Figure 3.

Selectively bred rats display distinct differences in extinction and retention behavior. During extinction learning, bHRs appear to show facilitated within-session learning compared with controls while bLRs show a slight reduction in extinction learning (a). This is confirmed by a significant main effect of phenotype where bHR freezing levels are significantly different from both control and bLR freezing levels, which also differ from each other, with bLRs having the highest freezing (two-way repeated measures ANOVA: main effect of phenotype F(2,90)=23.67, p<0.001, post hoc tests bHRs p<0.001, bLRs p<0.005 for all; b). Extinction retention reveals stark differences in freezing behavior, with bLRs showing strongly reduced extinction retention compared with controls and bHRs showing facilitated retention compared with controls (two-way repeated-measures ANOVA followed by Bonferroni-corrected post hoc tests; c). This is confirmed by a main effect of phenotype, where all phenotypes are significantly different from each other with bLRs showing the least retention (two-way repeated-measures ANOVA: main effect of phenotype F(2,90)=34.16, p<0.001, Bonferroni-corrected post hoc tests bHR<controls p<0.001 and controls<bLR p<0.001; d). The reduced extinction learning and retention evidenced by bLR rats indicates a more PTSD-like behavioral phenotype, while bHR rats seem to be particularly resilient. (N=8 bHRs, bLRs; N=32 Controls) ***p<0.001, **p<0.01.