Gastric pH changes following intramedullary electrical stimulation in anesthetized and decerebrate cats.

In anesthetized and decerebrate cats, a pH-sensitive glass electrode inserted into the gastric antral region through a fistula recorded immediate pH changes. In the anesthetized cats (pentobarbital sodium, 35-40 mg/kg, i.p.), electrical stimulation within the medulla oblongata with a coaxial electrode (train of pulses at 300-500 Hz for 10-30 sec; individual pulse width 0.1-0.5 msec and amplitude not exceeding 0.5 mA) induced an increase in gastric acid secretion equivalent to a delta pH of 1.26 +/- 0.1 units. In the decerebrate (following induction with ether), the same type of stimulation elicited a more intense gastric acid secretion equivalent to a delta pH of 5.18 +/- 0.09 units which is significantly different (P less than 0.001) from that recorded in the anesthetized cats. Reversible blockage of the vagus nerves eliminated these responses during the block. Our results indicate that electrical stimulation in the posterior region of the medulla oblongata evokes an immediate and significant increase in gastric acid secretion, which is mediated through the vagus nerve, and is most evident in decerebrate unanesthetized cats.