Afferent and efferent connections of the oculomotor cerebellar vermis in the macaque monkey

Saccadic eye movements were evoked with weak currents applied to a circumscribed vermal area. The area was confined to lobule VII in the majority of the monkeys and coincided with the distribution of saccade-related neural activity. We defined this area as the oculomotor vermis and studied its anatomical connections with wheat germ-agglutinin conjugated horseradish peroxidase (WGA/HRP) and HRP. When injected HRP was confined to the oculomotor vermis, most labeled Purkinje axons terminated ipsilaterally in an ellipsoidal region in the mediocaudal aspect of the fastigial nucleus. Retrogradely labeled cells were found in two relatively circumscribed regions in the fastigial nucleus: one group was in the lateral half of the ellipsoidal terminal region and the other group was in a spherical region near the lateral margin of the nucleus. Following the injection of HRP into the oculomotor vermis, the largest population of retrogradely labeled neurons was found in the nucleus reticularis tegmenti pontis. Labeled cells were located only in the medial and dorsolateral portions of the nucleus. The cell aggregates in the dorsolateral portion merged with densely labeled cells of the processus tegmentosus lateralis. The second largest population of labeled cells was found in the pontine nuclei. Approximately 28% of the labeled pontine cells aggregated in the paramedian pontine nucleus, whereas the other labeled pontine cells were widely distributed in the dorsal part of the pontine peduncular nucleus and the dorsolateral pontine nucleus. Labeled cells were scattered also in the pontine raphe, the paramedian pontine reticular formation, and the interfascicular nucleus at the rostral level of the hypoglossal nucleus. Fewer labeled cells were discovered in the vestibular nuclear complex and the prepositus hypoglossi. In the inferior olivary nucleus, labeled cells were located in the subnucleus b of the medial accessory nucleus.     

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.     

Brain stem afferents to the fastigial nucleus in the cat demonstrated by transport of horseradish peroxidase.

Although retrograde and anterograde degeneration studies have provided important information concerning brain stem afferents to the fastigal nucleus (FN), these data may be incomplete and should be confirmed by axonal transport methods. Attempts were made to inject horseradish peroxidase (HRP) unilaterally into the FN in a series of adult cats. Animals were perfused with dextran and a fixative solution of paraformaldehyde and glutaraldehyde in 0.1 M phospate buffer. Representative sections were treated by the Graham and Karnovsky ('66) method. Selective HRP injections in one FN resulted in retrograde transport of the marker to Purkinje cells of the ipsilateral vermis and distinctive appendages of the contralateral medial accessory olivary (MAO) nucleus (nucleus beta and the dorso-medial cell column). Retrograde transport of the label was found bilaterally in cells of the medial (MVN) and inferior (IVN) vestibular nuclei, in cell group x and in the nucleus prepositus (PP). Labeled vestibular neurons, most numerous in MVN, were identified in dorsal, caudal and lateral regions, with a slight ipsilateral preponderance. Only a few neurons in caudal, dorsal and lateral regions of the IVN were labeled and none of these included cells of group f. Labeled cells in the caudal third of PP were greatest ipsilaterally. Rostral and caudal injections of FN labeled smaller numbers of cells in MVN, IVN, cell group x and PP. HRP injections of FN and portions of lobules VIII and IX resulted in bilateral retrograde labeling of larger numbers of cells in MVN, IVN and cell group x, and ipsilateral labeling of cells in group y and the interstitial nucleus of the vestibular nerve. Injections of HRP into basal folia of lobules V and VI resulted in retrograde transport of the marker to cells of the medial and dorsal accessory olivary nuclei contralaterally, and to cells of the ipsilateral accessory cuneate nucleus. Transport of label injected into portions of the pyramis was detected in parts of the contralateral MAO and bilaterally in parts of the pontine and reticulotegmental nuclei. This study suggests that the principal afferents of the fastigial nucleus arise from: (1) Purkinje cells of the ipsilateral vermis, (2) restricted portions of the contralateral MAO (nucleus beta and dorsomedial cell column), (3) portions of the MVN and IVN (bilaterally) and (4) caudal parts of the PP. Secondary vestibular inputs to the fastigial nucleus probably are relayed mainly by Purkinje cells in the cerebellar cortex.     

