The studies described in this thesis were designed to address the hypothesis that stress and glucocorticoids modify the levels of corticotropin-releasing factor (CRF) and neuropeptide Y (NPY) mRNA in the rainbow trout ( Oncorhynchus mykiss) brain. Standard cloning techniques provided the full-length cDNA sequences coding for trout NPY and two CRF paralogues. Using a ribonuclease protection assay (RPA), a tissue distribution demonstrated that both CRF paralogues are primarily abundant in the preoptic area of the trout brain, whereas NPY mRNA is more abundant in the telencephalon.
The effects of social stress on CRF1 and NPY mRNA levels were examined with pairs of sized-matched juvenile female trout. After 72 h of interaction, CRF1 and NPY mRNA levels were respectively 51% and 32% higher in the preoptic area of subordinate trout. These results suggest that CRF and NPY may be involved in the control of the stress axis in trout. However, my experiments could not distinguish between the effects of stress and food deprivation.
The levels of plasma cortisol in isolated trout indicated that confinement in small boxes was more stressful than isolation in a large tank. The elevation in CRF1 mRNA levels was greater and more persistent in confined fish. CRF1 mRNA levels were also elevated in trout physically disturbed to exhaustion but only after repeated chasing events. Together, these results suggest that the duration and intensity of stress are important factors determining the magnitude and persistence of the elevation in CRF mRNA levels.
The effects of glucocorticoids on CRF and NPY mRNA levels were examined by exposing trout to cortisol, a glucocorticoid receptor antagonist (RU-486) or a cytochrome P450 inhibitor that blocks cortisol synthesis (metyrapone). My results suggest that glucocorticoids modify CRF1 and NPY mRNA levels but only part of the results support the presence of a glucocorticoid-induced negative feedback loop. Further studies are required to clarify the role of glucocorticoids in the regulation of the stress axis activity in fish.
| Identifer | oai:union.ndltd.org:uottawa.ca/oai:ruor.uottawa.ca:10393/29014 |
| Date | January 2003 |
| Creators | Doyon, Christian |
| Contributors | Moon, Thomas W.,, Trudeau, Vance L., |
| Publisher | University of Ottawa (Canada) |
| Source Sets | Université d’Ottawa |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | 176 p. |
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