The Roles of Inflammation, Oxidative Stress, and Neurotransmitters in an Animal Model of Post-Traumatic Stress Disorder

Abstract

Post-traumatic stress disorder (PTSD), a trauma- and stressor-related disorder, is a condition that can develop in response to life-threatening situations. According to the Diagnostic and Statistical Manual of Mental Disorders 5 (DSM-5), a diagnosis of PTSD necessitates exposure to a life-threatening event, intrusive recollections, avoidance of associated stimuli, hyperarousal, and a significant social impairment. All of these symptoms must persist for at least 30 days and not be due to illness, medication, or substance abuse. To date, no definitive diagnostic biomarkers have been identified for PTSD. Recent research, however, points toward physiological abnormalities in the brain, hypothalamic-pituitary-adrenal (HPA) axis, and immune system that may be partially responsible. Many chronic conditions such as hypertension, heart failure, and metabolic syndrome perpetuate in a state of increased inflammation and oxidative stress, exacerbating their pathophysiology. In many psychiatric conditions such as depression and anxiety disorders, neurotransmitter modulation may play a critical role in their pathogenesis. Based upon the literature and work from our laboratory, we hypothesized that similar pathophysiological mechanisms may play a role in PTSD development. We tested our theory by creating a PTSD-like syndrome in rats with the use of a predator exposure/psychosocial stress animal model. We then conducted a series of in vivo and ex vivo experiments in an attempt to discover the roles of inflammation, oxidative stress, and neurotransmitter modulation in PTSD development. First, we evaluated inflammation and oxidative stress in the brain, adrenal glands, and blood in response to the predator exposure model. We then analyzed neurotransmitter modulation in the hippocampus and prefrontal cortex. Next, we investigated the anti-inflammatory and neuromodulating effects of the histone deacetylase inhibitor (HDACi) valproic acid (VA) on inflammation/oxidative stress and neurotransmitters. Finally, we employed the selective-serotonin reuptake inhibitor (SSRI) sertraline to ascertain why SSRIs have historically been ineffective in treating PTSD. Taken together, our findings indicate inflammation, oxidative stress, and aberrant neurotransmitter profiles may play a significant role in PTSD development and progression. In addition, VA may prove to be a legitimate pharmacologic alternative in PTSD treatment, as SSRIs may increase the noradrenergic response and actually exacerbate anxiety in a clinical setting.