INHIBITION OF OCULAR DOMINANCE COLUMN FORMATION BY INFUSION OF NT-4 5OR BDNF/

During the development of the visual system of higher mammals, axons f rom the lateral geniculate nucleus (LGN) become segregated into eye-sp ecific patches (the ocular dominance columns) within their target, lay er 4 of the primary visual cortex. This occurs as a consequence of act ivity-dependent synaptic competition between axons representing the tw o eyes, The possibility that this competition could be mediated throug h neurotrophin-receptor interactions was tested. Infusion of neurotrop hin-4/5 (NT-4/5) or brain-derived neurotrophic factor (BDNF) into cat primary visual cortex inhibited column formation within the immediate vicinity of the infusion site but not elsewhere in the visual cortex. Infusion of nerve growth factor, neurotrophin 3 (NT-3), or vehicle sol ution did not affect column formation. These observations implicate Tr kB, the common receptor for BDNF and NT-4/5, in the segregation of LGN axons into ocular dominance columns in layer 4. Moreover, they sugges t that in addition to their better known roles in the prevention of ce ll death, neurotrophins may also mediate the activity-dependent contro l of axonal branching during development of the central nervous system .