5-羟色胺免疫阳性纤维和终末在大鼠舌下神经伸、缩舌肌运动神经元的分布

5-羟色胺（5－HT）参与舌和面口部精细运动的调节。5－HT对舌下神经运动神经元功能的调控表现为兴奋性作用。本文首先采用免疫组化方法，在光镜下观察了大鼠舌下神经核内5－HT免疫阳性纤维的形态和分布特征。又进一步采用荧光逆行追踪结合固定脑片细胞内LuciferYellow染色和荧光免疫组织化学染色，通过共聚焦激光扫描显微镜观察了伸舌肌（颏舌肌、颏舌骨肌）和缩舌肌（茎突舌肌）运动神经元与5－HT免疫阳性纤维及其终末的解剖学关系。结果证明：舌下神经核有较丰富的5－HT阳性纤维，以尾侧段的背侧部和吻侧段的腹侧部较为密集；根据纤维及其膨体的形态特征，本文将此阳性纤维分为三种类型。5－HT免疫阳性膨体样纤维及其终末与舌下运动神经元的胞体、树突分枝和轴丘及轴突起始段形成紧密接触；这些接触多呈不均匀的簇状（由2～7个紧密接触点组成）分布。定量分析发现：在额舌肌神经元和茎突舌肌神经元，除少量分布在胞体（密度为3．4～6．7／1000μm2）外，主要分布在近段和中段树突分权处附近；但是在颏舌骨肌神经元则集中分布在跑体（密度为10．8～17．6／1000μm2）和近侧树突上。以上所见提示：5－HT对舌下神经核整体行为的调节在不同功能的亚核可能有所选择；5－HT调制舌下运动神经元兴奋性的方式可

DISTRIBUTION OF SEROTONERGIC APPOSITIONS ON PROTRUDOR AND RETRACTOR MOTONEURONS IN RAT HYPOGLOSSAL NUCLEUS:CONFOCAL LASER SCANNING MICROSCOPY

The hypoglossal nucleus, which innervates extrinsic and intrinsic musculature of tongue and controlls the elaborate and coordinated tongue movement is composed of ventral (protrudor) and dorsal (retractor) Compartments. There is strong evidence that serotonin is an important modulator on oro-facial activity and excitation of hypoglossal motoneurons.In the present study, we studied the topographic distribution of the serotonergic immunoreactivity in rat hypoglossal nucleusby means of PAP imm unohis toe hemis t ry, and re tractor motone urons us lug a comb ined method. This comb ined me thod inc I udedFast Blue retrograde labeling, intracelluar Lucifer Yellow staining fluorescent immunohistochemistry and con focal laser scanningmicroscopy.The main results were as follows: (1)The serotonergic immunoreactivity was preferentially distributed in dorsal part in caudal hypoglossal nucleus and ventral part in rostral ; (2) Many immunoreactive fibers were derived from caudal pole and coursed along rostrocaudal axis ; (3) Based on the shape and size of the serotonergic varicosities as well as intercourse fibers, three different types of 5-HT a-cons were observed at the light microscopic level: fine fiber with various varicosities, fine fiber with small spindle-like varicosities and coarse fiber with large varicosities ; (4) By simultaneously viewing the morphology of identified neurons with intracelluar staining and serotonergic immunoreactive fibers and terminals, the close appositions were found on the surface of soma, dendritic domain, as well as a-conal hillock in hypoglossal motoneurons ; (5) A similar distribution and density of close appositions were found on genioglossal and styloglossal motoneurons ; these appositions were commonly observed on dendrites 50～100 μm away from soma ; (6) In geniohyoid subdivision, most of the close appositions were found to be aggregated on the surface of soma and proximal dendrites.The results suggested the modulation of serotonin on activity of hypoglossal nucleus is carried out by different selective patterns in different subcompartments. Combined with studies of localization of serotonergic subreceptors on postsynaptic motoneuron, distribution of serotonergic immunoreactive apposition on soma, dendrites and axonal hillock possibly operated differentpostsynaptic mechanisms for excitation activity of hypoglossal motoneurons.