Constitutive CaMKII activity, once silenced, remains silent for 2 wk in hippocampal slice cultures. (A) A diagram depicting the paired, simultaneous recording scheme. (B) A timeline of the experiment. A day or two after preparing slice cultures from P6–P8 rats, gold bullets coated in plasmids for paAIP2 and a reporter pCAGG-mCh were used to transfect slices. At least 2 d after transfection, the slices were illuminated with a blue laser pulsing at 0.1 Hz for 1 s for 30 min (day 0). Slices were returned to the incubator and kept in slice culture media that contained APV (100 μM) and nifedipine (20 μM). Transfected cells and wild-type cells were then recorded and their AMPA currents compared. (C) Paired AMPA currents measured from 1 day after light illumination of the slice. The example trace shown has scale bars of 20 pA vertical and 10 ms horizontal. AMPA currents of transfected cells are significantly reduced (wild-type = 88.9 ± 8.3, Transfected = 62.1 ± 12.8, n =14 pairs). (D) Paired AMPA currents measured 14 d after light illumination of the slice. Example trace shown has scale bars of 50 pA vertical and 10 ms horizontal. AMPAR currents of transfected cells remain significantly reduced (wild-type = 218.1 ± 32.6, Transfected = 106 ± 12.9, n = 12 pairs). Analyzed with Wilcoxon signed rank test. (C) **P = 0.0052. (D) **P = 0.0049.