Connections of the Fastigial Nucleus in the Cat and Monkey. In: Palay SL, Chan-palay V, editors. The Cerebellum—New Vistas. Berlin: Springer Berlin Heidelberg; 1982. pp. 250-95. [DOI: 10.1007/978-3-642-68560-6_13]

Emotion modulation of the startle reflex in essential tremor: Blunted reactivity to unpleasant and pleasant pictures

BACKGROUND

Essential tremor is a highly prevalent movement disorder characterized by kinetic tremor and mild cognitive-executive changes. These features are commonly attributed to abnormal cerebellar changes, resulting in disruption of cerebellar-thalamo-cortical networks. Less attention has been paid to alterations in basic emotion processing in essential tremor, despite known cerebellar-limbic interconnectivity.

OBJECTIVES

In the current study, we tested the hypothesis that a psychophysiologic index of emotional reactivity, the emotion modulated startle reflex, would be muted in individuals with essential tremor relative to controls.

METHODS

Participants included 19 essential tremor patients and 18 controls, who viewed standard sets of unpleasant, pleasant, and neutral pictures for six seconds each. During picture viewing, white noise bursts were binaurally presented to elicit startle eyeblinks measured over the orbicularis oculi.

RESULTS

Consistent with past literature, controls' startle eyeblink responses were modulated according to picture valence (unpleasant > neutral > pleasant). In essential tremor participants, startle eyeblinks were not modulated by emotion. This modulation failure was not due to medication effects, nor was it due to abnormal appraisal of emotional picture content.

CONCLUSIONS

Neuroanatomically, it remains unclear whether diminished startle modulation in essential tremor is secondary to aberrant cerebellar input to the amygdala, which is involved in priming the startle response in emotional contexts, or due to more direct disruption between the cerebellum and brainstem startle circuitry. If the former is correct, these findings may be the first to reveal dysregulation of emotional networks in essential tremor.

Electrical microstimulation of the fastigial oculomotor region in the head-unrestrained monkey

It has been shown that inactivation of the caudal fastigial nucleus (cFN) by local injection of muscimol leads to inaccurate gaze shifts in the head-unrestrained monkey and that the gaze dysmetria is primarily due to changes in the horizontal amplitude of eye saccades in the orbit. Moreover, changes in the relationship between amplitude and duration are observed for only the eye saccades and not for the head movements. These results suggest that the cFN output primarily influences a neural network involved in moving the eyes in the orbit. The present study further tested this hypothesis by examining whether head movements could be evoked by electrical microstimulation of the saccade-related region in the cFN. Long stimulation trains (200-300 ms) evoked staircase gaze shifts that were ipsi- or contralateral, depending on the stimulated site. These gaze shifts were small in amplitude and were essentially accomplished by saccadic movements of the eyes. Head movements were observed in some sites but their amplitudes were very small (mean=2.4 degrees). The occurrence of head movements and their amplitude were not enhanced by increasing stimulation frequency or intensity. In several cases, electrically evoked gaze shifts exhibited an eye-head coupling that was different from that observed in visually triggered gaze shifts. This study provides additional observations suggesting that the saccade-related region in the cFN modulates the generation of eye movements and that the deep cerebellar output region involved in influencing head movements is located elsewhere.

Regional brain variations of cytochrome oxidase activity and motor coordination in Girk2Wv (Weaver) mutant mice

The Girk2(Wv) (weaver) phenotype, caused by a mutated inward rectifying potassium channel, is characterized by degeneration of cerebellar granule cell population as well as midbrain dopamine-containing cells of the nigrostriatal pathway. To investigate the regional brain metabolic consequences of this combined pathology, cytochrome oxidase (CO) activity was measured by histochemistry from brain regions of wild-type and homozygous Girk2(Wv) mutant mice and correlated with motor performances. CO activity of Girk2(Wv) mutants was abnormal in cerebellar cortex, dentate nucleus, and brainstem regions (medial and lateral vestibular nuclei, prepositus, superior colliculus, lateral cuneiform nucleus, and reticular nuclei) implicated in the gaze system. CO activity increased in midbrain dopaminergic regions after correcting for tissue density, regions with severe depletion of tyrosine hydroxylase activity. Forebrain regions were relatively spared in term of CO activity, except for subthalamic nucleus, lateral geniculate nucleus, and cortical eye field. Similarly to the Rora(sg) cerebellar mutant, metabolic alterations in cerebellar and vestibular regions were linearly correlated with poor motor coordination, underlining the sensitivity of these tests to cerebellar dysfunction.

Possible pathways for cerebellar modulation of autonomic responses: micturition

Experimental and clinical studies have shown that the cerebellum participates in the regulation of various visceral responses, including micturition. It is not yet clear through which parts of the central nervous system such cerebellar influences are mediated. However, a series of investigations have shown that the cerebellum is directly or indirectly connected to various centres that appear to be involved in autonomic control. These include parts of the cerebral cortex, the hypothalamus, the periaquaductal grey, nuclei in and around the pontine micturition centre, the dorsal vagal nucleus and nucleus of the solitary tract, and the medullary reticular formation. This article examines some of the circuits that may be involved in cerebellar modulation of visceral reflexes, especially the micturition reflex.

