Apoptotic versus necrotic characteristics of retinal ganglion cell death after partial optic nerve injury

We have investigated time course and characteristics of retinal ganglion ce ll (RGC) death after partial optic nerve injury. In situ end labeling of DN A fragments with the terminal deoxynucleotidyl transferase (TdT)-mediated d eoxyuridine (dUTP)-biotin nick end labeling (TUNEL) method revealed the pre sence of apoptotic cells on as early as 5 days postcrush with a very high n umber of TUNEL-positive cells 1 week postinjury, At the ultrastructural lev el, features of apoptosis were clearly present in the ganglion cell layer a t this time point, Moreover, TUNEL-positive cells could be identified as re tinal ganglion cells by retrograde labeling with fluorogold, In addition, D NA laddering characteristic for apoptosis was found 1 week postinjury, A co nsiderable number of TUNEL-labeled cells was still found after 2 weeks post injury, Retinal whole mounts prepared at postlesion days 2-5, however, reve aled that many cell bodies with ruptured membranes as evidenced by nucleoso mal Sytox staining were present. These cells were also identified as retina l ganglion cells by retrograde labeling with fluorogold, Moreover, at this early stages of RGC degeneration necrotic cellular profiles could be detect ed by electron microscopic analysis. Thus, evidence is provided that necros is and apoptosis follow a distinctly different time course after partial op tic nerve injury.