Intensity coding by TMJ-responsive neurons in superficial laminae of caudal medullary dorsal horn of the rat

Temporomandibular disorders (TMD) represent a family of recurrent conditions that often cause pain in the temporomandibular joint (TMJ) region and muscles of mastication. To determine if TMJ-responsive neurons encoded the intensity of pro-inflammatory chemical signals, dose-effect relationships were assessed after direct injection bradykinin into the joint space and compared with responses after injection of glutamate or saline. Neurons were recorded from superficial laminae of the trigeminal subnucleus caudalis/upper cervical cord junction region (Vc/C(2)) and identified by palpation of the TMJ region in barbiturate-anesthetized male rats. The majority (62 of 84) of units received convergent input from facial skin, while 26% were driven only by deep input from the TMJ region. Conduction-velocity based on the latency to firing after electrical stimulation of the TMJ region indicated 64% of units were driven by A-delta fiber input only. Bradykinin (0.1-10 microM) excited 69% of neurons tested, and 70% (19 of 27) of these units were activated by the lowest dose (0.1 microM). Glutamate (50-200 mM) excited 27% of units; however, when tested after bradykinin, 58% of units were activated by glutamate. Some TMJ units (17%) were excited by saline injection alone and not enhanced further by bradykinin or glutamate. Most (88%) TMJ units were activated by injection of the small fiber excitant, mustard oil (20% solution), into the TMJ region. Units responsive to bradykinin or glutamate were not restricted to particular classes [e.g., wide dynamic range (WDR), nociceptive specific (NS), deep only]. A small percentage of TMJ units (approximately 15%) were activated antidromically from the contralateral posterior thalamus. In parallel studies using c-fos immunocytochemistry, bradykinin (1 microM) injection into the TMJ region produced a greater number of Fos-positive neurons at the Vc/C(2) region than glutamate (200 mM) or saline. These results revealed two broad classes of TMJ units that encoded the intensity of pro-inflammatory chemical stimuli applied to the TMJ region, units that received convergent nociceptive input from facial skin (i.e., WDR and NS units) and units that responded only to deep input from the TMJ region. On the basis of encoding properties and efferent projection status, it is concluded that activation of TMJ units within the superficial laminae at the Vc/C(2) region contribute to the diffuse and spreading nature of TMD pain sensation.

The influence of experimentally induced osteoarthrosis on articular nerve fibers of the sheep temporomandibular joint

AIMS

To study the effect of experimentally induced osteoarthrosis, or non-inflammatory degenerative changes, on the innervation of the sheep temporomandibular joint (TMJ) through the use of indirect immunohistochemistry and image analysis quantification.

METHODS

Bilateral condylar scarification was performed in 8 sheep, which were killed at 16 weeks post-operation; 3 unoperated sheep served as controls. Tissues from 8 osteoarthrotic joints and 4 control joints were processed for the immunostaining with antisera for protein gene product 9.5 (PGP 9.5), substance P (SP), calcitonin gene-related peptide (CGRP), neuropeptide Y (NPY), vasoactive intestinal peptide (VIP), and tyrosine hydroxylase (TH). An additional 10 joints were decalcified to study the morphologic changes induced by the condylar abrasion.

RESULTS

Osteoarthrotic changes were commonly seen in the anterior and lateral regions of the joint and included fibrosis, peripheral osteophyte formation, cysts, and erosion of articular surfaces. In the osteoarthrotic joints, the distribution of PGP 9.5-, CGRP-, and SP-immunoreactive (IR) nerve fibers was similar to that observed for control joints in the capsule, synovium, and capsule/disc junction. There were statistically detectable decreases in the percent surface area of IR nerve fibers in the capsule for both PGP 9.5 and CGRP in arthrotic joints compared with control joints. The lateral and anterior regions of the capsule had greater density of PGP 9.5- and CGRP-IR nerve fibers than other parts of the capsule in both control and arthrotic joints, and the medial capsule was poorly innervated in all joints. Immunostaining for substance P was always weaker.

