Responses of the cerebellar fastigial neurones to tilt

Hindlimb movement modulates the activity of rostral fastigial nucleus neurons that process vestibular input

Integration of vestibular and proprioceptive afferent information within the central nervous system is a critical component of postural regulation. We recently demonstrated that labyrinthine and hindlimb signals converge onto vestibular nucleus neurons, such that hindlimb movement modulates the activity of these cells. However, it is unclear whether similar convergence of hindlimb and vestibular signals also occurs upstream from the vestibular nuclei, particularly in the rostral fastigial nucleus (rFN). We tested the hypothesis that rFN neurons have similar responses to hindlimb movement as vestibular nucleus neurons. Recordings were obtained from 53 rFN neurons that responded to hindlimb movement in decerebrate cats. In contrast to vestibular nucleus neurons, which commonly encoded the direction of hindlimb movement (81 % of neurons), few rFN neurons (21 %) that responded to leg movement encoded such information. Instead, most rFN neurons responded to both limb flexion and extension. Half of the rFN neurons whose activity was modulated by hindlimb movement received convergent vestibular inputs. These results show that rFN neurons receive somatosensory inputs from the hindlimb and that a subset of rFN neurons integrates vestibular and hindlimb signals. Such rFN neurons likely perform computations that participate in maintenance of balance during upright stance and movement. Although vestibular nucleus neurons are interconnected with the rFN, the dissimilarity of responses of neurons sensitive to hindlimb movement in the two regions suggests that they play different roles in coordinating postural responses during locomotion and other movements which entail changes in limb position.

Vestibulo-sympathetic responses

Evidence accumulated over 30 years, from experiments on animals and human subjects, has conclusively demonstrated that inputs from the vestibular otolith organs contribute to the control of blood pressure during movement and changes in posture. This review considers the effects of gravity on the body axis, and the consequences of postural changes on blood distribution in the body. It then separately considers findings collected in experiments on animals and human subjects demonstrating that the vestibular system regulates blood distribution in the body during movement. Vestibulosympathetic reflexes differ from responses triggered by unloading of cardiovascular receptors such as baroreceptors and cardiopulmonary receptors, as they can be elicited before a change in blood distribution occurs in the body. Dissimilarities in the expression of vestibulosympathetic reflexes in humans and animals are also described. In particular, there is evidence from experiments in animals, but not humans, that vestibulosympathetic reflexes are patterned, and differ between body regions. Results from neurophysiological and neuroanatomical studies in animals are discussed that identify the neurons that mediate vestibulosympathetic responses, which include cells in the caudal aspect of the vestibular nucleus complex, interneurons in the lateral medullary reticular formation, and bulbospinal neurons in the rostral ventrolateral medulla. Recent findings showing that cognition can modify the gain of vestibulosympathetic responses are also presented, and neural pathways that could mediate adaptive plasticity in the responses are proposed, including connections of the posterior cerebellar vermis with the vestibular nuclei and brainstem nuclei that regulate blood pressure.

Responses of rostral fastigial nucleus neurons of conscious cats to rotations in vertical planes

The rostral fastigial nucleus (RFN) of the cerebellum is thought to play an important role in postural control, and recent studies in conscious nonhuman primates suggest that this region also participates in the sensory processing required to compute body motion in space. The goal of the present study was to examine the dynamic and spatial responses to sinusoidal rotations in vertical planes of RFN neurons in conscious cats, and determine if they are similar to responses reported for monkeys. Approximately half of the RFN neurons examined were classified as graviceptive, since their firing was synchronized with stimulus position and the gain of their responses was relatively unaffected by the frequency of the tilts. The large majority (80%) of graviceptive RFN neurons were activated by pitch rotations. Most of the remaining RFN units exhibited responses to vertical oscillations that encoded stimulus velocity, and approximately 50% of these velocity units had a response vector orientation aligned near the plane of a single vertical semicircular canal. Unlike in primates, few feline RFN neurons had responses to vertical rotations that suggested integration of graviceptive (otolith) and velocity (vertical semicircular canal) signals. These data indicate that the physiological role of the RFN may differ between primates and lower mammals. The RFN in rats and cats in known to be involved in adjusting blood pressure and breathing during postural alterations in the transverse (pitch) plane. The relatively simple responses of many RFN neurons in cats are appropriate for triggering such compensatory autonomic responses.

