Retinal TUNEL-positive cells and high glutamate levels in vitreous humor of mutant quail with a glaucoma-like disorder.

Purpose: To investigate whether retinal cell death observed in an avian glaucoma-like disorder occurs by apoptosis and whether an increase in excitotoxic amino acid concentration in the vitreous humor is associated temporally with cell death in the retina.

Methods: Presumptive retinal apoptotic nuclei were identified by histochemical detection of DNA fragmentation (by TdT-dUTP terminal nick-end labeling [TUNEL]), and vitreal concentrations of glutamate and several other amino acids were determined by high-pressure liquid chromatography with fluorometric detection in the al mutant quail (Coturnix coturnix japonica) in which a glaucoma-like disorder develops spontaneously.

Results: TUNEL-labeled nuclei were located mostly in the ganglion cell layer (GCL) in the retina of mutant quails 3 months after hatching. However, labeled nuclei were also observed in the inner and outer nuclear layers. At 7 months, most TUNEL-positive nuclei were detected in the inner nuclear layer, whereas labeled cells in the GCL were reduced in number. No TUNEL-labeled nuclei were detected in the retina of control quails at any age. Vitreal concentrations of glutamate and aspartate were significantly increased in 1-month-old mutant quails compared with control animals. Concentrations decreased at 3 months, and no significant differences were observed between strains at 7 months.

Conclusions: Presumptive apoptotic cell death is detected from 3 months after hatching in mutant quails and is not restricted to retinal ganglion cells. Cell death appears just after a significant increase in excitotoxic amino acid concentrations in the vitreous humor, suggesting a correlation between both events.