The role of context in the re-extinction of learned fear.
Extinction of learned fear is both amygdala- and NMDA receptor (NMDAr)-dependent. Recent studies, however, have shown that extinction the second time (re-extinction) does not involve the amygdala and is NMDAr-independent. The present study compared the effects of context change on extinction and re-extinction in adult Sprague-Dawley rats. Experiment 1 showed that both extinction and re-extinction are context-specific with a renewal effect occurring in both cases. Experiment 2 then examined whether the transition from an NMDAr-dependent to an NMDAr-independent process was context-specific. As expected, the results showed that MK-801 (0.1 mg/kg) impaired initial extinction but did not impair re-extinction (i.e., re-extinction was found to be NMDAr-independent). A novel finding was that if re-extinction occurred in a context different from initial extinction, then MK-801 impaired re-extinction. In other words, re-extinction is NMDAr-dependent (i.e., like initial extinction) when it occurs in a different context to initial extinction. Therefore, the switch from NMDAr-dependent to NMDAr-independent extinction is both stimulus [Langton, J.M., Richardson, R. (2008). D-cycloserine facilitates extinction the first time but not the second time: An examination of the role of NMDA across the course of repeated extinction sessions. Neuropsychopharmacology, 33, 3096-3102.] and context-specific (the present study). The precise conditions that govern whether extinction requires NMDAr activation are of considerable theoretical interest and remain to be fully characterized.
Langton
Julia M
JM
School of Psychology, University of New South Wales, Sydney NSW 2052, Australia. jlangton@psy.unsw.edu.au
Richardson
Rick
R
D000679:Amygdala / Q000187:drug effects / Q000502:physiology; D000818:Animals; D001245:Association Learning / Q000187:drug effects / Q000502:physiology*; D001362:Avoidance Learning / Q000187:drug effects / Q000502:physiology; D003214:Conditioning, Classical / Q000187:drug effects / Q000502:physiology; D016291:Dizocilpine Maleate / Q000494:pharmacology; D004777:Environment; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D005108:Extinction, Psychological / Q000187:drug effects / Q000502:physiology*; D005239:Fear / Q000502:physiology*; D008297:Male; D051381:Rats; D017207:Rats, Sprague-Dawley; D016194:Receptors, N-Methyl-D-Aspartate / Q000037:antagonists & inhibitors / Q000502:physiology*; D012153:Retention, Psychology / Q000502:physiology
D018691:Excitatory Amino Acid Antagonists; D016194:Receptors, N-Methyl-D-Aspartate; D016291:Dizocilpine Maleate