Tryptamine evoked ΔIsc is blocked by 5-HT4R antagonist irrespective of sex and microbial colonization. ΔIsc in response to tryptamine applied apically (3mM, paired t-test) and cumulative concentrations of tryptamine applied basolaterally (two-way ANOVA) respectively either alone or in the presence of 5-HT4R antagonist, GR-113808 (30nM) in GF male (A, B) and GF female mice (C, D). ΔIsc in response to tryptamine applied apically (3mM, paired t-test) and cumulative concentrations of tryptamine applied basolaterally (two-way ANOVA) respectively either alone or in the presence of 5-HT4R antagonist, GR-113808 (30nM) in HM male (E, F) and HM female mice (G, H). ΔIsc in response to tryptamine applied apically (3mM, paired t-test) and cumulative concentrations of tryptamine applied basolaterally (two-way ANOVA) respectively either alone or in the presence of 5-HT4R antagonist, GR-113808 (30nM) in CR male (I, J) and CR female mice (K, L). n=5–6, *P < 0.05.