Brainstem control of head movements during orienting; organization of the premotor circuits

When an object appears in the visual field, animals orient their head, eyes, and body toward it in a well-coordinated manner (orienting movement). The head movement is a major portion of the orienting movement. Interest in the neural control of head movements in the monkey and human have increased in the 1990's, however, fundamental knowledge about the neural circuits controlling the orienting head movement continues to be based on a large number of experimental studies performed in the cat. Thus, it is crucial now to summarize information that has been clarified in the cat for further advancement in understanding the neural control of head movements in different animal species. The superior colliculus (SC) has been identified as the primary brainstem center controlling the orienting. Its output signal is transmitted to neck motoneurons via two major separate pathways: one through the reticulospinal neurons (RSNs) in the pons and medulla and the other through neurons in Forel's field H (FFH) in the mesodiencephalic junction. The tecto-reticulo-spinal pathway controls orienting chiefly in the horizontal direction, while the tecto-FFH-spinal pathway controls orienting in the vertical direction. In each pathway, a subgroup of neurons functions as premotor neurons for both extraocular and neck motoneurons, while others are specified for each, which allows both coordinated and separate control of eye and head movements. Head movements almost always produce shifts in the center of gravity that might cause postural disturbances. The postural equilibrium may be maintained by transmitting the orienting command to the limb segments via descending axons of the reticulospinal and long propriospinal neurons. The SC and brainstem relay neurons receive descending inputs from higher order structures such as the cerebral cortex, cerebellum, and basal ganglia. These inputs may serve context-dependent control of orienting by modulating the activities of the primary brainstem pathways.

Gaze shifts evoked by electrical stimulation of the superior colliculus in the head-unrestrained cat. II. Effect of muscimol inactivation of the caudal fastigial nucleus

The medioposterior cerebellum [vermian lobules VI and VII and caudal fastigial nucleus (cFN)] is known to play a major role in the control of saccadic gaze shifts toward a visual target. To determine the relative contribution of the cFN efferent pathways to the brainstem reticular formation and to the superior colliculus (SC), we recorded in the head-unrestrained cat the effects of cFN unilateral inactivation on gaze shifts evoked by electrical microstimulation of the deeper SC layers. Gaze shifts evoked after muscimol injection still exhibited the typical qualitative features of normal saccadic gaze shifts. Nevertheless, consistent modifications in amplitude and latency were observed. For ipsiversive movements (evoked by the SC contralateral to the inactivated cFN), these changes depended on the locus of stimulation on the motor map: for the anterior 2/3 of the SC, amplitude increased and latency tended to decrease; for the posterior 1/3 of the SC, amplitude decreased and latency increased. For the contraversive direction, amplitude moderately decreased and latency tended to increase for all but the caudal-most stimulated SC site. These modifications of SC-evoked gaze shifts during cFN inactivation differed from the ipsiversive hypermetria/contraversive hypometria pattern observed for visually triggered gaze shifts recorded during the same recording sessions. We conclude that (i) the topographical organization of gaze shift amplitude in the deeper SC layers is influenced by the cerebellum and is either severely distorted or demonstrates an amplitude reduction during inactivation of the contralateral or ipsilateral cFN, respectively; (ii) gaze shifts evoked by SC microstimulation and visually triggered gaze shifts either rely on distinct cerebellar-dependent control processes or differ by the location of the caudal-most active SC population. We present a functional scheme providing several predictions regarding the modulatory influence of the cerebellum on SC neuronal activities and on the topographical organization of fastigial-SC projections.

Model of the control of saccades by superior colliculus and cerebellum

Experimental evidence indicates that the superior colliculus (SC) is important but neither necessary nor sufficient to produce accurate saccadic eye movements. Furthermore both clinical and experimental evidence points to the cerebellum as an indispensable component of the saccadic system. Accordingly, we have devised a new model of the saccadic system in which the characteristics of saccades are determined by the cooperation of two pathways, one through the SC and the other through the cerebellum. Both pathways are influenced by feedback information: the feedback determines the decay of activity for collicular neurons and the timing of the activation for cerebellar neurons. We have modeled three types of cells (burst, buildup, and fixation neurons) found in the intermediate layers of the superior colliculus. We propose that, from the point of view of motor execution, the burst neurons and the buildup neurons are not functionally distinct with both providing a directional drive to the brain stem circuitry. The fixation neurons determine the onset of the saccade by disfacilitating the omnipause neurons in the brain stem. Excluding noise-related variations, the ratio of the horizontal to the vertical components of the collicular drive is fixed throughout the saccade (i.e., its direction is fixed); the duration of the drive is such that it always would produce hypermetric movements. The cerebellum plays three roles: first, it provides an additional directional drive, which improves the acceleration of the eyes; second, it keeps track of the progress of the saccade toward the target; and third, it ends the saccade by choking off the collicular drive. The drive provided by the cerebellum can be adjusted in direction to exert a directional control over the saccadic trajectory. We propose here a control mechanism that incorporates a spatial displacement integrator in the cerebellum; under such conditions, we show that a partial directional control arises automatically. Our scheme preserves the advantages of several previous models of the saccadic system (e.g., the lack of a spatial-to-temporal transformation between the SC and the brain stem; the use of efference copy feedback to control the saccade), without incurring many of their drawbacks, and it accounts for a large amount of experimental data.

Visuospatial abilities

The importance of the hippocampus and its anatomical connections, including the medial septum, thalamic nuclei, and neocortical regions in many spatial tasks including the Morris water maze, has been emphasized. Studies in mutant mice with cerebellar atrophy and in rats with electrolytic lesions of the cerebellum have indicated that the cerebellum has a role in visuospatial and visuomotor processes in the Morris maze. Directional deficits in the water have also been noted in rats whose cerebellum was exposed to X-rays during different developmental stages. Cerebellar interactions with the superior colliculus, the hippocampus, and the neocortex via thalamic nuclei are suggested to be the basis of the cerebellar modulation of directional sense in maze tests.

