title: Hypoxemia-induced leptin secretion: a mechanism for the control of food intake in diseased fish.
abstract: Leptin is a potent anorexigen, but little is known about the physiological conditions under which this cytokine regulates food intake in fish. In this study, we characterized the relationships between food intake, O2-carrying capacity, liver leptin-A1 (lep-a1) gene expression, and plasma leptin-A1 in rainbow trout infected with a pathogenic hemoflagellate, Cryptobia salmositica. As lep gene expression is hypoxia-sensitive and Cryptobia-infected fish are anemic, we hypothesized that Cryptobia-induced anorexia is mediated by leptin. A 14-week time course experiment revealed that Cryptobia-infected fish experience a transient 75% reduction in food intake, a sharp initial drop in hematocrit and hemoglobin levels followed by a partial recovery, a transient 17-fold increase in lep-a1 gene expression, and a sustained increase in plasma leptin-A1 levels. In the hypothalamus, peak anorexia was associated with decreases in mRNA levels of neuropeptide Y (npy) and cocaine- and amphetamine-regulated transcript (cart), and increases in agouti-related protein (agrp) and pro-opiomelanocortin A2 (pomc). In contrast, in non-infected fish pair-fed to infected animals, lep-a1 gene expression and plasma levels did not differ from those of non-infected satiated fish. Pair-fed fish were also characterized by increases in hypothalamic npy and agrp, no changes in pomc-a2, and a reduction in cart mRNA expression. Finally, peak infection was characterized by a significant positive correlation between O2-carrying capacity and food intake. These findings show that hypoxemia, and not feed restriction, stimulates leptin-A1 secretion in Cryptobia-infected rainbow trout and suggest that leptin contributes to anorexia by inhibiting hypothalamic npy and stimulating pomc-a2.
authors.affiliation: Department of Integrative BiologyUniversity of Guelph, 50 Stone Road East, Guelph, Ontario, Canada N1G 2W1.
authors.forename: Lauren E
authors.initials: LE
authors.lastname: MacDonald
authors.affiliation: Department of Integrative BiologyUniversity of Guelph, 50 Stone Road East, Guelph, Ontario, Canada N1G 2W1.
authors.forename: Sarah L
authors.initials: SL
authors.lastname: Alderman
authors.affiliation: Department of Integrative BiologyUniversity of Guelph, 50 Stone Road East, Guelph, Ontario, Canada N1G 2W1.
authors.forename: Sarah
authors.initials: S
authors.lastname: Kramer
authors.affiliation: Department of Integrative BiologyUniversity of Guelph, 50 Stone Road East, Guelph, Ontario, Canada N1G 2W1.
authors.forename: Patrick T K
authors.initials: PT
authors.lastname: Woo
authors.affiliation: Department of Integrative BiologyUniversity of Guelph, 50 Stone Road East, Guelph, Ontario, Canada N1G 2W1 nbernier@uoguelph.ca.
authors.forename: Nicholas J
authors.initials: NJ
authors.lastname: Bernier
mesh_terms: D054369:Agouti-Related Protein / Q000235:genetics / Q000378:metabolism; D000818:Animals; D004435:Eating / Q000235:genetics / Q000502:physiology*; D005260:Female; D005393:Fish Diseases / Q000235:genetics / Q000378:metabolism / Q000469:parasitology; D029941:Fish Proteins / Q000097:blood / Q000235:genetics / Q000378:metabolism*; D015870:Gene Expression; D006400:Hematocrit; D006454:Hemoglobins / Q000378:metabolism; D006790:Host-Parasite Interactions; D007031:Hypothalamus / Q000378:metabolism; D000860:Hypoxia / Q000503:physiopathology*; D016830:Kinetoplastida / Q000502:physiology; D020738:Leptin / Q000097:blood / Q000235:genetics / Q000378:metabolism*; D008099:Liver / Q000378:metabolism; D008297:Male; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism; D009478:Neuropeptide Y / Q000235:genetics / Q000378:metabolism; D017686:Oncorhynchus mykiss / Q000235:genetics / Q000378:metabolism* / Q000469:parasitology; D011333:Pro-Opiomelanocortin / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D011863:Radioimmunoassay; D000098882:Cocaine- and Amphetamine-Regulated Transcript Protein
chemical_list: D054369:Agouti-Related Protein; D029941:Fish Proteins; D006454:Hemoglobins; D020738:Leptin; D009419:Nerve Tissue Proteins; D009478:Neuropeptide Y; D012333:RNA, Messenger; D000098882:Cocaine- and Amphetamine-Regulated Transcript Protein; D011333:Pro-Opiomelanocortin
keywords: anemia; appetite; fish disease; leptin; parasites