Neuroscientific study of functional morphology in the craniofacial area

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The distribution of motoneurons of muscles innervated by the trigeminal nerve was examined using a retrograde horseradish peroxidase (HRP) method in the house musk shrew. The trigeminal motor nucleus of the shrew can be roughly divided into two divisions ; a dorsolateral division (DL) throughout the whole rostrocaudal level of the nucleus, and ventromedial division (VM) in the caudal half. In the DL division, motoneurons of the temporal, masseter and medial pterygoid muscles were localized in the dorsal, intermediate and ventral parts, respectively, and the distribution patterns of the lateral pterygoid and tensor veli palatini motoneurons almost overlapped with each other in the medial part which existed only in the rostral half of the nucleus. The anterior digastric and mylohyoid motoneurons were situated in the dorsal and ventral parts of the VM division, respectively. The tensor tympani motoneurons were localized in the reticular formation rostroventral to the nucleus. Number and s … More ize of neurons labeled with HRP were measured, and number of muscle fibers was also counted in macerated muscles using hydrochloric acid under a dissection microscope. The ratios of mean number of muscle fibers to labeled motoneurons were as follows : the temporal muscle, 322 ; masseter, 337 ; medial pterygoid, 110 ; lateral pterygoid, 79 ; anterior digastric, 137 ; mylohyoid, 42 ; tensor veli palatini, 30 and tensor tympani, 3. For comparison, topographical representation of the masticatory muscles in the nucleus was also reexamined in the rat.NHF-3beta protain, which play inportant role in mesodarm early development, appeared at different atages and parts between suncus and mouse. this matter suggests some spicies differences in the role of the protain.The twost-related gene, Bbtwist, which is a marker of the mesodarm in early development, was cloned in the lancelet species. Furthermore, the pattern in the expression of the mRNA of this gene in anterior structures was the same as in the Drosophila and vertebrate, and there was little species difference in the pattern. Less