Changes in initiation of orienting gaze shifts after muscimol inactivation of the caudal fastigial nucleus in the cat

1. The production of a goal-directed saccadic gaze shift involves the specification of movement amplitude and direction, and the decision to trigger the movement. Behavioural and neurophysiological data suggest that these two functions involve separate processes which may interact. 2. The medio-posterior cerebellar areas are classically assigned a major contribution to the control of saccade metrics, and previous cerebellar lesion studies have revealed marked dysmetria of visually triggered gaze shifts. In contrast, these studies did not provide evidence for a cerebellar role in saccadic initiation. 3. In the present study, we investigated in the head-unrestrained cat the deficits in both the initiation and the metrics control of saccadic gaze shifts following pharmacological inactivation of the caudal part of the fastigial nucleus (cFN). 4. After cFN inactivation, latencies for contraversive gaze shifts increased to about 137 +/- 28% of normal, and latencies for ipsiversive gaze shifts decreased to about 84 +/- 8% of normal. Similar changes in head movement latency were observed, such that the temporal coupling between eye and head components remained largely unaffected. 5. Contraversive gaze shifts were more hypometric as their latency increased. In contrast, the degree of hypermetria in ipsiversive gaze shifts was unrelated to latency. 6. These results suggest a functional role of the medio-posterior cerebellum in gaze shift initiation and in storing information about the target location and/or the desired gaze shift amplitude.

Effects of midline and lateral cerebellar lesions on motor coordination and spatial orientation

Rats were lesioned in the midline cerebellum, comprising the vermis and fastigial nucleus, or the lateral cerebellum, comprising the cerebellar hemispheres and dentate nucleus, and evaluated in a series of motor and non-motor learning tests. Rats with midline lesions had difficulty in maintaining their equilibrium on a bridge and were slower before turning upward and traversed less squares on an inclined grid. They were not impaired for muscle strength when suspended from a horizontal wire. Rats with lateral lesions had milder deficits on the bridge and were not affected in the other two tests. In the Morris water maze test, rats with lateral lesions were deficient in spatial orientation, whereas rats with midline lesions were deficient in visuomotor coordination. Lateral lesions had no effects on visual discrimination learning. These results illustrate the differential influence of midline as opposed to lateral cerebellar regions on both motor and non-motor behaviors. Fastigial nucleus lesions decreased the time spent in equilibrium and latencies before falling on the bridge and the distance travelled along the inclined grid but had no effect on muscle strength when suspended from the horizontal string. Quadrant entries and escape latencies were higher in rats with fastigial lesions during the hidden platform condition of the Morris water maze but not during the visible platform condition. It is concluded that fastigial-lesioned rats are impaired in equilibrium and spatial orientation but with repeated trials learn to improve their performances.

Cerebellar contributions to instrumental learning

There is emerging evidence that the cerebellum is involved in spatial and nonspatial instrumental learning tasks. Cerebellar-lesioned animals have deficits in water maze learning tasks that may be explained by two-way interactions with higher order brain regions. There is suggestive evidence that cerebellar modulation extends to shock avoidance and discrimination learning. Although this evidence needs to be confirmed by a wider range of lesion methods and choice of learning tasks, it is in line with the hypothesis that the cerebellum affects cognitive processes and is not strictly concerned with motor control and the acquisition and retention of conditioned reflexes.

Role of the fastigial nucleus in generalized seizures as demonstrated by GABA agonist microinjections

The cerebellum is electrically and metabolically active during seizures. Numerous studies have also shown that cerebellar electrical stimulation and lesions of the cerebellar cortex or nuclei influence seizure threshold, but there are significant contradictions, with different effects observed even in investigations using the same species and similar seizure types and experimental manipulations. Discrete intracerebral microinjection of neuroactive agents has been used to characterize the way in which other brain regions control seizures, but has not been applied to the cerebellar systems. This approach has advantages because effects are restricted to specific receptors and spare passing axons; experimental variables also can be simply specified and reproduced. We used this method to characterize the role of the cerebellar nuclei in seizures and to determine if observed effects could be reproduced with different agents at different doses. Effects of bilateral control microinjections in the fastigial (medial) cerebellar nucleus were compared with different doses of the GABAA agonist piperidine-4-sulfonic acid and the GABAB agonist (-)baclofen (Bf). Soon after injection, the animals were ataxic. After 4 min, seizures were induced by timed continuous intravenous (i.v.) bicuculline (BIC) infusion. Both GABA agonists produced significant reductions in myoclonic, clonic, and tonic seizure thresholds. Injections just dorsal or anterior to this nucleus and bilateral dentate (lateral) nucleus injections had little effect on seizures. These results demonstrate that the cerebellar system does control seizures, but does not provide support for the early concept that cerebellar stimulation and systemic phenytoin block seizures through inhibition of cerebellar nuclei secondary to Purkinje cell activation.

Direct projections from the cerebellar fastigial nucleus to the thalamic suprageniculate nucleus in the cat studied with the anterograde and retrograde axonal transport of wheat germ agglutinin-horseradish peroxidase

Axonal transport of WGA-HRP injected into (1) the suprageniculate nucleus or (2) the fastigial nucleus, was investigated. Retrogradely labeled neurons were found in the caudal part of the bilateral fastigial nucleus following injection 1, and anterograde labeled axon terminals were observed in the bilateral suprageniculate nucleus following injection 2. Electron microscopic observations of these terminals revealed that they were large terminals making asymmetric synaptic contacts with dendrites. These results suggest that some neurons in the fastigial nucleus send their axons to the suprageniculate nucleus.

