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PubMed1980

Some electromyographic parameters of experimental tooth clenching in adult human subjects.

Eight adult human subjects exercised maximal voluntary tooth clenching until fatigue and pains were experienced, and could no longer be endured, in the right masseter muscle. The integrated electrical activity in the right masseter muscle was determined as a ratio of the different isometric exercises, and it showed a consistent decrease from onset of fatigue, via onset of pains, to the endurance of pains, possibly because of progressive muscle fatigue. The relative muscle activity might have determined the perception of the moment of onset of fatigue in the masseter muscle, and the perception of the moment of muscle exhaustion, but not the perception of the moment of onset of muscle pains.

Adult↗

PubMed1986

Fiber type composition of rostral and caudal portions of the digastric muscle in the dog.

The distribution of muscle fiber types in rostral and caudal portions of the musculus digastricus (digastric muscle) was studied in 6 dogs. Staining procedures which stain specifically for type IIM fibers, a fiber type found in other muscles supplied by the trigeminal nerve, were used. Rostral and caudal portions of the muscle were compared because the rostral portion is innervated by the trigeminal nerve, and the caudal portion is innervated by the facial nerve. The musculus triceps brachii (triceps muscle), which contains fiber types I and IIA, and the musculus masseter (masseter muscle), which contains type IIM, were used as controls. Mean fiber diameters were calculated for each of the muscles. Both portions of the digastric muscle exhibited the same histochemical behavior, possessing types I and IIA myofibers. Neither portion contained type IIM fibers. Type I fibers in the masseter muscle were histochemically different from type I fibers in the other muscles studied. Type II fibers predominated in all 3 muscles, but there were significantly (P less than 0.001) more type I fibers in the triceps muscle than in either portion of the digastric muscle or in the masseter muscle. Type II fibers were significantly larger than type I fibers in the caudal digastric (P less than 0.01) and masseter (P less than 0.05) muscles. There was no difference in the size of type I or type II fibers between any of the muscles studied (P greater than 0.20).

Adenosine Triphosphatases↗

PubMed2000

Comparison of sensitivity of sodium currents to tetrodotoxin in equine muscle specimens with that in murine and human muscle specimens.

OBJECTIVE: To determine sensitivity of equine skeletal muscle to tetrodotoxin and compare that with sensitivity of murine and human skeletal muscles. SAMPLE POPULATION: Semimembranosus, vastus lateralis, triceps brachii, and masseter muscle specimens from 22 euthanatized horses, vastus lateralis muscle biopsy specimens from 25 clinically normal humans, and diaphragmatic muscle specimens from 6 mice. PROCEDURE: Electrically elicited twitch responses were measured in muscle specimens incubated in medium alone and with tetrodotoxin (100 nM, 400 nM, 1.6 microM for equine specimens and 100 nM, 200 nM, 400 nM, 800 nM, 1.6 microM for murine and human specimens). Percentages of tetrodotoxin-sensitive and -resistant sodium channels were determined and compared among muscles and species. RESULTS: 2 sodium channels with different sensitivities to tetrodotoxin were identified in equine muscle. One was blocked with 100 nM tetrodotoxin and the other was unaffected by tetrodotoxin at concentrations up to 1.6 microM. The only difference detected among the 4 equine muscles was that masseter muscle specimens had a higher percentage of tetrodotoxin-sensitive channels than triceps brachii muscle specimens. Tetrodotoxin-resistant sodium channels constituted 31 to 66% of the equine muscle twitch response, which was greater than that determined for normal human and murine muscle (< 5%). CONCLUSION AND CLINICAL RELEVANCE: Equine skeletal muscle contains a high percentage of tetrodotoxin-resistant sodium channels. The 4 equine muscles evaluated were more similar to each other than to murine and human muscles. Shifts in expression of sodium channel subtypes may play a role in the manifestation of certain myopathies.

Animals↗

PubMed1994

Radiographic patterns of osteomyelitis in the mandible. Plain film/CT correlation.

