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Mécanismes neurobiologiques et comportementaux impliqués dans l'expression de la peur récente et ancienne à un contexte chez le rat

Abstract : At remote delays following contextual fear conditioning in rodents, generalization of fear responses is usually described, as fear responses are elicited by exposure to a context different from the one in which footshocks were delivered. This generalization has been proposed to rely on the degradation and/or transformation of the memory trace due to systemic consolidation. The latter corresponds to the time-dependent reorganization of structures implicated in contextual fear expression, from networks involving the hippocampus to mainly cortical networks. However, other studies suggest that changes in defensive behaviors’ expression tied to fear and anxiety might take place in the time period following a fear conditioning experience. Indeed, an incubation of fear responses, that is an overall increase in fear responses following contextual fear conditioning, has repeatedly been reported. Such changes in the processing of emotionally relevant information might represent an alternative explanation of a time-dependent generalization of fear responses. Using immediate early genes imaging and behavioral assessment, our studies aimed at disentangling the processes supporting fear generalization over time. Our results suggest that under some circumstances, changes in the fear responses’ specificity might less be due to the dynamics of a memory system supporting the context representation than to alterations attributable to emotional information processing and/or expression. They point out dissociations in the latter changes between animals conditioned to a foreground or a background context. Consistent with our observation of a preserved detailed context memory trace, they also suggest that changes in the brain networks supporting the expression of a remotely acquired contextual fear might not reflect a time-dependent hippocampal-independency. Rather, the observed reorganization of neuronal networks might sustain changes in the associative and / or emotional information processing evoked by context exposure. Altogether, our results point out the need to take account of the high complexity of information processing leading to the onset of fear responses, when trying to infer the quality of a contextual representation on the basis of fear discrimination between contexts.
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Submitted on : Thursday, November 7, 2013 - 3:47:11 PM
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Marc-Antoine Muller. Mécanismes neurobiologiques et comportementaux impliqués dans l'expression de la peur récente et ancienne à un contexte chez le rat. Neurosciences [q-bio.NC]. Université de Strasbourg, 2012. Français. ⟨NNT : 2012STRAJ131⟩. ⟨tel-00881141⟩

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