Multimodal signal integration in vestibular neurons of the primate fastigial nucleus

The rostral fastigial nucleus contains vestibular neurons, which presumably are involved in spinal mechanisms (neck, gait, posture) and which are not modulated with individual eye movements. Single-unit recordings in the alert behaving monkey during natural stimulus conditions reveal that virtually all neurons demonstrate integration of several sensory inputs. This applies not only for canal-canal and canal-otolith interaction, but also for otolith-otolith interaction. There is also some evidence that most neurons receive not only an utriculus but also a sacculus input. Furthermore, most neurons also respond to large-field optokinetic stimulation, reflecting visual-vestibular interaction. Neurons are also affected by the head on trunk position, which would allow these neurons to operate in a body-centered rather than a head-centered reference frame. These complex, multisensory features could permit fastigial nucleus neurons to rather specifically affect spinal motor functions.

Central projections of the vestibular nerve: a review and single fiber study in the Mongolian gerbil

The primary purpose of this article is to review the anatomy of central projections of the vestibular nerve in amniotes. We also report primary data regarding the central projections of individual horseradish peroxidase (HRP)-filled afferents innervating the saccular macula, horizontal semicircular canal ampulla, and anterior semicircular canal ampulla of the gerbil. In total, 52 characterized primary vestibular afferent axons were intraaxonally injected with HRP and traced centrally to terminations. Lateral and anterior canal afferents projected most heavily to the medial and superior vestibular nuclei. Saccular afferents projected strongly to the spinal vestibular nucleus, weakly to other vestibular nuclei, to the interstitial nucleus of the eighth nerve, the cochlear nuclei, the external cuneate nucleus, and nucleus y. The current findings reinforce the preponderance of literature. The central distribution of vestibular afferents is not homogeneous. We review the distribution of primary afferent terminations described for a variety of mammalian and avian species. The tremendous overlap of the distributions of terminals from the specific vestibular nerve branches with one another and with other sensory inputs provides a rich environment for sensory integration.

Otolith processing in the deep cerebellar nuclei

To investigate the otolith contribution to the responses of "vestibular only" neurons in the rostral fastigial nucleus (FN), single-unit activity was recorded in the alert monkey with the head fixed during static and dynamic stimulation (+/- 15 deg, 0.06-1.4 Hz) around an earth-fixed horizontal axis. Head orientation could be altered allowing for roll, pitch, and intermediate planes of orientation. For the vast majority of neurons a response vector orientation (RVO) with an optimal response and a null-response at a head orientation 90 deg apart could be determined. Presumably more than 30% of the vestibular only neurons had an otolith input, as indicated by responses to static tilt, head-position-related activity, large phase changes (> 100 deg) of neuronal activity between 0.06 and 1.4 Hz, changes of the RVO at different frequencies and complex responses (spatio-temporal convergence). Thus, neurons in FN reflecting an otolith or a combined canal-otolith input are much more common than up to now thought. Vestibular-only neurons are most likely involved in vestibulospinal mechanisms. Their precise functional role has yet to be determined.

Rostral fastigial nucleus activity in the alert monkey during three-dimensional passive head movements

