Figure 8.

Differential activation of Imp and IN during fear acquisition, extinction, and extinction retrieval. A, Percentage of freezing during each presentation of the CS for the conditioned (CS–US paired) fear expression (red circles), fear extinction (blue circles), and unconditioned (CS-only) control (open black circles) groups. B, Representative photomicrographs of Imp and IN expressing Zif268 in unconditioned control, fear expression, and fear extinction groups in different fear states. C, In the Imp, both the fear expression (red histogram) and fear extinction (blue histogram) groups showed a greater number of Zif268-positive cells relative to unconditioned mice (white histogram). D, In the IN, the fear extinction group showed a greater increase in the number of Zif268-positive cells relative to unconditioned and fear expression groups. E, Between-session extinction freezing changes (measured as fear expression during extinction retrieval minus fear expression during fear recall) in conditioned (black histogram) and unconditioned (white histogram) groups. F, No difference in the number of Zif268-positive cells was observed in the Imp between conditioned and unconditioned mice during retrieval of extinction. G, The fear extinction group displayed an increased number of Zif268-positive cells in the IN relative to unconditioned mice during retrieval of extinction. cond., Fear expression; ext., fear extinction; retr., extinction retrieval; uncond., unconditioned. *p < 0.05, **p < 0.01, fear expression versus unconditioned, ^#p < 0.05, ^##p < 0.01, fear extinction versus unconditioned, ^§p < 0.05 fear extinction versus fear expression, ^ap < 0.05 within-group CS presentation versus first CS presentation. Scale bars: B, left, 100 μm; B, middle and right, 40 μm.