Oral physiology, nutrition and quality of life in diabetic patients associated or not with hypertension and beta-blockers therapy.

The relationship between type 2 diabetes oral physiology, nutritional intake and quality of life has not been fully elucidated. We assessed the impact of type 2 diabetes - exclusive or associated with hypertension with beta-blockers treatment - on oral physiology, mastication, nutrition and quality of life. This cross-sectional study was performed with 78 complete dentate subjects (15 natural teeth and six masticatory units minimum; without removable or fixed prostheses), divided into three groups: diabetics (DM) (n = 20; 45·4 ± 9·5 years), diabetics with hypertension and receiving beta-blockers treatment (DMH) (n = 19; 41·1 ± 5·1 years) and controls (n = 39; 44·5 ± 11·7 years) matched for gender, age and socioeconomic status. Blood glucose, masticatory performance, swallowing threshold, taste, food intake, stimulated and unstimulated salivary flow, pH and buffering capacity of saliva were assessed. Glycemia was higher in DM than in controls (P < 0·01). No differences were observed between DM and controls for nutrition and quality of life. Both stimulated and unstimulated salivary flow rate were lower in DMH (P < 0·01), which also presented the lowest number of teeth and masticatory units (P < 0·0001), and reduction in the number of chewing cycles (P < 0·01). Controls showed lower Decayed Missing Filled Teeth index (DMFT) scores in comparison with DMH (P = 0·021). Masticatory performance and saliva buffering capacity were similar among groups. Exclusive type 2 diabetes did not alter oral physiology, nutrition or quality of life. However, when hypertension and beta-blockers treatment were associated with diabetes, the salivary flow rate, chewing cycles and number of teeth decreased.

Changes in masticatory function after injection of botulinum toxin type A to masticatory muscles.

This study examined changes in masticatory function after botulinum toxin type A (BTX-A) injection using objective and subjective tests during 12 weeks. Also, we compared differences in masticatory function between group in which only masseter muscle (M group) was injected and group in which masseter and temporal muscle (M-T group) were injected. Forty subjects were assigned into two groups; M group (n = 20) and the M-T group (n = 20). The Meditoxin(®) was used as BTX-A injection. The mixing ability index (MAI) was used as the objective indicator, and visual analogue scale (VAS) and food intake ability (FIA) index were used as subjective indicators. Overall, the masticatory function drastically declined after 4 weeks and gradually recovered with time. Compared with the pre-injection state, the masticatory function decreased by 89·2% (MAI), 12·2% (FIA) and 32·2% (VAS) 4 weeks after the injection (P < 0·05). When the results between M group and M-T group were compared, scores of VAS and FIA were significantly different 4 weeks after the injection (P < 0·05), but the MAI score showed no significant difference between two groups. In conclusion, this study showed that masticatory function was significantly decreased after BTX-A injection into the masticatory muscle after 4 and 8 weeks from injection. However, masticatory efficiency measured using MAI could completely recover after 12 weeks. Furthermore, after 8 weeks from the injection, the masticatory function measured after injection into only the masseter muscle was similar to that measured after injection into both masseter and temporal muscle.

Treatment effectiveness of arthrocentesis plus hyaluronic acid injections in different age groups of patients with temporomandibular joint osteoarthritis.

PURPOSE: To investigate for treatment effectiveness in different age groups of patients with temporomandibular joint osteoarthritis who underwent a cycle of 5 weekly arthrocenteses plus hyaluronic acid injections. MATERIALS AND METHODS: We implemented a retrospective study on 76 patients followed up for 1 year. Outcome variables were pain levels at rest and during chewing, subjective masticatory efficiency, functional limitation, perceived efficacy, and jaw range of motion. Three age groups of patients were identified, and treatment effectiveness was compared among groups by means of a multistrata permutation test. RESULTS: All the partial P values of the subtests related to the age groups, adjusted according to the close testing method for controlling multiplicity, were significant: P = .009 (aged <45 years), P = .001 (aged 45-65 years), and P = .001 (aged >65 years). For the younger age group, the treatment had a significant effect only on the pain at mastication and on the subjective efficacy. For the other age groups, the treatment effectiveness was evident with regard to almost all the considered symptoms. CONCLUSIONS: Our findings suggested that the treatment protocol was more effective in patients older than 45 years, thus having important clinical implications regarding attempts to define tailored treatment protocols for patients with temporomandibular disorders.