The fastigial nucleus (FN) receives vestibular information predominantly from Purkinje cells of the vermis. FN in the monkey can be divided in a rostral part, related to spinal mechanisms, and a caudal part with oculomotor functions. To understand the role of FN during movements in space, single-unit activity in alert monkeys was recorded during passive three-dimensional head movements from rostral FN. Seated monkeys were rotated sinusoidally around a horizontal earth-fixed axis (vertical stimulation) at different orientations 15 degrees apart (including roll, pitch, vertical canal plane and intermediate planes). In addition, sinusoidal rotations around an earth-vertical axis (yaw stimulus) included different roll and pitch positions (+/-10 degrees, +/-20 degrees). The latter positions were also used for static stimulation. One hundred fifty-eight neurons in two monkeys were modulated during the sinusoidal vertical search stimulation. The vast majority showed a uniform response pattern: a maximum at a specific head orientation (response vector orientation) and a null response 90 degrees apart. Detailed analysis was obtained from 111 neurons. On the basis of their phase relation during dynamic stimulation and their response to static tilt, these neurons were classified as vertical semicircular canal related (n = 79, 71.2%) or otolith related (n = 25; 22.5%). Only seven neurons did not follow the usual response pattern and were classified as complex neurons. For the vertical canal-related neurons (n = 79) all eight major response vector orientations (ipsilateral or contralateral anterior canal, posterior canal, roll, and nose-down and nose-up pitch) were found in Fn on one side. Neurons with ipsilateral orientations were more numerous and on average more sensitive than those with contralateral orientations. Twenty-eight percent of the vertical canal-related neurons also responded to horizontal canal stimulation. None of the vertical canal-related neurons responded to static tilt. Otolith-related neurons (n = 25) had a phase relation close to head position and were considerably less numerous than canal-related neurons. Except for pitch, all other response vector orientations were found. Seventy percent of these neurons responding during dynamic stimulation also responded during static tilt. The sensitivity during dynamic stimulation was always higher than during static stimulation. Sixty-one percent of the otolith-related neurons responded also to horizontal canal stimulation. These results show that in FN, robust vestibular signals are abundant. Canal-related responses are much more common than otolith-related responses. Although for many canal neurons the responses can be related to single canal planes, convergence between vertical canals but also with horizontal canals is common.

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.

The fastigial pressor response. Case report

A distinct vasomotor and cardioregulatory response first identified experimentally was elicited intraoperatively in a 6-year-old girl by local mechanical stimulation in the vicinity of the fastigial nucleus of the cerebellum. These findings are discussed in the light of current experimental knowledge of the anatomy and physiology of the fastigial pressor response.

Afferent and efferent connections of the oculomotor region of the fastigial nucleus in the macaque monkey

Afferent and efferent connections of the fastigial oculomotor region (FOR) were studied in macaque monkeys by using axonal transport of wheat germ agglutinin conjugated horseradish peroxidase (WGA-HRP). When injected HRP is confined to the FOR, retrogradely labeled cells appear in lobules VIc and VII of the ipsilateral vermis and in group b of the contralateral medial accessory olive (MAO). In reference to the maps of topographical organization, the extent of the effective site in the fastigial nucleus (FN) could be assessed from the distributions of labeled Purkinje cells (P cells) in the vermis and labeled olivary neurons in the MAO. In contrast to the unilateral nature of the P-cell and climbing-fiber projections, those from the other brainstem regions to the FOR were bilateral. Following the injection of HRP into the FOR, the largest number of retrogradely labeled cells appeared in the pontine nuclei. Although the number of labeled cells was greater on the contralateral side in both the peduncular and dorsomedial pontine nuclei (DMPN), the number of each side was virtually identical in the dorsolateral pontine nucleus (DLPN). In the nucleus reticularis tegmenti pontis (NRTP), labeled cells were located only in its medial and dorsolateral portions bilaterally. In the vestibular complex, labeled cells appeared in the superior (SVN), medial (MVN), and inferior vestibular nuclei (IVN) bilaterally. The lateral vestibular nucleus (LVN), including y group and the ventrolateral vestibular nucleus, were free of labeled cells. Labeled cells appeared also in the perihypoglossal nucleus (PHN) bilaterally. In the pontine raphe (PR) and paramedian pontine reticular formation (PPRF), labeled cells appeared bilaterally in the caudal third of the area between the oculomotor and abducens nuclei. Labeled cells appeared also in the mesencephalic and medullary reticular formation. Tracing of anterogradely labeled axons demonstrated that most fibers from the FOR decussated within the cerebellum and entered the brainstem via the contralateral uncinate fasciculus. Some crossed fibers ascended with the contralateral brachium conjunctivum and terminated in the midbrain tegmentum. A small contingent of fibers advanced further to the thalamus. In the mesodiencephalic junction, labeled terminals were found contralaterally in the rostral interstitial nucleus of medial longitudinal fasciculus (riMLF) and a medial portion of FOrel's H Field. They appeared also in the central mesencephalic reticular formation (cMRF), the periaqueductal gray (PAG), the posterior commissure nucleus, and the superior colliculus. The oculomotor and trochlear nuclei, the red nucleus, and the interstitial nucleus of Cajal were free of labeled terminals.(ABSTRACT TRUNCATED AT 400 WORDS)

