Analysis of neural mechanisms underlying coodination of jaw, tongue, lip and cheek movements

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Mastication is a highly coordinated movement of the jaw, tongue, lip and the cheek, in which food is hold by the tongue and cheek, and then food is crushed by the upper and lower jaws with closure of the lips. Motor commands for the coordinated movement patterns of the jaw, tongue, lip and the cheek are thought to be produced by the pattern generator for mastication ; however, the detail is not still clear. In the present study, we investigated regions in frontal brainstem slice preparation from neonatal rats where premotor neurons targeting for jaw-opening, jaw-closing and facial motoneurons were located, using voltage-sensitive dye, whole-cell patch-clamp recordings and laser photostimulation in order to examine the neural mechanisms underlying coordination of the movements of jaw and facial muscles. Electrical stimulation of the reticular formation located between the trigeminal motor nucleus and the facial nucleus elicited optical responses both in the trigeminal motor nucleus and the facial nucleus. Photostimulation of the reticular formation also evoked post synaptic currents (PSCs) in jaw-opening, jaw-closing and facial motoneurons; however, the region of which photostimulation evoked PSCs in these three kinds of motoneurons were different among them. These results suggest that premotor neurons targeting for jaw-opening, jaw-closing and facial motoneurons might be differentially located in the reticular formation between the trigeminal motor nucleus and the facial nucleus.