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Background: Muscle weakness negatively affects perioral muscles and quality of life. The button-pull exercise is used to teach lip closure (LC) and to strengthen muscles. However, how the muscles accomplish LC during button-pull and its training effect on each muscle are unknown., Objectives: This study aimed to investigate the LC mechanism and the efficacy of perioral muscle training., Methods: Electromyographic (EMG) activities were obtained from perioral muscles along with the lip closing force (LCF) and were normalised to the maximum LC activities. Correlations between muscle activities and LCF were assessed during LCF increment/decrement task. The effectiveness of training methods was evaluated during functional face tasks (FFT). The effects of button-pull on muscles were evaluated during static loadings with two sized buttons., Results: The muscles were active during LC, and the amplitudes changed with the LCF. In FFT, the muscles were simultaneously active and the total activity was highest during the blowing task. In button-pull, maximum button-pulling forces (BPFs) were significantly larger with the large button (p = .0001). In the static loading task, muscle activities increased with increasing button load. However, the small button produced significantly greater EMG activity than the large button in most of the load (p < .005)., Conclusion: LC is accomplished by the cooperation of perioral muscles. In button-pull, a larger button requires a larger BPF, but a smaller button shows higher muscle activities. Face expression exercises compare favourably with button-pull. Forceful LC and blowing tasks may be effective and balanced training of the perioral muscles., (© 2021 John Wiley & Sons Ltd.)

Objectives: The buccinator (BUC) is an important muscle for oral function. Since it lies deep in the facial skin, recording its activity is difficult; thus, studies on its function are limited. We developed a method to access the deep facial muscles from the mucosal side. The aim of this study was to test the reliability of the new recording method for the BUC and to investigate the BUC behavior in typical facial functions., Methods: To evaluate the new method, BUC activities were recorded simultaneously with a gel-type electrode on the skin and the newly developed surface electrode on the buccal mucosa. Electromyographic (EMG) activities in function, such as chewing and swallowing, along with the activities of the lower orbicularis oris (OO), zygomaticus major, masseter, and digastric muscles, were compared using the two recording methods. EMG activities among various tasks were compared using normalized values based on those obtained during maximum lip closure (MaxLC)., Results: The new surface electrode was made of gold plates on a thin plastic fixed to a stainless-steel wire frame and weighed less than 1 g. The BUC activity recorded from the mucosa was the highest during a corner-pulling task and was low during clenching. The BUC was active during MaxLC, similar to the OO, and the BUC activity pattern among tasks recorded from the mucosa was identical to that reported by previous studies using intramuscular electrodes. The new electrode evaluated the BUC activities quantitatively, and the recordings by the new electrode were free from contamination., Conclusions: The findings of this study confirmed the reliability of the new BUC recording method. It could be easily placed correctly within seconds, without the need for cleansing or sterilizing the skin. The BUC and OO were active during a MaxLC task, indicating that the BUC assists lip closure by pulling the corners of the mouth. The basic facial functions evaluated, including chewing, were similar to those studied by intramuscular electrodes., (Copyright © 2021 Elsevier Inc. All rights reserved.)

The ionotropic P2X receptor, P2X 7 , is believed to regulate and/or generate nociceptive pain, and pain in several neuropathological diseases. Although there is a known relationship between P2X 7 receptor activity and pain sensing, its detailed functional properties in trigeminal ganglion (TG) neurons remains unclear. We examined the electrophysiological and pharmacological characteristics of the P2X 7 receptor and its functional coupling with other P2X receptors and pannexin-1 (PANX1) channels in primary cultured rat TG neurons, using whole-cell patch-clamp recordings. Application of ATP and Bz-ATP induced long-lasting biphasic inward currents that were more sensitive to extracellular Bz-ATP than ATP, indicating that the current was carried by P2X 7 receptors. While the biphasic current densities of the first and second components were increased by Bz-ATP in a concentration dependent manner; current duration was only affected in the second component. These currents were significantly inhibited by P2X 7 receptor antagonists, while only the second component was inhibited by P2X 1, 3, and 4 receptor antagonists, PANX1 channel inhibitors, and extracellular ATPase. Taken together, our data suggests that autocrine or paracrine signaling via the P2X 7 -PANX1-P2X receptor/channel complex may play important roles in several pain sensing pathways via long-lasting neuronal activity driven by extracellular high-concentration ATP following tissue damage in the orofacial area.

