Fig. 4: Absence of CUS-induced generalization and the importance of contextual stimulus during extinction in context-unpaired rats.

Schematic representation of the experimental design (A). The control group (CTR) is always represented in green tones, and the stressed group (CUS) in pink tones. The unpaired protocol (B) demonstrates that the defensive response of unpaired CTR and CUS was context-dependent, as low freezing rates occurred in the neutral arena (NA); however, the unpaired CUS group showed higher freezing than the CTR group during the retrieval test (B’), extinction test (B”) and extinction sessions (B”’). Face to returning to the conditioning arena (CA) during the extinction test, unpaired CTR and CUS showed higher freezing, indicating that the extinction depends on successive re-exposures to the paired arena, although the time-lapse also had a negligible effect. CUS animals presented an increased freezing absence ratio (%) on the first extinction protocol day similar CTR group (C); moreover, CTR and CUS groups showed higher freezing absence ratio (%) during extinction test (C’ and C”). Results are represented as mean ± SEM (n = 5–6 animals/group in B, B’, B”, B”‘; n = 6–8 animals/group in C, C’, C”). In B, * (p < 0.05) vs. their respective group in the post-US period, and # (p < 0.05) vs. their respective group in the pre-US period. In B’, * (p < 0.05) vs. CTR group. In B”, ** (p < 0.01) vs. CTR group. In B”‘, #, ## and ### (p < 0.05, p < 0.01 and p < 0.001, respectively) vs. their respective CTR group. In C, **** (p < 0.0001) vs. their respective group in first. In C’, *** (p < 0.001) vs. CTR group in first. In C”, **** (p < 0.0001) vs. CUS group in first.