The anatomical organization of the cerebello-olivary projection in the cat.

The cerebello-olivary pathway in the cat has been examined using orthograde and retrograde neuroanatomical tracing techniques. The orthograde transport of 3H-leucine from injection sites in the deep cerebellar nuclei labeled dentate and interpositus projections to the rostral two-thirds of the contralateral inferior olivary complex. These projections are topographically organized, with the dentate nucleus projecting to the principal olivary nucleus and the posterior and anterior interpositus nuclei projecting to the medial and dorsal accessory olives respectively. Fibers from the ventral half of the dentate nucleus terminate in the lateral bend and ventral lamina of the principal olive, whereas the medial and lateral parts of the dorsal half of the nucleus project to the medial and lateral regions of the dorsal lamina respectively. It is apparent that the more caudal parts of the interpositus nuclei project to areas of the medial and dorsal accessory olives near the caudal end of the principal olivary nucleus, whereas neurons in the more rostral parts of the interpositus nuclei project to the more rostral areas of the accessory olivary nuclei. A connection between the fastigial ncleus and the inferior olive could not be demonstrated. The retrograde transport of horseradish peroxidase (HRP) from injections sites in the inferior olive labeled cells throughout the contralateral dentate and interpositus nuclei. The labeled cells were especially numerous in the ventral parts of the dentate and posterior interpositus nlclei. These HRP-positive neurons were consistently small (10--15 mu) ovoid or spindle-shaped cells, with relatively large nuclei and light-staining Nissl substance. This evidence strongly suggests that the cerebello-olivary pathway originates from a population of small neurons in the dentate and interpositus nuclei and projects to specific, topographically defined areas in the contralateral inferior olive.     

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)     

The dorsal column nuclear projections to the nucleus ventralis posterior lateralis thalami and the inferior olive in the cat: an autoradiographic study.

This autoradiographic study demonstrates a topical projection of the dorsal column nuclei to the contralateral nucleus ventralis posterior lateralis thalami and the accessory part of the inferior olive. In contrast to earlier anatomical studies the projections of the gracile nucleus and the internal cuneate nucleus proved to be independent and entirely contralateral. Fibers from the gracile nucleus terminate only in the lateral part of the nucleus ventralis posterior lateralis (VPL1) and from the internal cuneate nucleus only in the medial part of this nucleus (VPLm). Projections of the gracile nucleus to the contralateral inferior olive are restricted to the caudal one-third of the medial accessory olive and the ventrolateral part of the dorsal accessory olive. The internal cuneate nucleus is only connected with the dorsomedial part of the rostral two-thrids of the dorsal accessory olive. Our material does not allow conclusions about projections from the dorsal column nuclei to other thalamic nuclei and about rostrocaudal point to point relationships between the dorsal column nuclei and the thalamus or the inferior olive.     

Projections of the cerebellar and dorsal column nuclei upon the inferior olive in the rhesus monkey: an autoradiographic study.

Projections from the cerebellar and dorsal column nuclei to the inferior olive of the rhesus monkey were traced with anterograde autoradiographic methods. The cerebellar nuclei give rise to a massive projection which reaches the contralateral inferior olivary complex by way of the descending limb of the superior cerebellar peduncle. Dentato-olivary fibers project exclusively upon the principal olivary nucleus (PO) and observe a strict topography. The dorsal, lateral, and ventral dentate project respectively to the dorsal, lateral, and ventral lamellae of the PO. Within the lamellae, the dentato-olivary fibers are related point for point in the medio-lateral axis. By contrast, the rostro-caudal topography is reversed so that the rostral pole of the dentate projects to the caudal PO and the caudal dentate to the rostral PO. These connections are predominantly crossed but a small ipsilateral component recrosses the midline at the olivary commissure and mirrors the topography on the opposite side. The anterior interpositus projects only to the medial half of the DAO and the posterior interpositus projects only to the rostral two thirds of the MAO. The ipsilateral component is minor in comparison with the contralateral projection, but appears to be more substantial than the ipsilateral projection to the PO arising from the dentate nucleus. The fastigial nucleus does not project upon the olivary complex. The dorsal column nuclei project topographically upon the contralateral accessory nuclei with the gracile nucleus sending fibers primarily to the lateral half of the DAO and the cuneate nucleus projecting to rostral cell groups of the MAO. The present results when compared with other olivary connections described by previous studies in a variety of species suggest that regions of the MAO and DAO receiving sensory information from the periphery may lie outside the influence of cerebellar feedback loops.     

