| Neurons in the mouse retinal ganglion cell layer (GCL) are born over about 11 days, from embryonic day (E) 10.5 to postnatal day 3. The neurons in the adult GCL are divided roughly equally between two cell types: ganglion cells (a type of projection neuron) and displaced amacrine cells (a type of interneuron). No information exists on the cell types present in the developing GCL. In addition, developmental cell death is believed to be more important in projection neurons than in local circuit interneurons, but the degree of difference is in dispute. This thesis identifies two cohorts of GCL neurons, one born early and the other late, and determines the magnitude of their reduction through developmental cell death.; To address these goals, pregnant mice were implanted with osmotic pumps filled with the thymidine analog, bromodeoxyuridine (BrdU). The retinas of their offspring were examined either prenatally or postnatally. The early cohort came from embryonic and postnatal mice whose mothers had been implanted at E11.5–E12.5. The early cohort comprised cells that completed their terminal S-phase by 4–7 hours after either E11.5 or E12.5, and were recognized because their nuclei were BrdU-negative. The cells in the late cohort were identified in postnatal mice whose mothers had been implanted at E15.5. The late cohort comprised cells that had their terminal S-phase during a prolonged exposure to BrdU beginning at E15.5 and were recognized because their nuclei were BrdU-positive. In prenatal and postnatal retinas, ganglion cells were identified by retrograde labeling through the optic nerve. Unlabeled cells in the GCL were assumed to be displaced amacrines.; Of the cells in the early cohort, 97% were ganglion cells. Prenatally, cell death among early ganglion cells was negligible, but 55% of these cells died postnatally. Of the cells in the late cohort, 97% were displaced amacrines, and 29% of these cells died postnatally.; I conclude that the vast majority of ganglion cells are generated before displaced amacrine cells. Developmental cell death eliminates a significantly smaller fraction of displaced amacrines than ganglion cells. |