Afferent connections of the parvocellular reticular formation: a horseradish peroxidase study in the rat

The afferent connections of the parvocellular reticular formation were systematically investigated in the rat with the aid of retrograde and anterograde horseradish peroxidase tracer techniques. The results indicate that the parvocellular reticular formation receives its main input from several territories of the cerebral cortex (namely the first motor, primary somatosensory and granular insular areas), districts of the reticular formation (including its contralateral counterpart, the intermediate reticular nucleus, the nucleus of Probst's bundle, the dorsal paragigantocellular nucleus, the alpha part of the gigantocellular reticular nucleus, the dorsal and ventral reticular nuclei of the medulla, and the mesencephalic reticular formation), the supratrigeminal nucleus and the deep cerebellar nuclei. Moderate to substantial input to the parvocellular reticular formation appears to come from the central amygdaloid nucleus, the parvocellular division of the red nucleus, and the orofacial and gustatory sensory cell groups (comprising the mesencephalic, principal and spinal trigeminal nuclei, and the rostral part of the nucleus of the solitary tract), whereas many other structures, including the substantia innominata, the field H2 of Forel, hypothalamic nuclei, the superior colliculus, the substantia nigra pars reticulata, the retrorubral field and the parabrachial complex, seem to represent relatively modest additional input sources. Some of these projections appear to be topographically distributed within the parvocellular reticular formation. From the present results it appears that the parvocellular reticular formation receives afferents from a restricted group of sensory structures. This finding calls into question the traditional characterization of the parvocellular reticular formation as an intermediate link between the sensory nuclei of the cranial nerves and the medial magnocellular reticular districts, identified as the effector components of the reticular apparatus. Some of the possible physiological correlates of the fiber connections of the parvocellular reticular formation in the context of oral motor behaviors, autonomic regulations, respiratory phenomena and sleep-waking mechanisms are briefly discussed.

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.

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)

The human brain at stages 21-23, with particular reference to the cerebral cortical plate and to the development of the cerebellum

The development of the human brain during the eighth embryonic week was studied in serial sections of 22 embryos, and graphic reconstructions were prepared. The cortical plate appears in stage 21 in the area of the future insula and is an excellent feature for staging. The internal capsule contains neocortical fibres. Its three main outlets begin to be present in stage 22 and lead to epithalamus, to dorsal thalamus, and to mesencephalon. At this time a well developed lateral olfactory tract can be seen. The anterior commissure appears in stage 23. A clear developmental relationship between claustrum and olfactory area is described for the first time in human embryos. The optic tract reaches the ventral area of the lateral geniculate body. Scattered fibres of the lateral lemniscus reach at least as far as the caudal mesencephalon, in which superior and inferior colliculi can be distinguished at stage 23; two caudal Blindsäcke containing ventricular recesses form in stage 23. The cerebellum is still present as a plate, but its internal bulge is considerably enlarged. It possesses radially- and tangentially-arranged cells; the latter form the external germinal layer. The dentate nucleus, as well as the inferior and superior cerebellar peduncles and some of the cerebellar commissures, are present. Compared with the highly developed and probably already functional remainder of the hindbrain, the cerebellar plate shows far less differentiation. Two caudal migratory streams (marginal and submarginal) are present and represent the corpus pontobulbare. The decussation of the pyramids appears in stage 23. This article concludes the study of the developing human brain during the embryonic period, from stage 8 to stage 23. The series was based on 340 serially-sectioned embryos and graphic reconstructions from 89 brains. No comparable investigation of the fetal brain is available.

Projections of the medial cerebellar nucleus to oculomotor-related midbrain areas in the rat: an anterograde and retrograde HRP study

The mesencephalic projections of the medial cerebellar nucleus (MCN) were studied in the rat by using the method of anterograde transport of wheat germ agglutinin/horseradish peroxidase to establish connections of the nucleus with oculomotor-related nuclei as a basis for its proposed role in eye movement. The principal targets of projections were the supraoculomotor ventral periaqueductal gray (PAG) and lateral PAG, and paraoculomotor cell groups (nucleus of Darkschewitsch and medial accessory nucleus of Bechterew). Lesser projections were observed to the intermediate layer of the superior colliculus, nucleus of the posterior commissure, and prerubral field. Following transcannular HRP gel implants into the oculomotor complex that included adjacent paraoculomotor nuclei, the largest number of retrogradely labeled cells was found in the caudal MCN. The findings suggest that the caudal MCN in the rat, like the primate fastigial nucleus, is involved in the control of eye movement.

Olivocerebellar and cerebelloolivary connections of the oculomotor region of the fastigial nucleus in the macaque monkey

Anatomical connections of the caudal portion of the fastigial nucleus (FN) with the inferior olive (IO) were studied in macaque monkeys with wheat-germ-agglutinin-conjugated horseradish peroxidase (WGA/HRP) and HRP. When injected HRP was confined to a caudal portion of the FN, retrogradely labeled Purkinje cells (P cells) appeared in the oculomotor vermis. We defined the area that receives the projection from vermal lobule VII as the fastigial oculomotor region. The same HRP injection resulted in retrograde labeling of IO neurons in an area of group b (of Bowman and Sladek: J. Comp. Neurol. 152:299-316, '73) of the contralateral medial accessory olive (MAO). This area was designated as the Z-portion because in the coronal section it appears like the letter "Z." Retrogradely labeled IO neurons were also found in the Z-portion when HRP was injected into the oculomotor vermis, indicating that neurons in this portion project to both the fastigial and vermal oculomotor regions. Anterogradely labeled axons from the contralateral fastigial oculomotor region also terminated in the Z-portion. When the effective site included a region anterior to the fastigial oculomotor region, labeled P cells appeared in lobule V and labeled IO neurons appeared in group a. Labeled terminals of fastigial fibers were also found in group a. When the effective site included a region ventral to the oculomotor region, labeled P cells appeared in vermal lobules VIII and IX and labeled IO neurons appeared in caudal parts of a and b, in addition to group c. HRP injection into the posterior interposed nucleus (PIN) resulted in labeling of P cells in the paravermal zone and of IO neurons in the rostral two-thirds of the MAO and the dorsal accessory olive (DAO). The location of the labeled terminals coincided with the region where the densest labeling of IO neurons was found. Thus, the olivary projections to both the cerebellar cortex and deep cerebellar nuclei and the nucleoolivary projection exhibited a closely related topographical organization.

