title: Activation of muscarinic receptors protects against retinal neurons damage and optic nerve degeneration in vitro and in vivo models.
abstract: OBJECTIVE
  Muscarinic acetylcholine receptor agonist pilocarpine reduces intraocular pressure (IOP) of glaucoma mainly by stimulating ciliary muscle contraction and then increasing aqueous outflow. It is of our great interest to know whether pilocarpine has the additional properties of retinal neuroprotection independent of IOP lowering in vitro and in vivo models.
  
  
  METHODS
  In rat primary retinal cultures, cell viability was measured using an MTT assay and the trypan blue exclusion method, respectively. Retinal ganglion cells (RGCs) were identified by immunofluorescence and quantified by flow cytometry. For the in vivo study, the retinal damage after retinal ischemia/reperfusion injury in rats was evaluated by histopathological study using hematoxylin and eosin staining, transmission electron microscopy, and immunohistochemical study on cleaved caspase-3, caspase-3, and ChAT.
  
  
  RESULTS
  Pretreatment of pilocarpine attenuated glutamate-induced neurotoxicity of primary retinal neurons in a dose-dependent manner. Protection of pilocarpine in both retinal neurons and RGCs was largely abolished by the nonselective muscarinic receptor antagonist atropine and the M1-selective muscarinic receptor antagonist pirenzepine. After ischemia/reperfusion injury in retina, the inner retinal degeneration occurred including ganglion cell layer thinning and neuron lost, and the optic nerve underwent vacuolar changes. These degenerative changes were significantly lessened by topical application of 2% pilocarpine. In addition, the protective effect of pilocarpine on the ischemic rat retina was favorably reflected by downregulating the expression of activated apoptosis marker cleaved caspase-3 and caspase-3 and upregulating the expression of cholinergic cell marker ChAT.
  
  
  CONCLUSIONS
  Taken together, this highlights pilocarpine through the activation of muscarinic receptors appear to afford significant protection against retinal neurons damage and optic nerve degeneration at clinically relevant concentrations. These data also further support muscarinic receptors as potential therapeutic neuroprotective targets in glaucoma.
authors.affiliation: Department of Pharmacology, Institute of Medical Sciences, Shanghai Jiao Tong University School of Medicine, Shanghai, China.
authors.forename: Pan-Pan
authors.initials: PP
authors.lastname: Tan
authors.forename: Hai-Hong
authors.initials: HH
authors.lastname: Yuan
authors.forename: Xu
authors.initials: X
authors.lastname: Zhu
authors.forename: Yong-Yao
authors.initials: YY
authors.lastname: Cui
authors.forename: Hui
authors.initials: H
authors.lastname: Li
authors.forename: Xue-Mei
authors.initials: XM
authors.lastname: Feng
authors.forename: Yu
authors.initials: Y
authors.lastname: Qiu
authors.forename: Hong-Zhuan
authors.initials: HZ
authors.lastname: Chen
authors.forename: Wei
authors.initials: W
authors.lastname: Zhou
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D053148:Caspase 3 / Q000378:metabolism; D002478:Cells, Cultured; D002795:Choline O-Acetyltransferase / Q000378:metabolism; D004195:Disease Models, Animal; D004305:Dose-Response Relationship, Drug; D018690:Excitatory Amino Acid Agonists / Q000633:toxicity; D018698:Glutamic Acid / Q000633:toxicity; D008297:Male; D018721:Muscarinic Agonists / Q000627:therapeutic use; D009410:Nerve Degeneration / Q000209:etiology / Q000473:pathology* / Q000517:prevention & control*; D009474:Neurons / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D009900:Optic Nerve / Q000187:drug effects* / Q000473:pathology* / Q000648:ultrastructure; D010862:Pilocarpine / Q000627:therapeutic use; D051381:Rats; D017207:Rats, Sprague-Dawley; D011976:Receptors, Muscarinic / Q000378:metabolism*; D015427:Reperfusion Injury / Q000150:complications; D012160:Retina / Q000166:cytology
chemical_list: D018690:Excitatory Amino Acid Agonists; D018721:Muscarinic Agonists; D011976:Receptors, Muscarinic; D010862:Pilocarpine; D018698:Glutamic Acid; D002795:Choline O-Acetyltransferase; D053148:Caspase 3
keywords: Glaucoma; Glutamate; Ischemia/reperfusion; Neuroprotection; Pilocarpine