Models of passive and active dendrite motoneuron pools and their differences in muscle force control

Motoneuron (MN) dendrites may be changed from a passive to an active state by increasing the levels of spinal cord neuromodulators, which activate persistent inward currents (PICs). These exert a powerful influence on MN behavior and modify the motor control both in normal and pathological conditions. Motoneuronal PICs are believed to induce nonlinear phenomena such as the genesis of extra torque and torque hysteresis in response to percutaneous electrical stimulation or tendon vibration in humans. An existing large-scale neuromuscular simulator was expanded to include MN models that have a capability to change their dynamic behaviors depending on the neuromodulation level. The simulation results indicated that the variability (standard deviation) of a maintained force depended on the level of neuromodulatory activity. A force with lower variability was obtained when the motoneuronal network was under a strong influence of PICs, suggesting a functional role in postural and precision tasks. In an additional set of simulations when PICs were active in the dendrites of the MN models, the results successfully reproduced experimental results reported from humans. Extra torque was evoked by the self-sustained discharge of spinal MNs, whereas differences in recruitment and de-recruitment levels of the MNs were the main reason behind torque and electromyogram (EMG) hysteresis. Finally, simulations were also used to study the influence of inhibitory inputs on a MN pool that was under the effect of PICs. The results showed that inhibition was of great importance in the production of a phasic force, requiring a reduced co-contraction of agonist and antagonist muscles. These results show the richness of functionally relevant behaviors that can arise from a MN pool under the action of PICs.

Assessment of a Neurophysiological Model of the Mandibular Branch of the Facial Nerve in Rats by Electromyography

Objectives: Our objective was to develop an experimental model for the noninvasive and objective evaluation of facial nerve regeneration in rats using a motor nerve conduction test (electromyography). Methods: Twenty-two rats were submitted to neurophysiological evaluation using motor nerve conduction of the mandibular branch of the facial nerve to obtain the compound muscle action potentials (CMAPs). To record the CM APs, we used two needle electrodes that were inserted into the lower lip muscle of the rat. A supramaximal electrical stimulus was applied, and the values of CMAP latency, amplitude, length, area, and stimulus intensity obtained from each side were compared by use of the Wilcoxon test. Results: There was no significant difference (all p > 0.05) in latency, amplitude, duration, area, or intensity of stimuli between the two sides. The amplitudes ranged between 1.61 and 8.30 mV, the latencies between 1.03 and 1.97 ms, and the stimulus intensities between 1.50 and 2.90 mA. Conclusions: This is a noninvasive, easy, and highly reproducible method that contributes to an improvement of the techniques previously described and may contribute to future studies of the degeneration and regeneration of the facial nerve.

Differential cellular FGF-2 upregulation in the rat facial nucleus following axotomy, functional electrical stimulation and corticosterone: a possible therapeutic target to Bell's palsy

Abstract Background The etiology of Bell's palsy can vary but anterograde axonal degeneration may delay spontaneous functional recovery leading the necessity of therapeutic interventions. Corticotherapy and/or complementary rehabilitation interventions have been employed. Thus the natural history of the disease reports to a neurotrophic resistance of adult facial motoneurons leading a favorable evolution however the related molecular mechanisms that might be therapeutically addressed in the resistant cases are not known. Fibroblast growth factor-2 (FGF-2) pathway signaling is a potential candidate for therapeutic development because its role on wound repair and autocrine/paracrine trophic mechanisms in the lesioned nervous system. Methods Adult rats received unilateral facial nerve crush, transection with amputation of nerve branches, or sham operation. Other group of unlesioned rats received a daily functional electrical stimulation in the levator labii superioris muscle (1 mA, 30 Hz, square wave) or systemic corticosterone (10 mgkg-1). Animals were sacrificed seven days later. Results Crush and transection lesions promoted no changes in the number of neurons but increased the neurofilament in the neuronal neuropil of axotomized facial nuclei. Axotomy also elevated the number of GFAP astrocytes (143% after crush; 277% after transection) and nuclear FGF-2 (57% after transection) in astrocytes (confirmed by two-color immunoperoxidase) in the ipsilateral facial nucleus. Image analysis reveled that a seven days functional electrical stimulation or corticosterone led to elevations of FGF-2 in the cytoplasm of neurons and in the nucleus of reactive astrocytes, respectively, without astrocytic reaction. Conclusion FGF-2 may exert paracrine/autocrine trophic actions in the facial nucleus and may be relevant as a therapeutic target to Bell's palsy.

