Vestibular compensation in glutamate receptor delta-2 subunit knockout mice: dynamic property of vestibulo-ocular reflex.

The delta-2 subunit of the glutamate receptor delta subfamily is selectively localised in cerebellar Purkinje cells. Delta-2 knock-out mice have defects in Purkinje cell synapse formation, as well as cerebellar long- term depression. In order to elucidate the roles of neural transmission around Purkinje cells in vestibular compensation, the gain and phase of the vestibulo-ocular reflex were measured before and after unilateral vestibular differentiation in delta-2 knock-out mice. After unilateral injury of the inner ear, gain decreased and then recovered in both knock-out mice and wild-type mice. However, recovery of VOR gain after unilateral vestibular differentiation was slower in knock-out mice than in wild-type mice. The knock-out mice displayed lower VOR gain than wild-type mice during the period between the 1st and the 2nd postoperative weeks. The results suggest that the cerebellum is necessary for augmentation of vestibulo-ocular reflex gain during the partially compensated stage of vestibular compensation after unilateral vestibular differentiation.