Parasympathetic ocular control — functional subdivisions and circuitry of the avian nucleus of Edinger-Westphal

The nucleus of Edinger-Westphal (EW), the parasympathetic component of the oculomotor nuclear complex of the midbrain, controls several extraretinal ocular functions via its projection to the ciliary ganglion. Using a highly visual animal, the pigeon, we have identified three anatomically and functionally distinct subdivisions of EW: one controlling pupilloconstriction; one controlling lens curvature (accommodation); and one controlling the smooth muscle of the choroid. We have defined separate central visual pathways that provide bisynaptic retinal input to the first and last of these subdivisions. These pathways may provide the central neural substrate for the pupillary light reflex and for the visual control of blood flow within the choriocapillaris, respectively. Finally, we have found that the cholinergic preganglionic fibers of EW that innervate the ciliary ganglion contain both the neuropeptides substance P and enkephalin. Such information on the transmitters/ ‘neuromodulators’ used by the EW-ciliary ganglion system may provide insights into the pharmacological control of pupillocnstriction, accommodation and choroidal function