Projections to the inferior olive of the cat. II. Comparisons of input from the gracile, cuneate and the spinal trigeminal nuclei

The present experiments compared the projections to the inferior olive of the cat from the gracile, cuneate and spinal trigeminal nuclei. A differential labeling strategy was used for these comparisons. It was found that all three somatic sensory nuclei project to portions of all three major divisions of the contralateral inferior olive. The spinal trigeminal n. may also project less densely to the ipsilateral medial accessory olive. Projections to the dorsal accessory nucleus (DAO) and the medially-adjacent ventral lamella of the principal nucleus are roughly somatotopically organized. Although there is considerable overlap between the projection zones, the gracile n. projects predominantly to lateral DAO, the cuneate n. projects predominantly to medial DAO, and the spinal trigeminal nucleus pars caudalis projects predominantly to the most medial portions of DAO and the ventral lamella of principal olive. Projections to the medial accessory olive, on the other hand, are not as highly organized. Instead, they overlap extensively within a small egg-shaped area in the middle of the caudal half of the nucleus. Whereas all portions of the gracile and cuneate nuclei project to the inferior olive, only the pars caudalis of the spinal trigeminal nucleus appears to do so. These results were compared with the three available olivocerebellar maps as well as with the available behavioral and electrophysiological evidence on cerebellar somatotopic organization. This comparison indicated that the inputs to the cerebellum from the three second-order somatosensory nuclei via the inferior olive appear to be generally consistent with cerebellar somatotopic organization. This consistency is apparent not only with respect to the longitudinally-organized, vermal and paravermal differences in the anterior lobe, but also with respect to the transversely-organized specific somatotopy of the intermediate zone of the anterior lobe and the paramedian lobule.     

Afferents to the cerebellar lateral nucleus. Evidence from retrograde transport of horseradish peroxidase after pressure injections through micropipettes.

HRP was injected by pressure from glass capillary micropipettes unilaterally into the lateral nucleus of rat so as to encompass the entire nucleus, but without spread into the interpositus nuclei. The cells of origin of the afferents to the lateral nucleus were studied after retrograde transport of the HRP. The reticulotegmental nucleus of the pons was labelled bilaterally and is the major source of crossed and uncrossed reticular imputs. The pontine nuclei also provide extensive crossed and uncrossed afferents. The inferior olive gives a large crossed olivo-lateral nucleus projection and a minor uncrossed input. The trigeminal nuclear complex--the nucleus of the spinal tract and the mesencephalic, principal sensory, and motor nuclei--all provide uncrossed afferents. The rostral portion of the lateral reticular nucleus gives a small crossed and uncrossed projection while the perihypoglossal nuclei and the dorsal parabrachial body give crossed afferents to the lateral nucleus. The norepinephrine afferent system from the locus coeruleus is represented by one or two heavily labelled cells and the serotonin raphe systems come from at least five raphe subgroups, the dorsal, superior centralis, pontis, obscurus and magnus nuclei. No evidence was found for commissural fibers between ipsilateral or contralateral cerebellar nuclei, or afferent axons from the spinocerebellar nuclei and the paramedian retricular nucleus. The significance of these sources of afferent imputs to the lateral cerebellar nucleus is discussed. The question is raised of the direct relationship between size of terminal axonal arborization and the quantity of HRP granules present in a cell retrograde transport. The limitations of the HRP method for detecting subtle local differences in the distribution of afferents within the heterogeneous groups of neurons in the lateral nucleus are discussed.     

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.     

Distribution and brainstem origin of cholecystokinin-like immunoreactivity in the opossum cerebellum

In order to determine the distribution of the peptide cholecystokinin (CCK) within the cerebellum and medullary precerebellar nuclei of the adult opossum, sections of these brain regions were processed for peroxidase-antiperoxidase immunohistochemistry. Within the inferior and superior cerebellar peduncles, fine-beaded fibers are evident and a beaded plexus of fibers is present in all the cerebellar nuclei. In the overlying cerebellar cortex, CCK-positive mossy fiber rosettes are present in all lobules, where their morphology varies from simple enlargements to more complex rosettes. However, their distribution varies particularly in vermal lobules II, III, VII, and IX where they are organized in parasagittal bands. Climbing fibers that are positive for CCK are present in very restricted areas of vermal lobules IV, VII, and VIII. After colchicine pretreatment, CCK-positive cell bodies are seen in restricted regions of the posterior interposed and fastigial nuclei as well as within several precerebellar nuclei known to give rise to mossy fibers. Such nuclei include the lateral cuneate nucleus, the nucleus prepositis hypoglossi, the nucleus reticularis lateralis, the nucleus raphe obscurus, the paramedian reticular nucleus, the nucleus reticularis gigantocellularis, and the medial vestibular nucleus. To localize the brainstem origin(s) of the CCK fibers in the cerebellum, a double-label paradigm employing a retrograde tracer and CCK immunohistochemistry was used. These experiments indicate that CCK mossy fibers originate primarily within the lateral cuneate nucleus, the perihypoglossal complex, and the lateral reticular nucleus. Some also originate within the medial vestibular nucleus and the nucleus reticularis gigantocellularis. In addition, double-labeled cell bodies are present within the caudal medial accessory inferior olive, the likely source of the CCK-positive climbing fibers. These data indicate that specific populations of climbing fibers and mossy fibers may utilize CCK to alter the firing rate of their target neurons.     

