Evaluation of glutamate loss from damaged retinal cells of dogs with primary glaucoma.

Publications // Richard Dubielzig // Jun 01 2004

PubMed ID: 15198218

Author(s): McIlnay TR, Gionfriddo JR, Dubielzig RR, Powell CC, Madl JE. Evaluation of glutamate loss from damaged retinal cells of dogs with primary glaucoma. Am J Vet Res. 2004 Jun;65(6):776-86. PMID 15198218

Journal: American Journal Of Veterinary Research, Volume 65, Issue 6, Jun 2004

OBJECTIVE To determine whether retinal damage in dogs with primary glaucoma (PG) is consistent with ischemia-induced glutamate toxicosis.

SAMPLE POPULATION Retinal tissue sections from 25 dogs with PG and 12 normotensive control dogs.

PROCEDURE Retinal sections from control and glaucomatous dogs were stained for morphometric and terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) analyses to determine whether retinal damage was consistent with glutamate toxicosis. Immunohistochemical analysis was performed to detect ischemia-like loss of glutamate from neurons in damaged areas.

RESULTS In severely damaged glaucomatous retinas, all neurosensory layers had focal regions that were thin or disrupted. There was less thinning of the outer nuclear layer (ONL) and inner nuclear layer (INL) in moderately damaged retinas than in severely damaged retinas. Acute signs of damage in the INL included cells with dark, condensed chromatin and lightly stained cytoplasm interspersed with a few TUNEL-positive cells, which was consistent with glutamate toxicosis. Glutamate immunoreactivity was reduced in thin areas and in damaged cells of the INL and ONL, which was consistent with glutamate release in damaged areas. Glutamate immunoreactivity was increased in putative Müller cells in damaged areas, which also was consistent with glutamate release.

CONCLUSIONS AND CLINICAL RELEVANCE Retinal damage in dogs with PG differs in intensity in focal areas. Damage in affected regions resembles damage induced by glutamate. Glutamate is lost from damaged neurons and accumulates in Müller cells, which is consistent with increased glutamate release contributing to the damage. Glutamate antagonists may protect INL cells in dogs with glaucoma.