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 gla ucoma-like disorder occurs by apoptosis and whether an increase in excitoto xic amino acid concentration in the vitreous humor is associated temporally with cell death in the retina. METHODS. Presumptive retinal apoptotic nuclei were identified by histochemi cal detection of DNA fragmentation (by TdT-dUTP terminal nick-end labeling [TUNEL]), and vitreal concentrations of glutamate and several other amino a cids were determined by high-pressure liquid chromatography with fluorometr ic detection in the al mutant quail (Colurnix coturnix japonica) in which a glaucoma-like disorder develops spontaneously. RESULTS. TUNEL-labeled nuclei were located mostly in the ganglion cell laye r (GCL) in the retina of mutant quails 3 months after hatching. However, la beled nuclei were also observed in the inner and outer nuclear layers. At 7 months, most TUNEL-positive nuclei were detected in the inner nuclear laye r, whereas labeled cells In the GCL were reduced in number. No TUNEL-labele d 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 decr eased at 3 months, and no significant differences were observed between str ains at 7 months. CONCLUSIONS. Presumptive apoptotic cell death is detected from 3 months aft er hatching in mutant quails and is not restricted to retinal ganglion cell s. Cell death appears just after a significant increase in excitotoxic amin o acid concentrations in the Vitreous humor, suggesting a correlation betwe en both events.