03 May 1999

Evidence from several sources suggests that the dorsal hippocampus is critical for the formation and storage of spatial information. In the long term, such information is believed to be transferred to the neocortex for storage. While it is assumed that gene expression and protein synthesis in the hippocampus ultimately underlie this transfer, there is little information on the biochemical steps involved. In the May 1 issue of the Journal of Neuroscience, Pramod Dash, Sonja Blum, and colleagues present evidence that a mitogen-activated protein kinase (MAPK, also called ERK) cascade in the areas CA1 and CA2 of the dorsal hippocampus is critical for the formation of long-term spatial memories.

The authors first demonstrated that MAPK was activated (as evidenced by enhanced phosphorylation) in pyramidal neurons of CA1/CA2 in dorsal hippocampus in rats who had just completed a spatial memory task; in contrast, MAPK was not activated in the dentate gyrus or CA3 (nor in any part of the ventral hippocampus, which appears to process nonspatial information). An inhibitor of the MAPK cascade, whether administered before or soon after the task, was successful in blocking the long-term storage of the spatial memories related to this task, even though it did not interfere with the short-term acquisition of the memories.—Hakon Heimer