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).