Brain stem response to phasic gastric distension

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Abstract
To explore the physiological characteristics of central projections of gastric afferent fibers, single-unit activity was recorded extracellularly from neurons in the brain stem during phasic distension of the stomach in cats anesthetized by halothane and nitrous oxide. The brain stem units were identified on the basis of discharge patterns that were phase locked to distension or relaxation of the stomach. Based on stereotaxic coordinates, the units responding to the distension stimulus were located in the region of nucleus and tractus solitarius and extended ventrally toward nucleus ambiguus. Both phasically and tonically discharging units were identified, which exhibited either an excitatory or inhibitory response during distension of the stomach at pressures of 6-8 cm H2O. Units excited by distension increased their firing rate or began to discharge near the peak of distension at rates of 4-6 Hz. Other units responded only during the phase when the distending pressure was decreasing. Sectioning the vagi abolished the response of these brain stem units to gastric distension. The origin of the stimulus that initiated the unit response was localized in the fundus and body of the stomach in many instances. Neuronal activity in discrete areas of the brain stem of the cat is altered in response to phasic gastric distension, and this response is vagally mediated.

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