Immunohistochemical characterization of postnatal changes in cerebellar cortical cytoarchitectures in ferrets.

We immunohistochemically characterized postnatal changes in cerebellar cortical cytoarchitectures in ferrets using markers for cerebellar cortical neurons and glial cells. Although 10 lobules of the vermis were already observed on postnatal day (PD) 4, Purkinje cells were still arrayed into two to three layers. Purkinje cells were aligned in a monolayer by PD 10 and formed mature shapes on PD 42 by developing their dendritic arbors. Parvalbumin immunostaining revealed relatively slower maturation of Purkinje cells in the Lobule X cortex than in other lobules. Basket and stellate cells emerged in the molecular layer on PDs 21 and 42, respectively. Rosette-like arranged glutamate decarboxylase 65 and 67-positive puncta were observed in the inner granular layer (IGL) on PD 21. Proliferating cell nuclear antigen immunostaining appeared in the outer zone of the external granular layer (EGL) containing progenitors of granular neurons on PDs 4-21. Bergmann glial processes extending vertically through the molecular layer and EGL were visible with GFAP immunostaining on PD 10 and thereafter. Their somata, aligned in the Purkinje cell layer, showed immunopositivity to Sox2 already on PD 4 and subsequently to S100 protein on PD 10. Sox2-positive cells were found sparsely in the IGL. Few of them were NeuN positive on PD 90, predicting the possibility of adult neurogenesis. These immunohistochemical results revealed that ferrets underwent cerebellar cortical histogenesis during their postnatal life in sequences. Relatively slow development or maturation of the ferret cerebellum was revealed by the timing of the monolayer alignment and morphological maturation of Purkinje cells.