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).