Action potential duration increases as body temperature decreases during hibernation

The effect of temperature on the duration of both population spikes and action potentials of single neurons has been investigated in a variety of in vitro preparations. A few studies have examined the influence of temperature on spike potentials from spinal motoneurons of intact, anesthetized mammals. In all cases, the duration of the action potential or population spike increased as temperature decreased. A similar increase in the duration of action potentials accompanied hibernation in the ground squirrel (Spermophilus lateralis). Oscilloscope traces of 2 brainstem reticular formations, and 8 posterior thalamic single units were photographed at a body temperature (Tb) of 34-36 degrees C during euthermia prior to entrance into hibernation and at Tb's ranging from 10 to 27 degrees C during hibernation. There was a significant increase in the duration of the second component of the diphasic action potential at the lower Tb (P less than 0.01). This temperature effect was reversible, i.e. action potential durations returned to preentrance euthermic values following arousal from hibernation (Tb = 34-36 degrees C). This study is the first to use behaving animals to demonstrate that changes in biophysical characteristics of central nervous system neurons occur at low Tb. These changes in membrane characteristics probably result in alterations in neuronal functioning and information processing during hibernation.