Amaury de Luze

Fish growth hormone enhances peripheral conversion of thyroxine to triiodothyronine in the eel (Anguilla anguilla L.).

In the eel, a low dose of tilapia growth hormone (tGH) (45 ng/g body wt), like ovine GH (oGH), induces a decrease in plasma thyroxine and a concomitant increase in plasma triiodothyronine, which result from a stimulation of peripheral conversion of thyroxine to triiodothyronine. Salmon prolactin (sPrl), unlike ovine Prl (oPrl), has no such action. Recognition of this specific action of growth hormone (GH) on production of active thyroid hormone (T3) opens up a new approach to the problem of the action of both hormones (GH, T3) in growth and in seawater adaptation of fish.

Localization of microcystin-LR in medaka fish tissues after cyanotoxin gavage.

Microcystins (MCs) are toxic monocyclic heptapeptides produced by many cyanobacteria. Over 70 MCs have been successfully isolated and identified, of which MC-LR is the most commonly occurring toxin. Microcystins, especially MC-LR, cause toxic effects in mammals, birds and fish and are a recognized potent cause of environmental stress and pose a potential health hazard in aquatic ecosystems when heavy blooms of cyanobacteria appear. They also constitute a public health threat to people via drinking water and food chains. The concentrations of MC-LR can be very low, even in fish displaying severely disrupted tissues, which makes it essential to devise selective and sensitive histochemical methods for identifying and localizing MC-LR in target organs, such as liver and intestine. The aim of the study reported here was to analyze the presence of MC-LR in contaminated fish tissues using immunohistochemical methods. The present experiment involving subacute exposure confirmed our initial hypothesis that subacute and acute exposure to microcystin contamination can exacerbate physiological stress, induce sustained pathological damage, and affect the immune response in exposed medaka fish.

Effet de l'oestradiol sur l'axe hypophyso-thyroïdien de l'anguille

Abstract The effect of estradiol (E2) treatment on the hypophyso-thyroidal axis has been investigated in male and female eels in fresh water. The animals were injected with 150 μg/100 g body wt daily or every other day for 5 to 78 days; another group was treated for 40 days and sacrificed 40 days after the last injection. In the pituitary, the thyrotrophs (TSH cells) are activated and degranulated in long-term-treated eels. The histological structure of the thyroid follicles suggests a hypoactivity as shown by a reduced epithelial cell height in male and female eels injected with E2. Using radioimmunoassay of thyroxine (T 4 ) and triiodothyronine (T 3 ) in the plasma, a sharp decrease of both hormones is demonstrated which is highly significant. The ratio T 3 T 4 increases gradually. In animals sacrificed 40 days after the last injection, the thyroid function is still depressed although less than in eels sacrificed at the end of the treatment. These data suggest that thyroid hormone release is depressed by E2 although TSH release seems to be increased. The very important hypercalcemia induced by E2 could explain this paradoxical finding. The increased T 3 T 4 ratio could result from stimulation of prolactin releaseby E2.

Effects of vertebrate prolactins and growth hormones on thyroxine 5′-monodeiodination in the eel (Anguilla anguilla): A potential bioassay for growth hormone

Growth hormones (GHs) and prolactins (Prls) purified from representatives of each vertebrate class from bony fish onwards were tested for their ability to stimulate in vivo peripheral deiodination of labeled thyroxine (T4*) into triiodo-L-thyronine (T3*) in the eel. Plasma T3*/T4* ratio was used as parameter. All GHs significantly increased T3*/T4*, the magnitude of the response being unrelated to the phylogenic position of species. No significant stimulation was shown with the various Prl, with the exception of ovine Prl, suggesting a heterosomatotropic effect of this preparation in the eel. Furthermore, both tilapia and ovine GH produced a dose-related effect on plasma T3*, T4*, and T3*/T4*. The stimulation of the peripheral deiodination of T4* into T3* estimated in vivo in the eel could become a specific, sensitive, and rapid fish bioassay for GH.

MYCOBACTERIUM SZULGAI INFECTION IN A CAPTIVE POPULATION OF AFRICAN CLAWED FROGS (XENOPUS TROPICALIS)

Abstract A colony of captive Xenopus tropicalis became infected with Mycobacterium szulgai. Clinical signs, when observed, were lethargy, weight loss, and emaciation. Visceral granulomas were common findings at laparoscopy and necropsy. The diagnosis of mycobacteriosis was based on histologic appearance and Ziehl-Neelsen staining of tissues. The identification of M. szulgai organisms was based on comparison of the 16S rRNA gene sequence with several GenBank databases. There have been no reports of this mycobacterial species as the causative agent of naturally occurring disease in amphibians.

TAIL REGRESSION, APOPTOSIS AND THYROID HORMONE REGULATION OF MYOSIN HEAVY CHAIN ISOFORMS IN XENOPUS TADPOLES

T3 effects on myosin heavy chain gene expression were analysed in muscles undergoing different fates during metamorphosis. Muscle fate was followed by somatic gene transfer of a constitutively expressed luciferase vector. Persistent expression was found in dorsal muscle which is remodelled during metamorphosis whilst the signal disappeared in apoptosing caudal muscle. RNAse protection assay was used to follow production of myosin heavy chain isoforms: two isoforms identified as embryonic (E3 and E19) and one adult form (A7). The effects of T3 treatment were followed over 120 h. During this time frame E3 and A7 expression patterns were found to be similar in both caudal and dorsal muscles. Most notably, at 48 h E3 expression was significantly down-regulated and production of A7 significantly upregulated in both caudal and dorsal muscle. Thus T3-induced transitions in muscle gene expression are independent of muscle fate during amphibian metamorphosis.

Propagation Method of Saving Valuable Strains from a Mycobacterium liflandii Infection in Western Clawed Frogs (Silurana tropicalis)

Abstract:  Mycobacterium liflandii has been responsible for an emerging infection reported in the international trade of Western clawed frogs (Silurana tropicalis). This study shows that this mycolactone-producing Mycobacterium (MPM) has expanded its distribution range to France. The results of this study suggest that the use of in vitro fertilization to maintain genetic lines could be a temporary solution for valuable S. tropicalis propagation.