The overall goal of this research is to understand the role that trigeminal primary afferents play in coordinating movements involving the jaw, lip, tongue, pharynx and larynx. Many of the muscles of these structures lack classical proprioceptors, and it is hypothesized that mesencephalic primary afferent neurons provide sensory feedback for multiple structures. Four hypotheses are proposed: 1. Trigeminal proprioceptive afferents make monosynaptic connections onto hypoglossal and nucleus ambiguus motoneurons. 2. Trigeminal proprioceptive afferents integrate and coordinate activity of XII and AMB motoneurons via brainstem premotor neurons. This hypothesis will be tested by using intracellular recording in vivo to identify mono- and bisynaptic neural circuits between proprioceptive afferents and XII and AMB motoneurons and premotor neurons. The neurons will be identified, intracellularly stained, and connections of the stained neurons will be determined with the aid of additional neuroanatomical tracing techniques. 3. Trigeminal proprioceptive afferents participate in the inter-nuclear coordination of XII and trigeminal motoneurons through intrinsic interneurons. 4. Feedback and feedforward modulation between premotor and XII interneurons is conveyed via trigeminal proprioceptive afferents.
