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J Exp Psychol Anim Behav Process. 2003 Jul;29(3):222-32.

Anterograde amnesia for Pavlovian fear conditioning and the role of one-trial overshadowing: effects of preconditioning exposures to morphine in the rat.

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School of Psychology, University of New South Wales, Sydney, New South Wales 2052, Australia.


Four experiments studied anterograde deficits in Pavlovian fear conditioning following prolonged exposure to the mu-opioid receptor agonist morphine. Injections of morphine produced temporally graded anterograde amnesia characterized by deficits in contextual and conditioned-stimulus (CS) conditioning 1 or 7 days and selective impairment in CS conditioning 21 days after last injection. This anterograde deficit in conditioning did not recover across a retention interval, was absent when rats were tested immediately after conditioning, and required the presence of an auditory CS. These results suggest that anterograde deficits in Pavlovian fear conditioning emerged from differences in susceptibility to 1-trial overshadowing of context by CS.

[Indexed for MEDLINE]

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