Post-natal development of tonic activity and membrane excitability in mouse medial vestibular nucleus neurones

The development of tonic activity and membrane excitability of MVN neurones was examined using extracellular and intracellular recordings in slices prepared from mice at various stages in the first post-natal month. The tonic spontaneous discharge rates of MVN cells as post-natal day 5 (P5) were typically below 5 imp/s, and gradually increased to reach adult values of 11-20 imp/s by P30. While most MVN cells at P5 were electrophysiologically immature, by P10-P15 they had developed overshooting sodium spikes and pacemaker conductances which generated a steady discharge of spontaneous action potentials. From the earliest stages when tonic activity was observed, immature forms of the adult Type A and Type B action potential shapes could be recognized in tonically active cells. There was a marked rostro-caudal gradient in the time course of the maturation of MVN neurones, with cells in the rostral part of the MVN firing at higher rates and having more mature action potential shapes than caudally located cells.