Propagation of individual spikes as “patches” of activation in isolated feline duodenum

Abstract

Asynchrony of spikes has made it difficult to study the spatial and temporal behavior of spikes in the gastrointestinal system. By simultaneously recording from a large number of closely spaced electrodes, we investigated the propagation of individual spikes. Recordings were performed from the serosal surface of the isolated feline duodenum at 240 sites simultaneously. Analysis of the tracings made it possible to reconstruct the propagation of individual spikes. Spikes propagate in the longitudinal and circumferential directions in self-limiting areas or "patches." Conduction within patches may occur in the orad or aborad direction irrespective of the direction of the slow wave. Most of the patches are smaller (<40 mm(2)), although inhomogeneous activation by the preceding slow wave may increase their size. Stimulation by ACh, TTX, or tetraethylammonium does not affect the average patch size but does increase significantly their number and distribution in the duodenum [from 26% (control) to 56%, 61%, and 72%, respectively]. In conclusion, individual spikes activate limited areas or patches in the small intestine, and pharmacological stimulation increases the number and distribution of these patches. In the small intestine, this pattern of activation would induce localized contractions. Contraction could be modulated by the size, number, and distribution of spike patches.

Longitudinal and circumferential spike patches in the canine small intestine in vivo

“…3). The first type, the longitudinal spike patch, resembled that described earlier in the isolated cat duodenum in vitro (11) and showed predominant propagation in the longitudinal direction. A second type, not described before, showed mostly propagation from the antimesenteric border in the circumferential direction and toward the mesenteric border of the intestinal tube.…”

“…In contrast to previous mapping studies (13,11), the electrode tips were flush with the bottom surface of the assembly (Fig. 1B) so that there were no protruding sharp edges, avoiding the risk of damage to the underlying tissue.…”

“…The local activation time of a slow wave was identified by the moment of maximum negative slope (4,13) and marked with a cursor. The local activation times of the spikes were marked by the steepest slope of the signal, which was usually negative (11). All local activation times are related to a common reference time, determined by the timing of the first detected slow wave in the mapped area.…”

“…Analysis of the propagation of these spikes revealed the presence of spike patches at all levels in the small intestine. Two types of spikes were found; the first type, previously described in the cat duodenum (11,12), propagated in the longitudinal direction, originated anywhere around the intestinal tube, and occurred predominantly in the duodenum. The second type, which occurred much more frequently in the jejunum and the ileum, originated in most cases along the antimesenteric line and propagated in the circumferential direction.…”

“…Not much attention, however, has been given to the spatial pattern of spike propagation (6,17) or to possible regional variations along the small intestine. Recently, it was shown that spikes propagate for a limited extent in time and space before terminating spontaneously, thereby activating a relatively small area termed a spike "patch" (11). These patches were demonstrated in isolated tissues in vitro, in a single species, the cat, and in one part of the intestine, the duodenum.…”