a, Experimental design. Mice were removed from low levels of dox (40 mg kg−1) and given regular chow for 3 days to open up the GFP tagging window. After receiving administration of high dox (1 g kg−1) for 5 h, mice were injected with 30 mg kg−1 of pentylenetetrazole (PTZ), exposed to a novel context or left in their home cage (HC). An hour later, mice were transcardially perfused and processed for GFP expression. b, There was no difference in GFP expression between the three groups (one-way ANOVA, F2,5 = 0.04, not significant, n = 3, 3, 2 mice), demonstrating that 5 h was enough time for dox (1 g kg−1) to suppress expression of new GFP. c, To test excitability learning-related excitability changes, mice explored a novel context and then were administered high dox to shut off new GFP. Five hours later, mice were euthanized for in vitro slice physiology. d, A two-way repeated measures ANOVA (group × current step) had a significant main effect of group (F2,68 = 4.20, P < 0.05, n = 21, 29, 21 cells). The 5 h GFP+ group had more spikes than the 5 h GFP− group (t68 = 2.31, P < 0.05) and home cage GFP− (t68 = 2.72, P < 0.05). There was no difference between the 5 h GFP− and home cage GFP− groups (t68 = 0.61, not significant). Results show mean ± s.e.m.