Hippocampal Wnt3a is Necessary and Sufficient for Contextual Fear Memory Acquisition and Consolidation.

The Wnt signaling pathway plays critical roles in development. However, to date, the role of Wnts in learning and memory in adults is still not well understood. Here, we aimed to investigate the roles and mechanisms of Wnts in hippocampal-dependent contextual fear conditioning (CFC) memory formation in adult mice. CFC training induced the secretion and expression of Wnt3a and the activation of its downstream Wnt/Ca(2+) and Wnt/β-catenin signaling pathways in the dorsal hippocampus (DH). Intrahippocampal infusion of Wnt3a antibody impaired CFC acquisition and consolidation, but not expression. Using the Wnt antagonist sFRP1 or the canonical Wnt inhibitor Dkk1, we found that Wnt/Ca(2+) and Wnt/β-catenin signaling pathways were involved in acquisition and consolidation, respectively. Moreover, we found Wnt3a signaling is not only necessary but also sufficient for CFC memory. Intrahippocampal infusion of exogenous Wnt3a could enhance acquisition and consolidation of CFC. Overexpression of constitutively active β-catenin in the DH could rescue the deficit in CFC memory consolidation, but not acquisition induced by Wnt3a antibody injection, which suggests β-catenin signaling pathway acts downstream of Wnt3a to mediate CFC memory consolidation. Our study may help further the understanding of the precise regulation of Wnt3a in differential memory phases depending on divergent signaling pathways.