Intertrigeminal Region Research Articles

Expression of N-methyl-D-aspartate receptor subunits in the rat parabrachial and K�lliker-Fuse nuclei and in selected pontomedullary brainstem nuclei

In the present study, we investigated the expression of N-methyl-D-aspartate (NMDA) receptor subunits in the parabrachial/Kölliker-Fuse complex (PB/KF), the intertrigeminal region, the ventrolateral pons, the nucleus of the solitary tract, the ventrolateral medulla with the ambiguus nucleus, and the caudal spinal trigeminal nucleus, which are presumably involved in mediating the autonomic responses to nasotrigeminal stimulation (diving response). Our immunocytochemical data demonstrate that the majority of neurons in the respective nuclei stain for the NR1 subunit, which is a mandatory component of all NMDA receptors. NR1 immunoreactivity was found mainly on neuronal cell bodies and primary dendrites. The ubiquitous expression of the NR1 subunit was confirmed by in situ hybridization, revealing a strong NR1 mRNA signal over neurons in all nuclei investigated. Among the NR2A-D subunits, the strongest expression was observed for the NR2D transcript, both in the PB/KF and in the brainstem. For the PB/KF, we found in addition a moderate expression of NR2A mRNA in the internal lateral PB and of NR2B mRNA in the external lateral PB. The remaining PB nuclei and the KF were essentially devoid of NR2A-C transcripts. For the nucleus of the solitary tract and in the spinal trigeminal nucleus, we found, in addition to the strong NR2D mRNA signal, moderate expression of the NR2A-C transcripts. In the ventrolateral medulla, a moderate signal was seen for NR2C transcript, whereas signals for the NR2A and -B subunits were negligible. Our data suggest that, in PB/KF and pontomedullary brainstem nuclei involved in mediating the diving response, glutamatergic neurotransmission is apparently mediated through a specific type of NMDA receptor channels, consisting essentially of NR1 and NR2D subunits.

A Brainstem Network Mediating Apneic Reflexes in the Rat

Apnea is an important protective response to upper airway irritation, but the central mechanisms responsible for eliciting sensory-induced apnea are not well understood. Recent studies have emphasized the Kölliker-Fuse nucleus in producing apnea and proposed a trigeminoparabrachial pathway for mediating these reflexes. However, in our earlier study of apneic responses produced by glutamate stimulation in the dorsolateral pons, we found that apnea was elicited from the area just ventral to the Kölliker-Fuse nucleus, rather than within it. Because this region was not known to be involved in respiratory control, we combined chemical microstimulation with both anterograde and retrograde axonal tracing to characterize the sites in the pons that produce apneic responses. We found that apneic sites were consistently associated with the intertrigeminal region, between the principal sensory and motor trigeminal nuclei. Injections of anterograde tracer at these sites labeled terminals in the ventral respiratory group, in the ventrolateral medulla. Injection of retrograde tracer into this target region in the ventrolateral medulla disclosed a previously unrecognized population of neurons among the trigeminal motor rootlets. Injection of retrograde tracer into this intertrigeminal region demonstrated inputs from portions of the spinal trigeminal nucleus and the nucleus of the solitary tract that have been associated with producing sensory apnea. Our observations suggest that the intertrigeminal region receives a convergence of sensory inputs capable of driving apneic responses and that it may represent a common link between input from different portions of the airway and the respiratory neurons that mediate apneic reflexes.

GABAergic and glycinergic neurons projecting to the trigeminal motor nucleus: a double labeling study in the rat.

The distribution of GABAergic and glycinergic premotor neurons projecting to the trigeminal motor nucleus (Vm) was examined in the lower brainstem of the rat by a double labeling method combining retrograde axonal tracing with immunofluorescence histochemistry. After injection of the fluorescent retrograde tracer, tetramethylrhodamine dextran amine (TRDA), into the Vm unilaterally, neurons labeled with TRDA were seen ipsilaterally in the mesencephalic trigeminal nucleus, and bilaterally in the parabrachial region, the supratrigeminal and intertrigeminal regions, the reticular formation just medial to the Vm, the principal sensory and spinal trigeminal nuclei, the pontine and medullary reticular formation, especially the parvicellular part of the medullary reticular formation, the alpha part of the gigantocellular reticular nucleus, and the medullary raphe nuclei. Some of these neurons labeled with TRDA were found to display glutamic acid decarboxylase (the enzyme involved in GABA synthesis)-like or glycine-like immunoreactivity. Such double-labeled neurons were seen mainly in the supratrigeminal region, the reticular region adjacent to the medial border of the Vm, and the dorsal part of the lateral reticular formation of the medulla oblongata; a number of them were further scattered in the intertrigeminal region, the alpha part of the gigantocellular reticular nucleus, the nucleus raphe magnus, the principal sensory trigeminal nucleus, and the interpolar subnucleus of the spinal trigeminal nucleus. These neurons were considered to be inhibitory (GABAergic or glycinergic) neurons sending their axons to motoneurons in the Vm, or to local interneurons within and around the Vm.