Fastigial efferent projections in the monkey: an autoradiographic study.

Because fastigial efferent fibers partially decussate within the cerebellum and cerebellar corticovestibular projections pass near, or through, the fastigial nucleus (FN), degeneration studies based on lesions in the nucleus leave unresolved questions concerning fastigial projections. Attempts were made to determine fastigial projections in the monkey using autoradiographic tracing technics. Cells in rostral, caudal and all parts of the FN were labeled with [³H] amino acids. Selective labeling of neurons in either rostral or caudal parts of the FN results in transport of isotope primarily via fibers of the contralateral uncinate fasciculus (UF) and the ipsilateral juxtarestiform body (JRB). Fastigial projections to the vestibular nuclei are mainly to ventral portions of the lateral (LVN) and inferior (IVN) vestibular nuclei, are nearly symmetrical and are quantitatively similar on each side. Fastigiovestibular projections to cell groups f and x arise from all parts of the FN and are mainly crossed; modest projections to the medial vestibular nucleus are uncrossed. No fastigial efferent fibers end in the superior vestibular nucleus on either side, or in dorsal regions of the LVN. Crossed fibers descending in IVN terminate in the nucleus parasolitarius. Fastigioreticular fibers arise predominately from rostral regions of the FN, are entirely crossed and project mainly to: (1) medial regions of the nucleus reticularis gigantocellularis, (2) the dorsal paramedian reticular nucleus and (3) the magnocellular part of the lateral reticular nucleus. Fastigiopontine fibers, emerge with the UF, bypass the vestibular nuclei and terminate upon the contralateral dorsolateral pontine nuclei. Crossed fastigiospinal fibers separate from fastigiopontine fibers and descend in the ventrolateral tegmentum beneath the spinal trigeminal tract; in the medulla and upper cervical spinal cord these fibers are intermingled with those of the vestibulospinal tract. Fastigiospinal fibers terminate in the anterior gray horn at C-1 and probably descend further. Ascending fastigial projections arise from caudal parts of the FN, are entirely crossed and ascend in dorsal parts of the midbrain tegmentum. Label is transported bilaterally to the superior colliculi and the nuclei of the posterior commissure. Contralateral fastigiothalamic projections terminate in the ventral posterolateral (VPLc and VPLo) and in parts of the ventral lateral (VLo) thalamic nuclei. The major region of termination of fastigiothalamic fibers is in VPLo. Fastigiothalamic projections, probably conveying impulses concerned with equilibrium and somatic proprioception, appear to impinge upon thalamic neurons receiving inputs from less specialized receptors that signal information concerning position sense and body movement. More modest fastigial projections to VLo could directly influence activity of neurons in the primary motor cortex.     

Afferents to the oculomotor nucleus in the goldfish (Carassius auratus) as revealed by retrograde labeling with horseradish peroxidase.

The goal of this work was to compare the distribution and morphology of neurons projecting to the oculomotor nucleus in goldfish with those previously described in other vertebrate groups. Afferent neurons were revealed by retrograde labeling with horseradish peroxidase. The tracer was electrophoretically injected into the oculomotor nucleus. The location of the injection site was determined by the antidromic field potential elicited in the oculomotor nucleus by electrical stimulation of the oculomotor nerve. Labeled axons whose trajectories could be reconstructed were restricted to the medial longitudinal fasciculus. In order of quantitative importance, the afferent areas to the oculomotor nucleus were: (1) the ipsilateral anterior nucleus and the contralateral tangential and descending nuclei of the octaval column. Furthermore, a few labeled cells were found dorsomedially to the caudal pole of the unlabeled anterior octaval nucleus; (2) the contralateral abducens nucleus. The labeled internuclear neurons were arranged in two groups within and 500 microns behind the caudal subdivision of the abducens nucleus; (3) a few labeled cells were observed in the rhombencephalic reticular formation near the abducens nucleus, most of which were contralateral to the injection site. Specifically, stained cells were found in the caudal pole of the superior reticular nucleus, throughout the medial reticular nucleus and in the rostral area of the inferior reticular nucleus; (4) eurydendroid cells of the cerebellum, located close to the contralateral eminentia granularis pars lateralis, were also labeled; and (5) a small and primarily ipsilateral group of labeled cells was located at the mesencephalic nucleus of the medial longitudinal fasciculus. The similarity in the structures projecting to the oculomotor nucleus in goldfish to those in other vertebrates suggests that the neural network involved in the oculomotor system is quite conservative throughout phylogeny. Nevertheless, in goldfish these projections appeared with some specific peculiarities, such as the cerebellar and mesencephalic afferents to the oculomotor nucleus.     