Comparison Of Efficacy Of Steroids Alone And Combination Of Steroids With Hyaluronidase On Mouth Opening In Oral Submucous Fibrosis Patients.

BACKGROUND: Eventually Oral submucous fibrosis causes pronounced stiffness and failure to open the mouth. Objectives are to determine compare the efficacy of intralesional steroids alone and combination of steroids with hyaluronidase on mouth opening in oral submucous fibrosis. METHODS: It was a prospective comparative cohort study. Total of 74 patients both male and female having history of pan chewing and limited mouth opening and burning sensations were included in the study. Informed consent was taken and divided into two groups. Patients of group 1 were managed with mixture of betamethasone 1 ml and hyaluronidase 1500 IU and patients of group 2 were treated with only steroid injection of betamethasone 1 ml given intralesional, both injections were given intralesional, by multiple puncture technique and once a week and continued for twelve weeks (3 months). And data compiled and analyzed in SPSS-20. RESULTS: The mean age of group 1 was 40.027±6.97 years, and mean age of Group 2 was 37.351±5.48 years. In both groups, the greatest number of cases aged from 31-59 years. Compared to females in both groups, the majority of patients were males. In 32 (86.4)% patients of group 1 showed efficacy compared with 18[43.2] patients in group 2 [p-0.000]. Conclusion: In this study Intralesional steroids with hyaluronidase injections are more efficient for opening the mouth in patients with oral sub-mucus fibrosis.

Effects of analgesics on orthodontic pain.

INTRODUCTION: Our objective was too assess the effectiveness of 3 analgesics (ibuprofen, naproxen sodium, and acetaminophen) and a placebo administered before and after the placement of separators in reducing the severity of postseparator placement pain. We also examined the impact of treatment on chewing efficiency at 24 hours after separator placement. METHODS: Twenty-four subjects participated in the study. Each subject received 3 of 4 treatments: ibuprofen, naproxen sodium, acetaminophen, or placebo in random order at monthly intervals. The dosing times were 1 hour before separator placement and 3 and 7 hours after separator placement. Before placement, the subjects completed a masticatory efficiency test and a visual analog scale (VAS) for expected pain and pain experienced. A VAS pain diary was kept for 24 hours. Subjects returned to the clinic after 1 week for separator removal. RESULTS: VAS pain summary scores after separator placement were significantly affected by the administration of ibuprofen (P = 0.0298) and the time after separator placement (P <0.0001). Administering ibuprofen before and after separator placement significantly reduced pain compared with the placebo. The analgesic effects diminished by day 2, resulting in peak pain levels and decreased chewing efficiency. The expected pain after separator placement also played a role in experienced pain; subjects expecting more pain experienced more pain. CONCLUSIONS: Ibuprofen was superior to the placebo in relieving postseparator pain as measured by the VAS pain summary scores, whereas acetaminophen and naproxen sodium did not significantly differ from the placebo.

Bone changes in the mandible following botulinum neurotoxin injections.

In this study, botulinum neurotoxin type A (BoTx/A) was injected into the temporalis and masseter muscles of growing rats to induce masticatory hypoactivity. Sixty, 30-day-old, male Long-Evans rats were randomly divided into four groups. BoTx/A was bilaterally injected in the masseter muscles in group I, in the temporalis muscles in group II, and into both the masseter and the temporalis muscles in group III. Group IV served as the control in which saline was bilaterally injected into both muscles. Forty-five days after the injections, the rats were sacrificed. Observation of cortical bone thickness from bone biopsies of the right halves of the mandibles, evaluation of the volume of masseter and temporalis muscles with a plethysmometer, and scanning of bone mineral density (BMD) of the skull and mandibular bone structure with dual-energy X-ray absorptiometry were performed. One-way analysis of variance was employed to analyse measurements of muscle volume, BMD, and cortical bone thickness among the groups. The least square difference was then used to determine significance. Reduced cortical bone thickness and BMD of the skull and mandibular bone structure were observed. The volumes of the temporalis and masseter muscles injected with BoTx/A were smaller. Masticatory hypofunction affects bone structure during development.

