Morphological and morphometric studies of cerebellar fissuration and myelination in mice with trisomy 19.

The fissuration and myelination in cerebella of trisomy 19 mice and of chromosomally balanced control animals on postnatal days (PD) 2, 5, 10, 12, and 15 were analyzed morphologically and morphometrically. In trisomy 19 mice, an increasing fissuration lag with a fissuration pattern and sequence identical to those of the control animals was found. The nuclear volume density of the trisomic glia cell in the neocerebellar commissure also developed like that of control mice, with an increase shortly before and parallel to the beginning of myelination and with a decrease in its further course. The trisomic axons and myelin sheaths were normally structured but axonal growth and myelination in the neocerebellar commissure were retarded. The quantitative relations of the assumed axon/glia interactions were similar to those of the control animals. The fissuration and myelination in the cerebellum of trisomy 19 mice did not seem to be pathologically changed but seemed to be differently retarded. On PD 15, a myelination lag of less than 5 days but a fissuration lag of nearly 10 days was found. This observation and the assumption of a differently retarded growth of the cerebellar cortex compared with cerebellar subcortical regions lead to the suggestion that the trisomy might result in a progressively asynchronous and disproportional development of different CNS structures.