Time of neuron origin in the hippocampus and dentate gyrus of normal and reeler mutant mice: an autoradiographic analysis.

Abstract

AbstractThe hippocampus and dentate gyrus of reeler mutant mice contain the normal neuronal classes. The majority of cells are included in laminar aggregates reminiscent of normal structure though these are irregular in outline, interrupted at points, and less densely packed. Many hippocampal neurons and granule cells of the dentate gyrus are scattered in the external plexiform zone (strata radiatum and lacunosum‐moleculare) of the hippocampus rather than being included in the laminar aggregates.Neurons in the reeler are generated at the same time as their normal homologs. However, the relationship of adult cell position to sequence of cell generation is abnormal in two general ways in the mutant. First, although in both the mutant and normal, cells in the external plexiform zone of the hippocampus are among the earliest formed, a relatively greater proportion of cells generated through a relatively longer embryonic time are destined to be scattered in this distal location in the mutant. Secondly, within the laminar aggregates of the hippocampus in reeler, the more superficial cells tend to be formed earlier, and the more deeply located ones are the latest formed. A reversed relationship exists in the normal in which the deepest cells are formed earliest, the more superficial ones last. The observations are consistent with the view that a mechanism which provides for orderly lamination of cells in the normal is defective in reeler.