[Differentiation of cerebellar Purkinje neurons of the normal and chronically hypoxic chick embryo].

A microscopical and ultrastructural study on the cerebellum development, with peculiar attention to the Purkinje cell differentiation, has been undertaken in chick embryos from the 8th incubation day (i.d.) until hatching, both in normal and hypoxic conditions; the development under hypoxia was obtained by covering, at the 2nd i.d., a half of fertilized egg shells with melted wax (Menkes et al., 1975). The observations, carried out on paraffin, semithin, and ultrathin sections of cerebellum anlagen, indicate that, under normal conditions, the cerebellar "folia" begin to appear on the 9th-10th i.d., and the secondary and tertiary ones are completely formed at the 14th i.d., when also the cortex layers begin to be recognizable owing to the successive migration processes of cells from two germinal layers and the mitotic proliferation of neuroblasts. The Purkinje cells are identifiable only at the 10th i.d. as large neuroblasts, irregularly stratified beneath the external granular layer, and characterized by a scanty amount of basophilic cytoplasm; they progressively acquire features of neurocytes, with abundant basophilic cytoplasm and numerous ramifications of their dendritic tree. The differentiation of Purkinje neurocytes, complete at the 17th i.d., is accompanied by degeneration events affecting some of them, which appear modified in shape, size and both structural and ultrastructural features (e.g. nuclear pycnosis, condensation and/or vacuolization of the cytoplasm). In the hypoxic embryos the main morphogenetic and histogenetic processes normally unfold during the embryonic life and the Purkinje cell differentiation occur like in the normal embryos until the 15th i.d.; afterwards a progressively greater number of them undergoes severe morphological modifications, comparable to those affecting only few neurons in the cerebellum of normally developed embryos.(ABSTRACT TRUNCATED AT 250 WORDS)