msec) was longer than that of a separately presented light of equal length. Thus, when light and tone were presented simultaneously, there was a conflict in perceived duration. In that case, the perceived duration of an interval filled with both light and tone was close to that of an interval filled with tone alone. A silent gap in otherwise continuous tone was perceived as longer than a gap in otherwise continuous light, and the perceived duration of a gap occurring simultaneously in both light and tone was close to that of a gap in tone alone. Thus, auditory dominance occurred under the preceding conditions-that is, auditory-visual conflicts in perceived duration, whether occurring between filled intervals or gaps, were resolved in favor of the auditory modality. Visual dominance occurred only under one condition, in which the intensity of tone was reduced, and in which the perceived duration of a 500-msec light was longer than that of a 500-msec tone. The finding of auditory dominance in the perception of time runs counter to the results of studies of sensory conflicts in spatial perception, where vision typically dominates audition and touch.

Adolescent↗
PubMed1980

Small-organ dynamic imaging system.

Dynamic ultrasonic imaging of superficial body organs adds a new dimension to clinical sonographic examinations in that it enables the real-time evaluation of tissue motion and vascular pulsations. A high-frequency (7.2 MHz) linear-array system has been newly developed that generates simultaneous A- and B-mode displays at 60 frames/sec. The instrument produces real-time scan-converted images in standard television format for direct viewing on television (TV) monitors or clinical recording through videotape equipment. Clinical application of this dynamic imaging system has increased the diagnostic capabilities of ultrasound in ophthalmology, radiology, and pediatrics.

Data Display↗
PubMed1980

Mutations in coliphage p1 affecting host cell lysis.

A total of 103 amber mutants of coliphage P1 were tested for lysis of nonpermissive cells. Of these, 83 caused cell lysis at the normal lysis time and have defects in particle morphogenesis. Five amber mutants, with mutations in the same gene (gene 2), caused premature lysis and may have a defect in a lysis regulator. Fifteen amber mutants were unable to cause cell lysis. Artificially lysed cells infected with five of these mutants produced viable phage particles, and phage particles were seen in thin sections of unlysed, infected cells. However, phage production by these mutants was not continued after the normal lysis time. We conclude that the defect of these five mutants is in a lysis function. The five mutations were found to be in the same gene (designated gene 17). The remaining 10 amber mutants, whose mutations were found to be in the same gene (gene 10), were also unable to cause cell lysis. They differed from those in gene 17 in that no viable phage particles were produced from artificially lysed cells, and no phage particles were seen in thin sections of unlysed, infected cells. We conclude that the gene 10 mutants cannot synthesize late proteins, and it is possible that gene 10 may code for a regulator of late gene expression for P1.

Journal Article↗
PubMed1979

Histochemical investigation of the Mongolian gerbil's brain during unilateral ischemia.

The ischemic effect on cerebral enzymes and glycogen content was histochemically evaluated in mongolian gerbils subjected to unilateral common carotid artery occlusion for various periods of time from 1/2 to 9 h. In early stages (up to 2 h), the only enzyme affected was the phosphorylase which revealed a decreased activity. Thereafter, the observed changes inclusive of glycogen and other enzymes such as the dehydrogenase, nonspecific acid and alkaline phosphatases, leucine aminopeptidase and thiamine pyrophosphatase progressed proportionally to the duration of ischemia. There was an overall inverse appearance of histochemically demonstrated enzymatic disturbances between the severely damaged ischemic regions and its marginal zones; the former revealing a conspicuous decrease and/or loss of enzymatic activities while the latter showing an increase of the same enzymes. Correlating the various ischemic responses of the intracellular organelles it appears that the changes in the lysosomes and Golgi apparatus occurred slower than those of mitochondria.

Acid Phosphatase↗
PubMed1979

Permutation of the DNA in small-headed virions of coliphage P1.

Use of restriction endonucleases Bg/II, EcoRI, BamHI, and HindIII, has established that in small-headed (P1S) virions of coliphage P1, as a population, the entire genome found in big-headed (P1B) virions is represented. In addition, the origin and direction of DNA packaging are identical in P1S and P1B virions.

Coliphages↗
PubMed1977

Interaction of uncharged bile salt derivatives with the ileal bile salt transport system.

Two series of uncharged conjugated bile salt derivatives, N-conjugates of ethanolamine and 3-amino-1,2-propanediol were studied for interaction with the ileal bile salt transport system. Evidence for interaction is threefold. 1) In everted gut sac experiments more material was removed from the mucosal compartment when ileal sacs were used. 2) These derivatives inhibited the in vitro transport of taurocholate. 3) In vivo intestinal perfusion demonstrated greater absorption from ileum than from jejunum. Number three demonstrates that such interactions are followed by transmucosal movement. Their uphill transport was less than taurocholate transport. The Na(+) requirement for cholyl-3-amino-1,2-propanediol interaction with the system was greater than for taurocholate. This observation is similar to that previously observed with taurodehydrocholate, which had a greater Na(+) requirement for transport than taurocholate. Therefore removal of the anionic charge, as well as distortion of steroid shape, increases the Na(+) requirement for substrate interaction with the transport system. These observations support our hypothesis that this interaction involves two recognition components; one includes the steroid moiety, the other a coulombic interaction between the anionic bile salt and a cationic membrane site. Additionally the membrane would have an anionic group to accomodate the Na(+). Both factors (steroidal and coulombic) operate for optimal substrate attachment. Simultaneously the system's affinity for Na(+) increases and active transport then proceeds.

