Principios-guía y leyes especiales: Una distinción muy fructífera (y muy difícil de elucidar)

La finalidad de este trabajo es revisar una de las nociones centrales de la metateoría estructuralista, la noción de principio-guía, mostrar su fecundidad para abordar algunas cuestiones centrales tanto de filosofía general como de filosofía especial de la ciencia, así como de historia de la filosofía de la ciencia, y, por último, revisar y valorar algunas propuestas de elucidación de la misma. La conclusión es que se trata de una noción tan fructífera como difícil de analizar.O objetivo deste trabalho é revisar uma das noções centrais da metateoria estruturalista, a noção de princípio-guia, mostrar sua fecundidade para abordar algumas questões centrais tanto da filosofia geral quanto da filosofia especial da ciência, bem como da história da filosofia da ciência, e, finalmente, rever e avaliar algumas propostas para sua elucidação. A conclusão é que esta é uma noção tão frutífera quanto difícil de analisar

Cryopreservation of Brown Bear Skin Biopsies

Genetic resource banks and assisted reproductive technologies support the conservation of endangered or threatened species. In this study we assessed two procedures to cryopreserve skin biopsies from live brown bears. Skin biopsies were taken from six live, anesthetized brown bears. Single biopsies (n = 3) of each animal were cut into small pieces and assigned to one of the three experimental groups: freezing, vitrification, or untreated fresh. There were no differences on cell attachment. However, both freezing and fresh culture allowed for higher cell proliferation (p < 0.05) and less days to reach 70% to 80% confluence (p < 0.03) than vitrification. Skin biopsies from brown bears can be preserved long term, allowing fibroblasts to proliferate in culture. Slow freezing was effective to cryopreserve skin biopsies from brown bears

Effects of human versus mouse leukemia inhibitory factor on the in vitro development of bovine embryos

Leukemia inhibitory factor (LIF) is a cytokine that shows conflicting effects on in vitro produced (IVP) bovine embryos. Bovine LIF (bLIF) has been cloned and used in culture, but there is no commercially available bLIF. Thus, researchers use human LIF (hLIF) to supplement the culture medium for bovine embryos because of its greater sequence homology compared to murine LIF (mLIF). We compared the effects of mLIF and hLIF on the development of bovine embryos in culture with the effects described for bLIF. Oocytes were matured and fertilized in vitro and cultured in modified synthetic oviduct fluid with BSA. On Day 6 post-insemination, morulae were cultured for 48 h in the presence of: (1) mLIF, 100 ng ml−1; (2) hLIF, 100 ng ml−1; or (3) no LIF. Reduced blastocyst rates were observed on Day 8 for hLIF at the middle and expanded stages, while mLIF had no effect. In contrast, Day 8 blastocysts showed decreased cell counts both in terms of inner cell mass (ICM) and ICM/total cell proportions in the presence of mLIF, while hLIF had no effect. No changes were seen in trophectoderm (TE) and total cell counts. The increased hatching rates and TE cell counts previously described for bLIF, together with the disparate effects exhibited by hLIF and mLIF during blastocyst formation indicate these compounds are inappropriate to replace bLIF. We recommend that heterospecific LIF should not be used to supplement the culture medium for bovine embryo or embryonic stem cells

Green determination of brominated flame retardants and organochloride pollutants in fish oils by vortex assisted liquid-liquid microextraction and gas chromatography-tandem mass spectrometry

A "green", simple, and low-cost sample extraction procedure involving the use of a deep eutectic solvent (DES) in a vortex assisted liquid-liquid microextraction (VALLME) technique followed by gas chromatography-tandem mass spectrometry (GC-MS/MS) analysis was developed for the simultaneous determination of different PBDEs congeners and OCPs residues in fish oils. After evaluation of different eutectic mixtures, the extraction parameters (volume of DES, amount of oil sample and extraction time) were optimized by means of experimental design in order to maximise extraction efficiency. The developed method was validated in terms of linearity, accuracy and precision, presenting limits of detection in the low ng g−1 level. Its application in the analysis of five fish oil samples, allowed the detection of all the target analytes at levels up 21.5 ng g−1. Fish oils used in animal feed showed to be more contaminated than fish oils for human consumption.Sara C. Cunha and José O. Fernandes thanks REQUIMTE, FCT Fundação para a Ciência e a Tecnologia) and FEDER through the project UID/ QUI/50006/2013 - POCI/01/0145/FEDER/007265 with financial support from FCT/MEC through national funds and co-financed by FEDER, under the Partnership Agreement PT2020. Sara C. Cunha acknowledges FCT for IF/01616/2015 contract. Angela G. Solaesa acknowledges University of Burgos for her pre-doctoral contract and Iberoamerican Santander Research Grant (2017) for the mobility financial support. Thanks to European Regional Development Fund (ERDF) and Junta de Castilla y León for financial support of project BU055U16