Observation of Effects of Different Surgical Treatments on Unilateral Masticatory Muscle Spasm.

BACKGROUND: Unilateral masticatory muscle spasm is a rare disease without a generally accepted and efficacious treatment plan. OBJECTIVE: We sought to compare the effects of different surgical treatments on unilateral masticatory muscle spasm. METHODS: A retrospective analysis of the surgical treatment and effects of 10 cases of unilateral masticatory muscle spasm occurred between February 2010 and September 2016. Three cases underwent complete amputation of the trigeminal motor branch, 3 cases underwent partial amputation of the trigeminal motor branch, and 4 cases received only vascular decompression. All patients were followed up by telephone interview after surgery. RESULTS: In the simple vascular decompression group, 3 cases were cured and 1 was cured after a delay. Of these 3 cases, 1 case became aggravated 2 years after the operation, 1 case became aggravated 5 years after the operation, and 1 case showed no change during the follow-up period. In the partial amputation group, 2 cases were cured and 1 case was alleviated. Of the 2 patients who were cured, 1 suffered recurrence 2 years later, while the other case showed no recurrence during the follow-up period. In the complete amputation group, 1 case was cured with a delay and 2 cases were cured immediately with no recurrence during the follow-up. Mild atrophy of the temporal muscle occurred gradually with no restriction of the mouth opening in 2 cases. CONCLUSIONS: Complete amputation of the trigeminal nerve did achieve better effects than pure microvascular decompression and partial amputation of the trigeminal motor branch, but it may lead to mild temporal muscle atrophy.

Microvascular Decompression for Hemimasticatory Spasm: A Case Report and Review of the Literature.

BACKGROUND: Hemimasticatory spasm is a rare clinical entity characterized by involuntary and paroxysmal contractions of the jaw-closing muscles on 1 side of the face. Although its cause is not fully known, vascular compression of the trigeminal nerve has been speculated. CASE DESCRIPTION: Here, we report 1 case of hemimasticatory spasm that was cured by microvascular decompression of the motor branch of the trigeminal nerve; a relevant literature review was also performed. CONCLUSIONS: Hemimasticatory spasm is a rare disease that may be recalcitrant to conservative medical therapy, and vascular decompression of the trigeminal nerve may be required to relieve the spasm.

Treatment of hemimasticatory spasm with microvascular decompression.

Hemimasticatory spasm is a rare disorder characterized by paroxysmal involuntary contraction of the jaw-closing muscles. As the ideology and pathogenesis of the disease are still unclear, there has been no treatment that could give rise to a good outcome so far. Herein, we tried to use surgical management to cure the disease. Six patients with the disease were included in this study. These patients underwent microvascular decompression of the motor fibers of the trigeminal root. After the operation, all faces of the patients felt relaxed at varied degrees, except for 1 patient. Our study showed that microvascular decompression of the trigeminal nerve could lead to a better outcome. However, a control study with a large sample is needed before this technique is widely used.

Effects of changes in vertical occlusal dimension on heart rate fluctuations in guinea pigs.

BACKGROUND: We have previously reported that the decrease of the vertical occlusal dimension (VOD) led to heart failure and abnormalities in creatine phosphokinase (CPK) in guinea pigs. In the present study, we investigated the autonomic activity and the origin of the abnormality in CPK under different occlusal conditions. MATERIALS AND METHODS: Guinea pigs were separated into the following five groups: untreated control, reduced VOD, slit, restored VOD and increased VOD groups and compared for their electrocardiogram and heart rate fluctuations for two weeks using Fluclet, computer software. RESULTS: The control group revealed no changes in heart rate fluctuations or posture. The reduced VOD group exhibited a two-phase wave of heart rate fluctuations, with the first peak 0-2 days after teeth grinding, and the second peak starting from 4 days after teeth grinding until sudden death (usually 12th day), accompanied by head drop. The slit and the restored VOD groups exhibited only the first peak. The increased VOD group, with approximately 3 mm-thick acrylic pellets bonded to the posterior teeth, showed no heart rate fluctuations. Body weight loss was most prominent in the reduced VOD group, and became much milder in the order of increased VOD, restored and slit groups. The reduced VOD group exhibited transient elevation of skeletal muscle type of CPK isozyme activity within two days after treatment. CONCLUSION: The present study suggests that the first peak of heart rate fluctuations is caused by pulpal stimulation, and the second peak by excessive contraction (excessive excitation of the motor output system and the autonomic nervous system) of the masticatory muscles. On the other hand, increased VOD did not influence either the motor or the autonomic nervous system.

