Use of TUNEL to Measure Retinal Ganglion Cell Apoptosis

During development of the retina, a number of different cell types are produced in excess and then undergo programmed cell death (Young, 1984). Retinal ganglion cells, which are the tertiary neurons whose axons make up the optic nerve and provide connectivity between the eye and higher centers in the brain, are among those cells which die by programmed cell death (Rakic and Riley, 1983; Insausti et al., 1984; Provis and Penfold, 1988). The number of retinal ganglion cells that are born in the mammalian retina is approximately twice the number that survive. According to the neurotrophic hypothesis, the cells that die do so because they fail to receive the appropriate neurotrophic signal from their target tissue, in this case from the lateral geniculate nucleus (Cowan et al., 1984; Barde, 1989). This mechanism is thought to help ensure that inappropriate connections are not maintained and that the final steady-state number of innervating neurons is appropriately matched to the number of target cells.