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  • 1.
    Athanassiadis, Tuija
    et al.
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology.
    Olsson, Kurt A
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology.
    Kolta, A
    Westberg, Karl-Gunnar
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology.
    Identification of c-Fos immunoreactive brainstem neurons activated during fictive mastication in the rabbit2005In: Experimental Brain Research, ISSN 0014-4819, E-ISSN 1432-1106, Vol. 165, no 4, p. 478-489Article in journal (Refereed)
    Abstract [en]

    In the present study we used the expression of the c-Fos-like protein as a "functional marker" to map populations of brainstem neurons involved in the generation of mastication. Experiments were conducted on urethane-anesthetized and paralyzed rabbits. In five animals (experimental group), rhythmical bouts of fictive masticatory-like motoneuron activity (cumulative duration 60-130 min) were induced by electrical stimulation of the left cortical "masticatory area" and recorded from the right digastric motoneuron pool. A control group of five animals (non-masticatory) were treated in the same way as the experimental animals with regard to surgical procedures, anesthesia, paralysis, and survival time. To detect the c-Fos-like protein, the animals were perfused, and the brainstems were cryosectioned and processed immunocytochemically. In the experimental group, the number of c-Fos-like immunoreactive neurons increased significantly in several brainstem areas. In rostral and lateral areas, increments occurred bilaterally in the borderzones surrounding the trigeminal motor nucleus (Regio h); the rostrodorsomedial half of the trigeminal main sensory nucleus; subnucleus oralis-gamma of the spinal trigeminal tract; nuclei reticularis parvocellularis pars alpha and nucleus reticularis pontis caudalis (RPc) pars alpha. Further caudally-enhanced labeling occurred bilaterally in nucleus reticularis parvocellularis and nucleus reticularis gigantocellularis (Rgc) including its pars-alpha. Our results provide a detailed anatomical record of neuronal populations that are correlated with the generation of the masticatory motor behavior.

  • 2.
    Athanassiadis, Tuija
    et al.
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology.
    Westberg, Karl-Gunnar
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology.
    Olsson, Kurt A
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology.
    Kolta, A
    Physiological characterization, localization and synaptic inputs of bursting and nonbursting neurons in the trigeminal principal sensory nucleus of the rat2005In: European Journal of Neuroscience, ISSN 0953-816X, E-ISSN 1460-9568, Vol. 22, no 12, p. 3099-3110Article in journal (Refereed)
    Abstract [en]

    A population of neurons in the trigeminal principal sensory nucleus (NVsnpr) fire rhythmically during fictive mastication induced in the in vivo rabbit. To elucidate whether these neurons form part of the central pattern generator (CPG) for mastication, we performed intracellular recordings in brainstem slices taken from young rats. Two cell types were defined, nonbursting (63%) and bursting (37%). In response to membrane depolarization, bursting cells, which dominated in the dorsal part of the NVsnpr, fired an initial burst followed by single spikes or recurring bursts. Non-bursting neurons, scattered throughout the nucleus, fired single action potentials. Microstimulation applied to the trigeminal motor nucleus (NVmt), the reticular border zone surrounding the NVmt, the parvocellular reticular formation or the nucleus reticularis pontis caudalis (NPontc) elicited a postsynaptic potential in 81% of the neurons tested for synaptic inputs. Responses obtained were predominately excitatory and sensitive to glutamatergic antagonists DNQX and/or APV. Some inhibitory and biphasic responses were also evoked. Bicuculline methiodide or strychnine blocked the IPSPs indicating that they were mediated by GABA(A) or glycinergic receptors. About one-third of the stimulations activated both types of neurons antidromically, mostly from the masseteric motoneuron pool of NVmt and dorsal part of NPontc. In conclusion, our new findings show that some neurons in the dorsal NVsnpr display both firing properties and axonal connections which support the hypothesis that they may participate in masticatory pattern generation. Thus, the present data provide an extended basis for further studies on the organization of the masticatory CPG network.

