摂食行動の神経制御機構 Neural control of feeding behaviors
S3-5-2-1 Evolutionary neuromechanics of mammalian feeding ○Callum Ross1, Kazutaka Takahashi1, Kevin Brown1, Jose Iriarte-Diaz1, Nicholas Hatsopoulos1 University of Chicago, Department of Organismal Biology and Anatomy, Chicago1 Mammalian feeding provides a rich source of material for evolutionary neuromechanics: the use of comparative behavioral, physiological, and morphological data to test hypotheses about the origin and evolution of sensorimotor systems. Mammals suckle their young, with a weaning period of transition from suckling to chewing. Mammals also employ a unique form of chewing: mastication, characterized primitively by transverse movements of precisely occluding teeth. Mastication evolved in the morphological context of reduced mandibular postdentary bones, reduction in tooth replacement to a condition of diphyodonty, a shift from ankylosis of teeth in the dentary to anchoring the teeth to the mandible via a richly innervated periodontal ligament, and the development of gamma-motoneurons for control of muscle spindles. Behaviorally, early mammals are thought to have been able to modulate muscle activities to control dental and joint loads. Mammalian mastication is also more rhythmic than the chewing of lizards and fish. High rhythmicity is hypothesized to improve energetic efficiency and facilitate motor control, especially tongue-jaw coordination. All of these features allowed mammals to rapidly diversify into a wide range of niches and a diversity of feeding systems. The large number of unique sensorimotor components in the mammalian feeding system and the increases in brain size characteristic of mammals begs the question: what role did the central nervous system play in the evolution of mammalian feeding? Our recent work on the role of cortex in control of primate feeding suggests an important role for cortex in control of mammal feeding. The sensorimotor cortex precisely encodes 3D jaw and tongue movements and coordination, and manifests changes in dynamical states with changes in cycle type. The role of cortex, cerebellum and basal ganglia in control of mammal feeding promises important new insights into the origin and evolution of complex sensorimotor systems.	S3-5-2-2 Multimodal control for rank-ordered recruitment of motoneurons during voluntary jaw clenching - Leak K+ channel, stretch reflex pathway & cerebellar internal model - ○Youngnam Kang1, Mitsuru Saito1, Hiroki Toyoda1, Hajime Sato1 Department of Neuroscience and Oral Physiology, Osaka University Graduate School of Dentistry, Osaka, Japan1 The slow-closing phase of the mastication cycle plays a major role in the mastication of foods. The isometric contraction of jaw-closing muscles during the slow-closing phase is developed through the recruitment of jaw-closing α-motoneurons (αMNs). However, the neuronal mechanism underlying the recruitment of jaw-closing αMNs remains unknown. It is well established that motor units are recruited depending on the order of sizes or input resistances of αMNs, which is known as the size principle. Two-pore-domain acid-sensitive K+ (TASK1/3) channels are recently found to be the molecular correlates of the input resistance, and also found to be expressed in the masseter αMNs. First, we examined the involvement of spindle Ia inputs in the orderly recruitment of MNs during clenching in human subjects, and then examined the involvement of spindle Ia inputs onto masseter MNs and TASK channels in the orderly recruitment of MNs in rat slice preparations using whole-cell patch-clamp and immunohistochemical methods. Vibration of muscle spindle revealed a crucial involvement of spindle Ia inputs in regulating the clenching force in human subjects. Dual whole-cell recordings obtained from two adjacent MNs revealed the input-resistance (IR) ordered recruitment of MNs in response to repetitive stimulation of the presumed spindle Ia inputs. TASK1/3 channels were differentially distributed depending on the size of MNs. We also found that the size distribution of αMNs was bimodal or skewed to the left, revealing the presence of many αMNs as small as γMNs. Thus, Ia inputs are likely to play a crucial role in orderly recruitment of αMNs of the trigeminal motor nucleus, which would progress during the slow-closing phase of the mastication cycle. The orderly recruitment of αMNs could be modulated depending on the activities of TASK1/3 channels.
