Mapping slow waves and spikes in chronically instrumented conscious dogs: implantation techniques and recordings

Abstract

Myoelectric recordings from the intestines in conscious animals have been limited to a few electrode sites with relatively large inter-electrode distances. The aim of this project was to increase the number of recording sites to allow high-resolution reconstruction of the propagation of myoelectrical signals. Sets of six unipolar electrodes, positioned in a 3x2 array, were constructed. A silver ring close to each set served as the reference electrodes. Inter-electrode distances varied from 4 to 8 mm. Electrode sets, to a maximum of 4, were implanted in various configurations allowing recording from 24 sites simultaneously. Four sets of 6 electrodes each were implanted successfully in 11 female Beagles. Implantation sites evaluated were the upper small intestine (n=10), the lower small intestine (n=4) and the stomach (n=3). The implants remained functional for 7.2 months (median; range 1.4-27.3 months). Recorded signals showed slow waves at regular intervals and spike potentials. In addition, when the sets were positioned close together, it was possible to re-construct the propagation of individual slow waves, to determine their direction of propagation and to calculate their propagation velocity. No signs or symptoms of interference with normal GI-function were observed in the tested animals. With this approach, it is possible to implant 24 extracellular electrodes on the serosal surface of the intestines without interfering with its normal physiology. This approach makes it possible to study the electrical activities of the GI system at high resolution in vivo in the conscious animal.

Mapping slow waves and spikes in chronically instrumented conscious dogs: automated on-line electrogram analysis

“…With more raw computing powers, we can now expand towards the spatial dimension and analyze in greater detail the temporal and spatial relation between slow waves and individual spikes [20]. For example, with the data now obtained, a spatial frequency distribution of spikes in the wake of a slow wave could be constructed, similar to the slow wave propagation maps described in a previous study [22]. In addition, the recent description of two different spikes, longitudinal and circular, and the fact that they differ significantly in their waveforms would make it possible to differentiate between these two, for example by template matching.…”

“…As described previously [22], four sets of six electrodes each were implanted in a row on the serosal surface of the canine duodenum or of the antrum using full anesthesia and standard anti-septic procedures. The connecting wires were tunnelled to the back and exteriorized at the base of the neck where the wires ended in a connector.…”

“…Sampling frequencies were set at 200 or 1,000 Hz and a frequency range of 2-400 Hz was used [22]. After removal of a potential DC-offset, the signals were continuously stored on disk and displayed on screen.…”

“…In order to obtain more insight into these relationships, a project was initiated to develop and implant sets of minielectrode arrays to map the propagation of electrical signals with high temporal and spatial resolution in the small intestine of conscious dogs [22]. This approach allows the simultaneous recording of 24 electrograms from the serosal surface of the intestine.…”

Empirical mode decomposition: a method to reduce low frequency interferences from surface electroenterogram

“…The use of electrode arrays implanted in animal model provides a high spatial resolution in the recording of intestinal myoelectrical activity [12]. These recordings allow measuring the propagation velocity and direction of individual SWs and studying patterns under different circumstances.…”