Amygdala modulation of hippocampus-dependent memories and the influence on immediate early gene expression

Evidence suggests that the basolateral nuclei of the amygdala (BLA) modulate emotional memory storage in other brain regions (Cahill and McGaugh, 1998; McGaugh, 2004 for reviews). Consistent with the literature, this thesis reports behavioral and molecular findings to support the claim that the BLA influences memory storage in the hippocampus.;Here we demonstrate that post-training inactivation of the BLA with muscimol, a GABAA agonist, impairs memory for a recently explored context and memory for contextual fear conditioning. This is evidence that the BLA modulates both "non-emotional" (i.e. not aversively motivated) and emotional hippocampus-dependent memories (Barrientos, O'Reilly, Rudy, 2002; Maren, Aharanov, Fanselow, 1997). We also demonstrate that intra-BLA norepinephrine enhances memory for contextual fear conditioning. However, preexposure to the conditioning context obscures the memory modulatory effects of both intra-BLA norepinephrine and muscimol on contextual fear conditioning. This finding suggests that the BLA is modulating the representation of context for contextual fear conditioning.;Although we, and others, provide behavioral evidence to suggest that the BLA modulates hippocampus-dependent memories, there has been little investigation into the underlying molecular mechanisms. Here we investigate the hypothesis that the BLA influences experience-induced immediate early gene (IEG) expression in the hippocampus. We demonstrate that BLA inactivation with muscimol prior to contextual fear conditioning reduces expression of Arc (activity regulated cytoskeletal-associated protein) and c-fos mRNA in the hippocampus associated with contextual fear conditioning. We also investigated which component of contextual fear conditioning (context exploration, shock, or the combination) induces Arc and c-fos mRNA in the hippocampus. We report that context exposure, or context+shock, but not an immediate shock induces Arc and c-fos mRNA in the hippocampus. Together, these results demonstrate that contextual fear conditioning, but not immediate shock, induces Arc and c-fos expression in the hippocampus and the basolateral amygdala influences this expression.