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First published online May 5, 2005
Journal of Experimental Biology 208, 1855-1866 (2005)
Published by The Company of Biologists 2005
doi: 10.1242/jeb.01577

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Appetite-suppressing effects of ammonia exposure in rainbow trout associated with regional and temporal activation of brain monoaminergic and CRF systems

Van A. Ortega¹, Kenneth J. Renner² and Nicholas J. Bernier^1,*

¹ Department of Integrative Biology, University of Guelph, Guelph, ON, Canada, N1G 2W1
² Biology and Neuroscience, University of South Dakota, Vermillion, SD 57069, USA

View larger version (21K): [in a new window]   Fig. 1. Measured levels of total water (A) and plasma (B) [ammonia] in the 0 (N=10), 500 (N=10), 750 (N=10) and 1000 (N=10-12) µmol l-1 NH4Cl treatments after 24 or 96 h exposure periods. Values are means + 1 S.E.M. Treatments that do not share a common letter for a given time are significantly different from each other. *Significant differences between exposure periods for a given treatment (P<0.05).

View larger version (20K): [in a new window]   Fig. 2. Mean food intake (mg food g-1 body mass) of rainbow trout before and after exposure to 0 (N=10), 500 (N=10), 750 (N=10) or 1000 (N=10-12) µmol l-1 NH4Cl for either 24 (A) or 96 (B) h periods. Values are means + 1 S.E.M. Treatments that do not share a common letter for a given feeding time and exposure period are significantly different from each other. *Significant differences between the pre- and post-NH4Cl exposure values for a given treatment; significant differences between the 24 and 96 h post-NH4Cl exposure values for a given treatment (P<0.05).

View larger version (28K): [in a new window]   Fig. 3. Serotonergic activity in the hypothalamus (A), telencephalon (B), and posterior brain (C) regions of rainbow trout exposed to 0, 500, 750 or 1000 µmol l-1 NH4Cl for either 24 or 96 h periods. Serotonergic activity is expressed as a ratio of the metabolite 5-hydroxyindole acetic acid (5-HIAA) to serotonin (5-HT). Values are means + 1 S.E.M. Treatments that do not share a common letter for a given time and brain region are significantly different from each other. *Significant differences between exposure periods for a given treatment (P<0.05; N=8-11). (D) Relationship between plasma [ammonia] and hypothalamic serotonergic activity after 24 h NH4Cl exposure (r2=0.39, P<0.001).

View larger version (18K): [in a new window]   Fig. 4. Posterior brain dopaminergic activity (A) in rainbow trout exposed to 0, 500, 750 or 1000 µmol l-1 NH4Cl for either 24 or 96 h periods. Dopaminergic activity is expressed as a ratio of the metabolite 3, 4-dihydroxyphenylacetic acid (DOPAC) to dopamine (DA). Values are means + 1 S.E.M. Treatments that do not share a common letter for a given time are significantly different from each other (P<0.05; N=8-11). (B) Relationship between plasma [ammonia] and posterior brain dopaminergic activity after 24 hNH4Cl exposure (r2=0.45, P<0.001).

View larger version (27K): [in a new window]   Fig. 5. The ratio of corticotropin-releasing factor (CRF; A,B) or urotensin I (UI; C,D) mRNA levels to the housekeeping gene acidic ribosomal phosphoprotein P0 (ARP) mRNA levels in the hypothalamus (A,C) and telencephalon (B,D) of rainbow trout exposed to 0, 500, 750 or 1000 µmol l-1 NH4Cl for either 24 or 96 h periods. Values are means + 1 S.E.M. Treatments that do not share a common letter for a given time and brain region are significantly different from each other. *Significant differences between exposure periods for a given treatment (P<0.05; N=8-12).

View larger version (16K): [in a new window]   Fig. 6. (A) Plasma [cortisol] of rainbow trout exposed to 0, 500, 750 or 1000 µmol l-1 NH4Cl for either 24 or 96 h periods. Values are means + 1 S.E.M. Treatments that do not share a common letter for a given time are significantly different from each other. *Significant differences between exposure periods for a given treatment (P<0.05; N=20-23). (B) Relationship between plasma [ammonia] and plasma [cortisol] after 24 h NH4Cl exposure (r2=0.41, P<0.001). (C) Relationship between hypothalamic serotonergic activity and plasma [cortisol] after 24 h NH4Cl exposure (r2=0.25, P=0.002). Serotonergic activity is expressed as a ratio of the metabolite 5-hydroxyindole acetic acid (5-HIAA) to serotonin (5-HT).