The long-term objective of this proposal is to determine the neutral basis for the coordination and control of jaw and tongue movements during feeding and drinking. Two experimentally generated rhythmic oral-facial behaviors have been developed in the anesthetized guinea pig: (1) cortically evoked and, (2) apomorphie induced RJMs. Jaw and tongue muscle contraction patterns and mandibular movement trajectories of these RJM behaviors have characteristics that resemble, respectively, those found during mastication and lapping the awake animal. Recent investigations have indicated the importance of neutral networks in the pontomedullary reticular formation for the control and coordination of oral-facial motor behaviors. The purpose of the proposed studies is to investigate the organization and functional characeristics of these networks. The first area of investigation is the parvocellular nucleus (PVC). The PVC is in the lateral region of the reticular formation and is the location of trigeminal and hypoglossal premotoneurons. The second area of investigation involves nuclei in the medial region of the reticular formation. It is hypothesized that this region contains a neutral network responsible for rhythm generation in mastication and drinking. Methods to be used in these studies include intracellular recording in trigeminal and hypoglossal motoneurons, extracellular recording of reticular formation neurons, correlation of activity of neurons in the PVC with those in the medial nuclei, and correlation of PVC neutral activity with synaptic potentials evoked in motoneurons innervating jaw and tongue muscles. Two important clincial entities recognized in dentistry are the myofacial pain dysfunction syndrome and bruxism. Both have neuromuscular etiologies and can lead to pathologies of hard and soft tissues in the oral-facial area. Furthermore, aberrant habitual movements of the jaws and tongue are thought play a major role in generating morphological malformations that require orthodontic correction. The importance of jaow and tongue control in prosthodontics is becoming more evident. Dyskinesias involving the jaw and tongue are also manifest in tardive dyskinesia, senility, stroke and in comatose patients. There is, however, very little understanding of central nervous system mechanisms responsible for the coordination and control of oral-facial movements, the impairment of which is the central feature of all of these disorders. In spite its significance, the study of the mechanisms of motor control of oral-facial behaviors has lagged far behind those involving locomotion, respiration and eye movements. The results of experiments proposed here will provide insights into the neutral mechanisms underlying the central nervious sytem control of jaw and tongue coordination during rhythmic jaw movement behaviors. Such information is necessary for the development fo more effective clinical treatment paradigms for oral-facial motor disorders.
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