In recent years, the isthmo-optic nucleus (ION) in the avian centrifugal system became a new model to study the apoptosis and the development of central nervous system (CNS). During its development, together with the formation, folding and laminating of the nucleus, there exist some temporal pathways linked to the nucleus. More than half of its neurons befall apoptosis in this period. Researches show that proper efferent and afferent projections are essential to the survival of neurons. The molecular mechanism indicates that apoptosis is related to a series of neurotrophins and their receptors. Apoptosis plays an important role in the development of CNS.