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It was shown previously by Chinn and Wang that dogs exposed to 800 r total body irradiation vomited within 2 hours after completion of exposure. After chronic destruction of the chemoceptive emetic trigger zone, no dogs vomited within 2 hours of radiation. It was observed that these operated animals would vomit later throughout their period of survival. Visceral deafferentation alone (abdominal vagotomy and sympathectomy) did not prevent dogs from vomiting soon after irradiation or within several days. On the other hand, both acute and delayed emesis due to irradiation was not observed in dogs with chronic destruction of the chemoceptive trigger zone and abdominal visceral deafferentation. It appeared, therefore, that delayed vomiting following lethal total body irradiation was mediated through two mechanisms; the centrally located trigger zone, and the peripheral visceral afferent receptors of the vagus and sympathetic trunks.

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