The central pattern generator for vomiting may exist in the reticular area dorsomedial to the retrofacial nucleus in dogs

Abstract 

There is some controversy over whether or not a discrete site that integrates vomiting activities in somatic and autonomic nerves is present in the medulla oblongata. On the basis of our previous studies, we hypothesized that the temporal patterns of muscle contractions in vomiting are generated by a central pattern generator in the retrofacial area of the rostral medulla. To investigate this hypothesis further, the effects of electrical and chemical lesions of the medullary area were observed in decerebrate paralyzed dogs. Efferent activities of the phrenic and abdominal muscle nerves were recorded to recognize fictive vomiting. The right half of the medulla oblongata was transversely severed about 3 mm rostral to the obex. Fictive vomiting responses to vagal stimulation still appeared after hemisection in all 11 dogs. In addition, stimulation of the contralateral reticular area dorsomedial to the retrofacial nucleus produced fictive vomiting even after hemisection. An electrical lesion or injection of kainic acid (0.5–1.0 µl) was applied at the point where reticular stimulation induced fictive vomiting. After this destruction, no activities that corresponded to fictive vomiting could be induced by stimulation of vagal afferents or the reticular site. Salivation was decreased by hemisection, and decreased further, but was not completely abolished, with destruction of the reticular area. Kainic acid is known to selectively destroy neural cell bodies. Therefore, we concluded that neuronal somata in the reticular formation dorsomedial to the retrofacial nucleus play an essential role in the central patterning of vomiting activities in peripheral motor nerves.