The majority of studies on the electrical properties of neurons are carried out in rodents, and in particular in mice. However, the minute size of this animal compared to humans potentially limits the relevance of the resulting insights. To be able to extrapolate results obtained in a small animal such as a rodent, one needs to have proper knowledge of the rules governing how electrical properties of neurons scale with the size of the animal. Generally speaking, electrical resistances of neurons increase as cell size decreases and thus maintenance of equal depolarization across cells of different sizes requires the underlying currents to decrease in proportion to the size decrease. Thus, it would generally be expected that voltage-sensitive currents are smaller in smaller animals. In this study, we used in vivo preparations to record electrical properties of spinal motoneurons in deeply anesthetized adult mice and cats. We found that PICs do not scale with size but instead are constant in their amplitudes across these species. This constancy, coupled with the 3-fold differences in electrical resistances, means that PICs contribute a 3-fold larger depolarization in the mouse than cat. As a consequence, motoneuronal firing rate sharply increases as animal size decreases. These differences in firing rates are likely essential in allowing different species to control muscles with widely different contraction speeds (smaller animals have faster muscle fibers). Thus our results have identified a possible new mechanism for how electrical properties are tuned to match mechanical properties within the motor output system.
- Persistent Inward Currents (PICs)
- Electrical Properties
- Adult Spinal Motoneurons
- Copyright © 2017, Journal of Neurophysiology