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Control febrile responses to intravenous injections of endogenous pyrogen were determined in groups of rabbits and rats, exposed to their respective thermoneutral ambient temperatures. Discrete electrolytic lesions were placed within the confines of the organum vasculosum laminae terminalis (o.v.l.t.) of each species. The fever responses of the animals were remeasured 3 days later, and in every case there was a marked enhancement of the fevers produced, using the same doses of endogenous pyrogen that were used earlier. Similar lesions that were placed unilaterally within the preoptic anterior hypothalamic area in groups of control animals, were not effective in enhancing the febrile responses of these animals. The course of this lesion-induced fever enhancement in rabbits was studied during the succeeding 3 week period, when it was found to return gradually towards the control levels. It is postulated that the o.v.l.t. is involved in some manner in the process whereby circulating pyrogen is translated into a febrile stimulus. Lesions posited within this region are thought to either increase the amount of pyrogen entering the o.v.l.t., or to increase the sensitivity of pyrogen receptor sites within the o.v.l.t.
John T. Stitt (Fri,) studied this question.