On the identification of the afferent axon terminals in the nucleus lateralis of the cerebellum an electron microscope study

Summary Axon terminals in the neuropil of the lateral nucleus can be divided into six classes, each with a specific constellation of characteristics that consistently occur together. Two of these classes have synaptic varicosities with elliptical synaptic vesicles, one in a dense, the other in a sparse matrix, and both make axosomatic and axodendritic synapses. The remaining four classes all have round synaptic vesicles and do not make axosomatic synapses. In the first of these four, the vesicles are tightly packed in a dense matrix, in another they are loosely dispersed, and in the third they are clustered. In the fourth, large granular vesicles predominate. Of these six classes, the most numerous belong to the axons of the Purkinje cell terminal arborization. These boutons resemble their counterparts in the cerebellar cortex, the recurrent collaterals of the Purkinje axon. They have elliptical and flat synaptic vesicles in a dark matrix. The varicosities terminate on somata and dendrites of large and small neurons and constitute the majority of their input. Purkinje axons constitute 86% of the total population of terminals on large neuronal perikarya and 50% of those on their dendrites, but only 78% on the somata of small neurons and 31% on their dendrites. The terminals of climbing fiber collaterals are recognized by their resemblance in electron micrographs to the terminals of the climbing fiber arborization in the cerebellar cortex. They bear round synaptic vesicles packed into a dense axoplasmic matrix and make Gray's type 1 axodendritic synapses with large and small neurons. These axons are restricted to the lateral and ventral aspects of the nucleus and constitute 5% of the terminals on large cell dendrites and 6% of those on small neurons. The axons tentatively identified as collaterals of mossy fibers are myelinated fibers with a light axoplasm containing round synaptic vesicles, dispersed throughout their varicosities. They make Gray's type 1 synapses and constitute a fair percentage of the total axodendritic contacts in the neuropil, 22% on large neurons and 28% on small neurons. The bases for these tentative identifications are discussed in detail, as are the various synaptic relationships undertaken by each class of axon. The remaining 4 classes of axons of the neuropil will be described in subsequent papers.Supported in part by U.S. Public Health Service grants NS 10536 and NS 03659, Training grant NS 05591 from the National Institute of Neurological Diseases and Stroke, and a William F. Milton Fund Award from Harvard University.     

Evidence of an x zone in lobule V of the squirrel monkey (Saimiri sciureus) cerebellum: The distribution of corticonuclear fibers

Summary The distribution of corticonuclear fibers to medial-most parts of the posterior interposed nucleus (NIP) from lateral areas of the vermis was studied in the squirrel monkey (Saimiri sciureus), using a silver impregnation method. The origin and course of degenerated fibers were studied in serial sections. The distribution pattern of corticonuclear fibers from a series of small well localized lesions placed in the vermis and paravermal cortex of lobule V is compatible with the interpretation that an x zone is present inSaimiri. A comparison of the positions of lesions and the trajectory of fibers arising therein suggests that corticonuclear input to medial-most parts of the NIP originated from a narrow cortical area (about 0.5–0.7 mm wide) located between a cortical area projecting into the medial cerebellar nucleus (the A zone) and a laterally adjacent area (the B zone) which related to the lateral vestibular nucleus. This NIP-projecting cortical area, located about 1.7 mm to 2.5 mm off the midline in lobule V, is interpreted as the x zone in this primate; it extends from lobule IV into lobule VI in squirrel monkey. Corticonuclear fibers of zone x in this primate form a comparatively small terminal field in the medial-most portions of NIP. This contrasts with the distribution of corticonuclear fibers of the C₂ zone which consistently distribute to terminal fields that are shifted into more central areas of NIP. There appears to be no overlap of the corticonuclear terminal fields in the NIP for zone x versus the C₂ zone. These results were correlated with data from the literature on the distribution of olivocerebellar fibers to the x zone and the C₂ zone and the arrangement of cerebellar nucleoolivary projections into the inferior olive from the NIP. The x zone and the C₂ zone both receive input from the contralateral medial accessory olive (MAO), both zones project into the NIP, and the NIP projects into those regions of the MAO which, in turn, project to these respective cortical zonesand into the NIP. This suggest that the x zone is a component of the NIP-MAO circuit. Furthermore the proposed function of the x zone would support the view that this sagittal strip may have a more extensive rostrocaudal distribution in primates as compared to the cat.This paper is dedicated to Professor Fred Walberg on the occasion of his 70th birthday.     

