Journal of Neuroscience, Vol 8, 146-155, Copyright © 1988 by Society for Neuroscience
Target specificity of neuropeptide Y-immunoreactive cranial parasympathetic neurons
GG Leblanc and SC Landis
Department of Neurobiology, Harvard Medical School, Boston, Massachusetts 02115.
We recently showed that neuropeptide Y (NPY)-like immunoreactivity occurs
in subpopulations of neurons in 3 cranial parasympathetic ganglia: the
otic, sphenopalatine, and ciliary. The present work identifies the target
tissues innervated by cranial parasympathetic NPY- immunoreactive neurons.
Plexuses of NPY-immunoreactive fibers were observed in the parotid gland,
the target of the otic ganglion, and in the intraorbital lacrimal gland and
palate, targets of the sphenopalatine ganglion. NPY-immunoreactive fibers
of apparent parasympathetic origin innervated glandular acini in all 3
structures and were also present around small blood vessels in the parotid
and intraorbital lacrimal glands. These fibers were presumed to be
parasympathetic because they were not affected by removal of the superior
cervical ganglion and because their distribution was coextensive with that
of vasoactive intestinal polypeptide (VIP) immunoreactivity, which we have
previously shown to be colocalized with NPY in the cell bodies of otic and
sphenopalatine ganglion neurons. In contrast, no NPY-immunoreactive fibers
were observed in the iris or ciliary body of acutely sympathectomized rats,
suggesting that NPY- immunoreactive neurons in the ciliary ganglion do not
normally transport detectable levels of NPY to their terminals. The target
specificities of cranial parasympathetic NPY-immunoreactive neurons are
different from those of sympathetic NPY-immunoreactive neurons. Sympathetic
NPY-immunoreactive fibers innervated the iris and ciliary body, and the
blood vessels but not the parenchymal cells of all the glands examined. In
contrast, parasympathetic NPY-immunoreactive fibers primarily innervated
glandular acini. NPY-immunoreactive neurons in the sphenopalatine ganglion
displayed an additional level of specificity in their projection pattern in
that they innervated only a subset of the ganglion's array of target
glands: they innervated the intraorbital lacrimal gland and the seromucous
glands of the palate but not the exorbital lacrimal gland or the glands of
the nasal mucosa. The finding that NPY immunoreactivity is present in the
parasympathetic innervation of secretory acini in several craniofacial
glands raises the possibility that NPY plays a role in the parasympathetic
control of glandular secretion. The observed overlap in the distributions
of NPY- and VIP-immunoreactive fibers in these glands further suggests that
NPY may interact with VIP to stimulate secretion.
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