It has been suggested that the LGN protein is associated with Galphai2 by the yeast two-hybrid system and in vitro pull-down assay. To determine the functions of LGN in the central nervous system, we examined the expression and localization of LGN in mouse brain by immunoblotting and immunofluorescence microscopy. By immunoblotting, almost similar amounts of LGN were detected in the olfactory bulb, cerebral cortex, hippocampus, and cerebellum of the adult mouse brain, and the levels of the postnatal LGN expression in the whole brain were fairly constant. Immunofluorescence microscopy showed that LGN is localized in nuclei of the neurons in the olfactory bulb, cerebral cortex, and hippocampus, but in both nuclei and cytoplasm of Purkinje cells in the cerebellum. On the other hand, Galphai2 was distributed throughout the neuronal elements except for the nuclei. Thus, LGN and Galphai2 were colocalized in the cytoplasm of Purkinje cells, but not in other neurons examined. These results suggest that LGN may be involved not only in the Galphai2-mediated signaling but also in other signaling pathways.