Axon terminals of the intrinsic neurons in the nucleus lateralis of the cerebellum an electron microscope study

Summary The large projection neurons of the lateral nucleus have long axons, which leave the cell mass in the superior cerebellar peduncle. These axons emit myelinated recurrent collaterals which have synaptic varicosities en passant. The varicosities are 2–5 m in diameter and contain round, agranular synaptic vesicles ranging between 280 and 480 Å with diameters of approximately 400 Å. The vesicles lie in a moderately dark axoplasmic matrix with a mean packing density of 281/m². The varicosities synapse through Gray's type 1 junctions with dendrites and thorns of large and small neurons. They constitute 22% of the total axonal population on dendrites of large neurons and 10% on dendrites of small neurons. The recurrent collateral system may provide a means for positive feedback to the same neuron and other neurons of the neuropil.The small neuron or interneuron has a short axonal plexus. The axon is myelinated, and is distinctive with a light axoplasmic matrix and varicosities containing elliptical synaptic vesicles. The vesicles are loosely dispersed with a mean population density of 44/m². These varicosities synapse through an intermediate type of junction upon the somata of certain large and small neurons and they consitute 14% and 22% of the axosomatic synapses respectively. They also make synapses on dendrites, constituting 12% and 25% of the total population of axons synapsing with dendrites of large neurons and those of small neurons respectively. It is suggested that these are the inhibitory interneurons of the lateral nucleus.The corticonuclear input through Purkinje axons is the dominant influence on the lateral nucleus neurons. This inhibitory input is considerably larger on the large neurons than on the small ones. It is speculated that the axosomatic synapses are inhibitory. Excitatory influences, through the collaterals of mossy and climbing fibers and the recurrent collaterals of the large intrinsic neurons, impinge upon the dendrites, where the axons of both Purkinje cells and interneurons also terminate.Supported in part by U.S. Public Health Service grants NS10536, NS03659, Training grant NS05591 from the National Institute of Neurological Diseases and Stroke, and a William F. Milton Fund Award from Harvard University.     

Senescent pathology of cerebellum: Purkinje neurons and their parallel fiber afferents

Two groups of naive male Sprague-Dawley rats, 5-7 and 24-26 months of age, were anesthetized with continuous intraperitoneal infusion of 4% chloral hydrate. Stimulation of the cerebellar vermis molecular layer permitted measurements of 12 different electrophysiological properties of parallel fiber Purkinje cell circuitry: parallel fiber conduction velocity, refractory period, threshold, and current dependent volley amplitude; slow negative wave threshold and current dependent amplitude; Purkinje cell activation threshold, latency, and current dependent spike driving; and Purkinje cell inhibitory threshold, latency, and current dependent duration of inhibition. Old subjects demonstrated deficits on all parameters except Purkinje cell inhibitory threshold. The relevance of these findings to our previous research on senescent changes in cell number, lipofuscin deposition, and spontaneous firing of Purkinje cells is discussed.     

Interrelations of basket cell axons and climbing fibers in the cerebellar cortex of the rat

Summary An analytical study was undertaken with both electron microscopy and the rapid Golgi method in order to clarify the interrelations of climbing fibers, basket cell axons, and Purkinje cell dendrites. The two fibers are readily distinguished in electron micrographs by means of their differing content of microtubules and neurofilaments, the packing density of synaptic vesicles, and the disposition of their synaptic junctions on the Purkinje cell dendrite. Climbing fibers are generally thin and contain many microtubules. They give off attenuated collaterals, whose rounded varicosities are densely packed with vesicles and which form en passant synapses with clusters of thorns projecting from the major Purkinje dendrites. In contrast, basket axons are relatively thick and contain many neurofilaments. By means of slight dilatations containing loosely aggregated vesicles, the axon and its collaterals form numerous synapses en passant with the smooth dendritic shafts and the perikaryon of the Purkinje cell. Climbing fibers and basket cell axons run along parallel with each other but without forming axo-axonic synapses as they ascend over the surface of the Purkinje dendrites. Both fibers form especially elaborate intertwined festoons at the branching points of the major dendrites. The kinds of synapses found are described in detail, and the functional implications are discussed.The hypothesis is developed that the dendritic thorn is a device for isolating the subsynaptic membrane from electrical events in the rest of the dendrite at the cost of reducing the effectiveness of the synapse. This principle is incorporated in the Purkinje dendrite—parallel fiber synapses, in which an individual fiber can be expected to have little importance. The disadvantage of using thorns as postsynaptic surfaces can be mitigated by clustering them and increasing the number of thorns contacted by each presynaptic terminal. This method is utilized at the junctions between the climbing fiber and the Purkinje dendrite to produce one of the most powerful excitatory synapses known. It is furthermore suggested that the elaborate plexus of climbing fibers and basket cell axons synapsing in the crotches of branching dendrites is strategically located to control the flow of information in the Purkinje cell dendritic tree.Supported by U.S. Public Health Service Research Grant NS03659 and Training Grant NS05591 from the National Institute of Neurological Diseases and Stroke.Postdoctoral trainee in Anatomy under Training Grant GM906 from the National Institute of General Medical Sciences.     

