RNA polymerase i transcription is modulated by spatial learning in different brain regions

Long-term memory is accompanied by changes in neuronal morphology and connectivity. These alterations are thought to depend upon new gene expression and protein synthesis over a distributed network of brain structures. Although, much evidence supports the idea that the creation of stable, persistent memory traces requires synthesis of new proteins, the role of rRNA transcription and nucleolar activity in learning and memory has hardly been explored. rRNAs needed for protein synthesis result from the activity of two different RNA polymerases, RNA polymerase I and RNA polymerase III, transcribing for 47S RNA and 5S RNA respectively. In this study we first investigated the effects of spatial training in the Morris water maze on 47S RNA transcription in the central nervous system, demonstrating bi-directional modulation of its expression over a distributed neural network. We found learning induced increases in the nucleolar organizer regions in the hippocampus. Finally we demonstrated that intra-hippocampal administrations of CX-5461 (0.6μg/side), the specific RNA Polymerase I inhibitor, impair the ability of mice to locate the platform in the same task. These results suggest that de novo rRNA transcription is a necessary step for spatial memory consolidation and that after learning it occurs in several brain regions with a complex spatio-temporal dynamic.