The effect of firing rate on preoptic neuronal thermosensitivity

1. In anaesthetized rabbits, preoptic single units were recorded having positive or negative thermal coefficients (impulses/sec. degrees C) for changes in preoptic temperature.2. A population of forty-two positive coefficient units was divided into four groups based on their level of firing rate at 38 degrees C. In each group, the average thermoresponse curve was determined by averaging the firing rates of the units at 1 degrees C intervals over the 33-43 degrees C range of preoptic temperatures.3. A population of twenty-six negative coefficient units was divided into three groups based on their firing rates at 38 degrees C. Similar average thermoresponse curves were determined for each group.4. As the level of firing rate increased in the positive coefficient units, the preoptic thermosensitivity progressively decreased at temperatures above 39 degrees C, but generally increased at temperatures below 39 degrees C.5. In the negative coefficient units, preoptic thermosensitivity generally increased (especially above 39 degrees C) as the firing rate at 38 degrees C increased.6. The results indicate that in positive coefficient units the level of firing rate determines the temperature range in which units are most thermosensitive. This range reflects whether a neurone is more likely to function in heat-loss or heat-production responses.7. Since peripheral thermal input affects the level of firing rate of positive coefficient units, a neuronal model is suggested to explain the role of peripheral and central thermal signals in temperature regulation.