Opioid receptors regulate the extinction of Pavlovian fear conditioning.
Rats received a single pairing of an auditory conditioned stimulus (CS) with a footshock unconditioned stimulus (US). The fear (freezing) that had accrued to the CS was then extinguished. Injection of naloxone prior to this extinction significantly impaired the development of extinction. This impairment was mediated by opioid receptors in the brain and was not observed when naloxone was injected after extinction training. Finally, an injection of naloxone on test failed to reinstate extinguished responding that had already accrued to the CS. These experiments show that opioid receptors regulate the development, but not the expression, of fear extinction and are discussed with reference to the roles of opioid receptors in US processing, memory, and appetitive motivation.
McNally
Gavan P
GP
School of Psychology, University of New South Wales, Sydney, New South Wales, Australia. g.mcnally@unsw.edu.au
Westbrook
R Frederick
RF
D000161:Acoustic Stimulation; D000818:Animals; D003214:Conditioning, Classical / Q000187:drug effects / Q000502:physiology*; D005108:Extinction, Psychological / Q000187:drug effects / Q000502:physiology*; D005239:Fear / Q000187:drug effects*; D008297:Male; D011939:Mental Recall / Q000187:drug effects; D009270:Naloxone / Q000494:pharmacology; D009292:Narcotic Antagonists / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D011957:Receptors, Opioid / Q000502:physiology*; D012153:Retention, Psychology / Q000187:drug effects
D009292:Narcotic Antagonists; D011957:Receptors, Opioid; D009270:Naloxone