[Developmental mechanisms of neural network in the cerebellar system]

Various cell adhesion molecules and neurotrophic factors are involved in cell migration, axonal elongation and synaptogenesis during the development of neural networks. The developmental mechanisms of neural networks were investigated in the mouse cerebellar system in relation to the neuron-glia interactions and the expression of cell adhesion molecules. Radial migration of Purkinje cells in the cerebellar primordium is guided by contact with radial glial processes, and expression of the neuron-glia cell adhesion molecule tenascin is involved in this process. Purkinje cell migration is obstructed in the reeler mutant mouse, and the disorganized arrangement of radial glial processes is considered to be responsible for this defect. Pontine nuclei and inferior olivary nuclei constitute the cerebellar afferent system, and these neurons are generated from the rhombic lip which is originated from the alar plate of the metencephalon in common with the cerebellar primordium. Pontine nuclei migrate tangentially from the rhombic lip under the pia mater, and the binding sites for peanut lectin are specifically expressed on the migratory route. Thy-1 molecule, a member of the immunoglobulin superfamily is expressed transiently in the synaptogenesis between the cerebellar afferent fibers and their target neurons in the developing cerebellar cortex. The homophilic binding activity of this molecule is considered to be involved in the recognition between presynaptic terminals and postsynaptic structures.