The role of muscle in determining growth and size in teleost fish

Summary Rapid growth to large size in fish results from a sustained recruitment of new fibres into their axial series of myomeres. Cessation of recruitment at a small fish size leads to slow growth and a small final size of the fish. Fibre growth dynamics of fishes evidently govern growth and size through fibres' surface area to length ratios, which control their nutrient assimilation rates.     

Nucleolar hypertrophy and nuclear DNA replication in liver

Summary Hypertrophy of nucleoli is associated with DNA synthesis in the hepatocytes of untreated rats just as it is in stimulated animals. Nucleolar enlargement is not a sufficient change to ensure that the parenchymal liver cell can make DNA.This work was supported by a grant from the National Cancer Institute.     

DNA and RNA content in diploid and tetraploid amphibians

Resumen En el anuro tetraploide naturalOdontophrynus americanus, el contenido de DNA es el doble que el determinado, bioquimicamente, en los especimens de la población diploide deO. americanus. Sin embargo el contenido de RNA de ejemplares de las dos poblaciones es aproximadamente igual. Aparentemente, mecanismos de regulación bloquean el esceso de material genético en el tetraploide.

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This work was supported by the Fundação de Amparo à Pesquisa do Estado de São Paulo, the Conselho Nacional de Pesquisas, the Fundo de Pesquisas do Instituto Butantan and the Rockefeller Foundation.     

Relationship between size of muscle fibres and body dimensions in a number of teleosts.

In a survey of 17 species of teleosts, a direct relationship was found between the diameter of muscle fibres and estimated volume of the fish. The results also suggested an inverse relationship between muscle fibre diameter and 'streamlinedness' of the fish (as measured by length:height ratio).     

Metabolism of dimethylnitrosamine by amphibians and fish in vitro

Résumé On a examiné le métabolism de la (C¹⁴)-DMN par des coupes de foie de truite, de poisson rouge et de trois espèces d'amphibiens, ainsi que l'excretion du cancérogène après injection par voie intrapéritonéale chez le triton et le poisson rouge. La relation entre le métabolisme et l'activité toxique et/ou cancérogène est discutée.     

Messenger RNA differential display strategies in birds and amphibians

As an inroad to the discovery of genes involved in important biological activities, various techniques have been developed for detecting genes based on their expression levels. Arbitrary amplification of different messenger RNA (mRNA) populations and their comparison on display autoradiograms made mRNA differential display one of the most straightforward approaches to identification of differentially regulated mRNAs. Over the past decade this strategy has been employed in many in vitro and in vivo systems. The use of the method in bird and amphibian model systems is reviewed here, emphasizing several unique combinations of model system and design of differential display screen.     

Down's syndrome: permeability of the erythrocyte membrane for spin-labeled non-electrolytes

Summary A decreased rate of membrane transport of a hydrophobic non-electrolyte TEMPO was found. There were no significant changes in that of a hydrophilic non-electrolyte TEMPOL in erythrocytes of patients with trisomy 21. Changes of the same direction in erythrocyte membrane permeability were found to occur during the intravascular erythrocyte aging.We are indebted to Dr K. Gwodziski for the gift of spin labels synthesized by him and methodical advice.     

Nucleolar changes in non-growing and growing lemon fruit explants (Citrus limon L.)

Résumé L'expansion des nucléoles et la formation de corps réfractaires nucléolaires sont deux étapes dans l'activité cytologique observée dans la croissance de tissus de citron in vitro. En privant les tissus de substances nutritives, on a réussi à séparer ces deux étapes.     

Variation in the number and size of myelinated nerve fibers regenerated after repeated localized freezing of the sciatic nerve of rats]

The number and size of myelinated fibres have been determined in the nerve to medial head of the gastrocnemius muscle of Rats in which the sciatic nerve had been frozen locally 1 to 5 times at monthly intervals. The contralateral nerve was used as a control. When the measurements were made one month after the last freezing, the number of fibres increased progressively until the 3rd freezing, reaching about 220% of the normal value. No higher values were observed after 4 or 5 freezings. The mean diameter of fibres decreased with the number of operations. When the measurements were made 3, 6, 12 or 18 months after the 3rd freezing, the number of fibres decreased by about 30% between the 1st and the 3rd month and then stabilized. The mean diameter of fibres increased progressively. However, at the 18th month, the size of the myelinated fibres had not reached the normal value.     

Analysis of the tissue interactions responsible for the mesonephogenic determination in amphibians, by the in vitro culture technic]

The cultivation of mesonephric lateral mesoblast, in combination with the dorso-caudal endoblast, with or without cordomesoderm, leads to the differentiation of mesonephric tubules in Bufo bufo and Pleurodeles waltlii. Then, the nephric duct does not seem to be necessary to nephric differentiation under in vitro cultivation conditions.