IN the rat central nervous system (CNS), inositol 1,4,5-trisphosphate receptor (IP(3)R) type 3 was immunolocalized with a type 3-specific monoclonal antibody (mAb). The protein was expressed principally in prototype astrocytes, ependymal cells around the ventricle, and Bergmann glial cells in the cerebellum. These cells were stained by antibody against glial fibrillary acidic protein (GFAP), indicating the coexistence of GFAP and IP(3)R type 3. Immunoblot analysis using a brain homogenate detected a 240 kDa protein, verifying that the observed immunoreactivity is from the IP(3)R type 3 protein. IP(3)R type 1 and type 2 were not detected immunohistochemically in astrocytes. These results suggest that IP3-induced Ca2+ release (IICR) in astroglia is directed by IP(3)R type 3, whereas IICR in neuronal cells is mediated by IP(3)R type 1.