Motor recovery and synaptic preservation after ventral root avulsion and repair with a fibrin sealant derived from snake venom

Background: Ventral root avulsion is an experimental model of proximal axonal injury at the central/peripheral nervous system interface that results in paralysis and poor clinical outcome after restorative surgery. Root reimplantation may decrease neuronal degeneration in such cases. We describe the use of a snake venom-derived fibrin sealant during surgical reconnection of avulsed roots at the spinal cord surface. The present work investigates the effects of this fibrin sealant on functional recovery, neuronal survival, synaptic plasticity, and glial reaction in the spinal motoneuron microenvironment after ventral root reimplantation. Methodology/Principal Findings: Female Lewis rats (7 weeks old) were subjected to VRA and root replantation. The animals were divided into two groups: 1) avulsion only and 2) replanted roots with fibrin sealant derived from snake venom. Post-surgical motor performance was evaluated using the CatWalk system twice a week for 12 weeks. The rats were sacrificed 12 weeks after surgery, and their lumbar intumescences were processed for motoneuron counting and immunohistochemistry (GFAP, Iba-1 and synaptophysin antisera). Array based qRT-PCR was used to evaluate gene regulation of several neurotrophic factors and receptors as well as inflammatory related molecules. The results indicated that the root reimplantation with fibrin sealant enhanced motor recovery, preserved the synaptic covering of the motoneurons and improved neuronal survival. The replanted group did not show significant changes in microglial response compared to VRA-only. However, the astroglial reaction was significantly reduced in this group. Conclusions/Significance: In conclusion, the present data suggest that the repair of avulsed roots with snake venom fibrin glue at the exact point of detachment results in neuroprotection and preservation of the synaptic network at the microenvironment of the lesioned motoneurons. Also such procedure reduced the astroglial reaction and increased mRNA levels to neurotrophins and anti-inflammatory cytokines that may in turn, contribute to improving recovery of motor function.

Atividade muscular da mastigação na anquilose temporomandibular

Purpose: due to the presence of major masticatory dysfunction in patients with temporomandibular joint (TMJ) ankylosis, this study analyzed mouth opening and EMG activity of masticatory muscles in order to detect changes in these parameters after surgical release of mandible ankylosis. Method: in 7 patients with temporomandibular ankylosis, between 7 and 30 years (median = 9 years), the distance was measured as interincisal maximum active (DIMA) and we recorded the electromyographic activity (EMG) of masseter and temporal muscles during voluntary isometric contraction (VIC) and chewing, comparing the data before and after surgery using the Wilcoxon test. Results: higher values were observed for DIMA after surgery (p=0.0277), the asymmetry index showed no difference between the two evaluated periods for both studied muscles, the values of the EMG during VIC decreased after surgery for the right (p=0.0179) and left (p=0.0179) masseter but not for the temporal muscle, there were no changes in EMG values for the studied muscles during mastication. Conclusion: the surgical release of TMJ ankylosis resulted in an increase of mouth opening and decreased amplitude of action potentials generated during maximum isometric voluntary contraction of the masseter muscle on both sides, this did not change the asymmetry index of the masseter and temporal as well as the electromyographic activity of the temporal muscle bilaterally during isometric contraction and masseter and temporal muscles during mastication.

Plantar flexion force induced by amplitude-modulated tendon vibration and associated soleus V/F-waves as an evidence of a centrally-mediated mechanism contributing to extra torque generation in humans

Background: High-frequency trains of electrical stimulation applied over the human muscles can generate forces higher than would be expected by direct activation of motor axons, as evidenced by an unexpected relation between the stimuli and the evoked contractions, originating what has been called “extra forces”. This phenomenon has been thought to reflect nonlinear input/output neural properties such as plateau potential activation in motoneurons. However, more recent evidence has indicated that extra forces generated during electrical stimulation are mediated primarily, if not exclusively, by an intrinsic muscle property, and not from a central mechanism as previously thought. Given the inherent differences between electrical and vibratory stimuli, this study aimed to investigate: (a) whether the generation of vibration-induced muscle forces results in an unexpected relation between the stimuli and the evoked contractions (i.e. extra forces generation) and (b) whether these extra forces are accompanied by signs of a centrally-mediated mechanism or whether intrinsic muscle properties are the redominant mechanisms. Methods: Six subjects had their Achilles tendon stimulated by 100 Hz vibratory stimuli that linearly increased in amplitude (with a peak-to-peak displacement varying from 0 to 5 mm) for 10 seconds and then linearly decreased to zero for the next 10 seconds. As a measure of motoneuron excitability taken at different times during the vibratory stimulation, short-latency compound muscle action potentials (V/F-waves) were recorded in the soleus muscle in response to supramaximal nerve stimulation. Results: Plantar flexion torque and soleus V/F-wave amplitudes were increased in the second half of the stimulation in comparison with the first half. Conclusion: The present findings provide evidence that vibratory stimuli may trigger a centrally-mediated mechanism that contributes to the generation of extra torques. The vibration-induced increased motoneuron excitability (leading to increased torque generation) presumably activates spinal motoneurons following the size principle, which is a desirable feature for stimulation paradigms involved in rehabilitation programs and exercise training.

