Molecular mechanisms of vestibular compensation in the central vestibular system--review.

Vestibular compensation consists of two stages: the inhibition of the contralesional medial vestibular nucleus (contra-MVe) activities at the acute stage after unilateral labyrinthectomy (UL) and the recovery and maintenance of the ipsilesional MVe (ipsi-MVe) spontaneous activities at the chronic stage after UL. In this paper, we reviewed molecular mechanisms of vestibular compensation in the central vestibular system using several morphological and pharmacological approaches in rats. Based on our examinations, we propose the following hypotheses: i) at the acute stage after UL, the activated neurons in the ipsi-MVe project their axons into the flocculus to inhibit the contra-MVe neurons via the NMDA receptor, nitric oxide (NO) and/or GABA-mediated signalling, resulting in the restoration of balance between intervestibular nuclear activities. ii) At the chronic stage after UL, the flocculus depresses the inhibitory effects on the ipsi-MVe neurons via protein phosphatase 2A (PP2A) beta, protein kinase C (PKC) and glutamate receptor (GluR) delta-2, to help the recovery and maintenance of ipsi-MVe activities.