The two main theories on dental bruxism.

Bruxism is characterized by non-functional contact of mandibular and maxillary teeth resulting in clenching or grating of teeth. Theories on factors causing bruxism are a matter of controversy in current literature. The dental profession has predominantly viewed peripheral local morphological disorders, such as malocclusion, as the cause of clenching and gnashing. This etiological model is based on the theory that occlusal maladjustment results in reduced masticatory muscle tone. In the absence of occlusal equilibration, motor neuron activity of masticatory muscles is triggered by periodontal receptors. The second theory assumes that central disturbances in the area of the basal ganglia are the main cause of bruxism. An imbalance in the circuit processing of the basal ganglia is supposed to be responsible for muscle hyperactivity during nocturnal dyskinesia such as bruxism. Some authors assume that bruxism constitutes sleep-related parafunctional activity (parasomnia). A recent model, which may explain the potential imbalance of the basal ganglia, is neuroplasticity. Neural plasticity is based on the ability of synapses to change the way they work. Activation of neural plasticity can change the relationship between inhibitory and excitatory neurons. It seems obvious that bruxism is not a symptom specific to just one disease. Many forms (and causes) of bruxism may exist simultaneously, as, for example, peripheral or central forms.

Reflejo C evocado en el músculo digástrico: un nuevo método para evaluar actividad wind-up trigeminal aplicable a principios activos de plantas medicinales / C-reflex evoked in the digastric muscle: a new method for evaluating trigeminal wind-up activity applicable to active principles of medicinal plants

Wind-up is a measure of nociceptive neurons synaptic potentiation and constitutes an important mechanism in the generation of central sensitization in chronic pain. At the spinal level, the C-evoked reflex in the bicep femoris muscle, by low frequency repetitive stimulation of the sural nerve, has enabled us to evaluate the wind-up of nociceptive neurons of the dorsal horn, and also the effect of antinociceptive drugs with a possible potential therapeutic value in chronic pain. In the present work, we electrophysiologically evaluated the trigeminal wind-up activity, utilizing as an experimental paradigm the evoked C-reflex in the Sprague-Dawley rat digastric muscle. The results obtained indicate that: (a) It is possible to evoke an electromyographic reflex in the digastric muscle by stimulation of C-fibers belonging to the third trigeminal branch; (b) It is possible to potentiate the trigeminal C-reflex with low frequency stimuli (wind-up) and (c) it is possible to depress the trigeminal wind-up with the μ-opioid agonist morphine and with the NMDA receptor antagonist, ketamine. We can conclude that the simple measurement of the trigeminal wind-up will facilitate future studies on the analgesic efficacy of new drugs in oro-facial chronic pain syndromes like migraine and with special emphasis on medicinal plant active principles.

El wind-up refleja la potenciación sináptica en neuronas nociceptivas y constituye un importante mecanismo en la generación de sensibilización central en dolor crónico. A nivel espinal, el reflejo C evocado en el músculo bicep femoris por estimulación repetitiva de baja frecuencia del nervio sural ha permitido evaluar la actividad wind-up en neuronas nociceptivas del cuerno dorsal, así como el efecto de drogas antinociceptivas con un posible potencial terapéutico en dolor crónico. En el presente trabajo evaluamos electrofisiológicamente la actividad wind-up trigeminal, utilizando como paradigma experimental el reflejo C evocado en el músculo digástrico de ratas Sprague-Dawley. Los resultados obtenidos indican que: (a) es posible evocar un reflejo electromiográfico en el músculo digástrico de la rata por estimulación de fibras C de la tercera rama del trigémino; (b) es posible potenciar el reflejo C trigeminal con estímulos de baja frecuencia (wind-up) y (c) es posible deprimir el wind-up trigeminal con el agonista μ-opioide morfina y con el antagonista NMDA, ketamina. Podemos concluir que la medición simple del wind-up trigeminal mediante el reflejo C evocado en el músculo digástrico facilitará futuros estudios sobre eficacia analgésica de nuevos fármacos en cuadros de dolor orofacial crónicos, como la migraña, con especial énfasis en los principios activos de plantas medicinales.

