Setsuko Suemune

The distribution of muscle primary afferents from the masseter nerve to the trigeminal sensory nuclei

Transganglionic transport of horseradish peroxidase--wheat germ agglutinin conjugate was used to study the pattern of termination of somatic afferent fibers innervating the masseter muscle within the trigeminal sensory nuclear complex (TSNC) of the cat. The central processes of the masseteric nerve terminated in the caudal third of the pars interpolaris, and laminae I/V through the caudal two-thirds of caudalis and rostral parts of the C1 spinal cord segment. The functional significance of the masseteric afferent projections to the TSNC with a preferential pattern was discussed, particularly with respect to muscle pain.

Physiological and morphological characteristics of periodontal mesencephalic trigeminal neurons in the cat — intra-axonal staining with HRP

Intra-axonal recording and horseradish peroxidase (HRP) injection techniques were employed to define the response properties of periodontal mechanoreceptive afferents originating from the trigeminal mesencephalic nucleus (Vmes) and their morphological characteristics. The periodontal Vmes neurons were classified into two types: slowly adapting (SA) and fast adapting (FA) types. The central terminals of 7 SA and 4 FA afferents were recovered for detailed analyses. The whole profile of SA and FA neurons were unipolar in shape and their cell bodies were located in the dorsomedial parts of the Vmes. The united (U) fiber traveled caudally from the soma to the dorsolateral aspect of the trigeminal motor nucleus (Vmo), where it split into the peripheral (P) and C fibers with a T- or Y-shaped appearance. The P fiber joined the trigeminal sensory or motor tract. The C fiber descended caudally within Probsts tract. All 3 stem fibers issued main collaterals. The main collaterals of all neurons examined formed terminal arbors in the supratrigeminal nucleus (Vsup) and all but two SA neurons projected to the intertrigeminal region (Vint), while the projections to other nuclei of the trigeminal motor nucleus (Vmo), juxtatrigeminal region (Vjux), main sensory nucleus (Vp) and oral nucleus (Vo.r) differed between SA and FA afferents and between neurons of the same type. The SA and FA neurons were classified into three and two subgroups, respectively. The major differences in central projections between the two types were that all the FA neurons projected to the Vp or Vo.r but none of SA type and this relation was reversed in the projection to the Vjux, and that more than half of SA neurons projected to Vmo but only one FA neuron to the Vmo. The Vmes neurons which sent their collaterals into the Vmo had the P fiber passing through the tract of the trigeminal motor nerve. The average size of somata and mean diameters of U fibers and main collaterals from C fiber were significantly larger in SA neurons than FA neurons. The average size of fiber varicosities became smaller in the following nuclei, Vmo, Vsup, Vp, Vint and Vo.r, but not significant between the two functional types. The functional role of the periodontal Vmes afferents to jaw reflexes was discussed particularly with respect to their central projection sites in the brainstem nuclei.

Somatotopic organization of tooth pulp primary afferent neurons in the cat

Transganglionic transport of horseradish peroxidase-wheat germ agglutinin conjugate (HRP-WGA) was used to study the somatotopic organization of pulpal afferent neurons innervating the different types of teeth in the trigeminal ganglion and trigeminal sensory nuclear complex (TSNC). In separate animals, the upper first 3 incisors (UI1-3), canine (UC), second premolar (UP2) and third premolar (UP3), and the lower first three incisors (LI1-3), canine (LC), first premolar (LP1), second premolar (LP2) and molar (LM) were traced in this experiment. Cell bodies innervating posterior teeth were found with greater frequency in dorsal maxillary ganglion regions, while somata supplying more anterior teeth were predominant ventrally. In contrast, cell bodies innervating the lower teeth were not arranged in a somatotopic fashion in the mandibular subdivision. Each pulpal afferent from lower and upper teeth projected to the subnucleus dorsalis (Vpd) of the pars principalis, the rostrodorsomedial (Vo.r) and dorsomedial parts (Vo.dm) of the pars oralis (Vo), the medial regions of the pars interpolaris (Vi), and laminae I, II, and V of the medullary dorsal horn, and terminal fields between the upper and lower teeth were separated in each subdivision. Pulpal projections from both the upper and lower teeth to each subdivision were organized in a somatotopic manner, while an extensive overlap in projections was noted between the adjoining teeth. In the Vpd, the upper and lower teeth were represented dorsoventrally, and projections from the anterior to posterior teeth in the upper jaw were arranged in both rostrocaudal and ventrodorsal sequences whereas those in the lower jaw were organized caudarostrally and lateromedially. In the Vo.r and Vo.dm, the upper and lower teeth were represented in a mediolateral sequence and projections from the anterior to posterior teeth were organized in a ventrolateral to dorsomedial sequence. In the Vi, pulpal projections were organized in a topographic fashion similar to that observed in the Vo.r and Vo.dm. In the medullary dorsal horn, the upper and lower teeth were represented in laminae I, II and V in a lateromedial sequence. Their projections to laminae I and V were topographically organized in a mediolateral and rostrocaudal sequence.(ABSTRACT TRUNCATED AT 400 WORDS)

