Spatial learning enhances the expression of inositol 1,4,5-trisphosphate 3-kinase A in the hippocampal formation of rat.

Calcium-mediated signaling is crucial for the synaptic plasticity and long-term memory storage, which requires de novo protein synthesis. Inositol 1,4,5-trisphosphate 3-kinase A (IP(3)K-A) is an enzyme, which is involved in the maintenance of intracellular calcium homeostasis by converting inositol 1,4,5-trisphosphate (IP(3)) to inositol 1,3,4,5-tetrakisphosphate (IP(4)). Because IP(3)K-A is enriched in the dendritic spines of hippocampal neurons, it has been speculated that this enzyme is involved in the memory formation. In the present study, we demonstrated that the expression of IP(3)K-A is increased in the hippocampal formation of the rats during the Morris water maze training. Immunohistochemical analysis indicated the specific induction of IP(3)K-A protein in the hippocampal formation following 5-day water maze training. Furthermore, in situ hybridization histochemistry showed that the induction of IP(3)K-A mRNA in the hippocampal formation was observed on the first day of training, and the induced level of IP(3)K-A mRNA was maintained until the fifth day of training. These results suggest that IP(3)K-A plays a role in the processing of spatial memory, most likely by regulating the calcium signaling in the dendritic spines of hippocampal formation.