Morphological study of myoneural interaction between the levator labii superioris muscle and its motor nerve in rats / Estudio morfológico de la interacción mioneural entre el músculo elevador del labio superior y su nervio motor en ratas

The progress of science in search of new techniques of the nerve regeneration and the functional repair in reinnervated muscle has been the target of many researchers around the world. Consequently, nerves and muscles in different body segments asked for more enlightenment of their morphology, their interrelation with other anatomic structures and their peculiarities. One of the most significant areas that need deeper studies is the region of the head and neck, since they are often affected by important pathologies. In order to offer the researcher's community a morphological myoneural interaction model, this study elected the levator labii superioris muscle and its motor nerve, the buccal branch of the facial nerve (VII pair) not only for its special characteristics, but also its value on the facial expression. The rat was chosen for this investigation for being easy to obtain, to keep, to manipulate and to compare this experiment with many others studies previously published. The techniques used were Mesoscopic (dissection), histoenzymologic and morphometric ones.In the results the muscle proved to have a predominance of fast twich fibers (FG and FOG) and superficial location, with a proximal bone and a distal cutaneous insertion. Its motor nerve, the buccal branch of the facial nerve (VII pair), breaks through the muscle belly into its deep face, and comprised a heterogeneous group of myelinic nerve fibers disposed in a regular form in all fascicle. Near the motor point, the nerve showed to be composed of two fascicles with different sizes. Due to the small nerve dimensions, the nerve fibers have a smaller diameter if compared to the motor nerve of pectineus muscle of the cat. Further studies with neural tracers have already had a start in order to provide more information about the distribution and the architecture of these fibers.

El progreso de la ciencia en busca de nuevas técnicas para la regeneración neural y la recuperación funcional de los músculos reinervados, ha atraído el interés de muchos investigadores en todo el mundo. En consecuencia, los músculos y los nervios merecen más aclaraciones sobre su morfología, relaciones anatómicas y particularidades. Entre las áreas que merecen estudios más profundos y detallados, está la región de cabeza y cuello, que es a menudo afectada por enfermedades graves. Con el propósito de ofrecer a la comunidad científica un modelo morfológico de interacción mioneural, se eligió el músculo elevador del labio superior y su nervio motor, la rama bucal del nervio facial (VII par craneal), por sus especiales características y su importancia en la expresión facial. En esta investigación se optó por la rata, por las facilidades de obtención, de manejo y para comparar los datos obtenidos con estudios previos. Se utilizaron técnicas mesoscópicas de disección, histoenzimológicas y morfométricas. Los resultados mostraron un músculo con predominio de fibras de contracción rápida (FG y FOG), ubicación superficial, inserción proximal ósea e inserción distal en la piel. Su nervio motor, la rama bucal del nervio facial, ingresa en el vientre muscular en la cara profunda, y está compuesto por un grupo heterogéneo de fibras nerviosas mielínicas dispuestas de forma regular por todo el fascículo nervioso cerca del punto motor. El nervio es formado por dos fascículos de diferentes tamaños. Debido a las pequeñas dimensiones en la rata, el diámetro de las fibras nerviosas presenta valores reducidos, en comparación con el nervio motor del músculo pectíneo en el gato, por ejemplo. Los datos aportados podrán ser usados como referencia en estudios de regeneración en nervios y músculos. Otros estudios con marcadores neuronales se iniciaron para aclarar la distribución y la estructura de las fibras mencionadas.

Effects of the adenosine A 2A antagonist KW 6002 (istradefylline) on pimozide-induced oral tremor and striatal c-Fos expression: comparisons with the muscarinic antagonist tropicamide.

