D-cycloserine facilitates context-specific fear extinction learning

D-Cycloserine (I)CS) may facilitate fear extinction learning, but the behavioral consequences and mechanisms behind this effect are not well understood at present. In this paper, we re-analyze data from previously reported null result experiments and find that rats showing above-median extinction learning during DCS treatment benefited from the drug, whereas rats showing below-median (and in this case little) extinction learning did not. Two additional experiments found that DCS facilitated extinction learning when specifically combined with a moderate, but not a small, number of extinction trials. DCS thus facilitates extinction learning only if the behavioral procedure first engages the extinction learning process. The benefits of the drug, however, were specific to the context in which extinction was learned-i.e., DCS did not prevent or influence the renewal of fear observed when the extinguished cue was tested in the original conditioning context. (C) 2008 Elsevier Inc. All rights reserved.