No abstract

The effect of ambient temperature on the thermosensitivity of preoptic neurones was studied in euthermic golden hamsters. At skin temperatures (Tsk) of 20 degrees C, preoptic units were still responsive to hypothalamic temperatures (Thy) below 10 degrees C, while at Tsk = 36 degrees C these neurones became inactive at Thy = 15 degrees C on the average. These studies suggest that thermoreceptive preoptic neurones, influenced by a high activity of cutaneous cold-receptors, are capable of sensing core temperatures even in deep hibernation.

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.