A behavioral model of excitotoxicity: retinal degeneration, loss of vision, and subsequent recovery after intraocular NMDA administration in adult rats

Exp Brain Res. 1995;106(1):93-105. doi: 10.1007/BF00241359.


To establish a new behavioral animal model of excitotoxicity, we injected adult rats intraocularly with a single dose of 2, 20, or 100 nmol of N-methyl-D-aspartate (NMDA). We quantified visual impairment by plotting the size of the visual field in which the rats successfully oriented towards a small, moving target. In comparison to the saline-injected (contralateral) control side, the side injected with 2 nmol of NMDA was not significantly impaired. When injected with higher doses, the rats were nearly blind immediately after surgery, with only about 20% (20 nmol NMDA) or 10% (100 nmol NMDA) of residual vision. Within about 3 weeks, however, visual performance returned to near-normal levels. Simultaneous intraocular administration of a non-competitive NMDA-antagonist, MK-801 (1 nmol), resulted in complete behavioral protection. NMDA administration led to a dose-dependent loss of cells within the ganglion cell layer, as assessed in whole-mounted retinae which were retrogradely labelled with horseradish peroxidase (HRP). Whereas 2 nmol of NMDA led to the loss of about 30% of retinal ganglion cells (RGCs), at higher NMDA doses only 13% of the RGCs survived. After the injection of 20 nmol of NMDA, large-diameter RGCs (> 22 microns) survived the lesion to a greater extent than small diameter cells (8-21 microns); at 100 nmol cells of all diameters were equally affected. The number of Nissl-stained cells with small diameters (< 11 microns), presumed to be displaced amacrine cells, was also affected by NMDA, although to a lesser degree. Analysis of behavioral performance (vision score) and the number of cells in the retina revealed a correlation of r = 0.76 between visual performance and the number of HRP-filled RGCs immediately after surgery. Lower correlations were found between visual performance and cells stained with Nissl of diameters smaller than 11 microns (presumed RGCs without retinofugal connections; r = 0.55 and r = 0.58, respectively). Because of the spontaneous recovery of vision, all correlations declined to values near 0 after 3 weeks. Thus, despite a dramatic loss of RGCs following NMDA administration, visual deficits recover significantly in adult rats within 2-3 weeks.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Behavior, Animal / drug effects*
  • Cell Survival / drug effects
  • Dizocilpine Maleate / pharmacology
  • Excitatory Amino Acid Agonists / administration & dosage
  • Excitatory Amino Acid Agonists / toxicity*
  • Excitatory Amino Acid Antagonists / pharmacology
  • Eye
  • Horseradish Peroxidase
  • Injections
  • N-Methylaspartate / administration & dosage
  • N-Methylaspartate / antagonists & inhibitors
  • N-Methylaspartate / toxicity*
  • Orientation / drug effects
  • Rats
  • Rats, Inbred Strains
  • Retinal Degeneration / chemically induced
  • Retinal Degeneration / pathology*
  • Retinal Ganglion Cells / drug effects
  • Vision Disorders / chemically induced
  • Vision Disorders / pathology*
  • Visual Fields / drug effects
  • Visual Fields / physiology


  • Excitatory Amino Acid Agonists
  • Excitatory Amino Acid Antagonists
  • N-Methylaspartate
  • Dizocilpine Maleate
  • Horseradish Peroxidase