title: Neurotoxin-Induced Catecholaminergic Loss in the Colonic Myenteric Plexus of Rhesus Monkeys.
abstract: OBJECTIVE
  Constipation is a common non-motor symptom of Parkinson's disease (PD). Although pathology of the enteric nervous system (ENS) has been associated with constipation in PD, the contribution of catecholaminergic neurodegeneration to this symptom is currently debated. The goal of this study was to assess the effects of the neurotoxin 6-hydroxydopamine (6-OHDA) on the colonic myenteric plexus and shed light on the role of catecholaminergic innervation in gastrointestinal (GI) function.
  
  
  METHODS
  Proximal colon tissue from 6-OHDA-treated (n=5) and age-matched control (n=5) rhesus monkeys was immunostained and quantified using ImageJ software. All animals underwent routine daily feces monitoring to assess for constipation or other GI dysfunction.
  
  
  RESULTS
  Quantification of tyrosine hydroxylase (TH) and aromatic L-amino acid decarboxylase (AADC)-immunoreactivity (-ir) revealed significant reduction in myenteric ganglia of 6-OHDA-treated animals compared to controls (TH-ir: 87.8%,P<0.0001; AADC-ir: 61.7%P=0.0034). Analysis of pan-neuronal markers (PGP9.5, HuC/D), other neurochemical phenotypes (VIP, nNOS), PD-associated pathology proteins (α-synuclein, phosphorylated α-synuclein), glial marker GFAP and neuroinflammation and oxidative stress (HLA-DR, CD45, Nitrotyrosine) did not show significant differences. Monitoring of feces revealed frequent (>30% days) soft stool or diarrhea in 2 of the 5 6-OHDA-treated animals and 0 of the 5 control animals during the 2 months prior to necropsy, with no animals exhibiting signs of constipation.
  
  
  CONCLUSIONS
  Systemic administration of 6-OHDA to rhesus monkeys significantly reduced catecholaminergic expression in the colonic myenteric plexus without inducing constipation. These findings support the concept that ENS catecholaminergic loss is not responsible for constipation in PD.
authors.affiliation: Wisconsin National Primate Research Center (WNPRC) and Cellular and Molecular Pathology (CMP) Graduate Program, University of Wisconsin-Madison, Madison, WI, USA.
authors.forename: Jeanette M
authors.initials: JM
authors.lastname: Shultz
authors.affiliation: WNPRC, University of Wisconsin-Madison, Madison, WI, USA.
authors.forename: Henry
authors.initials: H
authors.lastname: Resnikoff
authors.affiliation: WNPRC, University of Wisconsin-Madison, Madison, WI, USA.
authors.forename: Viktorya
authors.initials: V
authors.lastname: Bondarenko
authors.affiliation: WNPRC, University of Wisconsin-Madison, Madison, WI, USA.
authors.forename: Valerie
authors.initials: V
authors.lastname: Joers
authors.affiliation: WNPRC, University of Wisconsin-Madison, Madison, WI, USA.
authors.forename: Andres
authors.initials: A
authors.lastname: Mejia
authors.affiliation: WNPRC, University of Wisconsin-Madison, Madison, WI, USA.
authors.forename: Heather
authors.initials: H
authors.lastname: Simmons
authors.affiliation: WNPRC, CMP Graduate Program and Department of Medical Physics, University of Wisconsin-Madison, Madison, WI, USA.
authors.forename: Marina E
authors.initials: ME
authors.lastname: Emborg
keywords: 6-hydroxydopamine; Catecholaminergic; Colon; Inflammation; Oxidative stress; Parkinson’s disease; Tyrosine hydroxylase; myenteric plexus; α-synuclein