猫红核脊髓束的体部定位——HRP法研究

本实验用六只成年猫分别于其颈、腰膨大和胸髓的右侧灰质内注入 HRP 溶液,观察红核脊髓束的投射。猫的红核脊髓束绝大部分是交叉的,有明确的体部定位,即红核的背内侧部投射于颈膨大,腹外侧部投射于腰膨大,两者之间的神经原投射于胸髓。在颈、腰膨大的注射例中还在同侧红核内观察到少数标记细胞,即红核还发出少数纤维投射于同侧的颈、腰膨大。胸髓注射例在同侧红核内未见到标记细胞。红核脊髓束在成年猫至少可达腰_6节段。     

猫下脑干至脊髓颈膨大和腰膨大的纤维投射——HRP法研究

用猫10只,分别干其颈膨大或腰膨大的一侧全灰质或一侧后角内注射HRP,研究下脑干到脊髓颈、腰膨大的投射。我们发现下列核群有细胞发出纤维投射到脊髓: 1.网状结构:巨细胞核、延髓中央核腹侧亚核、脑桥尾侧网状核和头侧网状核有较多脊髓投射细胞。延髓中央核背侧亚核、小细胞网状核、外侧旁巨细胞核、旁正中网状核腹侧亚核及中脑楔形核也向脊髓发出少量投射。除延髓中央核和小细胞网状核主要投至后角外, 其余核主要投射到后角以前灰质。 2.中缝核:大中缝核、苍白中缝核、隐中缝核向颈、腰膨大发出投射。背侧中缝核仅投射到颈膨大后角以前灰质。 3.薄束核及楔束核:向同侧颈、腰膨大发出部分重叠的定位投射。 4.脑神经核:E-W核、动眼神经主核、三叉神经脊束核、孤束核及前庭内侧核、外侧核、脊核和上核,前庭核ι细胞群均有细胞向脊髓发出投射。在前庭外侧核内,标记细胞有体部定位排列。 5.蓝斑、蓝斑下核、旁结合臂外侧核及内侧核、Kolliker-Fuse核、疑后核;投射至两侧脊髓。 6.红核:大量标记细胞出现在对侧红核内。红核的腹外侧部细胞投射至腰膨大,背内侧部投射到颈膨大。 7.上丘及中脑水管旁灰质投射到颈膨大后角以前的灰质。     

大鼠脊髓向中央颈核和外侧颈核的投射——PHA-L顺行追踪研究

将菜豆白细胞凝集素(PHA-L)分别注入下颈髓、胸髓、腰髓和骶髓等不同脊髓节段,顺行追踪脊髓向中央颈核和外侧颈核的投射。观察结果表明,脊髓不同节段注入PHA-L,在中央颈核和外侧颈核均可见到标记末梢;比较各节段脊髓的投射分布,未能发现明显的定位关系。一侧脊髓灰质注入,在两侧中央颈核均观察到标记末梢,但主要见于同侧;外侧颈核的标记末梢仅见于同侧。结果提示,各节段脊髓均发出纤维投射到同侧中央颈核和外侧颈核。     

家兔前庭核与脊髓的联系——HRP法研究

将HRP注入家兔颈、胸或腰髓的一侧灰质内,追踪前庭四核内的逆行标记细胞和顺行标记终支。发现同侧外侧核内标记细胞数量甚多,且具有体部定位规律。内侧核及降核的尾段标记细胞也较多,内侧核者甚为密集,它们投射到双侧脊髓的颈、胸、腰段,对侧多于同侧,无体部定位关系。降核的头段及在此平面的内侧核内也有一定数量的标记细胞,也投射到颈、胸、腰髓,同侧为主,无体部定位关系。上核内只有极少量标记细胞,主要投射到对侧颈髓。顺行标记终支于降核、内侧核的见端小范围内及外侧核的尾端背面较为恒定,颈、腰注射例在降核和内侧核的尾端尤为密集。     

大鼠脊髓向中央颈核和外侧颈核的投射：PHA—L顺行追踪研究

将菜豆白细胞凝集素（ＰＨＡ－Ｌ）分别注入下颈髓，胸髓，腰髓和骶髓等不同脊髓节段，顺行追踪脊髓向中央颈核和外侧颈核的投射。观察结果表明，脊髓不同节段注入ＰＨＡ－Ｌ，在中央颈核和外侧颈核均可见到标记末梢，比较各节段脊髓的投射分布，未能发现明显的定位关系。一侧脊髓灰质注入，在两侧中央颈核均观察到标记末梢，但主要见于同侧；外侧颈核的标记末梢仅见于同侧。结果提示，各节段脊髓均发出纤维投射到同侧中央颈核和外侧     

