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Biomedical subjects

J B Armstrong

Publications and source records attributed to J B Armstrong.

At least 37 records · Page 2Linked to original sources
PubMed1988

A rapid method for observing the internal morphology of amphibian embryos.

A simple, rapid method for visualizing the internal morphology of amphibian embryos is described. Fixed embryos of Ambystoma mexicanum are surrounded with commercial embedding material and are frozen. Internal structure is revealed by cutting the embryos with a cooled scalpel or razor blade, removing the frozen embedment with an aqueous buffer, and processing the halved embryos for scanning electron microscopy (SEM). This technique allows the internal anatomy of the embryo to be viewed but is much simpler and more rapid than previously described techniques. It should therefore prove useful for understanding and teaching the three-dimensional relationship between tissues in developing embryos. In addition, we believe that this technique could be used, with minor changes, as a rapid method for viewing the internal morphology of a variety of specimens.

Ambystoma↗
PubMed1987

Differentiation of cartilage from cranial neural crest in the axolotl (Ambystoma mexicanum).

Explants of cranial neural crest from neurula-stage Ambystoma mexicanum embryos form cartilage nodules in 10-14 days, when cultured with pharyngeal endoderm. The time course of formation of the nodules, and their appearance, correspond closely to that observed for visceral cartilage in vivo. Endoderm from any area of the sheet surrounding the pharyngeal cavity can induce cartilage formation, but endoderm from regions posterior to the pharyngeal cavity cannot. No other tissues are required for induction in vitro. Cranial neural crest cultured without inductive endoderm did not yield cartilage when taken prior to the stage at which migration begins, indicating that the crest was not determined for cartilage formation at this time. However, a small proportion of the cultures from neural crest taken during the early migratory phase did form cartilage, suggesting that interactions leading to their determination had begun.

Ambystoma↗
PubMed1985

Experimental evidence for a proteinaceous presegmental wave required for morphogenesis of axolotl mesoderm.

Mesoderm of axolotl embryos at various developmental stages was briefly exposed to a calcium-free 0.01% trypsin solution by temporary removal of the epidermis. This treatment was found to disrupt somite segmentation in a localized region and the pronephric duct was unable to migrate through this region. The affected area, consisting of 3.91 +/- 1.04 somites, traveled through the embryo in synchrony with, and 3.55 +/- 0.69-somite widths ahead of segmentation. Trypsinization in the presence of 340 microM calcium resulted in normal duct migration while somite segmentation was still affected. These results demonstrate the existence of a trypsin-sensitive region in the somitic mesoderm and the lateral mesoderm of the duct path that travels in advance of somite segmentation and in synchrony with it. In addition, the trypsin sensitivity of the duct path is calcium dependent whereas that of the somitic mesoderm is not.

Ambystoma↗
PubMed1984

Selenium deficiency in cattle associated with Heinz bodies and anemia.

Cattle grazing St. Augustine grass growing on peaty muck soils in the Florida Everglades developed anemia associated with the presence of Heinz bodies and suboptimal concentrations of selenium in blood. Selenium supplementation corrected the anemia, prevented Heinz body formation, increased the body weight of cows and calves, and elevated blood selenium. This may be the first recorded example of widespread anemia in a population due to selenium deficiency.

Anemia, Hemolytic↗
PubMed1984

Assessment of mutagenic damage by monofunctional alkylating agents and gamma radiation in haploid and diploid frogs, Xenopus laevis.

Adult male South African clawed frogs, Xenopus laevis, were mutagenized by 3-day immersion in aqueous solutions of ethyl methanesulfonate (EMS), diethyl nitrosamine (DEN), or ethyl nitrosourea (ENU), or by acute exposure to gamma radiation. They were then spawned repeatedly at 2-week intervals with untreated females, and embryonic survival of the progeny was used to assess genetic damage. Recessive lethal effects were assessed from reduced survival of androgenetic haploid progeny. Neither recessive nor dominant lethal effects were obtained after exposure to 100 mg/liter EMS or 2 g/liter DEN. At 250 mg/liter EMS, peak dominant lethality occurred 3-5 wk after treatment. Most embryos hatched, but many were abnormal and died shortly after hatching. Haploid survival was significantly reduced over a broader period, from 1 to 13 wk after mutagenesis. Treatment with 75 mg/liter ENU produced effects similar to the 250-mg/liter EMS mutagenesis. At 400 mg/liter EMS, the frequency and severity of the effects on both diploid and haploid embryos were increased over the lower dose. Gamma irradiation at 1,500 R produced effects similar to the 400-mg/liter mutagenesis, except that peak dominant lethality extended from 1 to 7 wk.

