Retinotopically inappropriate synapses of subnormal density formed by surgically misdirected optic fibers in goldfish tectum.

Selected optic fibers were surgically deflected from one tectum onto the opposite host tectum which was denervated by eye enucleation. At 6-8 months, deflected fibers were labeled with horseradish peroxidase and the retinotopically inappropriate part of tectum was examined using electron microscopy. Numerous (labeled) optic synapses were found in the primary optic innervation layer of the 'wrong' part of tectum but they were about half the normal density. The number and density of non-optic synapses was not found to be affected. These findings indicate optic fibers compete with each other but not with non-optic fibers for synaptic sites in tectum.