Deletion of NL3 from CA1 PV interneurons compromises contextual fear extinction. a, Schematic representation of fear conditioning and extinction protocols. b, Schematic representation of DIO-hM4D1-mCherry construct (left). Bar graph shows % time freezing for control PV-Cre (all of which received injections of AAV expressing Cre-dependent eGFP) and PV-Cre mice expressing hM4Di in hippocampal PV cells treated with CNO (10 mg/kg). Baseline (BL) habituation to context (PV-Cre mice, 0.7 ± 0.4%, n = 12; hM4Di expressing mice, 1.0 ± 0.3%, n = 8); average % time freezing for fear conditioning bouts 1–3 (FC1-3 PV-Cre mice, 31.3 ± 5.5%; hM4Di injected mice 33.8 ± 5.8%), and average % time freezing during Days 2–5 of extinction (Ext2-5 PV-Cre mice, 14.0 ± 4.1%; hM4Di injected mice, 29.5 ± 6.2%, *p < 0.05, posthoc Bonferroni test). Two right graphs show time course of % time freezing during BL, FC bouts 1–3, and 4 days of fear extinction. c, Schematic representation of AAV-DIO-eGFP construct injected into NL3fl/PV-Cre and PV-Cre mouse hippocampus (left). Graphs same as b. (Data for control PV-Cre mice are the same as shown in b.) (Bar graph: BL NL3fl/PV-Cre, 0.6 ± 0.2%, n = 16; FC1-3 NL3fl/PV-Cre, 34.6 ± 3.4%; Ext2-5 NL3fl/PV-Cre, 27.9 ± 3.1; *p < 0.05, posthoc Bonferroni test). d, Schematic representation of AAV-DIO-NL3-t2a-Venus construct injected into NL3fl/PV-Cre mouse hippocampus (left). Graphs same as b. (Data for control PV-Cre mice are the same as shown in b.) (Bar graph: BL NL3fl/PV-Cre rescue, 0.9 ± 0.2%, n = 8 mice; FC1-3 NL3fl/PV-Cre rescue, 29.5 ± 5.2%; Ext2-5 NL3fl/PV-Cre rescue, 17.2 ± 3.5%; *p < 0.05, posthoc Bonferroni test).