Behavioral and Neurobiological Assessments of Predator-Based Fear Conditioning and Extinction

Abstract

Shock, immobilization, and exposure to predator-related stimuli have all been used to study fear conditioning in rodents, but they have never been used in conjunction in a single study. Experi-ment 1 compared the effects of these three reinforcers, alone and in various combinations, on the expression of long-term conditioned fear memory and extinction in adult male rats. Whereas foot shock conditioning, alone, was rapidly extinguished; the combination of immobilization and cat exposure, or all 3 stimuli together, produced a significant increase in the magnitude of fear condi-tioning and greater resistance to extinction, which persisted for at least 5 weeks post-training (p < 0.05). Experiment 2 assessed the role of the hippocampus in predator-based context and cued fear conditioning. Pharmacological suppression of hippocampal activity during fear conditioning pro-duced a selective impairment of contextual, but not cued, fear memory. Experiment 3 investigated the effects of sleep deprivation prior to fear conditioning on the expression of fear memory. This experiment demonstrated that pre-training sleep deprivation blocked the expression of contex-tual (hippocampal-dependent), but not cued (hippocampal-independent), fear memory. Overall, this series of experiments has extended the use of predator exposure in conjunction with conven-tional reinforcers, such as foot shock and immobilization, to advance our understanding of the neurobiology of traumatic memory.