Immunohistochemical evidence for GABA and glycine‐containing trigeminal premotoneurons in the guinea pig

Electrophysiological studies have suggested that inhibition of trigeminal motoneurons during mastication and the jaw-opening reflex are mediated by last-order interneurons (premotoneurons) utilizing GABA and glycine [Chandler et al. (1985), Brain Res., 325:181-186; Enomoto et al. (1987), Neurosci. Res., 4:396-412; Goldberg and Nakamura (1968), Experientia, 24:371-373; Kidokoro et al. (1968), J. Neurophysiol., 31:695-708; Nakamura et al. (1978), Exp. Neurol., 61:1-14]. In the present study we performed a series of double-labeling experiments in guinea pigs to determine the location of neurons which contain GABA (gamma aminobutyric acid) or glycine that project to the trigeminal motor nucleus (Mo5). This was accomplished by performing immunohistochemical staining in combination with a retrograde tract tracing technique using colloidal gold bound to inactivated WGA-HRP (wheat germ agglutin-horseradish peroxidase) (gWGA-HRP) as our retrograde tracer. Neurons which had a positive immunoreactivity to GABA or GAD (glutamic acid decarboxylase) and contained the retrograde marker were located in regions adjacent to the Mo5 such as the intertrigeminal, supratrigeminal, peritrigeminal and rostral portions of the parvocellular reticular formation alpha. Neurons which had a positive immunoreactivity to glycine and contained the retrograde marker were identified in the parvocellular reticular formation, the spinal trigeminal nucleus oralis, supratrigeminal and intertrigeminal regions. These data provide anatomical evidence for GABAergic and glycinergic projections to Mo5.

Neurons in the intertrigeminal region of the rat send projection fibers to the superior colliculus

A retrograde WGA-HRP and anterograde PHA-L study in the rat indicated that many neurons in the intertrigeminal region (ITR) sent their axons to the superior colliculus (SC), bilaterally with a clear-cut contralateral dominance. These neurons were small to medium in size and their axons terminated in the lateral part of the SC, especially in the stratum griseum intermedium.

Gamma-aminobutyric acid-immunoreactive neurons in the rat trigeminal nuclei

The distribution of GABAergic neurons in the rat trigeminal nuclei was studied using a highly specific monoclonal antibody (mAb3A12) to gamma-aminobutyric acid (GABA). Immunopositive cells were relatively abundant in the marginal and gelatinosa beds of the caudal part of the trigeminal spinal tract nucleus, and in the dorsomedial areas of the oral subnucleus and the principal nucleus. A high density of GABA-immunoreactive somata was also found in the rostral part of the oral subnucleus and in the adjacent parvicellular reticular formation as well as in the supratrigeminal and intertrigeminal regions. Thus, the distribution of the GABAergic cells showed a relatively high density in areas related to the convergence of sensory stimuli, and in zones that contain interneurons inhibiting masticatory motoneurons. The results suggest, therefore, that GABA might play an important role both in discriminative sensory processing and in reflex modulation of the orofacial region.

Two types of jaw-muscle spindle afferents in the cat as demonstrated by intra-axonal staining with HRP

