An intrinsic time limit between genesis and death of individual neurons in the developing retinal ganglion cell layer.

We tested the possibility that a temporal relationship exists between genesis and death of individual neurons dying during development. For this purpose, we labeled neurons born in limited time intervals and determined when they die in the ganglion cell layer (GCL) of the rat retina. We found that most neurons that die do so within a maximal interval of 5 d after their birth, irrespective of the age of genesis or of the cell type. These findings suggest the existence of a cellular clock regulating neuronal death during development. We found also that neurons migrate in no less than 3 d to the GCL, where a majority of cells that die remain a maximum of 2 d. This fast cellular turnover implies that the magnitude of neuronal death is far greater than previously believed.