title: Fear memories induce a switch in stimulus response and signaling mechanisms for long-term potentiation in the lateral amygdala.
abstract: Activity-dependent modification of synapses is fundamental for information storage in the brain and underlies behavioral learning. Fear conditioning is a model of emotional memory and anxiety that is expressed as an enduring increase in synaptic strength in the lateral amygdala (LA). Here we analysed synaptic plasticity in the rat cortico-LA pathway during maintenance of fear memory. We show for the first time that the stimulus frequency for synaptic potentiation is switched during maintenance of fear memory, and the underlying signaling mechanisms are altered in the cortico-LA pathway. In slices from fear-conditioned animals, high-frequency stimulation-induced (HFS) long-term potentiation (LTP) was attenuated, whereas low-frequency stimulation (LFS) elicited a long-lasting potentiation. HFS generates robust LTP that is dependent on N-methyl-d-aspartate receptor (NMDAR) and L-type voltage-gated calcium channel (VGCC) activation in control animals, whereas in fear-conditioned animals HFS LTP is NMDAR- and VGCC-independent. LFS-LTP is partially NMDAR-dependent, but VGCCs are necessary for potentiation in fear memory. Collectively, these results show that during maintenance of fear memory the stimulus requirements for amygdala afferents and critical signaling mechanisms for amygdala synaptic potentiation are altered, suggesting that cue-engaged synaptic mechanisms in the amygdala are dramatically affected as a result of emotional learning.
authors.affiliation: Department of Pharmacology and Toxicology, The University of Texas Medical Branch, 301 University Blvd., Galveston, Texas, 77555-1031, USA. bwschroe@utmb.edu
authors.forename: Bradley W
authors.initials: BW
authors.lastname: Schroeder
authors.forename: Patricia
authors.initials: P
authors.lastname: Shinnick-Gallagher
mesh_terms: D015763:2-Amino-5-phosphonovalerate / Q000494:pharmacology; D000679:Amygdala / Q000187:drug effects / Q000502:physiology* / Q000528:radiation effects; D000704:Analysis of Variance; D000818:Animals; D001522:Behavior, Animal; D002121:Calcium Channel Blockers / Q000494:pharmacology; D003214:Conditioning, Classical / Q000187:drug effects / Q000502:physiology; D004307:Dose-Response Relationship, Radiation; D004347:Drug Interactions; D004558:Electric Stimulation / Q000379:methods; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D019706:Excitatory Postsynaptic Potentials / Q000187:drug effects / Q000528:radiation effects; D005239:Fear / Q000502:physiology*; D017774:Long-Term Potentiation / Q000187:drug effects / Q000502:physiology* / Q000528:radiation effects; D008297:Male; D008568:Memory / Q000187:drug effects / Q000502:physiology*; D009434:Neural Pathways / Q000187:drug effects / Q000502:physiology / Q000528:radiation effects; D009473:Neuronal Plasticity / Q000187:drug effects / Q000502:physiology* / Q000528:radiation effects; D009553:Nimodipine / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D013216:Reflex, Startle / Q000502:physiology
chemical_list: D002121:Calcium Channel Blockers; D018691:Excitatory Amino Acid Antagonists; D009553:Nimodipine; D015763:2-Amino-5-phosphonovalerate