Associations between PACAP levels and psychophysiological indicators of fear and arousal in adults with posttraumatic stress symptoms

Posttraumatic stress disorder (PTSD) is associated with heightened fear responding and decreased fear regulation, as demonstrated with psychophysiological measures (e.g., autonomic function) and circulating biomarkers of stress, such as pituitary adenylate cyclase-activating polypeptide (PACAP). The current study examined associations between PACAP levels and psychophysiological indicators of arousal in a sample of 168 trauma-exposed adults with a range of PTSD symptoms. We also examined sex differences in these relationships. Psychophysiological indicators included fear-potentiated startle (FPS), heart rate (HR), and heart rate variability (HRV) during a fear acquisition and extinction paradigm. PACAP levels were derived from fasting blood samples. PACAP levels were positively correlated with FPS during acquisition and HR during extinction, and negatively correlated with HRV during extinction. There were no significant PACAP-by-sex interaction effects in FPS, HR, or HRV models. Our results in the total sample are consistent with prior work demonstrating associations between PACAP and psychophysiological arousal. They add to previous evidence that circulating PACAP levels are associated with biological markers of centromedial amygdala-dependent functioning. Future research is needed among larger samples, including longitudinal designs to better determine causal relationships between PACAP levels and fear-related arousal.