Journal
BIOLOGICAL PSYCHIATRY
Volume 79, Issue 10, Pages 803-813Publisher
ELSEVIER SCIENCE INC
DOI: 10.1016/j.biopsych.2015.07.010
Keywords
Anxiety; Macrophages; Microglia; Neuroinflammation; PTSD; Stress
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Funding
- National Institute of Mental Health [R01-MH093473, R01-MH097243]
- National Institute of Dental and Craniofacial Research Training Grant [T32-DE014320]
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BACKGROUND: Neuroinflammatory signaling may contribute to the pathophysiology of chronic anxiety disorders. Previous work showed that repeated social defeat (RSD) in mice promoted stress-sensitization that was characterized by the recurrence of anxiety following subthreshold stress 24 days after RSD. Furthermore, splenectomy following RSD prevented the recurrence of anxiety in stress-sensitized mice. We hypothesize that the spleen of RSD-exposed mice became a reservoir of primed monocytes that were released following neuroendocrine activation by subthreshold stress. METHODS: Mice were subjected to subthreshold stress (i.e., single cycle of social defeat) 24 days after RSD, and immune and behavioral measures were taken. RESULTS: Subthreshold stress 24 days after RSD re-established anxiety-like behavior that was associated with egress of Ly6C(hi) monocytes from the spleen. Moreover, splenectomy before RSD blocked monocyte trafficking to the brain and prevented anxiety-like behavior following subthreshold stress. Splenectomy, however, had no effect on monocyte accumulation or anxiety when determined 14 hours after RSD. In addition, splenocytes cultured 24 days after RSD exhibited a primed inflammatory phenotype. Peripheral sympathetic inhibition before subthreshold stress blocked monocyte trafficking from the spleen to the brain and prevented the re-establishment of anxiety in RSD-sensitized mice. Last, beta-adrenergic antagonism also prevented splenic monocyte egress after acute stress. CONCLUSIONS: The spleen served as a unique reservoir of primed monocytes that were readily released following sympathetic activation by subthreshold stress that promoted the re-establishment of anxiety. Collectively, the long-term storage of primed monocytes in the spleen may have a profound influence on recurring anxiety disorders.
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