Spatial learning induced changes in expression of the ryanodine type II receptor in the rat hippocampus

Calcium signaling critical to neural functions is mediated through Ca2+ cha nnels localized on both the plasma membrane and intracellular organelles su ch as endoplasmic reticulum, Whereas Ca2+ influx occurs via the voltage- or /and ligand-sensitive Ca2+ channels, Ca2+ release from intracellular stores that amplifies further the Ca2+ signal is thought to be involved in more p rofound and lasting changes in neurons, The ryanodine receptor, one of the two major intracellular Ca2+ channels, has been an important target for stu dying Ca2+ signaling in brain functions, including learning and memory, due to its characteristic Ca2+-induced Ca2+ release, In this study, we report regional and cellular distributions of the type-2 ryanodine receptor (RyR2) mRNA in the rat brain, and effects of spatial learning on RyR2 gene expres sion at mRNA and protein levels in the rat hippocampus, Using in situ hybri dization, reverse transcription polymerase chain reaction, and ribonuclease protection assays, significant increases in RyR2 mRNA were found in the hi ppocampus of rats trained in an intensive water maze task, With immunopreci pitation and immunoblotting, protein levels of RyR2 were also demonstrated to be increased in the microsomal fractions prepared from hippocampi of tra ined rats, These results suggest that RyR2, and hence the RyR2-mediated Ca2 + signals, may be involved in memory processing after spatial learning. The increases in RyR2 mRNA and protein at 12 and 24 h after training could con tribute to more permanent changes such as structural modifications during l ong-term memory storage.