Behavioral problems and emotional stress in children with bruxism

Bruxism has a multifactorial etiology, and psychosocial factors have been considered to increase the risk of occurrence of this parafunction. The aim of this study was to evaluate the behavior profile of a group of children diagnosed with bruxism. Eighty 7-11-year-old children of both genders (mean age 8.8 years) first recruited as eligible participants. Twenty-nine children (18 males and 11 females) whose parents/guardians reported to present frequent episodes of tooth grinding/clenching while awake or during sleep (at least 3 nights a week) in the previous 3 months were enrolled in the study. The diagnosis of bruxism was established based on the parents/guardians' report about the children's behavior, habits and possible discomforts in the components of the stomatognathic system allied to the presence of signs and symptoms such as pain on the masticatory muscles, masseter muscle hypertrophy, wear facets, fractures of restorations, dental impressions on the cheek mucosa and tongue. As part of the psychological evaluation, the Rutter's Child Behavior Scale-A2 was applied to the parents/caregivers (one for each child) and the Child Stress Scale was applied to the children. Data were analyzed descriptively based on the frequency of each studied variable. Twenty-four (82.76%) children needed psychological or psychiatric intervention; 17 of them presented neurotic disorders and 7 children presented antisocial disorders. Six (20.70%) children presented significant physical and psychological manifestations of stress. The findings of the present study suggest that behavioral problems and potential emotional problems can be risk factors to bruxism in children.

Coronoid process hyperplasia: an unusual cause of mandibular hypomobility

A large number of disorders affecting the masticatory system can cause restriction of mouth opening. The most common conditions related to this problem are those involving the temporomandibular joint (TMJ) and the masticatory muscles, when facial pain also is an usual finding. Congenital or developmental mandibular disorders are also possible causes for mouth opening limitation, although in a very small prevalence. Coronoid process hyperplasia (CPH) is an example of these cases, characterized by an excessive coronoid process growing, where mandibular movements become limited by the impaction of this structure on the posterior portion of the zygomatic bone. This condition is rare, painless, usually bilateral and progressive, affecting mainly men. Diagnosis of CPH is made based on clinical signs of mouth opening limitation together with imaging exams, especially panoramic radiography and computerized tomography (CT). Treatment is exclusively surgical. This paper presents a case of a male patient with bilateral coronoid process hyperplasia, initially diagnosed with bilateral disk displacement without reduction, and successfully treated with intraoral coronoidectomy. It is emphasized the importance of differential diagnosis for a correct diagnosis and, consequently, effective management strategy.

Effect of low-level laser therapy on pain levels in patients with temporomandibular disorders: a systematic review

Temporomandibular disorders (TMD) are characterized by the presence of temporomandibular joint (TMJ) and/or masticatory muscle pain and dysfunction. Low-level laser is presented as an adjuvant therapeutic modality for the treatment of TMD, especially when the presence of inflammatory pain is suspected. Objective: To systematically review studies that investigated the effect of low level laser therapy (LLLT) on the pain levels in individuals with TMD. Material and Methods: The databases Scopus, embase, ebsco and PubMed were reviewed from January/2003 to October/2010 with the following keywords: laser therapy, low-level laser therapy, temporomandibular joint disorders, temporomandibular joint dysfunction syndrome, temporomandibular joint, temporomandibular, facial pain and arthralgia, with the inclusion criteria for intervention studies in humans. exclusion criteria adopted were intervention studies in animals, studies that were not written in english, Spanish or Portuguese, theses, monographs, and abstracts presented in scientific events. Results: After a careful review, 14 studies fit the criteria for inclusion, of which, 12 used a placebo group. As for the protocol for laser application, the energy density used ranged from 0.9 to 105 J/cm², while the power density ranged from 9.8 to 500 mW. The number of sessions varied from 1 to 20 and the frequency of applications ranged from daily for 10 days to 1 time per week for 4 weeks. A reduction in pain levels was reported in 13 studies, with 9 of these occurring only in the experimental group, and 4 studies reporting pain relief for both the experimental group and for the placebo. Conclusion: Most papers showed that LLLT seemed to be effective in reducing pain from TMD. However, the heterogeneity of the standardization regarding the parameters of laser calls for caution in interpretation of these results. Thus, it is necessary to conduct further research in order to obtain a consensus regarding the best application protocol for pain relief in patients with TMD.

A deglutição inadequada está associada à presença de dor miofascial mastigatória?