大鼠小脑核到脊髓的投射——HRP法研究

向23只大鼠的颈、胸、腰、骶各段脊髓的一侧灰质内注射30％HRP(Sigma Ⅵ)水溶液0.3～2.0μl,TMB反应,观察了小脑核中标记细胞的分布。小脑核到脊髓的投射细胞主要位于小脑顶核的中部,对侧较多。标记细胞分布于顶核各部,但以腹外侧及内侧部较为密集。在顶核和间位核之间的部位(有小脑皮质前庭纤维经过)以及间位核后部内侧亦有较多标记细胞。两侧的齿状核中有少量标记细胞。小脑核细胞主要投射到颈髓上部(C_(3～4)),少量可达颈髓下部(C_(5～8))。胸髓以下未见有投射纤维。     

前庭神经核纤维与投射至纹状体的束旁核神经元的突触联系

目的：观察发自前庭神经内侧核的纤维末梢与投射至纹状体的丘脑束旁核神经元的突触联系。方法：采用15只Wistar大鼠，应用顺行和逆行标记技术，免疫组织化学和免疫电镜方法。结果：将CTb单侧注入纹状体，同时将BDA注入同侧的前庭神经内侧核。在束旁核发现了CTb标记神经元和BDA标记轴突终末，BDA标记纤维和终末存在于外侧束旁核整个长度的背侧2／3区，而CTb标记神经元也存在于外侧束旁核背侧2／3区，2种标记相互重叠。电镜下可见标记终末与标记神经元形成非对称性的轴-体和轴-树突触。结论：由前庭神经内侧核发出的投射纤维在束旁核与投射至纹状体的束旁核神经元之间存在着非对称性的突触联系。     

大鼠前庭神经核群向腰髓投射特征——BDA法逆行研究

目的　研究大鼠前庭神经核群向脊髓的投射纤维特征。方法　在 7例SD大鼠采用结合生物素的葡聚糖胺(BDA)逆行法观察大鼠前庭核群向脊髓的投射。结果　除前庭神经上核 (SVN)外的其余各前庭核均有向大鼠腰髓的投射 ,单侧注射的实验动物中 ,前庭神经内侧核 (MVN)、外侧核 (LVN)和降核 (DVN)的标记神经元可见于双侧 ,其中MVN和LVN的标记神经元以注射同侧占优势 ,而DVN标记神经元两侧数量基本一致。结论　大鼠前庭脊髓尾侧束发出纤维投向脊髓腰段     

猫网状脊髓束的起源和终止——HRP法研究

选猫10只,分别于颈膨大或腰膨大的一侧灰质或一侧后角内注射HRP,对网状脊髓束的起止进行了研究。发现网状脊髓束不仅起自延髓及脑桥内侧网状结构的大细胞部,还起于其外侧网状结构小细胞部,此外还有少量发自中脑网状结构。网状脊髓束不仅止于前角,还止于后角。网状脊髓束主要起自延髓及脑桥网状结构腹内侧区,其起源细胞在巨细胞网状核内为数最多,延髓中央核腹侧亚核次之,脑桥尾侧网状核更次之。在脑桥吻侧网状核,延髓旁正中网状核腹侧亚核、外侧旁巨细胞核及中脑楔形核内也有标记细胞。由以上核发出的纤维均投向脊髓两侧灰质。除楔形核只投向颈髓外,其余都投射到颈髓和腰髓。在延髓网状结构腹外侧及脑桥头端网状结构外侧各有一群标记细胞,其位置各与去甲肾上腺素能神经元A_1和A_7群相当。由脑干腹内侧网状结构发出的纤维大部分止于颈、腰膨大后角以前的灰质,但也有少量止于后角,这些联系为脑干网状结构内侧区提供了一条直接影响脊髓运动及感觉功能的通路。 Brodal用逆行细胞变性法证明旁正中网状核全部细胞投射到小脑“脊髓区”。我们在颈、腰膨大一侧灰质注射组的旁正中网状核腹侧亚核内也发现了一些标记细胞。可能这些细胞的轴突是分叉的,一支投射到小脑“脊髓区”,另一支投射到脊髓后角以前的灰质。这群细胞对脊髓与小脑的联系可能有特殊的作用。在一般认为是“接受区”的延桥网状结构背外侧区,相当于延髓中央核背侧亚核及小细胞网状核内,也发现了标记细胞,由此发出的纤维主要止于脊髓后角。推测此通路可能主要影响脊髓的感觉功能。因此,不应把脑干网状结构外侧区仅仅看成是网状结构的“接受区”。     