Inhibition of spinal reflexes by paramedian reticular nucleus

The inhibitory actions of the paramedian reticular nucleus (PRN), and its neighbouring structures, i.e., midline raphe nuclei (MRN) and dorsal medullary depressor area (DMD) on the knee jerk (KnJ) and crossed extension movement (CEM) induced by central sciatic stimulation and on the L5 ventral root response (EVRR) evoked by central tibial stimulation, were studied in cats under urethane (400 mg/kg) and alpha-chloralose (40 mg/kg) anesthesia alone, IP or further paralyzed with atracurium besylate (0.5 mg/kg/30 min), IV. Electrical stimulation of the above areas with rectangular pulses (80 Hz, 1.0 msec, 100-200 microA) decreased systemic arterial blood pressure (SAP) in an average value of: 36 +/- 3 mmHg for PRN; 19 +/- 2 mmHg for MRN; and 23 +/- 3 mmHg for DMD. The KnJ and CEM were almost completely suppressed by simultaneous PRN stimulation. The EVRR, including mono- and polysynaptic spinal reflexes with transmission velocity from 10 to 60 m/sec or above, were also suppressed. MRN stimulation only inhibited the KnJ, CEM and polysynaptic spinal reflexes with transmission velocities between 25 and 60 m/sec, but facilitated spinal reflexes with conduction velocities below 10 m/sec. On the other hand, DMD stimulation resulted in small suppression of KnJ, CEM and inhibition of polysynaptic spinal reflexes with conduction velocities between 25 and 60 m/sec. Even though MRN and DMD partially inhibited polysynaptic spinal reflexes, the magnitude of such inhibition was much smaller than that produced by PRN (-20% and -22% vs. -48%). The above-mentioned PRN effects on SAP and EVRR persisted in chronic animals decerebellated 9-12 days before.(ABSTRACT TRUNCATED AT 250 WORDS)

Fastigial inputs to paraventricular neurosecretory neurones studied by extra- and intracellular recordings in rats

