Depletion of taurine and glutamate from damaged photoreceptors in the retinas of dogs with primary glaucoma.
OBJECTIVE
To determine whether taurine and glutamate contents are reduced in damaged photoreceptors in dogs with primary glaucoma (PG) in a manner consistent with an ischemia-like release of both of these amino acids from damaged cells.


METHODS
Retinas from 6 dogs with PG and 3 control dogs.


METHODS
Serial, semithin sections of each canine retina were stained with toluidine blue to identify damaged photoreceptors or via immunogold techniques to quantify taurine and glutamate content in retinal cells.


RESULTS
Regions with a thin outer nuclear layer and pathologic nuclear changes in photoreceptors were evident in retinas of dogs with PG. The density of immunostaining for taurine in damaged photoreceptors was significantly reduced to (mean +/- SEM) 37.5 +/- 2.6% of the density in adjacent undamaged photoreceptors. Photoreceptors with decreased taurine immunostaining also had decreased glutamate immunostaining, consistent with ischemia-like release of both of these amino acids from damaged cells. Immunostaining for glutamate, but not taurine, was increased in presumptive radial glial cells (i.e., Miller cells) in damaged regions, consistent with an ischemia-induced redistribution of amino acids in dogs with PG.


CONCLUSIONS
Retinal damage in dogs with PG includes ischemia-like losses of taurine and glutamate from photoreceptors and accumulation of glutamate, but not taurine, in nearby Müller cells. These changes are consistent with glutamate release and depletion of intracellular taurine in damaged regions, perhaps contributing to progressive damage in these areas.
Madl
James E
JE
Department of Biomedical Sciences, College of Veterinary Medicine and Biomedical Sciences, Colorado State University, Fort Collins, CO 80523-1601, USA.
McIlnay
Tonya R
TR
Powell
Cynthia C
CC
Gionfriddo
Juliet R
JR
D000818:Animals; D004283:Dog Diseases / Q000378:metabolism* / Q000473:pathology; D004285:Dogs; D005901:Glaucoma / Q000378:metabolism / Q000473:pathology / Q000662:veterinary*; D018698:Glutamic Acid / Q000378:metabolism*; D010786:Photoreceptor Cells / Q000378:metabolism*; D012160:Retina / Q000473:pathology; D013654:Taurine / Q000378:metabolism*
D013654:Taurine; D018698:Glutamic Acid