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1 Department of Physiology, University of Melbourne, Parkville, Victoria, Australia
2 Department of Internal Medicine, Sahlgrenska University Hospital, Goteburg, Sweden
* To whom correspondence should be addressed. E-mail: evan{at}evan-thomas.net.
The migrating motor complex (MMC) is a cyclic motor pattern with several phases enacted over the entire length of the small intestine. This motor pattern is initiated and coordinated by the enteric nervous system and modulated by extrinsic factors. Because in vitro preparations of the MMC do not exist, it has not been possible to determine the intrinsic nerve circuits that manage this motor pattern. We have used computer simulation to explore the possibility that the controlling circuit is the network of AH/Dogiel type II (AH) neurons. The basis of the model is that recurrent connections between AH neurons cause local circuits to enter a high firing rate state which provides the maximal motor drive observed in phase III of the MMC. This also drives adjacent segments of the network causing the slow migration. Delayed negative feedback within the circuit, provided by activity dependent synaptic depression, forces the network to return to rest after the passage of the phase III. The anal direction of propagation is a result of the slight anal bias observed in projections of AH neurons. The model relates properties of neurons to properties of the MMC cycle: phase III migration speed is governed by neuron excitability, MMC cycle length is governed by the rate of recovery of synaptic efficacy and phase III duration is governed by the duration of slow excitatory post synaptic potentials in AH neurons. In addition the model makes experimental predictions that can be tested using standard techniques.
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