Mandibular osteomyelitis often is associated with involvement of the masticator space. Assessment of mandibular osteomyelitis should therefore involve assessment of soft tissue involvement of the lesion. The purpose of this study was to clarify the relationship between computed tomography patterns and the presence of inflammation in soft tissues. Thirty-three cases diagnosed with osteomyelitis of the mandible were analyzed radiologically with conventional radiographs and with computed tomography scans. Computed tomography patterns of osteomyelitis were classified into four types, lytic, mixed, sclerotic, and sequestrum patterns. Location, extent of the lesion, and change of the cortical plate were evaluated and compared with conventional radiographic findings. Mixed pattern cases displayed diffuse bone abnormalities, which sometimes were accompanied by cortical plate disruption and periosteal reaction. In addition, most mixed pattern cases showed soft tissue involvement, especially of the masseter muscle. Inflammation of the masseter muscle was found to be related to periosteal reaction and disruption of the buccal cortical plate. The data demonstrate a close interaction between cortical plate disruption and muscle inflammation. The extent of inflammation including soft tissue involvement was better appreciated with computed tomography in osteomyelitis, especially in mixed pattern cases.

Adolescent↗

PubMed2003

Chewing behaviour and bolus formation during mastication of meat with different textures.

During chewing, meat is mashed under compression and shear bite forces whilst saliva is incorporated. The resulting mixture is shaped into a cohesive bolus by agglomeration of small particles, and triggers a swallow. This study aimed to investigate the relationship between chewing behaviour and bolus formation of meat with different textures. Twenty-five consenting young adults participated in this study. Electromyographic activity was recorded from surface electrodes on the elevator muscles (masseter and temporalis) during mastication of cold beef. Two different textures (T(1): tough and dry; T(2): tender and juicy) were studied, and subjects were asked to chew the beef and then spit out the bolus either: (1) after a constant chewing period of 7s or (2) when the bolus was ready to be swallowed. Meat samples were weighed before and after chewing to determine weight changes due to saliva incorporation and the release of meat juice. Cutting tests were applied to measure the maximum shear force. The mechanical shear force was maximal for meat before chewing (T(1)=124 N/cm(2); T(2)=83 N/cm(2)) and decreased with increased chewing duration. Texture differences analysed from mechanical measurements remained significant even when the boli were ready for swallowing (T(1)=39 N/cm(2); T(2)=32 N/cm(2)); the toughest meat gave the toughest bolus. Muscular activity adapted to the texture of the meat as soon as chewing began, and remained constant over the observed chewing period. Mean muscular activity was higher during the chewing of tough meat than during the chewing of tender meat. As a consequence, by the time a bolus was ready to be swallowed, more saliva had been incorporated into the tough meat samples (mean weight increase: 36%) than the tender meat samples (mean weight increase: 30%).

Adult↗

PubMed2002

The effects of lidocaine and adrenergic agonists on rat sciatic nerve and skeletal muscle blood flow in vivo.

UNLABELLED: It has been proposed that epinephrine prolongs lidocaine nerve blockade duration by exerting a local vasoconstrictive effect on tissues at the injection site, slowing lidocaine's local clearance. However, previous studies have failed to demonstrate consistent effects of lidocaine and epinephrine, injected alone and in combination, on vascular tone or regional blood flow. To reinvestigate this idea, in this study we used the radiolabeled microsphere technique to measure in vivo tissue blood flow before and at several time points after perisciatic nerve and intramasseter muscle injection of lidocaine alone, epinephrine, the selective alpha(1)-adrenergic receptor agonist phenylephrine, or lidocaine combined with these adrenergic receptor agonists. Repeated-measures analyses of variance were used to assess significant changes in blood flow over time. Lidocaine (2, 10, and 20 mg/mL) and epinephrine (10 micro g/mL or 1:100,000) injected alone did not alter blood flow in sciatic nerve, perisciatic muscle, or masseter muscle. Injections of lidocaine (10 mg/mL) combined with epinephrine (10 micro g/mL) did not affect adjacent muscle blood flow but caused a mild reduction in sciatic nerve blood flow, which was significant 30 min after injection. However, phenylephrine (10 micro g/mL), a potent vasoconstrictor, combined with lidocaine (10 mg/mL) significantly reduced blood flow in all three tissues. Our findings suggest that mechanisms other than local vasoconstriction may contribute to the prolongation of lidocaine nerve blocks by epinephrine. IMPLICATIONS: Accepting that the microsphere technique may be limited in its sensitivity to detect small but clinically relevant changes in tissue blood flow, our findings suggest that mechanisms other than local vasoconstriction may contribute to the prolongation of lidocaine nerve blocks by epinephrine.

Adrenergic Agonists↗

PubMed2002

Split thoracodorsal nerve funicular graft combined with functional latissimus dorsi musculocutaneous flap transfer for immediate facial reanimation after tumor ablation.