Thickened saliva after effective management of drooling with botulinum toxin A.

AIM: The aim of this study was to evaluate the rheological properties of saliva after submandibular botulinum toxin type A (BoNT-A) injections. METHOD: We enrolled 15 children (11 males and six females; age range 3-17 y, mean age 9 y 10 mo) diagnosed with spastic (n=9) or dyskinetic (n=6) quadriplegic cerebral palsy (CP); Gross Motor Function Classification System level IV or V; and two children with intellectual disability (IQ<70) who experienced moderate to severe drooling. Salivary flow rate and drooling quotient were measured at baseline and at different times after BoNT-A injections up to 24 weeks. The mucin concentration of saliva was analysed before and after BoNT-A treatment. RESULTS: Both submandibular salivary flow rate (baseline 0.38 mL/min; 24 wks after injection 0.26 mL/min) and drooling quotient (baseline 42.5%; 24 wks 28.80%) were substantially reduced, with a concomitant increase in mucin concentration within 8 weeks after BoNT-A injection (from 0.612 to 1.830 U/mL). The parents of nine children observed thickened saliva. Swallowing and chewing were problematic in seven children. Two of these children needed treatment with mucolytics because of pooling of thickened saliva in the throat. INTERPRETATION: When making decisions about the use of BoNT-A, the risk of problems with masticatory and swallowing functions as a result of thickening of saliva after BoNT-A treatment should be taken into account.

Efficacy and Safety of Botulinum Toxin Type A on Persistent Myofascial Pain: A Randomized Clinical Trial.

This study assessed the safety and efficacy of three different doses of BoNT-A for persistent myofascial pain (MFP). One hundred female subjects were randomly assigned into five groups (n = 20): oral appliance (OA), saline solution (SS) and three BoNT-A groups with different doses. Pain intensity and pressure pain threshold were evaluated up to 24 weeks after treatment. Adverse effects related to muscle contraction, masticatory performance, muscle thickness and mandibular bone volume were also assessed. Changes over time were compared within and between groups. The "nparLD" package and Wilcoxon signed-rank test were used to analyze the data. BoNT-A reduced pain intensity (p < 0.0001) and increased pressure pain threshold (p < 0.0001) for up to 24 weeks compared to the placebo. No differences were found between BoNT-A and OA at the last follow-up. A transient decline in masticatory performance (p < 0.05) and muscle contraction (p < 0.0001), and a decrease in muscle thickness (p < 0.05) and coronoid and condylar process bone volume (p < 0.05) were found as dose-related adverse effects of BoNT-A. Regardless of the dose, BoNT-A was as effective as OA on MFP. Notwithstanding, due to BoNT-A dose-related adverse effects, we suggest the use of low doses of BoNT-A in MFP patients that do not benefit from conservative treatments.

Post-operative discomforts in children after extraction of primary teeth.

OBJECTIVES: This prospective observational study aimed to evaluate discomfort after extraction of deciduous teeth under local anesthesia. The primary objective was to describe the prevalence of post-extraction pain (PEP), post-extraction bleeding (PEB), post-extraction biting injury (PEBI), and analgesic usage in children. The secondary objective was to define whether it is possible to determine a profile of patients or a type of extraction procedure predictive to PEP, administration of analgesics, PEB, or PEBI. METHODS: One hundred and twenty-five children, aged 3-13 years, with indications of at least one deciduous tooth extraction, were included. Immediately after extraction, information concerning the patient and the extraction were collected. Eighteen to 32 hr after extraction, parents were called by phone to request reports concerning the onset and intensity of PEP assessed using the Wong-Baker Faces (WBF) scale, the administration of paracetamol (acetaminophen) to their children, and the appearance of PEB and/or PEBI. RESULTS: Of the children, 37.3% reported PEP (WBF ≥2), but 23.3% of these children did not receive any analgesic drugs to help relieve pain. Pain appeared before 3 hr after extraction in 69% of the children. Higher incidences of PEP and usage of analgesics were found both in the group of children with unfavorable socioeconomic level compared to favorable level and in the group with pre-operative pain compared to no pre-operative pain (p < .05). CONCLUSIONS: About a third of the children reported pain after extraction, but the instructions for pain relief were not followed by all parents. The socioeconomic level of the young patient and the pain felt during the extraction were important predictors of discomfort. Therefore, our study could help the dentist to provide information on predicted post-operative discomfort and to allow suitable care depending on the patient's profile or procedure.

