Extinction of Contextual Fear Memories in Female Rats in the Presence of Pituitary Adenylate Cyclase Activating Polypeptide (PACAP)
Date of Completion
Honors College Thesis
College of Arts and Science Honors, Honors College
PACAP, contextual fear memory
Post-Traumatic Stress Disorder is a mental health disorder characterized by a sex disparity (Friedman et al., 2007). Females are much more likely to experience PTSD across the life course than males, however, the reasoning for this difference remains uncertain. Symptoms of PTSD suggest that the ability to extinguish fear learning may be compromised (Morey et al., 2015), and implicate regions of the brain involved in this function, including the hippocampal dentate gyrus (Hayes et al., 2017). Granule cells in this brain region highly express receptors for pituitary adenylate cyclase activating polypeptide, a neuropeptide associated with the endocrine and central nervous system’s stress response(Johnson et al., 2020). Prior work involving the infusion of PACAP into the dentate gyrus in male rats following fear learning displayed enhanced fear retention (Johnson, 2019).
The present study extended this research to an all-female animal model, assessing how retention of contextual fear memories was affected by infusion of PACAP into the dentate gyrus prior to extinction testing in female rats. Estrous was also tracked throughout the study to determine if a relationship was present between persistence of a fear memory and estrous high or low phases among the animals in the presence of PACAP. Results of this study showed enhanced freezing behavior and thus enhanced fear memory retention in female rats across extinction testing, a finding which aligns with the behaviors observed in male rats under the same conditions. Given the small sample size utilized in the study, no correlation could be drawn between estrous and freezing behaviors. This work will need to be expanded on in future research to further clarify estrus’s role and whether PACAP in female rats is truly influencing fear memory retention or increasing fear behaviors in a more general capacity.
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Webb, Carly E., "Extinction of Contextual Fear Memories in Female Rats in the Presence of Pituitary Adenylate Cyclase Activating Polypeptide (PACAP)" (2022). UVM Honors College Senior Theses. 504.