The authors report a case of immediate facial reanimation resulting from functional latissimus dorsi musculocutaneous flap transfer and funicular grafting of the thoracodorsal nerve after cheek tumor ablation. After wide excision of the tumor, including the facial nerve except the temporal branch and part of the zygomatic major muscle and masseter muscle, the authors reconstructed the cheek skin and provided movement by performing a small-segment latissimus dorsi musculocutaneous flap transfer using Harii's method and the defect of the buccal and marginal mandibular branches of the facial nerve by funicular grafting from one of the two funicles of the thoracodorsal nerve. After 6 months, the transplanted, small-segment latissimus dorsi muscle showed good voluntary movement, and the lower orbiculus oris and depressor oris presented good functional recovery. The authors believe the two funicles of the thoracodorsal nerve can be used independently for two purposes: one for functional segmental muscle transfer and the other for nerve grafting to defects of branches of the facial nerve. This concept makes it possible to reconstruct multiple facial movements while minimizing donor site morbidity by means of immediate facial reanimation.

Aged↗

PubMed1986

Histochemical and morphometric evaluation of skeletal muscle from horses with exertional rhabdomyolysis (tying-up).

Thirteen horses with histories of exertional rhabdomyolysis were exercised for 20 minutes to induce clinical signs of lameness, elevated serum creatine kinase (CK), and aspartate aminotransferase (AST) activities and skeletal muscle morphologic lesions. The clinical signs exhibited by affected horses included trembling, sweating, increased rate of respiration, and restricted limb movement. Serum CK reached maximal activity between 4 and 8 hours after the exercise period and serum AST activity peaked between 24 and 48 hours. Histologically, the skeletal muscle lesions in muscle biopsies 24 hours after the exercise period consisted of segmental muscle fiber degeneration. Damaged muscle fibers were repaired by myoblastic regeneration. Horses with moderate (greater than 1,500 U/liter) to severe (greater than 5,000 U/liter) elevations of serum CK activity accompanied by clinical signs of muscle soreness induced by exercise, had visible muscle fiber degeneration microscopically. Frozen sections of biopsies of the gluteus medius muscle from affected (n = 13) and control (n = 11) groups of horses were processed to demonstrate myofibrillar ATPase activity. These sections were then used to determine fiber types, area percentages, and mean cross sectional fiber sizes. The mean type I, type II, and intermediate fiber sizes were significantly larger in the affected group than in the control group. In the gluteus medius muscles of the affected group, there was a significantly greater percentage of intermediate fibers and a significantly greater percentage of area occupied by intermediate fibers than in the control group. In the muscle samples with acute lesions of exertional rhabdomyolysis, type II fibers were selectively but not exclusively affected. In one horse which was subsequently necropsied 24 hours after the exercise period, lesions were present in several postural muscles, the masseter muscle and the heart. We conclude that the gluteus medius muscle fibers of affected horses are larger in cross sectional area than those of control horses and that there is preferential degeneration of type II fibers in acute lesions of exertional rhabdomyolysis.

Adenosine Triphosphatases↗

PubMed2005

Malignant hyperthermia: a case report in Thai Anesthesia Incidents Study (THAI Study).

A 3-year-old Thai boy underwent open reduction and internal fixation with K-wire of condylar fracture of humerus under general anesthesia. The patients developed generalized muscle regidity, masseter muscle spasm, elevated creatinine kinase, high temperature (39.3 C), inappropriate tachycardia, and arterial base excess was more than-8 mEq/L. The clinical grading scale of diagnosis of malignant hyperthermia was 58 (grade D6; almost certain malignant hyperthermia). Succinylcholine has been identified as the trigger agent, as other possible trigger agents were not involved. The treatment included hyperventilation, external cooling and cold IV fluids without administration of dantrolene. The patient fully recovered and discharged on day 12. This case report showed an incidence of malignant hyperthermia of approximated 1:150,000 in Thai Anesthesia Incidents Study (THAI Study).

Child, Preschool↗

PubMed1990

[The influences of habitual side chewing and the character of food on the masticatory muscle activity in children].

