High variability of facial muscle innervation by facial nerve branches: A prospective electrostimulation study.

OBJECTIVES/HYPOTHESIS: To examine by intraoperative electric stimulation which peripheral facial nerve (FN) branches are functionally connected to which facial muscle functions. STUDY DESIGN: Single-center prospective clinical study. METHODS: Seven patients whose peripheral FN branching was exposed during parotidectomy under FN monitoring received a systematic electrostimulation of each branch starting with 0.1 mA and stepwise increase to 2 mA with a frequency of 3 Hz. The electrostimulation and the facial and neck movements were video recorded simultaneously and evaluated independently by two investigators. RESULTS: A uniform functional allocation of specific peripheral FN branches to a specific mimic movement was not possible. Stimulation of the whole spectrum of branches of the temporofacial division could lead to eye closure (orbicularis oculi muscle function). Stimulation of the spectrum of nerve branches of the cervicofacial division could lead to reactions in the midface (nasal and zygomatic muscles) as well as around the mouth (orbicularis oris and depressor anguli oris muscle function). Frontal and eye region were exclusively supplied by the temporofacial division. The region of the mouth and the neck was exclusively supplied by the cervicofacial division. Nose and zygomatic region were mainly supplied by the temporofacial division, but some patients had also nerve branches of the cervicofacial division functionally supplying the nasal and zygomatic region. CONCLUSIONS: FN branches distal to temporofacial and cervicofacial division are not necessarily covered by common facial nerve monitoring. Future bionic devices will need a patient-specific evaluation to stimulate the correct peripheral nerve branches to trigger distinct muscle functions. LEVEL OF EVIDENCE: 4 Laryngoscope, 127:1288-1295, 2017.

Effects of Neuromuscular Electrical Stimulation on the Masticatory Muscles and Physiologic Sleep Variables in Adults with Cerebral Palsy: A Novel Therapeutic Approach.

Cerebral palsy (CP) is a term employed to define a group of non-progressive neuromotor disorders caused by damage to the immature or developing brain, with consequent limitations regarding movement and posture. CP may impair orapharygeal muscle tone, leading to a compromised chewing function and to sleep disorders (such as obstructive sleep apnea). Thirteen adults with CP underwent bilateral masseter and temporalis neuromuscular electrical stimulation (NMES) therapy. The effects on the masticatory muscles and sleep variables were evaluated using electromyography (EMG) and polysomnography (PSG), respectively, prior and after 2 months of NMES. EMG consisted of 3 tests in different positions: rest, mouth opening and maximum clenching effort (MCE). EMG values in the rest position were 100% higher than values recorded prior to therapy for all muscles analyzed (p < 0.05); mean mouth opening increased from 38.0 ± 8.0 to 44.0 ± 10.0 cm (p = 0.03). A significant difference in MCE was found only for the right masseter. PSG revealed an improved in the AHI from 7.2±7.0/h to 2.3±1.5/h (p < 0.05); total sleep time improved from 185 min to 250 min (p = 0.04) and minimun SaO2 improved from 83.6 ± 3.0 to 86.4 ± 4.0 (p = 0.04). NMES performed over a two-month period led to improvements in the electrical activity of the masticatory muscles at rest, mouth opening, isometric contraction and sleep variables, including the elimination of obstructive sleep apnea events in patients with CP. Trial registration: ReBEC RBR994XFS http://www.ensaiosclinicos.gov.br.

The muscle engram: the reflex that limits conventional occlusal treatment.

The engram (the masticatory "muscle memory") is shown to be a conditionable reflex whose muscle conditioning lasts less than two minutes, far shorter than previously thought. This reflex, reinforced and stored in the masticatory muscles at every swallow, adjusts masticatory muscle activity to guide the lower arch unerringly into its ICP. These muscle adjustments compensate for the continually changing intemal and external factors that affect the mandible's entry into the ICP. A simple quick experiment described in this article isolates the engram, enabling the reader to see its action clearly for the first time. It is urged that every reader perform this experiment. This experiment shows how the engram, by hiding the masticatory muscles' reaction (the hit-and-slide), limits the success of the therapist in achieving occlusion-muscle compatibility. This finding has major clinical implications. It means that, as regards the muscle aspect of treating occlusion, the dentist treating occlusion conventionally is working blind, a situation the neuromuscular school of occlusal thought seeks to correct. The controversy over occlusion continues.

