Hormonal changes in humans during spaceflight have been demonstrated but the underlying mechanisms are still unknown. To clarify this point thyroid and testis/epididymis, both regulated by anterior pituitary gland, have been analyzed on long-term space-exposed male C57BL/10 mice, either wild type or pleiotrophin transgenic, overexpressing osteoblast stimulating factor-1. Glands were submitted to morphological and functional analysis.In thyroids, volumetric ratios between thyrocytes and colloid were measured. cAMP production in 10−7M and 10−8M thyrotropin-treated samples was studied. Thyrotropin receptor and caveolin-1 were quantitized by immunoblotting and localized by immunofluorescence. In space-exposed animals, both basal and thyrotropin-stimulated cAMP production were always higher. Also, the structure of thyroid follicles appeared more organized, while thyrotropin receptor and caveolin-1 were overexpressed. Unlike the control samples, in the space samples thyrotropin receptor and caveolin-1 were both observed at the intracellular junctions, suggesting their interaction in specific cell membrane microdomains.In testes, immunofluorescent reaction for 3β- steroid dehydrogenase was performed and the relative expressions of hormone receptors and interleukin-1β were quantified by RT-PCR. Epididymal sperm number was counted. In space-exposed animals, the presence of 3β and 17β steroid dehydrogenase was reduced. Also, the expression of androgen and follicle stimulating hormone receptors increased while lutenizing hormone receptor levels were not affected. The interleukin 1 β expression was upregulated. The tubular architecture was altered and the sperm cell number was significantly reduced in spaceflight mouse epididymis (approx. −90% vs. laboratory and ground controls), indicating that the space environment may lead to degenerative changes in seminiferous tubules.Space-induced changes of structure and function of thyroid and testis/epididymis could be responsible for variations of hormone levels in human during space missions. More research, hopefully a reflight of MDS, would be needed to establish whether the space environment acts directly on the peripheral glands or induces changes in the hypotalamus-pituitary-glandular axis.
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 complex control of food intake and energy metabolism in mammals relies on the ability of the brain to integrate multiple signals indicating the nutritional state and the energy level of the organism and to produce appropriate responses in terms of food intake, energy expenditure, and metabolic activity. Central regulation of feeding is organized as a long-loop mechanism involving humoral signals and afferent neuronal pathways to the brain, processing in hypothalamic neuronal circuits, and descending commands using vagal and spinal neurons. Sensor mechanisms or receptors sensitive to glucose and fatty acid metabolism, neuropeptide and cannabinoid receptors, as well as neurotransmitters and neuromodulators synthesized and secreted within the brain itself are all signals integrated in the hypothalamus, which therefore functions as an integrator of signals from central and peripheral structures. Homeostatic feedback mechanisms involving afferent neuroendocrine inputs from peripheral organs, like adipose tissue, gut, stomach, endocrine pancreas, adrenal, muscle, and liver, to hypothalamic sites thus contribute to the maintenance of normal feeding behavior and energy balance. In addition to transcriptional events, peripheral hormones may also alter firing and/or connection (synaptology) of hypothalamic neuronal networks in order to modulate food intake. Moreover, intracellular energy sensing and subsequent biochemical adaptations, including an increase in AMP-activated protein kinase activity, occur in hypothalamic neurons. Understanding the regulation of appetite is clearly a major research effort but also seems promising for the development of novel therapeutic strategies for obesity.
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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