大鼠前庭脊核和X细胞群向脑桥核的直接投射

目的:应用菜豆白细胞凝集素(PHA-L)顺行追踪和荧光金(FG)逆行追踪技术研究前庭脊核和X细胞群向脑桥核的直接投射.方法:SD大鼠随机分为PHA-L注射组和FG注射组.将顺行神经追踪剂PHA-L电泳至前庭脊核和X细胞群,逆行神经追踪剂FG分别电泳至脑桥核的外侧亚核和内侧亚核,动物存活7 d,灌流固定后,脑干作冠状冷冻切片,然后进行免疫组织化学显色.结果:PHA-L注射于前庭脊核后,顺行标记纤维和终末主要分布在对侧脑桥核的外侧亚核、内侧亚核及脑桥网状被盖核;FG分别注射于脑桥核的外侧和内侧亚核后,逆行标记细胞仅分布在对侧前庭脊核和X细胞群.结论:前庭脊核和X细胞群向对侧脑桥核的外侧和内侧亚核有直接的纤维投射,该投射可能与前庭-眼反射的调节有关.     

Ipsilateral and contralateral projections from upper cervical segments to the vestibular nuclei in the rat

The present study examined uncrossed and crossed projections from upper cervical segments to the vestibular nuclei, and the relationship between the afferents and vestibulospinal neurons in the rat. Afferent axons were labeled following unilateral injections of biotinylated dextran into the C2 and C3 segments, while vestibulospinal neurons were labeled following unilateral injections of cholera toxin subunit B into the same segments. The terminals of uncrossed afferents were distributed in the entire area of the rostrocaudal extent of the lateral vestibular nucleus (LV). In the magnocellular part (MVmc) of the medial vestibular nucleus (MV), they were seen near the parvocellular part (MVpc) of the MV at caudal levels. In the MVpc, terminals were seen laterally and ventromedially, close to the border of the MVmc. At caudal levels of the caudal part (MVc) of the MV, they were distributed within the groups of labeled neurons in the middle and lateral areas. In the descending vestibular nucleus (DV), terminals were abundant dorsally and laterally in the rostral two-thirds. The distribution of contralateral cervical afferents was similar to that of ipsilateral afferents. The terminals of ipsilateral and contralateral cervical afferents were seen in contact with vestibulospinal neurons in the DV. The present study demonstrates bilateral input from upper cervical segments to the LV, DV, and all subdivisions of the MV. The input to the LV would contribute to the tonic neck reflex or cervicovestibulospinal reflex.     

Connections of Purkinje cell axons of lobule X with vestibulospinal neurons projecting to the cervical cord in the rat

Connections of Purkinje cell axons of lobule X (nodulus vermis) with vestibulospinal neurons have been demonstrated in the rat, by anterograde labeling of axons with biotinylated dextran (BD) injected into sublobule Xa and by retrograde labeling of neurons with cholera toxin subunit B (CTB) injected into cervical segments. Labeled terminals of Purkinje cell axons were numerous in the superior vestibular nucleus, the parvocellular (MVpc) and the caudal part (MVc) of the medial vestibular nucleus (MV), and group y. A limited number of labeled terminals were seen in the caudal part of the descending vestibular nucleus (DV). Occasional labeled terminals were seen in the lateral part of the lateral vestibular nucleus (LV) whereas few labeled terminals were seen in the magnocellular part of the MV (MVmc). Vestibulospinal neurons labeled from the C2 and C3 segments were seen bilaterally in the MVmc, MVpc, MVc, and DV, and ipsilaterally in the LV. CTB-labeled vestibulospinal neurons in contact with BD-labeled terminals of Purkinje cell axons were identified in the lateral part of the MVpc, near the border between the MVpc and MVmc, or close to the dorsal acoustic stria, and in the middle part of the MVc at its rostral level. The present study suggests that Purkinje cells of lobule X regulate the output of cervical-projecting vestibulospinal neurons in the MVpc and MVc.     

