Figure 4.

Neurons of the infralimbic cortex are involved in the acquisition, but not the expression, of stress resiliency displayed by mice previously housed in EE. The diagram depicting experimental groups and second study design is shown in a. Resiliency to SD was measured by behavioral responses to the elevated zero maze (EZM, b), light/dark box (L/D, c), tail-suspension test (TST, d), forced-swim test (FST, e), and social interaction task (SI, f–i). Mice given IL lesions before EE showed a strong anxiety response to SD and spent significantly more time in the dark chamber of the light/dark box (c) compared with all other treatment groups. IL lesions before EE significantly increased depressive-like behaviors after SD; mice spent significantly more time immobile in the tail-suspension test (d) and forced-swim test (e) and spent significantly less time with the aggressor mice in the social interaction task (f, g) compared with all other treatment groups. IL lesions had no effect on behavior in non-defeated groups. In defeated groups, lesions made after EE had no effect on behavioral response to SD. ILinf, IL Infusion; ILx, IL lesion; Ms, mouse; Obj, object. Results are expressed as mean ± SEM (n = 8 per group). Two-way ANOVA followed by Bonferroni's post hoc test. Bonferroni's test: *p < 0.05; **p < 0.01.