title: Time-dependent involvement of the dorsal hippocampus in trace fear conditioning in mice.
abstract: Hippocampal and amygdaloid neuroplasticity are important substrates for Pavlovian fear conditioning. The hippocampus has been implicated in trace fear conditioning. However, a systematic investigation of the significance of the trace interval has not yet been performed. Therefore, this study analyzed the time-dependent involvement of N-methyl-D-aspartate (NMDA) receptors in the dorsal hippocampus in one-trial auditory trace fear conditioning in C57BL/6J mice. The NMDA receptor antagonist APV was injected bilaterally into the dorsal hippocampus 15 min before training. Mice were exposed to tone (conditioned stimulus [CS]) and footshock (unconditioned stimulus [US]) in the conditioning context without delay (0 s) or with CS-US (trace) intervals of 1-45 s. Conditioned auditory fear was determined 24 h after training by the assessment of freezing and computerized evaluation of inactivity in a new context; 2 h later, context-dependent memory was tested in the conditioning context. NMDA receptor blockade by APV markedly impaired conditioned auditory fear at trace intervals of 15 s and 30 s, but not at shorter trace intervals. A 45-s trace interval prevented the formation of conditioned tone-dependent fear. Context-dependent memory was always impaired by APV treatment independent of the trace interval. The results indicate that the dorsal hippocampus and its NMDA receptors play an important role in auditory trace fear conditioning at trace intervals of 15-30-s length. In contrast, NMDA receptors in the dorsal hippocampus are unequivocally involved in contextual fear conditioning independent of the trace interval. The results point at a time-dependent role of the dorsal hippocampus in encoding of noncontingent explicit stimuli. Preprocessing of long CS-US contingencies in the hippocampus appears to be important for the final information processing and execution of fear memories through amygdala circuits.
authors.affiliation: Department of Molecular Neuroendocrinology, Max Planck Institute for Experimental Medicine, Goettingen, Germany. ilga.misane@usask.ca
authors.forename: Ilga
authors.initials: I
authors.lastname: Misane
authors.forename: Philip
authors.initials: P
authors.lastname: Tovote
authors.forename: Michael
authors.initials: M
authors.lastname: Meyer
authors.forename: Joachim
authors.initials: J
authors.lastname: Spiess
authors.forename: Sven Ove
authors.initials: SO
authors.lastname: Ogren
authors.forename: Oliver
authors.initials: O
authors.lastname: Stiedl
mesh_terms: D015763:2-Amino-5-phosphonovalerate / Q000494:pharmacology; D000161:Acoustic Stimulation; D000679:Amygdala / Q000187:drug effects / Q000502:physiology; D000818:Animals; D003213:Conditioning, Psychological / Q000187:drug effects / Q000502:physiology*; D003463:Cues; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D005239:Fear / Q000187:drug effects / Q000502:physiology*; D018698:Glutamic Acid / Q000378:metabolism; D006624:Hippocampus / Q000187:drug effects / Q000502:physiology*; D007858:Learning / Q000187:drug effects / Q000502:physiology*; D008297:Male; D008568:Memory / Q000187:drug effects / Q000502:physiology*; D051379:Mice; D008810:Mice, Inbred C57BL; D009434:Neural Pathways / Q000187:drug effects / Q000502:physiology; D009473:Neuronal Plasticity / Q000187:drug effects / Q000502:physiology; D016194:Receptors, N-Methyl-D-Aspartate / Q000187:drug effects / Q000378:metabolism*; D009435:Synaptic Transmission / Q000187:drug effects / Q000502:physiology; D013997:Time Factors
chemical_list: D018691:Excitatory Amino Acid Antagonists; D016194:Receptors, N-Methyl-D-Aspartate; D018698:Glutamic Acid; D015763:2-Amino-5-phosphonovalerate