Effects of afferent signals from the extraocular muscles upon units in the cerebellum, vestibular nuclear complex and oculomotor nucleus of the trout

The responses of single units in the cerebellum, the vestibular nuclear complex and adjacent regions of the brainstem and in the oculomotor nucleus were studied in decerebrate, paralysed rainbow trout (Salmo gairdneri). Natural vestibular stimulation was provided by horizontal, sinusoidal oscillation of the fish and extraocular muscle afferents of the eye ipsilateral to the recording were activated either by passive eye-movement or by electrical stimulation of the trochlear (IV) nerve in the orbit. Unit responses to vestibular and/or orbital stimuli were examined in peristimulus-time histograms interleaved in time. In the cerebellum and brainstem, of 124 units exposed to both types of stimulus, 26 (21%) responded only to vestibular input, 26 (21%) were affected only by the orbital signal and 23 (18%) received both signals. The remaining 49 units (39%) responded to mechanical stimulation of the head or body or to vibration; they were labelled "polymodal" and discarded. The recording sites of 56 units were verified by histology; 30 were in the cerebellum and 26 in the brainstem. Input from the eye muscles had excitatory or inhibitory effects upon the vestibular responses. The effects of the orbital signal were usually phasic but rare tonic responses also occurred. About half (15 of 34) of the units which responded to passive eye-movement showed statistically significant differences in the magnitude of their responses to horizontal and to vertical eye-movement. More units preferred horizontal movement (11) than preferred vertical passive eye-movement (four). Note that the plane of vestibular stimulation was always horizontal. In the region of the oculomotor nucleus, of 19 units, five (26%) gave vestibular responses only and three (16%) were affected only by the orbital signal; three units (16%) with polymodal responses were discarded. Of the eight units carrying both signals, histological confirmation that the recording site lay in the column of cells forming the oculomotor/trochlear nuclei was obtained in four. The responses and interactions were similar to those found in the brainstem. The results present two principal points of interest. 1. They reinforce the accumulating body of evidence that, in species with widely different oculomotor and visual behaviour, signals from extraocular muscle proprioceptors reach the vestibulo-ocular system; this, in turn, suggests that these signals may play some rather fundamental role in the oculomotor system.(ABSTRACT TRUNCATED AT 400 WORDS)     

Directionally-specific effects of afferent signals from the extraocular muscles upon responses in the pigeon brainstem to horizontal vestibular stimulation

The responses of single units in the brainstem of the decerebrate, paralysed, pigeon were studied. Natural vestibular stimulation was provided by horizontal, sinusoidal, oscillation of the bird and extraocular muscle afferents of the ipsilateral eye were activated by passive eye-movement. Unit responses to vestibular and/or orbital stimuli were examined in sets of peristimulus time histograms interleaved in time. Of 352 units in the brainstem, in the region of the vestibular nuclei, which were exposed to the effects of both vestibular stimuli and passive eye-movement, 40 (11%) responded only to the latter; the other 312 units (89%) responded to vestibular stimulation at 0.4 Hz (amplitude +/- 8 degrees). Of these 312 units, 129 (41%) were affected only by vestibular stimuli; in the other 183 units (59%) passive eye-movement produced clear modification of the vestibular responses by adding excitation or inhibition, or both. There were phasic modifications in most units; in 77 there were longer-lasting changes in the vestibular responses, often following a phasic response. In 124 units whose responses were subjected to statistical analysis, the vestibular responses of 42 (34%) were modified only by horizontal eye-movement and eight (6%) were affected only by vertical movement. A further 18% showed larger effects from horizontal than from vertical eye-movement; in 2% vertical eye-movement was preferred. Further examination of the specificity of the effects of eye-movement in planes between the vertical and horizontal was possible in 29 units which showed various degrees of "tuning" of the effect. In some units there was additional specificity for eye-movement in (a) particular directions (towards the beak rather than towards the tail, for example); (b) in particular arcs of the orbit (centre-to-temporal rather than nasal-to-centre, for example). Note that all these effects were upon the responses of the units to horizontal vestibular stimulation. Thus, the modifications of the vestibular responses depended upon specific characteristics of the passive eye-movement. The exact recording sites of 29 units were determined histologically; some were in the medial vestibular nucleus but many were in the adjacent reticular formation. The principal interest of the results is that they provide more detailed information than was available previously on the specificity of the effects of afferent signals from the extraocular muscles upon the vestibular responses of units in regions of the brainstem known to be involved in oculomotor control. The decerebrate pigeon proves to be a particularly good preparation in which to study these effects.(ABSTRACT TRUNCATED AT 400 WORDS)     

