Fig. 2. Responses to 5-hydroxytryptamine (5-HT, serotonin) in stomach muscle. (A) Concentration-dependent effect on mean force in response to 5-HT. A statistically significant decrease was obtained at 0.01 µmol l^–1 in prometamorphosis (N=10) and at 10 µmol l^–1 in juveniles (N=8). There was no effect during metamorphosis (N=7). For concentration–response curves, statistical analysis was performed using repeated measures one-way ANOVA followed by Dunnett's post hoc test. (B) Representative trace of the response to an excitatory concentration of 5-HT (1 µmol l^–1) in juveniles. (C) Representative trace of the response to an inhibitory concentration of 5-HT (1 µmol l^–1) in juveniles. (D) Relaxing effect of 5-HT (1 µmol l^–1) in the presence and absence of the 5-HT receptor antagonist methysergide (Meth., 10 µmol l^–1) in prometamorphic (N=4) and juvenile (N=5) stomach muscle strips. (E) Contracting effect of 5-HT (0.1–1 µmol l^–1) in the presence and absence of the 5-HT receptor antagonist methysergide (10 µmol l^–1) in juvenile (N=12) stomach muscle strips. Statistical analysis was performed using repeated measures one-way ANOVA followed by Bonferroni's post hoc test. Asterisk indicates a statistically significant difference, P<0.05.