The central projections of tooth pulp afferent neurons in the rat as determined by the transganglionic transport of horseradish peroxidase

Abstract

Transganglionic transport of horseradish peroxidase (HRP) or horseradish peroxidase-wheat germ agglutinin conjugate (HRP-WGA) was used to map in detail the central projections of trigeminal primary afferent neurons that innervate the dental pulp organ of the rat. In each of ten animals, 0.5-2.0 microliters of enzyme solution was injected into the pulp chamber of the first maxillary molar tooth. Postmortem examination of the decalcified teeth in all cases showed that the HRP/HRP-WGA remained confined to the pulp chamber and pulp roots, with no spread of enzyme into periapical tissues. HRP-labeled tooth pulp afferent fibers projected to all four rostrocaudal subdivisions of the ipsilateral trigeminal brainstem nuclear complex (TBNC) and to the upper cervical spinal cord. The labeled terminal fields formed a column that stretched relatively uninterrupted from just caudal to the rostromedial tip of the trigeminal principal sensory nucleus to at least the C2 segment of the spinal cord. The density of the afferent projection varied markedly from one rostrocaudal level of the TBNC to the next but was heaviest in an area encompassing the caudal one-half of the principal sensory nucleus and the rostral two-thirds of pars oralis. Fibers projected only lightly to pars caudalis, where they terminated preferentially in laminae I, IIa, and the junctional zone between laminae IV and V. HRP-labeled terminals in C1 and C2 were located almost exclusively in laminae I. In the dorsoventral axis, the terminal fields in the TBNC were located in a surprisingly dorsal part of the complex, well within what has been shown by others to be largely an area of termination for mandibular division fibers. Most fibers ended in medial parts of the TBNC, with the exception of two modestly labeled terminal fields located in the lateral aspects of rostral pars oralis and rostral pars caudalis. No labeled fibers terminated in the contralateral TBNC or contralateral cervical spinal cord.

Central projection of calcitonin gene-related peptide (CGRP)- and substance P (SP)-immunoreactive trigeminal primary neurons in the rat

“…The dorsomedial nucleus, first described by Åstrøm (1953), can be distinguished from the rest of the Vo by its cytoarchitecture and is highly developed in rodents. The nucleus is known to receive trigeminal primary projection from exclusively intraoral structures (Arvidsson and Gobel, 1981;Marfurt, 1981;Jacquin et al, 1983;Marfurt and Turner, 1984;Shigenaga et al, 1986aShigenaga et al, ,b, 1989Takemura et al, 1987Takemura et al, , 1991. Prominent CGRP-and SP-ir projection of exclusively trigeminal primary neurons as shown in this study has added another characteristic that distinguishes the rodent dorsomedial nucleus from the rest of the BSTC.…”

“…This suggests that a considerable proportion of the trigeminal primary nociceptive projection, especially from the intraoral structures, is directed to the relay nuclei located in the rostral subdivisions of the BSTC. This idea is supported by the fact that a large proportion of central projection of presumed primary nociceptors innvervating the tooth pulp is directed to rostral subdivisions of the BSTC (Arvidsson and Gobel, 1981;Westrum et al, 1981;Marfurt and Turner, 1984;Shigenaga et al, 1986bShigenaga et al, , 1989Takemura et al, 1991;Sugimoto and Takemura, 1993).…”

Tooth Movement Activates the Central Amygdala and the Lateral Hypothalamus by the Magnitude of the Force Applied

“…Anatomic studies using transganglionic transport of neuronal tracers have shown that tooth afferents project to the principal sensory and spinal nuclei of the trigeminal system. 2 Accordingly, tooth movement in rats was seen to induce c-Fos expression in neurons localized in the rat trigeminal nucleus complex as revealed by Fos-immunoreactivity (Fos-IR). [3][4][5] It was also seen to activate neurons in the parabrachial nucleus, which is one of the important relay nuclei for processing information from the orofacial regions.…”

Central Projections of Trigeminal Afferents Innervating the Face in Naked Mole‐Rats (Heterocephalus glaber)

“…These results are consistent with previous investigations of trigeminal projections to the brainstem. For example, Marfurt and Turner (1984) investigated tooth pulp afferents from the maxillary molar tooth in rats, and revealed projections that extended throughout the rostrocaudal extent of the TBNC, but were concentrated in the dorsal and medial portions of the nuclei. Our procedure differed from Marfurt and Turner's, in that our injection into the tooth was not confined to the pulp chamber.…”