Unilateral labyrinthectomy downregulates glutamate receptor delta-2 expression in the rat vestibulocerebellum

The differential display method was applied to identify genes expression of which is altered in the flocculus after unilateral labyrinthectomy (UL). Total RNA from sham operated and labyrinthectomized rat flocculi was isolated, amplified by PCR using an arbitrary primer set and separated by electrophoresis on a polyacrylamide gel. PCR products the amounts of which were significantly lower in samples from labyrinthectomized animals than those from controls, were cut out of the gel and sequenced. One of the cDNA fragments showed 100% nucleotide sequence identity to the rat glutamate receptor (GluR) delta-2 subunit mRNA. In situ hybridization autoradiography showed that GluR delta-2 mRNA expression was intensely located to the floccular Purkinje cell layers. Furthermore, northern blot analysis showed that the delta-2 mRNA expression was decreased for at least two days after UL in accordance with diminishing UL-induced behavioral deficits. Therefore, it is suggested that the downregulation of delta-2 mRNA is involved in vestibular compensation. UL-induced spontaneous nystagmus (SN) was then examined in GluR delta-2 mutant mice. The frequency of SN in mutant mice was significantly more than that in wild mice until 12 h after UL. GluR delta-2-associated synaptic efficacy may be changed for the induction of vestibular compensation at the initial stage.