Distribution of glucocorticoid receptors in the brain of rainbow trout (Oncorhynchus mykiss): possible relationships with the neuroendocrine systems controlling reproduction

Abstract

The distribution of the glucocorticoid receptor (GR) within the forebrain of rainbow trout has been studied by means of in situ hybridization (ISH) and immunohistochemistry (ICC) using probes and antibodies directed against the AB-domain of the rainbow trout GR (rtGR).Both rtGR mRNA and protein exhibited the same pattern of distribution. A strong labelling was observed in ail subdivisions of the preoptic nucleus, in the thalamic région and in the mediobasal hypothalamus (nucleus recessus lateralis, nucleus lateralis tuberis). It was notably found that ail magnocellular neurons of the nucleus preopticus pars magnocellularis (NPOmc) were positive with both ISH and ICC. Furthermore, numerous cells of the anterior lobe of the pituitary were positively stained. Double staining studies allowed to identify part of the rtGR expressing cells. At the telencephalic level, it was found that GnRH neurons frequently express rtGR in vitellogenic females. Virtually ail tyrosine hydroxylase (TH) cells in the anteroventral part of the preoptic nucleus (NPOav) were rtGR-positive. In this same area, a colocalization between rainbow trout estradiol receptor (rtER) and TH has already been documented, indirectly demonstrating that rtER and rtGR are colocalized. The same holds true for the GTH-II cells of the anterior pituitary which express both types of receptors.Thèse results provide information on the potential sites of cortisol action on the reproductive axis directly at the pituitary level or indirectly on neuroendocrine Systems controlling GTH-II sécrétion, possibly via GR-ER interactions. DISTRIBUTION DES RÉCEPTEURS AUX GLUCOCORTICOÏDES DANS LE CERVEAU DE LA TRUITE ARC-EN-CIEL (ONCORHYNCHUS MYKISS) : RELATIONS POSSIBLES AVEC LES SYSTÈMES NEUROENDOCRINIENSCONTRÔLANT LA REPRODUCTION. RÉSUMÉLa distribution du récepteur aux glucocorticoïdes (GR) dans le cerveau de la truite arc-en-ciel a été étudiée par les techniques d'hybridation in situ (HIS) et d'immunocytochimie (ICC) utilisant des sondes et des anticorps dirigés contre le domaine AB du GR de truite (rtGR).Les sites d'expression de l'ARNm et de la protéine rtGR sont très similaires. Les deux méthodes ont permis de mettre en évidence un marquage au niveau des différentes sousdivisions du noyau préoptique (NPO), en particulier au niveau des neurones Article available at

ACTH does not mediate divergent stress responsiveness in rainbow trout

“…It is likely that DEX mimics the negative feedback effects of cortisol on the secretion of ACTH and/or corticotropin releasing hormone (CRH) by interacting with specific corticosteroid receptors in the brain, hypothalamus and/or pituitary (Allison and Omeljaniuk, 1998;Teitsma et al, 1998). In the present study the administration of DEX was successful in preventing the substantial stress-induced elevation of plasma cortisol levels which would be expected to occur consequent to handling and injection of PBS.…”