Mesostriatal dopaminergic axons transiently express high levels of NILE during development

The distribution of nerve growth factor-inducible large external (NILE) glycoprotein in the developing mesostriatal dopaminergic system was studied by immunolabeling prenatal, postnatal, and adult rat brains for both NILE and tyrosine hydroxylase (TH). NILE-immunoreactive (NILE-IR) material outlined the TH-immunoreactive (TH-IR) neurons in the ventral mesencephalon at ages E14, E15, and E16 but not at later ages. Fascicles of TH-IR axons in the developing mesostriatal dopaminergic tract were strongly immunoreactive for NILE from E15 through E20. In the postnatal brain, NILE-IR material no longer clearly outlined the fascicles of dopaminergic axons as they ran from the mesencephalon to the striatum. In the striatum of postnatal and adult rats, NILE-IR material was diffusely distributed through the neuropil. Our observations suggest that NILE may play a role in guidance of growing dopaminergic axons in the developing mesostriatal tract and aggregation of the dopaminergic axons into fascicles.