THIP injection into the MD attenuates fear extinction. (A) THIP injection (50 μM) into the MD (empty circles, n = 11) 30 min before extinction increased freezing levels in both extinction learning, and a day after that in the recall test compared with the mice that received vehicle injection into the MD (filled circles, n = 7), ↑, injection time point. (B) Normalizing within-session extinction to percentage of initial freezing levels of each group shows a difference in extinction rate between the two groups. (C and D) There was no difference between the two groups in the locomotion or anxiety level. Data are means ± SEM.