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The role of hippocampal NMDA receptors (NMDARs) and NMDAR-dependant synaptic plasticity in long-term spatial memory remains unclear. Current thinking implicates hippocampal NMDARs as important in storing long-term spatial memory. However, a recent study from Bannerman et al., in Experimental Psychology, working with researchers from the Max Planck Institute and the University of Oslo, shows that hippocampal NMDARs are actually involved in the use of spatial knowledge in selecting between alternative responses. In the study, published in Nature Neuroscience, Bannerman et al. used Grin1∆DGCA1 transgenic mice, which lack NMDARs in dentate gyrus granule cells and dorsal hippocampal CA1 pyramidal cells, in a series of spatial choice experiments

The Grin1∆DGCA1 mouse conducted the spatial reference memory Morris water maze task as well as control animals. In a spatial reference memory radial maze task, in which the mice were made to differentiate between baited and non-baited arms, Grin1∆DGCA1 mice had diminished success compared to controls.

When undergoing a spatial discrimination water maze task with identical visual beacons, the Grin1∆DGCA1 mice were unable to selectively inhibit choosing the ‘decoy’ beacon, when started close to it, even though they had knowledge of the correct location of the platform. When two visually differentiated beacons were used Grin1∆DGCA1mice were uninhibited in choosing the correct platform. These experiments show that the Grin1∆DGCA1 mice were unable to choose correctly between competing response options using acquired spatial knowledge, suggesting that hippocampal NMDARs are in fact involved in selecting between alternate responses using spatial knowledge, rather than in storing long-term spatial memory.

To read the full paper please click here.