BRIEF REP. ORTS .... Effects of Traumatic Stress on Defensive Burying: An Alternative Test of the Learned Helplessness Animal Model of Depression and Enhanced Retrieval of Unpleasant Memories J. Bruce Overmier, Robert Murison, Toril Taklo, and Randi Espelid i m | Key Words: Learned helplessness, defensive burying, memory, fear, stress Introduction Recently, two conceptually important papers have appeared in Biological Psychiatry (Kumar and Karanth 1991, 1993) that claim to have demonstrated "that learned helplessness primed the re- trieval of unpleasant memory in rats (and) is comparable to the qualitative shift that is seen in the retrieval process in clinical depression" (Kumar 1991, p 499). An unequivocal demonstration of such is an important step in the modelling process because selective, enhanced recall for unpleasant memories appears to be characteristic of those suffering depression (Dalgleish and Watts 1990; Willner 1985) and posttraumatic stress disorders (Foa et al Inn ~.,,1 k^. IAk,~m~tl a...t .~r, lmal aAalof,~i h~r/YPhutl2 and Antelman 1993). [ndeed, such a demonstration could provide an experimental basis for observed "emotive biasing" so charac- teristic of these two disorders (Adamec 1991; Mineka and Sutton 1992; Pitman et al 1993). Both of the intriguing demonstrations by Kumar and Karanth relied on rats showing increased passive avoidance (i.e., nonre- sponse or slowed response) following treatment with inescapable shocks relative to those experiencing equal escapable shocks or no shocks [and parallel a similar earlier finding by l.ashley et al (1987) who used less shock]. A concern about these demonstra- From the Department of Biological and Medical Psychology, Universtty of Bergen, Norway. Address reprint ~q~sts to Robert Munson, Biological & Medical Psychology, University of Bergen,/]wstadveien 21, N-5009 Bergen, NORWAY. This research was supported by grants from NAVF and NSF JBO's cament addressis Department of Psychology, University of Minnesota. ~ p o h s . MN. Recnived June 29,1993; revised March 28.1994. © 1994 Society of Biological Psychiatry tions arises, however, because slowed or nonresponding is itself the primary characteristic of the learned helplessness phenomenon (Overmier and Seligman 1967)! Hence the reduced behavior Kumar and Kaxanth took as evidence of the symptom of aug- merited memory for aversive events could just as well have been merely a direct ret~ection of the primary reduction in behavior that characterizes learned helplessness. Kumar and Karanth (1993), aware of this possible artifactual bias for their result, u.~d a choice procedure in their second study that, they argued, obviated our concern about passive-avoidance tests; but, then they go on to recognize that other learned.helplessness-induced changes (such as increased preference for the sucrose reinforcer;, see Dess 1992) could explain their result without reference to effects on retention of the passive avoidance. We believed that Kumar and Karanth's inference might well he correct, and we set out to confirm their result in a paradigm in which such learned helplessness enhanced responsivity to a prior aversive experience would be manifest through increased defen- sive activity. We briefly report here an experiment that we believe (1) confirms the earlier Kumar and Karanth reports and interpreta- tion, but (2) is not amenable to explanation in terms of the primary response--deficit symptom of learned helplessness. To this end, we used a species-characteristic acuve-defenszve behavior to assess the potentiating effect of traumatic stress (as in learned helpless- hess) on persistence of responding to a prior aversive experience (Pinel and Treit 1978). Methods Sixteen M¢llegaard Sprague-Dawley rats approximately 100 days of age were tirst habituated 1 hr per day for 3 days to a20 X 60cm 0006-3223/94/$07 00