A quantitative study of the vestibular commissures in the gerbil

Direct commissural connections between the bilateral vestibular nuclear complexes (VNC) were investigated in the gerbil using ionophoretic injections of horseradish peroxidase into individual vestibular nuclei. Labelled commissural neurons were counted, the cell counts adjusted by the relative nuclear volume, and the results treated quantitatively. The medial nucleus (MVN) contained the greatest number of commissural neurons. The MVN projected to each of the contralateral vestibular nuclei, but most strongly to the contralateral MVN and superior (SVN) nucleus. The SVN projected modestly to the contralateral VNC. Commissural connections of the descending nucleus were weak. Commissural afferents to the MVN were topographically organized. The crossed fastigiovestibular projection was also investigated.

Cerebellar cortical and nuclear afferents from the feline locus coeruleus complex

The origin and distribution of cerebellar cortical and nuclear afferents from the locus coeruleus complex (the nucleus locus coeruleus, the nucleus subcoeruleus, the medial and lateral subdivisions of the parabrachial nucleus and the Kölliker-Fuse nucleus) have been studied by means of retrograde transport of the wheat germ agglutinin-horseradish peroxidase complex in the cat. Cerebellar cortical depositions of the tracer were made by pressure injections, while nuclear depositions were made by implanting the tracer in crystalline form. The projection is bilateral with an ipsilateral preponderance. It reaches all the cerebellar nuclei as well as vermal, intermediate and lateral parts of the cerebellar cortex. The highest cell counts were made after tracer depositions in vermal and intermediate parts of the cerebellum. The projection in the cat has a more widespread origin than previously reported. It originates mainly within the nucleus locus coeruleus and the parabrachial nucleus (especially in its lateral subdivision), but retrogradely labelled neurons were also found in nucleus subcoeruleus, the Kölliker-Fuse nucleus and the A4 cell group. The cells of origin were of different shapes, but usually had a maximum diameter of the cell body between 15 and 30 micron. Cerebellar efferent axons passing through the locus coeruleus complex were anterogradely labelled following implants in all the cerebellar nuclei, but definite terminal labelling was not observed within the nuclei of the locus coeruleus complex.

Origin of cerebellar projections to the region of the oculomotor complex, medial pontine reticular formation, and superior colliculus in New World monkeys: a retrograde horseradish peroxidase study

Cerebellar projections to oculomotor-related brainstem regions were studied in four groups of New World (capuchin, squirrel) monkeys by using the retrograde transport of horseradish peroxidase (HRP) to determine the origin of the principal cerebellar influence on eye movement. Group A monkeys had HRP injections or transcannular HRP gel implants into the oculomotor complex (OMC), the largest of which involved adjacent paraoculomotor nuclei (e.g., ventral periaqueductal gray, PAG; nucleus of Darkschewitsch, ND; medial accessory nucleus of Bechterew, MAB; dorsomedial parvicellular red nucleus, dmPRN). All of these cases contained large numbers of retrogradely labeled cells in cell group Y. Whereas the smallest OMC injection only labeled a few cells in the dentate nucleus (DN), injections involving paraoculomotor nuclei produced labeling in all of the cerebellar nuclei except the basal interstitial nucleus (BIN). Injections extending into the ND and MAB produced particularly heavy labeling within the interposed nuclei. Group B monkeys had injections/implants into the medial pontine tegmentum and dorsomedial basilar pons. The pontine tegmental cases contained labeled cells in all cerebellar nuclei, but the DN was the most heavily labeled when the implant involved the nucleus reticularis tegmenti pontis (NRTP). Cases with injections into the caudal medial pontine tegmentum (nucleus reticularis pontis caudalis, NRPC), including the physiological paramedian pontine reticular formation (PPRF), but not NRTP, contained the largest number of labeled cells in the fastigial nucleus (FN) and lacked retrograde labeling in the DN. Dorsomedial basilar pontine cases contained almost no labeled cells in the FN, anterior interpositus nucleus (AIN), and posterior interpositus nucleus (PIN) but did contain DN labeling when the injection involved the NRTP. Two dorsomedial pontine tegmental cases and one dorsomedial basilar pontine case had more labeled cells in the BIN than in other cases. Tegmental cases also contained a few labeled cells in cell group Y. Group C monkeys had injections into the parvicellular red nucleus (PRN) and had their heaviest labeling in the DN, although the AIN and PIN also contained labeled cells. The FN, BIN, and cell group Y, on the other hand, contained almost no labeling. Group D consisted of monkeys which had injections into the intermediate and deep superior colliculus (SC). These cases contained the largest numbers of labeled cells in the PIN and a lesser number in the ventrolateral FN. The DN, AIN, BIN, and cell group Y lacked labeled neurons in these cases.(ABSTRACT TRUNCATED AT 400 WORDS)

Functional anatomy of pentylenetetrazol and electroshock seizures in the rat brainstem

