Kinetic Modeling of Norepinephrine Transporter Availability in PTSD

The objective of this proposal is to collect pilot data to characterize the binding of [11C]MENET in combat-exposed war veterans with posttraumatic stress disorder (PTSD). Approximately two hundred thousand veterans will be returning stateside upon the end of combat operations in Iraq, and 13% of returning veterans will have PTSD. 15% of all war veterans will develop chronic PTSD symptoms requiring a lifetime of mental health care. Little is known about the dysregulation of PTSD veteran's neurochemical state including the noradrenergic system which plays a primary role in memory and stress response. This includes heightened anxiety, fear and hyperarousal symptoms characteristic of PTSD. The noradrenergic system is a concentration of neurons in the brainstem nucleus, locus coerulues, that have projections to the amygdale and prefrontal cortex. The norepinephrine transporter (NET) is responsible for regulating and terminating noradrenergic transmission, and is a specific marker for neuronal integrity. Hyperactivity of the noradrenergic system up-regulates NET protein. An unresolved problem in studying the noradrenergic system is identification of suitable radiopharmaceutical to non-invasively measure alterations in the density of NET. The investigators propose to address this challenge by using positron emission tomography (PET) to measure stress-induced changes in NET expression in combat-exposed war veterans with PTSD. The central hypothesis of this proposal is that war veterans with PTSD have an up-regulation of NET in the locus coerulues resulting from hyperactivity of the noradrenergic system compared to healthy controls. Through a series of experiments, the investigators will determine the in vivo binding characteristics of [11C]MENET. The investigators will use this information to optimally design an experimental protocol to measure the availability of NET in a pilot group of combat-exposed war veterans with PTSD. The aims of this proposal are: 1) Measure the uptake kinetics and whole brain distribution of [11C]MENET in combat-exposed veterans with PTSD and healthy controls, 2) Develop a quantitative kinetic model of [11C]MENET uptake to calculate the NET availability in brain. The subjects undergoing imaging in this work will be recruited by Dr. J. Douglas Bremner (Co-Investigator) at Emory University and Atlanta Veteran Affairs Hospital. Our long-term goal is to develop a longitudinal study framework to assess the NETs dysregulation during onset of PTSD as well as its transition to chronic lifetime PTSD.