Evidence for state-dependent retrieval in conditioned place aversion.

State-dependent retrieval (SDR) in conditioned place aversion (CPA) was observed using Long-Evans male rats, with three different aversive drugs injected ip: lithium chloride (31.8 mg/kg), FG 7142 (10 mg/kg), and naloxone (5 mg/kg). Experiment 1 showed that state-dependent dissociation was complete with lithium chloride following two conditioning trials, but disappeared when the number of learning sessions was increased. Experiment 2 showed that following two conditioning trials, such complete state-dependent dissociations were also observed when FG 7142 or naloxone were used during conditioning. The results of this study showed that the expression of SDR is not monotonic in CPA paradigm but depends on the stage of learning. In addition, SDR can be observed following administration of a variety of drugs known to produce CPA, but differing in their neurochemical targets and the nature of the aversive effects they induce. Finally, these results are discussed with regard to what is known about SDR in other paradigms.