Topographical Representation of Motoneurons in Carnivora Lower Brainstem

用辣根过氧化物酶（HRP）逆行标记法，观察了食虫性麝香鼩三叉神经支配肌肉的运动神经元的分布。三叉神经运动核（trigeminal motor nucleus，TMN）在细胞结构上大致可分为大背外侧区和小腹内侧区。在背外侧区，颞肌、咬肌和翼内肌的运动神经元分别位于背侧、中间和腹侧，翼外肌和腭帆张肌的运动神经元在内侧区的分布几乎相互重叠，只存在于核的吻侧半区。二腹肌前运动神经元和下颌舌骨前运动神经元分别位于腹内侧部的背侧和腹侧。鼓张肌运动神经元位于外侧丘系腹外侧的网状结构内。用HRP标记神经元，在解剖显微镜下观察神经元的数目和大小，并用盐酸咀嚼肌，计数肌纤维的数目。颞肌的平均肌纤维数与标记运动神经元的比值为322，咬肌336，翼内肌106，翼外肌78，二腹肌前肌136，下颌舌骨42，腭帆张肌29，鼓膜张肌3。

In the house musk shrew (insectivore), distribution of motoneurons of the trigeminal nerve innervating muscles was examined by a retrograde horseradish peroxidase (HRP) method. Cytoarchitectonically, the trigeminal motor nucleus (TMN) of the shrew was roughly divided into the large dorsolateral division throughout a whole rostrocaudal level of the nucleus, and small ventromedial divisions being in a caudal half of that. In the dorsolateral division, motoneurons of the temporal, masseter and medial pterygoid muscles were localized in dorsal, intermediate and ventral parts, respectively, and distribution are a of the lateral pterygoid and tensor veli palatini motoneurons were almost overlapped each other in the medial part which existed only at a rostral half of the nucleus. The anterior digastric and mylohyoid motoneurons situated respectively in the dorsal and ventral parts of the ventromedial division. The tensor tympani motoneurons was localized in the reticular formation near the lateral lemniscus ventrolateral to the nucleus. Additionaly, number and size of labeled neuron with HRP were measured, and number of muscle-fibers of each muscle was also counted by mascerarating muscle using hydrochloride under a dissection microscope. Ratio of mean muscle-fiber number to a labeled motoneuron of the temporal muscle was 322, masseter 336, medial pterygoid 106, lateral pterygoid 78, anterior digastric 136, mylohyoid 42, tensor veli palatini 29, tensor tympani 3.