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.

Activation of TRPV1 and TRPA1 leads to muscle nociception and mechanical hyperalgesia.

The involvement of TRPV1 and TRPA1 in mediating craniofacial muscle nociception and mechanical hyperalgesia was investigated in male Sprague-Dawley rats. First, we confirmed the expression of TRPV1 in masseter afferents in rat trigeminal ganglia (TG), and provided new data that TRPA1 is also expressed in primary afferents innervating masticatory muscles in double-labeling immunohistochemistry experiments. We then examined whether the activation of each TRP channel in the masseter muscle evokes acute nocifensive responses and leads to the development of masseter hypersensitivity to mechanical stimulation using the behavioral models that have been specifically designed and validated for the craniofacial system. Intramuscular injections with specific agonists for TRPV1 and TRPA1, capsaicin and mustard oil (MO), respectively, produced immediate nocifensive hindpaw responses followed by prolonged mechanical hyperalgesia in a concentration-dependent manner. Pretreatment of the muscle with a TRPV1 antagonist, capsazepine, effectively attenuated the capsaicin-induced muscle nociception and mechanical hyperalgesia. Similarly, pretreatment of the muscle with a selective TRPA1 antagonist, AP18, significantly blocked the MO-induced muscle nociception and mechanical hyperalgesia. We confirmed these data with another set of selective antagonist for TRPV1 and TRPA1, AMG9810 and HC030031, respectively. Collectively, these results provide compelling evidence that TRPV1 and TRPA1 can functionally contribute to muscle nociception and hyperalgesia, and suggest that TRP channels expressed in muscle afferents can engage in the development of pathologic muscle pain conditions.

Corticofugal projections to trigeminal motoneurons innervating antagonistic jaw muscles in rats as demonstrated by anterograde and retrograde tract tracing.

Little is known about the organization of corticofugal projections controlling antagonistic jaw muscles. To address this issue, we employed retrograde (Fluorogold; FG) and anterograde (biotinylated dextran amine; BDA) tracing techniques in rats. Three groups of premotoneurons were identified by injecting FG into the jaw-closing (JC) and -opening (JO) subdivisions of the trigeminal motor nucleus (Vmo). These were 1) the intertrigeminal region (Vint) and principal trigeminal sensory nucleus for JC nucleus; 2) the reticular region medial to JO nucleus (RmJO) for JO nucleus; and 3) the parabrachial (Pb) and supratrigeminal (Vsup) nuclei, reticular regions medial and ventral to JC nucleus, rostrodorsomedial oralis (Vor), and juxtatrigeminal region (Vjuxt) containing a mixture of premotoneurons to both the nuclei. Subsequently, FG was injected into the representative premotoneuron structures. The JC and JO premotoneurons received main afferents from the lateral and medial agranular fields of motor cortex (Agl and Agm), respectively, whereas afferents to the nuclei with both JC and JO premotoneurons arose from Agl also and from primary somatosensory cortex (S1). Finally, BDA was injected into each of the three cortical areas representing the premotoneuron structures to complement the FG data. The Agl and Agm projected to reticular regions around the Vmo, whereas the Pb, Vsup, Vor, and Vjuxt received input from Agl. The S1 projected to the trigeminal sensory nuclei as well as to the Pb, Vsup, and Vjuxt. These results suggest that corticofugal projections to Vmo via premotoneuron structures consist of multiple pathways, which influence distinct patterns of jaw movements.

Cortical control for mastication in cats: changes in masticatory movements following lesions in the masticatory cortex.