Secondary vestibulocerebellar projections to the flocculus and uvulo-nodular lobule of the rabbit: a study using HRP and double fluorescent tracer techniques

Summary The distribution of vestibular neurons projecting to the flocculus and the nodulus and uvula of the caudal vermis (Larsell's lobules X and IX) was investigated with retrograde axonal transport of horseradish peroxidase and the fluorescent tracers Fast Blue, Nuclear Yellow and Diamidino Yellow. The presence of collateral axons innervating the flocculus on one hand and the nodulus and uvula on the other was studied with simultaneous injection of the different fluorescent tracers. The distribution of vestibular neurons projecting to either flocculus or caudal vermis is rather similar and has a bilateral symmetry. The projection from the magnocellular medial vestibular nucleus is very sparse, while that from the lateral vestibular nucleus is absent. The majority of labeled neurons was found in the medial, superior, and descending vestibular nuclei, in that order. Double labeled neurons were distributed in a similar way as the single labeled ones. Labeled neurons project to the nodulus and uvula, the flocculus, and to both parts of the cerebellum simultaneously in a ratio of 12:4:1. Five different populations of vestibulocerebellar neurons can be distinguished on the basis of their projection to the: (1) ipsilateral flocculus, (2) contralateral flocculus, (3) ipsilateral flocculus and nodulus/uvula, (4) contralateral flocculus and nodulus/uvula, and (5) nodulus/uvula.Abbreviations bc brachium conjunctivum - CE external cuneate nucleus - cr restiform body - CO cochlear nuclei - DV descending vestibular nucleus - F fastigial nucleus - FL flocculus - flm medial longitudinal fascicle - gV vestibular ganglion - gVII facial genu - IN interstitial nucleus of the eight nerve - LV lateral vestibular nucleus - MVc caudal medial vestibular nucleus - MVmc magnocellular medial vestibular nucleus - MVpc parvocellular medial vestibular nucleus - NVpar parabrachial vestibular nucleus - nVII facial nerve - PH prepositus hypoglossal nucleus - rV descending root of the trigeminal nerve - S solitary tract and nucleus - sad dorsal acustic striae - SV superior vestibular nucleus - X group X - Y group Y - VI abducens nucleus     

Pathways and terminations of axons arising in the fastigial oculomotor region of macaque monkeys.

The majority of axons from the fastigial oculomotor region (FOR) decussated in the cerebellum at all rostrocaudal levels of the fastigial nucleus (FN) and entered the brainstem via the contralateral uncinate fasciculus (UF). Some decussated axons separated from the UF and ran medial to the contralateral superior cerebellar peduncle and ascended to the midbrain. Uncrossed FOR axons advanced rostrolaterally in the ipsilateral FN and entered the brainstem via the juxtarestiform body. The decussated fibers terminated in the brainstem nuclei that are implicated in the control of saccadic eye movements. In the midbrain, labeled terminals were found in the rostral interstitial nucleus of the medial longitudinal fasciculus, a medial part of Forel's H-field, the periaqueductal gray, the posterior commissure nucleus, and the superior colliculus of the contralateral side. In the pons and medulla, FOR fibers terminated in a caudal part of the pontine raphe, the paramedian pontine reticular formation, the nucleus reticularis tegmenti pontis, the dorsomedial pontine nucleus of the contralateral side, and the dorsomedial medullary reticular formation of both sides. In contrast, FOR projections to the vestibular complex were bilateral and were mainly to the ventral portions of the lateral and inferior vestibular nuclei. No labeled terminals were found in the following brainstem nuclei which are considered to be involved in oculomotor function: oculomotor and trochlear nuclei, interstitial nucleus of Cajal, medial and superior vestibular nuclei, periphypoglossal nuclei, and dorsolateral pontine nucleus. Labeling appeared in the red nucleus only when HRP encroached upon the posterior interposed nucleus.     

