Journal of Neuroscience, Vol 2, 994-1003, Copyright © 1982 by Society for Neuroscience
Localization of substance P-like and enkephalin-like immunoreactivity within preganglionic terminals of the avian ciliary ganglion: light and electron microscopy
JT Erichsen, HJ Karten, WD Eldred and NC Brecha
The avian ciliary ganglion receives its only recognized input from the
nucleus of Edinger-Westphal. This is known to be a cholinergic input. In
the present study, using fluorescein isothiocyanate and peroxidase-
antiperoxidase immunohistochemical methods, substance P-like and
enkephalin-like immunoreactivity has been found within preganglionic
terminals of the avian ciliary ganglion. The ciliary ganglion is known to
consist of two distinct cell populations: small choroid cells that project
to the smooth muscle coat of the choroid and large ciliary neurons that
send axons to both the iris and the ciliary body. Preganglionic terminals
on choroid cells consist of small boutonal endings, whereas ciliary neurons
receive a calyx-like cap ending around the hilus of the cell. Substance
P-like and enkephalin-like immunoreactivity was localized to preganglionic
axons and to both boutonal and calyx-like terminations upon cells of the
ciliary ganglion. Electron microscopic studies of both substance P-like and
enkephalin-like immunoreactive terminals revealed small clear core vesicles
(approximately 58 nm in diameter) and two sizes of dense core vesicles
(approximately 85 and approximately 119 nm in diameter). Immunoreactive
staining was observed only in the smaller dense core vesicles. The
unlabeled clear core vesicles were clustered at synaptic release sites,
while the immunoreactive and larger unlabeled dense core vesicles usually
were not near these synaptic specializations. These observations strongly
imply that neuropeptides co-occur with acetylcholine in preganglionic axons
of the ciliary ganglion.