Modifications des cellules corticotropes de l'hypophyse chez l'anguille radiothyroïdectomisée

Résumé Chez les Anguilles dont la destruction totale ou sub-totale de la glande thyroïde a été réalisée avec des injections répétées de fortes doses d'iode radioactif ¹³¹I, l'interrénal présente un aspect histologique indiquant un hypofonctionnement traduit par une atrophie cellulaire et nucléaire. De même, après 2 à 8 mois d'expérience, les cellules corticotropes de l'hypophyse sont plus petites, moins granulées à l'apex qui devient finement vacuolisé, le diamètre nucléaire est significativement réduit. La réponse de l'interrénal à la thyroïdectomie est donc contrôlée en partie par l'hypophyse. Comme l'apport de thyroxine stimule l'axe hypophyso-corticosurrénalien de l'Anguille, et la réduction ou la disparition des hormones thyroïdiennes le déprime, il semble exister chez ce Téléostéen une synergie entre les activités de la thyroïde et de l'interrénal ayant l'hypophyse comme intermédiaire.

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Modifications of the Corticotrophic Cells of the hypophysis of the radiothyroidectomized eel

Summary Eels were completely or sub-totally radiothyroidectomized with repeated injections of high doses of radioiodine ¹³¹I. After 2 to 8 months, the histological picture of the interrenal suggests a hypoactivity, indicated by a nuclear and nucleolar atrophy. Simultaneously, in the pituitary gland, the corticotrophic cells are smaller, less granulated with a finely vacuolated apical cytoplasm. The diameter of their nuclei is significantly reduced. It then appears that the adrenal response to thyroidectomy is, at least partly, mediated by the pituitary gland. As thyroxine treatment induces a stimulation of the hypophyso-adrenocortical system in the eel, and a decrease or disappearance of thyroidal hormones exerts a depressing effect, it seems that there is a synergy between the activity of the thyroid gland and the interrenal in this species, the hypophysis playing a role of mediator in these responses.

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Ce travail a été réalisé avec la collaboration technique de Mademoiselle Jacqueline Olivereau, du CNRS, que nous remercions bien vivement.     

Pattern and pace of morphological change due to variable human impact: the case of Japanese macaques

Primates - Human impact influences morphological variation in animals, as documented in many captive and domestic animal populations. However, there are different levels of human impact, and their...     

Assessing the contribution of bacteria to the heat tolerance of experimentally evolved coral photosymbionts

Coral reefs are extremely vulnerable to ocean warming, which triggers coral bleaching—the loss of endosymbiotic microalgae (Symbiodiniaceae) from coral tissues, often leading to death. To enhance coral climate resilience, the symbiont, Cladocopium proliferum was experimentally evolved for >10 years under elevated temperatures resulting in increased heat tolerance. Bacterial 16S rRNA gene metabarcoding showed the composition of intra- and extracellular bacterial communities of heat-evolved strains was significantly different from that of wild-type strains, suggesting bacteria responded to elevated temperatures, and may even play a role in C. proliferum thermal tolerance. To assess whether microbiome transplantation could enhance heat tolerance of the sensitive wild-type C. proliferum, we transplanted bacterial communities from heat-evolved to the wild-type strain and subjected it to acute heat stress. Microbiome transplantation resulted in the incorporation of only 30 low-abundance strains into the microbiome of wild-type cultures, while the relative abundance of 14 pre-existing strains doubled in inoculated versus uninoculated samples. Inoculation with either wild-type or heat-evolved bacterial communities boosted C. proliferum growth, although no difference in heat tolerance was observed between the two inoculation treatments. This study provides evidence that Symbiodiniaceae-associated bacterial communities respond to heat selection and may contribute to coral adaptation to climate change.