Figure 4. EcN modulates 5-HT bioavailabiliy through interaction with secreted host derived factors.

The effect of secreted EcN or host derived factors on 5-HT overflow was determined by measuring 5-HT release after treatment of tissues with various culture or co-culture supernatants (at 37 °C with 5% CO₂ for 1 h). Extracellular 5-HT was measured by amperometry as for Fig. 1. Data are means ± S.E.M. (n = 4), and measurements normalized to the surface area of tissue sections. KB - Krebs buffer only; +I-SNT – Tissue sections exposed to supernatant derived from untreated ileal tissue (incubated in Krebs buffer only); +EcN-SNT – Tissue exposed to supernatants derived from E. coli Nissle 1917 cultures grown in Krebs buffer; +I-EcN- SNT – Tissue exposed to supernatants from untreated ileal tissue incubated with EcN cell suspensions. **p ≤ 0.01 vs KB, ^†p ≤ 0.05 vs I-SNT, ^###p ≤ 0.001 vs EcN-SNT.