Animals↗
PubMed1976

Experimental cerebral ischemia in Mongolian gerbils. IV. Behaviour of biogenic amines.

Behaviour of biogenic amines was studied in the brains of Mongolian gerbils subjected to unilateral occlusion of the common carotid artery. Assays on the hemispheres ipsilateral to occlusion revealed in symptom-positive animals a progressive decrease in norepinephrine and dopamine, and an increase in serotonin throughout the duration of an ischemic insult. In post-ischemic periods following the release of the clip, changes in biogenic amine levels generally conformed to the principles of a previously described "maturation" phenomenon, with delayed reactions occurring after the shorter ischemic insults.

Animals↗
PubMed1976

Experimental cerebral ischemia in Mongolian gerbils III. Behaviour of the blood-brain barrier.

The behavior of the BBB in cerebral ischemia was studied in symptom-positive Mongolian gerbils subjected to left common carotid artery occlusion using Evans Blue dye as indicator of BBB injury. The BBB damage was demonstrable grossly by the presence of areas of blue discoloration, and microscopically by the presence of a bright red fluorescent tracer, localized mostly in the neurons. The survey of various groups of animals revealed a direct relationship between the incidence and time of appearance of the BBB lesions and the duration of the ischemic occlusion. This relationship can be interpreted as another example of the previously described "maturation" phenomenon. A relatively late occurrence of the BBB injury in cerebral ischemia, at the time when the affected brain tissue shows severe, edematous histopathologic changes indicates that the brain edema, as the main complication of ischemia, could be regarded as being primarily of the cytotoxic type.

Animals↗
PubMed1976

Genetic studies of coliphage P1. II. Relatedness to P7.

Using semiquantitative spot tests, 107 independently isolated amber mutants of P1 were shown to be rescued by a nonpermissive strain of Escherichia coli lysogenic for P7 (previously called phiamp), indicating extensive genetic relatedness between P1 and P7. The amount of rescue observed varied with mutants from different genetic linkage clusters of P1. Although these rescue tests cannot distinguish between recombination, complementation, transactivation, or combinations thereof, a major role is indicated for recombination.

Ampicillin↗
PubMed1976

Genetic studies of coliphage P1. III. Extended genetic map.

An extensive genetic map of coliphage P1 has been constructed for 113 amber mutants, using primarily a modification of the conventional complementation spot test. These spot tests failed to classify the mutants into cistrons, but when they were quantitated they permitted assignment of the mutants into 10 linkage clusters. Furthermore, a linear order could be deduced for most of the mutants within each cluster. This strongly suggested that recombination was the predominant event generating plaques and that, for the practical purpose of rapid genetic mapping, such spot tests could be considered as a series of two-factor crosses. Six of the 10 linkage clusters correlated with the P1 genetic map established by Scott (1968). The locations of the remaining four clusters were determined by three-factor crosses and by prophage deletion mapping. The nonrandom occurrence of termini for 14 deletion prophages, which we established previously (Walker and Walker, 1975), and the coincidence of these termini with five out of ten regions demarcating the linkage clusters are discussed. Complementation tests in liquid frequently gave ambiguous results. Therefore, cistron designations were not assigned.

Chromosome Mapping↗
PubMed1976

Ionic requirements for the active ileal bile salt transport system.

Taurocholate transport by everted ileal gut sacs was studied in physiological media containing graded amounts of sodium ions. Significant uphill transport of taurocholate was observed when the bulk of NaCl was replaced by osmotic equivalents of mannitol or choline chloride. Seventy-seven percent of control transport activity was observed when 36 milliequivalents per liter of Na+ were present in the incubation medium with mannitol acting as the isosmotic replacement, and 74% of the control transport was retained when 31 milliequivalents per liter of Na+ were present in the incubation medium with choline chloride acting as the osmotic replacement. Lowering the Na+ concentration to 19 milliequivalents per liter (i.e., 84% replacement of Na+) still allowed for 69% of the uphill transport observed in the control incubations. Taurodehydrocholate transport by ileal everted sacs was more sensitive to decreased Na+ concentrations; 29% of control transport was observed at 31 milliequivalents per liter of Na+. A kinetic analysis comparing the transport of taurocholate with taurodehydrocholate, the triketo analogue, at different concentrations of Na+ indicated that the apparent affinity of the transport system for Na+ is greater in the presence of taurocholate than in the presence of taurodehydrocholate. The ability of taurodehydrocholate to depress taurocholate transport is less in media of low Na+ concentration. Finally, in vivo intestinal perfusion studies demonstrated that the depression of taurocholate absorption, following Na+ removal, is reversible. These results are in agreement with the idea that Na+ has a physiological role in intestinal bile salt transport, and that the affinities of the anionic bile salt and the sodium cation for the transport system appear to be cooperative in that one enhances the binding of the other.

Animals↗