  • 3.
    Johansson, Anders Sixten
    et al.
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology.
    Pruszynski, J Andrew
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology.
    Edin, Benoni Benjamin
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology.
    Westberg, Karl-Gunnar
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology.
    Biting intentions modulate digastric reflex responses to sudden unloading of the jaw2014In: Journal of Neurophysiology, ISSN 0022-3077, E-ISSN 1522-1598, Vol. 112, no 5, p. 1067-1073Article in journal (Refereed)
    Abstract [en]

    Reflex responses in jaw opening muscles can be evoked when a brittle object cracks between the teeth and suddenly unloads the jaw. We hypothesized that this reflex response is flexible and, as such, is modulated according to the instructed goal of biting through an object. Study participants performed two different biting tasks when holding a peanut-half stacked on a chocolate piece between their incisors. In one task, they were asked to split the peanut-half only (single-split task) and, in the other task, they were asked to split both the peanut and the chocolate in one action (double-split task). In both tasks, the peanut split evoked a jaw opening muscle response, quantified from EMG recordings of the digastric muscle in a window 20-60 ms following peanut split. Consistent with our hypothesis, we found that the jaw opening muscle response in the single-split trials was about twice the size of the jaw opening muscle response in the double-split trials. A linear model that predicted the jaw opening muscle response on a single trial basis indicated that task settings played a significant role in this modulation but also that the pre-split digastric muscle activity contributed to the modulation. These findings demonstrate that, like reflex responses to mechanical perturbations in limb muscles, reflex responses in jaw muscles not only show gain-scaling but also are modulated by subject intent.

  • 4.
    Johansson, Anders
    et al.
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology.
    Westberg, Karl-Gunnar
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology.
    Edin, Benoni B.
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology.
    Task-dependent control of the jaw during food splitting in humans2014In: Journal of Neurophysiology, ISSN 0022-3077, E-ISSN 1522-1598, Vol. 111, p. 2614-2623Article in journal (Refereed)
    Abstract [en]

    Although splitting of food items between the incisors often requires high bite forces, rarely do the teeth harmfully collide when the jaw quickly closes after split. Previous studies indicate that the force-velocity relationship of the jaw closing muscles principally explains the prompt dissipation of jaw closing force. Here, we asked whether people could regulate the dissipation of jaw closing force during food splitting. We hypothesized that such regulation might be implemented via differential recruitment of masseter muscle portions situated along the anteroposterior axis because these portions will experience a different shortening velocity during jaw closure. Study participants performed two different tasks when holding a peanut-half stacked on a chocolate piece between their incisors. In one task, they were asked to split the peanut-half only (single-split trials) and, in the other, to split both the peanut and the chocolate in one action (double-split trials). In double-split trials following the peanut split, the intensity of the tooth impact on the chocolate piece was on average 2.5 times greater than in single-split trials, indicating a substantially greater loss of jaw closing force in the single-split trials. We conclude that control of jaw closing force dissipation following food splitting depends on task demands. Consistent with our hypothesis, converging neurophysiological and morphometric data indicated that this control involved a differential activation of the jaw closing masseter muscle along the anteroposterior axis. These latter findings suggest that the regulation of jaw closing force after sudden unloading of the jaw exploits masseter muscle compartmentalization.

  • 5.
    Lund, James P
    et al.
    Faculty of Dentistry, McGill University, Montréal, Québec, Canada .
    Sadeghi, Somayeh
    Faculty of Dentistry, McGill University, Montréal, Québec, Canada .
    Athanassiadis, Tuija
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology.
    Caram Salas, Nadia
    Faculty of Dentistry, McGill University, Montréal, Québec, Canada .
    Auclair, François
    Groupe de Recherche sur le Système Nerveux Central du FRSQ, Département de Physiologie, Faculté de Médecine, Université de Montréal, Montréal, Québec, Canada .
    Thiverge, Benoît
    Faculté de Médecine Dentaire, Université de Montréal, Montréal, Québec, Canada.
    Arsenault, Isabel
    Groupe de Recherche sur le Système Nerveux Central du FRSQ, Département de Physiologie, Faculté de Médecine, Université de Montréal, Montréal, Québec, Canada.
    Rompré, Pierre
    Faculté de Médecine Dentaire, Université de Montréal, Montréal, Québec, Canada.
    Westberg, Karl-Gunnar
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology.
    Kolta, Arlette
    Groupe de Recherche sur le Système Nerveux Central du FRSQ, Département de Physiologie, Faculté de Médecine, Université de Montréal, Montréal, Québec, Canada .
    Evidence that muscle spindle mechanoreceptor afferents play a role in chronic muscle painManuscript (preprint) (Other academic)
  • 6.
    Lund, James P
    et al.
    Université de Montréal.
    Sadeghi, Somayeh
    McGill University, Montréal.
    Athanassiadis, Tuija
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology.
    Caram Salas, Nadia
    McGill University, Montréal.
    Auclair, François
    Université de Montréal.
    Thivierge, Benoît
    Université de Montréal.
    Arsenault, Isabel
    Université de Montréal.
    Rompré, Pierre
    Université de Montréal.
    Westberg, Karl-Gunnar
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology.
    Kolta, Arlette
    Université de Montréal, McGill University, Montréal.
    Assessment of the potential role of muscle spindle mechanoreceptor afferents in chronic muscle pain in the rat masseter muscle2010In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 5, no 6, p. e11131-Article in journal (Refereed)
    Abstract [en]

