A? Facilitates LTD at Schaffer Collateral Synapses Preferentially in the Left Hippocampus

Promotion of long-term depression (LTD) mechanisms by synaptotoxic soluble oligomers of amyloid-? (A?) has been proposed to underlie synaptic dysfunction in Alzheimer?s disease (AD). Previously, LTD was induced by relatively non-specific electrical stimulation. Exploiting optogenetics, we studied LTD using a more physiologically diffuse spatial pattern of selective pathway activation in the rat hippocampus in vivo. This relatively sparse synaptic LTD requires both the ion channel function and GluN2B subunit of the NMDA receptor but, in contrast to electrically induced LTD, is not facilitated by boosting endogenous muscarinic acetylcholine or metabotropic glutamate 5 receptor activation. Although in the absence of A?, there is no evidence of hippocampal LTD asymmetry, in the presence of A?, the induction of LTD is preferentially enhanced in the left hippocampus in an mGluR5-dependent manner. This circuit-selective disruption of synaptic plasticity by A? provides a route to understanding the development of aberrant brain lateralization in AD