Effect of feed type and essential oil product on equine chewing activity.

The ingestive and post-digestion effect of a blend of special essential oil compounds (EO) on eating, chewing and faecal parameters were measured in horses. Ingestive effects appear after no adaptation. Post-digestion effects appear after adaptation. Six Icelandic horses were assigned to two groups in a Latin Square subplot design with EO treatments to four different roughage types and four different concentrates. The horses were fed four different roughage meals and two different concentrate meals on each of the four sampling days. Eating time and saliva were observed during meals. Jaw movements (JM) were recorded using a special chewing halter. Eating time was derived from JM and related to DM intake. The size characteristics of faecal particles were measured by using image analysis. All chewing characteristics measured were significantly affected by roughage (p < 0.001) and concentrate type (p < 0.01). EO had a significant ingestive effect on the frequency of observed saliva during concentrate meals. No significant (p < 0.05) post-digestive or ingestive effect of EO was found for any measured chewing characteristic, which was reflected in the absence of effect on faecal particle dimensions. In conclusion, effect of type of roughage and concentrate was more significant than potential effects of EO.

Masticatory hypofunction effects induced by BTXA injection of hippocampal neurons in developing rats.

BACKGROUND AND OBJECTIVE: In clinical practice, malocclusion is often encountered during the period of growth and development of individuals. In addition to nutritional imbalance, some studies have found that mastication affects learning and memory ability. Tooth loss and masticatory hypofunction have been suggested as risk factors of Alzheimer disease. However, relatively little research has been done in developing animals. The present study evaluated the relationship between masticatory hypofunction and neuropathological changes of the hippocampus in developing rats. DESIGN: Four-week-old Wistar rats were randomly divided into saline-injected and botulinum toxin type A (BTXA)-injected groups. After an experiment period of 4 weeks, the rats were sacrificed for evaluation of neuropathological changes in the hippocampus through Nissl staining and phosphorylated cyclic AMP (cAMP) response element binding protein (CREB) immunohistochemistry. RESULTS: Nissl staining revealed a significant reduction in the density of neurons in the BTXA-injected rats. The BTXA-injected rats exhibited a decreased level of CREB phosphorylation. The degree of p-CREB immunoreactivity differed significantly between the two groups. CONCLUSION: The BTXA-injected rats exhibited a reduction in neuron density and phosphorylated CREB, indicating that mastication might influence the learning and memory ability during the growth period. Therefore, it is strongly suggested that malocclusion be corrected as soon as possible during growth and development.

A novel computational method to determine subject-specific bite force and occlusal loading during mastication.

The evaluation of three-dimensional occlusal loading during biting and chewing may assist in development of new dental materials, in designing effective and long-lasting restorations such as crowns and bridges, and for evaluating functional performance of prosthodontic components such as dental and/or maxillofacial implants. At present, little is known about the dynamic force and pressure distributions at the occlusal surface during mastication, as these quantities cannot be measured directly. The aim of this study was to evaluate subject-specific occlusal loading forces during mastication using accurate jaw motion measurements. Motion data was obtained from experiments in which an individual performed maximal effort dynamic chewing cycles on a rubber sample with known mechanical properties. A finite element model simulation of one recorded chewing cycle was then performed to evaluate the deformation of the rubber. This was achieved by imposing the measured jaw motions on a three-dimensional geometric surface model of the subject's dental impressions. Based on the rubber's deformation and its material behaviour, the simulation was used to compute the resulting stresses within the rubber as well as the contact pressures and forces on the occlusal surfaces. An advantage of this novel modelling approach is that dynamic occlusal pressure maps and biting forces may be predicted with high accuracy and resolution at each time step throughout the chewing cycle. Depending on the motion capture technique and the speed of simulation, the methodology may be automated in such a way that it can be performed chair-side. The present study demonstrates a novel modelling methodology for evaluating dynamic occlusal loading during biting or chewing.