CONCLUSION

This study suggests that while inflammatory arthritis has a marked influence on the density of sensory and autonomic nerve fibers in synovium in a variety of joints in different species, experimentally induced non-inflammatory osteoarthrosis in the sheep TMJ also leads to a depletion of the density of nerve fibers in the capsule, especially in the lateral part of the joint. Further work is required to determine whether other parts of the joint, such as synovium and marrow, respond differently to experimentally induced osteoarthrosis.

Sex differences in brainstem neural activation after injury to the TMJ region

The basis for a higher prevalence of painful temporomandibular disorders (TMD) among women than men is not known. The present study used Fos-like immunoreactivity (Fos-LI) to quantify the pattern and magnitude of neural activation within the trigeminal brainstem complex of male and female rats caused by acute inflammatory injury to the temporomandibular joint (TMJ) region. Also, Fos-LI was assessed in animals given morphine, a preferential mu opioid receptor agonist, or U50,488H, a selective kappa opioid agonist, prior to TMJ injury to determine if opioid modulation of neural activation was similar in males and females. The general pattern of Fos-LI after TMJ injury was similar in males and females. This pattern was characterized by a high density of Fos-positive neurons in the dorsal paratrigeminal nucleus (dPa5), subnucleus interpolaris/caudalis transition region (Vi/Vc-vl), and in the superficial laminae at the subnucleus caudalis/upper cervical spinal cord (Vc/C2) junction ipsilateral to TMJ injury. In contrast to other regions the number of Fos-positive neurons produced at the Vc/C2 junction was proportional to the concentration of mustard oil injected into the TMJ region. In addition, proestrus females produced higher levels of Fos-LI at the Vc/C2 junction than diestrus females or males. Morphine caused a greater dose-related reduction in Fos-LI at the dPa5 and Vc/C2 junction in males than females. By contrast, U50,488H caused a dose-related reduction in Fos-LI only at the Vc/C2 junction of proestrus females. These results support the hypothesis that the Vc/C2 junction region plays a critical role in the integration of pain signals originating from the TMJ region and may underlie sex differences in sensory processing related to TMJ pain.

Substance P and mast cells: preliminary histologic analysis of the human temporomandibular joint

PURPOSE

Neuropeptide-containing nerves can serve as a mechanism for nervous system regulation of host defense responses. Because bacteria associated with reactive arthritis have been identified in the temporomandibular joint (TMJ), this study investigates whether the presence of substance P (SP) neuropeptide-containing nerves and mast cells can be identified in the TMJ.

MATERIAL AND METHODS

Posterior bilaminar tissue removed during TMJ surgery from 9 women was evaluated for the presence of neuropeptide-containing nerves by staining with a monoclonal antibody to SP. Staining of the TMJ tissue sections with 0.5% toluidine blue was performed to identify the presence of mast cells.

RESULTS

SP-containing nerves and mast cells were identified within the posterior bilaminar tissue associated with the vasculature.

CONCLUSIONS

The presence of neuropeptide nerves and mast cells within the TMJ has been shown. Mast cell degranulation products and SP release can contribute to TMJ inflammation.

The effects of a home exercise program on pain and perceived dysfunction in a woman with TMD: a case study

There are few reports analyzing the effects of exercise on patients with temporomandibular disorders. This paper presents a case study examining whether there were additional benefits from performing neuromuscular control home exercises (NMCHE) in a patient with temporomandibular disorder who was already receiving conventional treatment. A woman, 41 years of age, completed a health status questionnaire called the TMJ Scale prior to being accepted. She completed additional TMJ Scales after receiving conventional treatment and again after conventional treatment was combined with neuromuscular control home exercises. Based on the TMJ Scale's best subscore indicator of the presence or absence of a temporomandibular disorder, the patient did not derive benefit from conventional treatment without exercise. However, she received a large benefit from the addition of NMCHE. It was concluded that exercises for patients with temporomandibular disorders may be beneficial to those who do not improve with conventional treatment alone.

Central mu opioid receptor mechanisms modulate mustard oil-evoked jaw muscle activity

The injection of the small-fibre excitant and inflammatory irritant mustard oil (MO) into the temporomandibular joint (TMJ) region of rats evokes a sustained and reversible increase in electromyographic (EMG) activity of jaw muscles. The 'rekindling' of this nociceptive reflex by intrathecal (i.t.) administration of the opiate antagonist naloxone and mu but not delta and kappa selective opioid antagonist, suggests that it may be modulated by endogenous opioid inhibitory mechanisms.

