Cellular basis of vestibular compensation: changes in intrinsic excitability of MVN neurones.

A systematic survey of the intrinsically generated in vitro discharge rates of rat medial vestibular nucleus (MVN) neurones was carried out in slices from normal animals and animals undergoing vestibular compensation over 48 h after unilateral labyrinthectomy (UL). Isolation of the individual MVN in vitro revealed that the tonic discharge rates of neurones in the rostral MVN ipsilateral to the lesion were not different from control 2 h post-UL, but increased significantly at 4 h post-UL and remained significantly higher until 24 h post-UL. There were no significant changes in the in vitro discharge rates of MVN cells in the contralateral nucleus. The increase in excitability of the ipsilateral MVN cells after UL may be accounted for by a down-regulation of GABA receptors on these cells, following their sustained exposure to excessive commissural inhibition after labyrinthectomy. We suggest that the increased intrinsic excitability of the ipsilateral MVN cells is responsible for the restoration of the resting discharge in these cells after UL and the consequent recovery of static vestibular function.