The recurrent collaterals of Purkinje cell axons: A correlated study of the rat's cerebellar cortex with electron microscopy and the Golgi method

Summary Each Purkinje cell axon with its recurrent collaterals occupies a roughly triangular space in the folium, apex pointed towards the white matter and base against the Purkinje cell layer. The axon is smooth initially but develops distensions that become more obvious at twists and turns and at points where collaterals originate. These thin, finely beaded collaterals make characteristic acute angles with the axon from which they issue. The collaterals bifurcate further, their terminal branches becoming more varicose, intertwining with each other to form plexuses in the molecular and granular layers. These fiber plexuses are found in three locations: (1) the recurrent collateral plexus in the granular layer which synapses with dendrites and somata of deep Golgi II neurons; (2) the profuse infraganglionic plexus, boutons of which terminate in relation with the somata and dendrites of Purkinje cells and Lugaro cells, in addition to participating in other complex synaptic arrangements in the neuropil; (3) the sparse supraganglionic plexus which forms synapses with dendrites of Purkinje cells and occasionally with basket cells.In electron micrographs, terminals belonging to recurrent collaterals contain a mixture of neurofilaments, microtubules, and slender mitochondria with a loose array of flat, elliptical, and round synaptic vesicles embedded in a dark filamentous matrix. It is usual to find a cluster of boutons on the postsynaptic surface. Each synapse consists of several separate macular junctional complexes. The synaptic cleft is widened and contains a dense fibrous material while both pre- and postsynaptic components have very shallow, symmetrical filamentous densities adherent to the cytoplasmic surfaces of the membranes.It is suggested that recurrent collaterals from axons of Purkinje cells may provide a rapid monosynaptic feed-back mechanism for inhibitory control of Purkinje cell responses. These collaterals may also participate in a slower positive feed-forward circuit or resetting mechanism involving at least two synapses. The existence of this circuit is indicated by synapses on deep Golgi II neurons. The inhibition of Golgi II cells may depress their inhibitory activity on surrounding granule cells, thus resetting the mechanism for the subsequent responses to excitatory afferent input. Recurrent collateral inhibition also may aid in the disinhibition of Purkinje cells through the depression of basket cell activity.Supported by U.S. Public Health Service Research Grant NS03659 and Training Grant NS05591 from the National Institute of Neurological Diseases and Stroke.     

Information about peripheral events conveyed to the cerebellum via the climbing fiber system in the decerebrate cat

Summary Discharges of Purkinje cells (PCs) with simple (SS) and complex spikes (CS) in the c₁zone of lobule Vc of the anterior lobe of the cerebellar cortex were analyzed in the decerebrate cat during a passive movement of the cat forepaw. The CS of the PC responded differentially and/or proportionally to the position of the extremity, amplitude of the movement, velocity and acceleration. Inphase and outphase responses of the climbing fiber (CF) system to sinusoidal movements could depend on the position of the extremity within the operational range. From these results we deduce that peripheral events can be signalled by the CF system. The possible function of the interaction between the two inputs at the PC level is discussed.Preliminary results were reported at the 47^th meeting of the Deutsche Physiologische Gesellschaft in Regensburg (Kolb and Rubia, 1976) and at the XXVII^th International Congress of Physiological Sciences in Paris (Rubia and Kolb, 1977)     

A horseradish peroxidase study of the projections from the lateral reticular nucleus to the cerebellum in the rat