In a previous paper (Hiraba and Sato 2004) we reported that an accurate mastication might be executed by the cortical processing in bilateral masticatory area (MA)and motor cortices. The aim of this study was to determine if cats with lesion of either unilateral or bilateral MA showed changes in mastication. After exploring mechanoreceptive fields and motor effects of mastication-related neurons (MRNs) in MA using the single unit recording and intracortical microstimulation methods, we made various lesions in MAs with injections of kainic acid (0.1%, 2.0 microl). Since the MA was divided into facial (F) and intraoral (I) projection areas as reported in the previous paper, cats with the unilateral lesion in F or I, and with the bilateral lesion in F and F, I and I or F and I (F on one side and I on other side) were prepared. Cats with unilateral lesion in F or I and with bilateral lesion in F and I showed no changes in mastication except for prolongation of the food intake and masticatory periods. Cats with bilateral lesion into F and F, or I and I showed wider jaw-opening during mastication. Particularly, the latter group showed enormous jaw-opening, delay in the start of mastication and difficulty in manipulating food on the tongue. In all cats with lesions of each type, masticatory and swallowing rhythms remained normal. These findings suggest that accurate mastication is executed by the close integration between F and F and I and I of the bilateral MA.

Different corticostriatal projections from two parts of the cortical masticatory area in the rabbit.

The cortical masticatory area (CMA) elicits rhythmic jaw movements in response to repetitive stimulation and is involved in the control of mastication. Based on jaw movement patterns, the CMA is divided into two parts. One is the part of the CMA in which a T-pattern similar to jaw movements during food transport in natural mastication is evoked by electrical stimulation. The other is more dorsomedially located, and during chewing a C-pattern similar to jaw movements can be induced. However, it is still not known which region of the putamen receives projections from the CMA and whether projections originate from both parts of the CMA. In this study, electrophysiological and histological experiments were undertaken in rabbits to investigate projections from the CMA to the putamen. Both experiments showed that the ventral region of the putamen received projections from the CMA. The density of the projections from the CMA area inducing the T-pattern seemed to be higher than that from the area inducing the C-pattern. Furthermore, the peak latency of the evoked potentials from stimulation of the CMA area inducing the T-pattern was shorter than that from stimulation of the area inducing the C-pattern. The data obtained from the present study indicate the functional role of the ventral region of the putamen in the regulation of mastication, and further suggest that the corticostriatal pathway is involved in the transition between behavioral jaw movement patterns.

Cortical orofacial motor representation in Old World monkeys, great apes, and humans. II. Stereologic analysis of chemoarchitecture.

This study presents a comparative stereologic investigation of neurofilament protein- and calcium-binding protein-immunoreactive neurons within the region of orofacial representation of primary motor cortex (Brodmann's area 4) in several catarrhine primate species (Macaca fascicularis, Papio anubis, Pongo pygmaeus, Gorilla gorilla, Pan troglodytes, and Homo sapiens). Results showed that the density of interneurons involved in vertical interlaminar processing (i.e., calbindin- and calretinin-immunoreactive neurons) as well pyramidal neurons that supply heavily-myelinated projections (i.e., neurofilament protein-immunoreactive neurons) are correlated with overall neuronal density, whereas interneurons making transcolumnar connections (i.e., parvalbumin-immunoreactive neurons) do not exhibit such a relationship. These results suggest that differential scaling rules apply to different neuronal subtypes depending on their functional role in cortical circuitry. For example, cortical columns across catarrhine species appear to involve a similar conserved network of intracolumnar inhibitory interconnections, as represented by the distribution of calbindin- and calretinin-immunoreactive neurons. The subpopulation of horizontally-oriented wide-arbor interneurons, on the other hand, increases in density relative to other interneuron subpopulations in large brains. Due to these scaling trends, the region of orofacial representation of primary motor cortex in great apes and humans is characterized by a greater proportion of neurons enriched in neurofilament protein and parvalbumin compared to the Old World monkeys examined. These modifications might contribute to the voluntary dexterous control of orofacial muscles in great ape and human communication.

Pericranial muscular, respiratory, and heart rate components of the orienting response.

We have earlier found that voluntary attention to weak auditory stimuli induces inhibition of respiration, heart rate, and electromyographic (EMG) activity of masticatory and lower facial muscles and that these responses lower the auditory threshold for low-frequency sounds. In the current study, we examined whether this inhibitory response pattern also occurs during involuntary orienting to novel, nonsignal sounds. Environmental sounds of low intensity were presented unexpectedly during the performance of a reading task. Orienting responses (ORs) were elicited as indicated by heart rate deceleration and skin conductance responses. Inhibitory respiratory and pericranial EMG responses appeared to be intrinsic components of the OR. Together with the autonomic responses, they habituated when a nonsignal auditory stimulus was repeatedly presented. Our results also suggest that eye and pinna movements occurred toward the sound source. The results of the current study are consistent with the hypothesis of Sokolov (1963) that the primary function of the OR is enhancement of sensory sensitivity.