Typical antipsychotic drugs, including haloperidol and pimozide, have been shown to produce parkinsonian motor effects such as akinesia and tremor. Furthermore, there is an antagonistic interaction between adenosine A(2A) and dopamine D(2) receptors in the basal ganglia, which is important for motor functions related to the production of parkinsonian symptoms. Several experiments were conducted to assess the effects of the selective adenosine A(2A) antagonist KW 6002 on both the motor and cellular effects of subchronic administration of pimozide. The motor test employed was tremulous jaw movements, which is used as a model of parkinsonian tremor. In addition, c-Fos expression in the ventrolateral neostriatum, which is the striatal area most associated with tremulous jaw movements, was used as a marker of striatal cell activity in animals that were tested in the behavioral experiments. Repeated administration of 1.0 mg/kg pimozide induced tremulous jaw movements and increased ventrolateral striatal c-Fos expression, while administration of 20.0 mg/kg of the atypical antipsychotic quetiapine did not. The tremulous jaw movements induced by pimozide were significantly reduced by co-administration of either the adenosine A(2A) antagonist KW 6002 or the muscarinic antagonist tropicamide. Pimozide-induced increases in ventrolateral striatal c-Fos expression were reduced by a behaviorally effective dose of KW 6002, but c-Fos expression in pimozide-treated rats was actually increased by tropicamide. These results indicate that two different drug manipulations that act to reduce tremulous jaw movements can have different effects on DA antagonist-induced c-Fos expression, suggesting that adenosine A(2A) antagonism and muscarinic receptor antagonism exert their motor effects by acting on different striatal circuits.

The effects of neuromuscular electrical stimulation for dysphagia in opercular syndrome: a case study.

A 76-year-old man with opercular syndrome characterized by complete bilateral loss of voluntary control of facial, lingual, pharyngeal and masticatory muscles is presented with focus on the severe dysphagia. Three years earlier the patient had experienced two strokes resulting in opercular syndrome with severe dysphagia. Despite initial logopedic dysphagia treatment, swallowing did not improve. A new treatment for dysphagia, consisting of neuromuscular electrical stimulation was applied on the patient. He returned to oral feeding. Clinical and treatment observations are reported.

Complex evaluation of pain after tonsillectomy.

CONCLUSION: Postoperative odynophagia should be assessed by a variety of methods including visual analogue scale (VAS) pain scores (subjective), clinical data (objective qualitative) and surface electromyography (sEMG; objective quantitative). sEMG might be used for quantitative evaluation of odynophagia when aggravation or hysteria-conversion reaction is suspected. Tonsillectomy affects muscle activity significantly by involving additional muscles in deglutition. OBJECTIVES: Complex evaluation of post tonsillectomy odynophagia was used for objective assessment of complaints of operated patients. PATIENTS AND METHODS: Parameters evaluated for 50 randomly chosen operated adults included VAS pain score, clinical data, and the EMG data such as the timing, electric amplitude and graphic patterns of muscular activity during deglutition. We investigated masseter (MS), infrahyoid (INF) and submental-submandibular (SUB) muscles. The results were compared with a normative database. The patients were first tested 12 h after surgery and were monitored for 30 days. The sEMG data were compared with VAS pain score with regard to changes in clinical condition of the patients. RESULTS: Signs of clinical recovery after tonsillectomy did not always correspond with the VAS pain score evolution. sEMG was more in concord with clinical recovery than VAS. Electric activity of MS and LSM was significantly higher among the patients in comparison with a normative database (p<0.005).

Intrinsic properties of the adult human mylohyoid muscle: neural organization, fiber-type distribution, and myosin heavy chain expression.

