Identification of a putative corticosteroid in Pacific Lamprey (Entosphenus tridentatus)

The mechanisms and interplay of multiple axes as well as the physiological components of the stress response have been studied in many vertebrate groups; however, the intricacies and chemical messengers involved in the stress response in lamprey have not been fully resolved. 11-Deoxycortisol is a functional corticosteroid in sea lamprey, but the identity of the functional corticosteroid used by other lamprey species and the evolution of the stress response in lamprey lineage remains unknown. Identification of the functional corticosteroid in a greater number of lamprey species will help elucidate the evolution of the stress response in lamprey. I have demonstrated that 11-deoxycortisol, a steroid precursor to cortisol, may be a functional corticosteroid in Pacific lamprey. The putative hormone was identified in Pacific lamprey plasma by employing an array of methods such as radioimmunoassay (RIA), high performance liquid chromatography (HPLC) and mass spectrometry analysis. I have demonstrated that plasma levels of 11-deoxycortisol significantly increased in Pacific lamprey 0.5 and 1 hr after stress exposure and that sea lamprey corticotropin releasing hormone (CRH) injections increased circulating levels of 11-deoxycortisol, suggesting that 11-deoxycortisol secretion is under control of the hypothalamic neuropeptide CRH. However, plasma 11-deoxycortisol concentrations did not increase in response to sea lamprey adrenocorticotropic hormone (ACTH) injections. The effect of artificially elevated 11-deoxycortisol on the expression of glucocorticoid receptor and progesterone receptor mRNA was examined in liver, gill, muscle, heart and testis using RT-qPCR. 11-Deoxycortisol was chronically elevated using coconut oil implants with two different doses of 11-deoxycortisol (0.5 and 1.0 µg per g of body weight). After 7 days of elevated plasma 11-deoxycortisol concentrations there was no significant difference in the expression of either receptor in the tissues examined. Overall, the results of this thesis demonstrate 11-deoxycortisol is a putative corticosteroid in Pacific lamprey; however, despite the evidence for hypothalamic control of 11-deoxycortisol release, the results do not conclusively support Pacific lamprey having a hypothalamic pituitary interrenal (HPI) axis.Science, Faculty ofZoology, Department ofGraduat