Synapse-specific insertion of AMPARs at Kir2.1/Syn-YFP spines is abolished in Arc KO neurons. (*A* and *B*) Dendritic segments from WT (*A*) and Arc KO (*B*) pyramidal neurons and the synaptic terminals from a Kir2.1/Syn-YFP–expressing neuron and associated current traces of 2P-EPSCs are shown. (*B*) The amplitude of 2P-EPSCs at control neighboring spines is plotted against the amplitude of 2P-EPSCs obtained from Kir2.1/Syn-YFP spines for WT (*n* = 18 pairs, *P* < 0.01, paired Student's *t* test; blue circles) and Arc KO neurons (*n* = 25 pairs, *P* = 0.54, paired Student's *t* test; red circles). (*C*) The average amplitude of 2P-EPSCs is plotted for WT (*n* = 27 control spines, *n* = 18 Kir2.1/Syn-YFP apposed spines; *P* < 0.05, unpaired Student's *t* test) and for KO (*n* = 55 control spines, *n* = 35 Kir/Syn-YFP spines; *P* = 0.14, unpaired Student's *t* test). (*D*) Dendritic segments from a WT and a KO neuron showing current traces depicting AMPAR-mediated 2P-EPSC elicited while holding the neuron at −60, −40, −20, 0, +20, and +40 mV. (*E*) Average rectification index obtained in WT (*n* = 11) and ARC KO (*n* = 23; *P* = 0.12, unpaired Student's *t* test). (*F*) Surface GluA1 labeling intensity at control and Kir2.1/Syn-YFP apposed synapses for WT neurons (*n* = 25 pairs; *P* < 0.01, paired Student's *t* test) and Arc KO neurons (*n* = 32 pairs; *P* = 0.62, paired Student's *t* test). (*G*) Surface GluA1 labeling intensity at control and Syn-YFP alone apposed synapses for WT neurons (*n* = 26 pairs; *P* = 0.97, paired Student's *t* test) and Arc KO neurons (*n* = 20 pairs; *P* = 0.09, paired Student's *t* test).

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