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Apoptosis is a form of naturally occurring cell death that plays fundamental roles during embryonic developement. In adults, it neatly disposes of cells damaged by injuries provoked by external causes such as UV radiation, ionisation and heat shock. Alteration of the gravity vector may be one of the external apoptosis inducers. Neurophysiological impairment signs were seen during space flights in astronauts, but very few studies were carried out on the nervous system and none at the cellular level. In this study, we submitted cultured C6 glioma cells to microgravity (0xg) of varying duration, obtained by clinorotation in a Fokker three-dimensional clinostat for 15min, 30min, 1h, 20h or 32h. After 30min at 0xg, numerous nuclei underwent the classical morphological alterations (chromatin condensation, nuclear fragmentation, apoptotic bodies) that lead to the programmed cell death. After 30min at 0xg, immunostaining for the enzyme caspase-7 was present in the cytoplasm of many cells concurrently with DNA fragmentation identified by the TUNEL method. At 32h, the number of apoptotic nuclei was much reduced indicating the ability of glial cells to adapt to altered gravity

We used scanning electron microscopy, the vital dye DASPEI and an antibody to the inner mitochondrial membrane to study the presence and localisation of mitochondria-rich cells in the gills and skin (opercular, dorsal and ventral) of the lungfish Protopterus annectens in its free-swimming conditions and at the beginning of aestivation. In the free-swimming period, the gills were short and thick and the pavement cells were extremely large (30-40 microns). The mitochondria-rich cells, which were distributed in the secondary and primary epithelium, occurred as two morphologically different types, i.e. elongated and oval, similar to the alpha and beta chloride cells of fresh water teleosts. In the skin, only one type of mitochondria-rich cells was found, resembling the alpha chloride cells. All the mitochondria-rich cells distributed in the gills and skin were labelled with anti Ca(2+)-ATPase serum indicating the possible uptake of Ca2+ at freshwater chloride cell level. At the start of aestivation, the skin and gills were covered by a thick layer of mucus and the epithelium of the gills was reduced. The mitochondria-rich cells were almost completely covered by the pavement cells.

The aim of this research was to induce, at will in the laboratory, aestivation of the Dipnoan Protopterus annectens, in order to compare the structure of organs in lungfish adapted to aquatic or aestivating conditions. The animals were placed in a glass tank containing warm water, and the bottom of the tank was filled with clay and sand. To start aestivation the water was allowed to slowly evaporate; as soon as the fish was in a dry environment, it began to excavate a hole in the mud and to burrow into it. Scanning electron microscopy and histological techniques compared the morphology of skin, gills, and lungs in aestivating and free-swimming animals. In the aestivating animals, the secondary lamellae of the gills became thick and were covered by mucus that pasted the lamellae together. The epidermis of the skin was thin and composed of layers of flattened cells. In contrast, in free-swimming animals, the secondary lamellae of the gills were widely separated and the epidermis of the skin was thick and contained numerous mucus-laden cells. The lungs, thin bloodless threads in the aquatic conditions, were, in the air-breathing animals, rich in blood and showed thick walls with ridges and pillars that protruded into the lung cavity, producing small alveolar protrusions. The features of the skin and lungs were similar to that of amphibians, testifying to the convergence of some tissue morphology in aquatic animals utilizing land as a cohabitat.

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