Alkylating Agents↗
PubMed1984

Genetic mapping in the Mexican axolotl, Ambystoma mexicanum.

In the Mexican axolotl, Ambystoma mexicanum, gynogenetic diploids can be produced by suppressing the release of the second polar body in eggs activated with irradiated sperm. If the female is heterozygous for a particular mutation, some of the progeny will be homozygous for the mutation. The proportion depends on the distance from the centromere and can be used to determine the gene--centromere (or gene-kinetochore) distance. The mapping function is based on the Neurospora tetrad mapping function. Several variations on this function, based on considerations of how coincidence varies with map distance, are considered. Three genes have been mapped: c at 5.9, t at 24.3, and m at 59.1 map units from their respective centromeres. Four other genes (a, ax, p, and the sex locus) appear to be distant from their centromeres but precise map distances cannot be determined. Based on these data, the total length of the genome has been estimated as at least 2600 map units.

Ambystoma↗
PubMed1983

Assessment of mutagenic damage following ethyl methanesulfonate mutagenesis in the axolotl (Ambystoma mexicanum).

When male axolots (Ambystoma mexicanus) were treated with 100 mg/liter of ethyl methanesulfonate (EMS), a dominant lethal effect was obtained. Embryonic survival of F1 progeny was most severely reduced between about 50 and 150 days after treatment. Dominant lethal lesions probably consist of chromosome breaks that lead to loss of parts of chromosomes or entire chromosomes. The appearance of embryos with a single nucleolus was used to assess this type of damage. The peak incidence of such embryos coincided with the peak of dominant lethality. At 25 mg/liter EMS, there was no significant dominant lethal effect, but as many as one-fourth of the embryos appeared morphologically abnormal during the period between 50 and 120 days after treatment. A small but significant number of embryos with a single nucleolus were also obtained. To assess possible recessive lethal damage, androgenetic haploids were produced from some of the mutagenized males. A broad trough of reduced haploid survival was obtained at 100 mg/liter, suggesting that damage is produced in most or all spermatogenic stages. At 10 mg/liter, where there was no dominant lethal effect or significant incidence of embryos with a single nucleolus, a broad period of reduced haploid survival was also obtained. Though we cannot exclude the possibility that chromosome abnormalities contribute to the reduced haploid survival, even at this low dose, the type of damage being assessed is almost certainly less severe than that leading to dominant lethality.

Ambystoma↗
PubMed1983

Experimental studies on a lethal gene (t) in the Mexican axolotl, Ambystoma mexicanum.

In the Mexican axolotl, Ambystoma mexicanum, the developmental mutation lethal t is inherited as a simple Mendelian recessive. Mutant larvae failed to feed and died, on the average, 17 days after hatching. Unfed wild-type larvae died an average of 23 days after hatching. By 15 days, forelimb development had progressed further in the wild type; a cartilaginous scapula and humerus were present, but no cartilage was seen in the mutant limb. Histological examination indicated that the visceral cartilage may also be abnormal, and the rectus cervicus muscle was found to have fewer and smaller fibers. Though the mutant was not rescued by parabiosis with wild-type embryos, transplants of presumptive gill and limb tissue to wild-type hosts survived, indicating that the mutation is not an autonomous cell lethal.

Ambystoma↗
PubMed1981

Alternatives in the handling, processing and storage of electrocardiograms.

Physicians and administrators are becoming aware that computer technology can play a significant role in the electrocardiology department. Problems related to the large number of requests for electrocardiograms, the production and communication of electrocardiographic tracings and reports, the access to stored tracings and the overall cost of providing effective services have led administrators to look for assistance through automation. Before expensive equipment and new procedures are introduced, a survey of the electrocardiology department's functions and procedures can lead to important insights. Automation can be achieved in stages, and problems can be solved by separate steps. Options range from basic word-processing support to completely automated electrocardiographic interpretation and computerized storage of records. Choosing the appropriate equipment and programs requires knowledge of the present system, awareness of the options and analysis of the costs and savings.

Computers↗
PubMed1981

Phase transition behaviour of artificial liposomes composed of phosphatidylcholines acylated with cyclopropane fatty acids.

Phase transitions of liposomes composed of synthetic phoshatidylcholines acylated with the cyclopropane fatty acids, lactobacillic and dihydrosterculic acid, were studied by differential scanning calorimetry. Transition temperatures were approx. 16 degrees C higher than for phosphatidylcholines acylated with the corresponding unsaturated fatty acids, cis-vaccenic and oleic acid. Though our transition temperatures were all several degrees lower than those determined by Silvius and McElhaney ((1979) Chem. Phys. Lipids 25, 125--134), the increase produced by replacement of the double bond with a cyclopropane ring was the same. We propose that this replacement, through its effect on membrane fluidity, may serve to regulate the activity of membrane-associated processes such as transport.

