Fig. 10: Intrinsic neural circuit identified that underlies propagating and non-propagating neurogenic contractions along the colon.

The central core of this enteric neural circuit is that ascending and descending interneurons synapse extensively with each other, such that when ascending or descending interneurons are activated this correspondingly activates descending or ascending interneurons, respectively. The major discovery is that long way downstream of any propagating contraction, there is repetitive activation of inhibitory and excitatory motor neurons at the same time. Aborally migrating contraction is temporally delayed downstream because activation of descending inhibitory motor neurons suppress EJPs from reaching action potential threshold by concurrently activated excitatory motor neurons. A major advance is that during the oral contraction in the proximal region, there is concurrent activation of excitatory and inhibitory motor neurons. The same circuit is found to occur in non-propagating contractions, see Supplementary Figs. 4&5 and Supplementary Movie 6.