Input from proprioceptors in the extrinsic ocular muscles to the vestibular nuclei in the giant toad,Bufo marinus

Summary Extracellular unit records were made from the left brain stem of decerebrate, paralysed giant toads (Bufo marinus) during passive movement of the ipsilateral eye. Units in the vestibular nuclear complex (VN) were identified by their short-latency responses to electrical stimulation of the anterior branch of the ipsilateral VIII cranial nerve.Of 58 units in the region of VN, as judged from field potentials to VIII nerve stimulation, fourteen gave phasic excitatory responses to passive movement of the eye and were also identified as vestibular nuclear units. A further twelve units which responded to eye-movement could not be assigned to VN; the remaining 32 units were in VN but did not respond to passive eye-movement. Also, of 16 units whose recording sites were identified histologically in the VN complex, 11 gave responses to vestibular nerve stimulation and to passive eye-movement and 5 responded to eye-movement only.Control experiments eliminated auditory, visual and cutaneous sources for the signal produced by passive eye-movement; thus, the signal must have arisen from intraorbital proprioceptors. Units in VN were also found which were excited by electrical stimulation of the intraorbital part of the fourth (trochlear) nerve; this provides strong evidence that proprioceptors in the extrinsic ocular muscles (EOM) are included in the receptors which provide the signal to VN during passive eye-movement.The effects of vestibular stimulation and of passive eye-movement were found to interact upon units in VN. When passive eye-movement and vestibular stimulation were paired the response to the second stimulus was significantly reduced over a range of interstimulus intervals.The conclusions are that orbital proprioceptive signals, including those from the EOM, project to the vestibular nuclei in the toad and, there, are able to influence processing of vestibular afferent signals. We suggest, therefore, that orbital proprioceptive signals may play a part in oculomotor control. The significance of the results is discussed in relation to the strategic position of the VN in the oculomotor control system.     

Vestibular projections to the nucleus intercalatus of Staderini mapped by retrograde transport of horseradish peroxidase

Medullary afferent projections to the nucleus intercalatus of Staderini have been studied by retrograde transport of horseradish peroxidase (HRP) from highly localized injections. This nucleus receives afferent projections particularly from the medial and descending vestibular nuclei as well as from the nucleus praepositus hypoglossi of both sides. The nucleus intercalatus of Staderini represents therefore an area of integration for the vestibular systems of both sides.     

大鼠动眼神经核的传入结构联系

目的：观察大鼠动眼神经核传入纤维的来源和特征。方法：采用ＨＲＰ标记法对２０只大鼠动眼神经核进行了逆行追踪研究。结果：脑干到动眼神经核的投射主要来源有同侧的舌下前置核;对侧的展神经核,脑桥尾侧网状核,Ｃａｊａｌ Ｄａｒｋｓｃｈｅｗｉｔｓｃｈ核,中脑网状核。结论：展神经核、前庭神经核、舌下前置核和网状结构是眼水平运动相关的直接运动前结构,它们的损伤都会影响两眼水平协同运动,但展神经核核间神经元起着最重     

Physiological and behavioral identification of vestibular nucleus neurons mediating the horizontal vestibuloocular reflex in trained rhesus monkeys.

