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Network properties of interstitial cells of Cajal affect intestinal pacemaker activity and motor patterns, according to a mathematical model of weakly coupled oscillators

Wei R, Parsons SP, Huizinga JD

Exp Physiol. 2016 Dec 30. doi: 10.1113/EP086077.

PMID:28036151

Abstract

What is the central question of this study? What are the effects of interstitial cells of Cajal (ICC) network perturbations on intestinal pacemaker activity and motor patterns? What is the main finding and its importance? Two-dimensional modelling of the ICC pacemaker activity according to a phase model of weakly coupled oscillators showed that network properties (coupling strength between oscillators, frequency gradient and frequency noise) strongly influence pacemaker network activity and subsequent motor patterns. figure-6The model explains motor patterns observed in physiological conditions and provides predictions and testable hypotheses for effects of ICC loss and frequency modulation on the motor patterns. Interstitial cells of Cajal (ICC) are the pacemaker cells of gut motility and are associated with motility disorders. Interstitial cells of Cajal form a network, but the contributions of its network properties to gut physiology and dysfunction are poorly understood. We modelled an ICC network as a two-dimensional network of weakly coupled oscillators with a frequency gradient and showed changes over time in video and graphical formats. Model parameters were obtained from slow-wave-driven contraction patterns in the mouse intestine and pacemaker slow-wave activities from the cat intestine. Marked changes in propagating oscillation patterns (including changes from propagation to non-propagating) were observed by changing network parameters (coupling strength between oscillators, the frequency gradient and frequency noise), which affected synchronization, propagation velocity and occurrence of dislocations (termination of an oscillation). Complete uncoupling of a circumferential ring of oscillators caused the proximal and distal section to desynchronize, but complete synchronization was maintained with only a single oscillator connecting the sections with high enough coupling. The network of oscillators could withstand loss; even with 40% of oscillators lost randomly within the network, significant synchronization and anterograde propagation remained. A local increase in pacemaker frequency diminished anterograde propagation; the effects were strongly dependent on location, frequency gradient and coupling strength. In summary, the model puts forth the hypothesis that fundamental changes in oscillation patterns (ICC slow-wave activity or circular muscle contractions) can occur through physiological modulation of network properties. Strong evidence is provided to accept the ICC network as a system of coupled oscillators.

Ruihan Wei, a high school student working in Jan Huizinga’s lab with Jan and Sean Parsons, won the best biology prize and the best mathematics prize at the 2016 Bay Area Science Fair. This work was then submitted to Experimental Physiology and just got accepted with Ruihan as first author, since he did all the work shown in the paper and contributed to original ideas pursued.

The study shows that the intestinal pacemaker system does not work like an axon where action potentials propagate from one end to the other but it works as a system of oscillators that synchronize. Ruihan showed that his two dimensional model could show how pacemakers interact and how they propagate. With 13 video’s he explained how the system works and showed that published explanation are wrong. He also showed how changes in network properties can switch the intestine from peristalsis to segmentation, opening up new treatment options.

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