    Low pH leads to changes in several electrical properties of MSA, including initiation of ectopic action potentials which could propagate centrally but could also invade the peripheral endings causing glutamate release and activation of nearby nociceptors within the spindle capsule. This peripheral drive could contribute both to the transition to, and maintenance of, persistent muscle pain as seen in some "functional" pain syndromes.

  • 7.
    Scott, G
    et al.
    McGill University, Montréal and Université de Montréal.
    Westberg, Karl-Gunnar
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology.
    Vrentzos, N
    McGill University, Montréal.
    Kolta, A
    Université de Montréal.
    Lund, J P
    McGill University, Montréal and Université de Montréal.
    Effect of lidocaine and NMDA injections into the medial pontobulbar reticular formation on mastication evoked by cortical stimulation in anaesthetized rabbits2003In: European Journal of Neuroscience, ISSN 0953-816X, E-ISSN 1460-9568, Vol. 17, no 10, p. 2156-2162Article in journal (Refereed)
    Abstract [en]

    Neurons of the dorsal nucleus reticularis pontis caudalis (nPontc) fire rhythmically during fictive mastication, while neurons of the ventral half tend to fire tonically (Westberg et al., 2001). This paper describes the changes in the pattern of rhythmical mastication elicited by stimulation of the sensorimotor cortex during inhibition or excitation of neurons in this nucleus and adjacent parts of nucleus reticularis gigantocellularis (Rgc) in the anaesthetized rabbit. Masticatory movements and electromyographic (EMG) activity of the masseter and digastric muscles produced by cortical stimulation were recorded before, during and after injections of a local anaesthetic (lidocaine) or excitatory amino acid N-methyl-d-aspartate (NMDA) into nPontc and Rgc through a microsyringe with attached microelectrode to record neuronal activity. Lidocaine inhibited local neurons and modified the motor program, and the effects varied with the site of injection. Most injections into the ventral half of nPontc increased cycle duration, digastric burst duration and burst area. The action of lidocaine in dorsal nPontc was more variable, although burst duration and area were often decreased. The effects on the muscle activity were always bilateral. Lidocaine block of the rostromedial part of Rgc had no effect on movements or on EMGs. Injections of NMDA excited local neurons and when injected into ventral nPontc, it completely blocked mastication. Dorsal injections either had no effect or increased cycle frequency, while decreasing burst duration and area. No increases in EMG burst duration or area were observed with NMDA. Our findings suggest that neurons of ventral nPontc tonically inhibit other parts of the central pattern generator during mastication, while dorsal neurons have mixed effects. We incorporated these findings into a new model of the masticatory central pattern generator.

  • 8.
    Westberg, Karl-Gunnar
    et al.
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology.
    Kolta, Arlette
    Faculté de médecine dentaire, and Groupe de Recherche sur le Système Nerveux Central du FRSQ, Université de Montréal C.P. 6128, succursale Centre-villeMontréal (Qc), Canada.
    The trigeminal circuits responsible for chewing2011In: Translating mechanisms of orofacial neurological disorder: from the peripheral nervous system to the cerebral cortex / [ed] Masayuki Kobayashi, Noriaki Koshikawa, Koichi Iwata och John Waddington, London ; Waltham, MA: Academic Press, 2011, Vol. 97, p. 77-98Chapter in book (Refereed)
    Abstract [en]

    Mastication is a vital function that ensures that ingested food is broken down into pieces and prepared for digestion. This review outlines the masticatory behavior in terms of the muscle activation patterns and jawmovements and gives an overview of the organization and function of the trigeminal neuronal circuits that are known to take part in the generation and control of oro-facial motor functions. The basic pattern of rhythmic jaw movements produced during mastication is generated by a Central Pattern Generator (CPG) located in the pons and medulla. Neurons within the CPG have intrinsic properties that produce a rhythmic activity, but the output of these neurons is modified by inputs that descend from the higher centers of the brain, and by feedback from sensory receptors, in order to constantly adapt the movement to the food properties.