Intra-axonal records and horseradish peroxidase (HRP) injection techniques were employed to define the response properties of the jaw-closing muscle spindle afferents in the trigeminal mesencephalic nucleus (Vmes) and their morphological characteristics. The axonal trajectories of 9 spindle afferents from the masseter and 4 afferents from the temporalis were recovered for detailed analyses. Of 13 afferents, 6 cell bodies were stained and they were located at the rostrocaudal mid-levels of the Vmes. The central courses of the stem fibers were organized in a similar manner to the Vmes periodontal afferent nerves 30 with the exception that peripheral (P) fibers of all spindle afferents passed through the trigeminal motor tract and root. On the basis of collateral terminal arborizations, the Vmes spindle afferents could be classified into two types: type I (n = 6) and type II (n = 7). Type I afferents sent their collaterals into the trigeminal motor nucleus (Vmo), intertrigeminal region (Vint) and juxtatrigeminal region (Vjux), but collaterals from the two neurons also projected to Vmes and the nucleus oralis (Vo). The collaterals from type II afferents formed their terminal arbors in the supratrigeminal nucleus (Vsup) in addition to the Vmo, Vint and Vjux, but collaterals from one neuron also projected to the Vo. In type I afferents, terminal arbors encompassed the whole Vmo including jaw-closing motoneurons. In contrast, boutons from type II afferents were restricted to a few small portions within the Vmo in proximity to its lateral and dorsal boundaries. The diameters of the united (U), central (C) and peripheral (P), fibers were larger in type I than type II afferents; those of the U fibers were statistically significant. Any differences between the two distinct types were not found in the response pattern to the sustained jaw opening. These results suggest that the difference of primary and secondary muscle-spindle afferent nerves is reflected in a distinctive morphology in the terminal arborizations and in the diameters of united fibers rather than the response patterns in deeply anesthetized cats.

Projections of two separate cortical areas for rhythmical jaw movements in the rat

The cortico-bulbar projection from two separate cortical areas which induce different types of rhythmical jaw movements (RJM), and the relationship between these cortical areas were studied with horseradish peroxidase tracing method. One area (A-area) corresponded to the primary jaw motor area and the other (P-area) was located in the agranular insular cortex. Separate descending pathways from two areas passed through the pyramidal tract and projected to the supratrigeminal nucleus, the intertrigeminal region, the dorsal part of the trigeminal sensory complex, and the reticular formation. In the reticular formation, the A-area projected more medially than the P-area did, and the ipsilateral projection from the P-area was more prominent than that from the A-area, although contralateral projections were dominant in the majority of regions. The two areas had only a sparse reciprocal connection. We suppose that the difference in patterns of RJM induced by the two cortical RJM areas may be due to the different projection patterns from these two areas.

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 Probst's 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.

Sensory and motor responses of trigeminal and reticular neurons during ingestive behavior in rats.

Activities of 53 neurons in the brain stem were recorded with chronically implanted fine wires in freely eating and drinking rats. Twenty units were isolated from the trigeminal mesencephalic nucleus; 18 were spindle afferents and 2 periodontal afferents. The spindle units were classified into 4 types: 5 units showed rhythmical activity related only to the jaw opening phase during both licking and chewing, 8 units discharged at jaw opening phase during licking, but both at jaw opening and jaw closing phases during eating, 2 units increased phasic activity at jaw opening phase during licking, but increased tonically independent of jaw movements during eating, and the remaining 3 units responded only at jaw closing phase both in licking and eating behavior. Nine units were assumed to be alpha motoneurons isolated from the trigeminal motor nucleus; 2 innervating the temporalis muscle, 3 the masseter muscle, 2 the digastric muscle, and the remaining 2 presumably the pterygoid muscles. These units, with a mean tonic spontaneous rate of about 10 impulses/s, showed phase-related rhythmical burst activities during licking and eating. Four units were isolated from the trigeminal main sensory nucleus. Sixteen units were isolated from the medullary reticular formation and 1 from the pontine reticular formation. Of these 16 units, 3 from the parvocellular part of the medullary reticular formation were presumably premotor interneurons, and 3 units in the "intertrigeminal region", 2 units in the "juxtatrigeminal region", and 8 units in the "supratrigeminal region" were responsive to multiple sensory modalities. These results demonstrate that almost all the units sampled showed characteristic rhythmic activities associated with the position of the tongue or mandible during rhythmical jaw movements.

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 rat within the tract and sensory root to exit the brainstem. The C axon traveled caudally within Probst's 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 rostrodorso-medial 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. The axon collaterals given off from the proximal C axon sent their terminals to the Vsup. Other axon collaterals sent their terminal branches to the Vmo, while some terminal branches extended into the Vint.

