Motoneurons differ in the behaviours they control and their vulnerability to disease and ageing. For example, brainstem motoneurons such as hypoglossal motoneurons (HMs) are involved in licking, suckling, swallowing, respiration, and vocalization. In contrast spinal motoneurons (SMs) innervating the limbs are involved in postural and locomotor tasks requiring higher loads and lower movement velocities. Surprisingly, the properties of these two motoneuron pools have not been directly compared even though studies on HMs predominate in the literature compared to SMs, especially for adult animals. Here, we used whole cell patch clamp recording to compare the electrophysiological properties of HMs and SMs in age-matched neonatal mice (P7-10). Passive membrane properties were remarkably similar in HMs and SMs and afterhyperpolarization properties did not differ markedly between the two populations. HMs had narrower action potentials (AP), and a faster upstroke on their APs compared to SMs. Furthermore, HMs discharged APs at higher frequencies in response to both step and ramp current injection than SMs. Therefore, while HMs and SMs have similar passive properties, they differ in their response to similar levels of depolarizing current. This suggests each population possess differing suites of ion channels that allow them to discharge at rates matched to the different mechanical properties of the muscle fibers that drive their distinct motor functions.
- patch clamp
- action potential
- Copyright © 2015, Journal of Neurophysiology