Effects of experimental muscle pain on electromyographic activity of masticatory muscles in the rat.

The aim of the present study was to investigate the effects of noxious chemical stimulation of a jaw muscle on postural electromyographic (EMG) activity from several masticatory muscles in lightly anesthetized rats. Unilateral injection of a substance known to induce acute muscle pain (5% NaCl) or longer duration of pain with inflammation (mustard oil) was made into the masseter muscle. The changes in EMG activity following the injection were recorded from the injected and contralateral masseter muscles and the ipsilateral digastric muscle. The algesic chemicals produced a significant but transient increase in EMG activity in all three muscles. The data from the present study and similar observations from clinical and experimental human studies suggest that increased activity from muscle nociceptors is not sufficient to produce a prolonged increase in postural EMG activity. Therefore, the development and maintenance of chronic jaw muscle pain does not appear to result from a feedback cycle mechanism.

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.

Involvement of GABA(A) receptor in modulation of jaw muscle activity evoked by mustard oil application to the rat temporomandibular joint.

The effect of intrathecal administration of the GABA(A) receptor antagonist bicuculline methylbromide on jaw muscle electromyographic (EMG) activity evoked by mustard oil injection into the rat temporomandibular joint was studied. Bicuculline given prior to mustard oil augmented the EMG activity evoked by mustard oil, and "rekindling" of EMG activity was induced by bicuculline given 30 min after mustard oil. These results suggest that central GABA(A) receptors modulate reflex responses to noxious craniofacial stimuli.

Clinical study of location and reproducibility of three mandibular positions in relation to body posture and muscle function.

Clinical studies have confirmed the adequate reproducibility of both centric occlusion and centric relation when used as reference positions during treatment; however, the reproducibility of the neuromuscular position has been found inadequate. This study evaluated the location and reproducibility of these three mandibular positions in relation to body posture, sitting and supine, and bilateral muscle activity before and after the insertion of a flat mandibular positioning device equilibrated to balance the muscle functions, as shown by two electromyography biofeedback instruments. Intraoral recordings were made in 11 young subjects with complete natural dentition. Acrylic resin clutches that supported a screw point in the maxillary arch and painted glass in the mandibular arch were used and positioned not to interfere with the occlusion. The distances of the screw scratch from two of the edges of the painted glass were used to measure the anteroposterior and mediolateral locations with a micrometer. The reproducibility was evaluated by measuring the scratch surface by measuring the weight of the print cutouts made from photographs of the scratches taken with a stereoscope. The location and reproducibility of centric occlusion and centric relation were not affected by body posture. A more precise posterior neuromuscular position was obtained in the supine position. The insertion of a mandibular positioning device did not affect centric occlusion but gave a more precise centric relation. Neuromuscular position became as precise as centric occlusion and was located anteroposteriorly between centric occlusion and centric relation.

Inputs from identified jaw-muscle spindle afferents to trigeminothalamic neurons in the rat: a double-labeling study using retrograde HRP and intracellular biotinamide.

Projections from physiologically identified jaw-muscle spindle afferents onto trigeminothalamic neurons were studied in the rat. Trigeminothalamic neurons were identified by means of retrograde transport of horseradish peroxidase from the ventroposteromedial nucleus of the thalamus. Labeled neurons were found contralaterally in the supratrigeminal region (Vsup), the trigeminal principal sensory nucleus, the ventrolateral part of the trigeminal subnucleus oralis, the spinal trigeminal subnuclei interpolaris and caudalis, the reticular formation, and an area ventral to the trigeminal motor nucleus (Vmo) and medial to the trigeminal principal sensory nucleus (AVM). Jaw-muscle spindle afferents were physiologically identified by their increased firing during stretching of the jaw muscles and intracellularly injected with biotinamide. Axon collaterals and boutons from jaw-muscle spindle afferents were found in Vmo; Vsup; the dorsomedial part of the trigeminal principal sensory nucleus (Vpdm); the dorsomedial part of the spinal trigeminal subnuclei oralis, interpolaris (Vidm) and caudalis; the parvicellular reticular formation (PCRt); and the mesencephalic trigeminal nucleus. Trigeminothalamic neurons in Vsup, Vpdm, Vidm, PCRt, and AVM were associated with axon collaterals and boutons from intracellularly stained jaw-muscle spindle afferents. Trigeminothalamic neurons in Vsup, Vpdm, Vidm, and PCRt were closely apposed by one to 14 intracellularly labeled boutons from jaw-muscle spindle afferents, suggesting a powerful input to some trigeminothalamic neurons. These data demonstrate that muscle length and velocity feedback from jaw-muscle spindle afferents is projected to the contralateral thalamus via multiple regions of the trigeminal system and implicates these pathways in the projection of trigeminal proprioceptive information to the cerebral cortex.

