Figure 4. Deconditioning-update is based on memory destabilization mechanisms.

(A) Experimental design: rats were fear-conditioned with five tone-shock pairings (context A; 5CS+US, 0.5mA). 48 hr later, the no-footshock and footshock groups underwent a single extinction session (context B, 24 CSs), followed by test (context B), renewal (context A) and spontaneous recovery (context B) sessions. (B) Freezing levels during extinction. Weak footshocks impaired extinction within the session and in the test session (C), but not in renewal (D) or spontaneous recovery (E). (F) Experimental design: rats were fear-conditioned (context A; 5CS+US, 0.5mA). 48 hr later, all animals underwent daily reactivation sessions (context B), receiving nimodipine (16 mg/kg, i.p.) or vehicle 30 min before each one. They then underwent test (context B), renewal (context A) and spontaneous recovery (context B) sessions. Nimodipine prevented freezing decrease across reactivation sessions in both groups (G). Freezing was similar between groups in the test session (H), but was lower in the vehicle-footshock group in the renewal (I) and spontaneous recovery (J) sessions. Bars represent mean ± SEM. Statistical comparisons are performed using two-way repeated-measures ANOVA followed by Bonferroni post-hoc (extinction), one-way ANOVA followed by Tukey post-hoc (test, renewal, and spontaneous recovery following extinction), three-way repeated-measures ANOVA followed by Bonferroni post-hoc (reactivation sessions with nimodipine/vehicle) and two-way ANOVA followed by Bonferroni post-hoc (test, renewal, and spontaneous recovery following nimopidine/vehicle). *p<0.05; **p<0.005; ***p<0.0005; ****p<0.0001 in between-group comparisons. For full statistics, see Supplementary file 4. For pre-CS freezing, see Supplementary file 14.

Figure 4—figure supplement 1. Effects of deconditioning-update in a single 12-CS extinction session.

(A) Experimental design: rats were fear-conditioned with five tone-shock pairings (context B; 5 CS + US, 0.5mA). 48 hr later, both groups underwent a single extinction session (context A, 12 CSs) with or without a weak footshock (0.1 mA) at the end of tones. Animals then underwent test (context A), renewal (context B) and spontaneous recovery (context A) sessions. Black circles represent context A and white squares represent context B. (B) Freezing levels during the extinction session. No differences were found between the groups during extinction or in the test and spontaneous recovery sessions, but the deconditioning-update group showed less renewal (C). Bars represent mean ± SEM. Statistical comparisons are performed using two-way repeated-measures ANOVA followed by a Bonferroni post-hoc (extinction session) or one-way ANOVA followed by a Tukey post-hoc (test, renewal and spontaneous recovery). For full statistics, see Supplementary file 10. For pre-CS freezing, see Supplementary file 20.

Figure 4—figure supplement 2. Nimodipine does not induce a state-dependent memory and does not affect open field behavior.

(A) Experimental design: rats were fear-conditioned with five tone-shock pairings (context A; 5CS+US, 0.5mA). 48 hr later, all animals underwent daily reactivation sessions (context B), receiving nimodipine (16 mg/kg, i.p.) or vehicle 30 min before each one. They were tested 24 hr (Test 1) and 48 hr (Test 2) later in context B. Half of the animals treated with nimodipine during reactivation received nimodipine and half received vehicle before Test 1; treatments were reversed in Test 2. Black circle represents context A, while white rectangles represent context B. (B) Nimodipine treatment before reactivation prevented freezing reduction across reactivation sessions. (C) Nimodipine injection before the test did not affect freezing expression, suggesting that it prevented deconditioning instead of inducing state-dependent extinction. Sessions in which each group received nimodipine are marked with plus signs below the graph, while those in which vehicle was given are marked with minus signs. (D) Experimental design of the open field task. Nimodipine administered 30 min before the test did not influence the number of crossings (E) or time spent in the periphery of the arena (F). Bars represent mean ± SEM. Statistical comparisons are performed using two-way repeated-measures ANOVA followed by a Bonferroni post-hoc (reactivation sessions), one-way ANOVA followed by a Tukey post-hoc (test sessions) or Student’s t test (open field test). ****p<0.0001. For full statistics, see Supplementary file 11. For pre-CS freezing, see Supplementary file 21.