1. To describe in detail the secondary neurons of the horizontal vestibuloocular reflex (VOR), we recorded the extracellular activity of neurons in the rostral medial vestibular nucleus of alert, trained rhesus monkeys. On the basis of their activity during horizontal head and eye movements, neurons were divided into several different types. Position-vestibular-pause (PVP) units discharged in relation to head velocity, eye velocity, eye position, and ceased firing during some saccades. Eye and head velocity (EHV) units discharged in relation to eye velocity and head velocity in the same direction so that the two signals partially canceled during the VOR. Two cell types discharged in relation to eye position and velocity but not head velocity; other types discharged in relation to head velocity only. 2. The position in the neural path from the primary vestibular afferents to abducens motoneurons was examined for each type. Direct input from the vestibular nerve was indicated if the cell could be activated by shocks to the nerve at latencies less than or equal to 1.4 ms. A projection to abducens motoneurons was indicated if spike-triggered averaging of lateral rectus electromyographic (EMG) activity yielded responses with a sharp onset at monosynaptic latencies. 3. PVP neurons were the principal interneuron in the VOR "three-neuron arc." Eighty percent received primary afferent input, and 66% made excitatory connections with contralateral abducens motoneurons. Surprisingly few, approximately 11%, made inhibitory connections with ipsilateral abducens motoneurons. This imbalance in the ipsi- and contralateral projections was confirmed by measuring the EMG activity evoked by electrical microstimulation in regions where PVP neurons were located. 4. EHV neurons whose activity increased during contralaterally directed head or eye movements were also interneurons in the ipsilateral inhibitory pathway. Eighty-nine percent received ipsilateral primary afferent input, and 25% projected to ipsilateral abducens motoneurons. EHV neurons excited during ipsilateral movements received neither direct primary afferent input nor projected to either abducens nucleus. A small proportion of each of two other cell types having sensitivity to contralateral eye position made excitatory connections with contralateral abducens motoneurons. Other types rarely were activated from the eighth nerve or projected to the abducens nucleus. 5. The significance of the connections of VOR interneurons and the signals they convey is discussed for three situations: smooth pursuit of a moving target, suppression of the VOR, and the VOR itself. PVP neurons convey a signal with a ratio of eye position and velocity components that is inappropriate to drive motoneurons during pursuit or the VOR.(ABSTRACT TRUNCATED AT 400 WORDS)     

Discharge patterns in nucleus prepositus hypoglossi and adjacent medial vestibular nucleus during horizontal eye movement in behaving macaques.

1. Monkeys were trained to perform a variety of horizontal eye tracking tasks designed to reveal possible eye movement and vestibular sensitivities of neurons in the medulla. To test eye movement sensitivity, we required stationary monkeys to track a small spot that moved horizontally. To test vestibular sensitivity, we rotated the monkeys about a vertical axis and required them to fixate a target rotating with them to suppress the vestibuloocular reflex (VOR). 2. All of the 100 units described in our study were recorded from regions of the medulla that were prominently labeled after injections of horseradish peroxidase into the abducens nucleus. These regions include the nucleus prepositus hypoglossi (NPH), the medial vestibular nucleus (MVN), and their common border (the "marginal zone"). We report here the activities of three different types of neurons recorded in these regions. 3. Two types responded only during eye movements per se. Their firing rates increased with eye position; 86% had ipsilateral "on" directions. Almost three quarters (73%) of these medullary neurons exhibited a burst-tonic discharge pattern that is qualitatively similar to that of abducens motoneurons. There were, however, quantitative differences in that these medullary burst-position neurons were less sensitive to eye position than were abducens motoneurons and often did not pause completely for saccades in the off direction. The burst of medullary burst position neurons preceded the saccade by an average of 7.6 +/- 1.7 (SD) ms and, on average, lasted the duration of the saccade. The number of spikes in the burst was well correlated with saccade size. The second type of eye movement neuron displayed either no discernible burst or an inconsistent one for on-direction saccades and will be referred to as medullary position neurons. Neither the burst-position nor the position neurons responded when the animals suppressed the VOR; hence, they displayed no vestibular sensitivity. 4. The third type of neuron was sensitive to both eye movement and vestibular stimulation. These neurons increased their firing rates during horizontal head rotation and smooth pursuit eye movements in the same direction; most (76%) preferred ipsilateral head and eye movements. Their firing rates were approximately in phase with eye velocity during sinusoidal smooth pursuit and with head velocity during VOR suppression; on average, their eye velocity sensitivity was 50% greater than their vestibular sensitivity. Sixty percent of these eye/head velocity cells were also sensitive to eye position. 5. The NPH/MVN region contains many neurons that could provide an eye position signal to abducens neurons.(ABSTRACT TRUNCATED AT 400 WORDS)     

Vestibular projections to the nuclei of the extraocular muscles Degeneration resulting from discrete partial lesions of the vestibular nuclei in the monkey