S3-5-2-3 下顎と舌の運動制御メカニズム Neural mechanisms controlling jaw and tongue movements ○井上富雄1, 野中睦美1, 伊原良明1, 中村史朗1, 中山希世美1, 矢沢格2, 望月文子1 ○Tomio Inoue1, Mutsumi Nonaka1, Yoshiaki Ihara1, Shiro Nakamura1, Kiyomi Nakayama1, Itaru Yazawa2, Ayako Mochizuki1 昭和大学歯学部口腔生理学講座1, 昭和大・医・第1解剖2 Department of Oral Physiology, Showa University School of Dentistry, Tokyo, Japan1, Dept Anat I, Showa Univ Sch Med, Tokyo2 Feeding is one of the most important survival functions for mammals. To understand neural mechanisms underlying oral-motor functions during feeding, we have carried out two series of experiments. We first examined the properties of synaptic inputs from premotor neurons located in various regions around the trigeminal motor nucleus (MoV) to masseter motoneurons (MMNs) and digastric motoneurons (DMNs) in brainstem slice preparations obtained from P1-12 rats using whole-cell recordings and laser photolysis of caged glutamate. Photostimulation of multiple regions induced postsynaptic currents (PSCs) in the majority of MMNs and DMNs. Stimulation of the lateral supratrigeminal region (SupV) induced PSCs more frequently induced burst PSCs in MMNs in P1-5 rats, while low-frequency PSCs are predominant at P9-12. Furthermore, SupV stimulation induced PSCs more often in MMNs than in DMNs at P9-12. These developmental changes in properties of synaptic inputs from the SupV may contribute to the conversion from suckling to chewing. Next, we investigated the neuronal mechanisms of the left/right and jaw/tongue coordinations during NMDA-induced fictive suckling using isolated brainstem-spinal cord preparations from P0-2 mice. Bath application of NMDA induced synchronized low-frequency rhythmic activity (lfRA) in the left/right trigeminal motor nerves and in the hypoglossal nerve. The high-frequency rhythmic trigeminal activity which was side-independent appeared following the trigeminal lfRA. A midline separation of the preparation abolished the trigeminal lfRA but spared the hypoglossal lfRA. These results suggest that the neuronal network that generates lfRA likely contributes to the synchronized activity of the left/right jaw muscles and of the jaw/tongue muscles, where it sends its command to the trigeminal motoneurons mainly via the commissural pathway. Such a neuronal network may underlie the coordinated movements of the jaw and tongue during suckling.	S3-5-2-4 Sleep is not a period of motor quiescence for jaw motor system ○Takafumi Kato1, Atsushi Yoshida1 Department of Oral Anatomy and Neurobiology, Osaka University Graduate School of Dentistry, Osaka, Japan1 As the vigilance level shifts from wakefulness to sleep, purposeful behaviors disappear while transient activation of the skeletal muscles was found to occur during sleep in healthy subjects and animals. Among various types of jaw motor events, however, swallowing, chewing-like rhythmic jaw movements and twitches are occasionally found during sleep in humans. In patients with sleep related movement disorders, specific motor events in selected body regions are exaggerated during sleep, which causes health-related problems. Currently, neurophysiological mechanisms generating sleep related movements remain to be fully understood. In animals, the modulation of EMG activity level over sleep states, such as NREM and REM sleep, differed between the muscles in the jaw and neck. Within the jaw motor system, EMG activity level of the jaw-closing and -opening muscles exhibits similar stage-dependent changes while the temporal fluctuations of activity level were not correlated between two muscles. In addition, EMG bursts of the jaw muscles are generally of a low activity level and inhomogeneous for the duration, amplitude and intervals. These suggest that motoneurons of two antagonistic jaw muscles received heterogeneous facilitatory inputs with quantitative and temporal components during sleep. Antagonistic jaw muscle twitches during REM sleep exhibit rhythmic and coordinated patterns similar to those during mastication. Although only a few repetitive jaw muscle bursts spontaneously occurred during NREM sleep, rhythmic jaw movements can be elicited by repetitive electrical stimulation to the corticobulbar tract. Thus, sleep regulatory systems do not simply bring down the entire jaw motor systems and neural networks orderly regulating antagonistic jaw muscle activities during wakefulness can be activated under distinct motor controls in sleep states.
