Abstract
The effects of endogenous pyrogen (E.P.) injected directly into the tissue near the recording site were examined on the activities of the medullary temperature-responsive (TR) neurons in rabbits anesthetized with urethane.Endogenous pyrogen prepared from rabbit's whole blood was administered by a fine glass cannula (100-200μm in diameter) in a fluid volume of 1 to 4μl.The cannula was fixed to the manipulator in parallel with a microelectrode and their tips were less than 0.5mm apart.In rabbits with the intact preoptic/anterior hypothalamic (PO/AH) region, 4 warm-responsive neurons out of 7 were inhibited and 6 cold-responsive neurons out of 7 were excited by the direct administration of the E.P.In rabbits with lesions of the PO/AH, 5 warm-responsive neurons out of 9 were inhibited and 6 cold-responsive neurons out of 8 were facilitated by E.P.Antipyretics administered locally after the E.P.antagonized the pyretic effect, causing a return of the discharge of TR neuron to the control rate within 2.4±1.2 (mean±S.D.) min.The medullary TR neuron itself has the ability to respond to the E.P.and contributes to the development of fever.