Acylation↗
PubMed1981

Suppression of first cleavage in the Mexican axolotl (Ambystoma mexicanum) by heat shock or hydrostatic pressure.

Androgenetic diploid axolotls were produced by ultraviolet inactivation of the egg pronucleus shortly after fertilization, followed by suppression of the first cleavage division by hydrostatic pressure or heat shock. After treatment at 14,000 psi for 8 minutes, diploidy was restored in 74% of the embryos, but only 0.8% survived to hatching. A 36-37 degrees C heat shock of 10-minutes duration, applied 5.5 hours after the eggs were collected, yielded a slightly lower percentage of diploids. However, the proportion surviving to hatching was significantly greater (up to 4.6%). A second generation of androgenetic diploids was produced from one of the oldest of the first generation males with a similar degree of success. The lack of significant improvement suggests that the low survival is due to the heat shock per se and not to the uncovering of recessive lethal genes carried by the parent.

Ambystoma↗
PubMed1981

The effect of temperature and other growth conditions on the fatty acid composition of Escherichia coli.

During exponential growth, strain AW405 of Escherichia coli K-12 did not regulate the fatty acid composition of its lipids in response either to temperature or to the addition of NaCl, KCl, or MgCl2 to the medium. Growth was severely restricted at temperatures below 21 degrees C. Differential scanning calorimetry (DSC) of the isolated lipids from a culture with a typical exponential-phase composition yielded a broad transition, extending from approximately 0 to 33 degrees C, with a midpoint at 19 degrees C. During late stages of growth, the fatty acid composition changed. The percentage of palmitic acid increased and cyclopropane fatty acids replaced some of the equivalent unsaturated fatty acids. The increase in palmitate seemed largely independent of growth conditions, whereas the increase in the cyclopropane fatty acids was stimulated by the addition of salts or sucrose. Cultures grown in the presence of sucrose also had higher cyclopropane fatty acid levels during exponential growth. DSC of lipids from a sucrose culture, in which the compositional changes were most pronounced, yielded a much narrower transition with a midpoint at 27 degrees C.

Escherichia coli↗
PubMed1980

Dominant lethal induction by ethyl methanesulfonate in the male axolotl (Ambystoma mexicanum).

When male axolotls (Ambystoma mexicanum) were treated with ethyl methanesulfonate (EMS) and mated at regular intervals thereafter, the incidence of embryonic abnormalities among the F1 progeny increased until a time was reached when none survived to hatching. At 100 mg/1 EMS, this point was reached about 130 days after treatment. Thereafter, the frequency of abnormalities gradually decreased to control levels. At higher concentrations, abnormalities were seen in spawnings obtained sooner after treatment, and also at earlier development stages. The pattern is similar to that reported for the mouse, which has been attributed to differential sensitivity of the various germ-cell stages to the mutagenic agent. The time course, however, is greatly extended in the axolotl. In future experiments we will be looking for gene mutations, primarily before and after the period of peak mortality.

Ambystoma↗
PubMed1980

Lipid metabolism during embryonic and early postembryonic development of Xenopus laevis.

Xenopus laevis embryos were analyzed for their lipid content from fertilization to feeding stage. The amounts of the major lipids did not change until after hatching, but at the feeding stage the amounts of phosphatidylcholine (PC), phosphatidylethanolamine (PE), and sterol esters (SE) increased approximately twofold. Prior to hatching, [14C]acetate label was incorporated primarily into the fatty acyl chains of PE. After hatching, increasing amounts of label were found in other phospholipids, in their glycerol backbones, and in nonglycerol lipids. The most marked changes occurred just before the onset of feeding, and pulse-chase experiments suggest that nonlipid reserves are mobilized at this stage for de novo lipid synthesis.

Acetates↗
PubMed1980

Evidence that the premature death mutation (p) in the Mexican axolotl (Ambystoma mexicanum) is not an autonomous cell lethal.

Cell-lethal developmental mutations, which are presumed to affect the viability of all cells in a mutant embryo, have been distinguished from other development lethals on the basis of the results of parabiosis and transplant experiments. Premature death (p), previously classified as a cell lethal, does not survive parabiosis. However, transplants involving mutant eye, flank epidermis and primordial limb tissue all survived on a normal recipient. The mutant, therefore, cannot be considered a true cell lethal, though it suffers from serious and widespread abnormalities that cannot be corrected by parabiosis. In addition, transplants of mutant branchial mound tissue did not develop into normal gills on a normal recipient. These transplants were the only ones involving mutant endoderm, and their failure supports our hypothesis that the mutation leads to a specific endoderm defect.

Ambystoma↗