Differences of the primate flocculus and ventral paraflocculus in the mossy and climbing fiber input organization

Potential sources of cerebellar cortical afferent fibers were identified in the vestibular ganglion, medulla oblongata, pons, and cerebellar nucleus of seven anesthetized Macaca fuscata after local injections of wheat germ agglutinin-conjugated horseradish peroxidase or Fast Blue into the flocculus (FL) or ventral paraflocculus (VP). There were differences in the sources of mossy fibers to the FL and VP. Labeled neurons, after injections into the FL, were located mainly in the ipsilateral vestibular ganglion, bilaterally in the vestibular and prepositus hypoglossal nuclei, nucleus reticularis tegmenti pontis, and the central part of the mesencephalic reticular formation including the raphe nuclei. Labeled neurons were rarely seen in the pontine nuclei after injections into the FL. By contrast, after injections into the VP, numerous labeled neurons were located in the contralateral pontine nuclei, but relatively few in the vestibular nuclei bilaterally. Sources of climbing fibers to the FL and VP were completely contralateral to the injection side. After the injection into the FL and VP, labeled neurons were located in the dorsal cap, ventrolateral outgrowth, and ventral part of the medial accessory olivary nucleus. The projections from these three olivary areas were generally consistent with a zonal pattern of terminations in the FL and VP. The present results are consistent with a hypothesis that the FL is mainly involved in the control of vestibulo-ocular reflex and that the VP is mainly involved in the control of smooth pursuit eye movements. J. Comp. Neurol. 382:480-498, 1997. © 1997 Wiley-Liss Inc.     

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)     

Anatomical and physiological characteristics of vestibular neurons mediating the horizontal vestibulo-ocular reflex of the squirrel monkey

The anatomical characteristics of vestibular neurons, which are involved in controlling the horizontal vestibulo-ocular reflex, were studied by injecting horseradish peroxidase (HRP) into neurons whose response during spontaneous eye movements had been characterized in alert squirrel monkeys. Most of the vestibular neurons injected with HRP that had axons projecting to the abducens nucleus or the medial rectus subdivision of the oculomotor nucleus had discharge rates related to eye position and eye velocity. Three morphological types of cells were injected whose firing rates were related to horizontal eye movements. Two of the cell types were located in the ventral lateral vestibular nucleus and the ventral part of the medial vestibular nucleus (MV). These vestibular neurons could be activated at monosynaptic latencies following electrical stimulation of the vestibular nerve; increased their firing rate when the eye moved in the direction contralateral to the soma; had tonic firing rates that increased when the eye was held in contralateral positions; and had a pause in their firing rate during saccadic eye movements in the ipsilateral or vertical directions. Eleven of the above cells had axons that arborized exclusively on the contralateral side of the brainstem, terminating in the contralateral abducens nucleus, the dorsal paramedian pontine reticular formation, the prepositus nucleus, medial vestibular nucleus, dorsal medullary reticular formation, caudal interstitial nucleus of the medial longitudinal fasciculus, and raphé obscurus. Eight of the cells had axons that projected rostrally in the ascending tract of Deiters and arborized exclusively on the ipsilateral side of the brainstem, terminating in the ipsilateral medial rectus subdivision of the oculomotor nucleus and, in some cases, the dorsal paramedian pontine reticular formation or the caudal interstitial nucleus of the medial longitudinal fasciculus. Two MV neurons were injected that had discharge rates related to ipsilateral eye position, generated bursts of spikes during saccades in the ipsilateral direction, and paused during saccades in the contralateral direction. The axons of those cells arborized ipsilaterally, and terminated in the ipsilateral abducens nucleus, MV, prepositus nucleus, and the dorsal medullary reticular formation. The morphology of vestibular neurons that projected to the abducens nucleus whose discharge rate was not related to eye movements, or was related primarily to vertical eye movements, is also briefly presented.     

