Distal and deglutitive inhibition in the rat esophagus: role of inhibitory neurotransmission in the nucleus tractus solitarii.

This study aimed to show the presence of deglutitive and distal inhibition in the rat esophagus and to differentiate the underlying neural mechanisms. Under urethane anesthesia, the pharyngoesophageal tract was fitted with water-filled balloons for luminal distention and pressure recording. Neural activity was recorded in the nucleus tractus solitarii subnucleus centralis and rostral nucleus ambiguous. Distal esophageal distention evoked both rhythmic local contractions and burst discharges of ambiguous neurons that were simultaneously inhibited by a swallow or proximal esophageal distention. In subnucleus centralis interneurons, type I rhythmic burst discharges correlated with distal esophageal pressure waves and were suppressed by midthoracic esophageal distention; type II non-rhythmic excitatory responses, like type III inhibitory responses, were evoked by distention of either the thoracic or distal esophagus. When applied to the surface of the solitarius complex, bicuculline and, less effectively, strychnine suppressed distal inhibition, and 2-(OH)-saclofen and 3-aminopropylphosphonic acid were ineffective. None of the drugs tested, including systemic picrotoxin, affected deglutitive inhibition. Distal and deglutitive inhibition are present in the rat esophagus. The former, unlike the latter, depends on activation of ligand-gated chloride channels associated with subnucleus centralis premotor neurons. Inhibitory aminoacidergic local interneurons are a probable source of type II responses.