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Three-spined sticklebacks ( Gasterosteus aculeatus L.) of the Camargue region (Rhone delta, northern Mediterranean Sea) occupy coastal mesohaline lagoons and freshwater canals. In this study, the acclimation capacity to different salinities of a population living in freshwater canals was investigated. Freshwater ( FW; 5 ‰) individuals were compared to fish acclimated for at least 2 weeks to brackish water ( BW; 15 ‰) and seawater ( SW; 30 ‰). Blood osmotic pressure and gill Na+/K+- ATPase ( NKA) gene expression of the α1 subunit and α1a and α1b isoforms were determined at these salinities. NKA protein expression in the gill ionocytes and the remodelling of these cells were also investigated through NKA immunolabelling and electron microscopy. Blood osmolalities of fish acclimated to FW, BW and SW were significantly different. Branchial NKA α1a and α1b expressions also differed, with a higher expression of NKA α1b in fish acclimated to SW. Gill ionocytes in fish acclimated to FW were located along the lamellae and at their base and appeared elongated, whereas these cells were restricted to gill filaments in fish acclimated to SW with a round shape. Finally, electron microscopy revealed three different types of apical structures for these ionocytes: a honeycomb-like structure and a dome shape in FW, and deeply encrypted in SW. This study shows that ionocyte cell type and morphology, and gill NKA expression are salinity-dependent. This branchial remodelling is directly linked to the physiological homeostatic status reached by the fish. It also highlights that sticklebacks of the Camargue region can rapidly acclimate to different salinities and can easily migrate between FW canals and mesohaline coastal lagoons. [ABSTRACT FROM AUTHOR]

The study tests the physiological responses of Persian sturgeon, Acipenser persicus, during the abrupt release of juveniles from freshwater ( FW) into brackish waters ( BW = 11‰) of the Caspian Sea. Fish weight at release was 2-3 g (2.55 ± 0.41 g; 8.8 ± 0.58 cm TL). Totals of 160 individuals were randomly distributed into four fiber-glass aerated tanks (volume 60-L). Two tanks served as controls ( FW groups), and two as exposure tanks for BW (Caspian Sea water = CSW). Fish were sampled at 0, 3, 6, 12, 24, 48 and 96 hr after abrupt transfer to CSW. Plasma osmolality, immunolocalization of Na+, K+ - ATPase ( NKA) and Na+/K+/2Cl- ( NKCC) Co-transporter, NKA activity and the NKA α-subunit mRNA expression were analyzed. Blood osmolality of fish transferred from FW to CSW increased significantly within hours post-transfer ( p < .05) and remained at a high level for up to 96 hr. Immunolocalization of NKCC indicated co-localization with NKA in the chloride cells in the gill epithelium. A partial sequence of the NKA α-subunit (632 bp) is described. Its expression levels were up-regulated at 12 and 48 hr following salinity transfer ( p < .05). However, NKA activity sharply increased in CSW specimens by almost 2.8-fold ( p < .05) between 48 and 96 hr after transfer. Gill NKCC co-transporter abundance increased, coinciding with increased gill NKA activity. The increased activity of NKCC during salt excretion in CSW may lead to an influx of Na+ into the chloride cells. Consequently, NKA activity increases to maintain intracellular Na+ homeostasis. [ABSTRACT FROM AUTHOR]

Background: Intestinal mucosa atrophy following a period of starvation characterized by the mobilization of fat stores for energy expenditure (phase II) worsen after a long fast marked by an increase in protein catabolism (phase III). However, the morphology of the jejunum is completely restored after 3 days of refeeding. The aim of this study was to determine the mechanisms involved in the rapid jejunal restoration following the critical phase III. Methods: Jejunal structure was observed through conventional and environmental scanning electron microscopy, whilst cellular dynamics were studied using classical optic microscopy tools and immunohistochemistry. Results: Mucosal structural atrophy during fasting proved to worsen over the two phases. During phase II, apoptosis is still present at the tip of the villi, the number of mitosis in crypts showed a 30% decrease and a transient drop in cell migration is observed. During phase III, however, an 85% rise in mitosis was noticed along with an increase in cell migration and the disappearance of apoptotic cells at the villus tips. This increased cell renewal continues after food ingestion. Conclusions: Starved rats appeared to be in a phase of energy sparing in phase II, with depressed cellular events in the intestinal mucosa. In phase III, however, the preservation of functional cells and the early increase in crypt cell proliferation should prepare the mucosa to refeeding and could explain why jejunal repairs are complete after 3 days of refeeding following either phase II or phase III. [ABSTRACT FROM AUTHOR]