The ability of discrete brainstem injections of gamma-vinyl-gamma-aminobutyric acid (GVG), an irreversible inhibitor of gamma-aminobutyric acid transaminase, to prevent pentylenetetrazol (PTZ) seizures and maximal electroshock seizures (MES) was studied and compared in rats. PTZ seizures were prevented by GVG injections in the anterior thalamus, the caudal hypothalamus, the superior colliculus, cerebellar nuclei, and in a large area of the medial medullary, pontine, and mesencephalic tegmentum encompassing the vestibular nuclei, the reticular formation, and portions of the central gray. GVG injections in the substantia nigra did not protect against PTZ seizures. In contrast, tonic hindlimb extension in MES was prevented consistently by injections in the substantia nigra. A minority of injections in the vestibular nuclei, cerebellar nuclei, and parts of the reticular formation also protected against tonic hindlimb extension of MES. These results indicate a striking difference in the functional anatomy of PTZ-induced seizures and MES. PTZ seizures appear to be mediated by an extensive system involving the reticular formation, diencephalic regions in the vicinity of the anterior medial thalamus and caudal hypothalamus, and bulbar regions which give rise to descending motor pathways to the spinal cord. In contrast to PTZ seizures, MES appears to be mediated by a different neuroanatomical substrate with the present data implicating only the substantia nigra definitely in that process.

Autoradiography of mossy fiber terminals in the fastigial nucleus of the cat

Terminal boutons of mossy fiber collaterals in the fastigial nucleus originating from the nucleus reticularis tegmenti pontis, the bulbar reticular formation, and the medial vestibular nucleus were studied with high-resolution autoradiography in order to examine their ultrastructural features and synaptic relations. Labeled mossy fiber boutons ranged in size from 0.5 to 5 micron in diameter, and they all contained clear and spherical vesicles in an electron-lucent matrix, mitochondria, and some fine tubular elements. These boutons form asymmetric synapses with dendritic profiles of different sizes. No evidence was found for mossy fiber termination on the soma of fastigial neurons. Two types of mossy fiber terminals were distinguished on the basis of the aggregation of synaptic vesicles: one type with clustered vesicles and one type with densely packed vesicles, occurring in equal number from all sources. Furthermore, the applicability of the congruity hypothesis is confirmed for the general identification of terminals.

Afferent connections of the nuclei reticularis pontis oralis and caudalis: a horseradish peroxidase study in the rat

The afferent connections of the nuclei reticularis pontis oralis and caudalis were studied experimentally in the rat by the aid of either free horseradish peroxidase or horseradish peroxidase conjugated with wheat germ agglutinin used as retrograde tracers. The results suggest that the nucleus reticularis pontis oralis receives its main input from the zona incerta and field H1 of Forel, the superior colliculus, the central gray substance, and the mesencephalic and magnocellular pontomedullary districts of the reticular formation. Many other structures seem to represent modest additional sources of projections to the nucleus reticularis pontis oralis; these structures include numerous cortical territories, the nucleus basalis, the central amygdaloid nucleus, hypothalamic districts, the anterior pretectal nucleus, the substantia nigra, the cuneiform, the accessory oculomotor and the deep cerebellar nuclei, trigeminal, parabrachial and vestibular sensory cell groups, the nuclei raphe dorsalis and magnus, the locus coeruleus, the dorsolateral tegmental nucleus, and the spinal cord. While the afferentation of the rostral portion of the nucleus reticularis pontis caudalis appears to conform to the general pattern outlined above, some deviations from that pattern emerge when the innervation of the caudal district of the nucleus reticularis pontis caudalis is considered; the most striking of these differences is the fact that both spinal and cerebellar inputs seem to distribute much more heavily to the referred caudal district than to the remaining magnocellular pontine reticular formation. The present results may contribute to the elucidation of the anatomical substrate of the functionally demonstrated involvement of the nuclei reticularis pontis oralis and caudalis in several domains that include the regulation of the sleep-waking cycle and cortical arousal, somatic motor mechanisms and nociceptive behavior.

Responses of neurones in the brainstem raphe nuclei to stimulation of the cerebellar fastigial nuclei in the cat

Stimulation of the fastigial nuclei of the cerebellum was found to excite units located throughout the raphe nuclei of the brainstem. Raphe spinal units with axons conducting at velocities below 20 m/s were either unaffected by fastigial nucleus stimulation or inconsistently excited at long latency. In contrast units with faster conducting spinal axons throughout the raphe and more dorsally in the reticular formation were excited by stimulation of the fastigial nuclei. Many of these units responded at short latency and followed high rates of repetitive stimulation.

The cerebellar nucleo-olivary and olivocerebellar nuclear projections in the cat as studied with anterograde and retrograde transport in the same animal after implantation of crystalline WGA-HRP. III. The interposed nuclei

The bidirectional connections between the inferior olive and the cerebellar nuclei were investigated by means of anterograde and retrograde transport after implantation of crystalline wheat germ agglutinin-horseradish peroxidase complex in the interposed nuclei. The projections from the interposed nuclei to the inferior olive show a detailed topical arrangement. The main projection from the anterior interposed nucleus reaches the rostral two thirds of the dorsal accessory olive, while the main projection from the posterior interposed nucleus reaches the rostral half of the medial accessory olive. The projections from the inferior olive to the interposed nuclei show a more widespread distribution and appear to be less precisely organized. Both interposed nuclei receive afferents from the medial and dorsal accessory olives, the dorsomedial cell column, nucleus beta and the dorsal cap. Our findings give evidence that the olivo-interposed and interposito-olivary projections are in part reciprocally organized. Our observations are discussed and related to previous investigations on the cerebello-olivary and olivocerebellar pathways. Some methodological comments are made. It appears from our results that anterograde transport in some of our cases has occurred only from a restricted part of the stained area at the implantation site.