In 35 monkeys attempts were made to produce localized unilateral lesions in individual vestibular nuclei in order to study vestibular projections to nuclei of the extraocular muscles. Portions of the medial, superior and inferior vestibular nuclei were destroyed selectively; lesions in Deiters' nucleus involved small portions of either the superior or inferior vestibular nuclei. Fiber degeneration was studied by the Nauta-Gygax technic. Exclusively ascending fibers from the superior vestibular nucleus project to ipsilateral extraocular nuclei. Ascending fibers from the inferior vestibular arise only from rostral portions of the nucleus, are not numerous and pass to all extraocular nuclei. The medial vestibular nucleus projects ascending fibers via the MLF bilaterally, asymmetrically and differentially to all extraocular nuclei. Prominent projections pass to: (a) the contralateral trochlear nucleus, and (b) the contralateral intermediate cell column and the ipsilateral ventral nucleus of the oculomotor complex. Ascending fibers from Deiters' nucleus, arising only from ventral portions of the nucleus, project primarily to: (a) the contralateral abducens and trochlear nuclei, and (b) specific asymmetrical portions of the oculomotor complex. Ascending vestibular fibers from the medial and lateral vestibular nuclei appear capable of mediating all patterned eye movements resulting from stimulation of ampullary nerves from individual semicircular canals. Vestibular projections to nuclei of the extraocular muscles are most abundant to those nuclei innervating muscles whose primary functions concern horizontal and rotatory eye movements.     

Evidence for corrective effects of afferent signals from the extraocular muscles on single units in the pigeon vestibulo-oculomotor system

The role of extraocular muscle (EOM) afferent feedback signals in the control of eye movement is still controversial. We recorded from 106 single units in the vestibular nuclei, oculomotor nuclei and reticular formation of 80 decerebrate, paralysed pigeons. EOM afferents were stimulated by passive eye movement (PEM) during vestibular stimulation by sinusoidal oscillation in the horizontal plane. We found that EOM afferent signals profoundly modified the vestibular responses of 91 (86%) of the single units recorded. As well as using PEM to simulate eye movements similar to saccades, we moved the eye in a manner which mimicked the slow phase of the vestibulo-ocular reflex (artificial VOR, AVOR). We have found evidence that, as well as providing signals closely related to the parameters of eye movement, PEM alters the vestibular responses of cells during AVOR in a manner which suggests that EOM afferent signals may play a corrective role in the moment-to-moment control of eye movement in the vestibulo-ocular reflex.     

Behavior of reticular,vestibular and prepositus neurons terminating in the abducens nucleus of the alert cat

Summary The activity of pontomedullary reticular, vestibular, and prepositus neurons has been recorded in the alert cat during spontaneous and vestibular-induced eye movements. Neurons were identified by their antidromic activation from the abducens nucleus. Spikes of these neurons were used to trigger the recording of field potentials in the abducens nucleus. The analysis by post-spike averaging of the field potentials showed the presence of a trifold system of reciprocal (excitatory and inhibitory) direct projections that originated in the above nuclei and terminated in the abducens nucleus with a distinctly graded effectiveness. This trifold afferent system is involved in the generation of fast eye movements, slow compensatory movements of vestibular origin, and eye fixation, respectively.     

Eye movement related activity and morphology of second order vestibular neurons terminating in the cat abducens nucleus

Summary Intracellular records were obtained from axons of second order vestibular neurons in, and around, the left abducens nucleus in alert cats implanted with stimulating electrodes on both vestibular nerves and the left VIth nerve. Twelve secondary vestibular neurons were identified by their increase in firing rate with horizontal head rotation to the left and/or increasing eye position to the right. Following HRP injection, somatic location, axonal trajectory and termination sites were determined. Each of the above cells collateralized extensively in the abducens nucleus in a fashion consistent with their being either inhibitory (n = 7; left) or excitatory (n = 6; right) vestibular neurons in the disynaptic horizontal vestibulo-ocular reflex pathway. These vestibular neurons also arborized extensively in other posterior brainstem eye-movement related areas as well as sending an axon to the spinal cord.This work was supported by CNRS, NS-13742, and EY-02007     

Abducens internuclear neurons carry an inappropriate signal for ocular convergence

