The gastrointestinal motor correlates of vomiting were examined in 8 dogs. Each dog was chronically implanted with extramural strain gage force transducers distributed along the gastrointestinal tract. The following gastrointestinal motor responses accompanied vomiting activated spontaneously or after apomorphine administration (2.5-15 μg/kg, i.v.): (a) a retrograde peristaltic contraction (RPC), (b) a peri-RPC inhibitory period, (c) a post-RPC series of phasic contractions, and (d) a post-RPC inhibitory period. These same motor patterns occurred without the somatomotor responses associated with vomiting but sometimes with regurgitation under the following conditions: (a) spontaneously, (b) one-third of the time after low doses of apomorphine (2.5-5.0 μg/kg, i.v.), or (c) after the intragastric administration of hypertonic saline or a vinegar solution. We concluded that a set of gastrointestinal motor responses accompany vomiting and that this set of responses represents an independent phenomenon. This phenomenon was vagally mediated but only one phase, the RPC, was cholinergically mediated, Our results suggest that the vomiting center may consist of two functionally distinct parts that are activated sequentially: one controlling the gastrointestinal responses and the other the somatomotor responses.
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