Degeneration in the nucleus of origin of the preganglionic fibers to the chick ciliary ganglion following early removal of the optic vesicle

Extirpation of the optic vesicle in chick embryos towards the end of the second day of incubation leads to a progressive hypoplasia in the ciliary ganglion and to a secondary, or retrograde transneuronal degeneration, in the accessory oculomotor nucleus from which the preganglionic fibers to the ciliary ganglion are derived. The primary changes in the ciliary ganglion are first observed at about the eighth day of incubation and the resulting cell loss proceeds over the next three or four days to include almost all of the ganglion cells. At the tenth day of incubation (when the volume of the ciliary ganglion is reduced by just over 70%) early signs of cell degeneration can be recognized in both the medial and lateral divisions of the accessory oculomotor nucleus in the form of cell shrinkage, loss of Nissl material and some cell loss. By the fourteenth day of incubation (Stage 40) the nucleus is virtually depleted of neurons with only an occasional shrunken cell persisting in the medial accessory nucleus. After even longer survival periods complete cell loss may occur in the nucleus, but in many of the experiments a small number of cells survive: these are probably related to ciliary ganglion cells which have established aberrant peripheral connections, or in those cases in which the lesion of the optic vesicle was incomplete, to the cells which innervate the surviving ocular tissue.