Figure 3. Propagation of pellets of different diameters.

A, propagation of an artificial thin (diameter, 1.5 mm; length, 5 mm) pellet, which did not noticeably distend the bowel, along the Tph1^+/+ colon. Dotted ellipses show the location of the pellet along the colon, pictured at either end of the spatiotemporal map. Note that the thin pellet propagated at a velocity of 0.6 mm s⁻¹ (white box). B, propagation (velocity, 0.82 mm s⁻¹) of a thin pellet along the Tph1^+/+ colon was blocked on reaching a 10 mm zone of colon from which the mucosa had been removed (dotted lines across spatiotemporal map). Filled rectangle (expanded above) shows spatiotemporal map of faecal pellet propagation. C, a larger (diameter, 2.5 mm; length, 5 mm) faecal pellet, which distended the bowel, also propagated (velocity, 0.5 mm s⁻¹) down the Tph1^+/+ colon. However, when this faecal pellet entered the zone from which the mucosa had been removed, it stopped, but continued on its way after 40 min, but at a reduced velocity (0.22 mm s⁻¹). Black rectangles show faecal pellet propagation. D, plot of velocity of pellet propagation versus the diameter of a faecal pellet, as well as the percentage increase in the resting diameter generated by a faecal pellet, in Tph1^+/+ and Tph1^−/− mice (average of three to five passes of each pellet, n= 5). Vertical dotted lines show the average diameter of a faecal pellet in Tph1^+/+ (1.7 mm) and Tph1^−/− (2.8 mm) colon. ***P < 0.001