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Biomedical subjects

J T Walker

Publications and source records attributed to J T Walker.

85 records · Page 5Linked to original sources
PubMed1975

Experimental cerebral ischemia in Mongolian gerbils. II. Changes in carbohydrates.

A cerebral ischemia was produced by unilateral ligation of the common carotid artery in the neck of Mongolian gerbils (Meriones unguiculatus), which are frequently characterized by deficiencies in the circulus of Willis. Concentrations of glucose, lactate, pyruvate and glycogen were measured in the hemisphere on the side of occlusion and in the contralateral control hemisphere of animals sacrificed after 5, 15 and 30 min, as well as after 1,3,5 and 9 hrs of carotid clamping. Significant decrease of glucose, and increase in lactate and pyruvate concentration were found in the hemisphere ipsilateral to occlusion; the extent of the changes was proportional to the duration of the ischemia. After an initial fall, an increase in the glycogen content occurred in the later stages of ischemia. Glycogen, glucose, lactate and pyruvate were determined also at 1, 5, 20 hrs and 1 week intervals following release of an occlusion lasting for 1 hr. Return to normal values of glucose and pyruvate was seen at 1 hr after release. The lactate and glycogen levels were significantly raised on the occluded side after 20 hrs release. An increased level of glycogen was observed as long as 1 week after a 1-hr carotid occlusion.

Animals↗
PubMed1975

Experimental cerebral ischemia in mongolian gerbils. I. Light microscopic observations.

Light microscopic observations were carried out on Mongolian gerbils (Meriones unguiculatus) subjected to a partial cerebral ischemia by occlusion of the left common carotid artery at the neck. About 30% of gerbils developed an ischemic injury in the ipsilateral hemisphere and their brains revealed the following histopathologic features: 1. the changes were related to the intensity (duration) of the ischemic insult and to the time elapsed following release of the occlusion. The ischemic lesions appear to progress after re-establishment of the circulation and this presents one facet of a "maturation" phenomenon which seems to be a general principle applicable to various parameters of ischemic injury. The rate of "maturation" of the lesions is related to the intensity of the ischemic insult, a lesser intensity resulting in longer development of lesions. 2. The changes were either focal or diffuse in character. The former were assumed to be directly related to a vascular involvement; among the latter the topistic distribution of the hippocampal changes suggested a feature of selective vulnerability. 3. An indirect indication of neuronal recovery was surmised from observations on animals sacrificed after different periods following occlusions of the same duration. Also capable of recovery was a "reactive change" observed in the H3 neurons of the hippocampus. This change was characterized by central chromatolysis and resembled the "rimäre Reizung" of Nissl.

Animals↗
PubMed1975

Genetic studies of coliphage P1. I. Mapping by use of prophage deletions.

One hundred and ten amber mutants of coliphage P1 were isolated and localized into groups with respect to the existing genetic map by use of nonpermissive Escherichia coli K-12 strains lysogenic for P1 with deletions. These lysogens contain one of three types of deletion prophages: P1cry and its derivatives, P1dlacs, and P1dpros. Fourteen such lysogens were tested for their ability to rescue the amber mutants which were then assigned to one of nine deletion segments of the P1 genome defined by the termini of the various prophage deletions. The relationship of the nine deletion segments with the published P1 map is described, two new segments having been added. The deletions of the 14 prophages overlapped sufficiently to indicate that the P1 genetic prophage map should be represented in circular form, which is consistent with the fact that P1 is normally a circular plasmid in the prophage state. The distribution of mutants into deletion segments is nonrandom for at least one segment. In addition, the deletion termini of the 14 defective prophages coincided in five out of nine regions separating the nine deletion segments. Various possible explanations are discussed for the nonrandom recurrence of these deletion termini, including the evidence of hot spots of recombination.

Alleles↗
PubMed1975

Interactions of cationic bile salt derivatives with the ileal bile salt transport system.

Previous structure-activity studies of the active ileal bile salt transport system have demonstrated that a single negative charge on the side chain is essential for active transport. Furthermore, mutual inhibition studies between different pairs of bile salt substrates indicated that dihydroxy bile salts had a greater apparent affinity for the transport system than the trihydroxylated compounds and triketo bile salts had the least such affinity. In this study, a series of cationic bile salt derivatives (cholamine conjugates) were prepared with one, two, and three alpha-hydroxyl groups on the steroid moiety. Based on the previous observations one would expect (1) no active transport of any of the cholamine conjugates by the ileal transport system; (2) interaction of these compounds with the transport system in such a way as to inhibit the transport of bile salts, with inhibition potency of the transport of any single bile salt inversely related to the number of hydroxyl groups present on the cholamine conjugate; and (3) transport of triketo anionic bile salts to be most readily inhibited, trihydroxy compounds less readily inhibited, and dihydroxy bile salts least inhibited. Using everted gut sac preparations it was demonstrated that all three aforementioned expectations did occur. Furthermore, reversible inhibition of ileal absorption of taurocholate and the bile salt derivative taurodehydrocholate could be demonstrated in vivo. The dihydroxy cholamine conjugates were better inhibitors than the trihydroxy compound. Relative specificity for the bile salt system of these cationic bile salt derivatives was demonstrated in the in vivo preparation by comparing its inhibition of taurodehydrocholate absorption with their lesser capacity to inhibit glucose transport.

Animals↗
PubMedDate not supplied

A multiphasic approach for describing serial height data of Fels children: a hexaphasic-logistic-additive growth model.

In this paper, we reported the results obtained from fitting a new growth model to serial height data of 80 Fels children. The model assumed that human height growth curves are due to the combined effects of six macroscopic logistic growth processes, each reaching the same asymptotic height value. It was named the Walker and Walker-Hexaphasic-Logistic-Additive (WWHLA) growth model. An advantage to using this model is that it allowed us to easily fit entire growth curves with 14 biologically interpretable parameters. We tested the model using a computerized nonlinear least squares technique. The results showed that the new model worked extremely well. The fits resulted in high R, R2, and adjusted R2 values, large F values, relatively low residual mean squares, Durbin-Watson statistics that were very close to 2, and relatively small standard error estimates for the model parameters. In addition, the normality and constant variance test passed for more than 95 percent of the children, and the graphs of the residuals essentially showed no model bias. The new model identified the six growth components or processes in both male and female growth curves. The processes were named according to when they reached their peak height velocity: neonatal, infantile, early-childhood, middle-childhood, late-childhood, and pubertal. Preliminary results suggest that the WWHLA model appears to be the best that is currently available at this time for describing the human growth curve.

Body Height↗