Summary The projection from the lateral reticular nucleus (LRN) to the cerebellar cortex was studied in the rat by utilizing the retrograde transport of horseradish peroxidase (HRP). In order to study the topographic features of this projection, small amounts of HRP were injected into various sites in the cerebellar cortex. The results demonstrated that the caudal lobules of the anterior lobe vermis tend to receive afferents from the medial LRN and the rostral lobules of the vermis receive afferents from more laterally situated cells. Lobules IV and V receive inputs primarily from the magnocellular division of the LRN of both the ventromedial and dorsolateral parts of the LRN, while lobules II and III receive inputs mainly from cells which lie in the border area between the parvocellular and magnocellular division of the ventromedial part. Following injections within various areas of the posterior lobe vermis, the results indicated that lobule VIII receives the most abundant projection from the LRN and that the cells of origin are present within the parvocellular and the adjacent part of the magnocellular division throughout the rostrocaudal extent of the LRN. Following injections within lobules VI and VII, few labelled cells were found and they tended to lie within the rostral two-thirds of the magnocellular division. Little or no projection from the LRN to lobule IX was evident. The hemispheres were found to receive a modest projection from the dorsal aspect of the LRN. The projection to lobulus simplex originates mainly from the caudal two-thirds of the magnocellular division, while the projection to the ansiform and paramedian lobules originates mainly from the dorsal aspect of the rostral two-thirds of the magnocellular division. Finally, there appears to be extensive overlapping of the orgins of all three projections to the cerebellar cortex studied, and this occurs within the central area of the magnocellular division throughout the rostrocaudal extent of the LRN.     

The cerebellar corticonuclear projection from lobule Vb/c of the cat anterior lobe: a combined electrophysiological and autoradiographic study

Summary The present study examines the projection to the cerebellar nuclei of Purkinje cells in particular sagittal zones within the intermediate region of the cerebellar cortex. The boundaries between the zones were delimited electrophysiologically on the basis of their climbing fibre input so that a small volume (10–120 nl) of ³H-leucine could be injected into the centre of a chosen zone. The subsequent uptake and orthograde transport of labelled material by the Purkinje cells was studied autoradiographically. It was found that the smallest injections resulted in injection sites restricted to a single cortical zone and extremely reproducible results could be obtained using such a combined electrophysiological/autoradiographic technique. Larger injections sometimes spread to a neighbouring zone but the resultant terminal labelling within the deep nuclei was invariably consistent with the results obtained from smaller injections. The c₁ and c₃ olivocerebellar zones, which are known to receive climbing fibre input transmitted from the ipsilateral forelimb via a dorsal funiculus spino-olivo-cerebellar pathway (DF-SOCP), were found to project to partially overlapping regions within nucleus interpositus anterior (NIA). No projection to nucleus interpositus posterior (NIP) was demonstrated for either zone. No distinction could be seen between the terminal fields for the medial and lateral halves of the c₁ zone which are, however, known to receive their climbing fibre input from quite separate regions within the inferior olive. The c₂ zone, which was delimited on the basis of its climbing fibre input which is transmitted from both forelimbs via a lateral funiculus SOCP, was found to project exclusively to interpositus posterior. The hemispheral d₁ zone was found to project to the transitional region where interpositus anterior and the dentate nucleus adjoin.     

Purkinje cell age-distribution in fissures and in foliar crowns: a comparative study in the weaver cerebellum

Generation and settling of Purkinje cells (PCs) are investigated in the weaver mouse cerebellum in order to determine possible relationships with the fissuration pattern. Tritiated thymidine was supplied to pregnant females at the time that these neurons were being produced. Autoradiography was then applied on brain sections obtained from control and weaver offspring at postnatal (P) day 90. This makes it possible to assess the differential survival of neurons born at distinct embryonic times on the basis of the proportion of labeled cells located at the two foliar compartments: fissures and foliar crowns. Our data show that throughout the surface contour of the vermal lobes, generative programs of PCs were close between wild type and homozygous weaver. Similar data were found in the lobules of the lateral hemisphere. On the other hand, the loss of PCs in weaver cerebella can be related to foliar concavities or convexities depending on the vermal lobe or the hemispheric lobule studied. Lastly, we have obtained evidence that late-generated PCs of both normal and mutant mice were preferentially located in fissures. These quantitative relationships lead us to propose a model in which the final distribution of PCs through the vermal contour would be coupled to two factors: the cortical fissuration patterning and a “time-sequential effect” of weaver mutation.     