Administration of opiate antagonist naloxone induces recurrence of increased jaw muscle activities related to inflammatory irritant application to rat temporomandibular joint region.

1. Our recent studies in rats have demonstrated that the small-fiber excitant and inflammatory irritant mustard oil injected into the temporomandibular joint (TMJ) region can evoke a sustained and reversible increase of electromyographic (EMG) activity in jaw muscles and an acute inflammatory response. The aim of the present study was to test if opioid mechanisms are involved in modulating the EMG increase evoked by mustard oil. 2. Mustard oil injected into the rat TMJ region evoked significant increases of jaw muscle EMG activity; the vehicle mineral oil had no such effect. The increased EMG activity lasted up to 20 min, and by 30 min after the mustard oil injection had returned to control (preinjection) levels, at which time administration of the opiate antagonist naloxone (1.3 mg/kg i.v.) induced a significant recurrence of the increase in EMG activity. This "rekindling" of EMG activity appeared at 5 to 10 min after the naloxone administration and lasted for 10 to 20 min. In contrast, naloxone administration in the animals receiving mineral oil injection into the TMJ region did not "rekindle" the EMG activity, nor did the administration of the peripherally acting opiate antagonist methylnaloxone or the vehicle of naloxone. 3. These findings reveal that the application of the opiate antagonist naloxone produces a recurrence of increased jaw muscle activity reflexively evoked by mustard oil injection into the rat TMJ region. They suggest that central opioid depressive mechanisms activated by the mustard oil-induced afferent barrage limit the duration of the evoked EMG changes.

Integration in trigeminal premotor interneurones in the cat. 1. Functional characteristics of neurones in the subnucleus-gamma of the oral nucleus of the spinal trigeminal tract.

The profile of integration in a sample of 183 interneurones localized in the subnucleus-gamma of the oral nucleus of the spinal trigeminal tract (NVspo-gamma) has been analyzed. 134 neurones were tested for inputs from primary afferents of the trigeminal, facial and cervical nerves as well as for inputs from the midbrain and from the cervical spinal cord. The remaining 49 neurones were tested for inputs from the primary afferents and for descending convergence from defined sites within the oro-facial primary projections of the cerebral cortex. It was found that the interneurones, mainly recorded in the dorsal and dorsomedial aspect of the NVspo-gamma, receive short latency inputs from the low threshold oral and perioral afferents and longer latency inputs from the high threshold jaw and neck muscle afferents. There was evidence for convergence from the cervical segmental level (29%) and some of the neurones had axon terminals in the superior colliculus. However, the interneurones did not receive a descending tectal input. About 80% of the NVspo-gamma interneurones were activated from the orofacial primary projection fields within cytoarchitectonic areas 3a and 3b of the coronal gyrus. This input was topographically organized and the neurones were activated from the same oral and perioral region of the periphery as the cortical region from which the descending projections themselves originated. Minimum latencies indicated a monosynaptic connection. The convergence profile onto the NVspo-gamma interneurones appeared unique as compared with interneurones located in the intertrigeminal area. Aspects of the possible functional roles of the NVspo-gamma neurones are discussed in relation to ongoing oro-facial ("masticatory") movements. The properties of a selected sample of NVspo-gamma interneurones, which were antidromically activated from the digastric subnucleus of the trigeminal motor nucleus, are reported in a companion paper (Olsson and Westberg 1991).