Involvement of adenosinergic receptor system in an animal model of tardive dyskinesia and associated behavioural, biochemical and neurochemical changes.

Tardive dyskinesia is a syndrome characterized by repetitive involuntary movements usually involving the mouth, face and tongue. It is considered as the late onset adverse effect of prolonged administration of typical neuroleptic drugs. Adenosine is now widely accepted as the major inhibitory neuromodulators in the central nervous system besides GABA. Both, agonists of adenosine A(1) and A(2) receptors and the antagonists of A(2A) receptors are known to protect against neuronal damage caused by toxins as well as they can also protect against the cell damage inflicted by reactive oxygen species. The present study investigated the effect of adenosine and A(2A) receptor antagonist, caffeine in an animal model of tardive dyskinesia by using different behavioural (orofacial dyskinetic movements, stereotypic rearing, locomotor activity, % retention), biochemical (lipid peroxidation, reduced glutathione levels, antioxidant enzyme levels (superoxide dismutase and catalase) and neurochemical (neurotransmitter levels) parameters. Chronic administration of haloperidol (1 mg/kg i.p. for 21 days) significantly increased vacuous chewing movements (VCMs), tongue protrusions, facial jerking in rats which was dose dependently inhibited by adenosine and caffeine. Chronic administration of haloperidol also resulted in an increased dopamine receptor sensitivity as evident by increased locomotor activity and stereotypic rearing after day 14. Chronic administration of haloperidol also decreased % retention time on elevated plus maze paradigm. Treatment with adenosine or caffeine reversed these behavioural changes. Besides, haloperidol also induced oxidative damage in all regions of brain which was prevented by caffeine and adenosine, especially in striatum. On chronic administration of haloperidol there was a decrease in dopamine and norepinephrine turnover which was dose-dependently reversed by treatment with adenosine or caffeine. When caffeine and adenosine were co-administered, there was no synergistic effect, possibly due to mutual antagonistic effects. The findings of the present study suggested the involvement of adenosinergic receptor system in the genesis of neuroleptic-induced tardive dyskinesia.

Chemical Sensing Regulates Mastication/Swallowing.

Mastication and swallowing are the first stage of digestion involving several motor processes such as food intake, intra-oral food transport, bolus formation and chewing and swallowing reflex. These complicated motor functions are accomplished by the well-coordinated activities in the jaw, hyoid, tongue, facial and pharyngeal muscles. Although the basic activity patterns of these movements are controlled by the brainstem pattern generators, these movements generate various peripheral sensory inputs. Among the sensory inputs, it is well-known that somatic sensory inputs play important roles in reflexively modulating the movements so that the final motor outputs fit the environmental demand. However, little is known about the effects of chemical sensory inputs such as taste and olfaction originating from the ingested foods by these movements. A possible reason could be raised that cognition of the chemical sensory inputs at the higher brain also influences the movements, so it is difficult to discuss the neural mechanisms underlying the observed effect. In this review, we focus on the effects of chemical sensory inputs on the masticatory movements and initiation of swallowing. We first summarize chemical sensory inputs occurring during mastication and swallowing, and their receptive mechanisms. In addition, we will introduce the effect of application of monosodium L-glutamate (MSG) solution as an umami taste to the oropharynx on the swallow initiation which is involuntary controlled and the possible neural mechanisms underlying this effect is discussed.

Chewing efficiency and occlusal forces in PMMA, acetal and polyamide removable partial denture wearers.