An in vitro temporomandibular joint-nerve preparation for pain study in rats

A novel in vitro TMJ-nerve preparation was developed to quantitatively study peripheral sensory mechanisms of temporomandibular joint (TMJ). The TMJ region on one side (including mandibular head, disc, retrodiscal tissue and mandibular fossa) of adult Wistar albino rats was excised together with the auriculo-temporal nerve. The block was preserved in a modified Krebs-Henseleit solution saturated with O(2)/CO(2) (95/5%) gas mixture. Using a calibrated von Frey type apparatus, mechanical noxious stimulation was applied directly to various sites within the TMJ region. In addition, thermal and chemical noxious stimuli were also attempted. Stable recordings of single unit activities from the auriculo-temporal nerve could be obtained for as long as 5 h, which was sufficient to analyze the response properties of the TMJ units to various stimuli. This new preparation would be useful for investigating TMJ peripheral sensory mechanisms, especially pain, and potentially makes it possible to reveal neural mechanisms of temporomandibular arthralgia, a syndrome that has recently shown an increased incidence in clinical dentistry.

Temporomandibular-evoked jaw muscle reflex: role of brain stem NMDA and non-NMDA receptors

This study investigated the possible involvement of brain stem excitatory amino acid receptor mechanisms and the trigeminal subnucleus caudalis (Vc) in temporomandibular joint (TMJ)-evoked reflex jaw muscle activity. Glutamate injected into the TMJ of anesthetized rats reflexly evoked activity in the jaw muscles. Application of lidocaine, but not saline, to the surface of the caudal brainstem overlying Vc significantly suppressed TMJ-evoked jaw muscle activity, while application of NMDA or non-NMDA receptor antagonists also significantly attenuated jaw muscle activity. These results provide evidence that Vc is a critical relay in the TMJ-evoked reflex activation of the jaw muscles, and that both NMDA and non-NMDA receptor mechanisms may contribute to these effects.

Characteristics of glutamate-evoked temporomandibular joint afferent activity in the rat

Injection of glutamate into the rat temporomandibular joint (TMJ) capsule can reflexly induce a prolonged increase in the electromyographic (EMG) activity of the jaw muscles, however, the characteristics of TMJ afferents activated by glutamate have not been investigated. In the present study, we examined the effect of glutamate injection into the TMJ capsule on jaw muscle EMG activity and the extracellularly recorded activity of single trigeminal afferents that had receptive fields in the TMJ tissue and antidromically identified projections to the brain stem subnucleus caudalis (Vc) in rats of both sexes. Glutamate (0.05--1.0 M, 10 microl) injection into the TMJ capsule evoked EMG activity in a dose-related manner; however, at concentrations of 0.5 and 1.0 M, glutamate-evoked digastric muscle responses were greater in female than in male rats. In experiments where jaw muscle EMG and afferent activity were recorded simultaneously, glutamate (0.5 M, 10 microl) injection into the TMJ capsule evoked activity in the jaw muscles as well as in 27 (26 A delta and 1 C-fiber afferent) of 34 trigeminal afferents that could be activated by blunt mechanical stimulation of the TMJ tissue. In these experiments, glutamate-evoked jaw muscle activity was significantly increased for 6 min after the glutamate injection, whereas afferent activity was significantly increased only during the first minute after the glutamate injection. The glutamate-evoked afferent activity was inversely related to conduction velocity and, in afferents with conduction velocities <10 m/s, was significantly greater in female (n = 6) than in male (n = 10) rats. These results suggest that glutamate excites putative nociceptive afferents within the TMJ to a greater degree in female than in male rats. This sex-related difference in afferent discharge may, in part, underlie sex-related differences in glutamate-evoked jaw muscle EMG activity.

