Prior contextual fear learning makes the ACC-to-BLA connectivity necessary for recent memory.

(A and B) To investigate the involvement of the ACC descending pathway to the BLA in the retention of recent and remote contextual fear memories, the ACC was injected with rAAV5/CamKIIa-eNpHR3.0-mCherry-WPRE or rAAV5/CamKIIa-mCherry-WPRE. Optic fibers were implanted above the BLA. (C) Representative micrograph showing the expression of AAV-mCherry in the ACC and its terminals in the BLA. Scale bars, 300 and 20 μm, respectively. (D) The optogenetic inhibition of ACC axon terminals in the BLA affected the retention of recent fear memory only in animals that had undergone another contextual fear learning previously (1-way ANOVA, F(2,23) = 9.90, p = 0.0008, η2 = 0.4628; Tukey: CtxA-CtxB eNpHR3.0-mCherry n = 8 vs. CtxA-CtxB control-mCherry n = 8, p = 0.0055; CtxA-CtxB eNpHR3.0-mCherry vs. shock-CtxB eNpHR3.0-mCherry n = 10, p = 0.0010; CtxA-CtxB control-mCherry vs. shock-CtxB eNpHR3.0-mCherry, p = 0.8629). (E) Freezing to another different context was lower in rats where this context was previously paired to the US (remote fear memory) (1-way ANOVA, F(2,23) = 5.269, p = 0.0131, η2 = 0.3142; Tukey: CtxA-CtxB eNpHR3.0-mCherry vs. CtxA-CtxB control-mCherry p = 0.0098; CtxA-CtxB eNpHR3.0-mCherry vs. shock-CtxB eNpHR3.0-mCherry, p = 0.3203; CtxA-CtxB control-mCherry vs. shock-CtxBeNpHR3.0-mCherry, p = 0.1521), thus showing that optogenetic inhibition of the ACC-to-BLA pathway also affected the retention of remote memory. **P P S5 Data. ACC, anterior cingulate cortex; BLA, basolateral amygdala; US, unconditioned stimulus.