Lesion-induced regulation of netrin receptors and modification of netrin-1expression in the retina of fish and grafted rats

To determine whether netrin receptors (DCC, UNC5H1, UNC5H2) and netrin-1 ar e present in the adult rat retina and may affect regeneration of retinal ga nglion cell (RGC) axons into peripheral nerve (PN) grafts, in situ hybridiz ation (ISH) and immunostaining experiments were performed in normal and ope rated rats. Netrin-1 expression was not found in the optic nerve head of ad ult rats, normal and postlesion, but appeared transiently at 7 and 14 days after PN grafting. ISH signals of netrin receptors, however, disappeared fr om RGCs within 2 days after lesion and remained absent after PN grafting ex cept for UNC5H2, which transiently occurred in a few RGCs. Netrin-1 express ion was observed in the optic nerve head of adult fish, normal and postlesi on, and the netrin-1 Fc fusion protein bound to young growing and all regen erating axons. Thus, the netrin-1-dependent guidance system continues to fu nction in fish but apparently no longer operates in adult rats.