PURPOSE: Thermoplastic materials, such as acetal (AC) and polyamide (PA), constitute an alternative to polymethyl methacrylate (PMMA) based resins as the materials for removable partial dentures. However, none of the previous studies compared chewing efficiency and occlusal forces in the wearers of dentures made of various materials. Therefore, the aim of this study was to determine and compare the chewing efficiency and occlusal forces in PMMA, PA and AC RPDs' wearers. The hypothesis was that the type of denture base material shows a significant effect on chewing efficiency (expressed as a degree of food fragmentation) and occlusal force. METHODS: The experiment included the group of 30 patients using removable partial dentures. The dentures made of PMMA, acetal and polyamide were tested in each patient. Each denture was worn for 90 days, with a random sequence of the denture manufacturing and insertion. After 7, 30 and 90 days of each denture wear, chewing efficiency coefficient was determined with the aid of a sieving method, and occlusal force was measured with a dynamometer. RESULTS: The use of dentures made of PMMA or acetal was reflected by a marked increase in chewing efficiency and occlusal force. None of these parameters changed significantly with the time of denture wear. Moreover, no significant correlation was found between chewing efficiency and occlusal forces. CONCLUSIONS: Denture base material exerts significant effects on the degree of food fragmentation and the level of occlusal forces. The use of dentures and clasps made of materials with lower modulus of elasticity is associated with lower chewing efficiency and lower occlusal forces.

Influence of bitter taste on mastication pattern.

Mastication is a rhythmic activity that can be modified by peripheral information generated in the mouth. To study whether taste cognition could influence the way in which a food is broken down in the mouth, subjects masticated firm, sugar-based gelatine gels with differing concentrations of quinine, up to 1500 micromol/kg, while electromyography (EMG) of masticatory muscles was recorded. Taste intensity and composition of saliva were measured. With increasing quinine concentration, the average number of chews for nine subjects decreased from 30 to 22, and their average clearance time increased from 7 to 14 sec. Quinine concentration had no effect on chewing frequency (1.3 Hz) or on the rate of salivation (5.5 g/min). Bitterness increased, while acceptability and sweetness decreased, with increasing concentration of quinine in the gel and in saliva. Taste cognition could therefore modify food breakdown in the mouth.

Effect of Postnatal Myostatin Inhibition on Bite Mechanics in Mice.

As a negative regulator of muscle size, myostatin (Mstn) impacts the force-production capabilities of skeletal muscles. In the masticatory system, measures of temporalis-stimulated bite forces in constitutive myostatin KOs suggest an absolute, but not relative, increase in jaw-muscle force. Here, we assess the phenotypic and physiologic impact of postnatal myostatin inhibition on bite mechanics using an inducible conditional KO mouse in which myostatin is inhibited with doxycycline (DOX). Given the increased control over the timing of gene inactivation in this model, it may be more clinically-relevant for developing interventions for age-associated changes in the musculoskeletal system. DOX was administered for 12 weeks starting at age 4 months, during which time food intake was monitored. Sex, age and strain-matched controls were given the same food without DOX. Bite forces were recorded just prior to euthanasia after which muscle and skeletal data were collected. Food intake did not differ between control or DOX animals within each sex. DOX males were significantly larger and had significantly larger masseters than controls, but DOX and control females did not differ. Although there was a tendency towards higher absolute bite forces in DOX animals, this was not significant, and bite forces normalized to masseter mass did not differ. Mechanical advantage for incisor biting increased in the DOX group due to longer masseter moment arms, likely due to a more anteriorly-placed masseter insertion. Despite only a moderate increase in bite force in DOX males and none in DOX females, the increase in masseter mass in males indicates a potentially positive impact on jaw muscles. Our data suggest a sexual dimorphism in the role of mstn, and as such investigations into the sex-specific outcomes is warranted.

Neuropeptide-Y modulates eating patterns and masticatory muscle activity in rats.

Neuropeptide Y (NPY) is a powerful orexigenic peptide secreted by hypothalamic neurons. The present study investigates how NPY injection into the lateral ventricle modulates masticatory movements and eating behavior. Behavioral experiments showed that cumulative food intake over a 4-h period and latency to eating were increased and decreased, respectively, in NPY-injected rats compared to saline-injected control rats. The feeding time for 2 g pellets was shorter in NPY-injected rats and resulted in an increased feeding rate, with more potent effects observed at 1 µg compared to 10 µg NPY. After injection of 10 µg NPY, a greater number of bouts with shorter average bout duration for eating 2g, compared to 1 µg NPY, were observed. Furthermore, 10 µg NPY injection resulted in prolonged periods of moving and shortened sleep and grooming. Electromyography recordings from the digastric and masseter muscles showed two distinct patterns of bursts corresponding to the gnawing and chewing phases. After the injection of 1 µg NPY, the burst magnitude of masseter muscle during the gnawing phase increased, reflecting strong jaw-closing muscle activity. The relative integrated EMG of masseter muscle in both phases was smaller following injection of 10 µg NPY in comparison with that of 1 µg NPY. The present study indicates that 1 µg NPY administration promotes feeding behavior together with increased feeding rate and powerful jaw-closing muscle activity; whereas 10 µg NPY administration lowers jaw-closing muscle activity during biting and produces mastication with shorter and more frequent feeding bouts than 1 µg NPY.