Projections of the lateral terminal accessory optic nucleus of the common marmoset (Callithrix jacchus)

The connections of the lateral terminal nucleus (LTN) of the accessory optic system (AOS) of the marmoset monkey were studied with anterograde ³H-amino acid light autoradiography and horseradish peroxidase retrograde labeling techniques. Results show a first and largest LTN projection to the pretectal and AOS nuclei including the ipsilateral nucleus of the optic tract, dorsal terminal nucleus, and interstitial nucleus of the superior fasciculus (posterior fibers); smaller contralateral projections are to the olivary pretectal nucleus, dorsal terminal nucleus, and LTN. A second, mejor bundle produces moderate-to-heavy labeling in all ipsilateral, accessory oculornotor nuclei (nucleus of posterior commissure, interstitial nucleus of Cajal, nucleus of Darkschewitsch) and nucleus of Bechterew; some of the fibers are distributed above the caudal oculomotor complex within the supraoculornotor periaqueductal gray. A third projection is ipsilateral to the pontine and mesencephalic reticular formations, nucleus reticularis tegmenti pontis and basilar pontine complex (dorsolateral nucleus only), dorsal parts of the medial terminal accessory optic nucleus, ventral tegmental area of Tsai, and rostral interstitial nucleus of the medial longitudinal fasciculus. Lastly, there are two long descending bundles: (1) one travels within the medial longitudinal fasciculus to terminate in the dorsal cap (ipsilateral > > contralateral) and medial accessory olive (ipsilateral only) of the inferior olivary complex. (2) The second soon splits, sending axons within the ipsilateral and contralateral brachium conjunctivum and is distributed to the superior and medial vestibular nuclei. The present findings are in general agreement with the documented connections of LTN with brainstem oculomotor centers in other species. In addition, there are unique connections in marmoset monkey that may have developed to serve the more complex oculomotor behavior of nonhuman primates. © 1995 Wiley-Liss, Inc.     

Anatomical connections of the nucleus prepositus of the cat

The afferent and efferent connections of the nucleus prepositus hypoglossi with brainstem nuclei were studied using anterograde and retrograde axonal transport techniques, and by intracellular recordings and injections of horseradish peroxidase into prepositus hypoglossi neurons. The results of experiments in which horseradish peroxidase was injected into the prepositus hypoglossi suggest that the major inputs to the prepositus hypoglossi arise from the ipsi- and contralateral perihypoglossal nuclei (particularly the prepositus hypoglossi and intercalatus), vestibular nuclei (particularly the medial, inferior, and ventrolateral nuclei), the paramedian medullary and pontine reticular formation, and from the cerebellar cortex (flocculus, paraflocculus, and crus I; the nodulus was not available for study). Regions containing fewer labeled cells included the interstitial n. of Cajal, the rostral interstitial n. of the medial longitudinal fasciculus, the n. of the posterior commissure, the superior colliculus, the n. of the optic tract, the extraocular motor nuclei, the spinal trigeminal n., and the central cervical n. The efferent connections of the prepositus hypoglossi were studied by injecting 3H-leucine into the prepositus hypoglossi, and by following the axons of intracellularly injected prepositus hypoglossi neurons. The results suggest that in addition to the cerebellar cortex, the most important extrinsic targets of prepositus hypoglossi efferents are the vestibular nuclei (particularly the medial, inferior, and ventrolateral nuclei, and the area X), the inferior olive (contralateral dorsal cap of Kooy and ipsilateral subnucleus b of the medial accessory olive), the paramedian medullary and pontine reticular formation, the reticular formation surrounding the parabigeminal n., the contralateral superior colliculus and pretectum, the extraocular motor nuclei (particularly the contralateral abducens nucleus and the ipsilateral medial rectus subdivision of the oculomotor nucleus), the ventral lateral geniculate n., and the central lateral thalamic nucleus. Other areas which were lightly labeled in the autoradiographic experiments were the contralateral spinal trigeminal n., the n. raphe pontis, the Edinger Westphal n., the zona incerta, and the paracentral thalamic n. Many of the efferent connections of the prepositus hypoglossi appear to arise from principal prepositus hypoglossi neurons whose axons collateralize extensively in the brainstem. On the other hand, small prepositus hypoglossi neurons project to the inferior olive, and multidendritic neurons project to the cerebellar flocculus, apparently without collateralizing in the brainstem.(ABSTRACT TRUNCATED AT 400 WORDS)     