Synaptic organization of the Purkinje cells in the cerebellum of the cat

Summary An attempt at distinction between excitatory and inhibitory synapses is made in the cat cerebellum. The former are assumed to contain spheroid vesicles (S-type) of average diameter of 500 Å, while the latter flattened vesicles (F-type) of smaller size than the former. The elongation index (the ratio of the length of major versus minor axis of the vesicles) of S-type synaptic vesicles was about 1.2, while that of the F-type was more than 1.7. Parallel fibers of granule cells make S-type synaptic contacts (en-passant type or crossing-over synapse) mostly on the spines of the smaller branchlets of Purkinje cells. Climbing fibers make also S-type synapses on the smaller spines with short necks of the larger dendrites of Purkinje cells, but not frequently on the direct surface of them. It must be emphasized that almost no F-type synapse has been recognized which makes synaptic contacts directly on the spine of any type. It makes synaptic contacts usually on the direct surface of dendrites of Purkinje cells. Basket cell axons embrace directly the somas of the Purkinje cells. Their synaptic contacts were always of F-type and of en-passant character.The hypothesis is proposed that excitatory (E-type) synapses can be identified with synapses of S-type, whereas inhibitory (I-type) synapses would correspond to the F-type terminals.     

The adrenergic innervation of the rat central amygdaloid nucleus: a light and electron microscopic immunocytochemical study using phenylethanolamine N-methyltransferase as a marker

Using immunocytochemistry of phenylethanolamine N-methyltransferase for light and electron microscopy, investigations were carried out to document the morphology of adrenergic afferents innervating the rat central amygdaloid nucleus and to analyse the manner in which contacts with neurons of the nucleus are formed. With the light microscope, dense terminal plexus of phenylethanolamine N-methyltransferase-immunoreactive axons with typical large boutons (diameter>1 m) were found in the medial central nucleus, extending into its ventral subdivision and the adjacent intra-amygdaloid portion of the bed nucleus of the stria terminalis. Electron microscopy of the medial central nucleus showed phenylethanolamine N-methyltransferase-immunoreaction product in the cytoplasm of intervaricose axons and boutons. Large adrenergic boutons contained numerous small clear vesicles and, occasionally, large dense-cored vesicles. In serial sections, most boutons formed synaptic contacts. Synapses of immunoreactive terminals were mainly of the asymmetric type and localized preferentially on medium sized to small dendrites and dendritic spines. Structures postsynaptic to adrenergic boutons were often additionally contacted by non-labelled terminals. The study gives evidence that adrenergic afferents exert a direct synaptic influence on medial central nucleus neurons. The peripheral localization of the majority of adrenergic synapses, their asymmetric configuration, and the presence of non-adrenergic synapsing terminals in their immediate vicinity indicate that the major component of the adrenergic input is of an excitatory nature, and is integrated with innervation from other sources.Abbreviations BNST _i Intra-amygdaloid portion of the bed nucleus of the stria terminalis - CL lateral central amygdaloid nucleus - CLc lateral capsular central amygdaloid nucleus - CM medial central amygdaloid nucleus - CN central amygdaloid nucleus - CV ventral central amygdaloid nucleus - DAB diaminobenzidine - EM electron microscopy - ir immunoreactive - LM light microscopy - NPY neuropeptide tyrosine - PBS phosphate buffered saline - PFA paraformaldehyde - PNMT phenylethanolamine N-methyltransferase     

Spatial distribution of afferent information to the anterior lobe of the cat's cerebellum

Summary In the decerebrate cat discharges of Purkinje cells with simple and complex spikes as well as granule cell discharges in the c₁-zone of lobules Va, b and c of the cerebellar anterior lobe were analyzed during a passive movement of the cat's forepaw. Penetrations were made 50 m apart along the mediolateral and parasagittal directions, the depth never exceeding 500 m. The response of the Purkinje cells to the climbing fiber input was surprisingly constant, while simple spike responses of the same cells showed a great variability to the same input. The variability between granule cell discharges recorded at a 50 m distance from each other was similar to that of the simple spikes of the Purkinje cell. It is assumed that because of a patchy distribution of excited granule cells, two neighbouring Purkinje cells may receive a different information via their parallel fiber inputs. This difference is considered to be responsible for the great variability of their responses to mossy fiber inputs.     

