Spinal motoneuron firing properties mature from rostral to caudal during postnatal development of the mouse

Abstract

Key points Many mammals are born with immature motor systems that develop through a critical period of postnatal development In rodents, postnatal maturation of movement occurs from rostral to caudal, correlating with maturation of descending supraspinal and local spinal circuits We asked whether development of fundamental electrophysiological properties of spinal motoneurons follows the same rostro‐caudal sequence We show that in both regions, repetitive firing parameters increase and excitability decreases with development; however, these characteristics mature earlier in cervical motoneurons We suggest that in addition to autonomous mechanisms, motoneuron development depends on activity resulting from their circuit milieu Abstract Altricial mammals are born with immature nervous systems comprised of circuits that do not yet have the neuronal properties and connectivity required to produce future behaviours. During the critical period of post‐natal development, neuronal properties are tuned to participate in functional circuits. In rodents, cervical motoneurons are born prior to lumbar motoneurons, and spinal cord development follows a sequential rostro‐caudal pattern. Here we asked whether birth order is reflected in the post‐natal development of electrophysiological properties. We show that motoneurons of both regions have similar properties at birth and follow the same developmental profile, with maximal firing increasing and excitability decreasing into the 3^rd post‐natal week. However, these maturative processes occur in cervical motoneurons prior to lumbar motoneurons, correlating with the maturation of premotor descending and local spinal systems. These results suggest that motoneuron properties do not mature by cell autonomous mechanisms alone, but also depend on developing pre‐motor circuits. This article is protected by copyright. All rights reserved