Morphogenesis of the cerebellum of trisomy 19 mice

Cerebellar development of Ts19 mice aged 1 to 16 days post partum has been examined morphologically and morphometrically. The structural organization of the cerebellar cortex is not altered in Ts19 mice, but the development of cortical neurons lags behind that of control littermates. Maturation of Purkinje cells, differentiation of basket cells, disappearance of mitotic figures and regression of the external granular layer are each delayed by approximately 2 days. Myelination is similarly retarded by 2 days both in the anterior medullary velum and in the cerebellar white matter. Quantitative data, e.g. the thickness of the external granular layer and of the molecular layer, are in agreement with this delay in development, the values of Ts19 mice corresponding to those of control mice 2 days younger. The number of pyknotic nuclei in the external granular layer of Ts19 mice is not noticeably increased. The total cross-sectional area of the cerebellar vermis as well as the area occupied by the external granular layer and by the molecular layer are each markedly reduced in Ts19. The reduction in proliferative cells is suggestive of a permanent hypoplasia of the cerebellar vermis. There is no indication that in Ts19 mice, the maturational delay of the cerebellar cortex is different from that of the white matter.