Block of gamma-aminobutyric acid-A receptor insertion in the amygdala impairs extinction of conditioned fear.
BACKGROUND
Extinction is a complex phenomenon but generally is regarded as a new inhibitory learning that suppresses the original memory. However, how or from where the inhibition originates remains to be determined. In the present study, we examine whether increase in the expression of gamma-aminobutyric acid (GABA)(A) receptors in the amygdala is required for extinction by employing cell-permeable TAT-conjugated peptide (TAT)-GABA receptor-associated protein (GABARAP) inhibitory peptide to block GABA(A) receptor insertion.


METHODS
Retention of fear memory was assessed with fear-potentiated startle paradigm. Whole cell patch clamp recordings were performed to record miniature inhibitory postsynaptic current (mIPSC). Western blotting analysis was used to measure the expression of gephyrin, beta2, and gamma2 subunits of GABA(A) receptor.


RESULTS
Fear conditioning decreased frequency and amplitude of mIPSC and surface protein levels of beta2 and gamma2 subunits of GABA(A) receptor. Extinction training, by contrast, reversed the decreased frequency and amplitude of mIPSC and surface protein levels of gephyrin and beta2 subunit of GABA(A) receptor. Disruption of GABARAP-GABA(A) receptor interaction in the amygdala with GABARAP inhibitory peptide blocked N-methyl-D-aspartate-mediated GABA(A) receptor insertion in the amygdala. Importantly, it also blocked extinction-induced increase in the frequency and amplitude of mIPSCs, and the reduction of fear-potentiated startle.


CONCLUSIONS
GABA(A) receptor insertion in the amygdala contributes a significant part to the extinction of fear memory.
Lin
Hui-Ching
HC
Institute of Basic Medical Sciences and Department of Pharmacology, Center for Gene Regulation and Signal Transduction Research, National Cheng Kung University, Tainan, Taiwan.
Mao
Sheng-Chun
SC
Gean
Po-Wu
PW
D015763:2-Amino-5-phosphonovalerate / Q000494:pharmacology; D018750:6-Cyano-7-nitroquinoxaline-2,3-dione / Q000494:pharmacology; D000679:Amygdala / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D000704:Analysis of Variance; D000818:Animals; D019921:Biotinylation / Q000379:methods; D003214:Conditioning, Classical / Q000187:drug effects / Q000502:physiology*; D004305:Dose-Response Relationship, Drug; D004597:Electroshock / Q000009:adverse effects; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D005108:Extinction, Psychological / Q000187:drug effects / Q000502:physiology*; D005239:Fear / Q000187:drug effects / Q000502:physiology*; D058787:GABA-A Receptor Antagonists; D008297:Male; D018782:Maze Learning / Q000187:drug effects / Q000502:physiology; D008869:Microtubule-Associated Proteins / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000378:metabolism; D055369:Miniature Postsynaptic Potentials / Q000187:drug effects / Q000502:physiology; D009474:Neurons / Q000187:drug effects / Q000502:physiology; D018408:Patch-Clamp Techniques / Q000379:methods; D010455:Peptides / Q000494:pharmacology; D021122:Protein Subunits / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D011963:Receptors, GABA-A / Q000737:chemistry / Q000502:physiology; D026941:Sodium Channel Blockers / Q000494:pharmacology; D013779:Tetrodotoxin / Q000494:pharmacology
D018691:Excitatory Amino Acid Antagonists; D058787:GABA-A Receptor Antagonists; C502186:GABARAP protein, rat; D008869:Microtubule-Associated Proteins; D010455:Peptides; D021122:Protein Subunits; D011963:Receptors, GABA-A; D026941:Sodium Channel Blockers; D013779:Tetrodotoxin; D018750:6-Cyano-7-nitroquinoxaline-2,3-dione; D015763:2-Amino-5-phosphonovalerate