Figure 2. Auditory cued fear conditioning training, memory, extinction and spontaneous recovery tests in euthyroid and adult-onset hypothyroid rats.

(A) Scheme showing the experimental design for Experiment 2. Shadowed areas indicate periods of animal manipulations. (B) Conditioning session. No differences were found in neither pre-shock nor post-shock periods. (C) Auditory cued fear test session 2 days after conditioning. H animals showed a significant increase in conditioned behavior. (D) Extinction sessions for the auditory cue fear memory. The extinction of fear memory was delayed in H animals. (E) Re-exposition to the tone for the assessing of spontaneous recovery of fear memory. H rats showed a remarkable increase (four-fold) in fear response as compared to E rats. Bars show mean ± SEM. *, p<0.05; **, p<0.01; NS, no significant. n = 7 for E rats and n = 8 for H rats.