A direct projection from the medial vestibular nucleus to the cervical spinal dorsal horn of the rat, as demonstrated by anterograde and retrograde tracing

Summary Phaseolus vulgaris leucoagglutinin and wheat germ agglutinin-horseradish peroxidase were iontophoretically injected into different parts of the vestibular nuclear complex (VNC) of the rat. Injections centered into the caudal part of the medial vestibular nucleus revealed a vestibulospinal projection predominantly to the dorsal horn of the cervical spinal cord, besides the expected projection to the intermediate zone (IZ) and ventral horn (VH). While most of the anterogradely labelled fibres could be localized in laminae III to V, some scattered fibres were also seen in laminae I and VI. Lamina II remained free of labelling. The dorsal horn (DH) area with detectable anterograde labelling showed a rostrocaudal extension from C₁-C₆. Injections into other parts of the VNC labelled fibres and terminals in the IZ and VH while the DH remained almost free of labelling. Additionally, fluorogold and wheat germ agglutininhorseradish peroxidase were pressure- or iontophoretically injected at different levels into the spinal cord to confirm the projection to the dorsal horn by means of retrograde tracing. Labelled neurons in the area of the medial vestibular nucleus (MVN), from which anterograde labelling in the DH was obtained, were only detectable after fluorogold and wheat germ agglutinin-horseradish peroxidase injections into the cervical spinal cord, in particular its DH. This projection from the caudal medial vestibular nucleus to the dorsal horn of the cervical spinal cord probably enables the VNC to influence sensory processing in the DH, in addition to its well-established influence on posture and locomotion via projections to the intermediate zone and ventral horn.Abbreviations BSA bovine serum albumin - CuN cuneate nucleus - CCN central cervical nucleus - cMVN caudal medial vestibular nucleus - cVST caudal vestibulospinal tract - DAB diaminobenzidine - DH dorsal horn - DRG dorsal root ganglia - DVN descending vestibular nucleus - ECN external cuneate nucleus - FCS fetal calf serum - FG fluorogold - HRP horseradish peroxidase - icp inferior cerebellar peduncle - In intercalated nucleus - IZ intermediate zone - LVN lateral vestibular nucleus - LVST lateral vestibulospinal tract - mlf medial longitudinal fasciculus - MVN medial vestibular nucleus - MVST medial vestibulospinal tract - PHA-L Phaseolus vulgaris leucoagglutinin - PrH praepositus hypoglossi nucleus - rMVN rostral medial vestibular nucleus - Ro Roller's nucleus - SVN superior vestibular nucleus - TMB tetramethylbenzidine - VH ventral horn - VNC vestibular nuclear complex - WGAHRP wheat germ agglutinin-horseradish peroxidase - 12 hypoglossal nucleus Dedicated to Prof. J.W. Rohen on the occasion of his 70th birthday     

Descending projections from brainstem and sensorimotor cortex to spinal enlargements in the cat

Summary Single and double retrograde tracer techniques were employed in cats to investigate: (1) the topographical relationships between supraspinal neurons projecting to either the brachial or lumbosacral enlargement, (2) the distribution and relative frequency of single supraspinal neurons which project to both enlargements by means of axonal branching.In one group of cats large injections of horseradish peroxidase (HRP) were made throughout either the brachial or lumbosacral enlargement. The results from these experiments support recent observations on the multiplicity of brainstem centers giving origin to descending spinal pathways and provide evidence for a population of corticospinal neurons in area 6.In a second set of experiments, HRP was injected in one enlargement, and ³H-apo-HRP (enzymatically inactive) was injected in the other enlargement. Relatively large numbers of neurons with collateral projections to both enlargements (double-labeled) were observed in the medullary and pontine reticular formation, the medial and inferior vestibular nuclei bilaterally, the ipsilateral lateral vestibular nucleus, Edinger-Westphal nucleus, caudal midline raphe nuclei and nuclear regions surrounding the brachium conjunctivum. By contrast, double-labeled neurons were infrequently observed in the red nucleus and sensorimotor cortex, contralateral to the injections.In the red nucleus, lateral vestibular nucleus and sensorimotor cortex, neurons projecting to the brachial enlargement were largely segregated topographically from neurons projecting to the lumbosacral enlargement. However, there was some overlap, and double-labeled neurons were consistently observed within the region of overlap. In the sensorimotor cortex, the overlap between brachial- and lumbar-projecting neurons was most prominent in areas 4 and 3a, along the cruciate sulcus, but also involved other cytoarchitectonic regions in the medial aspect of the hemisphere.Abbreviations AM nucleus ambiguus - ap area postrema - aq aqueduct - BC brachium conjunctivum - ci central inferior nucleus of the raphe - cs central superior nucleus of the raphe - Cun cuneate nucleus - EC external cuneate nucleus - EW Edinger-Westphal nucleus - ETC central tegmental field - FTG gigantocellular tegmental field - FTL lateral tegmental field - FTM magnocellular tegmental field - FTP paralemniscal tegmental field - Gr gracile nucleus - IO inferior olive - K-F Kölliker-Fuse nucleus - LC nucleus locus coeruleus - li rostral linear nucleus of the raphe - LR lateral reticular nucleus - mlf medial longitudinal fasciculus - PAG periaqueductal gray - PbL lateral parabrachial nucleus - PG pontine gray - PON preolivary nucleus - ppr post-pyramidal nucleus of the raphe - RB restiform body - RNm red nucleus, magnocellular division - RNp red nucleus, parvocellular division - SC superior colliculus - SN substantia nigra - SOl lateral nucleus of the superior olive - SOm medial nucleus of the superior olive - Spin V spinal trigeminal nucleus - SubC nucleus subcoeruleus - TB trapezoid body - tb nucleus of the trapezoid body - trm tegmental reticular nucleus - VInf inferior vestibular nucleus - VLd lateral vestibular nucleus, dorsal division - VLv lateral vestibular nucleus, ventral division - VM medial vestibular nucleus - VSm superior vestibular nucleus, medial division Cranial Nerves and their Nuclei III oculomotor nucleus or nerve - V sensory nucleus of the trigeminal nerve - VI abducens nucleus - VII I facial nucleus, lateral part - VII m facial nucleus, medial part - X vagus nucleus - XII hypoglossal nucleus The research was supported by USPHS grants NS 12440 and MH 14277. ³H-apo-HRP was generously provided by New England Nuclear     

