title: Reversible plasticity of fear memory-encoding amygdala synaptic circuits even after fear memory consolidation.
abstract: It is generally believed that after memory consolidation, memory-encoding synaptic circuits are persistently modified and become less plastic. This, however, may hinder the remaining capacity of information storage in a given neural circuit. Here we consider the hypothesis that memory-encoding synaptic circuits still retain reversible plasticity even after memory consolidation. To test this, we employed a protocol of auditory fear conditioning which recruited the vast majority of the thalamic input synaptic circuit to the lateral amygdala (T-LA synaptic circuit; a storage site for fear memory) with fear conditioning-induced synaptic plasticity. Subsequently the fear memory-encoding synaptic circuits were challenged with fear extinction and re-conditioning to determine whether these circuits exhibit reversible plasticity. We found that fear memory-encoding T-LA synaptic circuit exhibited dynamic efficacy changes in tight correlation with fear memory strength even after fear memory consolidation. Initial conditioning or re-conditioning brought T-LA synaptic circuit near the ceiling of their modification range (occluding LTP and enhancing depotentiation in brain slices prepared from conditioned or re-conditioned rats), while extinction reversed this change (reinstating LTP and occluding depotentiation in brain slices prepared from extinguished rats). Consistently, fear conditioning-induced synaptic potentiation at T-LA synapses was functionally reversed by extinction and reinstated by subsequent re-conditioning. These results suggest reversible plasticity of fear memory-encoding circuits even after fear memory consolidation. This reversible plasticity of memory-encoding synapses may be involved in updating the contents of original memory even after memory consolidation.
authors.affiliation: School of Biological Sciences, College of Natural Sciences, Seoul National University, Seoul, Korea.
authors.forename: Ingie
authors.initials: I
authors.lastname: Hong
authors.forename: Jihye
authors.initials: J
authors.lastname: Kim
authors.forename: Junuk
authors.initials: J
authors.lastname: Lee
authors.forename: Sungmo
authors.initials: S
authors.lastname: Park
authors.forename: Beomjong
authors.initials: B
authors.lastname: Song
authors.forename: Jeongyeon
authors.initials: J
authors.lastname: Kim
authors.forename: Bobae
authors.initials: B
authors.lastname: An
authors.forename: Kyungjoon
authors.initials: K
authors.lastname: Park
authors.forename: Hyun Woo
authors.initials: HW
authors.lastname: Lee
authors.forename: Seungbok
authors.initials: S
authors.lastname: Lee
authors.forename: Hyun
authors.initials: H
authors.lastname: Kim
authors.forename: Sang-Hyun
authors.initials: SH
authors.lastname: Park
authors.forename: Khee Dong
authors.initials: KD
authors.lastname: Eom
authors.forename: Sukwon
authors.initials: S
authors.lastname: Lee
authors.forename: Sukwoo
authors.initials: S
authors.lastname: Choi
mesh_terms: D000679:Amygdala / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D000818:Animals; D003214:Conditioning, Classical / Q000502:physiology; D018683:Excitatory Amino Acid Agents / Q000494:pharmacology; D019706:Excitatory Postsynaptic Potentials / Q000502:physiology; D005108:Extinction, Psychological / Q000502:physiology; D005239:Fear / Q000502:physiology; D005998:Glycine / Q000031:analogs & derivatives / Q000494:pharmacology; D017774:Long-Term Potentiation / Q000502:physiology; D008297:Male; D008568:Memory / Q000502:physiology*; D009434:Neural Pathways / Q000502:physiology; D009473:Neuronal Plasticity / Q000502:physiology*; D018408:Patch-Clamp Techniques; D051381:Rats; D017207:Rats, Sprague-Dawley; D012118:Resorcinols / Q000494:pharmacology; D055366:Synaptic Potentials / Q000502:physiology; D009435:Synaptic Transmission / Q000502:physiology*; D013788:Thalamus / Q000166:cytology / Q000187:drug effects / Q000502:physiology
chemical_list: D018683:Excitatory Amino Acid Agents; D012118:Resorcinols; C079215:3,5-dihydroxyphenylglycine; D005998:Glycine