Thermosensitivity of preoptic neurones in a hibernator (golden hamster) and a non-hibernator (guinea pig).

Thermosensitivity of preoptic units was studied at hypothalamic temperatures (Thy) ranging from 8-43 degrees C in golden hamsters in a non-hibernating state as well as in guinea pigs. In golden hamsters 2 types of thermoresponsive preoptic neurones were found: 1. Neurones sensitive to Thy ranging from 10-42 degrees C with an exponential characteristic and very high spontaneous firing rates (29-59 imp/s) at Thy 36-37 degrees C. 2. Neurones with a bell-shaped temperature-firing rate characteristic, a negative temperature coefficient at Thy 40-30 degrees C, a maximal activity at Thy 20-30 degrees C and a positive temperature coefficient (+0.8 to +4 imp/s-degrees C) even at Thy close to 10 degees C. In guinea pigs thermoresponsive preoptic units became inactive or insensitive to thermal stimulation as soon as Thy fell below 30 degrees C. These results suggest that in hibernators central nervous structures involved in temperature regulation are adapted to maintain their function over the wide range of core temperatures which occur during the different phases of hibernation.