The long term objectives of this project are to determine the role of craniofacial sensory feedback in the control of jaw movement and to determine how these sensori-motor processes may be altered in oro-facial dysfunctions including bruxism, masticatory muscle and temporomandibular disorders. Three hypotheses are proposed: 1) Sensory feedback from trigeminal ganglion masticatory muscle afferents reaches trigeminal motoneurons via disynaptic and trisynaptic neuronal circuits involving the spinal trigeminal nucleus and adjacent reticular formation. This hypothesis will be tested by investigating relationships between intracellularly labeled trigeminal ganglion jaw-muscle afferent neurons and retrogradely-labeled trigeminal premotor neurons. 2) Brainstem interneurons which respond to jaw movement include one type which manifests responses similar to low-threshold muscle proprioceptive afferents and responds to small amplitude jaw displacement and a second type which is activated by large amplitude jaw displacement and provides sensory feedback related to the extremes of mandibular movement and masticatory muscle stress. Both groups include interneurons which project to the trigeminal motor nucleus and others which project to higher centers. This hypothesis will be tested by examining the physiology and morphology of trigeminal and reticular formation neurons which respond to jaw movement via intracellular recording and staining. 3) Sensory integration occurs in the mesencephalic trigeminal nucleus (Vme) via interactions between jaw-muscle spindle primary afferent neurons and between muscle spindle and periodontal mechanoreceptor primary afferent neurons. This hypothesis will be tested by: a) Examining the morphological relationships between Vme muscle spindle and Vme periodontal afferent neurons using intracellular staining and retrograde neuronal labeling and b) investigating cellular interactions between Vme neurons using intracellular stimulus, and spike-triggered averaging techniques. These studies will provide data fundamental to understanding on the role of sensory feedback in normal oral motor function and insight into the pathophysiological mechanisms involved in craniofacial dysfunctions and the effects of craniofacial clinical manipulations.
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