Differentiated horizontal cells seem not to be affected by apoptosis during development of the chick retina

Natural occurring cell death has been recognised as a feature of normal ver tebrate development (Glucksman, 1951; Saunders, 1966). We have studied the temporal and cellular patterns of cell death in the developing chicken reti na using the terminal transferase dUTP nick end-labelling (TUNEL) technique . This technique was combined with other methods to identify dying cells. F luorescent retrograde tracing of ganglion cells or immunohistochenistry for GABA and TrkA as cell markers were combined with the TUNEL technique. The timing and distribution of dying cells suggest that each neuronal cell type in the retina dies during specific and overlapping periods: ganglion cells first, followed by amacrine cells and bipolar cells. Little cell death cou ld be found among horizontal cells orphotoreceptors. These populations seem to be protected from death. We have previously shown evidence of NGF expre ssion among the horizontal cell population during these stages of developme nt and also a protective role of this factor (Karlsson et al., 2001), which supports the present data.