Fastigial nucleus projections in the midbrain and thalamus in dogs

Efferent connections to midbrain and thalamus from portions of the cerebellar fastigial nucleus were investigated using autoradiographic techniques. Bipolar stimulating electrodes were placed in the fastigial nucleus of anesthetized beagles and the area which produced maximal increases in blood pressure and heart rate was localized in each dog. A mixture of [3H]leucine and [3H]proline (4:1) was injected into that area and autoradiograms were prepared. Injections filled the rostral and various parts of the caudal fastigial nucleus. The rostral-caudal extent of injection sites were mapped in the horizontal plane from sequential coronal, thionin-stained sections and "primary" and "secondary" injection zones were defined according to specific criteria. Labeled axons reached the mesencephalon via the contralateral uncinate fasiculus. Ascending fibers assembled in a diffuse contingent at the prerubral level adjacent to the ventrolateral periaqueductal gray. The heaviest projections were contralateral to the injection site, but ipsilateral terminals were observed as well. In the midbrain, axons entered the contralateral and ipsilateral superior colliculus to branch repeatedly and terminate in the deep and intermediate layers. Additional terminals were observed bilaterally in the nuclei of the posterior commissure and pretectal areas at the midbrain-diencephalic junction. In the thalamus, labeled axons formed into three groups which terminated in: the contralateral paraventricular complex and medial dorsal nucleus; the contralateral central medial, paracentral, parafasicular and central lateral nuclei, and the contralateral ventral medial and ventral lateral nuclei. There was a sparse projection to the ipsilateral ventral lateral nucleus. The contralateral projection to the ventral medial and ventral lateral nuclei was marked by dense clusters of label ventral to the internal medullary lamina extending, in the dorsal ventral lateral nucleus, to its rostral pole. Projections to specific somesthetic thalamus or the hypothalamus were not observed. These ascending projections in the canine brain generally conform to those described in other nonprimate mammals. The fastigial nucleus presumably provides information concerning equilibrium and body proprioception to the superior colliculus and to thalamic nuclei including both specific motor relay and "nonspecific" midline and intralaminar nuclei, much the same as reported in the cat. The projection to the ventral medial and ventral lateral thalamic nuclei terminate in areas known to participate in the control of axial and proximal limb muscle activity.(ABSTRACT TRUNCATED AT 400 WORDS)

The cerebellar nucleo-olivary and olivo-cerebellar nuclear projections in the cat as studied with anterograde and retrograde transport in the same animal after implantation of crystalline WGA-HRP. II. The fastigial nucleus

The bidirectional connections between the inferior olive and the fastigial nucleus were studied by means of anterograde and retrograde transport after implantation of crystalline wheat germ agglutinin-horseradish peroxidase (WGA-HRP) complex into the fastigial nucleus. The fastigio-olivary fibres terminate in the caudal half of the medial accessory olive, nucleus beta and the dorsal cap, and the olivo-fastigial projection has its origin within the same olivary regions. A topical arrangement is indicated for both pathways. The lateral part of the medial accessory olive appears to be connected with the lateral part of the fastigial nucleus, while the medial part of the medial accessory olive appears to be connected with more medial fastigial regions. Retrogradely labelled olivo-fastigial neurons were often located within the terminal field of anterogradely labelled fastigio-olivary fibres, indicating that the olivo-fastigial and fastigio-olivary projections are at least in part reciprocally organized. The findings are discussed and related to previous studies on the olivo-cerebellar nuclear and cerebellar nucleo-olivary pathways. Some methodological considerations are made, and comments are made concerning the active area for uptake and transport from the stained area at the WGA-HRP injection site.

The cerebellar and vestibular nuclear complexes in the turtle. I. Projections to mesencephalon, rhombencephalon, and spinal cord

Cerebellar and vestibular projections were investigated in the turtle Pseudemys scripta elegans following injection of 35S-methionine into the cerebellar and vestibular nuclear complexes at various locations. Fibers arising from the cerebellar nuclei were traced via the cerebellar commissure to the contralateral vestibular nuclear complex (particularly the n. vestibularis inferior and n. vestibularis ventrolateralis) and caudal rhombencephalic tegmentum. Ascending projections crossing the midline in the ventral isthmomesencephalic tegmentum terminated in the contralateral red nucleus and nuclei of the fasciculus longitudinalis medialis (f lm). Vestibular projections ascending mainly via the f lm terminated in the nuclei of the f lm, the nuclei of the posterior commissure, and particularly the extraocular motor nuclei. Vestibulo-ocular projections arising from the rostral vestibular nuclear complex were almost exclusively ipsilateral; those from the caudal vestibular nuclear complex were bilateral. Evidence for a topographic organization of the projections to the trochlear and oculomotor nuclei was also obtained. There were some vestibular projections to the contralateral rhombencephalic tegmentum and n. vestibularis inferior. Spinal projections coursing within the ipsilateral ventral descending tract and the ipsilateral fasciculus longitudinalis medialis were found to arise from both rostral and caudal vestibular regions. The caudal vestibular nuclear complex in addition gave rise to fibers descending in the contralateral fasciculus longitudinalis medialis. Evidence for the existence of labeled fibers crossing at spinal levels was also obtained. Vestibulospinal terminations appeared restricted to the ventral horn.