JUSTIFICATIVA E OBJETIVOS: Os músculos da mastigação, envolvidos na fisiopatologia da dor miofascial mastigatória, também participam da função de deglutição. Diante dos resultados controversos sobre a relação entre disfunção temporomandibular (DTM) e alterações na deglutição, o objetivo deste estudo foi verificar a presença de alterações na função da deglutição em mulheres com dor miofascial mastigatória. MÉTODO: Três testes de deglutição (um sólido e dois líquidos) foram realizados em 30 mulheres com dor miofascial (grupo de estudo = GE) e 30 mulheres saudáveis (grupo controle = GC). Alterações nos padrões de deglutição como: contração da musculatura periorbicular, contração mentual, movimentos de cabeça, deglutição acompanhada de ruído, engasgos, interposição de lábio inferior, dor após deglutição e deglutição com projeção de língua para anterior foram observadas durante os três testes. Os resultados foram descritos e comparados entre os grupos através dos testes Qui-quadrado e Exato de Fisher com nível de significância de 0,05 e intervalo de confiança a 95%. RESULTADOS: Participantes do GE apresentaram chance maior de presença de atipias durante um dos testes de deglutição de líquido [teste Qui-quadrado; p < 0,05; OR: 3,29; IC 95% (1,08 - 9,95)]. Entretanto, não houve associação entre a presença de DTM e características atípicas da deglutição avaliadas em todos os testes. CONCLUSÃO: Deglutição inadequada esteve associada com a presença de dor miofascial mastigatória apenas durante a ingestão de líquido. Entretanto, não foi possível associar um tipo específico de atipia à DTM nesta amostra.

Temporomandibular disorders and parafunctional oral habits: an anamnestic study

OBJECTIVE: To assess the frequency and severity of the signs and symptoms of temporomandibular disorders (TMD), the frequency of parafunctional oral habits and the correlation between the variables by means of the patients' perception regarding their problem. METHODS: One hundred patients diagnosed with TMD, through a clinical examination of their masticatory system, answered the questions of a previously published protocol concerning the signs and symptoms most frequently reported in the literature. RESULTS: According to the results from the non parametric statistical analysis, the frequency for the following signs and symptoms was significant: Fatigue and muscle pain, joint sounds, tinnitus, ear fullness, headache, chewing impairment and difficulty to yawn (p<0.01) and otalgia (p<0.05). As to the parafunctional oral habits, there was a significant presence of teeth clenching during the day and night (p<0.01) and teeth grinding at night (p<0.05). The variable correlation analysis showed that there was a positive correlation between symptom frequency and severity; age was correlated with the presence of otalgia, cervical pain and teeth sensitivity, besides being correlated with muscle and joint pain severity. Habit frequency was negatively correlated with age. TMD duration was also positively correlated with the symptoms of tinnitus, ear fullness, muscle and joint pain. CONCLUSION: The study results showed that the anamnestic assessment using ProDTMMulti can predict the severity of the TMD case.

Caracterização eletromiográfica e ultrassonográfica da função mastigatória em indivíduos com oclusão normal

OBJETIVO: Caracterizar o controle motor dos músculos masseter e temporal e a morfologia do músculo masseter em atividades da função mastigatória em indivíduos com oclusão normal; verificar a compatibilidade entre os exames de eletromiografia de superfície (EMGs) e ultrassonografia (USG). MÉTODOS: Participaram 22 indivíduos adultos, de ambos os gêneros, sem alterações no sistema miofuncional orofacial. Os procedimentos adotados para avaliação dos participantes foram: EMGs dos músculos masseteres (MM) e temporais (MT); e USG dos MM, na realização de três tarefas - repouso muscular, apertamento dentário com algodão, apertamento dentário sem algodão. RESULTADOS: Para análise estatística dos dados foram utilizados os testes de Kolmogorv-Smirnov, teste-T pareado e Correlação de Spearman, com nível de significância de 5%. Na EMGs observou-se diferença entre a ativação de MM e MT no apertamento dentário com e sem algodão, sendo MT mais ativo que MM em ambas as tarefas. Não foram observadas diferenças entre as hemifaces, tanto na EMGs quanto na USG. Observou-se também correlação positiva entre os exames na condição de apertamento dentário sem algodão esquerdo e na condição de apertamento dentário esquerdo com algodão, e tendência à significância no apertamento dentário direito sem algodão. CONCLUSÃO: A associação da EMGs e USG na investigação da funcionalidade muscular traz importantes informações sobre fisiologia da musculatura esquelética. Os resultados do presente estudo indicam haver correlação entre a EMGs e a USG, ou seja, o aumento da atividade elétrica e o aumento correspondente da espessura do músculo.