Fine structure of the branchial epithelium in the teleost Oreochromis niloticus

We have studied the gill epithelium of Oreochromis niloticus using transmission electron microscopy with the particular interested relationship between cell morphology and osmotic, immunoregulatory, or other non‐regulatory functions of the gill. Pavement cells covered the filament epithelium and lamellae of gills, with filament pavement cells showing distinct features from lamellar pavement cells. The superficial layer of the filament epithelium was formed by osmoregulatory elements, the columnar mitochondria‐rich, mucous and support cells, as well as by their precursors. Light mitochondria‐rich cells were located next to lamellae. They exhibited an apical crypt with microvilli and horizontal small dense rod‐like vesicles, sealed by tight junctions to pavement cells. Dark mitochondria‐rich cells had long dense rod‐like vesicles and a small apical opening sealed by tight junctions to pavement cells. The deep layer of the filament epithelium was formed by a network of undifferentiated cells, containing neuroepithelial and myoepithelial cells, macrophage and eosinophil‐like cells and their precursors, as well as precursors of mucous cells. The lateral‐basal surface was coated by myoepithelial cells and a basal lamina. The lamellar blood lacunae was lined by pillar cells and surrounded by a basal lamina and pericytes. The data presented here support the existence of two distinct types of pavement cells, mitochondria‐rich cells, and mitochondria‐rich cells precursors, a structural role for support cells, a common origin for pavement cells and support cells, a paracrine function for neuroepithelial cells in the superficial layer, and the control of the lamellar capillary base by endocrine and contractile cells. Data further suggest that the filament superficial layer is involved in gill osmoregulation, that may interact, through pale mitochondria‐rich cells, with the deep layer and lamellae, whereas the deep layer, through immune and neuroendocrine systems, acts in the regeneration and defense of the tissue. J. Morphol. 2010. © 2010 Wiley‐Liss, Inc.     

Quantitative histopathology of Oreochromis niloticus gills after copper exposure

In order to test whether histopathological changes of gills demonstrated a good dose–response relationship with water copper levels, juvenile Nile tilapia Oreochromis niloticus, of both sexes and similar mass (36·3 + 7·7 g), were kept in dechlorinated tap water (temperature 25° C, range ±1° C; pH 6·5–7·5; hardness 74·5 mg l^?1 CaCO₃) and exposed to 40 and 400 μg l^?1 of copper. Gill samples were collected after 3, 7, 14 and 21 days. Six major histopathological changes (oedema, lifting, changes in filament epithelium thickness, lamellar fusion, vasodilatation and aneurisms) and three minor ones (proliferation of the lamellar epithelium, necrosis and adjacent lamellar fusion) were found and their prevalence estimated. The extent and severity of each histopathological change were used to develop a severity gradation scale (SGS). Semi‐quantitative analysis of the histopathological changes and measurements of gill copper deposition levels revealed a good dose– and time–response relationship. Oedemas and aneurisms were significantly correlated with acute exposure periods and lamellar fusion with chronic exposure. Epithelial lifting and changes in filament epithelial thickness were seen at lower and higher metal concentrations, respectively. The data also revealed that the SGS profile of each lesion was dependent of gill copper burden.     

Truncated PrP(c) in mammalian brain: interspecies variation and location in membrane rafts

A key molecular event in prion diseases is the conversion of cellular prion protein (PrP(c)) into an abnormal misfolded conformer (PrP(sc)). The PrP(c) N-terminal domain plays a central role in PrP(c) functions and in prion propagation. Because mammalian PrP(c) is found as a full-length and N-terminally truncated form, we examined the presence and amount of PrP(c) C-terminal fragment in the brain of different species. We found important variations between primates and rodents. In addition, our data show that the PrP(c) fragment is present in detergent-resistant raft domains, a membrane domain of critical importance for PrP(c) functions and its conversion into PrP(sc).     

A Spatio-temporal Model of African Animal Trypanosomosis Risk

Background

African animal trypanosomosis (AAT) is a major constraint to sustainable development of cattle farming in sub-Saharan Africa. The habitat of the tsetse fly vector is increasingly fragmented owing to demographic pressure and shifts in climate, which leads to heterogeneous risk of cyclical transmission both in space and time. In Burkina Faso and Ghana, the most important vectors are riverine species, namely Glossina palpalis gambiensis and G. tachinoides, which are more resilient to human-induced changes than the savannah and forest species. Although many authors studied the distribution of AAT risk both in space and time, spatio-temporal models allowing predictions of it are lacking.

