Enhanced retrieval of unpleasant memories influenced by shock controllability, shock sequence, and rat strain.

The propensity to recall unpleasant events may be related to depression and posttraumatic stress disorder. This study examined the extent to which the recall of a previously unpleasant event (i.e., passive avoidance training) may be influenced by another aversive event. The other aversive event was tail shock. Since the Wistar Kyoto (WKY) rat strain has been proposed as an animal model of depressive behavior, this study was conducted with WKY and Wistar rats. Parameters manipulated included shock controllability, shock sequence (i.e., tail shock before avoidance training versus tail shock after training), and rat strain. Performance of the passive avoidance (PA) response was greater in WKY rats. Exposure to inescapable tail shock was related to greater PA performance compared to exposure to escapable or no-shock treatments. Tail shock prior to PA training led to a greater recall of the PA response. The magnitude of the PA response was influenced by the rat strain, shock controllability, and shock sequence. The applicability of these data to the memory bias phenomenon in depression is discussed.