Figure 7 - Evidence of dual innervation of esophageal peristalsis.

a: Vagal efferent nerve simulation using high stimulus frequency produced a B wave only (i.e., contraction after the end of stimulation). Following administration of N-nitro-L-arginine methyl ester (L-NAME), an inhibitor of NO synthase, the B wave is abolished, and an A wave (i.e., intrastimulus contraction) is unmasked, which in turn is abolished by the administration of atropine. Subsequent administration of L-arginine (a substrate of NO synthase that reverses the effect of L-NAME), the B-wave returns. b: Following the administration of L-NAME, the amplitude of the swallow-induced peristaltic wave is diminished and peristaltic velocity increases owing to a shortening of the onset of contraction in the distal esophageal site (1 cm above the LES). Subsequent administration of atropine abolishes primary peristalsis in the opossum smooth muscle esophagus. (Source: Anand and Paterson,⁵¹ with permission from the American Physiological Society.)