Morphological and functional characteristics of motoneurons including facial motoneurons playing in mastication and swallowing.

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Mastication and swallowing are consisted of a series of contractions of several kinds of muscles. However it is still unclear how premotoneurons (preMo) controlling their target motoneurons are regulated for these movements. Therefore, in the first year, 2004,of this grant, we tried to reveal locations of the preMo and connection between these preMo and the cortical neurons. Adult rats were used. We revealed that preMo projecting to the trigeminal motor nucleus are located in the trigeminal oral (Vo) nucleus, the pontine lateral reticular formation where posterior digastic motoneurons and stylohyoid motoneurons exist, and that there are cortical neurons giving off their axon terminals in the trigeminal oral nucleus and the two parts of the reticular formation.In the second year,2005,of this grant, we tried to promote the study done in 2004,and revealed that there exist two kinds of Vo neurons which project ipsilaterally to either the jaw-closing or -opening motor nucleus, and that, in the Vo neurons with the ipsilateral projection, some neurons also project to the contralateral jaw-closing or -opening motor nucleus. Further, we revealed that the Vo neurons receive direct descending projections from neurons in the rostral part of the primary and secondary somatosensory cortex and that the descending projections are bilateral with a contralateral predominance.As described above, this study succeeded in producing a useful information of the central neuronal mechanisms of the swallowing and in contributing greatly to the progress of oral biology.