Abstract
Pituitary adenylate cyclase-activating peptide (PACAP) is a neuropeptide that plays a key role in the neurobiology of the stress response, and prior studies suggest that its function is dysregulated in post-traumatic stress disorder (PTSD). Transcutaneous cervical vagus nerve stimulation (tcVNS) acts through PACAP and other neurobiological systems to modulate stress responses and/or symptoms of PTSD. In this pilot study, we examined the effects of tcVNS on PACAP in a three day chronic stress laboratory paradigm involving serial traumatic and mental stress exposures in healthy individuals with a history of exposure to psychological trauma (n = 18) and patients with PTSD (n = 12). METHODS: A total of 30 subjects with a history of exposure to psychological trauma experience were recruited (12 with PTSD diagnosis) for a three-day randomized double-blinded study of tcVNS or sham stimulation. Subjects underwent a protocol that included both personalized trauma recall and non-personalized mental stressors (public speaking, mental arithmetic) paired to tcVNS or sham stimulation over three days. Blood was collected at baseline and multiple time points after exposure to stressors. Linear mixed-effects models were used to assess changes in PACAP over time (in response to stressors) and its relation to active tcVNS or sham stimulation. RESULTS: PACAP blood levels increased over the course of three days for both active tcVNS and sham groups. This increase was statistically-significant in the sham group at the end of the second (Cohen's d(rm) = 0.35, p = 0.04), and third days (d(rm) = 0.41, p = 0.04), but not in the active tcVNS group (d(rm) = 0.21, d(rm) = 0.18, and p > 0.20). CONCLUSION: These pilot findings suggest tcVNS may attenuate this neurobiological stress-response. Larger studies are needed to investigate gender and interaction effects.