Morphology of single mesencephalic trigeminal neurons innervating masseter muscle of the cat

The morphology of functionally identified single axons of mesencephalic trigeminal neurons was studied in the cat by the method of intra-axonal injection of horseradish peroxidase (HRP). Each axon can be divided into united (U), peripheral (P) and central branches (C). The united axon (U) descends from its soma within the tract of the trigeminal mesencephalic nucleus to the dorsal aspect of the trigeminal motor nucleus (Vmo), where it splits into peripheral and descending central branches with a Y-shaped bifurcation. The peripheral axon (P) joins the motor root of the trigeminal nerve to exit the brainstem. The central axon (C) travels caudally within the juxtatrigeminal regions (or lateral reticular formation). All 3 branches issue axon collaterals that distribute terminal boutons within the dorsolateral subdivision of Vmo, supra- and intertrigeminal regions. Collaterals emanating from the central axon (C) except for its proximal segment travel ventrolaterally within the juxtatrigeminal regions, and send their terminal branches into the lateral boundaries adjacent to the spinal trigeminal nucleus. The trajectory of terminal branches distinguishes group Ia afferents from the possible group II afferents. The majority of terminal boutons are found to distribute in the supra- and intertrigeminal regions for group II afferent fibers and in the dorsolateral subdivision of Vmo for group Ia afferents.

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

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)

Differential distribution of cell bodies and central axons of mesencephalic trigeminal nucleus neurons supplying the jaw-closing muscles and periodontal tissue: A transganglionic tracer study in the cat

Distribution of cell bodies and central axons of mesencephalic trigeminal nucleus (MTN) neurons were examined in the cat by the method of transganglionic transport of horseradish peroxidase (HRP). Jaw-closing muscle afferent MTN neurons were distributed throughout the whole rostrocaudal extent of the MTN, and sent their axons ipsilaterally to the supratrigeminal and intertrigeminal regions, dorsolateral division of the motor trigeminal nucleus, lateral part of the medullary reticular formation, lamina VI of C1-C3 cord segments, and cerebellum. On the other hand, periodontal receptor afferent MTN neurons were located mainly in the caudal part of the MTN, and sent their axons ipsilaterally to the supratrigeminal region and cerebellum. The existence of multipolar MTN neurons with 1-9 smooth dendrites was also confirmed; most of them were jaw-closing muscle afferent neurons.

Cerebral cortical projections to the reticular regions around the trigeminal motor nucleus in the cat.

Cerebral cortical regions which send projection fibers to the reticular regions around the trigeminal motor nucleus were identified in the cat by the horseradish peroxidase (HRP) method. The reticular region around the trigeminal motor nucleus are known to contain many interneurons for masticatory motoneurons. After injections of HRP into the reticular regions around the trigeminal motor nucleus, HRP-labeled neuronal cell bodies in the cerebral cortex were found in layer V. They were distributed bilaterally in the orbitofrontal cortical regions, mainly in the rostral extension of the orbital gyrus close to the presylvian sulcus; more were located in the floor and lateral bank of the presylvian sulcus than in the crown of the orbital gyrus. After injections of HRP conjugated with wheat germ agglutinin (WGA-HRP) into these cortical regions, many labeled presumed axon terminals were distributed bilaterally in the reticular regions around the trigeminal motor nucleus; mainly in the region ventral to the trigeminal motor nucleus and in the intertrigeminal region between the main sensory trigeminal nucleus and the trigeminal motor nucleus. Terminal labeling in these regions was more prominent after WGA-HRP injection into the lateral bank of the presylvian sulcus than after WGA-HRP injection into the crown of the orbital gyrus. Thus, the present results indicate that the main part of the cortical region projecting directly to the reticular regions around the trigeminal motor nucleus in the cat is folded into the presylvian sulcus.

Commissural interneurons for masticatory motoneurons: A light and electron microscope study using the horseradish peroxidase tracer technique

Commissural interneurons for masticatory motoneurons of the cat were investigated using the horseradish peroxidase tracing technique. After injection of horseradish peroxidase into the motor trigeminal nucleus, neurons labeled with the enzyme were seen contralaterally around the motor trigeminal nucleus, mainly in the supra- and intertrigeminal regions and the lateral tegmental regions close to the medial border of the motor trigeminal nucleus, and additionally within the confines of the motor and main sensory trigeminal nuclei and the parabrachial nuclei. After placing lesions in the supra- and intertrigeminal regions, degenerated axon terminals were found electron microscopically in the motor trigeminal nucleus contralateral to the lesion. In accordance with these findings, axon terminals in the motor trigeminal nucleus were labeled orthodromically with horseradish peroxidase injected contralaterally into the supra- and intertrigeminal regions; both terminals filled with round synaptic vesicles and those containing flattened vesicles were labeled with the enzyme. The existence of many commissural neurons around the motor trigeminal nucleus would be consistent with the intricacy of bilateral mechanisms of jaw movements.