Increased Axon Initial Segment Length Results in Increased Na+ Currents in Spinal Motoneurones at Symptom Onset in the G127X SOD1 Mouse Model of Amyotrophic Lateral Sclerosis

•In vivo electrophysiological recordings were made in symptomatic G127X SOD1 mice.•There were no deficits in repetitive firing in motoneurones in G127X mice.•Increased persistent inward currents were still present in the symptomatic mice.•Results suggest increases in Na+ currents at axon initial segments (AISs).•Immunohistochemistry showed that motoneurone AISs were longer and thinner.