The origin of brainstem afferents of the paramedian pontine reticular formation in the cat

Transcannular microinjections of horseradish peroxidase (HRP) were made into the paramedian pontine reticular formation (PPRF) in adult cats to determine the origin of the principal sources of inputs to this important preoculomotor center for the production of saccadic eye movements. Retrogradely labeled cells were observed in numerous oculomotor-related structures, including the prerubral field (rostral interstitial nucleus of the medial longitudinal fasciculus), nucleus of Darkschewitsch, nucleus of the posterior commissure, deep superior colliculus, supraoculomotor ventral periaqueductal gray, contralateral paramedian pontine reticular formation, pontine raphe and dorsal medial pontine tegmentum medial to the abducens nucleus (purported to contain omnipause neurons), cell group Y, and the perihypoglossal complex (nucleus prepositus hypoglossi). Other sources of afferents to the region included the zona incerta, lateral and medial habenular nuclei, medial hypothalamus, medial mammillary nucleus, nucleus cuneiformis, medial medullary reticular formation, and the medial and lateral cerebellar nuclei. The results are discussed in terms of the potential influence of these nuclei on the control of eye movement.     

The vestibular nuclei in the domestic hen (Gallus domesticus) III. Ascending projections to the mesencephalic eye motor nuclei

Following injections of horseradish peroxidase in the oculomotor and the trochlear nuclei in the hen, the occurrence of labeled cells was plotted in the vestibular nuclei. The majority of labeled cells was localized in the superior, the medial, and the tangential nucleus. Within the superior nucleus the cells were found mainly caudally, extending medially and ventrally in central areas. In the medial nucleus labeled cells were localized exclusively in its rostral half, mainly in ventrolateral regions. Most, if not all, cells in the nucleus tangentialis project rostrally. In addition, rostrally projecting vestibular cells were found in the cell group A and the rostrolateral part of the descending nucleus. The projection to the oculomotor nuclear complex is from the superior nucleus and the cell group A bilateral but chiefly ipsilateral, from the medial nucleus bilateral, from the tangential nucleus and the rostral pole of the descending nucleus chiefly contralateral. Massive labeling was found in the abducens nucleus, somewhat less in the reticular formation, mainly in the lateral regions of the medial part at the level of the abducens and facial nuclei. Labeled cells were, in addition, found in the deep layers of the optic tectum, and scattered cells in the nucleus raphe. The findings are discussed in the light of what is known of the organization of the vestibular nuclei in the hen and the rostral projection of the vestibular nuclei in mammals.     

Afferents to the flocculus of the cerebellum in the rhesus macaque as revealed by retrograde transport of horseradish peroxidase