Topography and distribution of sympathetic nerve fibers in the rat temporomandibular joint: immunocytochemistry and ultrastructure

The distribution and fine structure of nerve fibers containing neuropeptide Y (NPY), tyrosine hydroxylase (TH), and vasoactive intestinal polypeptide (VIP) in the temporomandibular joint were investigated by both the avidin-biotin complex method and an indirect immunofluorescence technique. The innervation pattern of NPY- and TH-positive fibers differed from that of VIP-positive fibers. Specifically, the former was distributed in both the superficial and deep sublining layers, while the latter was mostly located in the deep sublining layer. NPY- and TH-immunoreactive fibers were largely confined to vascular elements; occasional fibers were observed in the synovial lining layer close to the joint cavity. More nerves with NPY and TH immunoreactivity were observed close to the upper joint compartment than near the lower compartment NPY and TH immunoreactivity was dramatically reduced in the TMJ of superior cervical ganglionectomized animals, indicating the sympathetic origin of these nerves. NPY immunoreactivity was found only in unmyelinated axons, which were located in the adventitia and adventitia-medial border of arteries or arterioles. Occasionally, axons were near the joint cavity, in areas free of vascular structures. These observations show that abundant sympathetic nerves supply the temporomandibular joint of the rat and provide a morphological basis for the involvement of different neuropeptides in vascular regulatory and modulatory functions in physiological and pathophysiological conditions.

Stimulation of the locus coeruleus suppresses trigeminal sensorimotor function in the rat

The nucleus locus coeruleus (LC) has been implicated in the modulation of the spinal sensorimotor function. The aim of the present study was to examine the effect of electrical stimulation of the LC on sensorimotor function in the trigeminal system. The following two cases of sensorimotor behaviors mediated by the trigeminal brainstem sensory nuclear complex were examined: (1) the activity of the masseter muscle evoked by pressure on the region of the temporomandibular joint (TMJ); and (2) the activity of the digastric muscle evoked by electrical stimulation of the tooth pulp, resulting in the jaw-opening reflex. In the first case, LC stimulation at 10, 30 and 50 microA resulted in a 70%, 68% and 55% reduction in the magnitude of electromyogram (EMG) activity of the masseter muscle compared with the control (without LC stimulation), respectively. The threshold intensity for the onset of masseter EMG activity increaced to 106%, 111% and 121% of the control with 10, 30 and 50 microA LC stimulation, respectively. In the second case, EMG magnitude in response to the digastric muscle decreased to 42% of the control when 30 microA of LC stimulation was delivered. These results suggest that descending influences from the LC can act in suppression of the trigeminal sensorimotor function.

Distribution of substance P-like immunoreactive fibers in feline temporomandibular joint

OBJECTIVE

To study the distribution of substance P-like immunoreactive fibers in feline temporomandibular joint.

METHODS

The immunohistochemical PAP method was used for the investigation of the distribution of substance P-like immunoreactive fibers in feline temporomandibular joint.

RESULTS

The TMJ capsule and the anterior and posterior disc attachments all contained SP-immunoreactive nerve fibers, but the medium fibers in diameter were mainly observed. The density of the distribution of SP-positive nerve fibers was the highest in the subsynovium of the TMJ capsule. The density of distribution was similar in the anterior and posterior disc attachments, but lower than in the subsynovium and the lateral joint capsule. Such fibers in the synovial membrane were sparser, and a part of the fibers were seen around the thin blood vessels in all the foregoing tissues.

CONCLUSION

These results provide the morphological data for exploring the neurobiological mechanisms of temporomandibular joint disorder and its pain.

Innervation pattern of different cartilaginous tissues in the rat

BACKGROUND

The innervation of skeletal tissues by sensory nerves is poorly understood - especially of nerve fibres which reach into the bony and cartilaginous tissue.

METHODS

Samples of rat cartilaginous tissues from different locations (knee joint, vertebral column, temporomandibular joint) were fixed by perfusion and decalcified. The distribution of protein gene product (PGP) 9.5-, calcitonin gene-related peptide (CGRP)- and tachykinin (TK)-immunoreactive axons was analysed using fluorescence immunohistochemistry.

RESULTS

Nerve fibres were detected in the outer regions of the hyaline cartilage of the knee joint, in the hyaline cartilage of the vertebral body, in the fibrocartilage of the intervertebral disc and menisci, and in the articular disc of the temporomandibular joint. Predominantly, they were found to be CGRP-immunoreactive.

CONCLUSION

The neuropeptidergic innervation of the hyaline cartilage in different locations and the presence of nerve fibres in the fibrocartilage might indicate that in addition to the classical neuronal afferent and efferent pathway these fibres may also mediate trophic actions like tissue adaptation and repair.