Distinct association between the antagonistic jaw muscle activity levels and cardiac activity during chewing and NREM sleep in the freely moving guinea pigs.

The aim of this study was to investigate the changes of the association between cardiac activity and the electromyographic (EMG) level of the antagonistic jaw muscles during chewing and NREM sleep in guinea pigs after systemic clonidine injections. Ten animals were prepared for chronic experiments to monitor sleep, cardiac activity and EMG activity of jaw-closing masseter (MAS) and jaw-opening anterior belly of digastric (ADG) muscles. The recordings were made for ten hours with the injections of saline or clonidine (10 µg/kg, i.p.). Integrated EMG activity of the two muscles and mean heart rate (mHR) were calculated for every 10-s epoch. During the two hours after clonidine injection, the duration of REM sleep and mHR were significantly reduced. During chewing, the high EMG activity level of the two muscles and the activity ratio between the two muscles were not modified although mHR was decreased. During NREM sleep, after clonidine injection, the low EMG activity level at baseline was further decreased by 20-30% in parallel to a decrease of mHR although the heterogeneity of the activity ratio remained unaltered. The results suggest that the maintenance of the activity level for the antagonistic jaw muscles are regulated by the distinct physiological mechanisms reflecting the behavioral states during conscious chewing and unconscious NREM sleep.

Effects of chemical stimulation of masseter muscle nociceptors on trigeminal motoneuron and interneuron activities during fictive mastication in the rabbit.

An electrophysiological study was carried out in sixteen decerebrate and paralyzed New Zealand rabbits to determine how a bolus injection of a nociceptor stimulant (hypertonic saline, 5%) into the masseter muscle influences the activity of the trigeminal motor circuitry during fictive jaw movements. Hypodermic needles connected to a syringe held in a computer-controlled infusion pump were inserted into the anterior deep layer of either the right or the left masseter. Twenty-three infusions of 50, 70 or 80 microl saline were made in fourteen animals at constant rates over 1 min. Eight control infusions of normal saline (0.9%) were made in a subpopulation of five animals in an identical manner. Fictive jaw movements were evoked before and after the infusions by repetitive electrical stimulation of the corticobulbar tract. Effects were assessed by extracellular microelectrode recordings made from the digastric motoneuron pool and from putative last-order interneurons in the oral subnucleus of the spinal trigeminal tract and adjacent structures. In comparison with pre-infusion control cycles, nociceptor stimulation caused significant slowing of the rhythm and a reduction of the area of the digastric motoneuron bursts in the majority of the animals (12/14). The decrease in cycle frequency was due almost entirely to a lengthening of the time between the digastric bursts. Changes usually began 1-2 min after the infusion and returned to pre-infusion values within 10-15 min. No significant effects were seen when isotonic saline was applied. Recordings were obtained from nine interneurons, eight of which had low threshold mechanosensitive receptive fields. One neuron was, in addition, excited by pinch. Eight were not active in the absence of motor activity and this did not change when hypertonic saline was applied. However, once fictive movements began, all started to fire rhythmic bursts of spikes. In five cases, there was a significant post-infusion increase in spike frequency, and three showed decreases. Seven showed significant post-infusion changes in mean phase and/or concentration of their firing within the movement cycle. Changes in the preferred phase of interneuronal firing were significantly correlated to changes in the phase of offset of the digastric burst. The present results provide evidence that the stimulation of nociceptors in a muscle slows the frequency of rhythmical movements in the absence of sensory feedback. They confirm that infusions into one muscle affect the output of its antagonist. The results also suggest that neurons in the oral subnucleus of the spinal trigeminal tract and adjacent reticular formation appear to participate in programming these changes in motor output.