Graduation Year

2015

Document Type

Dissertation

Degree

Ph.D.

Degree Name

Doctor of Philosophy (Ph.D.)

Degree Granting Department

Psychology

Major Professor

David M. Diamond, Ph.D.

Committee Member

Kenneth J. Malmberg, Ph.D.

Committee Member

Cheryl L. Kirstein, Ph.D.

Committee Member

Paul B. Jacobsen, Ph.D.

Committee Member

Brent J. Small, Ph.D.

Keywords

Adrenalectomy, Corticosterone, Epinephrine, Memory, Novel Object Recognition, Stress

Abstract

The vivid memory of an emotional event, as well as memory for incidental details associated with the arousing event, has been referred to collectively as a “flashbulb memory”. An important aspect of flashbulb memory in people is that an emotional event enhances memory of contextual details, such as the weather, or clothes one was wearing at the time of the event. Therefore, an emotional event not only produces a detailed memory of the event, itself, but also enhances memory for contextual details that would otherwise not be remembered. The first goal of this work is to describe the development of my animal model of flashbulb memory, including a discussion of the importance of the timing between an emotional event and incidental, contextual cues. The second goal is to address the time-dependent neuroendocrine processes involved in stress-induced memory enhancement in rats. The involvement of brain structures, namely the hippocampus and amygdala, and hormones, including corticosterone and epinephrine, that interact to produce a composite memory of the contextual cues occurring in close temporal proximity to an emotional event are discussed. The results of Experiment 1 validate the animal model of flashbulb memory whereby an emotional event (predator exposure) produced memory for context cues that, under control conditions, would be forgotten. This memory enhancement only occurred when the emotional event was close in temporal proximity to training in the task. Experiment 2 provided evidence that epinephrine administration close in time to training mimicked the context memory formation induced by brief predator exposure, while propranolol, a β-adrenergic antagonist, as well as CPP, an NMDA receptor antagonist, blocked this effect. The results of Experiment 3 revealed that propranolol, CPP, and dexamethasone also blocked the brief predator stress-induced context memory formation. The results of Experiment 4 revealed that cannulated animals infused with aCSF (control) did not show evidence of predator stress-induced memory, therefore methodological issues within this experiment are addressed. Finally, the results of Experiment 5 revealed that adrenalectomy eliminated the predator stress-induced context memory compared to sham operated animals, suggesting that endogenous stress hormones are required for stress-induced context memory formation. Further, adrenalectomized rats supplemented with epinephrine before training did show evidence of context memory enhancement suggesting that epinephrine eliminated the memory impairment produced by adrenalectomy, and was sufficient to enhance memory in the absence of corticosterone. Overall this approach has provided insight into the time-dependent neuroendocrine processes involved in the formation of flashbulb, and potentially traumatic, memories in people.

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