POSTNATAL-DEVELOPMENT OF TONIC ACTIVITY AND MEMBRANE EXCITABILITY IN MOUSE MEDIAL VESTIBULAR NUCLEUS NEURONS

The development of tonic activity and membrane excitability of MVN neu rones was examined using extracellular and intracellular recordings in slices prepared from mice at various stages in the first post-natal m onth. The tonic spontaneous discharge rates of MVN cells as post-natal day 5 (P5) were typically below 5 imp/s, and gradually increased to r each adult values of 11-20 imp/s by P30. While most MVN cells at P5 we re electrophysiologically immature, by P10-P15 they had developed over shooting sodium spikes and pacemaker conductances which generated a st eady discharge of spontaneous action potentials. From the earliest sta ges 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 c ourse of the maturation of MVN neurones, with cells in the rostral par t of the MVN firing at higher rates and having more mature action pote ntial shapes than caudally located cells.