Embryogenesis of the rat telencephalon--a morphologic and stereologic analysis.

Comparative researches of borderline between telencephalon neuroepithelium and its surrounding mesenchyme in successive early developing stages lack in literature. The aim of this investigation was to carry out systematic morphologic and stereologic analyses of rat telencephalon in early developmental stages. We analysed semithin (1 microm) serial sections of rat embryonic brain from the 12th (E12) to the 15th (E15) day of gestation. The surface densities (SV) of an external mesenchymal surface, an internal mesenchymal surface and a neuroepithelial (ventricular) surface were examined stereologically and compared. The surface density of the external mesenchymal surface was the biggest at E12 (4,05 mm-1) and the least at E15 (1,87 mm-1)-p<0,0005. The surface density of the internal mesenchymal surface was the biggest at E12 (4,02 mm-1) and the least at E15 (2,69 mm-1)-p<0,0005. The surface density of the internal neuroepithelial surface was the biggest at E12 (3,31 mm-1) and the least at E15 (2,01 mm-1)-p<<0,0005. Our stereological examines give objective numerical proof of significant morphogenetic changes in telencephalon shape described by morphologic analyses. The major advantage of stereological methods is the possibility to carry out the estimation procedures in specified, well-defined brain regions or layers.