A, Representative images of surface GluR1 immunofluorescence in low-density dissociated hippocampal cultures infected with lentivirus expressing shArc or shDsRed treated with media (control), DHPG, or NMDA and fixed 15 min after treatment onset. B, Group data reveal that knockdown of Arc blocks DHPG- induced decreases in surface GluR1. Data pooled from 5 cultures. C, Arc knockdown does not affect NMDA-induced decreases in surface GluR1. N = # cells on each from 3 cultures/condition. D, Representative mEPSCs recorded from neurons infected with shArc or shDsRed before DHPG treatment and 10 min after DHPG washout. Recordings performed in the presence of 1 µM TTX and 100 µM picrotoxin. E, mEPSC frequency 15 minutes after onset of DHPG treatment in shArc and shDsRed infected neurons plotted as a percentage of pre-treatment mEPSC frequency. Group data reveal that Arc knockdown blocks DHPG-induced decreases in mEPSC frequency. N = # cells on each bar from 4 cultures/condition. F, Representative images of internalized GluR1 immunofluorescence in low-density dissociated hippocampal cultures infected with lentivirus expressing shArc or shDsRed. Neurons were live labeled with N-terminal GluR1 antibody immediately after treatment with media (control) or DHPG (100 µM; 5 min) and fixed 15 min later. G, Group data reveal that knockdown of Arc reduces DHPG- induced endocytosis of surface GluR1. Data pooled from 5 cultures. In all images scale bars = 10 µm.