BRAIN STEM MECHANISMS CONTROLLING JAW MOVEMENT

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The proper functioning of oral-facial motor behaviors is necessary for the survival of humans. The ingestive behaviors of mammals begins with suckling and progresses to drinking and feeding. Presently, there are very few studies addressing how the brain is organized to produce these behaviors. Even less is known about the etiology of various oral-motor dysfunctions such as tardive dyskinesia. bruxism, and myofacial pain dysfunction syndromes. The long-term goals of this research are to understand both the mechanism underlying the central nervous system control of normal jaw movements that occur during activities such as feeding and drinking, as well as the abnormal jaw movements that occur during various disorders. The specific aims of this proposal are to continue investigations, at the cellular level, into the neuronal processes controlling jaw movements in the guinea pig. We will combine intracellular or whole cell patch clamp recording methods with retrograde-tract tracing techniques to identify specific populations of jaw-opener and closer motoneurons, and trigeminal premotoneurons in thin and thick brain slices. The project is divided into two main parts. In part I, we will determine for identified jaw-opener and closer motoneurons and premotoneurons, I) the presence of specific intrinsic membrane conductances and their contribution to neuronal burst discharge, 2) whether these conductances are substrates for modulation by two monoamines (5-HT and NE). Part II will focus on modulation of excitatory amino acid mediated synaptic transmission by monoamines. We will determine if there are fundamental similarities and differences in modulation by serotonin and norepinephrine between NMDA and non-NMDA components of synaptic transmission to trigeminal motoneurons from mesencephalic of V afferents (Mes V). We will examine these relationships by recording the compound EPSP or EPSC and the single fiber EPSP or EPSC evoked from Mes V nucleus or single Mes V neuron stimulation, respectively. The results of the proposed studies will provide insights into the cellular mechanisms controlling discharge of distinct populations of neurons involved in production of jaw movements and will serve as a cellular foundation for neuronal models on masticatory rhythm and burst pattern generation.