Morphology of single mesencephalic trigeminal neurons innervating periodontal ligament of the cat

The morphology of single neurons in the trigeminal mesencephalic nucleus (Vmes) that innervate periodontal ligament was studied in cats by the method of intraaxonal injection of horseradish peroxidase (HRP). Two kinds of Vmes neurons were distinguished on the basis of differences in axon profile and its central projection. The first type of Vmes neurons was unipolar in shape and its axon was divided into united (U), peripheral (P), and central axons (C). The U axon traveled caudally within the Vmes from the soma to the dorsolateral aspect of trigeminal motor nucleus (Vmo), where it split into the P and C axons with a T-shaped appearance. The P axon joined the spinal trigeminal tract across the trigeminal principal nucleus and ran within the tract and sensory root to exit the brainstem. The C axon traveled caudally within Probsts tract. All 3 axons issued axon collaterals. Axon collaterals from the U, P and the proximal C axons sent their terminal branches into the supra (Vsup) and intertrigeminal regions (Vint). Most axon collaterals from the C axon sent their terminal branches into the juxtatrigeminal regions (Vjuxta). The second type of Vmes neurons was bipolar and issued P and C axons. The C axon ran a short distance in the Vmes to leave the Vmes, and then it traveled caudolaterally in the rostrodorsomedial aspect of the Vmo. Finally, it entered in the Vmo and traveled caudally in the dorsolateral subdivision of the nucleus to its rostrocaudal mid-level. The C axon gave off massive axon collaterals.(ABSTRACT TRUNCATED AT 250 WORDS)

Central terminations of periodontal mechanoreceptive and tooth pulp afferents in the trigeminal principal and oral nuclei of the cat.

Intra-axonal recording and horseradish peroxidase (HRP) injection techniques were employed to define the response properties of low-threshold mechanoreceptive periodontal afferents and of the tooth pulp afferents and the morphological characteristics of their axon arbors in the nucleus principalis (Vp) and rostrodorsomedial (Vo.r) and dorsomedial parts (Vo.dm) of the nucleus oralis (Vo). The central terminals of 3 fast adapting (FA) and 4 slowly adapting (SA) periodontal afferents and 4 tooth pulp (TP) afferents were recovered for detailed analyses. Stained axons in the trigeminal sensory tract ascended and descended (bifurcating fibers), or descended without bifurcation (descending non-bifurcating fibers). The ratio of the bifurcating fibers to the descending non-bifurcating fibers was about three to one for each type of afferents. The main collaterals given off from the ascending branches terminated in the Vp. Most collaterals given off from the descending branches terminated in the Vo with the exception of few instances. In case of the FA afferents, the ascending branches gave off all main collaterals into the Vp with rostrocaudal and dorsoventral continuities in their arbors, whereas the descending branches gave off all main collaterals, except two collaterals, into the Vo with rostrocaudal discontinuities. The projections from the FA afferents to the Vo.dm was predominant in terms of the number of boutons and the length of preterminal and terminal branches. In case of the SA afferents, the collaterals from the ascending and descending branches formed rostrocaudally and dorsoventrally discontinuous terminal arbors. In terms of the density of boutons the SA afferents were divided into two subtypes. One had a preferential projection into the Vp or Vo, whereas others lacked a selective projection. In case of the TP afferents, the main collaterals of the ascending branches formed partially overlapping terminal arbors, but the terminal arbors formed by the collateral of the descending branches did not overlap. The frequency of collaterals of the TP afferents was less than that of the other types of afferents. The terminal arbors including the density of boutons of the pulpal afferents were less extensive than those of the other types of afferents. The average size of varicosities became smaller in the following subdivisions. Vp, Vo.r and Vo.dm for SA and TP afferents. The size of varicosities of the TP afferents was smaller and that of the FA afferents was larger than that of the SA afferents.(ABSTRACT TRUNCATED AT 400 WORDS)

Morphology of central terminations of low-threshold trigeminal primary afferents from facial skin in the cat — intra-axonal staining with HRP