1. Single-unit recording studies in alert Rhesus monkeys characterized the vergence signal carried by abducens internuclear neurons. These cells were identified by antidromic activation and the collision of spontaneous with antidromic action potentials. The behavior of abducens internuclear neurons during vergence was compared with that of horizontal burst-tonic fibers in the medial longitudinal fasciculus (MLF) and to that of a large sample of unidentified abducens cells (presumably both motoneurons and internuclear neurons). 2. The results indicate that abducens internuclear neurons and lateral rectus motoneurons behave similarly during vergence eye movements: the majority of both groups of cells decrease their firing rate for convergence eye movements: a minority show no change for vergence. This finding is strongly supported by recordings of horizontal burst-tonic fibers in the MLF, the majority of which decrease their activity significantly for convergence eye movements. 3. These findings indicate that a net inappropriate vergence signal is sent to medial rectus motoneurons via the abducens internuclear pathway. Because medial rectus motoneurons increase their activity appropriately during symmetrical convergence, this inappropriate MLF signal must be overcome by a more potent direct vergence input. 4. Overall, both abducens internuclear neurons and lateral rectus motoneurons decrease their activity for convergence less than would be expected based on their conjugate gain. This implies that some degree of co-contraction of the lateral and medial rectus muscles occurs during convergence eye movements. 5. Some horizontal burst-tonic MLF fibers decrease their activity more for convergence than any recorded abducens neuron. These fibers may arise from cells in the nucleus prepositus hypoglossi or vestibular nuclei.     

The fasciculus longitudinalis medialis in the lizard Varanus exanthematicus. 2. Vestibular and internuclear components

Summary In the present study the vestibular components of the fasciculus longitudinalis medialis (flm) were investigated in the lizard Varanus exanthematicus with various tracing techniques: anterograde transport of horseradish peroxidase to study vestibulo-oculomotor and vestibulospinal projections, the multiple retrograde fluorescent tracer technique for the cells of origin of such projections. Internuclear projections between the oculomotor and abducens nuclei could also be studied in this way.Rather extensive vestibulo-ocular projections passing via the flm were demonstrated. Mainly ipsilateral ascending projections arise in the dorsolateral vestibular nucleus, mainly contralateral ascending projections in the ventromedial vestibular nucleus and adjacent parts of the ventrolateral and descending vestibular nuclei. Furthermore, distinet bilateral ascending projections of the nucleus prepositus hypoglossi were demonstrated. Extensive vestibulospinal projections pass via the flm and form the medial vestibulospinal tract. This largely contralateral descending pathway arises predominantly in the ventromedial and descending vestibular nuclei. Terminal structures presumably arising in the ventromedial and descending vestibular nuclei were found on contralateral neurons, probably motoneurons innervating neck muscles.Vestibular neurons with both ascending (presumably to extra-ocular motoneurons) and descending projections to the spinal cord are present in all vestibular nuclei, although preferentially in the ventromedial vestibular nucleus and adjacent parts of the ventrolateral and descending vestibular nuclei. However, also in the dorsolateral vestibular nucleus a substantial number of double labeled neurons were found. These vestibular neurons with both vestibulomesencephalic and vestibulospinal projections are probably involved in combined movements of eyes and head.Evidence for reciprocal internuclear connections between the oculomotor and abducens nuclei was found. Neurons in the dorsal part of the oculomotor nucleus probably project to the ipsilateral abducens nucleus, while neurons in the abducens nucleus most likely project to the contralatcral oculomotor nucleus. These recpprocal internuclear connections between the oculomotor and abducens nuclei probably play an important role in conjugate horizontal eye movements.This investigation was supported in part by the Foundation for Medical Research FUNGO, which is subsidized by the Netherlands Organization for the Advancement of Pure Research (Z.W.O.).     

The time course of retrograde transsynaptic transport of tetanus toxin fragment C in the oculomotor system of the rabbit after injection into extraocular eye muscles