To investigate the afferent projections to the flocculus in a nonhuman primate, we injected horseradish peroxidase into one flocculus of six rhesus macaques (Macaca mulatta) and processed their brains according to the tetramethylbenzidine protocol to reveal retrogradely labeled neurons. Labeled neurons were found in a large set of nuclei within the rostral medulla and the pons. The greatest numbers of labeled neurons were in the vestibular complex and the nucleus prepositus hypoglossi. There were neurons labeled bilaterally throughout all the vestibular nuclei except the lateral vestibular nucleus, but most of the labeled neurons were in the caudal parts of the medial and inferior vestibular nuclei and in the central part of the superior vestibular nucleus; the nucleus prepositus was also labeled bilaterally, primarily caudally. Modest numbers of labeled neurons were found in the y-group, most ipsilaterally, and many neurons were labeled in the interstitial nucleus of the vestibular nerve. No labeled neurons were found in the vestibular ganglion following a large injection into the flocculus. A second large source of afferents to the flocculus was the medial, paramedial, and raphe reticular formation. Dense aggregates of labeled neurons were located in several pararaphe nuclei of the rostral medulla and the rostral pons and in the nucleus reticularis paramedianus of the medulla and several component nuclei of the nucleus reticularis tegmenti pontis bilaterally. Several groups of cells within and abutting upon the medial and rostral aspects of the abducens nucleus were labeled bilaterally. There was a modest projection from two parts of the pontine nuclei. Both a dorsal midline nucleus ventral to the nucleus reticularis tegmenti pontis and a collection of nuclei in a laminar region adjacent to the contralateral middle cerebellar peduncle contained labeled neurons whose numbers, while modest, were large compared to the projections to the flocculus in other animals. This generic difference may be due to the greater development of the smooth pursuit system in monkeys and the consequent need for a more substantial input from the cerebral cortex. As in other genera, the inferior olive projected to the flocculus via the dorsal cap of Kooy and the contiguous ventrolateral outgrowth. The projection was completely crossed and large injections labeled virtually every neuron in the dorsal cap, suggesting that the dorsal cap is the principal source of climbing fiber afferents.(ABSTRACT TRUNCATED AT 400 WORDS)     

Afferents to the abducens nucleus in the monkey and cat

The abducens nucleus is a central coordinating element in the generation of conjugate horizontal eye movements. As such, it should receive and combine information relevant to visual fixation, saccadic eye movements, and smooth eye movements evoked by vestibular and visual stimuli. To reveal possible sources of these signals, we retrogradely labeled the afferents to the abducens nucleus by electrophoretically injecting horseradish peroxidase into an abducens nucleus in four monkeys and two cats. The histologic material was processed by the tetramethyl benzidine (TMB) method of Mesulam. In both species the largest source of afferents to the abducens nucleus was bilateral projections from the ventrolateral vestibular nucleus and the rostral pole of the medial vestibular nucleus. Scattered neurons were also labeled in the middle and caudal levels of the medial vestibular nucleus. Large numbers of neurons were labeled in the ventral margin of the nucleus prepositus hypoglossi in the cat and in the common margin of the nucleus prepositus and the medial vestibular nucleus in the monkey, a region we call the marginal zone. Substantial numbers of retrogradely labeled neurons were found in the dorsomedial pontine reticular formation both caudal and rostral to the abducens nuclei. In the monkey, large numbers of labeled neurons were present in the contralateral medial rectus subdivision of the oculomotor complex, while smaller numbers occurred in the ipsilateral medial rectus subdivision and elsewhere in the oculomotor complex. In the cat, large numbers of retrogradely labeled cells were present in a small periaqueductal gray nucleus immediately dorsal to the caudal pole of the oculomotor complex, and a few labeled neurons were also dispersed through the caudal part of the oculomotor complex. Occasional labeled neurons were present in the contralateral superior colliculus in both species. The size and distribution of the labeled neurons within the intermediate gray differed dramatically in the two species. In the cat, the retrogradely labeled neurons were very large and occurred predominantly in the central region of the colliculus, while in the monkey, they were small to intermediate in size and were distributed more uniformly within the middle gray. Among the afferent populations present in the monkey, but not in the cat, was a group of scattered neurons in the ipsilateral rostral interstitial nucleus of the medial longitudinal fasciculus and a denser, bilateral population in the interstitial nucleus of Cajal.(ABSTRACT TRUNCATED AT 400 WORDS)     

Brainstem afferents to the intralaminar nuclei of the cat thalamus studied by the horseradish peroxidase method