Calcitonin gene-related peptide and substance P immunoreactivity in rat trigeminal ganglia and brainstem following adjuvant-induced inflammation of the temporomandibular joint

The immunoreactivity of two inflammatory mediators, calcitonin gene-related peptide (CGRP) and substance P, was measured in the trigeminal ganglia and brainstem to characterize an adjuvant-induced inflammation within the rat temporomandibular joint at various acute (6, 24 and 48 h) and intermediate (10 day) time intervals. Concentrations of adjuvant-related neuropeptides were compared to those in both contralateral vehicle-related tissues and non-injected controls. By 6 h, CGRP immunoreactivity in the trigeminal ganglia was significantly above that in contralateral vehicle-injected tissue. The CGRP had decreased at each of the following time-points, but remained significantly elevated at 10 days. Substance P in the ganglion on the injected side was significantly increased for all four time periods. In brainstem subnucleus caudalis, CGRP was significantly increased for all four time periods. Substance P immunoreactivity in the subnucleus caudalis was significantly increased for the initial three time periods, but by day 10 had been reduced to that of the control. These data show that the pattern of changes in neuropeptides following the induction of inflammation is different between substance P and CGRP. Moreover, the pattern of change varies between the brainstem and the trigeminal ganglion. This suggests that the two neuropeptides may have different roles in the inflammatory process, and that this process may be modulated by different mechanisms at the brainstem and ganglion.

[Distribution of calcitonin gene-related peptide-like immunoreactive fibres in the temporomandibular joint of rat]

OBJECTIVE

To observe the distribution of calcitonin gene-related peptide-like immunoreactive (CGRP-LI) nerve fibres in rat's temporomandibular joint (TMJ).

METHODS

The avidin-biotin-peroxidase complex method and image analysis were employed to detect CGRP-LI nerve fibres in frozen sections of TMJs in eight rats.

RESULTS

CGRP-LI nerve fibres were plentifully distributed in TMJs except the central disc band and bone, mainly in the periphery of blood vessels, especially arteries. Density: anterior disc attachment and capsule, (454.6 +/- 72.8) mm(2); posterior portion, (302.7 +/- 43.4) mm(2); lateral portion, (240.2 +/- 23.6) mm(2); medial portion, (229.6 +/- 25.0)mm(2); and peripheral portion of disc, (202.4 +/- 35.2) mm(2).

CONCLUSION

CGRP-LI nerve fibres were widely distributed in rat TMJ and were a part of trigeminal sensory nerve. Density was highest in anterior disc attachment and capsule.

[The temporomandibular joint: recentering...some debate!]

In comparison with hip pathology, the authors emphasize the importance of the biomechanical factor in the stomatognathic systems physiology and pathology. They denounce a syllogism which is set as a reference for the justification of orthodontics and dentistry.

Osseoperception: sensory function and proprioception

Tooth loss and its replacement have significant functional and psychosocial consequences. The removal of intra-dental and periodontal mechanoreception accompanying tooth loss changes the fine proprioceptive control of jaw function and influences the precision of magnitude, direction, and rate of occlusal load application. With the loss of all teeth, complete denture restoration is a compromise replacement which only partially restores function. Implant-supported prostheses restore jaw function more appropriately, with improved psychophysiological discriminatory ability and oral stereognosis. Osseoperception is defined as depending on central influences from corollary discharge from cortico-motor commands to jaw muscles, and contributions from peripheral mechanoreceptors in orofacial and temporomandibular tissues. The processing of central influences is considered with the recognition of the plasticity of neuromotor mechanisms that occurs to accommodate the loss of dental and periodontal inputs.

