Development of the avian accessory optic system: effects of embryonic optic lesions

Representative cross-sections of the nuclei ectomammillaris (EM) from both normal and optically lesioned chick embryos (45 h of incubation, stage 12), were analyzed and compared on days 6, 8, 10, 12, 14 and 16 of incubation. An identifiable EM is clearly present at 8 days, in both normal and lesioned embryos, and increases in cell number and area up to embryonic day 12. However, embryos with partial or complete unilateral optic ablations demonstrate an apparent acceleration in cell death rate when compared with normals, from days 12-16, when a relatively mature and stable form of EM is apparently reached. Thus, early optic lesions do not affect the morphology of EM until day 12. These data also indicate that embryonic ipsilateral pathways to EM may persist and even expand when one eye primordium is removed or partially lesioned.