Intra-axonal recording and horseradish peroxidase (HRP) injection techniques were employed to examine the response properties of low-threshold mechanoreceptive afferents and the morphological characteristics of their axon arbors in the main sensory nucleus (Vp) and oral nucleus (Vo). Thirteen afferents were characterized and recovered. One gave fast or rapidly adapting (FA) and 3 slowly adapting (SA) responses to mystacial vibrissa deflection, 5 were sensitive to deflection of non-vibrissae hairs or hair (4 were guard hair afferents and the other responded to deflection of a long hair in slowly adapting fashion) and two were responsive to indentation of the hairy skin. The remainder were responsive to indentation of the glabrous skin on the lower lip: one was of FA type and the other of SA type. All of the axons had bifurcating fibers that ascended in the ascending tract (ascending fiber) and descended in the trigeminal spinal tract (descending fiber). The main collaterals given off from the ascending fiber and rostral segment of the descending fiber terminated in the Vp, and the other collaterals from the descending fiber projected to the Vo. Terminal arbors produced by the main collaterals formed a rostrocaudally continuous column, but generally the adjacent arbors did not overlap except when pairs of collaterals arose near each other on the ascending and descending fibers. Projections of collaterals to Vp and Vo were organized topographically. The head was represented in an inverted fashion with its anteroposterior axis in a mediolateral sequence, but the lower glabrous lip was represented more dorsally than the other mandibular facial regions. Vibrissa afferents formed a rostrocaudally continuous, densely packed terminal column throughout the length of Vp and Vo. SA vibrissa afferents gave rise to more dense and roundish arbors in Vp than the FA afferent, while the Vo.c arbors were more compact and smaller than those of the FA afferent. Guard hair afferents had arbors that were highly variable throughout the nuclei and were characterized by less developed arbors in Vp than in Vo. Unlike vibrissa afferents, hairy skin afferents gave rise to sparse and widespread arbors characterized by a string-like appearance, while the Vo collaterals were more stringy. Facial lip afferents were characterized by a great difference in collateral morphology between FA and SA type.(ABSTRACT TRUNCATED AT 400 WORDS)

The cells of origin of the hypoglossal afferent nerves and central projections in the cat

The cells of origin for the hypoglossal afferent nerves of the cat and their central projections were examined using the transganglionic and somatopetal transport of horseradish peroxidase (HRP). Primary afferent neurons from the hypoglossal nerve were located in the trigeminal ganglion, the superior ganglion of glossopharyngeal and vagal nerves, and the first 3 cervical ganglia. The central projections of hypoglossal afferents were organized in a selective manner according to their cells of origin. The primary afferent nerves originating from the trigeminal ganglion terminated in the subnucleus dorsalis (Vpd) of the principal nucleus (Vp), lateral margin of the caudal pars interpolaris (Vi), interstitial nucleus and laminae I and V of the pars caudalis (Vc). The projection of the afferent nerves for glossopharyngeal and vagal origins are similarly organized in the Vi and Vc to those of trigeminal origin, but differed in that they terminated ipsilaterally in the caudal half of the solitary nucleus and bilaterally in the commissural nucleus. The primary afferents arising from the first 3 cervical ganglia terminated in laminae I and V of the corresponding cervical cord segments.

Laminar-related projection of primary trigeminal fibers in the caudal medulla demonstrated by transganglionic transport of horseradish peroxidase

The mode of termination of primary afferent fibers within the cat trigeminal nucleus caudalis was investigated by means of the transganglionic transport of horseradish peroxidase (HRP). Several types of laminar-related labeling were observed, depending upon the survival time after HRP application. At the earliest survival time (28-34 h) the highest density of labeling was found in laminae I and II. At 2 and 3 days survival laminae III and IV were heavily labeled, in addition to laminae I and II where the amount of labeling was greatly increased in lamina I, but not in lamina II. At 5 days survival time an abrupt drop of labeling occurred in laminae I and II, while this pattern was not predominant in laminae III and IV. In lamina V the pattern of labeling was less intense and not changeable through all survival times observed. These findings indicating a differentiation of the primary afferent terminals have good correspondence with a functional specialization of neuronal locations since the functional properties of neurons vary according to their locations.

Trigeminal nerve endings of lingual mucosa and musculature of the rat

Horseradish peroxidase conjugated with wheat germ agglutinin (HRP-WGA) was injected into the trigeminal ganglion of adult rats to label the peripheral sensory receptors of the tongue. The conjugate was transported anterogradely to all the ipsilateral fungiform papillae and filiform papillae. Some labeled fibers crossed over to the contralateral papillae. In the intrinsic tongue muscle undulating nerve fibers along or across muscle fibers were often observed, and formed simple spiral endings.

Representation of upper and lower primary teeth in the trigeminal sensory nuclear complex in the young dog

Transganglionic transport of horseradish peroxidase-wheat germ agglutinin conjugate entrapped in polyacrylamide gel was used to study the patterns of termination of primary afferents that innervate the upper and lower primary tooth pulps within the trigeminal sensory nuclear complex of the young dog. The lower and upper primary tooth pulp afferents projected to the subnucleus dorsalis of the principal nucleus, the rostrodorsomedial part and subnucleus dorsomedialis (Vo.dm) of the pars oralis, the nucleus of the intermediate plexus (Vi.ip) of the pars interpolaris, and laminae I, II and V of the caudalis. The lower and upper primary teeth were topographically represented in the Vo.dm, rostrocaudal mid-levels of Vi.ip, and in laminae I/V of the caudal levels of the pars caudalis, whereas an extensive overlapped projection was seen in other subdivisions.