Bromodeoxyuridine specifically labels the regenerative stem cells of planarians

There has been a rapid progress in research activities concerning nanofluids since a large enhancement in their thermal conductivity has been reported a decade ago. While this extraordinary thermal conductivity of nanofluids deserves scientific investigation, the inconsistency and controversy of the results reported by different groups for identical nanofluids across the world raises fundamental doubts and poses a hindrance in the potential applications of nanofluids. This paper presents a critical review of the several techniques for the measurement of thermal conductivity of nanofluids employed by the researchers. Additionally, a detailed description of a unique thermal conductivity measurement device based on the thermal comparator principle, developed by the present authors has been described. Besides the principle of this measurement device, the constructional details have been elaborated. Finally, some suggestions have been made for improving the reliability of the measurement of thermal conductivity.

Techniques for measuring the thermal conductivity of nanofluids: A review

Planarian regeneration involves distinct stem cell responses to wounds and tissue absence

Mitotic activity during regeneration in the planarian Dugesia (G) tigrina shows a biphasic pattern, with a first maximum at 4-12 h, a second and higher maximum at 2-4 days, and a relative minimum in between. The first peak is mainly due to pre-existing G2 cells entering mitosis shortly after cutting, whereas the second maximum is due to cells that divide after going through the S period from the onset of regeneration. From a spatial point of view, the highest mitotic values are found in stump (postblastema) regions near the wound (0-300 micron), though regions far from it also show increased mitotic values but always lower overall values. As regeneration continues the postblastema maximum shifts slightly to more proximal regions. In contrast, no mitosis has been found within the blastema, even though the number of blastema cells increases steadily during regeneration. The results suggest that blastema in planarians forms through an early accumulation of undifferentiated cells from the stump to the base of blastema. The results obtained demonstrate that blastema formation in planarians occurs through mechanisms somewhat different to those shown to occur in the classical epimorphic models of regeneration (Annelida, Insecta, Amphibia), and suggest that planarian regeneration could represent an intermediate stage between morphallactic and epimorphic modalities of regeneration.

Regeneration and pattern formation in planarians: I. The pattern of mitosis in anterior and posterior regeneration in Dugesia (G) tigrina, and a new proposal for blastema formation

Having an almost unlimited capacity to regenerate tissues lost to age and injury, planarians have long fascinated naturalists. In the Western hemisphere alone, their documented history spans more than 200 years. Planarians were described in the early 19th century as being 'immortal under the edge of the knife', and initial investigation of these remarkable animals was significantly influenced by studies of regeneration in other organisms and from the flourishing field of experimental embryology in the late 19th and early 20th centuries. This review strives to place the study of planarian regeneration into a broader historical context by focusing on the significance and evolution of knowledge in this field. It also synthesizes our current molecular understanding of the mechanisms of planarian regeneration uncovered since this animal's relatively recent entrance into the molecular-genetic age.

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The history and enduring contributions of planarians to the study of animal regeneration.

Thermal analyses of Ohio bituminous coals

Temperature and stress dependence of electrical and mechanical properties of Green River oil shale

The rate of mitosis in planarians was measured by two methods. First, by tabulating the proportion of nuclei displaying metaphase mitotic figures after varying lengths of time in colchicine. Second, by measuring the total DNA in a colony of planarians as a function of time. The first method gave a rate of mitosis by non-regenerating Dugesia dorotocephala of 1.4 × 10−4 divisions/cell hour. This rate remains constant for the first 24 hours following decapitation but increases to 2.7 × 10−4 divisions/cell hour by 54 hours. The rate of mitosis in the blastema was no larger than that of the mesenchymal tissues of the older portions. Measurements of the total DNA versus time gave an estimate of the average rate of cell division for spontaneously fissioning planarians of 5.8 × 10−4 divisions/cell hour which, in view of the tendency of the colchicine method to underestimate the true rate, is in satisfactory agreement. The implications of these results for mechanisms of regeneration are discussed.

Mitosis in normal and regenerating planarians.

Measurement of thermal conductivity of Green River oil shales by a thermal comparator technique

Neither intact nor regenerating planaria incorporated any significant amount of tritiated thymidine, tritiated L-leucine, or C14-L-leucine from free solution even over long periods of exposure. Tritiated thymidine was incorporated into regenerating rat liver and fed to planaria, but tritium hydrogen exchange rendered this method useless. A large incorporation of C14-uracil and C14-L-leucine into planaria was obtained by growing baker's yeast in a defined medium containing the labeled compound and then feeding the acetone dried yeast to the planaria. C14 assay of the amino acid components of planaria fed on C14-L-leucine labeled yeast showed C14 in only the L-leucine component and yielded a minimum estimate for protein turnover of 46% in seven weeks. Radioautographs of planaria fed on C14-uracil labeled yeast exhibited specific incorporation into ribonucleic acid. Previous radioisotopic studies on planaria are evaluated and criticized. The amino acid composition of planarian protein was determined.

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Robert Rosenvold

Papers

Thermal analyses of Ohio bituminous coals

Temperature and stress dependence of electrical and mechanical properties of Green River oil shale

Mitosis in normal and regenerating planarians.

Measurement of thermal conductivity of Green River oil shales by a thermal comparator technique

Studies on the Incorporation of Isotopically Labeled Nucleotides and Amino Acids in Planaria