Oral motor behaviors comprise a unique grouping of important, motor/sensory activities that include suckling deglutition, respiration, mastication and, in man, articulated speech. However, despite their universality and, indeed essentiality (with the exception of speech) among mammals, the mechanisms and neural substrates that subserve these behaviors remain largely unknown. Of critical importance for understanding the neural basis of oral motor behavior is knowledge of the synaptic relationships between brainstem interneurons and the cranial nerve motor nuclei they innervate. Recent results from my laboratory have begun to elucidate the synaptic organization of the hypoglossal nucleus, the motor pool that controls the tongue, although several issues regarding the organization of inputs from various brainstem interneurons remain unresolved. Of particular interest is the sensory trigeminal complex since it conveys the majority of sensory signals from the tongue and oral cavity and, importantly, is a site of convergence for both central and peripheral signals, the two primary determinants of movements. Thus, a logical assumption is that information detailing the synaptic relationship between components of the sensory trigeminal complex and the hypoglossal nucleus may be essential to our understanding how peripheral and central influences converge on hypoglossal motoneurons and control oro-lingual and related oral motor behaviors. The experiments described in the present proposal are designed to evaluate the synaptic relationships between components of the sensory trigeminal complex and the hypoglossal nucleus. This will be accomplished by utilizing complementary anterograde (autoradiography, HRP histochemistry) and retrograde (HRP and cholera-conjugated HRP histochemistry) axonal transport methodologies in conjunction with a recently developed flat-embedding technique that allows for correlative study of the same neuronal elements at both the light and electron microscopic level. The results from these experiments will provide essential information on brainstem mechanisms that control oral motor function. These data will advance our knowledge of the neural basis of tongue control and provide the requisite morphological foundation upon which future functional, behavioral and neuropharmacological studies may be based. Furthermore, these data are highly relevant to several dental and medical health related issues including malocclusion, tongue thrusting, oral motor dyskinesias due to aging and neuroleptic drugs, TMJ joint dysfunction and obstructive sleep apnea.