The caudal subnucleus caudalis (medullary dorsal horn) acts as an interneuronal relay site in craniofacial nociceptive reflex activity

We have recently documented that bilateral increases in electromyographic (EMG) activity of digastric (DIG) and masseter (MASS) muscles can be evoked by injection into the rat's temporomandibular joint (TMJ) region of the small-fiber excitant and inflammatory irritant mustard oil and that this increased jaw muscle activity can be significantly reduced by extensive lesions of the trigeminal subnucleus caudalis (Vc). This study was carried out in 34 anaesthetized rats to test whether neurones in the caudal Vc are indeed of critical importance in these craniofacial nociceptive reflexes. The effects of micro-injection of the cellular neurotoxic chemical ibotenic acid in histologically confirmed sites of the caudal brainstem on the mustard oil-evoked EMG activity of ipsilateral and contralateral DIG and MASS were tested. Ibotenic acid micro-injection in the left caudal Vc significantly reduced the increased EMG activity of all four muscles evoked by mustard oil injection into the left TMJ region whereas mustard oil injection into the right TMJ region in these same rats still readily evoked an increase in EMG activity. In other groups of rats, ibotenic acid micro-injection into the rostral Vc, the C2 segment or the reticular formation at the obex level did not produce any significant reduction in the reflexly evoked EMG activity. These findings suggest that neurones in the caudal Vc may be critical elements in neural pathways underlying the reflex responses evoked in jaw muscles by noxious stimulation of the TMJ region.

Orofacial deep and cutaneous tissue inflammation differentially upregulates preprodynorphin mRNA in the trigeminal and paratrigeminal nuclei of the rat

Preprodynorphin (PPD) and preproenkephalin (PPE) gene expression in a rat model of orofacial inflammation were examined in order to further characterize the neurochemical mechanisms underlying orofacial inflammation and hyperalgesia. Deep and cutaneous orofacial inflammation was produced by a unilateral injection of complete Freund's adjuvant (CFA) into the rat temporomandibular joint (TMJ) or perioral skin (PO), respectively. RNA blot analysis of the tissues including the spinal trigeminal complex revealed that the PPD mRNA level ipsilateral to TMJ inflammation was increased by 56.5+/-14.7% (n=4) when compared to the Naive group, and was significantly greater than the contralateral PPD mRNA level (p<0.05). The distribution of neurons that exhibited PPD mRNA after inflammation was localized by in situ hybridization (naive approximately 0). In TMJ-inflamed rats (n=6) PPD mRNA-positive neurons were found ipsilaterally in the medial portion of laminae I-II of the upper cervical dorsal horn (4.5+/-0.3), the dorsal portion of the subnucleus caudalis and caudal subnucleus interpolaris (5.2+/-0.3), and the paratrigeminal nucleus (6.4+/-1.2). A very localized induction of PPD mRNA was also identified in a group of neurons in the intermediate portion of the subnucleus caudalis (2.4+/-0.4) in PO-inflamed rats (n=6). The distribution of these PPD mRNA-positive neurons was somatotopically relevant to the site of injury. There were no significant changes in PPE mRNA expression in both TMJ- and PO-inflamed rats. These results indicate that TMJ inflammation resulted in a more intense and widespread increase in PPD mRNA expression when compared to PO inflammation. These changes may contribute to persistent central hyperexcitability and pain associated with temporomandibular disorders.

Activation of peripheral GABAA receptors inhibits temporomandibular joint-evoked jaw muscle activity

We have previously shown that injection of mustard oil or glutamate into rat temporomandibular joint (TMJ) tissues, an experimental model of acute TMJ injury, can reflexly induce a prolonged increase in the activity of both digastric (jaw-opener) and masseter (jaw-closer) muscles. In this study, GABA was applied to the TMJ region by itself or in combination with glutamate, and the magnitude of evoked jaw muscle electromyographic (EMG) activity was measured. Application of GABA alone to the TMJ region did not evoke significant jaw muscle EMG activity when compared with normal saline controls. In contrast, co-application of GABA and glutamate into the TMJ region decreased the magnitude of glutamate-evoked EMG activity. This GABA-mediated inhibition of glutamate-evoked EMG activity followed an inverse dose-response relationship with an estimated median inhibitory dose (ID50) of 0.17 +/- 0.05 (SE) micromol and 0.031 +/- 0.006 micromol for the digastric and masseter muscles, respectively. Co-administration of the GABAA receptor antagonist bicuculline (0.05 micromol) but not the GABAB receptor antagonist phaclofen (0.05 or 0. 15 micromol) reversed the suppressive actions of GABA, indicating that this action of GABA may be mediated by peripheral GABAA receptors located within the TMJ region. Our results suggest that activation of peripheral GABAA receptors located within the TMJ region could act to decrease the transmission of nociceptive information.