The cerebellar nucleo-olivary and olivo-cerebellar nuclear projections in the cat as studied with anterograde and retrograde transport in the same animal after implantation of crystalline WGA-HRP. I. The dentate nucleus

The implantation technique described by Mori et al. has been modified for the implantation of crystalline wheat germ agglutinin-horseradish peroxidase (WGA-HRP) complex. This method permits a detailed analysis of the afferent and efferent connections of the cerebellar nuclei without the complication of uptake and transport of the tracer into passing fibres. We have used this method for studies of the olivo-dentate and dentato-olivary projections in the cat. After implantation of WGA-HRP into the dentate nucleus in all our cases, both anterogradely labelled terminal dentato-olivary fibres and retrogradely labelled olivo-dentate neurons were found in the contralateral inferior olive. It appears from our findings that both projections are topically organized. The dorsal part of dentate nucleus is bidirectionally connected with the rostral part of the principal olive, the ventrolateral part of the dentate is connected with the intermediate portion of the principal olive, while its ventromedial part is connected with the caudal portion of the principal olive. The olivo-dentate and dentato-olivary connections appear to be largely reciprocally organized. The advantages and drawbacks encountered with implantation of crystalline WGA-HRP are discussed, and our observations are considered in relation to previous studies on the olivo-cerebellar and cerebello-olivary connections.

Afferent and efferent connections of the medial, inferior and lateral vestibular nuclei in the cat and monkey

Attempts were made to determine the afferent and efferent connections of the medial (MVN), inferior (IVN) and lateral (LVN) vestibular nuclei (VN) in the cat and monkey using retrograde and anterograde axoplasmic transport technics. Injections of HRP and [3H]amino acids were made selectively into MVN, IVN and LVN and into: (1) MVN and IVN, (2) LVN and IVN and (3) all 4 VN. Contralateral afferents to MVN arise from (1) the nuclei prepositus (NPP) and intercalatus (NIC), (2) all parts of MVN and cell group 'y' and (3) parts of the superior vestibular nucleus (SVN), IVN and the fastigial nucleus (FN). Ipsilateral projections to MVN arise from: (1) a central band of the flocculus and the nodulus and uvula, (2) the interstitial nucleus of Cajal (INC), and (3) visceral nuclei of the oculomotor nuclear complex (OMC). Efferent projections of MVN are to: (1) the ipsilateral supraspinal nucleus (SSN), and (2) the contralateral central cervical nucleus (CCN), MVN, SVN, cell group 'y', the rostroventral region of LVN, the trochlear nucleus (TN) and the INC. Projections to the abducens nuclei (AN) and the OMC are bilateral. Some ascending fibers in the cat cross within the OMC. In the monkey fibers from MVN end in a central band of the ipsilateral flocculus. Afferents to IVN arise ipsilaterally from SVN, the nodulus, the uvula and the anterior lobe vermis. Contralateral afferents arise from: (1) parts of CCN, MVN, SVN, IVN and cell group 'y' and (2) the central third of the FN. IVN receives bilateral projections from the perihypoglossal nuclei (PH) and the visceral nuclei of the OMC. Efferents from IVN project: (1) ipsilaterally to nucleus beta of the inferior olive, (2) contralaterally to parts of MVN, SVN and cell group 'y' and (3) bilaterally to the paramedian reticular nuclei. No commissural fibers interconnect cell groups 'f' and 'x'. Ascending fibers from IVN terminate contralaterally in the TN and the OMC. In the monkey fibers from IVN terminate in the ipsilateral nodulus, uvula and anterior lobe vermis; no fibers project to FN in either the cat or the monkey. Afferents to the LVN arise primarily from the ipsilateral anterior lobe vermis and bilaterally from rostral parts of the FN. No commissural fibers interconnect the LVN. Projections of the LVN are primarily to spinal cord via the vestibulospinal tract (VST); collaterals of the VST terminate in the lateral reticular nucleus (LRN). Ascending uncrossed projections from LVN in the cat terminate in the medial rectus subdivision of the OMC.(ABSTRACT TRUNCATED AT 400 WORDS)

The percentage of interneurons in the dorsal lateral geniculate nucleus of the cat and observations on several variables that affect the sensitivity of horseradish peroxidase as a retrograde marker

Ten cats ranging in age from 4 weeks postnatal to adult received large bilateral injections of horseradish peroxidase (HRP) into cortical areas 17 and 18. In one cat additional unilateral injections of HRP were made into the lateral suprasylvian visual areas (PMLS). The purpose of these injections was to label relay cells in lamina A of the dorsal lateral geniculate nucleus (LGN), in order to distinguish them from neurons that could not be labeled retrogradely. Several factors thought to influence the effectiveness of HRP as a retrograde marker were varied in an effort to label as many relay cells as possible. These factors included the (1) rate and duration of HRP injections; (2) volume and concentration of HRP injected; (3) addition of L-alpha-lysophosphatidylcholine or dimethyl sulfoxide to the injected HRP; and (4) aldehyde and buffers used for fixation. In all experiments DAB (3,3'-diaminobenzidine tetrahydrochloride) was used as the chromogen, either alone or with the addition of cobalt chloride, nickel, and cobalt salts, or cobalt-glucose oxidase. In 1-micrometer plastic sections, the influence of each of the above factors and DAB methods was determined by measuring the percentage of unlabeled neurons and the cytoplasmic HRP grain density of cells that were labeled. Our results show that approximately 22% of the neurons in lamina A of the LGN remain unlabeled following injections of HRP into areas 17 and 18 alone or combined with injections into PMLS. The percentage of unlabeled cells is similar at each of the ages that we studied and is not affected significantly by any of the factors that were varied or DAB methods that were used. Cross-sectional area measurements show that unlabeled cells tend to be among the smallest neurons in lamina A. Regardless of age, the mean size of labeled neurons was about twice that of unlabeled cells. However, we found only a weak correlation between the size of a labeled cell and the cytoplasmic density of HRP grains. Thus it is unlikely that small cell body size alone can account for the unlabeled cells in lamina A, since small neurons can be as effective in transporting HRP retrogradely as large neurons. We therefore conclude that there is a distinct population of small neurons in lamina A of the LGN that do not project to cortex. Although we cannot rule out the possibility that these cells project subcortically, we believe that it is reasonable to regard them as interneurons.