title: Fractalkine receptor (CX3CR1) deficiency sensitizes mice to the behavioral changes induced by lipopolysaccharide.
abstract: BACKGROUND
  Interactions between fractalkine (CX3CL1) and fractalkine receptor (CX3CR1) regulate microglial activation in the CNS. Recent findings indicate that age-associated impairments in CX3CL1 and CX3CR1 are directly associated with exaggerated microglial activation and an impaired recovery from sickness behavior after peripheral injection of lipopolysaccharide (LPS). Therefore, the purpose of this study was to determine the extent to which an acute LPS injection causes amplified and prolonged microglial activation and behavioral deficits in CX3CR1-deficient mice (CX3CR1-/-).
  
  
  METHODS
  CX3CR1-/- mice or control heterozygote mice (CX3CR1+/-) were injected with LPS (0.5 mg/kg i.p.) or saline and behavior (i.e., sickness and depression-like behavior), microglial activation, and markers of tryptophan metabolism were determined. All data were analyzed using Statistical Analysis Systems General Linear Model procedures and were subjected to one-, two-, or three-way ANOVA to determine significant main effects and interactions.
  
  
  RESULTS
  LPS injection caused a prolonged duration of social withdrawal in CX3CR1-/- mice compared to control mice. This extended social withdrawal was associated with enhanced mRNA expression of IL-1β, indolamine 2,3-dioxygenase (IDO) and kynurenine monooxygenase (KMO) in microglia 4 h after LPS. Moreover, elevated expression of IL-1β and CD14 was still detected in microglia of CX3CR1-/- mice 24 h after LPS. There was also increased turnover of tryptophan, serotonin, and dopamine in the brain 24 h after LPS, but these increases were independent of CX3CR1 expression. When submitted to the tail suspension test 48 and 72 h after LPS, an increased duration of immobility was evident only in CX3CR1-/- mice. This depression-like behavior in CX3CR1-/- mice was associated with a persistent activated microglial phenotype in the hippocampus and prefrontal cortex.
  
  
  CONCLUSIONS
  Taken together, these data indicate that a deficiency of CX3CR1 is permissive to protracted microglial activation and prolonged behavioral alterations in response to transient activation of the innate immune system.
authors.affiliation: Department of Molecular Virology, Immunology and Medical Genetics, The Ohio State University, 333 W. 10th Ave., Columbus, OH 43210, USA. Angela.Wynne@osumc.edu
authors.forename: Angela W
authors.initials: AW
authors.lastname: Corona
authors.forename: Yan
authors.initials: Y
authors.lastname: Huang
authors.forename: Jason C
authors.initials: JC
authors.lastname: O'Connor
authors.forename: Robert
authors.initials: R
authors.lastname: Dantzer
authors.forename: Keith W
authors.initials: KW
authors.lastname: Kelley
authors.forename: Phillip G
authors.initials: PG
authors.lastname: Popovich
authors.forename: Jonathan P
authors.initials: JP
authors.lastname: Godbout
mesh_terms: D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects*; D000073883:CX3C Chemokine Receptor 1; D054428:Chemokine CX3CL1 / Q000276:immunology*; D003863:Depression / Q000276:immunology; D006801:Humans; D007113:Immunity, Innate / Q000276:immunology; D053583:Interleukin-1beta / Q000235:genetics / Q000378:metabolism; D008070:Lipopolysaccharides / Q000276:immunology / Q000494:pharmacology*; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D017628:Microglia / Q000166:cytology / Q000187:drug effects / Q000276:immunology* / Q000502:physiology; D009043:Motor Activity / Q000187:drug effects; D010105:Oxygenases / Q000235:genetics / Q000378:metabolism; D019707:Receptors, Chemokine / Q000172:deficiency* / Q000235:genetics / Q000276:immunology; D012919:Social Behavior; D014364:Tryptophan / Q000378:metabolism
chemical_list: D000073883:CX3C Chemokine Receptor 1; D054428:Chemokine CX3CL1; C471885:Cx3cr1 protein, mouse; D053583:Interleukin-1beta; D008070:Lipopolysaccharides; D019707:Receptors, Chemokine; D014364:Tryptophan; D010105:Oxygenases