Analysis of avian retinotectal projection.

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The alar plate of the prosencephalon of the guail embryo was haterotopically transplanted into the alar plate of the mesencephalon of the chick embryo at the 7-10 somite stage. When the transplant was completely integrated into the host mesencephalon, the transplant differentiated into the laminar structures resmbling to the optic tectum. Immunohistochemistry with MAb-39B11, which recognizes a species-specific antigen on chick never fibers, showed that the host optic nerve fibers innervated both in the host and the transplant when the transplant was integrated into the host, but that optic nerve fibers did not invade the transplant when it had not a laminar pattern of the tectum. Our study suggests that the prosencephalon has the capacity to differentiate into the optic tectum at the 7-10 somite stage.Next, we studied in E9 to E18 chicks the development of topographic order of the projection from temporal retina to rostral optic tectum using the anterograde fluorescent tracers DiI and … More DiO. The trajectories and branching patterns were studied whole mounts of retina and tectum.Retinal fibers enter the contralateral optic tectum at its rostral edge and grow caudally. We labeled the temporal retinal fibers. They terminate on the rostral edge of the tectum. Many axons grow caudally and mediolaterally beyond the expected terminal zone. A small number of overshooting axons reverse course 180゜ and grow back to the terminal zone. After considerable elongation, an axon develops numerous side branches and arbors both in and outside of the appropriate terminal zone. Aberrant arbors and axon collaterals that fail to arborize in the appropriate terminal zone are rapidly eliminated over about a 2 day period. These events lead to the establishment by E16 of the discrete and highly focused zone o fterminal arborization characteristio of the mature projection. The topographic projection is very precise, leaving course corrections along mediolateral and rostrocaudal tectal axis after maturation. Less