THULIUM BIOACCUMULATION BY THE SHORE CRAB CARCINUS MAENAS COLLECTED FROM THE FRENCH COASTS OF THE CHANNEL : A STRUCTURAL, ULTRASTRUCTURAL AND MICROANALYTICAL STUDY BY SECONDARY ION MASS AND X RAY SPECTROMETRY

Deux méthodes de microanalyse ont été utilisées : la spectrographie des rayons X à l'échelon des microscopes optique et électronique et l'émission ionique secondaire à l'échelon du microscope optique, pour montrer que des Carcinus maenas récoltés de Novembre 1982 à Janvier 1983, dans 8 stations des côtes de la Manche (de Boulogne à Roscoff), ainsi que des animaux contaminés expérimentalement, accumulent 169 Tm. Le site principal de retention est l'exosquelette et les organites cibles sont les lysosomes qui contiennent des microgranules à haute teneur en Tm associé à P. Les hémocytes macrophages jouent un rôle important dans la capture, le transport, le stockage et l'excrétion de cette terre rare. C. maenas apparait comme un système biologique accumulant Tm qui, présent dans l'environnement marin à l'état de traces, est stocké et concentré sous forme insoluble par le crabe.Two microanalytical methods have been used : X ray emission at the light and electron microscopes levels and secondary ion emission at the light microscope level to show that Carcinus maenas collected from November 1982 to January 1983, in 8 stations of the channel coasts (from Boulogne to Roscoff) and experimentally contaminated samples, bioaccumulate 169 Tm. The major retention site is the exoskeleton and the target organelles are the lysosomes which contain microprecipitates with high level of Tm associated with P. Macrophage haemocytes play an important part in ingestion, transport, storage and excretion of the rare earth. C. maenas appears as a biological systern accumulating Tm which, present in the marine environment at trace level, is stored and concentrated under an unsoluble form by the crab

Pros and cons: cryo-electron microscopic evaluation of block faces versus cryo-sections from frozen-hydrated skin specimens prepared by different techniques

Over the last two decades, several different preparative techniques have been developed to investigate frozen-hydrated biological samples by electron microscopy. In this article, we describe an alternative approach that allows either ultrastructural investigations of frozen human skin at a resolution better than 15 nm or sample throughput that is sufficiently high enough for quantitative morphological analysis. The specimen preparation method we describe is fast, reproducible, does not require much user experience or elaborate equipment. We compare high-pressure freezing with plunge freezing, and block faces with frozen-hydrated slices (sections), to study variations in cell thickness upon hydration changes. Plunge freezing is optimal for morphological and stereological investigations of structures with low water content. By contrast, high-pressure freezing proved optimal for high-resolution studies and provided the best ultrastructural preservation. A combination of these fast-freezing techniques with cryo-ultramicrotomy yielded well-preserved block faces of the original biological material. Here we show that these block faces did not exhibit any of the artefacts normally associated with cryo-sections, and - after evaporating a heavy metal and carbon onto the surface - are stable enough in the electron beam to provide high-resolution images of large surface areas for statistical analysis in a cryo-SEM (scanning electron microscope). Because the individual preparation steps use only standard equipment and do not require much experience from the experimenter, they are generally more usable, making this approach an interesting alternative to other methods for the ultrastructural investigation of frozen-hydrated material