BLOCKADE OF ENDOGENOUS LIGANDS OF TRKB INHIBITS FORMATION OF OCULAR DOMINANCE COLUMNS

We have examined the hypothesis that the segregation of LGN axon termi nals into ocular dominance (OD) patches in layer 4 of the visual corte x requires neurotrophins, acting as signals to modulate the pattern of synaptic connectivity. Neurotrophin receptor antagonists, composed of the extracellular domain of each member of the trk family of neurotro phin receptors fused to a human Fc domain, were infused directly into visual cortex during the peak phase of OD column formation. Infusion o f trkB-IgG, which binds BDNF and NT-4/5, inhibited the formation of OD patches within layer 4, while trkA-IgG and trkC-IgG, which preferenti ally bind NGF and NT-3, respectively, had no effect. The autoradiograp hic labeling of LGN terminals in cortical layer 4 was reduced by trkB- IgG, in contrast with the increased labeling observed following NT-4/5 infusion. These data suggest that an endogenous ligand of trkB, norma lly present in limiting amounts within visual cortex, is necessary for the selective growth and remodeling of LGN axons into eye-specific pa tches.