Defense Date


Document Type


Degree Name

Master of Science


Anatomy & Neurobiology

First Advisor

Dr. Gretchen Neigh


Post-traumatic stress disorder is a stress and trauma based psychological disorder that is defined by the DSM-IV as an anxiety disorder that affects approximately 7.8% of people in the United States. PTSD is when those who suffer a traumatic event have intense and distressing feelings, emotions, and memories for a prolonged period of time after the event. A prominent feature of PTSD is the impaired ability to properly extinguish a fear response after a dangerous trigger or stressor is no longer present, also known as safety learning. Stressors are threats perceived within the environment that activate a response within the hypothalamic-pituitary-adrenal (HPA) axis as well as the autonomic nervous system (ANS). During adolescence, the brain is within a critically sensitive period that is susceptible to damage or alterations in cognition or morphology due to stressors. Chronic stress during adolescence alters brain morphology and cognitive function into adulthood, as seen in studies involving laboratory animals. In addition to the effects of chronic adolescent stress, there are also morphological and cognitive differences due to sex caused by differences in sex hormones. Women are disproportionately affected by PTSD and are twice as likely to develop PTSD after a traumatic event. Combining these factors, we hypothesize that the ability to safety learn will be impaired by chronic adolescent stress and further hindered within female wistar rats. A mixed-modality chronic adolescent stress paradigm was used to create social stress, which simulates negative social interaction and aggression, and chronic restraint stress, which simulates a stressful situation that forces immobility. Safety learning ability was assessed using a startle paradigm created based on fear conditioning that has been used previously in multiple studies testing for behavior that is indicative of PTSD-like behavior. In contradiction to the hypothesis, the females who underwent chronic adolescent stress did extinguish the fear and safety learn successfully better than the nonstress counterparts. In order to look at the predictability of the startle response due to the effects of chronic adolescent stress, multiple linear regression analyses were run. It was found that for the baseline, fear conditioning, and extinction days within the startle response paradigm were able to be predicted significantly, however, the days that were testing the actual fear potentiated startle response and safety learning had no significant predictability. The results of this study found that CAS increased the ability to safety learn as well as sex did not influence the ability to safety learn, which were both not supportive of the hypothesis. In addition, the regression analysis was not a reliable model of predicting startle response within CAS data. This study can be a useful steppingstone in determining the ways that chronic adolescent stress can predict how a stressor can cause an increase in the risk of psychological disorders later in adulthood.


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