Synaptic Correlates of Anterograde Amnesia and Intact Retrograde Memory in a Mouse Model of Alzheimer's Disease.

BACKGROUND

Clinical evidence indicates that patients affected by Alzheimer's Disease (AD) fail to form new memories although their memories for old events are intact. This amnesic pattern depends on the selective vulnerability to AD-neurodegeneration of the hippocampus, the brain region that sustains the formation of new memories, while cortical regions that store remote memories are spared.

OBJECTIVE

To identify the cellular mechanisms underlying impaired recent memories and intact remote memories in a mouse model of AD.

METHODS

Glutamatergic synaptic currents were recorded by patch-clamp in acute hippocampal and anterior Cingulate Cortical (aCC) slices of AD-like Tg2576 mice and Wild-type (Wt) littermates subjected to the Contextual Fear Conditioning (CFC) task or in naïve conditions.

RESULTS

We identified a deficit in the formation of recent memories, but not in the recall of remote ones, in Tg2576 mice. With electrophysiological recordings, we detected CFC-induced modifications of the AMPA/NMDA ratio in CA1 pyramidal cells of Wt, but not Tg2576, mice one day after training. CFC-induced changes in the AMPA/NMDA ratio were also detected in the aCC of both Wt and Tg2576 mice 8 days after training.

CONCLUSION

Our data suggest that in the early AD stages synaptic plasticity of CA1 synapses, crucial to form new memories, is lost, while plasticity of aCC synapses is intact and contributes to the persistence of long-term memories.