Brainstem afferents to the intralaminar thalamic nuclei of the cat have been studied by retrograde axonal transport of horseradish peroxidase (HRP) or wheat germ agglutinin conjugated to HRP (WGA-HRP). Injections of HRP or WGA-HRP into the lateral central and paracentral nuclei led to labeling of cells in various diencephalic structures of the injected side. Some cells were labeled in the intralaminar and medial pulvinar nuclei. A large number of labeled cells were detected in the thalamic reticular and ventral lateral geniculate nuclei. The zona incerta and field of Forel contained a few labeled cells. Occasional labeled cells were seen in the dorsomedial, ventromedial, posterior and lateral hypothalamic nuclei. Labeling of cells in the more caudal brainstem structures was found bilaterally, mostly with ipsilateral predominance. Some labeled cells were detected in the pretectal nuclei, the periaductal gray and the pars reticulata of the substantia nigra as well. The nuclei of Darkschewitsch and Cajal contained occasional labeled cells. Numerous cells were labeled in the superior colliculus, mainly in layers 3 and 4. A number of labeled cells were distributed in almost the entire extent of the brainstem reticular formation. It should be mentioned that the gigantocellular reticular nucleus contained labeled cells bilaterally with contralateral predominance. Very few labeled cells were encountered in the ipsilateral dorsal tegmental and parabrachial nuclei. A few cells were labeled in the vestibular nuclei and nucleus prepositus hypoglossi bilaterally. Some labeled cells were detected mainly contralaterally in three cerebellar nuclei; the fastigial, the interposed and the dentate. Injections of WGA-HRP into the medial central nucleus showed a different pattern of labeling. It is noteworthy that no labeled cells were found in the dorsal thalamus, the hypothalamus (except for the lateral mamillary nucleus), the superior colliculus or the cerebellar nuclei.     

Cerebellar, medullary and spinal afferent connections of the paramedian reticular nucleus in the cat

The topographic organization of afferent projections from the deep cerebellar nuclei, medulla oblongata and spinal cord to the paramedian reticular nucleus (PRN) of the cat was studied using the horseradish peroxidase (HRP) method of retrograde labelling. Discrete placements of HRP within each of the dorsal (dPRN) and ventral (vPRN) regions of the PRN showed some segregation of input. The deep cerebellar nuclei project in a predominantly contralateral fashion upon the PRN. A small but significant ipsilateral fastigial afferent component is also present. The fastigial and dentate nuclei contribute the majority of fibers to the dPRN whereas the interposed nucleus provides very little. The vPRN receives a relatively uniform input from all 3 cerebellar nuclei. Both lateral vestibular nuclei contribute the majority of fibers from the vestibular nuclear complex largely from their dorsal division. Additional input arises from bilateral medial and inferior vestibular nuclei. The vPRN receives relatively more fibers from the inferior vestibular nuclei than does the dPRN while inputs from the medial vestibular nuclei are comparably sparse. The PRN receives bilateral projections from the nucleus intercalatus (of Staderini). A significant projection to the contralateral PRN occurs from the ventrolateral subnucleus of the solitary complex and its immediate vicinity. Additional sources of medullary afferent input include the lateral, gigantocellular and magnocellular tegmental fields, the contralateral PRN and the raphe nuclei. Sites of origin of spinal afferents to the dPRN are bilaterally distributed mainly within Rexed's laminae VII and VIII of the cervical cord whereas those to the vPRN are confined largely to the medial portion of the contralateral lamina VI in the C1 segment. A few labelled cells are found in the thoracolumbar cord with those to the vPRN being more caudal. These data provide the neuroanatomical substrate for a better understanding of the functional role of the PRN in mediating cardiovascular responses appropriate to postural changes.     

Connections of the caudal cerebellar interpositus complex in a new world monkey (Cebus apella)

