Electrical stimulation of gastric electrical control activity

Gastric electrical control activity in anesthetized dogs was stimulated by voltage pulses of 100 msec duration and 10 to 25 v amplitude. The gastric control waves could be entrained from any site in the electrically active region on the anterior and posterior sides. The maximum frequency at which the gastric control waves could be entrained by the electronic pacemaker varied from dog to dog. Mean maximum driven frequency (MDF) was 6.98 cycles/min. The strength of stimulus required to entrain gastric control waves increased for larger differences between the driven frequency and the natural frequency of gastric control waves. Total phase lag between control waves in the corpus and in the antrum increased when the control waves were driven at a frequency higher than their natural frequency. The stomach was divided into 3 segments by circumferential cuts in muscle layers. The proximal segment that contained the highest intrinsic frequency oscillator had the least MDF (mean 6.92 cycles/min). The mean MDF increased distally (middle segment mean MDF, 7.55 cycles/min; distal segment mean MDF, 7.74 cycles/min). Intravenous injection of physostigmine (20-60 μg/kg) decreased the MDF of the distal segment, whereas intravenous injection of atropine (5-20 μg/kg) increased its MDF. These drugs, in particular physostigmine, had a small effect on the MDF of the middle segment and very little or no effect on the MDF associated the proximal segment. This study confirms that a system of bidirectionally coupled relaxation oscillators can account for more characteristics of the gastrointestinal electrical control activity than a relaxation oscillator model with only forward coupling or a cable model. The study also shows that nerves could have an important role to play in determining some of the characteristics of gastric relaxation oscillators, such as their ability to be driven by electronic pacemakers.