[Start of mastication by esophageal distension in sheep]

Oesophageal wall distension was performed on standing conscious sheep by inflating a rubber balloon at four different levels inside the cervical and thoracic oesophagus. Although no retrograde oesophageal peristalsis was ever recorded, these stimulations were always followed by a conspicuous increase of parotid saliva secretion. They frequently induced the onset of chewing movements, whatever the level of the oesophageal distension. The cyclical reticular activity does not bear any relationship to the occurrence of the chewing movements. The masticatory response could be either of the "ON" or "ON - OFF" type, but most often of the "OFF" type. The response to thoracic oesophageal distension was suppressed by mid-cervical anaesthetic blockage of vagal conduction. A possible involvement of any sort of stimulation of the oral cavity was thus ruled out. The masticatory response to oesophageal distension is a reflex mechanism whose afferent pathway from the distal part lies in the vagal trunk. Such a reflex may participate early in the initiation of chewing movements during rumination, prior to the arrival of the regurgitated bolus into the mouth.