The long-term objectives of this application are to understand the function of trigeminal proprioceptive feedback in control of jaw movements. Four specific hypotheses are proposed: 1) When the brainstem segmental pathways that transmit tooth directional and force feedback information are activated by specific spatial and temporal patterns of tooth displacement, they will activate portions of the trigeminal motor pool to produce appropriate mandibular movement. 2) The brainstem pathways that transmit tooth displacement information to jaw-depressor motoneurons will be activated by a variety of higher threshold intra-oral inputs and will elicit a nonspecific activation of the jaw-depressor motor pool.These hypothesis will be tested by recording intracellularly from trigeminal motoneurons and interneurons during functionally meaningful spatial and temporal patterns of tooth displacement. 3) Intracellular staining of the axonal projections of single, physiologically characterized jaw-muscle spindle afferents will be performed. Their subsequent projections and density of synaptic contacts to individual trigeminal motoneurons will be assessed to test the hypothesis that spindle input from particular masticatory muscles is partitioned centrally to motoneurons innervating the muscles from which they arise. 4) The direct and indirect projections of periodontal and muscle spindle afferents to cerebellum will be determined by injecting the muscles of mastication or the periodontal ligament and selected regions of cerebellum with anatomical tracers and locating double labeled neurons within the trigeminal ganglion or mesencephalic nucleus of V. Individual trigeminal afferent projections to trigemino- cerebellar relay neurons will be demonstrated by the presence of labeled afferent terminals on cerebellar relay neurons retrogradely filled by prior injections into cerebellum. These studies will provide basic information on the function of trigeminal proprioceptive feedback in the normal control of jaw movement and insight into the inappropriate masticatory muscle activity which occurs in craniofacial muscle disorders.
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