Whitehead M C, Frank M E
J Comp Neurol. 1983 Nov 10;220(4):378-95. doi: 10.1002/cne.902200403.
The sensory modalities of taste and touch, for the anterior tongue, are relegated to separate cranial nerves. The lingual branch of the trigeminal nerve mediates touch: the chorda tympani branch of the facial nerve mediates taste. The chorda tympani also contains efferent axons which originate in the superior salivatory nucleus. The central projections of these two nerves have been visualized in the hamster by anterograde labelling with horseradish peroxidase (HRP). Afferent fibers of the chorda tympani distribute to all rostral-caudal levels of the solitary nucleus. They synapse heavily in the dorsal half of the nucleus at its rostral extreme; synaptic endings are sparser and located laterally in caudal regions. These taste afferents travel caudally in the solitary tract and reach different levels by a series of collateral branches which extend medially in the the solitary nucleus, where they exhibit preterminal and terminal swellings. Taste afferent axons range in diameter from 0.2 micrometer to 1.5 micrometers. The thickest axons project exclusively to the rostral and intermediate subdivisions of the solitary nucleus; the find ones may distribute predominantly to the caudal subdivision. Afferent fibers of the lingual nerve terminate heavily in the dorsal one-third of the spinal nucleus of the trigeminal nerve and also as a dense patch in the lateral solitary nucleus at the midpoint between its rostral and caudal poles. This latter projection overlaps that of the chorda tympani. Thus the two sensory nerves which subserve taste and touch from coincident peripheral fields on the tongue converge centrally on the intermediate subdivision of the solitary nucleus. Efferent neurons of the superior salivatory nucleus were labelled retrogradely following application of HRP to the chorda tympani. These cells are located ipsilaterally in the medullary reticular formation ventral to the rostral pole of the solitary nucleus; their dendrites are oriented dorsoventrally. The efferent axons course dorsally, form a genu lateral to the facial somatomotor genu, and course ventrolaterally through the spinal nucleus of the trigeminal nerve to exit the brain ventral to the entering facial afferents.
对于舌前部而言，味觉和触觉这两种感觉形式由不同的脑神经负责。三叉神经的舌支介导触觉，面神经的鼓索支介导味觉。鼓索还包含起源于上泌涎核的传出轴突。通过用辣根过氧化物酶（HRP）进行顺行标记，已在仓鼠中观察到这两条神经的中枢投射。鼓索的传入纤维分布于孤束核的所有头-尾水平。它们在孤束核头端的背侧半部大量形成突触；在尾侧区域，突触末梢较稀疏且位于外侧。这些味觉传入纤维沿孤束向尾侧走行，并通过一系列向孤束核内侧延伸的侧支到达不同水平，在那里它们呈现终末前和终末膨大。味觉传入轴突的直径范围为0.2微米至1.5微米。最粗的轴突仅投射到孤束核的头端和中间亚区；较细的轴突可能主要分布到尾侧亚区。舌神经的传入纤维大量终止于三叉神经脊束核的背侧三分之一处，并且在孤束核头端和尾端中点的外侧孤束核中形成一个密集区。后一种投射与鼓索的投射重叠。因此，这两条分别负责舌上味觉和触觉的感觉神经在中枢汇聚于孤束核的中间亚区。将HRP应用于鼓索后，对上泌涎核的传出神经元进行了逆行标记。这些细胞位于孤束核头端腹侧的同侧延髓网状结构中；它们的树突呈背腹向排列。传出轴突向背侧走行，在面神经躯体运动膝的外侧形成一个膝状弯曲，然后通过三叉神经脊束核向腹外侧走行，在进入的面神经传入纤维的腹侧离开脑。
