title: Differential protection of injured retinal ganglion cell dendrites by brimonidine.
abstract: OBJECTIVE
  To determine whether brimonidine protects against the retraction and loss of retinal ganglion cell (RGC) dendrites after optic nerve crush (ONC).
  
  
  METHODS
  Fluorescent RGCs of mice expressing yellow fluorescent protein (YFP) under the control of the Thy-1 promoter (Thy1-YFP mice) were imaged in vivo and assigned to one of six groups according to dendrite structure. The mice then received brimonidine every other day starting 2 days before, or 2 or 6 days after, unilateral ONC. Control animals received vehicle every other day starting 2 days before ONC. Control animals received vehicle every other day starting 2 days before ONC. Total dendrite length, dendrite branching complexity, and the time until complete loss of dendrites were assessed weekly for 4 weeks.
  
  
  RESULTS
  Overall, brimonidine treatment significantly slowed the complete loss of RGC dendrites and significantly slowed the reduction of total dendrite length and branching complexity. Separate analysis of each RGC group showed brimonidine significantly delayed the time until complete loss of dendrites in four of the RGC groups. These delays generally were similar when treatment started either 2 days before or 2 days after ONC, but were smaller or absent when treatment started 6 days after ONC Protection against loss of total dendrite length and loss of branching complexity was observed in three of the RGC groups. In two of these RGC groups, protective effects persisted until the end of the study.
  
  
  CONCLUSIONS
  Brimonidine protects many RGC types against dendrite retraction, loss of branching complexity, and complete loss of dendrites following ONC. However, the pattern and magnitude of this protection differs substantially among different RGC types. These results indicate that requirements for RGC-protective therapies following optic nerve injury may differ among RGC types.
authors: Hamilton Glaucoma Center and Department of Ophthalmology, University of California San Diego, La Jolla, California, United States.
authors: James D
authors: JD
authors: Lindsey
authors: Hamilton Glaucoma Center and Department of Ophthalmology, University of California San Diego, La Jolla, California, United States.
authors: Karen X
authors: KX
authors: Duong-Polk
authors: Hamilton Glaucoma Center and Department of Ophthalmology, University of California San Diego, La Jolla, California, United States.
authors: Dustin
authors: D
authors: Hammond
authors: Hamilton Glaucoma Center and Department of Ophthalmology, University of California San Diego, La Jolla, California, United States.
authors: Panida
authors: P
authors: Chindasub
authors: Department of Ophthalmology and Visual Sciences, Chinese University of Hong Kong, Hong Kong.
authors: Christopher Kai-Shun
authors: CK
authors: Leung
authors: Hamilton Glaucoma Center and Department of Ophthalmology, University of California San Diego, La Jolla, California, United States.
authors: Robert N
authors: RN
authors: Weinreb
mesh_terms: D000818:Animals; D000068438:Brimonidine Tartrate; D019610:Cytoprotection / Q000187:drug effects*; D003712:Dendrites / Q000187:drug effects* / Q000473:pathology; D005260:Female; D008297:Male; D051379:Mice; D008815:Mice, Inbred Strains; D008856:Microscopy, Fluorescence; D009409:Nerve Crush; D020221:Optic Nerve Injuries / Q000473:pathology*; D011810:Quinoxalines / Q000494:pharmacology*; D012165:Retinal Ganglion Cells / Q000187:drug effects* / Q000473:pathology
chemical_list: D011810:Quinoxalines; D000068438:Brimonidine Tartrate
keywords: brimonidine; dendrite; neurodegeneration; neuroprotection; optic nerve crush; retinal ganglion cell