American Jokknal of Physiology

EISENMAN, J. S. Pyrogen-induced changes in the thermosensitiuity of septal and preoptic neurons. Am. J. Physiol. 216(Z): 330-334. 19697Single-unit responses were studied in urethan-anesthetized cats. Highly thermosensitive, preoptic cells (Qro > Z), the presumed central thermodetectors, responded to bacterialpyrogen (Piromen) injection (2-3 pg/kg, iv) with a decrease in thermosensitivity, without any change in firing rate at normal core temperature (38 C). Units whose characteristics suggest that they were interneurons in the regulatory pathways showed both a change in sensitivity and in firing rate following pyrogen administration. Warm-sensitive cells decreased their sensitivities and firing rates, while cool-sensitive ones increased their firing rates. These responses are appropriate for the decrease in heat loss and increase in heat production that would be seen in an unanesthetized animal during the rising phase of a pyrogeninduced fever. Thermally insensitive (Qlol) or normally sensitive (Qr&!) units were unaffected by the pyrogen. The observed interneuron responses support the view that fever represents a shift of the thermoregulatory set point. Since the firing rate of the high Qro units was unchanged at 38 C, the neural drive for this resetting must originate from a change in the activity of some other, as yet undetermined, class of cells; perhaps from specialized thermoinsensitive neurons.