Minor L B, McCrea R A, Goldberg J M
Department of Pharmacological, University of Chicago, IL 60637.
Exp Brain Res. 1990;83(1):9-21. doi: 10.1007/BF00232188.
Recordings were made from secondary vestibular axons in the medial longitudinal fasciculus (MLF) of barbiturate-anesthetized squirrel monkeys. Antidromic stimulation techniques were used to identify the axons as belonging to one of three classes of neurons: vestibulo-oculo-collic (VOC) neurons project both to the extraocular motor nuclei and to the spinal cord; vestibulo-ocular (VO) neurons do not have a spinal projection; and vestibulocollic (VC) neurons do not have an oculo-motor projection. Galvanic stimulation was used to show that axons of all three classes received excitatory inputs from one labyrinth and inhibitory inputs from the other. VOC axons were confined to the MLF contralateral to the labyrinth from which they were excited. They made up more than half of the vestibular axons descending in the contralateral medial vestibulospinal tract (MVST), but less than one-quarter of those ascending in the contralateral MLF to the level of the oculomotor nucleus. Spinal projections were restricted to cervical segments with about half of the axons reaching segment C6. Conduction velocities, measured for C6-projecting axons, were similar for VOC and VC axons and were typically 25-50 m/s. Unlike the situation in the rabbit (Akaike et al. 1973) and cat (Akaike 1983), none of the MVST axons had conduction velocities greater than 75 m/s. The morphology of VOC neurons was studied by injection of horseradish peroxidase (HRP) into 60 physiologically identified axons in the MLF. Since individual axons were only stained for short distances, it was not possible to ascertain their complete branching patterns. Labeled fibers could be traced to an origin in and around the ventral lateral vestibular nucleus. This localization was confirmed by comparing the distributions within the vestibular nuclei of neurons retrogradely labeled from the upper cervical spinal cord (this study) and from the oculomotor nucleus (McCrea et al. 1987a; Highstein and McCrea 1988). VOC axons reached the contralateral MLF at the level of the abducens nucleus and immediately divided into an ascending and a descending, usually thicker, branch. Seven VOC axons could be traced to the extraocular motor nuclei; three terminated in the medial aspect of the oculomotor nucleus bilaterally and four terminated in the medial aspect of the contralateral abducens nucleus. The former axons may be part of a crossed, excitatory anterior-canal pathway; the latter, part of a similar horizontal-canal pathway. There were no terminations in the trochlear nucleus even though 12 labeled fibers passed close to it.(ABSTRACT TRUNCATED AT 400 WORDS)
在巴比妥麻醉的松鼠猴的内侧纵束（MLF）中，对次级前庭轴突进行了记录。采用逆向刺激技术将轴突鉴定为三类神经元之一：前庭眼脊髓（VOC）神经元既投射到眼外运动核，也投射到脊髓；前庭眼（VO）神经元没有脊髓投射；前庭脊髓（VC）神经元没有动眼神经投射。采用电刺激来表明，所有这三类轴突都接受来自一个迷路的兴奋性输入和来自另一个迷路的抑制性输入。VOC轴突局限于其受兴奋的迷路对侧的MLF。它们在对侧内侧前庭脊髓束（MVST）中下行的前庭轴突中占一半以上，但在对侧MLF中上行至动眼神经核水平的轴突中不到四分之一。脊髓投射仅限于颈段，约一半的轴突到达C6节段。对投射到C6的轴突测量的传导速度，VOC和VC轴突相似，通常为25 - 50米/秒。与兔（赤池等人，1973年）和猫（赤池，1983年）的情况不同，MVST的轴突传导速度均不大于75米/秒。通过将辣根过氧化物酶（HRP）注入MLF中60条经生理学鉴定的轴突来研究VOC神经元的形态。由于单个轴突仅在短距离内被染色，因此无法确定它们完整的分支模式。标记纤维可追溯到腹外侧前庭核及其周围的起源。通过比较从颈上段脊髓（本研究）和动眼神经核逆行标记的神经元在前庭核内的分布（麦克雷等人，1987a；海斯坦和麦克雷，1988年），证实了这种定位。VOC轴突在展神经核水平到达对侧MLF，并立即分成一个上行分支和一个下行分支，下行分支通常较粗。七条VOC轴突可追溯到眼外运动核；三条双侧终止于动眼神经核的内侧，四条终止于对侧展神经核的内侧。前者的轴突可能是交叉的兴奋性前半规管通路的一部分；后者是类似水平半规管通路的一部分。即使有12条标记纤维靠近滑车神经核，也没有在其中终止。（摘要截断于400字）
