Thesis

Neuroendocrine regulation of food intake following acute stress in the Tilapia, Oreochromis Mossambicus

The general stress response principally results in the release of cortisol, with the overall effect of mobilizing metabolic energy and redirecting it towards homeostatic maintenance. Consequently, an important factor altered by stress is food intake. In several teleost species, a decrease in food intake following stress has been observed, though the neuroendocrine mechanism controlling the reduction in food intake during stress has yet to be determined. These studies were designed to investigate the effect of an acute stress on food intake and brain expression of corticotropin-releasing hormone (CRH), neuropeptide Y (NPY), ghrelin and ghrelin�s receptor and whether these effects are mediated by cortisol. Therefore, metyrapone, a cortisol synthesis inhibitor, was administered via feed in three doses of 10, 25, and 50 mg/kg body weight for 1 wk prior to a 30 min crowding and handling stress. Following the stressor, fish were allowed to feed for 1 h. Stress reduced food intake, while elevating mRNA levels of CRH, an appetite suppressor. Additionally, metyrapone treatment dose-dependently blocked the stress-induced reduction in food intake. While NPY and ghrelin levels were unchanged, an increase in ghrelin receptor activity suggests a function for ghrelin in regulating overall metabolism in response to stress. The elevation of CRH mRNA levels was also reversed with metyrapone treatment, suggesting cortisol and CRH play a role in mediating reduction of food intake during stress in tilapia.

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