The central projection of masticatory afferent fibers to the trigeminal sensory nuclear complex and upper cervical spinal cord

Abstract

Retrograde and anterograde transport of horseradish peroxidase-wheat germ agglutinin (HRP-WGA) conjugate was used to study the organization of primary afferent neurons innervating the masticatory muscles. HRP applied to the nerves of jaw-closing muscles--the deep temporal (DT), masseter (Ma), and medial pterygoid (MP)--labeled cells in the trigeminal ganglion and the mesencephalic trigeminal nucleus (Vmes), whereas HRP applied to nerves of the jaw-opening muscles--anterior digastric (AD) and mylohyoid (My)--labeled cells only in the trigeminal ganglion. Cell bodies innervating the jaw-closing muscles were found with greater frequency in the intermediate region of the mandibular subdivision, while somata supplying the jaw-opening muscles were predominant posterolaterally. The distribution of their somatic sizes was unimodal and limited to a subpopulation of smaller cells. Projections of the muscle afferents of ganglionic origin to the trigeminal sensory nuclear complex (TSNC) were confined primarily to the caudal half of pars interpolaris (Vi), and the medullary and upper cervical dorsal horns. In the Vi, Ma, MP, AD, and My nerves terminated in the lateral-most part of the nucleus with an extensive overlap in projections, save for the DT nerve, which projected to the interstitial nucleus or paratrigeminal nucleus. In the medullary and upper cervical dorsal horns, the main terminal fields of individual branches were confined to laminae I/V, but the density of the terminals in lamina V was very sparse. The rostrocaudal extent of the terminal field in lamina I differed among the muscle afferents of origin, whereas in the mediolateral or dorsoventral axis, a remarkable overlap in projections was noted between or among muscle afferents. The terminals of DT afferents were most broadly extended from the rostral level of the pars caudalis to the C3 segment, whereas the MP nerve showed limited projection to the middle one-third of the pars caudalis. Terminal fields of the Ma, AD, and My nerves appeared in the caudal two-thirds of the pars caudalis including the first two cervical segments, the caudal half of the pars caudalis and the C1 segment, and in the caudal part of the pars caudalis including the rostral C1 segment, respectively. This rostrocaudal arrangement in the projections of muscle nerves, which corresponds to the anteroposterior length of the muscles and their positions, indicates that representation of the masticatory muscles in lamina I reflects an onion-skin organization. These results suggest that primary muscle afferent neurons of ganglionic origin primarily mediate muscle pain.(ABSTRACT TRUNCATED AT 400 WORDS)

Systemic administration of monosodium glutamate elevates intramuscular glutamate levels and sensitizes rat masseter muscle afferent fibers

“…The rat's head was placed in a stereotaxic frame, the skin over the dorsal surface of the skull reflected and a trephination made on the left side of the skull to allow a microelectrode to be lowered through the brain and into the trigeminal ganglion. The skin, muscle and dura overlying the brainstem and upper cervical spinal cord were removed to permit placement of a stimulating electrode in contact with the brainstem for antidromic activation of brainstem projecting masticatory muscle afferent fibers that have been shown to project predominantly to the caudal brainstem (Shigenaga et al, 1988;Capra and Wax, 1989;Cairns et al, 2001Cairns et al, , 2002. Physiological parameters were continuously monitored throughout the experiment as described above.…”

Differential Effects of Estradiol on Encoding Properties of TMJ Units in Laminae I and V at the Spinomedullary Junction in Female Rats

“…Studies in rat and cat indicate the TMJ region is innervated mainly by small-diameter myelinated and unmyelinated fibers (Ioi et al 2006;Kido et al 1995;Takeuchi and Toda 2003;Takeuchi et al 2001) that project to second-order neurons at the trigeminal subnucleus caudalis/upper cervical cord (Vc/C1-2) junction (Shigenaga et al 1986(Shigenaga et al , 1988. Lesion of the Vc/C1-2 junction, but not more rostral trigeminal brain stem areas, prevents increases in masseter muscle activity after TMJ inflammation (Hu et al 1997).…”

Efferent and collateral organization of paratrigeminal nucleus projections: An anterograde and retrograde fluorescent tracer study in the rat

“…Neuroanatomical studies have shown that the PTN receives input from the periphery through cranial nerves V (Nishimori et al, 1986;Shigenaga et al, 1986Shigenaga et al, , 1988Pfaller and Arvidsson, 1988;Panneton, 1991), IX, and X Mizuno, 1982, 1983;Arvidsson and Thomander, 1984;Hamilton and Norgren, 1984;Altschuler et al, 1989;Nazruddin et al, 1989). Afferent projections coursing in branches of the facial nerve, which have their cell bodies in the nodose ganglion, also terminate in the PTN (Arvidsson and Thomander, 1984).…”