Objectives: The exact timings associated with swallowing are difficult to measure with the currently available methods. In this study, we aimed to elucidate the timings of action of the swallowing organs in the oral and pharyngeal stages of swallowing by recording the barometric pressure (BP) and tongue muscle activities., Methods: Dry and water swallows were studied in 10 adults using electromyography and small barometers. BPs were recorded during swallowing in the oral cavity (BP-o) and pharynx (BP-p), associated with muscle activities of the anterior (TA) and posterior (TP) parts of the tongue and of the suprahyoid (SHy) muscle. To analyze the temporal pattern of each activity, times of onset, cessation, and peak were measured., Results: Two characteristic waveforms were obtained. BP-o peaked immediately after onset and decreased to atmospheric pressure following a short plateau. However, BP-p gradually increased, reached a peak, and returned to the atmospheric pressure immediately before the end of BP-o. Since pressure increments indicated that the sensor was compressed in a closed space, onset and cessation of BP-p could correspond to the duration of nasopharyngeal closure. The onset of BP-p and the peak time of BP-o occurred in close succession. Thus, nasopharyngeal closure could be evaluated from BP-o. The sensor and EMG measured durations of oral and pharyngeal stages as 0.4 and 0.6 sec, respectively. TA activation began earlier than the TP. TA and TP peaks appeared before the BP-o peak, suggesting that the tongue begins the activity for swallowing before nasopharyngeal closure., Conclusions: This study revealed movements of swallowing organs in the two stages with high temporal resolution. BP-o detected the duration of nasopharyngeal closure., Competing Interests: Declaration of Competing Interest The authors declare no conflicts of interest associated with this manuscript., (Copyright © 2020 Elsevier Inc. All rights reserved.)

Objective: To test a novel sensor for assessing lip function., Methods: The electromyographic (EMG) activity of the upper orbicularis oris muscle (OOM), lip-closing pressure (LP) and intraoral baro-pressure (IP) were simultaneously recorded in 20 healthy subjects (10 women and 10 men) by using a novel composite sensor (CS). Subjects performed the lip-closure, blow and suck tasks. EMG activity of the upper and lower OOMs was recorded using conventional surface electrodes to evaluate the accuracy of CS electrodes. The subjects also rated the user-friendliness of the CS., Results: Integrated EMG signals recorded using the CS and conventional electrodes from the upper OOM were highly correlated (r = 0.77 ± 0.12 in women and r = 0.81 ± 0.10 in men). The signal-to-noise ratio was higher with the CS than with the conventional electrodes. The mean LP during maximum lip closure, blowing and sucking ranged between 2 and 6 kPa in women and between 5 and 7 kPa in men. The corresponding IPs in women were 0.0 ± 0.5, 3.2 ± 1.4 and -4.4 ± 2.6 kPa, respectively, and in men were -0.5 ± 1.4, 4.9 ± 1.8 and -5.6 ± 2.8 kPa, respectively. All subjects rated the recording technique as excellent or good., Conclusion: The CS was highly user-friendly and accurate in recording the EMG activity of the OOM and could simultaneously measure the LP and IP. Therefore, it could be an effective tool for evaluating lip function., (© 2019 John Wiley & Sons Ltd.)

Merkel cells (MCs) have been proposed to form a part of the MC-neurite complex with sensory neurons through synaptic contact. However, the detailed mechanisms for intercellular communication between MCs and neurons have yet to be clarified. The present study examined the increases in intracellular free Ca 2+ concentration ([Ca 2+ ] i ) induced by direct mechanical stimulation of MCs. We also measured [Ca 2+ ] i in the trigeminal ganglion neurons (TGs) following direct mechanical stimulation to the MCs in an MC-TGs coculture. The MCs were isolated from hamster buccal mucosa, while TGs were isolated from neonatal Wistar rats. Both cell populations showed depolarization-induced [Ca 2+ ] i . Direct mechanical stimulation to MCs increased [Ca 2+ ] i , showing stimulation strength dependence. In the MC-TGs coculture, the application of direct mechanical stimulation to MCs resulted in increased [Ca 2+ ] i in the TGs. These changes were significantly suppressed by antagonists of glutamate-permeable anion channels (4,4'-diisothiocyanato-2,2'-stilbenedisulfonic acid; DIDS), and non-competitive antagonist of the N -methyl- D -aspartate (NMDA) receptors (MK801). Apyrase, an ATP-degrading enzyme, and suramin, a non-selective P2 purinergic receptor antagonist, did not exert inhibitory effects on these [Ca 2+ ] i increases in the TGs following MC stimulation. These results indicated that MCs are capable of releasing glutamate, but not ATP, in response to cellular deformation by direct mechanical stimulation. The released glutamate activates the NMDA receptors on TGs. We suggest that MCs act as mechanoelectrical transducers and establish synaptic transmission with neurons, through the MC-neurite complex, to mediate mechanosensory transduction.