Feasibility of Using PET Imaging for Detection of Treatment-Induced Changes in Chronic Neuroinflammation Following TBI

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Abstract The purpose of this study is to test the feasibility of developing a preclinical platform for the study of TBI-induced chronic neuroinflammation using PET imaging for the detection and surveillance of inflammation. In addition, these studies will test the putative efficacy of pharmacologic treatment (methylphenidate) to upregulate central noradrenergic and dopaminergic innervation. This proposal addresses a clinical problem, (chronic neuroinflammation) that is known to be a major factor in secondary brain injury and the worsening of TBI-induced disabilities. The studies will use a weight drop impact acceleration close-head TBI (chTBI) rat model that is known to capture significant features of TBIs produced by falls, vehicular accidents, training, and sports injuries common to the civilian and military population. Our previous work has shown that the model produces significant and enduring injuries to the brainstem region that hosts the cells and projection fibers of noradrenergic and dopaminergic systems. These injuries correlate with the injuries from peak shear forces that occur in the human brainstem following impact acceleration TBI. We hypothesize that the persistence of chTBI-induced chronic neuroinflammation is, in part, due to the injury of these NA and DA projections that normally play a significant role in the regulation of the brain’s innate immune system. Our previous work has quantitated long- term cognitive and anxiety disabilities, and these will serve an important purpose in the present studies to evaluate the safety and efficacy of MP treatments on these behaviors as chronic outcome measures of TBI disabilities. *FDG-18 PET MRI will be used to image the rostral brainstem and two functions-specific regions (hippocampus (cognitive function) and the central nucleus of the amygdala (anxiety function). Three weeks of daily treatments will be initiated two months following injury. PET MRI, cognitive, and anxiety assessment will be performed three months following injury. To ensure appropriate measures of safety, the studies will be performed using Normal, Normal treated, Sham, Sham treated, TBI, and TBI treated groups. Cognitive function will be assessed using four-daily sessions of serial learning in a Morris Water Maze. Anxiety behavior will be tested in an Elevated Plus Maze. Following the behavioral studies, the animals will be sacrificed and immunohistochemistry for conventional measures of neuroinflammation and microglia, noradrenergic cells and fibers, and dopaminergic cells and fibers, will be performed. Hypotheses: *FDG-18 PET/MRI imaging will reveal chronic microglial activation patterns that will correlate with conventional immunohistochemical (IHC) markers for activated microglia (CD68, IBA-4) and accompanying markers for chronic neuroinflammation (NFkB) in tissues from time-matched TBI animals. TBI animals will reveal significant disabilities in tests of cognitive and anxiety functions. Compared with untreated animals, MP-treated TBI animals will reveal decreased cognitive and anxiety disabilities. Compared with untreated TBI animals, MP-treated TBI animals will reveal decreased chronic microglial activation patterns in both *PET/MRI imaging and IHC markers for activated microglia and accompanying neuroinflammation. Significance. Collectively, these data are designed to provide companion *FDG-18 PET / MRI imaging, behavioral disability assessments, and conventional IHC assessments of NA and DA, microglial proliferation, and the expression of neuroinflammation markers. These data will provide an opportunity to comprehensively test the hypotheses regarding TBI-induction of neuroinflammation and the impact of MP treatment on neuroinflammation, microglial proliferation, and long-term outcome assessments of TBI-induced disabilities. It will provide much need research on chronic inflammation in this concussion model of brain injury which is greatly understudied. Methylphenidate is currently widely used and this study could provide important new safety data in regard to its use. *FDG-18 PET is widely available, accessible, and enhances the potential for clinical translation of findings.