Summary The aim of this study was to determine the optimal survival time for labelling those neurons that monosynaptically terminate on extraocular motoneurons, i.e. the premotor neurons, after an injection of tetanus toxin fragment C, a retrograde transsynaptic tracer substance, into the eye muscle of the rabbit. Concentrated fragment C was injected into the inferior rectus or inferior oblique muscle and detected immunocytochemically in the brain after survival times of 8 h, 17 h, 2 d, 3 d, 4 d, 5 d, 6 d, 8 d and 12 d. Immunoreactivity was confined to granules within motoneuronal and premotor neuronal cell bodies, but became associated with punctate profiles outlining the somata with longer survival times. The strongest and most consistent labelling of premotor cell bodies was seen after 4 days survival time. The transsynaptic labelling pattern was shown to vary for individual premotor pathways.Abbreviations III oculomotor nucleus - IV trochlear nucleus - Vmes mesencephalic trigeminal nucleus - Vmt motor trigeminal nucleus - VI abducens nucleus - VIacc accessory abducens nucleus - VII facial nucleus - BC brachium conjunctivum, co cochlear nucleus - CR restiform body - d dentate nucleus - DAB diamino-benzidine-tetrahydrochloride - HRP horseradish peroxidase - iC interstitital nucleus of Cajal, iv inferior vestibular nucleus - lgn_d lateral geniculate nucleus dorsalis - lgn_v lateral geniculate nucleus ventralis - lv lateral vestibular nucleus - mgn medial geniculate nucleus - MLF medial longitudinal fasciculus - mv_p medial vestibular nucleus pars parvocellularis - mv_m medial vestibular nucleus pars magnocellularis (= ventral part of the lv) - NIII oculomotor nerve - NV trigeminal nerve - NVII facial nerve - NVIII vestibular nerve - PC posterior commissure - pg periaquaeductal grey - ppH nucleus praepositus hypoglossi - riMLF rostral interstitial nucleus of the medial longitudinal fasciculus - rn red nucleus - sc superior colliculus - sn substantia nigra - so superior olive - sv superior vestibular nucleus - sv_c superior vestibular nucleus contralateral - sv_i superior vestibular nucleus ipsilateral - TR tractus retroflexus - Y Y-group zi zona incerta     

Inhibitory connections of nystagmus-related reticular burst neurons with neurons in the abducens,prepositus hypoglossi and vestibular nuclei in the cat

Summary Action potentials of inhibitory burst neurons (IBNs) were extracellularly recorded in the pontomedullary reticular formation in the cat. These neurons were identified by their burst activity coincident with the quick inhibitory phase of the contralateral abducens nerve during vestibular nystagmus and by their antidromic activation from the contralateral abducens nucleus.During extracellular recording from the soma of single IBNs, another electrode for microstimulation was systematically tracked throughout the brain stem. For each IBN investigated, the effective sites for antidromic activation were invariably found in the contralateral abducens, prepositus hypoglossi, medial vestibular nuclei and the area ventral to the prepositus hypoglossi nucleus. Stimulation of neither the ipsilateral brain stem nor the oculomotor nuclei evoked antidromic responses in IBNs.Extracellular spikes of single IBNs and neurons in the overlying projection area were recorded simultaneously. Their correlation was examined by using peri-spike time histograms. Shortly after the spikes of single IBNs, the activity of motoneurons and internuclear interneurons in the abducens nucleus, and of type II neurons in the prepositus hypoglossi and vestibular nuclei, was depressed.Connections of IBNs with ipsilateral medial rectus motoneurons were studied by spike-triggered averaging of membrane potentials of the motoneurons and action potentials of the medial rectus nerve. Single IBN spikes induced a di- or polysynaptic disfacilitation in the motoneurons. This disfacilitation was concluded to be mediated by some of the above-described interneurons which were directly inhibited by IBNs. Their depressant effect on medial rectus motoneuronal spike activity was comparable to that on the spike activity of contralateral abducens motoneurons.     

Effects of electrode penetrations into the abducens nucleus of the monkey: eye movement recordings and histopathological evaluation of the nuclei and lateral rectus muscles

Two adult rhesus monkeys that had undergone 2 years of electrode penetrations into their abducens and vestibular nuclei, for chronic eye movement studies, were examined histologically. An analysis of their VIth nucleus neurons and lateral rectus muscles revealed the following. Twenty-two percent of the large neurons (30 µm in diameter), on average, were missing and extensive neuropil disruption and gliosis was evident in the experimental side abducens nuclei as compared with the control side in each animal. While the lateral rectus muscles showed small, but inconsistent, changes in total fiber number, the muscle fiber diameters were altered, leading to a more homogenous muscle and making the typical orbital and global subdivisions of the muscle less distinct. Eye movement records from before and after the electrophysiological studies were comparable. We discuss how the complex architecture of the extraocular muscles as well as the possibility of polyneuronal innervation of single muscle fibers could explain our results.     

