An implication of protein phosphatase 2A-beta in the rat flocculus for lesion-induced vestibular plasticity

The differential display method was applied to identify genes, the expression of which is up-regulated in the cerebellar flocculus after unilateral labyrinthectomy (UL). Total RNA from sham-operated and labyrinthectomized rat flocculi was isolated, amplified by polymerase chain reaction (PCR) using a single arbitrary primer and separated by electrophoresis on a polyacrylamide gel. PCR products in amounts significantly higher in samples from labyrinthectomized animals than in those from controls were cut out of the gel and sequenced. One of the cDNA fragments showed 100% nucleotide sequence identity to the rat protein phosphatase 2A (PP2A)-beta catalytic subunit mRNA. In situ hybridization histochemistry and Northern blot analysis showed that PP2A-beta mRNA expression was intensely localized to the floccular Purkinje cell layer and up-regulated with a maximum increase within 2 days after UL. In labyrinthectomized rats, UL-induced nystagmus gradually disappeared within 3 days after UL. However, in animals with continuous floccular infusion of okadaic acid, a potent inhibitor of PP2A, UL-induced nystagmus lasted significantly longer. All these findings suggest that up-regulation of PP2A-beta mRNA in floccular Purkinje cells after UL is involved in lesion-induced vestibular plasticity. So far, various kinds of neural plasticity-associated molecules have been investigated mainly by slice in vitro studies. This paper indicates that differential display is the feasible molecular biological in vivo method for an investigation about the mechanism of neural plasticity.