Disruption of AMPA receptor endocytosis impairs the extinction, but not acquisition of learned fear.
Synaptic plasticity in the form of long-term potentiation (LTP) plays a critical role in the formation of a Pavlovian fear association. However, the role that synaptic plasticity plays in the suppression of a learned fear response remains to be clarified. Here, we assessed the role that long-term depression (LTD) plays in the acquisition, expression, and extinction of a conditioned fear response. We report that blockade of LTD with a GluR2-derived peptide (Tat-GluR2(3Y); 1.5 micromol/kg, i.v.) that blocks regulated alpha-amino-3-hydroxy-5-methyl-isoxazole-4-propionic acid (AMPA) receptor endocytosis during an initial extinction training session disrupted both the expression and recall of extinction learning. A similar impairment of extinction during training, but not recall, was observed when NMDA receptor-dependent LTD was inhibited through the selective blockade of NMDA NR2B receptors with Ro 25-6981. In contrast, blockade of LTD with Tat-GluR2(3Y) during fear conditioning or during a fear recall test did not effect the expression or recall of either contextual or cue-induced conditioned fear. Similarly, administration of Tat-GluR2(3Y) prior to an extinction recall test did not affect spontaneous recovery or rate of re-extinction in previously extinguished rats. These data demonstrate that AMPA receptor endocytosis does not mediate acquisition or expression of conditioned fear, but may play a role in the extinction of fear memories. Furthermore, these findings suggest that LTD may be a molecular mechanism that facilitates the selective modification of a learned association while leaving intact the ability to form a new memory.
Dalton
Gemma L
GL
Department of Psychology, University of British Columbia, Vancouver, BC, Canada.
Wang
Yu Tian
YT
Floresco
Stan B
SB
Phillips
Anthony G
AG
D000818:Animals; D001362:Avoidance Learning / Q000187:drug effects / Q000502:physiology*; D001921:Brain / Q000187:drug effects / Q000378:metabolism*; D003213:Conditioning, Psychological / Q000187:drug effects / Q000502:physiology; D004705:Endocytosis / Q000187:drug effects / Q000502:physiology*; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D005108:Extinction, Psychological / Q000187:drug effects / Q000502:physiology*; D005239:Fear / Q000187:drug effects / Q000502:physiology*; D018698:Glutamic Acid / Q000378:metabolism; D036881:Long-Term Synaptic Depression / Q000187:drug effects / Q000502:physiology*; D008297:Male; D010446:Peptide Fragments / Q000737:chemistry / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D018091:Receptors, AMPA / Q000037:antagonists & inhibitors / Q000187:drug effects / Q000378:metabolism*; D016194:Receptors, N-Methyl-D-Aspartate / Q000037:antagonists & inhibitors / Q000378:metabolism; D009435:Synaptic Transmission / Q000187:drug effects / Q000502:physiology
D018691:Excitatory Amino Acid Antagonists; C121001:NR2B NMDA receptor; D010446:Peptide Fragments; D018091:Receptors, AMPA; D016194:Receptors, N-Methyl-D-Aspartate; D018698:Glutamic Acid; C104722:glutamate receptor ionotropic, AMPA 2