Development of adrenergic innervation of the iris and fluorescent ganglion cells in the choroid of the chick eye.
The developing innervation of the chick eye has been studied using catecholamine histofluorescence. The innervation of the pupillary dilator by the superior cervical ganglion begins on day 13 of incubation when fluorescent axons can be seen in the ciliary zone circumscribing the dilator. On day 14 a few processes are seen to branch from this band into the dilator. The number of processes in the dilator increases on days 15 and 16. After day 16 there is a reorganization of the fibers radially accompanied by a moderate increase in the number of processes. In addition, a group of fluorescent cells can be seen in the choroid adjacent to the ciliary body. These cells are bipolar at day 9 and become multipolar by 12 days of incubation. These cells contribute to a fluorescent plexus of processes in the choroid which stops abruptly at the border of the choroid and ciliary zone. It is thought that they represent a terminal sympathetic ganglion receiving preganglionic input from the carotid nerve.