Undergraduate Honors Theses

Thesis Defended

Spring 2013

Document Type

Thesis

Department

Psychology & Neuroscience

First Advisor

Dr. Serge Campeau

Abstract

Historically, stress habituation research has largely focused on the reduction of the hypothalamic-pituitary-adrenal axis response to repeated stress exposures. The habituation of the HPA axis to prolonged stress is caused, in part, by negative feedback mechanisms, the activation of extensive stress-related neural circuitries, but also more complex enzymatic cascades underlying associative memory mechanisms. The results of previous investigations have implicated the MAP Kinase and CaM Kinase pathways as potential signal transduction pathways activated in stress adaptation. In addition, the amygdala and the hippocampus are well-known brain areas for learning and memory, however a recent study has shown that the posterior hypothalamus may also be a critical site for simple forms of learning like habituation. Building on this research, this project seeks to determine if microtubule associated protein kinases 1/2 (ERK) and calcium-dependent calmodulin kinase II alpha (CaMKIIα) are in cells characterized as active by stress-induced c-Fos protein expression in the posterior hypothalamic (PH) nucleus. In the following series of studies, we demonstrate with immunohistochemistry that ERK and CaMKIIα , but not Elk-1 can be localized in stress-responsive neurons of the posterior hypothalamus. Immunohistochemistry was used to measure the functional activation of ERK by assessing its level of phosphorylation (pERK) and the presence of CaMKII, in the posterior hypothalamus of acutely stressed rats. The phosphorylation of ERK is time-dependent; whereas basal expression was observed in control animals, a significant increase was observed in rats exposed to 15-30 minutes of stress. It has been shown that Fos protein is expressed in active pathways in the brain and we found that pERK but not CaMKII is significantly co-expressed in the same cells with Fos. These findings suggest that ERK is present in neurons that are likely signaling during stressful exposures, and could be involved in long-term plastic changes underlying, for example, habituation to repeated stress.

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