Persistent Nav1.6 current drives spinal locomotor functions through nonlinear dynamics

Persistent sodium current (INaP) in the spinal locomotor network promotes two distinct nonlinear firing patterns: a self-sustained spiking triggered by a brief excitation in bistable motoneurons and bursting oscillations in interneurons of the central pattern generator (CPG). Here, we identified the NaV channels responsible for INaP and their role in motor behaviors. We report the axonal Nav1.6 as the main molecular player for INaP in lumbar motoneurons. The motoneuronal inhibition of Nav1.6, but not of Nav1.1, impairs INaP, bistability, postural tone and locomotor performance. In interneurons of the CPG region, Nav1.6 with Nav1.1 equally mediate INaP and the inhibition of both channels is required to abolish oscillatory bursting activities and the locomotor rhythm. Overall, Nav1.6 plays a significant role both in posture and locomotion by governing INaP-dependent bistability in motoneurons and working in tandem with Nav1.1 to provide INaP-dependent rhythmogenic properties of the CPG.