Origin of high slow-wave frequency in the dog colon

Using intraparietal and intraluminal electrodes, duodenal and colonic electrical activities were simultaneously recorded in dogs under pentobarbital anaesthesia to study the temporal relationship between the slow-wave frequency of the colon and that of the proximal duodenum. The colonic electromyogram showed two distinct slow-wave frequencies, one in the range of 7-9 cycles/min, and the other in the range of 18-19 cycles/min. The latter was synchronized to that observed on the duodenum, and disappeared after removal of the entire duodenum and the proximal jejunum over 90 cm, from 8 to 98 cm from the pylorus. After transversally cutting the muscular layers of the duodenum at 8 cm from the pylorus, the high slow-wave frequency of the colon decreased to 16-16.5 cycles/min, similarly to that observed on the duodenum aborally to the section. When another section was performed 5 cm aborally to the first cutting level, the colonic slow-wave frequency was again synchronized to that of the duodenum observed aborally to the second section. Intraduodenal infusion of cold water decreased the amplitude of both the duodenal and the colonic slow-waves by 50% and the frequency by 30%. Since all these experimental procedures did not affect the colonic slow-wave frequency at 7-9 cycles/min, and no temporal relationship was found between duodenal and colonic spiking activities, it was concluded that (i) the colonic slow-wave frequency at 18-19 cycles/min, recorded from both the intraparietal and the intraluminal electrodes in dog, was an 'artefact' of duodenal activity acting as an electric dipole and (ii) that the only slow-wave frequency of 7-9 cycles/min was generated by the colon.