S3-5-2-5 ヒト咽頭への電気刺激がもたらす嚥下機能への効果 Effects of pharyngeal electrical stimulation on the swallowing behaviors in humans ○井上誠1 ○Makoto Inoue1 新潟大学大学院医歯学総合研究科　摂食・嚥下リハビリテーション学分野1 Division of Dysphagia Rehabilitation, Niigata University Graduate School of Medical and Dental Sciences, Niigata, Japan1 The present study tested whether electrical stimulation increases the number of voluntary repetitive swallows in humans. In addition, summation of peripheral inputs increases neuronal activities of swallowing center in the brain stem and hence the number of swallows. Furthermore, potential of initiating both voluntary and involuntary swallowing was compared and the effect of chewing behaviors on the initiation of swallowing evoked by the electrical stimulation was evaluated. Facilitatory effect of either the mid- or hypo-pharyngeal stimulation was much larger than that of hyper-pharyngeal stimulation. The longer the pulse duration was, the larger the number of swallows was, suggesting temporal and spatial summation of peripheral inputs into the swallowing center. There was a wide variation in the number of swallows among subjects. The number of reflexively evoked swallowing (i.e., involuntary swallow) by pharyngeal stimulation also varied greatly, and there was a significant linear correlation in the number of swallows between voluntary and involuntary swallowing, which suggests that the swallowing central pattern generator is a common component of both neuronal networks and therefore is responsible for inter-individual variations. The chewing significantly inhibited the initiation of swallows. Although it should be clarified how the chewing behaviors modulate swallowing function, these data suggest the functional interaction between chewing and swallowing centers.	S3-5-2-6 Kinematically defined state dependent changes in functional connectivity of neurons and in local field potentials in orofacial motor cortex during chewing and swallowing ○Kazutaka Takahashi1, Jose Iriarte-Diaz1, Lorenzo Pesce2,3, Kevin Brown1, Matt Best1, Nicholas Hatsopoulos1,2, Callum Ross1 University of Chicago, Department of Organismal Biology and Anatomy, Chicago, IL, USA1, Committee of Computational Neuroscience, Univ of Chicago2, Computation Institute, Univ of Chicago3 Primate feeding behavior is characterized by a series of cycles of different types making it ideal for investigating the role of distinct brain regions in controlling transitions between different, discrete kinematic states. We trained two female macaque monkeys to eat while restrained in a primate chair with the head restrained with a halo coupled to the cranium through chronically implanted head-posts. 3-D jaw kinematic data were collected in the coordinate system of the cranium using an infrared light video-based motion analysis system. Using movements of a mandibular marker, jaw movement cycles were defined by two consecutive maximum gapes. The cycles in each feeding sequence were then assigned into five different cycle types: ingestion, manipulation, stage-1 transport, rhythmic chew and swallow. In this study, we focused on transitions between two consecutive rhythmic chew cycles and between rhythmic chewing and swallow cycles. We recorded multiple single unit spiking activities as well as local field potentials from a chronically implanted a Utah microelectrode array in the orofacial area of primary motor cortex (MIo) on the left side of the monkey. We first analyzed local field potentials and found that power in the beta oscillation frequency range increased during transitions from chewing to swallowing cycles. Furthermore, we analyzed unit spiking activities using a Granger causality model, estimated their functional connectivity during transitions between chewing cycles and during chew-to-swallow transitions. We found that during rhythmic chewing, the network was dominated by excitatory connections and exhibited a few out-degree hub neurons, while during transitions from rhythmic chews to swallows, the numbers of excitatory and inhibitory connections became comparable, and more in-degree hub neurons emerged. These results suggest that networks of neurons in MIo change their operative states with changes in kinematically defined behavioral states.

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