Neurotransmitter organization of the nucleus of Edinger–Westphal and its projection to the avian ciliary ganglion

Abstract

Two morphologically distinct types of preganglionic endings are observed in the avian ciliary ganglion: boutonal and cap-like. Boutonal endings synapse on ciliary ganglion neurons (called choroidal neurons) innervating choroidal blood vessels, while cap-like endings synapse on ciliary ganglion neurons (called ciliary neurons) controlling the lens and pupil. Some of both types of preganglionic endings contain the neuropeptides substance P (SP) and/or leucine-enkephalin (LENK). Although both types of preganglionic terminals are also known to be cholinergic, there has been no direct evidence that SP and LENK are found in cholinergic endings in the ciliary ganglion. The present studies in pigeons, which involved the use of single- and double-label immunohistochemical techniques, were undertaken to examine this issue, as well as to (1) determine the relative percentages of the boutonal and cap-like endings that contain SP, LENK, or both SP and LENK; and (2) determine if the two different types of terminals in the ciliary ganglion arise from different subdivisions of the nucleus of Edinger-Westphal (EW).Single- and double-label immunohistochemical studies revealed that all neurons of EW, regardless of whether they contained immunohistochemically detectible amounts of SP or LENK, are cholinergic. In the medial subdivision of EW (EWM), which was found to contain approximately 700 neurons, 20.2% of these neurons were observed to contain both SP and LENK, while 11.6% were observed to contain SP only and 10.7% were observed to contain LENK only. In contrast, in lateral EW (EWL), which was found to contain approximately 500 neurons, 16.2% of the neurons were observed to contain both SP and LENK, while 19.2% of the neurons were observed to contain SP only and 12.6% were observed to contain LENK only. Retrograde-labeling studies involving horseradish peroxidase injections into the ciliary ganglion revealed that EW was the sole source of input to the ciliary ganglion and all, or nearly all, neurons in EW innervate the ciliary ganglion.Immunohistochemical labeling of the ciliary ganglion neurons with an antiserum against choline acetyltransferase revealed that approximately 900 choroidal neurons and approximately 600 ciliary neurons are present in the ganglion, all of which receive cholinergic preganglionic endings. Of the choroidal neurons, 94% receive butonal terminals containing both SP and LENK, while only 2% receive SP+ only boutonal endings and 2% receive LENK+ only butonal endings. Of the ciliary neurons, 25% receive cap-like endings containing both SP and LENK, 30% receive cap-like endings containing only SP and 3% receive cap-like endings containing only LENK. Total unilateral lesions of EW resulted in the loss of all SP+ or LENK+ terminals in the ipsilateral ganglion. Subtotal EW lesions that spared either part of EWM or part of EWL revealed that boutonal endings arise from EWM neurons and cap-like endings from EWL neurons.The present results suggest that the choroidal neurons, which regulate choroidal blood flow, may be relatively uniform in their functional properties since they nearly all receive boutonal endings from EWM that co-contain SP, LENK, and acetylcholine. In contrast, the ciliary neurons, which receive their preganglionic input from EWL, may consist of at least three major functionally distinct subgroups: (1) those receiving SP/LENK/acetylcholine-containing cap-like endings; (2) those receiving SP/acetylcholine-containing cap-like endings; and (3) those receiving acetylcholine-containing cap-like endings. The functional diversity of ciliary neurons may in part be related to the fact that some ciliary neurons innervate the iris and others the ciliary body.

PHOX2A regulation of oculomotor complex nucleogenesis

“…By contrast, the chicken shares with all birds a cleanly segregated OMC with discrete subnuclei that innervate specific autonomic and ocular muscle targets (Evinger, 1988;Gamlin et al, 1984;Heaton and Wayne, 1983). Indeed, in birds the preganglionic motoneurons arise exclusively from the Edinger-Westphal (EW) nucleus, which is the dorsal component of the OMC (Gamlin and Reiner, 1991;Reiner et al, 1991). The segregation of neurons in the developing chick OMC into discrete subnuclei occurs in a series of migrations, as documented in the classic histological studies of Levi-Montalcini (Levi-Montalcini, 1963) and Puelles (Puelles, 1978).…”

Evidence that urocortin is absent from neurons of the Edinger-Westphal nucleus in pigeons

“…The Edinger-Westphal nucleus (EWN) of birds is the autonomic part of the oculomotor complex and the source of preganglionic inputs to the ciliary ganglion (1)(2)(3)(4). In avian species, the EWN can be divided into two portions, lateral and medial, which are distinct in cell size and shape and in their physiological roles.…”

“…In avian species, the EWN can be divided into two portions, lateral and medial, which are distinct in cell size and shape and in their physiological roles. In pigeons, the lateral portion (EWL) consists of bigger and more spherical cells that project to ciliary neurons of the ciliary ganglion, giving rise to the ciliary nerve innervating the ciliary body and the iris sphincter muscle (1)(2)(3)(4). The ciliary neurons mediate pupilloconstriction and accommodation.…”

“…The ciliary neurons mediate pupilloconstriction and accommodation. The medial portion of the EWN (EWM), in turn, innervates choroidal neurons of the ciliary ganglion, which project to the choroid and regulate its blood flow (4,5).…”

Morphological Analogy of the Rostral Midline Area in the Chicken Midbrain to the Anteromedian Nucleus in the Mammalian Midbrain.

“…On the other hand, it has been known that a small neuron group called the anteromedian nucleus (AM) exists in the midline area of the mammalian midbrain. This neuron group in mammals also contains many SP-IR neurons [10,11], and these neurons send their axons to the spinal cord [14]. In this paper, we attempted to reason about the homology between the avian RMA and the mammalian AM on the basis of the neuroanatomical analogy in these small areas.…”