title: Systemic administration of 6-OHDA to rhesus monkeys upregulates HLA-DR expression in brain microvasculature.
abstract: BACKGROUND
  We recently developed a nonhuman primate model of cardiac dysautonomia by systemic dosing of the catecholaminergic neurotoxin 6-hydroxydopamine (6-OHDA). The aim of this study was to assess whether systemic 6-OHDA affects the central nervous system of nonhuman primates, in particular the dopaminergic nigrostriatal system.
  
  
  METHODS
  Brain sections from adult rhesus monkeys that received systemic 6-OHDA (50 mg/kg intravenously; n=5) and were necropsied 3 months later, as well as normal controls (n=5) were used in this study. Tissue was cut frozen at 40 μm on a sliding microtome, processed for immunohistochemistry, and blindly evaluated.
  
  
  RESULTS
  Neither the optical density of tyrosine hydroxylase immunoreactivity (TH-ir; a dopaminergic neuronal marker) in the caudate and putamen nucleus nor the TH-ir cell number and volume in the substantia nigra showed significant differences between groups. Yet within groups, statistical analysis revealed significant individual differences in the 6-OHDA-treated group, with two animals showing a lower cell count and volume. Optical density quantification of α-synuclein-ir in the substantia nigra did not show differences between groups. As α-synuclein intracellular distribution was noted to vary between animals, it was further evaluated with a semiquantitative scale. A greater intensity and presence of α-synuclein-positive nigral cell bodies was associated with larger TH-positive nigral cell volumes. Increased human leukocyte antigen (HLA-DR; a microglial marker) expression was observed in 6-OHDA-treated animals compared with controls. HLA-DR-ir was primarily localized in endothelial cells and perivascular spaces throughout cortical and subcortical structures. Semiquantitative evaluation using a rating scale revealed higher HLA-DR-ir in blood vessels of 6-OHDA-treated animals than controls, specifically in animals with the lowest number of dopaminergic nigral neurons.
  
  
  CONCLUSIONS
  Our results demonstrate that systemic 6-OHDA administration to rhesus monkeys can affect the dopaminergic nigrostriatal system and upregulate inflammatory markers in the cerebrovasculature that persist 3 months post neurotoxin challenge. The variability of the subject response suggests differences in individual sensitivity to 6-OHDA.
authors.affiliation: Preclinical Parkinson's Research Program, Wisconsin National Primate Research Center, University of Wisconsin-Madison, Madison, WI, USA ; Neuroscience Training Program, University of Wisconsin-Madison, Madison, WI, USA.
authors.forename: Valerie
authors.initials: V
authors.lastname: Joers
authors.affiliation: Preclinical Parkinson's Research Program, Wisconsin National Primate Research Center, University of Wisconsin-Madison, Madison, WI, USA ; Neuroscience Training Program, University of Wisconsin-Madison, Madison, WI, USA.
authors.forename: Scott
authors.initials: S
authors.lastname: Vermilyea
authors.affiliation: Preclinical Parkinson's Research Program, Wisconsin National Primate Research Center, University of Wisconsin-Madison, Madison, WI, USA.
authors.forename: Kristine
authors.initials: K
authors.lastname: Dilley
authors.affiliation: Preclinical Parkinson's Research Program, Wisconsin National Primate Research Center, University of Wisconsin-Madison, Madison, WI, USA ; Neuroscience Training Program, University of Wisconsin-Madison, Madison, WI, USA ; Department of Medical Physics, University of Wisconsin-Madison, Madison, WI, USA.
authors.forename: Marina E
authors.initials: ME
authors.lastname: Emborg
keywords: 6-hydroxydopamine; blood–brain barrier; neuroinflammation; nonhuman primates; parkinsonism