Showing papers by "Laura López-Mascaraque published in 1995"

Persistence of early-generated neurons in the rodent subplate: assessment of cell death in neocortex during the early postnatal period

Abstract: In the rat, the deepest neocortical layer forms a conspicuous cell band known as layer Vlb. Cells in layer Vlb are among the first to differentiate, and it has been regarded as an homolog to the subplate of primates and carnivores. Cell death has been considered a universal feature of subplate cells. In order to assess the validity of this assertion, we examined the sequence of generation and the extent of cell death in layer Vlb. This was achieved using injections of 3H- thymidine and two methods for the direct visualization of apoptotic figures. Single injections of 3H-thymidine were performed between E12 and E15 (E0 is the day of insemination), and brains were examined at different postnatal ages between P1 and P63. The number of heavily labeled cells were counted in layer Vlb in six standard, equally spaced coronal sections in each brain. Single injections at E12 labels about 3% of the entire population of layer Vlb cells, 17% at E13, 30% at E14, and < 1% at E15. Our results indicate that the absolute number of heavily labeled cells in layer Vlb remains constant. The analysis of variance (one-way ANOVA) showed that the difference among the group means was not significant from P1 to P63 after injections at either E12, E13, or E14. In order to confirm these results, we evaluated the distribution of pyknotic (apoptotic) cell bodies in the neocortex. Apoptotic cells were visualized in Nissl preparations and by histochemical staining using an in situ apoptosis detection kit. The analysis was performed in rats from E18 to P15. Both methods gave comparable results. We found that the amount of cell death in layer Vlb is neither particularly prominent nor significantly different from that which occurs in the remaining neocortical layers, apart from layer II and in the white matter of the corpus callosum. We conclude that neuronal death does not play any significant role in the rodent subplate.

Time of Origin and Early Fate of Preplate Cells in the Cerebral Cortex of the Rat

Abstract: The time of origin, development, and morphology of neurons originating before the establishment of the cortical plate (preplate cells) were studied in the telencephalic vesicle of the rat from the embryonic day 10 (E10) to E15. The first postmitotic neurons settle superficial to the ventricular zone in the preplate at E12. We have observed mitotic figures in the preplate at E12 and E13, and regarded them as a possible source of cortical neurons outside the ventricular zone. It is suggested that these cells may correspond to Cajal-Retzius cells. The appearance of cells before the formation of the cortical plate was studied in animals injected with tritiated thymidine at E12 and E13 and correlated with observations made using an antibody to neuron specific class III beta-tubulin that becomes detectable immediately after the last mitotic division. Immunoreactive cells detected with this antibody concentrate at E12 immediately below the pial surface constituting the preplate. Radially oriented cells, most probably subplate neurons, were also present spanning the full thickness of the neuroepithelium, suggesting that the preplate contains different cell classes. We present a working hypothesis that explains the sequence of developmental events during the early phases of cortical histogenesis.