Takashi Nokubi

A CCAAT/Enhancer Binding Protein β Isoform, Liver-Enriched Inhibitory Protein, Regulates Commitment of Osteoblasts and Adipocytes

ABSTRACT Although both osteoblasts and adipocytes have a common origin, i.e., mesenchymal cells, the molecular mechanisms that define the direction of two different lineages are presently unknown. In this study, we investigated the role of a transcription factor, CCAAT/enhancer binding protein β (C/EBPβ), and its isoform in the regulation of balance between osteoblast and adipocyte differentiation. We found that C/EBPβ, which is induced along with osteoblast differentiation, promotes the differentiation of mesenchymal cells into an osteoblast lineage in cooperation with Runx2, an essential transcription factor for osteogenesis. Surprisingly, an isoform of C/EBPβ, liver-enriched inhibitory protein (LIP), which lacks the transcriptional activation domain, stimulates transcriptional activity and the osteogenic action of Runx2, although LIP inhibits adipogenesis in a dominant-negative fashion. Furthermore, LIP physically associates with Runx2 and binds to the C/EBP binding element present in the osteocalcin gene promoter. These data indicate that LIP functions as a coactivator for Runx2 and preferentially promotes the osteoblast differentiation of mesenchymal cells. Thus, identification of a novel role of the C/EBPβ isoform provides insight into the molecular basis of the regulation of osteoblast and adipocyte commitment.

Coordination of Tongue Pressure and Jaw Movement in Mastication

The tongue plays an important role in mastication and swallowing by its contact with the hard palate. Using an experimental palatal plate with 7 pressure sensors, and recording jaw movement using mandibular kinesiography, we assessed, in healthy subjects, the coordination of tongue and jaw movements during the entire masticatory sequence of solids, by measuring tongue pressure against the hard palate. Tongue pressure appeared during the occlusal phase, reached a peak near the start of opening, and disappeared during opening. Specific patterns in order, duration, and magnitude of tongue pressure were seen at the 7 pressure sensors in each chewing stroke. Magnitude and duration were significantly larger in the late stage of chewing (8 strokes before initial swallowing) than in the early stage (until 8 strokes after starting mastication). The normal pattern of tongue contact against the hard palate, control of tongue activity, and coordination with jaw movement during mastication is described.

Association of masticatory performance with age, gender, number of teeth, occlusal force and salivary flow in Japanese older adults: Is ageing a risk factor for masticatory dysfunction?

OBJECTIVE In general, ageing is a risk factor for sensory and motor deterioration, with the rate of decline varying amongst individuals. Concerning masticatory function, missing teeth along with oral disease seem to accelerate the dysfunction. Here, we aimed to confirm whether masticatory dysfunction by ageing is inevitable. This study investigated the effect of age, gender, number of natural teeth, occlusal force and salivary flow on the masticatory performance in a large sample of elderly adults. DESIGN The study sample consisted of 1288 independently living people aged 60-84 years. Masticatory performance was determined by the comminuted particles of test food. Bilateral maximal occlusal force in the intercuspal position was measured with pressure sensitive sheets. Stimulated whole saliva was collected. RESULTS Masticatory performance was significantly correlated to age, number of residual teeth, occlusal force and stimulated salivary flow rate by Pearsons correlation test. The multiple linear regression analysis showed that, with other variables controlled, masticatory performance was significantly associated with the number of residual teeth (β=0.456, P<0.001), occlusal force (β=0.244, P<0.001) and stimulated salivary flow rate (β=0.069, P=0.003). Age was not related to masticatory performance (β=-0.007, P=0.753). CONCLUSIONS Declines in the number of residual teeth, occlusal force and salivary flow were associated with a reduction of masticatory performance in older adults. If tooth loss is not considered as an attribute of physiological ageing, then ageing by itself may not be a risk factor for masticatory dysfunction.

Influence of human jaw movement on cerebral blood flow.