The afferent and efferent connections of the cerebellar interpositus complex were studied in a capuchin monkey (Cebus apella) that had received a transcannular horseradish peroxidase implant into the caudal portion of the anterior interpositus nucleus and posterior interpositus nucleus. While the heaviest anterogradely labeled ascending projections were observed to the contralateral ventral posterolateral nucleus of the thalamus, pars oralis (VPLo), efferent projections were also observed to the contralateral ventrolateral thalamic nucleus (VLc) and central lateral (CL) nucleus of the thalamic intralaminar complex, magnocellular (and to a lesser extent parvicellular) red nucleus, nucleus of Darkschewitsch, zona incerta, nucleus of the posterior commissure, lateral intermediate layer and deep layer of the superior colliculus, dorsolateral periaqueductal gray, contralateral nucleus reticularis tegmenti pontis and basilar pontine nuclei (especially dorsal and peduncular), and dorsal (DAO) and medial (MAO) accessory olivary nuclei, ipsilateral lateral (external) cuneate nucleus (LCN) and lateral reticular nucleus (LRN), and to a lesser extent the caudal medial vestibular nucleus (MVN) and caudal nucleus prepositus hypoglossi (NPH), and dorsal medullary raphe. The heaviest retrograde labeling was corticonuclear Purkinje cells in the paramedian cerebellar cortex lateral to the vermis of lobules IV-VIII. Otherwise, retrogradely labeled sources of afferents were predominantly contralateral in the dorsal, dorsomedial, paramedian, and peduncular sectors of the basilar pons, NRTP, and dorsal accessory (DAO) and medial accessory (MAO) of olivary nuclei, but were predominantly ipsilateral in the LCN, LRN, and in the medullary reticular formation along the roots of the hypoglossal (XII) cranial nerve. It appeared that the connections with the contralateral dorsal basilar pons, NRTP, DAO and MAO, and ipsilateral LCN and LRN are reciprocal.(ABSTRACT TRUNCATED AT 250 WORDS)     

Ultrastructural identification and localization of climbing fiber terminals in the fastigial nucleus of the cat

Following injections of 3H-leucine and 35S-methionine in the caudal half of the medial accessory olive, labeled climbing fibers were found contralateral to the injection site in the sagittal A-zone of the cerebellar vermis and in the fastigial nucleus. Labeling in the fastigial nucleus was analyzed with ultrastructural autoradiography. Labeled boutons of climbing fibers were found in the neuropil but never on somata. They contain spherical vesicles and occasionally some dense core vesicles in an electron-lucent matrix. The terminals of climbing fiber collaterals in the fastigial nucleus resemble climbing fiber terminals in the molecular layer with respect to their internal ultrastructural characteristics.     

Location of abducens afferent neurons in the cat.

The sites of afferent neurons to the abducens nucleus were determined by the use of horseradish peroxidase hydraulically placed into the VIth nucleus in nine cats. Labeled neurons were found bilaterally in the medial vestibular nuclei, the prepositus nucleus of the hypoglossus, the contralateral dorsomedial gigantocellular tegmental field, the contralateral reticular formation, and the ipsilateral vestibular nerve ganglion.     

Cerebellopontine projections in the American opossum. A study of their origin, distribution and overlap with fibers from the cerebral cortex

The origin, course and distribution of cerebellopontine fibers was studied in the opossum by employing the Nauta-Gygax and Fink-Heimer techniques. Our results substantiate and extnd those of Brodal, Destombes, Lacerda and Angaut ('72) concerning the existence of cerebellopontine projections and provide evidence for a hitherto unreported fastigial projection to the basilar pons. Destruction of the caudal, medial division of the fastigial nucleus elicits bilateral degeneration in a restricted area of the medial pontine nucleus. This small terminal field is located in the angle between the medial lemniscus and the pyramidal tract and is found throughout the caudal three-fifths of the pons. The degenerating fibers do not course within the descending brachium conjunctivum, but reach the pons by filtering through the reticular formation from the uncinate fasciculus. Lesions that involve either the interpositus anterior or the dentate nucleus produce degeneration within the contralateral descending brachium conjunctivum and basilar pons. Terminal fields are located within the median, medial (paramedian nucleus of cat), peduncular, ventral and lateral nuclei. The heaviest degeneration is in the medial nucleus. Although cerebellar and cortical projections have different targets in the basilar pons, there is some overlap. Fastigial and preorbital fibers have partial overlap in the dorsal part of the medial nucleus, whereas the peduncular and lateral nuclei are the areas of overlap between the interpositus anterior and dentate projections with those from forelimb (and probably face) cortical areas. This overlap is particularly obvious in the caudal part of the lateral nucleus and occurs between fibers from limb motor-sensory cortex and those arising mainly within the anterior interpositus nucleus. There is no pontine overlap between cerebellar and visual or auditory cortical projections.