John R. Slack

Anisotropic propagation in the small intestine.

Abstract  Measuring propagation anisotropy may help in determining the tissue layers involved in the propagation of electrical impulses in the intestine. We used 240 extracellular electrograms recorded from the isolated feline duodenum. The conduction velocities of slow waves and of individual spikes were measured from their site of origin into all directions. Both slow waves and spikes propagate anisotropically in the small intestine but in different directions and to a different degree. Slow waves propagated anisotropically faster in the circumferential (1.7 ± 0.8 cm s−1) than in the axial direction (1.3 ± 0.5 cm s−1; P < 0.001). Spikes, on the other hand, propagated faster in the longitudinal direction (7.8 ± 4.5 cm s−1) than in the circumferential direction (3.3 ± 4.3 cm s−1; P < 0.001). Furthermore, the average conduction velocity of spikes (6.3 ± 4.5 cm s−1) was significantly higher than that of slow waves (1.5 ± 1.1 cm s−1; P < 0.001). The anisotropic propagation of spikes supports the argument that these propagate in the longitudinal muscle layer. The anisotropic propagation of slow waves may be the result of the interaction between the myenteric layer of interstitial cells of Cajal and their electrotonic connection to both the longitudinal and the circular muscle layer.

Two‐dimensional high‐resolution motility mapping in the isolated feline duodenum: methodology and initial results

Several types of electrical events occur in the small intestine but their spatial and temporal contributions to overall motility are not clear. In order to quantify local motility in greater detail, a new technique of recording and analysing movements at multiple sites was developed. Use was made of isolated segments of feline duodenum superfused in a tissue bath. Multiple marker dots (20–75) were placed on the serosal surface by applying fine spots of candle soot in rectangular arrays (1–2 mm dot separation). A digital video camera was used to record spontaneous movements of the dots for periods of 10–30 min. After each experiment, 4–6 periods (10–60 s each) of video frames were transferred to a computer (25 fps, 720 × 576 pixels) and the movements of the dots was tracked every 40 ms using custom‐made software. Initial results (eight experiments) show that spontaneous motility is remarkably variable, both in space and time. Three types of movement could be discerned: (i) periodic, rolling or pendular movements, with a frequency of approximately 15 min–1 occurring predominantly in the longitudinal direction; (ii) twitches, wherein a subset of dots were suddenly displaced longitudinally; and (iii) drifts of most of the dots in a circular or oblique direction. All three types of movement occurred throughout every recording session although their relative magnitudes differed greatly from moment to moment. Occasionally, it was possible to detect propagated ‘contractions’ with an apparent velocity of 10 mm s–1. Immobilizing the preparation at one point by inserting a needle through the middle of the array of markers had a negligible effect on the displacements, whereas application of verapamil (10–5  mol L–1) reduced or abolished motility. In summary, we present a new technique to map in detail two‐dimensional motility at the surface of the intestine. Initial results seem to suggest that motility at the serosal surface is not uniform and highly anisotropic.