Intra-amygdala infusion of the N-methyl-D-aspartate receptor antagonist AP5 blocks acquisition but not expression of fear-potentiated startle to an auditory conditioned stimulus

Behav Neurosci. 1992 Jun;106(3):569-574. doi: 10.1037//0735-7044.106.3.569.


The fear-potentiated startle paradigm, in which the amplitude of the startle reflex is enhanced in the presence of a stimulus previously paired with footshock, was used to measure aversive conditioning after intra-amygdala infusion of the competitive N-methyl-D-aspartate (NMDA) receptor antagonist DL-2-amino-5-phosphonopentanoic acid (AP5). Infusion of 2.5 micrograms/side AP5 immediately before five noise-footshock pairings on each of 2 consecutive days dose-dependently blocked acquisition or consolidation of auditory fear-potentiated startle, consistent with previous results from our laboratory obtained with a visual stimulus. Somatosensory or auditory transmission deficits do not appear to be induced by intra-amygdala AP5 because rats reacted normally to footshocks and showed reliable potentiated startle expression after pretesting AP5 infusion at a dose that blocked acquisition. Together with earlier reports, these data suggest that an NMDA-dependent process localized in or near the amygdala may be necessary for the acquisition of conditioned fear across different sensory modalities.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • 2-Amino-5-phosphonovalerate / pharmacology*
  • Amygdala / drug effects*
  • Animals
  • Association Learning / drug effects
  • Auditory Perception / drug effects*
  • Brain Mapping
  • Conditioning, Classical / drug effects*
  • Dose-Response Relationship, Drug
  • Fear / drug effects*
  • Male
  • Mental Recall / drug effects*
  • Rats
  • Rats, Inbred Strains
  • Receptors, N-Methyl-D-Aspartate / drug effects*
  • Reflex, Startle / drug effects*


  • Receptors, N-Methyl-D-Aspartate
  • 2-Amino-5-phosphonovalerate