Cerebellar afferent projections from the perihypoglossal nuclei: An experimental study with the method of retrograde axonal transport of horseradish peroxidase

Summary Details of cerebellar afferent projections from the perihypoglossal nuclei were studied in the cat by means of retrograde axonal transport of horseradish peroxidase (HRP). Labeled cells were observed bilaterally (with a preponderance ipsilaterally) in nuclei intercalatus and praepositus hypoglossi following injections in various folia of the entire vermis, paraflocculus, flocculus, fastigial nucleus, and the nucleus interpositus anterior and posterior. Relatively high densities of labeled cells were found in nucleus intercalatus following injections in the anterior part of the vermis, whereas labeled cells in nucleus praepositus hypoglossi were found more frequently following injections in the posterior part of the vermis. Labeled cells in the nucleus of Roller were found only following injections in the anterior lobe vermis, posterior vermal lobules VI and VII, in the flocculus and in the nucleus interpositus anterior. No labeled cells could be detected in the three subdivisions of the perihypoglossal nuclei following HRP injections in crus I, crus II, paramedian lobule, and lateral cerebellar nucleus. The distribution of the HRP positive cells indicated the presence of a topographically organized projection from certain regions of the perihypoglossal nuclei to different parts of the cerebellum. The afferent and efferent connections of the perihypoglossal nuclei in relation to a functional role in eye and head movements are discussed.Abbreviations in Figures a,b,c sublobules of lobules V, VI and VII - f.apm. ansoparamedian fissure - f.icul. intraculminate fissure - f.in.cr. intercrural fissure - f.pc. preculminate fissure - f.pfl. parafloccular fissure - f.p.l. posterolateral fissure - f.ppd. prepyramidal fissure - f.pr. fissura prima - f.prc. precentral fissure - f.prc.a. precentral fissure a - f.p.s. posterior superior fissure - f.sec. fissura secunda - fl. flocculus - g.n. VII genu of facial nerve - HII-HVI, HIX hemispheral lobules II–VI, IX - HVIIA cr.Ia,p; cr.IIa,p anterior and posterior folia of crus I and II of the ansiform lobule - HVIIB, HVIIIA,B sublobules A and B of hemispheral lobules VII and VIII - ic nucleus intercalatus - l.ans. ansiform lobule - N.f. nucleus fastigii - Nfc nucleus cuneatus - Nfg nucleus gracilis - N.i.a. nucleus interpositus anterior - N.i.p. nucleus interpositus posterior - N.l. nucleus lateralis - pfl.d. dorsal paraflocculus - pfl.v. ventral paraflocculus - Ph nucleus praepositus hypoglossi - Ro nucleus of Roller - S solitary tract - s.int.cr.1,2 intracrural sulcus 1 and 2 - SL lateral nucleus of the solitary tract - SM medial nucleus of the solitary tract - VIN inferior vestibular nucleus - VLD lateral vestibular nucleus, dorsal division - VMN medial vestibular nucleus - I-VI vermian lobules I–VI - VI nucleus of abducent nerve - VIIA,B; VIIIA,B anterior and posterior sublobules of lobules VII and VIII - IX uvula - X dorsal motor nucleus of vagus nerve; nodulus - XII nucleus of hypoglossal nerve Parts of this paper were presented at the Symposium Control of Gaze by Brain Stem Neurons, Paris, July 13–15, 1977On leave from the Laboratory of Neurobiology, Faculty of Science, Mahidol University, Bangkok, Thailand, under NORAD Fellowship Program from the Norwegian Agency for International Development     

Discharge dynamics of oculomotor neural integrator neurons during conjugate and disjunctive saccades and fixation

Burst-tonic (BT) neurons in the prepositus hypoglossi and adjacent medial vestibular nuclei are important elements of the neural integrator for horizontal eye movements. While the metrics of their discharges have been studied during conjugate saccades (where the eyes rotate with similar dynamics), their role during disjunctive saccades (where the eyes rotate with markedly different dynamics to account for differences in depths between saccadic targets) remains completely unexplored. In this report, we provide the first detailed quantification of the discharge dynamics of BT neurons during conjugate saccades, disjunctive saccades, and disjunctive fixation. We show that these neurons carry both significant eye position and eye velocity-related signals during conjugate saccades as well as smaller, yet important, "slide" and eye acceleration terms. Further, we demonstrate that a majority of BT neurons, during disjunctive fixation and disjunctive saccades, preferentially encode the position and the velocity of a single eye; only few BT neurons equally encode the movements of both eyes (i.e., have conjugate sensitivities). We argue that BT neurons in the nucleus prepositus hypoglossi/medial vestibular nucleus play an important role in the generation of unequal eye movements during disjunctive saccades, and carry appropriate information to shape the saccadic discharges of the abducens nucleus neurons to which they project.     

