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.
Campeau
S
S
Department of Psychology, Yale University School of Medicine, New Haven, Connecticut 06508.
Miserendino
M J
MJ
Davis
M
M
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