Methodology/Principal Findings

We used datasets generated by various projects, including two baseline surveys conducted in Burkina Faso and Ghana within PATTEC (Pan African Tsetse and Trypanosomosis Eradication Campaign) national initiatives. We computed the entomological inoculation rate (EIR) or tsetse challenge using a range of environmental data. The tsetse apparent density and their infection rate were separately estimated and subsequently combined to derive the EIR using a “one layer-one model” approach. The estimated EIR was then projected into suitable habitat. This risk index was finally validated against data on bovine trypanosomosis. It allowed a good prediction of the parasitological status (r² = 67%), showed a positive correlation but less predictive power with serological status (r² = 22%) aggregated at the village level but was not related to the illness status (r² = 2%).

Conclusions/Significance

The presented spatio-temporal model provides a fine-scale picture of the dynamics of AAT risk in sub-humid areas of West Africa. The estimated EIR was high in the proximity of rivers during the dry season and more widespread during the rainy season. The present analysis is a first step in a broader framework for an efficient risk management of climate-sensitive vector-borne diseases.     

Copper induced alterations of biochemical parameters in the gill and plasma of Oreochromis niloticus

The main objective of this study was to determine the effects of copper exposure on copper accumulated in branchial tissue, gill Na+/K+-ATPase activity and plasma Na+, Cl-, osmolality, protein, glucose and cortisol, in Oreochromis niloticus. Fish were experimentally exposed to 40 and 400 microg L(-1) of waterborne copper and sacrified after 0, 3, 7, 14 and 21 days. Copper accumulation and Na+/K+-ATPase activity were determined in branchial tissue, whereas osmolality, Na+, Cl-, protein, glucose and cortisol concentrations were measured in plasma samples. Gill copper accumulation increased linearly with exposure time and concentration, whereas gill Na+/K+-ATPase activity was maximally inhibited after 3 days of exposure and showed a significant negative correlation with copper tissue levels. Plasma Cl- values decreased with time of exposure but only at 400 microg L(-1) of copper. Plasma Na+, protein and osmolality decreased with exposure time at the highest copper concentration tested, whereas at 40 microg L(-1) of copper this effect was only observed after 21 days of exposure. Plasma glucose and cortisol levels increased in a dose and time dependent manner, while showing complex fluctuations during the intermediate exposure times. In conclusion, copper induces an early maximum inhibition of gill Na+/K+-ATPase activity in O. niloticus. The subsequent slow decrease in ion plasma levels was related to compensatory mechanisms involving a non-specific stress response that appeared overcome at long-term exposures.     

Temperature and gender influences on the hepatic stroma (and associated pancreatic acini) of Nile tilapia, Oreochromis niloticus (Teleostei, Cichlidae): a stereological analysis by light microscopy

The normal organ morphology and function in fishes varies according to several natural factors, and such variability is found in liver. Knowledge about the normal liver microanatomy is fundamental to pathological evaluation. Even though gender and temperature are important factors for modulating morphophysiological processes in fishes, their influences on liver stroma are virtually unknown. Because temperature- and gender-related changes exist in liver parenchyma, we predict both factors should also influence the normal stromal structure. Using Nile tilapia as a model, we undertook a study to: 1) establish baseline quantitative structural data on the hepatic stroma (and intimately associated pancreatic acini); 2) compare data with those available from other species, namely, salmonids that do not have a liver with pancreatic acini; and 3) test our hypothesis that, within normal healthy limits, the stroma and its structural components may vary significantly with temperature and gender. We used 1-year-old male and female specimens acclimated to 17 degrees C (breeding noncompatible) and 27 degrees C (breeding compatible) for 45 days. Basic morphometric fish parameters were recorded. After estimation of liver volume, the organ was sliced and pieces systematically sampled for light microscopy. Stereology allowed estimation of the relative volumes of organ components. The total volumes were computed by combining the relative volumes with the total liver volumes. Nile tilapia of both genders, held at 17 vs. 27 degrees C, showed structural quantitative differences in the relative volumes of stroma and most of its components, and in the total volumes of certain stromal elements. The total volume of the stroma and of associated pancreatic acini did not differ. We first established that, in fishes, the total amount (volume) of liver biliary ducts and of eosinophilic granule cells might significantly change (increase and decrease, respectively) with a higher acclimation temperature. Indeed, virtually all the stereological changes were, essentially, temperature- and not gender-related. At 27 degrees C, parallel changes in the parenchyma caused a decreased liver volume and hepatic-somatic index (HSI). The relative volumetric proportion of stroma vs. parenchyma in tilapia is higher than in salmonids. The differences found in this study could not be detected with a qualitative approach, thus stressing the importance of using stereology for analyzing histological patterns and for establishing reliable baseline values in healthy conditions. It was also anticipated that in experimental settings with fish the baseline liver stromal architecture may be different according to temperature and breeding status; in consequence, the effects of the tested variable may also diverge. Our data do not fully explain the lower liver volume and HSI at 27 degrees C, thus justifying studies on the parenchyma, particularly on cell size and number.