Figure 1. Memory retrieval re-silences cocaine-generated synapses.

(a) Diagram showing experimental timeline.

(b and c) Summary showing that after cocaine (b), but not saline (c), self-administration, cue-induced seeking was higher on withdrawal day 45 than withdrawal day 1 (withdrawal day 1 active = 3.08 ± 5.787, n = 12; withdrawal day 45 active = 87.13 ± 20.367, n = 11, F_1,38=12.27, p=0.0012, two-way ANOVA; **p<0.01, Bonferroni posttest).

(d) Diagram showing the recording area.

(e) Example EPSCs in the minimal stimulation assay, in which failed and successful responses were readily discernable at both −70 mV and +50 mV, and the small vs. large failure rate differences between these two holding potentials connotes low % (upper) vs. high % silent synapses.

(f and g) EPSCs evoked at −70 mV or +50 mV (insets) over 100 trials from example recordings 1 day after saline (f) or cocaine (g) self-administration.

(h) Summary showing that the % silent synapses was increased on withdrawal day 1 after cocaine self-administration (saline = 5.93 ± 1.44, n = 5 animals; cocaine = 24.95 ± 7.13, n = 6 animals, t₉=2.38, p=0.04, two-tail unpaired t-test). On withdrawal day 45, the % silent synapses returned to basal levels, while CP-AMPAR inhibition restored the high % silent synapses (saline = 11.71 ± 5.35, n =5 animals; cocaine = 10.53 ± 1.49, n = 12 animals; cocaine naspm = 28.37 ± 4.68, n = 6 animals, F_2,19=8.61, p=0.0022, one-way ANOVA; *p<0.05, **p<0.01, Bonferroni posttest).

(i) Diagram showing experimental timeline.

(j-l) EPSCs evoked at −70 mV or +50 mV by minimal stimulation (insets) over 100 trials from example recordings after cue re-exposure from saline- (j) and cocaine-trained rats (k) in the absence or presence (l) of naspm.

(m) Summary showing that cue re-exposure increased the % silent synapses in cocaine-trained, but not saline-trained, rats on withdrawal day 45, and the effects of naspm (saline re-exp = 7.74 ± 1.89, n = 5 animals; cocaine 45w/d = 8.01 ± 1.89, n = 16 animals; cocaine 45w/d naspm = 31.31 ± 5.22, n = 8 animals; cocaine re-exp = 32.89 ± 5.41, n = 12 animals; cocaine re-exp naspm = 29.74 ± 3.85, n = 10, F_4,47=10.11, p<0.0001, one-way ANOVA; n.s.>0.05 *p<0.05, **p<0.01, Bonferroni posttest).

(n) Summary showing increased sensitivity to Ro256981 of NMDAR EPSCs in rats 1 day after cocaine self-administration (saline = 0.91 ± 0.03 at 24min, n = 5 animals; cocaine = 0.74 ± 0.03 at 24min, n = 5 animals, F_26,104=7.66, p<0.0001, two-way ANOVA repeated measure; **p<0.01, Bonferroni posttest). Subsequent application of APV (50 μM) confirmed that currents were mediated by NMDARs. Inset showing example NMDAR EPSCs before and during Ro256981 application.

(o) Summary showing cue re-exposure did not affect the Ro256981 sensitivity of NMDAR EPSCs in NAcSh MSNs (saline = 0.93 ± 0.03 at 24min, n =3 animals; cocaine = 0.92 ± 0.06 at 24min, n = 5 animals; cocaine re-exp = 0.93 ± 0.05 at 24min, n = 5, F_52,260=0.50, p=0.9984, two-way ANOVA repeated measures).

(p) Example AMPAR EPSCs evoked from holding potentials of −70 mV to +50 mV with 10 mV increments.

(q) (Left) I-V curves of AMPAR EPSCs showing rectification in cocaine-trained rats on withdrawal day 45, and the rectification was abolished by cue re-exposure (saline = 52.51 ± 5.68, n = 6 animals; cocaine = 29.98 ± 3.17, n = 5 animals; cocaine re-exp = 43.93 ± 6.01, n = 4 animals, F_4,33=4.15, p=0.0078, two-way ANOVA; *p< 0.05, Bonferroni posttest). EPSC amplitudes at −70 mV were used to normalize EPSCs at other membrane potentials. (Right) Summary showing that on withdrawal day 45, the decreased rectification index in cocaine-trained rats was abolished by cue re-exposure (saline = 0.79 ± 0.051, n = 6 animals; cocaine = 0.54 ± 0.041, n = 5 animals; cocaine re-exp = 0.79 ± 0.057, n = 4 animals, F_2,12=8.06, p=0.006, one-way ANOVA; *p < 0.05, Bonferroni posttest).

(r) Diagram showing the timepoints at which the effects of cue re-exposure on silent synapses were assessed.

(s-u) EPSCs evoked at −70 mV or +50 mV by minimal stimulation (insets) over 100 trials from example recordings 2 (o) and 6 hr (p) after cue re-exposure in cocaine-trained rats, and 6 hr after re-exposure in the presence of naspm (q).

(v) Summary showing that after cue re-exposure, % silent synapse was immediately increased, remained at high levels for a few hr, and declined to basal levels by ~6 hr, and the declined % silent synapses were restored to high levels by naspm (10-min = 32.89 ± 5.404, n = 12 animals; 2hr = 37.23 ± 4.86, n = 5 animals; 4hr = 23.62 ± 7.78, n = 8 animals; 6hr = 10.91 ± 3.07, n = 12 animals; 6hr naspm = 39.47 ± 5.77, n = 7, F_4,39=5.02, p=0.0023, one-way ANOVA; *p<0.05, **p<0.01, Bonferroni posttest). The 10-min data taken from m. See Supplemental Table 1 for exact p values for all comparisons made during posthoc tests. Data presented as mean±SEM.