The mylohyoid (MH) muscle plays a critical role in chewing, swallowing, respiration, and phonation. The present study was designed to test the hypothesis that the functional properties of the MH are reflected by its intrinsic specializations, including the neural organization, fiber-type distribution, and myosin heavy chain (MHC) expression. Adult human MH muscles were investigated to determine the nerve supply pattern using Sihler's stain, banding pattern and types of motor endplates using acetylcholinesterase (AChE) staining and silver impregnation, and muscle fiber type and MHC composition using immunocytochemical and immunoblotting techniques. The adult human MH was found to have the following neuromuscular specializations. First, the muscle was innervated by several branches of the MH nerve derived from the mandibular division of the trigeminal nerve. Each of the nerve branches supplied a distinct region of the muscle, forming a segmental innervation pattern. Second, the MH had a single motor endplate band which was located in the middle of the muscle length. Both en plaque and en grappe types of motor endplates were identified on the MH muscle fibers. Finally, the adult human MH fibers expressed unusual MHC isoforms (i.e., slow-tonic, alpha-cardiac, embryonic, and neonatal) which coexisted with the major MHC isoforms (i.e., slow type I, fast type IIa, and fast type IIx), thus forming various major/unusual (or m/u) MHC hybrid fiber types. The m/u hybrid fibers (84% of the total fiber population) were the predominant fiber types in the adult MH muscle. Determination of the neuromuscular specializations of the MH is helpful for better understanding of the muscle functions and for development of strategies to treat MH-related upper airway disorders.

Identification of c-Fos immunoreactive brainstem neurons activated during fictive mastication in the rabbit.

In the present study we used the expression of the c-Fos-like protein as a "functional marker" to map populations of brainstem neurons involved in the generation of mastication. Experiments were conducted on urethane-anesthetized and paralyzed rabbits. In five animals (experimental group), rhythmical bouts of fictive masticatory-like motoneuron activity (cumulative duration 60-130 min) were induced by electrical stimulation of the left cortical "masticatory area" and recorded from the right digastric motoneuron pool. A control group of five animals (non-masticatory) were treated in the same way as the experimental animals with regard to surgical procedures, anesthesia, paralysis, and survival time. To detect the c-Fos-like protein, the animals were perfused, and the brainstems were cryosectioned and processed immunocytochemically. In the experimental group, the number of c-Fos-like immunoreactive neurons increased significantly in several brainstem areas. In rostral and lateral areas, increments occurred bilaterally in the borderzones surrounding the trigeminal motor nucleus (Regio h); the rostrodorsomedial half of the trigeminal main sensory nucleus; subnucleus oralis-gamma of the spinal trigeminal tract; nuclei reticularis parvocellularis pars alpha and nucleus reticularis pontis caudalis (RPc) pars alpha. Further caudally-enhanced labeling occurred bilaterally in nucleus reticularis parvocellularis and nucleus reticularis gigantocellularis (Rgc) including its pars-alpha. Our results provide a detailed anatomical record of neuronal populations that are correlated with the generation of the masticatory motor behavior.

Evidence of parasympathetic postganglionic neurons in the rat hypoglossal nerve trunk.

Previous studies have indicated that the geniohyoid (GH) muscle is innervated by efferent axons from both the hypoglossal nerve (CN XII) and ansa cervicalis. To clarify the physiological significance of this dual innervation of the GH muscle, we examined properties of efferent innervations in rat GH muscle using electrophysiological, horseradish peroxidase (HRP) tracing and immunohistochemical techniques. Recordings from the branch of the XII nerve that innervates the GH (GH.Br) revealed that bursts of impulses during fictitious swallowing were conducted via the XII nerve trunk, in which neuronal cell bodies were labeled in the ventrolateral subnucleus of the XII nucleus by HRP tracing. In contrast, in vivo experiments demonstrated that tonic discharges in GH.Br were conducted via the ansa cervicalis. However, HRP-labeled efferent neurons were observed in neither brainstem nor upper spinal cord, but sensory neurons were labeled in the most rostral cervical spinal ganglia via the ansa cervicalis. Tonic activity was abolished in vitro by mecamylamine, an antagonist of nicotinic acetylcholine receptors (nAChR), and by pirenzepine, an antagonist of muscarinic M1 receptors. Incubation of isolated XII nerve segments with antisera to vasoactive intestinal peptide, nAChR, and muscarinic M1 receptor yielded small numbers of labeled neurons with each antiserum. All labeled neurons displayed similar diameters and were located approximately 1.5 mm proximal to the bifurcation of the XII nerve into medial and lateral branches. Our findings indicate that GH muscle in the rat is innervated by both somatic and parasympathetic nervous systems.

Influence of sex on reflex jaw muscle activity evoked from the rat temporomandibular joint.

