Effect of temperature and pyrogens on single-unit activity in the rabbit's brain stem.

Abstract

Single-unit activity was recorded in the brain stem of urethanized rabbits during changes in local temperature from 32-42[degree]C. Thermosensitive units were found which respond to temperature with bell-shaped curves peaking generally either above or below the usual range of body temperature, 37[degree]-39[degree]C. Units which increased firing rate with increase in temperature in the 37-39 C range were designated warm units, and those with the opposite response, as cold units. Temperature response of a total of 50 warm and 27 cold units and a large number of temperature-insensitive units were observed; 19 units were studied following the injection of pyrogens. Seven to 13 min. following intravenous injection of typhoid vaccine 10 warm units were inhibited, 1/2 these units showed a decrease in both spontaneous activity and temperature sensitivity; 5 others completely stopped firing. Seventeen to 21 min. after injection of pyrogen, 3 cold units increased both spontaneous activity and temperature sensitivity; in 2 instances there was no change in cold-neuron response. Three out of 4 insensitive units were unchanged following pyrogen; 1 was inhibited. These findings confirm that pyrogens affect the hypothalamus and provide added information as to the specific action on temperature sensitive neurons.