Muscular vs. Neural Activation in Propulsion Induced by Electrical Stimulation in the Descending Colon of Rats

The present experiments were performed on rat colon to study neurogenic and myogenic elicited propulsion induced by 0.3 and 30 msec long current pulses. The colon segments were stimulated sequentially and randomly. The obtained contractions displaced the intraluminal content in individual propulsion steps. The propulsion steps differed in displacement onset latency, distance, and velocity; the latency decreased while the distance and velocity increased from the proximal to the distal colon segments when performing sequential stimulation; the propulsion steps differed in latency when stimulation was performed randomly; the latency in the first propulsion step was three times longer when using 0.3 vs. 30 msec long pulses. When inhibiting cholinergic transmission by atropine, the propulsion induced by 0.3 msec pulses was blocked, while partially inhibited when using 30 msec pulses. Inhibiting nitric oxide synthesis by N(G) -nitro-L-arginine methyl ester (L-NAME) blocked propulsion induced by both of the pulse durations. In conclusion, electrical stimulation induces propulsion when using both 0.3 and 30 msec long pulses; stimulation using 0.3 msec pulses activates neurons, whereas 30 msec pulses depolarize muscles; in the absence of nitrergic transmission, propulsion cannot be induced by electrical stimulation.