Cell Proliferation and Cytogenesis in the Mouse Hippocampus

Abstract

In the present work, processes of cell proliferation, cell death, neurogenesis, and gliogenesis in the mouse hippocampus were studied. The mapping of distribution of hippocampal mitoses and counting of their number allowed a more precise definition of the data concerning the disposition and age reduction of proliferative sites in Ammon's horn and the dentate gyrus in the mouse. As a result, the following generalized scheme of development and age reduction of the germinal zones in the mouse hippocampus has been suggested. 1. Ammon's horn a) The ventricular zone, from the beginning of formation of the hippocampus (E11) until E20 b) The suprafimbrial zone, from E16 until P7 2. Dentate gyrus a) The prime germinal zone ("the anlage of the dentate gyrus" of Stanfield and Cowan1979b), from E15 until P3 b) The proliferative zone of the hilus, from P3 until P14 c) The subgranular zone, from P3 until adult age The adduced scheme needs some comments: 1. In the hippocampus (as well as in other formations of the developing brain), primary precursors of all types of cells of neuroectodermal origin are represented by cells of the ventricular zone. They give rise to cells of secondary germinal zones in the dentate gyrus and Ammon's horn and are direct precursors of the majority (if not of all) neuronal cells in Ammon's horn, the earliest originating generations of neurons in the dentate gyrus, hippocampal radial glial cells, and, evidently, of a considerable part of astroblasts and oligodendroblasts in Ammon's horn. 2. In contrast to the subiculum, Ammon's horn in the mouse lacks a subventricular (subependymal) zone. These data differ from the results obtained in the rat, where the subventricular zone is described both in the subiculum and Ammon's horn (Bayer 1980b) and from the study in the monkey, where the subiculum and Ammon's horn lack the subventricular zone (Nowakowski and Rakic 1981). Thus, in the case of the mouse, the subventricular zone can serve as a cytoarchitectural characteristic allowing detection of a border between the developing subiculum and Ammon's horn. (Another developmental feature which also identifies the border between Ammon's horn and the subiculum is a considerable number of dying cells in the region of the joint of these structures on E20-P3). 3. In the developing dentate gyrus and Ammon's horn, several extraventricular (i.e., located at a distance from brain ventricles) secondary germinal zones exist. Thus, during embryonic and early postnatal periods of the mouse development, the prime germinal zone occupies a larger part of the presumptive dentate gyrus.(ABSTRACT TRUNCATED AT 400 WORDS)