Figure 1.
3,4-Methylenedioxymethamphetamine (MDMA) treatment before extinction training reduced conditioned freezing 24 h later. Unless otherwise noted, all treatments were given intraperitoneally 30 min before extinction training on Day 3. (a) Primary behavioral procedure for exploring MDMA's effect on fear extinction. (b) MDMA dose-dependently decreased freezing to the tone during extinction training across four CS tones (F(3,30)=4.58, P=0.0093 for main effect of dose; n=8–10 per group). (c) Animals previously extinguished under MDMA exhibited dose-dependent reductions in freezing to four CS tones 24 h later (F(3,30)=8.30, P=0.0004 for main effect of dose; n=8–10 per group). (d) MDMA did not affect freezing before the first CS-tone re-exposure (F(3,30)=0.67, P=0.5742 for main effect of treatment; n=8–10/group), but 7.8 mg kg−1 MDMA increased locomotor activity in a 10- min test (F(2,26)=3.62, P=0.0411 for main effect of dose; n=9–10 per group). (e) MDMA (7.8 mg kg−1) administered immediately following extinction training on Day 3 did not affect freezing in response to four CS tones the following day (t(10)=1.19, P=0.26 for effect of treatment; n=6 per group). Bars represent mean±s.e. values of %freezing. *P<0.05. CS, conditioned stimulus; US, unconditioned stimulus.