Temporal changes in cerebral blood flow induced by jaw movement have yet to be investigated. To assess the influence of pattern and intensity of muscle contraction during jaw movement on task-induced change in cerebral blood flow, we performed bilateral transcranial Doppler ultrasound examination during clenching, gum chewing, and tooth tapping in healthy volunteers. A random-effects model analysis revealed a significant increase in middle cerebral artery blood flow velocity during clenching (high muscle activity) and gum chewing (moderate muscle activity), compared with the preceding rest period; however, such an increase was not detected during tooth tapping (low muscle activity). Cerebral blood flow was greater on the working side during the intensive isometric contraction of the masseter muscle in clenching. These results suggest that task-induced change in cerebral blood flow during jaw movement is influenced by the change in peripheral circulation evoked by muscle contraction.

Inhibitory effect of sympathetic stimulation on activities of masseter muscle spindles and the jaw jerk reflex in rats.

1. To evaluate sympathetic effects on jaw muscles, the discharges of masseter muscle spindle afferents, jaw muscle electromyographic (EMG) activities and blood flow changes were compared in anaesthetized decerebrate rats before and during electrical stimulation of the cervical sympathetic trunk. 2. To eliminate the possibility of efferent control from the trigeminal motoneurones, muscle spindle activity was recorded from the cut peripheral end of the masseter nerve. The absence of a sympathetic component in the masseter nerve was confirmed by the horseradish peroxidase method. 3. Electrical stimulation of the sympathetic nerve at frequencies within the physiological range reduced muscle spindle afferent discharges evoked by passive jaw opening. 4. Sympathetic stimulation also reduced the EMG activity evoked by the jaw jerk reflex, which may reflect a sympathetic effect on spindle afferents. After cessation of stimulation, a transient increase in EMG activity was observed, which may be due to efferent supply from the trigeminal motoneurones. During rhythmical jaw movements, no sympathetic effect on EMG activity was detected. 5. The above sympathetic effect on muscle spindle afferents and EMG activity was independent of blood flow changes.

Mapping of c-Fos in the trigeminal sensory nucleus following high- and low-intensity afferent stimulation in the rat

Abstract Although previous studies have suggested that nociceptive afferents from intra-oral and facial structures are organized differently in the trigeminal sensory nucleus (TSN), more detailed data are needed. The present study aimed to fill this gap, by examining the changes in the expression of c-Fos within the rat TSN following high- and low-intensity electrical stimulation applied to the Gasserian ganglion (GG). A low-intensity stimulus (0.1 mA) induced c-Fos in many neurons in the dorsomedial subdivision (Vodm) of the oral subnucleus (Vo; mean±SEM in a certain segment=163.0±42.7), in the medial part of the dorsomedial subdivision (Vidm) of the interpolar subnucleus (Vi; 120.5±40.1), in the medial corner of the magnocellular zone (VcIII/IV; 47.5±10.5), and in the superficial layers (VcI/II; 1330.0±65.6) along the entire length of the dorsomedial-ventrolateral axis of the caudal subnucleus (Vc). A modest number of Fos-positive neurons were induced in the dorsal principal subnucleus (Vp; 10.0±4.9) and in the lateral VcIII/IV (11.5±1.6). A high-intensity stimulus (1.0 mA) significantly increased the number of Fos-positive neurons in each subdivision compared with the low-intensity stimulus (Vp 32.3±10.8; Vodm 270.3±75.3; Vidm 189.3±38.5; medial VcIII/IV 77.5±18.2; lateral VcIII/IV 24.8±9.3; VcI/II, 2155.8±470.2). At both low- and high-intensity stimulation, the fields where Fos-positive neurons appeared are restricted to the dorsal or dorsomedial subdivisions of the rostral subnuclei, Vp, Vo and Vi, where the main projectional fields of primary afferents from the intraoral structures are found, while Fos-positive neurons were distributed in the entire VcI/II, along the dorsomedial-ventrolateral axis of Vc, where the main projectional fields of primary afferents from the facial skin are found. The threshold to induce c-Fos is, however, different according to the fields. These results suggest that nociceptive processing in the intra-oral region is mediated through the entire length of the rostrocaudal axis of TSN, but is mediated primarily through VcI/II in the facial region.