The purpose of this study was to investigate the influences of habitual side chewing and the characteristics of food on the masticatory muscle function in children. A total of thirty persons were subjected to the study; 10 with deciduous dentition (designated as G1), 10 with mixed dentition (as G2), 10 with permanent dentition (as G3), none of whom had any gnatho-facial dysfunction. EMGs were recorded from the temporal anterior muscles and masseter muscles on both sides, and the mandibular movement on the frontal plane was recorded during chewing of boiled fish cake paste, chewing-gum and chewing of dried cuttlefish on both the habitual side and the non-habitual side. EMG activities obtained and periods of closed phase, occlusal phase and open phase in the pathway of the mandibular movement were measured with a personal computer system. The relationship between the total muscle activities at clenching in the intercuspal position and the total muscle activities at chewing were also evaluated. The results obtained in the present study were as follows: 1) Influence of habitual side chewing on the rhythm of the mandibular movement during chewing of chewing-gum was not found in all groups. Influence on EMG activities was not found in G1 and G2, but were presented in G3. 2) Influence of the character of food on rhythm of mandibular movement was not clear in G1, but as found in the other groups, while EMG activities were influenced by the character of food in all groups. 3) The MA Index (the ratio of total muscle activities while chewing to total muscle activities at clenching) showed a decrease with age. As far as the results of the present study is concerned, it could be suggested that the proficiency of the chewing ability is dependent on the dentitional growth. Furthermore, the MA Index was considered to be appropriate for evaluating the masticatory muscle function in children.

Child↗

PubMed1990

[Influences of changing vertical dimension, occlusal contacts of bite plane and body position on masticatory muscle activities].

The Bite plane therapy has been accepted to be useful for treatment of the patients with the stomatognathic dysfunction. The purpose of this study is to make clear the influences of changing the vertical dimension and occlusal contacts of the bite plane on masticatory muscle activities in order to improve the bite plane therapy. The full arch bite plane with an interincisal distance of 5 mm was fabricated for each one of 30 subjects without stomatognathic dysfunction. The EMG activities were recorded from the anterior part of the temporal muscles, the masseter muscles and the anterior belly of the digastric muscles bilaterally while the subject exerted tapping and maximal voluntary clenching in a postural position. Four kinds of experiments were performed as follows. In Exp. 1, integrated EMG activities of each muscle were compared with and without the bite plane. In Exp. 2, the influences of changing the vertical dimension of the bite plane (2.5 mm, 5 mm and 7.5 mm) were tested in 17 subjects. In Exp. 3, the influences of changing the location of occlusal contacts of the bite plane were studied in 12 subjects. In Exp. 4, the influence of changing the body positions on EMG activities and mandibular positions was compared in 30 subjects between the sitting and supine positions. Furthermore, the influence of the same factor was compared with and without the bite plane which was adjusted in each position. The results were summarized as follows: 1. Wearing the bite plane mainly reduced activities of the temporal muscles. 2. The bite plane with an interincisal distance of 5 mm was most effective in reducing activities of the temporal muscles. 3. Wearing the bite plane with anterior occlusal contacts reduced activities of the elevator muscles significantly. 4. Significant differences in activities of the temporal and digastric muscles were recognized between the two body positions when the bite plane was not applied. However, no significant difference was recognized when the bite plane was inserted. Furthermore, those differences were correlated with the difference in the antero-posterior mandibular displacement between the two body positions while the subject tapped the teeth. These results suggest the possibility to control masticatory muscle activities by applying the bite plane with the proper vertical dimension and occlusal contacts. In addition, it is necessary to take a suitable body position for the patient who has a difference in the mandibular displacement between the sitting and supine positions when applying the bite plane.

Dental Occlusion↗

PubMed1996

Use of the buccal fat pad as a pedicle graft.

A technique was developed to use the pedicle buccal fat pad as method for closing an oro-antral communication. The buccal fat pad is situated in the posterior part of the maxilla and bounded by the pterygopalatine fossa, buccal muscle, and masseter muscle. It is supplied by blood from small branches of the maxillary artery, the superficial temporal artery, and the facial artery. Generally, the buccal fat pad can be easily reached by a horizontal incision over the periosteum near the maxillary third molar. As much as 60 x 50mm2 can be obtained. For reconstructive surgery, the buccal fat pad is suitable for closing the sinus near the hard and soft palate and naso-oral fistulae. In our case, graft tissues after surgery healed satisfactorily, began to epithelialize at two weeks after operation, and appeared with normal mucous-like changes at about one month. Thus, the pedicle buccal fat pad is a safe, simple, convenient, and effective grafting method, if it is applied to appropriate cases.

Adipose Tissue↗

PubMed1998

Pre-anesthetic oral clonidine is effective to prevent post-spinal shivering.

