Effects of Pyrogen on the Medullary Temperatureresponsive Neurone of Rabbits

Abstract

Effects of i.v. injected endogenous pyrogen on the unit activity of temperature-responsive neurons (TR neurons) of medulla oblongata were investigated in urethanized rabbits with an intact or lesioned preoptic/anterior hypothalamic area (PO/AH). TR neurons of the medulla responded to pyrogen in the same manner as did those of the PO/AH; the firing rate in the warm-responsive neurons were depressed and the cold-responsive neurons augmented. Of the medullary TR neurons 1/4 did not respond to pyrogen in the PO/AH intact group (the control group). Following lesion of the PO/AH, the relative frequencies of TR neurons affected by pyrogen decreased compared to those of controls, and such was suggested to be more apparent in TR neurons, discharging at rates of 10 imp[impulse]/s or more. The magnitude of the facilitatory or inhibitory effect of pyrogen was reduced in the PO/AH-lesioned group to the control group. In some TR neurons an antipyretic agent (Sulpyrine, 48-151 mg/kg) abolished responses to pyrogen.