Projections from the lateral vestibular nucleus to the spinal cord in the mouse

The present study investigated the projections from the lateral vestibular nucleus (LVe) to the spinal cord using retrograde and anterograde tracers. Retrogradely labeled neurons were found after fluoro-gold injections into both the cervical and lumbar cord, with a smaller number of labeled neurons seen after lumbar cord injections. Labeled neurons in the LVe were found in clusters at caudal levels of the nucleus, and a small gap separated these clusters from labeled neurons in the spinal vestibular nucleus (SpVe). In the anterograde study, BDA-labeled fiber tracts were found in both the ventral and ventrolateral funiculi on the ipsilateral side. These fibers terminated in laminae 6–9. Some fibers were continuous with boutons in contact with motor neurons in both the medial and lateral motor neuron columns. In the lumbar and sacral segments, some collaterals from the ipsilateral vestibulospinal tracts were found on the contralateral side, and these fibers mainly terminated in laminae 6–8. The present study reveals for the first time the fiber terminations of the lateral vestibular nucleus in the mouse spinal cord and therefore enhances future functional studies of the vestibulospinal system.     

Properties of utricular nerve-activated vestibulospinal neurons in cats

The axonal pathway, conduction velocities, and locations of the cell bodies of utricular nerve-activated vestibulospinal neurons were studied in decerebrated or anesthetized cats using the collision test of orthodromic and antidromic spikes. For orthodromic stimulation, bipolar tungsten electrodes were placed on the utricular nerve and the other vestibular nerve branches were transected. Monopolar tungsten electrodes were positioned on both sides of the upper cervical segments (C2–4), caudal end of the cervical enlargement (C7-T1), and from the lower thoracic to the upper lumbar segments (T12-L3) and were used for antidromic stimulation of the spinal cord. Another monopolar electrode was also placed in the oculomotor nucleus to study whether utricular nerve-activated vestibulospinal neurons have ascending branches to the oculomotor nucleus. Of the 173 vestibular neurons orthodromically activated by the stimulation of the utricular nerve, 46 were second-order vestibulospinal neurons and 5 were third-order neurons. The majority of the utricular nerve-activated vestibulospinal neurons were located in the rostral part of the descending vestibular nucleus and the caudal part of the ventral lateral nucleus. Seventy-three percent of the utricular nerve-activated vestibulospinal neurons descended through the ipsilateral lateral vestibulospinal tract. Approximately 80% of these neurons reached the cervicothoracic junction, but a few reached the upper lumbar spinal cord. Twenty-seven percent of the utricular nerve-activated vestibulospinal neurons descended through the medial vestibulospinal tract or the contralateral vestibulospinal tracts. Those axons terminated mainly in the upper cervical segments. Almost none of the utricular nerve-activated vestibular neurons had ascending branches to the oculomotor nucleus.