The developmental appearance of Thy-1 in the avian cerebellum.

The cellular localization of the Thy-1 antigen during development of the chick cerebellum has been investigated using a monoclonal antibody SB1-20.11. Improved cellular morphology and retention of both membrane and intracellular antigenicity was achieved by the immunohistochemical labelling of polyester wax sections using an indirect peroxidase visualization protocol. A parallel histological investigation was carried out using a modified silver staining procedure based on that of Bodian. Immunoreactivity was found throughout development in the soma and dendritic tree of the Purkinje cell, in the internal granular layer, white matter and elements of the deep cerebellar nuclei. The antigen's expression closely correlates to the morphological maturation of Purkinje cell population. Furthermore, it appears to reflect the formation of glomeruli and the basket cell interaction with the Purkinje cell. An association of Thy-1 with climbing fibres, as reported previously in rodent species, cannot be unambiguously shown in the chick because of the high levels of Thy-1 expressed throughout development on the Purkinje cell dendrites in the molecular layer. The spatial and temporal pattern of expression in the chick cerebellum suggests that Thy-1 contributes to the definition of synaptic fields.