Masters Theses

Date of Award

5-2013

Degree Type

Thesis

Degree Name

Master of Arts

Major

Psychology

Major Professor

Matthew A. Cooper

Committee Members

Todd M. Freeberg, Jim Hall

Abstract

Social defeat leads to both increased anxiety-like behavior and the formation of a fear memory for a specific opponent. We have shown that serotonin (5-HT) signaling, particularly in the basolateral amygdala (BLA), alters the acquisition of the conditioned defeat response in Syrian hamsters. While activation of 5-HT1A receptors impairs the acquisition of conditioned defeat, it is unclear whether these receptors alter the development of anxiety-like behavior or formation of fear memories. One method for investigating the formation of defeat-induced fear memories is to measure avoidance of former opponents, and many researchers have reliably used the open field as a measure of anxiety in rodents. In this study, we investigated whether activation of 5-HT1A receptors prior to social defeat would reduce subsequent avoidance of a former opponent but not alter anxiety-like behavior. We also investigated whether activation of 5-HT1A receptors prior to social defeat would reduce the expression of Arc immunoreactivity in the BLA. We administered 8-OH-DPAT (0.0, 0.25, 0.5 mg/kg), a 5-HT1A receptor agonist, prior to 3, 5-minute social defeats and 24- hours later exposed hamsters (Mesocricetus auratus) to a social interaction test to measure the conditioned defeat response immediately followed by a Y-maze test to measure avoidance of a former opponent and an open field test to measure anxiety. In a separate experiment, we administered 8-OH-DPAT (0.0, 0.25 mg/kg) prior to 3, 5-minute social defeats and 2- hours later brains were perfused and removed for Arc immunohistochemistry. We found that administration of 8-OH-DPAT prior to social defeat reduced the acquisition of conditioned defeat compared to vehicle controls. We also found that administration of 8-OH-DPAT prior to social defeat reduced subsequent avoidance of former opponents but did not alter the classic measures of anxiety in the open field. 8-OH-DPAT administration prior to defeat also impaired Arc immunoreactivity in the BLA. These results suggest that 5-HT1A receptors modulate the fear memory associated with the social defeat experience. Furthermore, these results raise the possibility that 5-HT1A receptor activation disrupts Arc expression in the BLA and thereby impairs the development of a fear memory that is essential for the conditioned defeat response.

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