The regulation of cell number and, more specifically, neuron number in the developing CNS is a largely unexplored question. Investigators will examine this issue in the developing dentate gyrus of the mouse. Within the dentate gyrus of a single inbred strain of mice the number of granule cells is similar from animal to animal (of the same sex), but this number varies markedly in different inbred strains. This project has two specific aims. First, investigators will examine changes in cell proliferation during the period of cell proliferation in the normal mouse. Second, investigators will determine the relative contribution of cell production and cell death to the variable numbers of granule cells in two inbred stains which have significantly different numbers of granule cells in the adult. Three aspects of cell production will be measured: 1) the period of time during which neurons are produced, 2) the length of the cell cycle of the proliferative population, 3) the proportion of cell that leave the proliferative population during each cycle (i.e., leaving fraction). These measurements will be used to estimate the size of the proliferative population at the beginning of the period of neuron generation for the dentate gyrus granule cells. The major methods to be used are bromodeoxyuridine immunohistochemistry and tritiated thymidine autoradiography both alone and in a series of double labeling experiments. In addition, the role of cell death in producing these differences in cell numbers will be assessed using a silver degeneration method, immunohistochemical detection of Alz-50 (a newly developed marker for naturally occurring neuronal death) and analysis of differential and non-differential survival of BUdR labeled cells.