BACKGROUND: Shivering is a common event during spinal anesthesia. Customarily we just treat it rather than prevent it. This study was designed to evaluate the efficacy of oral clonidine as a premedication to prevent post-spinal shivering. METHODS: One hundred males of ASA physical status I-III, aged above 40, scheduled for elective urological surgery under spinal anesthesia, were included in this study. All participants were randomly divided into the clonidine and control groups. They received either oral clonidine 150 micrograms (n = 48) or placebo (n = 52) 90 min before spinal anesthesia in a double-blind fashion. Spinal blockade was induced with heavy bupivacaine to a dermatomal level near T10. The shivering was graded as: none, no perceptible tension of muscles observed; mild, slight muscle tonus (masseter muscle); moderate, real shivering (proximal muscles); and severe, generalized shivering (whole body). The tympanic membrane temperature was recorded 30 min after spinal anesthesia. Data were expressed as mean +/- standard deviation. Chi-square and Student's t-test were used. A p value less than 0.05 was considered statistically significant. RESULTS: The incidence of post-spinal shivering, which was graded as none, mild, moderate, and severe, showed statistically significant differences (p < 0.05) between clonidine 150 micrograms and placebo (83% vs. 42%, 10% vs. 6%, 10% vs. 19%, 0% vs. 33%, respectively) during the 30 min immediately after spinal anesthesia. The respective mean tympanic temperature in oral clonidine and placebo groups showed no difference (clonidine vs. control = 35.9 +/- 0.8 degrees C vs. 35.9 +/- 0.7 degrees C). CONCLUSIONS: Pre-anesthetic medication with oral clonidine 150 micrograms is effective to prevent post-spinal shivering in patients undergoing elective urological surgery.

Administration, Oral↗

PubMed2001

Superficial architecture of the jaw-closing muscles of the cat (Felis catus): the temporo-masseteric complex.

The muscle fiber fascicles of the temporo-masseter complex of the cat were minutely dissected. Some heads were embedded in paraffin while others were put into methyl-methacrylate resin and sections were made. The results of this anatomical study demonstrate that this complex consists of the masseter muscle, the temporal muscle and two well individualized transitional fascicles: the maxillomandibularis and zygomato-comandibularis muscles. The masseter and temporal muscles are composed of individualized compartments in which the orientation and aponeuroses of the fibers of which they are composed differ with regard to the centric occlusion plane. The masseter muscle consists of a superficial fascicle made up of two layers, an intermediate fascicle, and a deep fascicle composed of two layers. The temporal muscle consists of one anterior orbital part and one posterior temporal part. This structure is in accordance with the mammalian archetype described by Gaspard and Saban. These findings should lead towards a homology-based nomenclature founded on comparative anatomy studies of mammalian species. Such a classification would permit the comparison of results obtained from physiological and histochemical studies of these complex muscle fibers when they are published by different researchers.

Aging↗

PubMed1985

Lateral preference in mastication: relation to pain.

Ten subjects performed deliberate right and left-sided chewing of gum, each exercise with a duration of 60 s, followed by maximum voluntary teeth clenching (MVC) until onset of pains in the masseter muscles (pain threshold). Contractile activities of the right and left masseter muscles were assessed by integrated and cumulative surface electromyography (EMG). When the right and left muscles functioned as chewing side muscles only, they generated practically identical levels of chewing force; the same applied when they functioned as non-chewing side muscles only. During identical functions, EMGs suggested identical motor unit recruitment and firing patterns in the two paired muscles; i.e., units producing relatively high tensions for chewing side activity, and other units producing relatively low tensions for non-chewing side activity. During isometric MVC activity, until onset of pains, the right and left muscles generated practically identical levels of bite force, but right and left motor unit activity patterns seemed to differ. Right and left motor units might have fired at different rates or begun to drop out at different times. In the latter case, rapidly before slowly fatigued units. There was a tendency for a low pain threshold with high chewing side activity in both masseter muscles. Motor units producing high levels of tension, but easily fatigued, might have caused early onset of muscle pains. No relationships could be established between preferred chewing side and side of initial muscle pains, nor between MVC activity and side of pain onset and preferred chewing side.

Adult↗

PubMed2003

Modulation of masseter exteroceptive suppression by non-nociceptive upper limb afferent activation in humans.

