title: Chronic Psychological Distress as an Inducer of Microglial Activation and Leukocyte Recruitment into the Area Postrema.
abstract: BACKGROUND
  Chronic psychological distress can cause neuroinflammation, but the involvement of leukocytes in this inflammatory response remains unclear. The area postrema (AP) is considered a neural-immune interface because it lacks a blood-brain barrier and a site for leukocyte recruitment in neuroinflammatory conditions induced by immunological insults, but its role in chronic psychological distress has not been explored.
  
  
  OBJECTIVE
  To determine leukocyte recruitment to the AP after chronic psychological distress.
  
  
  METHODS
  Rats were exposed to cat odor for 5 consecutive days to induce distress, and, on the 6th day, their brains were dissected to perform immunohistofluorescence studies of the AP. Immune cells were identified and quantified with CD45 and CD11b markers. The distribution of neurons and immune cells was determined using TrkA and CD45 markers, respectively.
  
  
  RESULTS
  Distress induced a significant increase in CD45(+) and CD11b(+) cells in the AP. Three immunophenotypes were determined in the control and distress groups: CD45(+)/CD11b(-), CD45(+)/CD11b(+) and CD45(-)/CD11b(+). CD expression, morphology and fluorescence intensity enabled the identification of different immune cell types: starting from longitudinal ramified microglia (mainly in the control group) to amoeboid microglia, monocytes and lymphocytes (mostly in the distressed group). TrkA and CD45 expression in the AP revealed the proximity between soma neurons and leukocytes. Interestingly, some CD45(+) cells expressed TrkA, with increased expression in the distressed group.
  
  
  CONCLUSIONS
  The identification of microglial activation, leukocyte recruitment and the close proximity between neurons and leukocytes in the AP after chronic psychological distress exposure suggests the AP as a site for distress-induced immune responses and engraftment of leukocytes infiltrating the CNS.
authors.affiliation: Escuela Nacional de Medicina y Homeopatía, Instituto Politécnico Nacional, and Centro de Investigación en Biotecnologia Aplicada del IPN, México, México.
authors.forename: Alejandra
authors.initials: A
authors.lastname: Vargas-Caraveo
authors.forename: David Guillermo
authors.initials: DG
authors.lastname: Pérez-Ishiwara
authors.forename: Alejandro
authors.initials: A
authors.lastname: Martínez-Martínez
mesh_terms: D000818:Animals; D031608:Area Postrema / Q000473:pathology*; D039481:CD11b Antigen / Q000378:metabolism; D002908:Chronic Disease; D004195:Disease Models, Animal; D005434:Flow Cytometry; D017493:Leukocyte Common Antigens / Q000378:metabolism; D007962:Leukocytes / Q000378:metabolism / Q000473:pathology*; D008262:Macrophage Activation; D008297:Male; D017628:Microglia / Q000473:pathology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D020917:Receptor, trkA / Q000378:metabolism; D013315:Stress, Psychological / Q000473:pathology*
chemical_list: D039481:CD11b Antigen; D020917:Receptor, trkA; D017493:Leukocyte Common Antigens