Early-life stress (ELS) has been found to increase the risk of mental illness and physically alter brain structures and cognition. Research shows that exposure to acute ELS leads to enhanced fear learning later in life. There is some evidence that serotonin signalling mediates anxiety-induced increases in adult fear learning. Specifically, 5HT-2C serotonergic receptors appear to mediate anxiety-induced increases in adult fear learning. Interestingly, many of the existing treatments that are effective in treating PTSD and other anxiety-related disorders target the serotonergic system, resulting in high translational significance of our study to treating human psychological disorders. We hypothesized that systemic blockade of 5HT-2C receptors prior to adult fear conditioning will eliminate the stress enhancement in adult fear learning (SEFL) that is observed in animals that have previously been exposed to acute ELS. To test acute early life stress, Long-Evans rats underwent a context-dependent stress exposure, receiving 15 foot shocks. In adulthood they were injected with SB-242084, a 5HT-2c antagonist, or a vehicle and went through a separate context-dependent fear test. Vehicle and drug were re-administered in four new groups for a context-dependent fear retest. Our results showed that SEFL was observed in rats exposed to early life stress. We also found there was no significant effect of SB-242084 on fear acquisition or fear expression in adulthood. Further research may want to explore direct injection of SB-242084 into the BNST as well as the role of 5HT-1a receptors in mediating stress-enhanced fear learning following exposure to early life stress.
Authors: Mya Dirksen, Sophie Elleman, Savanna Fee, Tori Ladu, Katie Prazak
Faculty Advisor: Jennifer Quinn, Psychology
Graduate Student Advisor: Brianna Minshall, Psychology
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