An autoradiographic study of the rubroolivary tract in the rhesus monkey.

Autoradiographic tracing methods were employed to study the course and distribution of the rubroolivary tract following unilateral injections of tritiated leucine into the rostral red nucleus of seven rhesus monkeys. A topographic organization of projections to the ipsilateral principal nucleus of the inferior olivary complex was demonstrated. Lateral and medial portions of the rostral red nucleus projected to medial parts of the dorsal and ventral laminae of the principal inferior olive respectively; neurons in intermediate lateralities emitted fibers which terminated in lateral parts of the principal olive. Injections involving the oral end of the rostral red nucleus elicited label overlying the medial accessory olive in addition to the principal nucleus. Projections to the medial accessory olive may have arisen from the rostral end of the red nucleus and/or the immediately adjacent tegmentum. There were no projections to the dorsal accessory olive. Fibers of rubral origin also were distributed ipsilaterally to several reticular nuclei including the pedunculopontine, pontis oralis, caudalis, and gigantocellularis.     

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)     

Organization of projections from the inferior olive to the cerebellar nuclei in the rat

The detailed organization of projections from the inferior olive to the cerebellar nuclei of the rat was studied by using anterograde tracing. The presence of a collateral projection to the cerebellar nuclei could be confirmed, and a detailed organization was recognized at the nuclear and subnuclear level. Olivary projections to the different parts of the medial cerebellar nucleus arise from various parts of the caudal half of the medial accessory olivary nucleus. The interstitial cell groups receive olivary afferents from the intermediate part of the medial accessory olive and from the dorsomedial cell column. A mediolateral topography was noted in the projections from the rostral half of the medial accessory olive to the posterior interposed nucleus. Olivary projections to the lateral cerebellar nucleus are derived from the principal olive according to basically inversed rostrocaudal topography. Projections from the dorsomedial group of the principal olive to the dorsolateral hump were found to follow a basically rostrocaudal topography. The anterior interposed nucleus receives olivary afferents from the dorsal accessory olive. Its rostromedial parts are directed to the lateral part of the anterior interposed nucleus and its caudolateral part reach the medial anterior interposed nucleus. No terminal arborizations in the cerebellar nuclei were found to originate from (1) the dorsal fold of the dorsal accessory olive, which resulted in projections to the lateral vestibular nucleus and (2) the dorsal cap of Kooy. It was noted that the olivary projection to the cerebellar nuclei is strictly reciprocal to the nucleo-olivary projection as described by Ruigrok and Voogd (1990). Moreover, it is suggested that the olivonuclear projection adheres to the organization of the climbing fiber projection to the cerebellar cortex and to the corticonuclear projection, thus, establishing and extending the detailed micromodular organization of the connections between inferior olive and cerebellum.     

The inferior olivary nucleus of the opossum (Didelphis marsupialis virginiana), its organization and connections

Although the inferior olivary nucleus of the opossum is small, sections stained either for Nissl substance, normal axons or cholinesterase activity reveal distinct medial, dorsal and principal nuclei. The medial nucleus contains three major subdivisions (labelled a, b, c after Bowman and Sladek, 1973) and a group of neurons which is comparable to the cap of Kooy. In contrast to the cat and monkey, the major portion of the “medial” nucleus (subgroup a) lies lateral to the principal nucleus in rostral sections. The dorsal nucleus can also be subdivided, as can the principal nucleus which contains distinct dorsal and ventral lamellae. A small area is identified which based on position and connections may conform to the dorsal medial cell group. The experimental portion of the study provides evidence for an olivary projection from the motor-sensory cortex and a massive input from the midbrain (red nucleus, pretectum, midbrain tegmentum). In addition, the opossum inferior olive receives fibers from the deep cerebellar nuclei (cerebellar feedback loops), the spinal cord and the dorsal column nuclei. Of particular interest is the finding that fibers from the nucleus cuneatus and nucleus gracilis have distinctly different olivary targets and that those from the nucleus gracilis, but not the cuneate nucleus, overlap (in part, at least) with the direct spinal fibers. Other examples of overlapping fields of terminal degeneration are present and are discussed. In general our results reveal that although certain relationships between the nuclear divisions are different, the opossum olive conforms well to that of placental mammals and provides a basic mammalian model for future experimental electron microscopic and physiological studies.     

