Undergraduate Honors Theses

Thesis Defended

Fall 2012

Document Type




First Advisor

Robert Spencer


Psychological stress contributes to the etiology of a wide variety of mood and anxiety disorders. We know that how an individual reacts to stress is based on prior stress experience. Our goal is to better understand the factors that modulate the development of stress response habituation. In order for an individual to habituate to stress, the brain must be able to form stress‐associated memories. Formation of these memories requires a cellular consolidation process that proceeds for several hours. NMDA receptors in the brain are known to be important for many forms of learning and memory, although it is unknown whether they are necessary for stress response habituation. Specifically, our main study aimed to determine whether activation of NMDA receptors after initial exposure to a stressor is necessary in order for stress response habituation to occur in rats. In order to adequately interpret the results of this study, it was also necessary to perform preliminary studies to look at the acute effects of an NMDA receptor antagonist drug (MK‐801) on the stress response. Our results show that blocking NMDA receptors immediately after initial stress experience prevented subsequent expression of stress response habituation. This indicates that NMDA receptor activation during initial exposure to a stressor is indeed an important factor contributing to stress response habituation. However, these results cannot be taken as definitive evidence owing to an unexpected long‐lasting excitatory effect of MK‐801 on the stress response in our preliminary studies. Intriguing explanations exist for why this drug effect may have occurred, and future studies should test for these hypotheses in an attempt to solidify the conclusions we have made here.