Text

theses

Arc (Activity-regulated cytoskeleton-associated protein) is an effector neuronal immediate-early gene (IEG) and has been closely linked to behaviorally-induced neuronal plasticity. The present experiments are the first to characterize the regional distribution of Arc expression induced by hippocampal-dependent learning. More specifically, these studies examined the regionally-selective, dissociable patterns of Arc expression induced by Pavlovian trace fear conditioning, delay fear conditioning, and contextual fear conditioning as well as novel context exposure. This research was guided by anatomical studies identifying heterogeneity of connectivity across the transverse (CA1, CA3) and septo-temporal (dorsal vs. ventral) axes of the hippocampus; companion neuropsychological experiments suggest that these subregions likely play functionally dissociable roles in different forms of hippocampal-dependent learning. Hence the primary goal of the present study was to characterize the expression of Arc protein across both the septotemporal and transverse axes of the hippocampus induced by hippocampal dependent trace fear conditioning and compare these expression patterns to those induced by other fear conditioning paradigms. A second goal of these studies was to explore which specific paradigmatic features of the trace fear conditioning task itself are responsible for the observed patterns of Arc expression. These goals were accomplished by directly comparing behavior and Arc protein expression patterns following trace fear conditioning to that following novel context exposure, contextual fear conditioning, and delay fear conditioning in either a novel or familiar context. The results of these studies suggest that, within the dorsal hippocampus, Arc expression in CA3 induced by trace fear conditioning may play a unique role in representing the context, while Arc protein expression within ventral CA3 may reflect CS processing. Arc protein expression in dorsal and ventral CA1 are likely not meaningfully involved in trace fear conditioning as there is either a lack of significant enhancement (dorsal CA1) or enhancement is not unique to subjects trained in trace fear conditioning (ventral CA1). The specific regional pattern of Arc protein enhancement induced by trace fear conditioning may reflect the unique temporal parameters of the task which critically engages the hippocampus in processing both contextual representations as well as the explicit CS. This additional hippocampal processing may account for the greater enhancement in Arc protein in dorsal and ventral CA3 for subjects trained in trace fear conditioning compared to novel context exposure, or contextual and delay fear conditioning.

ETD_7769

Ph.D.

Includes bibliographical references

by Caleb Deneb Hudgins

doi:10.7282/T3ZP48JP

ETD doctoral

The author owns the copyright to this work.