We produced CA1-specific NMDA receptor 1 subunit-knockout (CA1-KO) mice
to determine the NMDA receptor dependence of nonspatial memory formation and
of experience-induced structural plasticity in the CA1 region. CA1-KO mice
were profoundly impaired in object recognition, olfactory discrimination and
contextual fear memories. Surprisingly, these deficits could be rescued by
enriching experience. Using stereological electron microscopy, we found that
enrichment induced an increase of the synapse density in the CA1 region in
knockouts as well as control littermates. Therefore, our data indicate that
CA1 NMDA receptor activity is critical in hippocampus-dependent nonspatial
memory, but is not essential for experience-induced synaptic structural changes.