Projection systems and terminal localization of dorsal column afferents: an autoradiographic and horseradish peroxidase study in the rat

Projection systems from the gracile nucleus and the cuneate nuclear complex to their terminal sites in the mesencephalon, diencephalon, and cerebellum were examined by means of anterograde autoradiography and retrograde horseradish peroxidase methods. Three projection systems emerge from the dorsal column nuclei, decussate via internal arcuate fibers, and form the contralateral medial lemniscus (ML). At the obex, some fibers split off the ML and course dorsolaterally, forming an ascending lateral system which fits the "lemniscal adjunct channel" (LAC) concept of Graybiel ('72). The ML continues rostrally as the "main lemniscal line channel" (MLLC). At the inferior colliculus, some LAC fibers terminate in the pontine nuclei, parabrachial, dorsal reticular nuclei, and the external and ventral medial part of the central nucleus of the inferior colliculus. More rostrally at the level of the superior colliculus, terminal fields are found in the medial nucleus of the medial geniculate body, the suprageniculate, pretectal, and mesencephalic reticular nuclei, marking the end of the LAC. In the diencephalon, gracile fibers leave the MLLC and form a crescentlike terminal field along the extreme lateral border of the ventral posterior lateral nucleus (VPL) of the thalamus. Cuneate MLLC fibers terminate in a bandlike formation in the VPL medial to the gracile termination. The third fiber system, the cuneocerebellar projection, emerges from the cuneate, the external cuneate nuclei, and the "cellular bridge" and immediately enters the ipsilateral inferior cerebellar peduncle. Upon entering the cerebellum, the major fiber component remains ipsilateral and terminates as vertical bands in vermal and paravermal lobules, and lobules I through IVa. The posterior cerebellar lobe contains terminal bands in lobules VII-IX, the copula pyramidis, and the paramedian lobule. It is concluded that the dorsolateral fiber system conforms to Graybiel's LAC. It is more divergent and probably less modality specific, whereas the medial lemniscal system conforms to the MLLC, which is said to be modality specific, less divergent, and locked to specific sensory-motor response characteristics. The topography of cerebellar terminal bands indicates that there is sensory-motor representation from all parts of the body to all parts of the cerebellum, at least in the rat.     

Subcortical afferents to the interstitial nucleus of Cajal: an anatomical retrograde tracing study in the rabbit.

Organization of brainstem projections to the interstitial nucleus of Cajal (INC) in the rabbit has been studied using the method of retrograde transport of horseradish peroxidase or wheat germ agglutinin-horseradish peroxidase conjugate. Injections of tracers into INC resulted in bilateral labelling in the medial terminal nucleus of the accessory optic tract, medial region of the zona incerta, vestibular nuclei (superior, medial, inferior), rostral portion of the prepositus nucleus and several nuclei of the pontine and medullary reticular formation. Retrograde labelling on the contralateral side was noted in all 4 deep cerebellar nuclei, the lateral vestibular nucleus, group Y, the rostral interstitial nucleus of the medial longitudinal fascicle, INC and mesencephalic reticular formation dorsal and lateral to the red nucleus. Cells of origin for the ipsilateral afferents of INC were found only in the nucleus of the posterior commissure. These data are discussed in relation to other morphological and physiological studies of afferent connectivity of INC in other species.     

Vestibular afferents of the inferior olive and the vestibulo-olivo-cerebellar climbing fiber pathway to the flocculus in the cat

The projection of the vestibular nuclei to the inferior olive was investigated by means of anterograde transport of tritiated leucine. Following injections in the medial and descending vestibular nuclei, terminal labeling was found ipsilaterally in the dorsomedial cell column, subnucleus beta and the caudal medial accessory olive, while the latter also received afferents from the nucleus prepositus hypoglossi. At the contralateral side termination in the dorsomedial cell column and the medial accessory olive was found after injections in the nucleus vestibularis superior and group Y. The ventrolateral outgrowth and different parts of the principal olive also received afferents from these two nuclei and also from ventral parts of the lateral cerebellar nucleus. The dorsal cap was labeled exclusively from the contralateral nucleus prepositus hypoglossi. The termination in the inferior olive of the vestibular afferents is compared with the projection from a number of pretectal nuclei. Furthermore the consequences of the divergence and convergence of both types of projections at the level of the inferior olive is discussed in relation to the subsequent climbing fiber projection to the flocculus.     