Effect of Reinforcement on Overdenture Strain

Because the abutment becomes the fulcrum, and the denture base over the coping is usually thin, the overdenture is susceptible to fracture. We hypothesized that rational reinforcement can reduce strain and prevent deformation and fracture of the overdenture. We investigated the effect of reinforcement on overdenture strain around the copings and at a midline. A mandibular edentulous model with a 2-mm-thick artificial mucosa and abutment teeth installed bilaterally in the canine position was produced. The coping had a dome-shaped upper surface with a height of 6 mm. On the lingual polished surface, strain gauges were attached at the canine position and at the midline. A vertical load of 49 N was applied on the occlusal surface. Among several kinds of reinforcements, the cast metal reinforcement that covers both the midline and the coping top significantly reduced the strain on the overdenture. It is suggested that this simple reinforcement is effective in preventing deformation and fracture of the overdenture.

Differential Columnar Processing in Local Circuits of Barrel and Insular Cortices

The columnar organization is most apparent in the whisker barrel cortex but seems less apparent in the gustatory insular cortex. We addressed here whether there are any differences between the two cortices in columnar information processing by comparing the spatiotemporal patterns of excitation spread in the two cortices using voltage-sensitive dye imaging. In contrast to the well known excitation spread in the horizontal direction in layer II/III induced in the barrel cortex by layer IV stimulation, the excitation caused in the insular cortex by stimulation of layer IV spread bidirectionally in the vertical direction into layers II/III and V/VI, displaying a columnar image pattern. Bicuculline or picrotoxin markedly extended the horizontal excitation spread in layer II/III in the barrel cortex, leading to a generation of excitation in the underlying layer V/VI, whereas those markedly increased the amplitude of optical responses throughout the whole column in the insular cortex, subsequently widening the columnar image pattern. Such synchronous activities as revealed by the horizontal and vertical excitation spreads were consistently induced in the barrel and insular cortices, respectively, even by stimulation of different layers with varying intensities. Thus, a unique functional column existed in the insular cortex, in which intracolumnar communication between the superficial and deep layers was prominent, and GABAA action is involved in the inhibition of the intracolumnar communication in contrast to its involvement in intercolumnar lateral inhibition in the barrel cortex. These results suggest that the columnar information processing may not be universal across the different cortical areas.

Ontogeny of NADPH-diaphorase in rat forebrain and midbrain

Abstract This study characterizes the developmental expression of NADPH-diaphorase from embryo to adulthood in the forebrain, midbrain and cerebellum of rat brain via histochemical staining. On embryonic day 12 no neurons stained. Labeling was observed in certain nuclei from E15 through the postnatal period to adulthood. Labeling in neurons increased or maintained a constant level with increased age. The embryo demonstrated substantial labeling in neurons of the caudate putamen, bed nucleus of the stria terminalis, preoptic area, lateral hypothalamic area, paraventricular thalamic nucleus, ventromedial hypothalamic nucleus, magnocellular nucleus posterior commissure, and periaqueductal central gray. Additional neuronal labeling was observed postnatally in the olfactory bulb, cerebral cortex, amygdala, various nuclei of the thalamus, interpeduncular nucleus, linear nucleus of the raphe, pretectal area and superior colliculus. In the cerebellum, labeling appeared only after P14 in cells of the molecular cell layer and granular cell layer. The sizes of labeled neurons developed significantly from P4 to P14 in several nuclei. The distinctive temporal and spatial expression pattern of NADPH-diaphorase implies that the NO/cGMP system may play an important role in physiological and developmental functions.

Task-induced activation and hemispheric dominance in cerebral circulation during gum chewing

In elderly persons, it is thought that maintenance of masticatory function may have a beneficial effect on maintenance of cerebral function. However, few studies on cerebral circulation during mastication exist. This study aimed to verify a possible increase in cerebral circulation and the presence of cerebral hemispheric dominance during gum chewing. Twelve healthy, young right-handed subjects with normal dentition were enrolled. Bilateral middle cerebral arterial blood flow velocities (MCAV), heart rate, and arterial carbon dioxide levels were measured during a handgrip exercise and gum chewing. During gum chewing, electromyography of the bilateral masseter muscle was recorded.MCAV and heart rate significantly increased during exercise compared to values at rest.During gum chewing, there were no differences in the rate of increase in MCAV between the working and non-working sides, but during the handgrip exercise, the rate of increase in MCAV was significantly greater for the non-working side than for the working side.During gum chewing,muscle activity on the working side was significantly greater than that on the non-working side. These results suggest that during gum chewing, cerebral circulation increases bilaterally and does not show contralateral dominance, as it does during the handgrip exercise.