Loss of the neural integrator of the oculomotor system from brain stem lesions in monkey

Eye movement were recorded from four juvenile rhesus monkeys (Macaca mulatta) before and after the injection of neurotoxins (kainate or ibotenate) in the region of the medial vestibular and prepositus hypoglossi nuclei, an area hypothesized to be the locus of the neural integrator for horizontal eye movement commands. Eye movements were measured in the head-restrained animal by the magnetic field/eye-coil method. The monkeys were trained to follow visual targets. A chamber implanted over a trephine hole in the skull permitted recordings to be made in the brain stem with metal microelectrodes. The abducens nuclei were located and used as a reference point for subsequent neurotoxin injections through cannulas. The effects of these lesions on fixation, vestibuloocular and optokinetic responses, and smooth pursuit were compared with predicted oculomotor anomalies caused by a loss of the neural integrator. Kainate and ibotenate did not create permanent lesions in this region of the brain stem. All the eye movements returned toward normal over the course of a few days to 2 wk. Histological examination revealed that the cannula tips were mainly located between the vestibular and prepositus hypoglossi nuclei, in their rostral 2 mm, bordered rostrally by the abducens nuclei. Dense gliosis clearly demarcated the cannula tracks, but for most injections there were no surrounding regions of neuronal loss. Thus the eye movement disorders were due to a reversible, not a permanent, lesion. The time constant for the neural integrator was determined from the velocity of the centripetal drift of the eyes just after an eccentric saccade in total darkness. For intact animals this time constant was greater than 20 s. Shortly after bilateral injections of neurotoxin, the time constant began to decrease and reached a minimum of 200 ms; every horizontal saccade was followed by a rapid centripetal drift with a time constant of approximately 200 ms. For vertical eye movements, in this acute phase, the time constant was approximately 2.5 s. The vestibuloocular reflex (VOR) was drastically changed by the lesions. A step of constant head velocity in total darkness evoked a step change in eye position rather than in velocity. In the absence of the neural integrator, the step velocity command from the canal afferents was not integrated to produce a ramp of eye position (normal slow phases); rather this signal was relayed directly to the motoneurons and caused a step in eye position. The per- and postrotatory decay of the head velocity signal was decreased to 5-6 s indicating that vestibular velocity storage was also impaired.(ABSTRACT TRUNCATED AT 400 WORDS)     

Neck proprioceptive inputs to primate vestibular nucleus neurons

The contribution of neck proprioceptive signals to signal processing in the vestibular nucleus was studied by recording responses of secondary horizontal canal-related neurons to neck rotation in the squirrel monkey. Responses evoked by passive neck rotation while the head was held stationary in space were compared with responses evoked by passive whole body rotation and by forced rotation of the head on the trunk. Most neurons (76%; 45/59) were sensitive to neck rotation. The nature and strength of neck proprioceptive inputs varied and usually combined linearly with vestibular inputs. In most cases (94%), the direction of the neck proprioceptive input was "antagonistic" or "reciprocal" with respect to vestibular sensitivity and, consequently, reduced the vestibular response during head-on-trunk rotation. Different types of vestibular neurons received different types of proprioceptive input. Neurons whose firing behavior was related to eye position (position-vestibular-pause neurons and position-vestibular neurons) were often sensitive to the position of the head with respect to the trunk. The sensitivity to head position was usually in the same direction as the neuron's eye position sensitivity. Non-eye-movement related neurons and eye-head-velocity neurons exhibited the strongest sensitivity to passive neck rotation and had signals that were best related to neck velocity. The results suggest that neck proprioceptive inputs play an important role in shaping the output of the primate vestibular nucleus and its contribution to posture, gaze and perception.