BERNIER, N.J.*; CRAIG, P.M.; Univ. of Guelph, Guelph, ON, Canada: Central mechanisms regulating food intake in hypoxic rainbow trout: evidence for a role of CRF-related peptides

Hypoxia inhibits growth in a variety of fish species primarily via a reduction in food intake. While the appetite-suppressing effects of hypoxia are well recognized, the mechanisms mediating this response are not known. Among the signals that suppress food intake in fish are the two related neuropeptides corticotropin-releasing factor (CRF) and urotensin I (UI; Neuroendocrinol. 73:248-260, 2001). Thus, to determine whether CRF and UI maybe involved in mediating the appetite-suppressing effects of hypoxia, we examined the effects of hypoxia on food intake and on the gene expression pattern of CRF and UI in the brain of rainbow trout. Exposure to 50 and 35% O₂ saturation for 24h significantly decreased food intake by 28 and 48%, respectively, and concomitantly elevated brain CRF and UI mRNA levels in the 35% O₂ saturation treatment. Similarly, increases in plasma cortisol and lactate were only observed in the 35% O₂ saturation treatment. In addition, relative to fish infused with saline only, chronic intra-cranial infusion of the CRF receptor antagonist alpha-helical CRF _(9-41) significantly reduced the appetite-suppressing effects elicited by 24h exposure to 35% O₂ saturation. Overall, our findings indicate that CRF-related peptides play a physiological role in mediating at least a portion of the appetite-suppressing effects of hypoxia in rainbow trout. Whether the CRF and UI neurons involved in the control of food intake are the same as those involved in the control of the hypothalamic-pituitary-interrenal axis, and whether CRF, UI, or a related CRF-like peptide plays a lead role in mediating the CRF-related peptide changes in feeding behaviour in response to a hypoxic stress remains to be determined.