Injection of glutamate into the rat temporomandibular joint (TMJ) evoked a concentration-dependent increase in jaw muscle activity. We investigated whether there are sex-related differences in glutamate-evoked jaw muscle activity that are mediated by sex hormones and whether prior injection of glutamate into the TMJ alters the magnitude of jaw muscle activity evoked by a subsequent injection of the algesic and inflammatory compound mustard oil (MO) into the TMJ. The magnitude of glutamate-evoked digastric and masseter muscle activity was significantly greater in female than male rats when 1000 mM glutamate was injected into the TMJ. Gonadectomy significantly reduced the magnitude of glutamate-evoked digastric muscle activity in female rats. Treatment of gonadectomized female rats with estrogen (20 microg/day) increased the magnitude of glutamate-evoked digastric muscle activity. Glutamate-evoked jaw muscle activity in gonadectomized and estrogen-treated gonadectomized males was not significantly different from intact males. Prior injection of glutamate over a concentration range of 10-1000 mM significantly increased digastric muscle activity evoked by MO injection into the TMJ 30 min later. In contrast, MO-evoked masseter muscle activity was significantly increased by prior injection of 250 mM glutamate only. There were, however, no sex-related differences in the enhancement of MO-evoked jaw muscle activity by prior injection of glutamate. These findings indicate that there are sex-related differences in glutamate-evoked jaw muscle activity that are dependent on female sex hormones, and increased glutamate concentrations sensitize the TMJ to noxious chemical stimuli.

Denervation atrophy of the masticatory muscles in a patient with nasopharyngeal cancer: MR examinations before and after radiotherapy.

We report on a patient with denervation atrophy of the masticatory muscles due to nasopharyngeal cancer who received therapeutic irradiation. Magnetic resonance imaging has significantly contributed to aid diagnosis of this pathology. Masticatory muscle atrophy should be a definitive finding of perineural invasion caused by head and neck tumors. Radiologists should be familiar with this appearance to avoid confusion with tumor invasion of the muscle.

Intrathecal administration of 5-HT(3) receptor agonist modulates jaw muscle activity evoked by injection of mustard oil into the temporomandibular joint in the rat.

The effect of intrathecal administration of the 5-HT(3) receptor agonist 2-methyl-5-hydroxytryptamine (2m-5HT) on jaw muscle activity evoked by mustard oil (MO) injection into the temporomandibular joint of anesthetized rats was examined. One microgram or 100 microg of 2m-5HT significantly enhanced or suppressed jaw muscle responses, respectively. Pre-administration of tropisetron, a 5-HT(3) receptor antagonist, attenuated the effect of 2m-5HT. These results indicate that activation of 5-HT(3) receptors can modulate trigeminal nociceptive responses.

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.

trkA modulation of developing somatosensory neurons in oro-facial tissues: tooth pulp fibers are absent in trkA knockout mice.

To investigate the nerve growth factor requirement of developing oro-facial somatosensory afferents, we have studied the survival of sensory fibers subserving nociception, mechanoreception or proprioception in receptor tyrosine kinase (trkA) knockout mice using immunohistochemistry. trkA receptor null mutant mice lack nerve fibers in tooth pulp, including sympathetic fibers, and showed only sparse innervation of the periodontal ligament. Ruffini endings were formed definitively in the periodontal ligament of the trkA knockout mice, although calcitonin gene-related peptide- and substance P-immunoreactive fibers were reduced in number or had disappeared completely. trkA gene deletion had also no obvious effect on the formation of Meissner corpuscles in the palate. In the vibrissal follicle, however, some mechanoreceptive afferents were sensitive for trkA gene deletion, confirming a previous report [Fundin et al. (1997) Dev. Biol. 190, 94-116]. Moreover, calretinin-positive fibers innervating longitudinal lanceolate endings were completely lost in trkA knockout mice, as were the calretinin-containing parent cells in the trigeminal ganglion.These results indicate that trkA is indispensable for developing nociceptive neurons innervating oral tissues, but not for developing mechanoreceptive neurons innervating oral tissues (Ruffini endings and Meissner corpuscles), and that calretinin-containing, trkA dependent neurons in the trigeminal ganglion normally participate in mechanoreception through longitudinal lanceolate endings of the vibrissal follicle.