  • 9.
    Westberg, Karl-Gunnar
    et al.
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology.
    McFarland, David
    Kolta, Arlette
    Stohler, Christian
    Feine, Jocelyne
    Woda, Alain
    From movement to pain: a tribute to professor James P. Lund2008In: Journal of Orofacial Pain, ISSN 1064-6655, E-ISSN 1945-3396, Vol. 22, no 4, p. 297-306Article in journal (Refereed)
    Abstract [en]

    This tribute article to Professor James P. Lund stems from 6 of the presentations delivered at the July 1, 2008, symposium that honored 3 "giants" in orofacial neuroscience: B. J. Sessle, A. G. Hannam, and J. P. Lund. It was noted that soon after his training as a dentist in Australia, Jim Lund became interested in research. At the time he decided to do a PhD, there was a lot of discussion about how rhythmic movements were programmed. The early belief, based on Sherrington's studies of motor systems, was that these movements were simply an alternating series of reflexes. In the late 1960s and early 1970s, some still shared this belief, whereas others favored Graham Brown's hypothesis that repetitive movements were centrally programmed and did not depend on reflexes triggered by sensory inputs. There was no strong evidence then for either scenario except for the rhythmic movements of respiration. Lund's pioneering work during his PhD proved the existence of a central pattern generator (CPG) for mastication in the brainstem. Since then he has been interested in understanding how CPGs function and how sensory feedback works to adjust the motor patterns that they produce. Sections in this tribute article to Lund are written by some of his close collaborators and reflect the evolution of his work throughout the years. The first 4 presentations in this article (by K.-G. Westberg, D. McFarland, A. Kolta, and C. Stohler) highlight various aspects of these interests, and the final 2 presentations (by J. Feine and A. Woda) focus especially on clinical aspects of Lund's interests. The last section of this article is a final commentary from Professor Lund.

  • 10.
    Westberg, Karl-Gunnar
    et al.
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology.
    Scott, G
    Université de Montréal, McGill University, Montréal.
    Olsson, Kurt
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology.
    Lund, J P
    Université de Montréal, McGill University, Montréal.
    Discharge patterns of neurons in the medial pontobulbar reticular formation during fictive mastication in the rabbit2001In: European Journal of Neuroscience, ISSN 0953-816X, E-ISSN 1460-9568, Vol. 14, no 10, p. 1709-1718Article in journal (Refereed)
    Abstract [en]

    In this study, we describe functional characteristics of neurons forming networks generating oral ingestive motor behaviours. Neurons in medial reticular nuclei on the right side of the brainstem between the trigeminal and hypoglossal motor nuclei were recorded in anaesthetized and paralysed rabbits during two types of masticatory-like motor patterns induced by electrical stimulation of the left (contralateral) or right (ipsilateral) cortical masticatory areas. Sixty-seven neurons in nucleus reticularis pontis caudalis (nPontc), nucleus reticularis parvocellularis (nParv), and nucleus reticularis gigantocellularis (Rgc) were studied. These were classified as phasic or tonic depending on their firing pattern during the fictive jaw movement cycle. Phasic neurons located in the dorsal part of nPontc were active during the jaw opening phase, whilst those in dorsal nParv tended to fire during the closing phase. In most neurons, burst duration and firing frequency changed between the two motor patterns, but there was little change in phase of firing. Tonic units were mainly recorded in the ventral half of nPontc, and at the junction between Rgc and caudal nParv. Cortical inputs with short latency from the contralateral masticatory area were more frequent in phasic (82%) than tonic (44%) neurons, whilst inputs from the ipsilateral cortex were equal in the two subgroups (57% and 56%). Phasic neurons had significantly shorter mean contralateral than ipsilateral cortical latencies, whilst there was no difference among tonic neurons. Intra- and perioral primary afferent inputs activated both types of neurons at oligo-synaptic latencies. Our results show that subpopulations of neurons in medial reticular nuclei extending from the caudal part of the trigeminal motor nucleus to the rostral third of the hypoglossal motor nucleus are active during the fictive masticatory motor behaviour. Unlike masticatory neurons in the lateral tegmentum, the medial subpopulations are spatially organized according to discharge pattern.

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