1. The effects of stimulation of the cerebellar fastigial nucleus (FN) on the activity of neurosecretory neurones in the hypothalamic paraventricular nucleus (PVN) of rats, anaesthetized with urethane and alpha-chloralose, were investigated by extracellular and intracellular recordings. 2. With extracellular recording, 139 PVN neurosecretory neurones were identified by antidromic activation following stimulation of the pituitary stalk, of which 120 were spontaneously firing and 19 were silent. Three types of responses to FN stimulation (1 or 2 pulses at 333 Hz) were observed in 43% of spontaneously firing PVN neurosecretory neurones: inhibition (type I) with a latency of 4.3 +/- 4.1 ms (mean +/- S.D., 32 of 120 neurones, 27%); excitation (type E) with 22.3 +/- 8.1 ms latency (14 of 120, 11%); and inhibition-excitation type (I-E) with 5.5 +/- 3.4 ms latency (6 of 120, 5%). Silent neurosecretory neurones did not respond to FN stimulation. Twelve per cent of non-neurosecretory cells (three out of twenty-six tested) responded to FN stimulation (one was inhibited, and two were excited). 3. Repetitive stimulation (60 Hz, 10 s) of the FN, which evoked a stimulus-locked pressor response, suppressed on-going activity of PVN neurosecretory neurones in 43% (twenty-nine of sixty-eight) of neurones tested. In 40% of these neurones, the activity was also inhibited by intravenous injection of phenylephrine (3 micrograms in 0.3 ml Ringer solution), while in other neurones the injection had no effect. Rebound excitation of neurone activity lasting for 1-5 min after termination of repetitive stimulation was observed in 28% of the neurones. Ten neurones (14%) were excited by repetitive stimulation. 4. Successful intracellular recordings were made from seventy-two PVN neurones, of which thirty-seven were neurosecretory cells. The mean resting membrane potential was -51 mV (n = 72; range from -40 to -75 mV). The input resistance of neurosecretory cells was 117 +/- 21 M omega (range 93-153 M omega; n = 8). This value was higher than that for non-neurosecretory cells which was found to be 53 +/- 10 M omega (range 35-72 M omega; n = 9). The difference was statistically significant (P less than 0.01, Student's t test). 5. In response to FN stimulation, sixteen (43%) of the thirty-seven neurosecretory neurones showed IPSPs with latencies of 7.4 +/- 2.8 ms and three (8%) exhibited EPSPs with latencies of 13.3 +/- 4.2 ms.(ABSTRACT TRUNCATED AT 400 WORDS)

Modeling slow phase velocity generation during off-vertical axis rotation

1. Rotation about an off-vertical axis (OVAR) causes continuous unidirectional nystagmus in darkness. An analysis of the dynamics of the nystagmus suggests that the continuous slow-phase velocity is generated by a signal that is an estimate of the velocity of a traveling wave pattern associated with the excitation and inhibition of the cells of the otolith maculae. The estimated velocity signal then excites the velocity storage integrator. 2. A mathematical model has been developed that shows how the velocity of the traveling wave might be estimated from patterns of otolith activation related to head position. The estimation of velocity is based on a "template matching" algorithm. It is assumed that the signal arising in each cell of the macula is delayed by a certain time (T). As the head rotates in the gravitational field, a delayed pattern representing a previous position of the head is available as a "template" that can be compared to the pattern associated with the present position of the head. 3. The delayed signal level for each cell is approximated from the present pattern by a spatial extrapolation in pattern space using information from the given cell and an adjacent one. The value of the displacement that minimizes the mean square error between the extrapolated and the delayed signal values over all cells gives a best estimate of head rotation (d) in time T. The estimated head velocity is proportional to the estimated head displacement (d) and inversely proportional to the delay time (T). 4. By using a linear spatial extrapolation function and assuming a uniformly spaced distribution of polarization vectors over 360 degrees, sinusoidal spatial patterns are obtained. The formula for the estimated head velocity (ŵ) reduces to a sinusoidal function of angular head velocity (w) and delay time (T). For T = 0.85 seconds, the model predicts that the steady state estimate of head velocity will rise as a function of stimulus velocity (w) to a peak value at w = 50 deg/sec. The estimate then declines for larger values of stimulus velocity (w). This type of behavior is observed in the slow-phase velocity characteristics of OVAR in monkeys. 5. The model predicts that when animals are tilted after prolonged rotation about a vertical axis, the estimate of head velocity is delayed relative to actual head velocity. This accounts for the delay in the buildup of slow-phase velocity during the initial second.(ABSTRACT TRUNCATED AT 400 WORDS)

Cardiovascular afferent and fastigial nucleus inputs to paramedian reticulospinal neurons

