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.
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.
Department of Psychology, Yale University School of Medicine, New Haven, Connecticut 06508.
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Campeau
M J
MJ
Miserendino
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M
Davis
D015763:2-Amino-5-phosphonovalerate / Q000494:pharmacology*; D000679:Amygdala / Q000187:drug effects*; D000818:Animals; D001245:Association Learning / Q000187:drug effects; D001307:Auditory Perception / Q000187:drug effects*; D001931:Brain Mapping; D003214:Conditioning, Classical / Q000187:drug effects*; D004305:Dose-Response Relationship, Drug; D005239:Fear / Q000187:drug effects*; D008297:Male; D011939:Mental Recall / Q000187:drug effects*; D051381:Rats; D011919:Rats, Inbred Strains; D016194:Receptors, N-Methyl-D-Aspartate / Q000187:drug effects*; D013216:Reflex, Startle / Q000187:drug effects*
D016194:Receptors, N-Methyl-D-Aspartate; D015763:2-Amino-5-phosphonovalerate