Abstract
Refinement of neural circuits in the mammalian cerebral cortex shapes brain function during development and in the adult. However, the signaling mechanisms underlying the synapse-specific shrinkage and loss of spiny synapses when neural circuits are remodeled remain poorly defined. Here, we show that low-frequency glutamatergic activity at individual dendritic spines leads to synapse-specific synaptic weakening and spine shrinkage on CA1 neurons in the hippocampus. We found that shrinkage of individual spines in response to low-frequency glutamate uncaging is saturable, reversible, and requires NMDA receptor activation. Notably, shrinkage of large spines additionally requires signaling through metabotropic glutamate receptors (mGluRs) and inositol 1,4,5-trisphosphate receptors (IP(3)Rs), supported by higher levels of mGluR signaling activity in large spines. Our results support a model in which signaling through both NMDA receptors and mGluRs is required to drive activity-dependent synaptic weakening and spine shrinkage at large, mature dendritic spines when neural circuits undergo experience-dependent modification.