title: Cognitive deficits develop 1month after diffuse brain injury and are exaggerated by microglia-associated reactivity to peripheral immune challenge.
abstract: Traumatic brain injury (TBI) elicits immediate neuroinflammatory events that contribute to acute cognitive, motor, and affective disturbance. Despite resolution of these acute complications, significant neuropsychiatric and cognitive issues can develop and progress after TBI. We and others have provided novel evidence that these complications are potentiated by repeated injuries, immune challenges and stressors. A key component to this may be increased sensitization or priming of glia after TBI. Therefore, our objectives were to determine the degree to which cognitive deterioration occurred after diffuse TBI (moderate midline fluid percussion injury) and ascertain if glial reactivity induced by an acute immune challenge potentiated cognitive decline 30 days post injury (dpi). In post-recovery assessments, hippocampal-dependent learning and memory recall were normal 7 dpi, but anterograde learning was impaired by 30 dpi. Examination of mRNA and morphological profiles of glia 30 dpi indicated a low but persistent level of inflammation with elevated expression of GFAP and IL-1β in astrocytes and MHCII and IL-1β in microglia. Moreover, an acute immune challenge 30 dpi robustly interrupted memory consolidation specifically in TBI mice. These deficits were associated with exaggerated microglia-mediated inflammation with amplified (IL-1β, CCL2, TNFα) and prolonged (TNFα) cytokine/chemokine expression, and a marked reactive morphological profile of microglia in the CA3 of the hippocampus. Collectively, these data indicate that microglia remain sensitized 30 dpi after moderate TBI and a secondary inflammatory challenge elicits robust microglial reactivity that augments cognitive decline.
  
  
  CONCLUSIONS
  Traumatic brain injury (TBI) is a major risk factor in development of neuropsychiatric problems long after injury, negatively affecting quality of life. Mounting evidence indicates that inflammatory processes worsen with time after a brain injury and are likely mediated by glia. Here, we show that primed microglia and astrocytes developed in mice 1 month following moderate diffuse TBI, coinciding with cognitive deficits that were not initially evident after injury. Additionally, TBI-induced glial priming may adversely affect the ability of glia to appropriately respond to immune challenges, which occur regularly across the lifespan. Indeed, we show that an acute immune challenge augmented microglial reactivity and cognitive deficits. This idea may provide new avenues of clinical assessments and treatments following TBI.
authors.affiliation: Department of Neuroscience, The Ohio State University, 333 W. 10th Ave, Columbus, OH, United States.
authors.forename: Megan M
authors.initials: MM
authors.lastname: Muccigrosso
authors.affiliation: Department of Neuroscience, The Ohio State University, 333 W. 10th Ave, Columbus, OH, United States.
authors.forename: Joni
authors.initials: J
authors.lastname: Ford
authors.affiliation: Department of Neuroscience, The Ohio State University, 333 W. 10th Ave, Columbus, OH, United States.
authors.forename: Brooke
authors.initials: B
authors.lastname: Benner
authors.affiliation: Department of Neuroscience, The Ohio State University, 333 W. 10th Ave, Columbus, OH, United States.
authors.forename: Daniel
authors.initials: D
authors.lastname: Moussa
authors.affiliation: Department of Neuroscience, The Ohio State University, 333 W. 10th Ave, Columbus, OH, United States.
authors.forename: Christopher
authors.initials: C
authors.lastname: Burnsides
authors.affiliation: Department of Neuroscience, The Ohio State University, 333 W. 10th Ave, Columbus, OH, United States.
authors.forename: Ashley M
authors.initials: AM
authors.lastname: Fenn
authors.affiliation: Department of Neuroscience, The Ohio State University, 333 W. 10th Ave, Columbus, OH, United States; Center for Brain and Spinal Cord Repair, The Ohio State University, 460 W. 12th Ave, Columbus, OH, United States; Institute for Behavioral Medicine Research, The Ohio State University, 460 Medical Center Dr., Columbus, OH, United States.
authors.forename: Phillip G
authors.initials: PG
authors.lastname: Popovich
authors.affiliation: Barrow Neurological Institute at Phoenix Children's Hospital, Department of Child Health, University of Arizona, College of Medicine-Phoenix, Phoenix, AZ, United States.
authors.forename: Jonathan
authors.initials: J
authors.lastname: Lifshitz
authors.affiliation: School of Biomedical Sciences and Pharmacy, University of Newcastle, Callaghan 2308, South Wales, Australia.
authors.forename: Fredrick Rohan
authors.initials: FR
authors.lastname: Walker
authors.affiliation: Department of Surgery, The Ohio State University, 395 W. 12th Avenue, Columbus, OH, United States.
authors.forename: Daniel S
authors.initials: DS
authors.lastname: Eiferman
authors.affiliation: Department of Neuroscience, The Ohio State University, 333 W. 10th Ave, Columbus, OH, United States; Center for Brain and Spinal Cord Repair, The Ohio State University, 460 W. 12th Ave, Columbus, OH, United States; Institute for Behavioral Medicine Research, The Ohio State University, 460 Medical Center Dr., Columbus, OH, United States. Electronic address: jonathan.godbout@osumc.edu.
authors.forename: Jonathan P
authors.initials: JP
authors.lastname: Godbout
mesh_terms: D000818:Animals; D001253:Astrocytes / Q000378:metabolism / Q000473:pathology; D000070625:Brain Injuries, Diffuse / Q000276:immunology / Q000378:metabolism / Q000473:pathology; D000070642:Brain Injuries, Traumatic / Q000276:immunology / Q000378:metabolism / Q000473:pathology* / Q000523:psychology*; D018925:Chemokines / Q000378:metabolism; D003071:Cognition / Q000502:physiology; D003072:Cognition Disorders / Q000378:metabolism / Q000473:pathology; D016207:Cytokines / Q000378:metabolism; D004195:Disease Models, Animal; D007249:Inflammation / Q000378:metabolism; D018836:Inflammation Mediators / Q000378:metabolism*; D008297:Male; D008568:Memory / Q000502:physiology; D051379:Mice; D008807:Mice, Inbred BALB C; D017628:Microglia / Q000378:metabolism / Q000473:pathology*; D011788:Quality of Life
chemical_list: D018925:Chemokines; D016207:Cytokines; D018836:Inflammation Mediators
keywords: Astrocytes; Cognitive decline; Fluid percussion injury; Lipopolysaccharide; Microglia; Neuroinflammation; Traumatic brain injury