The effects induced by non-noxious electrical stimulation of upper limb nerves on exteroceptive suppression (ES) of masseter muscle EMG activity were studied in 15 healthy subjects. EMG activity of masseter muscles was recorded bilaterally and great care was taken to minimise the activation of afferents other than the stimulated ones. Masseter ES was elicited by applying a non-noxious electrical stimulus to the skin above the mental nerve (Mt) of one side, during a voluntary contraction of masseter muscles at a prescribed steady clenching level. Onset and offset latencies and duration of early and late components of masseter ES (ES1 and ES2, respectively) were evaluated in control conditions and compared to those obtained when a non-noxious electrical stimulation was delivered separately to Med or Rad or simultaneously to both nerves (Med-Rad) of one side. Upper limb nerve stimulation could be simultaneous or it could precede or follow Mt stimulation by various time intervals. In control conditions, ES1 latency onset and duration values (mean +/- SD) were 11.3+/-2.9 ms and 16.9+/-2.1 ms, respectively, and ES2 latency onset and duration values were 44.5+/-6.0 ms and 28.6+/-11.1 ms, respectively. No significant differences were observed which were related to the side being recorded. Two types of effects, opposite in nature, were shown on masseter ES, depending on the time intervals between Mt and upper limb nerve stimulation. The first effect, which was facilitatory, consisted of a significant increase in ES1 and ES2 duration. A maximal increase in ES1 duration (134-155% compared to control value) occurred when upper limb nerve stimulation preceded that of Mt by 18-30 ms. Maximal ES2 lengthening (115-145%) was observed when upper limb nerve stimulation followed that of the Mt by 10 ms. The second effect was inhibitory and affected only ES2, which appeared completely eliminated when Med stimulation preceded that of Mt by 40-80 ms. By contrast, ES1 was never suppressed at any interstimulus interval. These data might reflect the different action of the central outflow, following the upper limb-induced effects, on the different neuronal circuits mediating ES1 and ES2.

Adult↗

PubMed1997

Body position effects on sternocleidomastoid and masseter EMG pattern activity in patients undergoing occlusal splint therapy.

This study was conducted in order to determine the effects of body position on electromyographic (EMG) activity of sternocleidomastoid and masseter muscles, in 15 patients with myogenic cranio-cervical-mandibular dysfunction undergoing occlusal splint therapy. EMG activity was recorded by placing surface electrodes on the sternocleidomastoid and masseter muscles (contralateral to the habitual sleeping side of each patient). EMG activity at rest and during swallowing of saliva and maximal voluntary clenching was recorded in the following body positions: standing, supine and lateral decubitus. In the sternocleidomastoid muscle significant higher EMG activities at rest and during swallowing were recorded in the lateral decubitus position, whereas during maximal voluntary clenching EMG activity did not change. In the masseter muscle significant higher EMG activity during maximal voluntary clenching in a standing position was observed, whereas EMG activity at rest and during swallowing did not change. The opposite pattern of EMG activity supports the idea that there may exist a differential modulation of the motor neuron pools of the sternocleidomastoid and masseter muscles, of peripheral and/or central origin. This suggests that the presence of parafunctional habits and body position could be closely correlated with the clinical symptomatology in these muscles in patients with myogenic craniomandibular dysfunction.

Adult↗

PubMed2004

Contribution of peripheral N-methyl-D-aspartate receptors to c-fos expression in the trigeminal spinal nucleus following acute masseteric inflammation.

In this study, we examined the contribution of N-methyl-D-aspartate (NMDA) receptors on c-fos expression in the trigeminal brainstem nuclei following acute muscle inflammation. Mustard oil (MO; 20%, 30 microL) injected into the masseter muscle induced extensive peripheral edema and Fos-like immunoreactivity (Fos-LI) in several trigeminal brainstem areas including the subnucleus caudalis of the trigeminal spinal nucleus (Vc), the ventral and dorsal regions of the Vc/subnucleus interpolaris transition zone, and the paratrigeminal nucleus. In order to assess the effect of antagonizing NMDA receptors on MO-induced Fos-LI, rats were pre-treated with two different doses of i.v. MK-801 (0.3 mg/kg, 3 mg/kg), a non-competitive NMDA receptor antagonist, 30 min prior to MO injection. Additional groups of rats received MK-801 (0.3 mg/kg) directly in the masseter muscle or in the biceps muscle 5 min prior to MO injection. A higher dose of i.v. MK-801 (3 mg/kg) and MK-801 given locally into the masseter muscle (0.3 mg/kg) produced a significant reduction in total number of MO-induced Fos-LI. Further analyses revealed that pre-treatment with MK-801 (3 mg/kg i.v.) significantly reduced the Fos-LI all throughout the Vc. Only at the caudal Vc, there was a dose-dependent reduction of MO induced Fos-LI. Pre-treatment with masseteric MK-801 also significantly reduced the Fos-LI in the caudal Vc, with the effect greater than that produced by the same dose of MK-801 given intravenously. These results suggest that peripheral NMDA receptors contribute to nociceptive processing from craniofacial muscles.

Animals↗