Comparative localization of Cajal-Retzius cells in the neocortex of normal and reeler mutant mice fetuses

The Cajal-Retzius cells (CRc) appear as an histochemically advanced subpopulation, since they are the only neocortical neurons able to express an acetylcholinesterase activity at an early stage of corticogenesis. Thus a comparative study of the CRc population was carried out on normal and reeler mice fetuses. The use of an appropriate cytochemical technique to reveal this endogenous cell marker, in conjunction with coronal and tangential sections show that: (1) the Cajal-Retzius cells form a sheet in the more superficial layer of the embryonic cortex, with a relative cell density giving the same value in both phenotypes; (2) a difference is observed in the relative depth position of these cells with regard to the pial basal lamina and in the pattern of cell grouping between the heterozygous and homozygous mutant littermates. This technique appears of great interest for a further analysis of the CRc population during cortical ontogenesis.