Distribution of cells projecting to thalamus vs. those projecting to cerebellum in subdivisions of the dorsal column nuclei in raccoons

To learn the distribution of cells projecting to the thalamus, as opposed to the cerebellum, in the mechanosensory nuclei of the dorsal medulla of raccoons, we analyzed the retrograde transport of horseradish peroxidase from the ventrobasal complex of the thalamus and from the cerebellum. We found six nuclear regions projecting heavily to the thalamus with very small projections to the cerebellum: Bischoff's, central cuneate, central gracile, rostral cuneate, rostral gracile nuclei, and cell group z. Two regions showed heavy projections to the cerebellum with no projections to the thalamus: the lateral portion of the external cuneate nucleus and the compact portion of cell group x. Four regions showed more equivalent projections to both target regions: basal cuneate, medial portion of the external cuneate nucleus, medial tongue extension of the external cuneate nucleus, and reticular portion of cell group x. Three more ventral regions were labeled: lateral cervical nucleus from thalamic injections but not from cerebellar injections; central cervical nucleus from cerebellar injections, which crossed the midline, but not from thalamic injections; and lateral reticular nucleus from both target regions. In most medullary regions, most cells project to one target and very few project to the other; we suggest that the cells projecting to the minor target convey samples of the information going to the major target.     

Topical projection of the olivocerebellar system in the cat: an electrophysiological study

Using electrophysiological recording, topical aspects of the olivocerebellar projection were studied in the locally anesthetized cat immobilized with Flaxedil. Transcortical evoked potentials were recorded simultaneously from eight electrodes distributed over the cerebellar surface, and averaged with a LINC computer. Precautions were taken to eliminate virtual potentials from this volume conductor situation. The evoked potentials consisted of a 4–6 msec positive spike, latency 4.5–7 msec, followed by a 15–30 msec slow negative deflection. Each was recorded from one or two folia contralateral in distribution. Medial and dorsal accessory nuclei project largely to cerebellar vermis. A rostrocaudal relationship was found between posterior vermis and medial accessory nucleus, and vermal anterior lobe received its projection from the caudal and midportions of medial and dorsal accessory components. A dense representation of accessory nucleus responses was present over the declive as compared with other cerebellar areas. Paravermal responses of anterior lobe derived from rostral dorsal accessory olive, and principal olive connected to the hemispheral region. The ventral lamella of principal olive projected to Crus II, dorsal lamella to Crus I. These lobules are represented rostrally in the principal nucleus, whereas the source for paramedial lobules was situated more caudally. The results correlate well with the retrograde degeneration studies of Brodal ('40, '54) but differ in the detail of some projections.     

Cholecystokinin innervation of rat thalamus, including fibers to ventroposterolateral nucleus from dorsal column nuclei

The distribution of cholecystokinin octapeptide immunoreactive fibers and puncta in the adult rat thalamus was studied using immunocytochemical methods. Small to moderate numbers of immunoreactive fibers were present in the lateral habenular nucleus, ventral lateral geniculate nucleus, zona incerta, parataenial, mediodorsal, medioventral, and submedial nuclei, the rhomboid, paracentral, central lateral and parafascicular nuclei, and in the medial geniculate and dorsal lateral geniculate nuclei. Moderate to large numbers of cholecystokinin (CCK)-positive fibers were present in the paraventricular nuclei, the reticular nucleus, the anteroventral, anteromedial, and central medial nuclei, and in the rostral extension of the internal medullary lamina between the parataential and anteroventral nuclei. Dense concentrations of immunoreactive fibers were also found in a principal sensory relay nucleus, the ventroposterolateral nucleus (VPL), of the ventrobasal complex. The number of CCK-positive fibers in VPL showed a marked unilateral decrease in rats which had received lesions of the contralateral gracile and cuneate nuclei. The results of this study demonstrate that CCK-immunoreactive fibers and puncta are widely distributed in the rat thalamus, and that the source of these fibers in VPL is probably the dorsal column nuclei.