Migrating action potential complex: unmasked by 6-hydroxydopamine.

We have previously described the myoelectric characteristics of a single moving ring contraction, the migrating action potential complex (MAPC), in rabbit ileal loops exposed to certain bacteria or their enterotoxins. The MAPC is thought to act as a defense mechanism of the host, clearing unwanted substances from the lumen. In the present study, 6-hydroxydopamine, a substance that selectively destroys adrenergic varicosities containing the neurotransmitter norepinephrine, unmasked the MAPC from the activity front of the migrating motor complex in an unanesthetized rat model. The animals developed diarrhea and lost weight. The study suggests that the MAPC may also be a physiological complex and under the modulation of the enteric nervous system. The MAPC may not be seen under normal control conditions because the complex migrates with the activity front and is under inhibitory control. Destroying the inhibitory mechanisms unmasked the MAPC from the activity front of the migrating motor complex and allowed neural transmission of the ring contraction.