In chloralose anesthetized, paralyzed and artificially ventilated cats, the region of the paramedian reticular nucleus (PRN) was systematically explored for single units antidromically activated by electrical stimulation of histologically verified sites in the intermediate gray region of the upper thoracic cord (T2). These antidromically identified units were then tested for their orthodromic responses to electrical stimulation of ipsilateral carotid sinus nerve (CSN) and of pressor sites in the contralateral fastigial nucleus (FN). Sixty-two histologically verified single units, located predominantly in the caudal half of the ventral PRN, were antidromically activated with latencies corresponding to a mean conduction velocity of 36.4 +/- 2.1 m/s. Of these units 25 (40%) were excited orthodromically by stimulation of the CSN and/or FN: 5 to stimulation of the CSN only (mean latency, 18.3 +/- 9.9 ms), 6 to stimulation of the FN only (mean latency, 7 +/- 1.7 ms), and 14 to stimulation of both the CSN and FN (mean latencies, 12.3 +/- 2.9 ms and 8.4 +/- 1 ms, respectively). These data provide electrophysiological evidence for the existence of PRN reticulo-spinal neurons that integrate and relay cardiovascular afferent information from the CSN and FN to spinal autonomic neurons.

Single neuron activity of rat hypothalamic paraventricular nucleus during body suspension

Single neuron activity in the hypothalamic paraventricular nucleus (PVN) was recorded during horizontal and 45 degrees head-down tilt suspension in unanesthetized rats. When the rats were raised in the head-down position, 13 of 34 neurons (38%) in the PVN changed activity as follows: gradual decrease (11/13, type I), or gradual increase (2/13, type II). Responses of 6 type I and 1 type II neuron were smaller during horizontal suspension. Intracerebroventricular or intraperitoneal injection of hypertonic saline caused an increase in activity of 4 of 5 type I neurons tested. This hyperosmotic stimulation had no effect during suppressed activity induced by head-down tilt. These results suggest that the activity of PVN neurons is altered during body suspension, probably by information from baroreceptors in the thoracic activity, proprioreceptors and/or the vestibular organ, and these neurons might be involved in regulation of the autonomic and neuroendocrine systems.

Posture-correlated responses to vestibular polarization in vermal versus intermediate posterior cerebellar cortex

Cerebellar lesion experiments have led to the concept that the medial longitudinal zone controls postural tone while the intermediate zone controls discrete movement. This study is a test of the hypothesis that, of the two zones, the medial zone is more closely linked to the resting discharge of vestibular afferent fibers, a prime source of neural tonus underlying the tonus of posture. Unilateral polarizations of the vestibular apparatus via the round window in awake, unrestrained guinea pigs caused step changes of postural attitude, the direction of which was polarity dependent. In anesthetized animals, these currents caused nonadapting step changes, or posture-correlated responses in the level of resting discharge in vestibular primary afferent fibers. In the medial and the intermediate cerebellar cortices of the posterior lobe, the proportion of step-like responses was similar, in contradiction to the hypothesis. This suggests that the cerebellar computations for controlling both postural tonus and discrete movements require information about vestibular tonus in terms of simple spike activity.

Vestibular inputs to the fastigial nucleus; evidence of convergence of macular and ampullar inputs

1. Experiments have been undertaken on 11 decerebrate cats to investigate the effects of natural vestibular stimulation on the activity of cerebellar fastigial neurons. 2. From recordings in the rostral portion of the nucleus during sinusoidal lateral (roll) and horizontal (yaw) rotation, distinctive patterns of response were observed. 3. The majority of neurons sensitive to vestibular stimulation showed responses to a single modality of vestibular activation. During lateral tilt some neurones showed positional sensititivy, others gave responses related tothe velocity of movement. Other neurones responded in phase with the velocity of movement in the horizontal plane. 4. Aside from these neuronal responses, others provided indications of a convergence of inputs from different sets of vestibular receptors. In particular, several neurons showed a pattern of response that indicated tht they received inputs from otolith receptors and ampullar receptors of the vertical canal. At low velocities of movement their response was positional but with inreasing velocity the magnitude of the response increased and there was a marked phase shift of the discharge towards head velocity. 5. Neurons responding to horizontal rotation often showed positional responses during lateral tilt. There were also indications of a convergence of ampullar inputs from both vertical and horizontal canals. 6. The neural pathways mediating these resonses are discussed in consideration of previous neuroanatomical and neurophysiological data. We consider it likely that several pathways may act to evoke the patterns of response observed, and a role of the cerebellar cortex is indicated.