NEURONAL APOPTOSIS AND RESULTANT MICROCEPHALY WITH CORTICAL DYSPLASIA PRODUCED BY CYTOSINE ARABINOSIDE IN MICE

Objectives: This experiment was undertaken to elucidate the pathogenesis of microcephaly with cortical dysplasia, produced by the administration of cytosine arabinoside (Ara-C) to mice during pregnancy.

Methods: Pregnant ICR strain mice were injected intraperitoneally with Ara-C at 30mg/kg body weight on days 13.5 and 14.5 of gestation. Brain tissues from their offspring were examined by nestin, calretinin and TUNEL (terminal deoxynucleotidyl transferase (TdT)- mediated dUTP nick end labeling) immunohistochemistry. 5-bromodeoxyuridine (BrdU) was also injected intraperitoneally on 15.5 of gestation, and embryos were examined by BrdU-nestin double staining.

Results: On embryos of day 15.5, some clusters of degenerative neurons were scattered in the ventricular zone, intermediate zone, and neuroepithelial cell layers in the ganglionic eminence. Most of these clusters were TUNEL-positive. BrdU-positive cells were densely accumulated in the whole parts of the ventricular zone. However, in the cingulate cortex, the neuroepithelial cells lacked the BrdU immunoreactivity, and nestin-immunoreactive radial glial fibers were markedly disrupted. Calretinin-immunoreactive subplate fibers were shortened, and not detected in the cingulate cortex. On the birth day, small number of ectopic neurons became detectable in the cingulum, and recognizable as bilateral small subcortical heterotopia by 3 days after birth. On 13 days after birth, microcephaly was apparent. In the rostral sections of the frontal cortex, subependymal nodular heterotopia was formed in the dorso-lateral part of the lateral ventricles, which did not include calretinin-positive elements.

Conclusion: Ara-C induced marked neuronal apoptosis to the proliferating young neurons especially in the ventricular and intermediate zones. The location of the subcortical and subependymal heterotopia was closely associated with the areas of disruption of radial glia. We suggest that the neuronal apoptosis and resultant disruption of radial glia are the main factors producing microcephaly with cortical dysplasia in this experiment.