Previous research indicates that serotonin (5-HT) enhances the acquisition of stress-induced changes in behavior; although it is unclear which serotonin receptors mediate this enhancement. 5-HT2 receptors are potential candidates because activation at these receptors is associated with increased fear and anxiety. In this study we investigated whether pharmacological treatments targeting 5-HT2A and 5-HT2C receptors modulated the acquisition and expression of conditioned defeat. Conditioned defeat is a social defeat model in Syrian hamsters (Mesocricetus auratus) that is characterized by increased submissive and defensive behavior and a loss of territorial aggression following social defeat. In experiment 1, we injected the 5-HT2C receptor agonist mCPP (0.3, 1.0, or 3.0 mg/kg) or vehicle prior to social defeat and tested subjects for conditioned defeat behavior in a social interaction test 24 hours later. In experiment 2, subjects received a social defeat, and 24 hours later we injected mCPP (0.3, 1.0, or 3.0 mg/kg) or vehicle prior to a social interaction test. We found that injection of mCPP increased the expression, but not acquisition, of conditioned defeat. In experiment 3, we injected the 5-HT2A receptor antagonist MDL 11,939 (0.5 or 2.0 mg/kg) or vehicle prior to a social defeat and tested subjects for conditioned defeat behavior. In experiment 4, subjects received a social defeat, and 24 hours later we injected MDL 11,939 (0.5 or 2.0 mg/kg) or vehicle prior to a social interaction test. We found that injection of MDL 11,939 significantly decreased the acquisition, but not expression, of conditioned defeat. These data suggest that pharmacological activation of 5-HT2C receptors enhances the expression of conditioned defeat, while pharmacological blockade of 5-HT2A receptors impairs the acquisition of conditioned defeat. These data extend other studies indicating that 5-HT signaling at 5-HT2A receptors facilitate memories for aversive events and 5-HT signaling at 5-HT2C receptors enhance stress-induced anxiety.
| Identifer | oai:union.ndltd.org:UTENN/oai:trace.tennessee.edu:utk_gradthes-2023 |
| Date | 01 May 2011 |
| Creators | Lee, Marquinta Juvon |
| Publisher | Trace: Tennessee Research and Creative Exchange |
| Source Sets | University of Tennessee Libraries |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | Masters Theses |
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