GAP-43,netrin-1,collapsin-1,and neuropilin-1 have been regarded to play crucial roles in the formation of patterned neural connections.The cerebellum consists of five distinct concentric layers:white matter,internal granule layer (IGL),Purkinje cell layer (PCL),molecular layer (ML),and external granule layer (EGL) in young rodents.Cells in EGL are generated after birth.In contrast Purkinje neurons are born before birth,which receive main innervations of climbing fibers fi'om the inferior olivary nucleus and parallel fibers from the internal granule cells.These innervations are mostly established in the first three postnatal weeks,accompanying the sprouting and maturation of Purkinje cells.The potential roles of GAP-43,netrin-1,collapsin-1 and neuropilin-1 in the postnatal development of cerebellum remain unclear.To get insights into the above issue,the expression of GAP-43,netrin-1,collapsin-1,and neuropilin-1 mRNAs and proteins were examined in the cerebellum of mice at postnatal days (P) 5,P10,P20 and adulthood.The results showed that these four molecules were expressed in different temporal and spatial patterns in the postnatal cerebellum of mice,which was in match with axonal synaptogenesis,elongation and synapse formation during postnatal development and adulthood.By using double immunohistocbemistry,it was found that the Purkinje cells stained for GAP-43 were also positive for either netrin-1 or collapsin-1 at P10,and cells stained for collapsin-1 were also positive for netrin-1 or neuropilin-1.It was suggested that the four molecules are involved in the postnatal development of cerebellum.