Our purpose was to determine the effects on acute
radiation sickness of interrupting afferent neural pathways that converge upon the medullary
vomiting center but which bypass the
emetic chemoreceptor trigger zone in the area postrema. A comparison was made of the
vomiting response and other signs of sickness in three groups of chronic cats surgically prepared as follows: high spinal cord section of the dorsal columns, subdiaphragmatic
vagotomy, and the combination of procedures. Every cat was exposed over the whole body to 45 Gy 60Co gamma-radiation which was effective in evoking
emesis in 11 of 12 normal cats. Neither
cordotomy alone (8 cats) nor
vagotomy alone (2 cats) reliably blocked the
vomiting response but they separately delayed its onset. On the other hand, the
cordotomy prevented the loss of appetite and behavioral malaise that was invariably caused by the irradiation in normal cats. Finally, the combination of
cordotomy and
vagotomy protected all of 3 cats against the entire
radiation syndrome. These cats then vomited appropriately in response to the injection of
deslanoside which induces
emesis through an action on the area postrema. Histological examination of the lower medulla revealed no damage of the area postrema resulting from the
cordotomies. We conclude that acute
radiation sickness in the cat is signaled through afferent neural pathways originating in the abdomen and that the area postrema does not participate in the causation of this syndrome.