title: Degeneration and dysfunction of retinal neurons in acute ocular hypertensive rats: involvement of calpains.
abstract: OBJECTIVE
  Retinal ischemic diseases primarily lead to damage of the inner retinal neurons. Electrophysiological studies also suggest impairment of the inner retinal neurons. Our recent studies with acute ocular hypertensive rats confirmed damage predominantly in the inner retinal layer along with the ganglion cell layer, changes that are ameliorated by the calpain inhibitor SNJ-1945. However, we do not know which specific neuronal cells in the inner retinal layer are damaged by calpains. Thus, the purpose of the present study was to identify specific calpain-damaged neuronal cells in the inner retina from acute ocular hypertensive rats.
  
  
  METHODS
  Intraocular pressure was elevated to 110 mm Hg for 40 min. One hour after ocular hypertension (OH), SNJ-1945 was administrated as a single oral dose of 50 mg/kg. Retinal function was assessed by scotopic electroretinography (ERG). Histological degeneration was evaluated by hematoxylin and eosin, terminal deoxynucleotidyl transferase (TdT)-mediated dUTP nick-end-labeling (TUNEL), and immunostaining in thin sections and flat mounts of the retina. Calpain activation was determined by proteolysis of the calpain substrate α-spectrin.
  
  
  RESULTS
  OH caused calpain activation, increased TUNEL-positive staining, decreased thickness of the inner nuclear layer (INL), and decreased amplitudes of the ERG a- and b-waves and oscillatory potentials (OPs). SNJ-1945 significantly inhibited calpain activation and the decrease in ERG values. Interestingly, the changes in the b-wave and OPs amplitudes were significantly correlated to changes in the thickness of the INL. In the inner retinal layer, the numbers of rod bipolar, cone-ON bipolar, and amacrine cells were decreased after OH. SNJ-1945 suppressed the loss of cone-ON bipolar and amacrine cells, but did not inhibit the loss of rod bipolar cells. We also observed increased glial fibrillary acid protein-positive staining in the Müller cells after OH and the treatment with SNJ-1945.
  
  
  CONCLUSIONS
  Calpains may contribute to ischemic retinal dysfunction by causing the loss of cone-ON bipolar and amacrine cells and causing the activation of Müller cells. Calpain inhibitor SNJ-1945 may be a candidate compound for treatment of retinal ischemic disease.
authors.affiliation: 1 Senju Laboratory of Ocular Sciences, Senju Pharmaceutical Co., Ltd. , Kobe, Japan .
authors.forename: Rie
authors.initials: R
authors.lastname: Suzuki
authors.forename: Takayuki
authors.initials: T
authors.lastname: Oka
authors.forename: Yoshiyuki
authors.initials: Y
authors.lastname: Tamada
authors.forename: Thomas R
authors.initials: TR
authors.lastname: Shearer
authors.forename: Mitsuyoshi
authors.initials: M
authors.lastname: Azuma
mesh_terms: D000208:Acute Disease; D000818:Animals; D002154:Calpain / Q000037:antagonists & inhibitors* / Q000378:metabolism; D002219:Carbamates / Q000494:pharmacology / Q000627:therapeutic use; D008297:Male; D009798:Ocular Hypertension / Q000188:drug therapy / Q000378:metabolism / Q000473:pathology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012162:Retinal Degeneration / Q000188:drug therapy / Q000378:metabolism / Q000473:pathology*; D055351:Retinal Neurons / Q000187:drug effects / Q000378:metabolism / Q000473:pathology*
chemical_list: C515164:((1S)-1-((((1S)-1-benzyl-3-cyclopropylamino-2,3-di-oxopropyl)amino)carbonyl)-3-methylbutyl)carbamic acid 5-methoxy-3-oxapentyl ester; D002219:Carbamates; D002154:Calpain