Origin of sensory and autonomic innervation of the rat temporomandibular joint: a retrograde axonal tracing study with the fluorescent dye fast blue

Previous studies that have used retrograde axonal tracers (horseradish peroxidase alone or conjugated with wheat germ agglutinin) have shown that the temporomandibular joint (TMJ) is supplied with nerve fibers originating mainly from the trigeminal ganglion, in addition to other sensory and sympathetic ganglia. The existence of nerve fibers in the TMJ originating from the trigeminal mesencephalic nucleus is unclear, and the possible innervation by parasympathetic nerve fibers has not been determined. In the present work, the retrograde axonal tracer, fast blue, was used to elucidate these questions and re-evaluated the literature data. The tracer was deposited in the supradiscal articular space of the rat TMJ, and an extensive morphometric analysis was performed of the labeled perikaryal profiles located in sensory and autonomic ganglia. This methodology permitted us to observe labeled small perikaryal profiles in the trigeminal ganglion, clustered mainly in the posterior-lateral region of the dorsal, medial, and ventral thirds of horizontal sections, with some located in the anterior-lateral region of the ventral third. Sensory perikarya were also labeled in the dorsal root ganglia from C2 to C5. No labeled perikaryal profiles were found in the trigeminal mesencephalic nucleus. On the other hand, autonomic labeled perikaryal profiles were distributed in the sympathetic superior cervical and stellate ganglia, and parasympathetic otic ganglion. Our results confirmed those of previous studies and also demonstrated that: (i) there is a distribution pattern of labeled perikaryal profiles in the trigeminal ganglion; (ii) some perikaryal profiles located in the otic ganglion were labeled; and (iii) the trigeminal mesencephalic nucleus did not show any retrogradely labeled perikaryal profiles.

The "missing link" in the origin of trigeminal neuralgia: a new theory and case report

Tic Douloureux (Trigeminal Neuralgia) has afflicted mankind for centuries, perhaps for all time. This sharp stabbing paroxysm of pain along the branches of the trigeminal nerve is described as "...one of the most painful problems that plagues mankind." Many theories about the cause of trigeminal neuralgia have been previously presented. Often these theories build on the previous foundations when new research presents itself. The complete picture still eludes researchers today. Much of the mechanism has been proposed, but researchers lacked one essential component. There has never been an answer to why these pains only occur in cranial segments and why, thankfully, TN is rare. What sets the stage for the development of TN? The unique neurophysiology of the trigeminal nerve and the accompanying ability of the Temporomandibular Joints to create a sensitized neural system are the last piece of the puzzle. This central sensitization of the Trigeminal Nerve allows the development of a small cluster of neurons that act as a central trigger for the paroxysmal pain. The role of the TMJ in trigeminal neuralgia is illustrated by this case report.

Concomitant mandibular and head-neck movements during jaw opening-closing in man

To test the hypothesis of a functional relationship between the human mandibular and cranio-cervical motor systems, head-neck movements during voluntary mandibular movements were studied in 10 healthy young adults, using a wireless optoelectronic system for three-dimensional (3D) movement recording. The subjects, unaware of the underlying aim of the study, were instructed to perform maximal jaw opening-closing tasks at fast and slow speed. Movements were quantified as 3D movement amplitudes. A consistent finding in all subjects was parallel and coordinated head-neck movements during both fast and slow jaw opening-closing tasks. Jaw opening was always accompanied by head-neck extension and jaw closing by head-neck flexion. Combined movement and electromyographic recordings showed concomitant neck muscle activity during head-neck movements, indicative of an active repositioning of the head. No differences in 3D movement amplitudes could be seen with respect to speed. The head movement was 50% of the mandibular movement during jaw opening, but significantly smaller (30-40%), during the jaw closing phase. In repeated tests, the 3D movement amplitudes of the concomitant head movements were less variable during slow jaw movement and during the jaw opening phase, than during fast and jaw closing movements, suggesting speed- and phase-related differences in the mechanisms controlling the integrated mandibular and head-neck motor acts. The present results give further support to the concept of a functional trigeminocervical coupling during jaw activities in man.