Akifumi Enomoto

Participation of Sodium Currents in Burst Generation and Control of Membrane Excitability in Mesencephalic Trigeminal Neurons

Subthreshold sodium currents are important in sculpting neuronal discharge and have been implicated in production and/or maintenance of subthreshold membrane oscillations and burst generation in mesencephalic trigeminal neurons (Mes V). Moreover, recent data suggest that, in some CNS neurons, resurgent sodium currents contribute to production of high-frequency burst discharge. In the present study, we sought to determine more directly the participation of these currents during Mes V electrogenesis using the action potential-clamp method. In postnatal day 8–14 rats, the whole-cell patch-clamp method was used to record sodium currents by subtraction in response to application of TTX in voltage-clamp mode using the action potential waveform as the command protocol. We found that TTX-sensitive sodium current is the main inward current flowing during the interspike interval, compared with the h-current (Ih) and calcium currents. Furthermore, in addition to the transient sodium current that flows during the upstroke of action potential, we show that resurgent sodium current flows at the peak of afterhyperpolarization and persistent sodium current flows in the middle of the interspike interval to drive high-frequency firing. Additionally, transient, resurgent, and persistent sodium current components showed voltage- and time-dependent slow inactivation, suggesting that slow inactivation of these currents can contribute to burst termination. The data suggest an important role for these components of the sodium current in Mes V neuron electrogenesis.

High Incidence of Blood Exposure Due to Imperceptible Contaminated Splatters During Oral Surgery

PURPOSE To evaluate the incidence of blood exposure during outpatient oral surgery from splattering caused by use of high-speed rotary instruments at the Referral and Teaching Center, University Dental Hospital. MATERIALS AND METHODS Twenty-five consecutive patients who had impacted mandibular third molars were selected. The attending surgeon wore an operation gown and visor mask, and carried out the tooth extraction with the regular procedure. We counted the number of bloodstains found on the operation gown and visor mask, and confirmed the presence of diluted and invisible bloodstains using a leucomalachite green presumptive test, which was able to detect dilutions up to 1:4,000. RESULTS There were 469 separate bloodstains on the gown and visor mask of oral surgeons, which came from 19 (76%) of 25 patients during impacted mandibular third molar surgery. Presumptive tests for invisible bloodstains resulted in 1,206 positive reactions, 2.57-fold greater than the visible stains, from 88% of the cases. All of the surgeons were right-handed and the common areas of staining were the right forearm, face, and thorax regions. CONCLUSIONS Dental procedures with high-speed instruments exposed surgeons to possible blood-borne infections by splashing in nearly 90% of the cases. Greater than 50% of the stains were invisible to the naked eye. Based on our results, strict compliance with barrier precautions, including routine use of an operation gown and visor mask, is recommended whenever oral surgery is carried out with high-speed rotary instruments.

Evidence of aerosolised floating blood mist during oral surgery

Dental surgery performed with high speed instruments, such as a dental turbine, air motor, or micro-engine handpiece, produces a large amount of splattering and particles, which can be contaminated by micro-organisms from the oral cavity. It has been speculated that such particulate mists contain blood-based elements. In the present study, we investigated whether blood-contaminated aerosol was present in a room where oral surgery was performed with high speed instruments. An extra-oral evacuator system was used for sample collection (N=132). For the experiment, a non-woven towel was set on the nozzle of the evacuator as a filter and invisible mist was collected at distances of 20, 60 and 100 cm from the surgical site. A leucomalachite green presumptive test was performed with each filter after every tooth extraction. At locations 20 and 100 cm from the surgical site, 76% and 57%, respectively, of the particulates were positive in blood presumptive tests. Based on our results, we consider that blood-contaminated materials have the potential to be suspended in air as blood-contaminated aerosol. These results indicate the risk of cross-infection at the dental practice for immunocompromised patients as well as healthy personnel.

Effect of Serotonin (5-HT) on Trigeminal Rhythmic Activities Generated in in vitro Brainstem Block Preparations

We used rat isolated brainstem block preparations to analyze the functional roles of serotonin receptors in the generation of trigeminal rhythmic activities. We previously reported that trigeminal rhythmic activities could be induced by some pharmacological applications in an isolated brainstem preparation with a rostral boundary at the border between the inferior and superior colliculus, and a caudal border at the level of the rostral facial nucleus. However, the same stimulation did not induce trigeminal rhythmic activities in a whole brainstem block preparation with the same rostral boundary and a caudal border at the obex level. In the present study, both the 5-HT1A phthalimido-butyl-piperazine, and the 5-HT2C agonist, 1-2,5-dimethoxy-4-iodophenyl-2-aminopropane, combined with N-methyl-D,L-aspartate and bicuculline, elicited trigeminal rhythmic activities in a whole brainstem block preparation. Our results suggest that serotonin has both facilitation and inhibition effects on the generation of trigeminal rhythmic activities in an isolated brainstem block preparation in vitro.

Oral-motor patterns of rhythmic trigeminal activity generated in fetal rat brainstem in vitro

Development of neural circuits generating fetal oral-motor activity was characterized in an in vitro isolated brainstem block preparation. Rhythmical trigeminal activity (RTA) at E20-E21 resembled either the pattern or rhythm of neonatal RTA. Conversely, at E18-E19, RTA displayed a different pattern of discharge from neonatal RTA, and output was not regular but intermittent with another slow rhythm.

