Cytokine Effects on Amphetamine-Induced Dopamine Release using PET Neuroimaging

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This proposal is designed to provide the applicant with supervised education and research training in translational neuroimaging to assess the impact of innate immune cytokines on basal ganglia dopamine (DA). Neuropsychiatric disorders including depression are common in medically ill patients, possibly as a result of chronic peripheral immune system activation and release of innate immune cytokines. Although innate immune cytokines have been shown to interact with virtually every pathophysiologic domain relevant to depression including neurotransmitter metabolism, the exact mechanisms by which these cytokines exert behavioral effects are unknown. Basal ganglia DA plays a pivotal role in regulating behaviors including mood, motor activity, motivation and reward, and mounting evidence indicates that the DA system may be targeted by innate immune cytokines. For example, administration of the innate immune cytokine, interferon (IFN)-alpha, is associated with behavioral changes consistent with DA depletion including depressive behavior, fatigue, and reduced locomotor activity. In addition, neuroimaging studies using positron emission tomography (PET) in patients undergoing IFN-alpha therapy have revealed increased basal ganglia glucose metabolism similar to that seen in Parkinson¿s disease. Increased uptake and decreased release of the DA precursor, [18F]fluorodopa, in the caudate and putamen of IFN-alpha-treated patients has also been observed. Preliminary findings from in vivo microdialysis indicate decreased basal ganglia DA under resting conditions and following amphetamine (AMPH) administration via reverse microdialysis. The goal of the proposed research is to use neuroimaging techniques to examine DA availability and release in basal ganglia during IFN-alpha-treatment. The primary hypothesis of the study is that reduced DA availability and/or release is a key mechanism of cytokine-induced behavioral change. To test the hypothesis, [11C]raclopride neuroimaging with intravenous AMPH challenge will be used to indirectly measure DA availability and release during IFN-alpha or saline administration. This PET protocol will be complemented by direct measurement of extracellular DA using in vivo microdialysis in the striatum under basal conditions and in response to AMPH administered via reverse microdialysis. In addition to providing important insight into the effects of cytokines on basal ganglia DA, these studies will help the applicant develop an independent line of research in neuro-immune interactions, while fostering her career development. To accomplish her goals, the applicant¿s training plan will include a combination of mentored research, coursework, seminars, and attendance at national and international meetings.