Retinotectal projection after partial ablation of chick optic vesicles.

We excised the dorsal part of the optic vesicle of chick embryos at stages 13-14 (embryonic day 2). The remainder of the optic vesicle reoganized and developed a small eye. This study was undertaken to determine how locus specificity is kept within the reorganized retina. The projection pattern from the reorganized eyes was examined with HRP and DiI, a fluorescence axon tracer. Whole retinal fibers labeled with HRP were found on the medial half of the contralateral tectum, thus showing the lateral half of the tectum as being devoid of retinal fibers. DiI labeling revealed a detailed projection map, with the dorsoposterior to ventroanterior axis of the reorganized eye being projected as the rostrocaudal axis on the medial half of the tectum. These results suggest that the positional specificity along the anteroposterior axis of the optic vesicle was already determined at the time of excision, and that the ventral part of the optic vesicle reorganized the "whole" retina, keeping its original anteroposterior polarity.