Inhibition of Trigeminal Respiratory Activity by Suckling

The trigeminal motor system is involved in many rhythmic oral-motor behaviors, such as suckling, mastication, swallowing, and breathing. Despite the obvious importance of functional coordination among these rhythmic activities, the system is not well-understood. In the present study, we examined the hypothesis that an interaction between suckling and breathing exists in the brainstem, by studying the respiratory activity in trigeminal motoneurons (TMNs) during fictive suckling using a neonatal rat in vitro brainstem preparation. The results showed that fictive suckling, which was neurochemically induced by bath application of N-methyl-D,L-aspartate and bicuculline-methiodide, or by local micro-injection of the same drugs to the trigeminal motor nucleus, inhibited the inspiratory activities in both respiration TMNs and respiratory rhythm-generating neurons. Under patch-clamp recording, fictive suckling caused membrane potential hyperpolarization of respiration TMNs. We conclude that the brainstem preparation contains an inhibitory circuit for respiratory activity in the trigeminal motor system via the rhythm-generating network for suckling. Abbreviations: BIC, bicuculline methiodide; GABA, gamma aminobutyric acid; NMA, N-methyl-D,L-aspartate; NMDA, N-methyl-D-aspartate; and TMN, trigeminal motoneuron.

α2-Adrenoceptors Coordinate Swallowing and Respiration

Because the discoordination between swallowing and respiration may cause severe respiratory disorders such as aspiration pneumonia, understanding the neuronal mechanisms underlying such coordination is important. Recently, it was reported that medullary noradrenergic neurons are involved in evoking esophageal-gastric relaxation reflex, leading to a hypothesis that such neurons are also involved in swallowing-respiration coordination. We tested this hypothesis using an in vitro brain-stem preparation obtained from neonatal rats. A temporal inhibition of respiratory rhythm was consistently observed when swallowing activity was induced by electrical stimulations to the supralaryngeal nerve. We found that a broad adrenergic receptor agonist, norepinephrine, markedly blocked the swallowing-induced temporal inhibition of respiration. Further studies revealed that swallowing-induced respiratory inhibition is blocked by an α2-adrenergic receptor agonist and enhanced by an α2-adrenergic receptor antagonist, indicating an important role of α2-adrenergic receptors in regulation of the coordination between swallowing and respiration in vitro.

Regulation of Trigeminal Respiratory Motor Activity in the Brainstem

The trigeminal motor system participates in the control of respiration as well as suckling and mastication. However, the central mechanism underlying respiratory activity in trigeminal motoneurons is not well-understood. In this study, we aimed to elucidate brainstem circuitry for rhythm generation and signal transmission of trigeminal respiratory activity in in vitro neonatal rat brainstem-spinal cord preparations. We further examined the role of midline-crossing trigeminal interneurons in the bilateral synchronization of respiratory and suckling activity in trigeminal motor nerves. The results of brainstem-sectioning experiments indicated that respiratory rhythms were generated in the medulla and ipsilaterally transmitted to trigeminal motoneurons in the pons. We conclude that the trigeminal motor system, as well as the hypoglossal and phrenic motor system, is regulated by medullary respiratory networks, and that pontine interactions between bilateral trigeminal interneurons are not critical for the generation or synchronization of trigeminal respiratory activity, but are crucial for trigeminal suckling activity.

Suppurative arthritis of the temporomandibular joint associated with bisphosphonate: a case report.

a o The prevalence of bisphosphonate-related osteonecrosis of the jaw (BRONJ) has recently increased, and this condition is difficult to manage. A patient is diagnosed with BRONJ if the following 3 characteristics are present: 1) current or previous treatment with a bisphosphonate (BP), 2) exposed bone in the maxillofacial region that has persisted for more than 8 weeks, and 3) no history of radiotherapy of the jaws. BPs are potent inhibitors of osteoclastic bone resorption for the control of hypercalcemia associated with malignancy, multiple myeloma, metastatic bone disease, and bone loss resulting from breast cancer treatment. Other well-established indications are osteoporosis and Paget disease of bone. Suppurative arthritis of the temporomandibular joint (TMJ) is not common. It arises either from hematogenous spread of microorganisms through the highly vascularized synovial membrane or from direct extension of contiguous infection. Several cases have been reported in the literature, and most of hem are associated with predisposing factors. Supurative arthritis of the TMJ has multiple etiologies ncluding trauma, head and neck infection, extraction f a third molar, TMJ arthrosis, or TMJ arthroscopy. Suppurative arthritis of the TMJ associated with BP dministration has not been previously reported. We resent a rare case of suppurative arthritis of the TMJ

Effects of subglottal air pressure on velopharyngeal muscle activity in dogs.

OBJECTIVE To analyze the effects of airflow in the larynx on activity of the levator veli palatini and pterygopharyngeal muscles. DESIGN Ten adult beagle dogs were anesthetized with sodium pentobarbital. In each dog, two tracheal tubes were inserted subsequent to tracheotomy, one in the direction of the vocal folds and the other toward the lungs for respiration. In the first of three experiments, the effect of artificial airflow on electromyographic activity of the levator and pterygopharyngeal muscles was studied. In the second experiment, the effect of air pressure beneath the vocal folds on the activity of these muscles was studied. For the third experiment, the larynx was isolated surgically without cutting the bilateral superior laryngeal nerves and the effect of airflow through it examined. RESULTS AND CONCLUSION Both outward airflow and higher pressure enhanced expiratory activity of the levator and pterygopharyngeal muscles. Receptors in the subglottal area play major roles in this enhancement. Furthermore, an increase in air pressure during expiration enhances closure of the velopharynx.