Journal of Dental Research, Vol 78, 49-53, Copyright © 1999 by International & American Associations for Dental Research Online Journals
Origin of primary sensory neurons innervating the buccal stretch receptor
T. Yamamoto, M. Onozuka, S. Nagasaki, K. Watanabe and S. Ozono
Department of Physiology, Tokyo Dental College, Chiba, Japan.
The primary sensory neurons innervating mechanoreceptors in oro-facial
regions have their cell bodies in either the trigeminal ganglion or the
mesencephalic nucleus of the trigeminal nerve. The buccal stretch receptor
(BSR), a type of mechanoreceptor in the jaw of rodents, has recently been
recognized as signaling the position of the mandible. The location of the
primary afferent neurons innervating this receptor is unknown. To
investigate the cell bodies of the BSR afferent neurons in rats, we applied
wheat germ agglutinin-horseradish peroxidase (WGA-HRP) to the proximal
stump of the severed nerve branch of the buccal nerve that supplied the
BSR. HRP-labeled cell bodies were observed in the posterolateral portion of
the ipsilateral trigeminal ganglion. None was found in the contralateral
trigeminal ganglion or in the brainstem. All labeled cell bodies were oval
or round and closely resembled pseudo-unipolar neurons. The mean diameter
of the labeled somata ranged between 25.5 and 52.5 microm, with small (<
or = 30 microm), medium (from 31 to 40 microm), and large somata (> or =
41 microm) accounting for 8.8%, 54.9%, and 36.3%, respectively. Among the
myelinated nerve fibers in the branch in which WGA-HRP was applied, 78.5%
terminated in the BSR and had larger fiber diameters than the rest,
indicating that most of the medium and large HRP-labeled cell bodies were
BSR afferents. From these results and the ontogenetic origin of this
receptor, it is suggested that the BSR differentiated from the
mechanoreceptors in the oral mucosa or the fascia of masticatory muscles.
