Distribution within the choroid of cholinergic nerve fibers from the ciliary ganglion in pigeons.

The distribution of the ciliary ganglion (CG) innervation to the pigeon choroid was determined immunohistochemically, using antisera against choline acetyltransferase (CHAT) and a neurofilament-related protein (the 3A10 antigen). Single-labeling revealed that the nerve fibers containing these two antigens were similarly distributed in the pigeon choroid, with the superior and temporal quadrants of the eye containing the most fibers. Both types of fibers surrounded and ramified on choroidal blood vessels. Additionally, CHAT+ varicosities were evident among vessels in the choroid and choriocapillaris. Double-label immunofluorescence revealed that CHAT and the 3A10 antigen were almost completely colocalized in choroidal nerve fibers, but absent from CHAT+ varicosities. Substance P-containing and calcitonin gene-related peptide-containing choroidal nerve fibers were poor in 3A10+ labeling. Transection of the postganglionic fibers of the CG reduced CHAT+ and 3A10+ nerve fibers in the choroid to 3-5% of normal abundance, with most of the residual fibers being located in the nasal and inferior quadrants. The present results suggest that the CG in pigeon preferentially influences choroidal blood flow in the superior and temporal parts of the eye, which are involved in high acuity and binocular vision.