Zonal organization of cortico-nuclear and nucleo-cortical projections of the paramedian lobule of the cat cerebellum. 2. The C2 zone

 The cortico-nuclear (C-N) and nucleo-cortical (N-C) projections of the C₂ cortical zone in pars anterior (pa) and pars posterior (pp) of the paramedian lobule (PML) in the posterior lobe of the cat cerebellum were investigated with a combined electrophysiological and neuroanatomical technique. In each experiment the medio-lateral boundaries of the zone were localized on the cortical surface by recording field potentials mediated via climbing fibres and evoked in the zone by activity elicited in spino-olivocerebellar paths through percutaneous stimulation of the fore- and hindlimbs; a small (15–30 nl) injection of 1–2% WGA-HRP was then made into the zone. Distributions in the deep cerebellar nuclei were determined with light microscopy both for C-N terminal labelling due to anterograde axonal transport by Purkinje cells and for cell bodies labelled due to retrograde transport in N-C axons. The extent to which retrogradely labelled olivary neurones were confined to the part of the rostral medial accessory olive that innervates the C₂ zone was estimated to provide an indication of the degree to which the injected tracer might have spread beyond the boundaries of the zone. The C-N projection from the part of the C₂ zone in PML pa terminates almost exclusively (probably exclusively) in nucleus interpositus posterior (NIP) at all medio-lateral levels of the nucleus but most extensively at middle and lateral levels. At most levels the C-N termination territory forms a crescent with its outer curve following the caudal, dorsal and rostral borders of the nucleus and as a result it is mainly in the dorsal half of the nucleus. There is heavy overlap with the projection from the lobule V part of the C₂ zone previously studied by us. The projection from the C₂ zone in PML pp terminates entirely in NIP, but although at middle medio-lateral levels in the nucleus there is substantial overlap with the PML pa and lobule V projections, the projection territory is confined to the medial half of the nucleus. Evidence was obtained compatible with the view that throughout the C₂ zone its lateral and medial parts project to different parts of NIP. In both PML pa and pp the C₂ zone receives N-C projections from NIP. Most of the N-C cells concerned are in the dorsal half of NIP and the great majority lie within the corresponding C-N projection territory. However, the N-C projection to PML pa appears c. 6 times heavier than that to PML pp and the PML pa part of the zone also receives a minor additional projection from nucleus lateralis (NL). The findings are discussed in relation to the hypothesis of olivo-cortico-nuclear complexes or compartments, with particular reference to the internal organization of the C₂ complex. Received: 28 April 1997 / Accepted: 22 July 1997     

Process of differentiation of cerebellar Purkinje neurons in the chick embryo

Summary The microscopic and ultrastructural differentiation of Purkinje neurons has been studied in 40 chicken embryo cerebella, from the 10th incubation day to hatching, and the transverse diameter of the cell body measured, for each developmental stage, on 30 electron micrographs of sagittally cut Purkinje cells. The developing Purkinje cell bodies, bipolar, at first, given the presence of two processes emerging from the opposite poles of the oval perikaryon, grow progressively in size. After the 12th incubation day, they develop a branched dendritic tree, and, shortly before hatching time, the cells acquire the characteristic flask or pear-shaped configuration. On the 10th incubation day, microtubules are already detectable together with Golgi complexes and a few vesicles of rough endoplasmic reticulum; on the 14th incubation day, RER cisterns are recognizable in the supranuclear cytoplasm, later extending into the whole perikaryon, and attaining their definitive distribution by the 18th incubation day. Pinocytotic and coated vesicles, as well as subsurface cisterns are seen during the whole embryonic life. In the earliest stages of development, three distinct types of junctional contacts between Purkinje cells and surrounding axons are described, and their functional role in relation to synaptogenetic processes is discussed. Beginning with the 16th incubation day, some Purkinje neurons undergo degenerative changes similar to those described in other types of neurons of the central and peripheral nervous system.     

Zonal organization of cortico-nuclear and nucleo-cortical projections of the paramedian lobule of the cat cerebellum. 1. The C1 zone

 The cortico-nuclear (C–N) and nucleo-cortical (N–C) projections of the C₁ cortical zone in pars anterior (pa) and pars copularis (pc) of the paramedian lobule (PML) in the posterior lobe of the cat cerebellum were investigated with a combined electrophysiological and neuroanatomical technique. In each experiment the medio-lateral boundaries of the zone were located on the cortical surface by recording field potentials mediated via climbing fibres and evoked in the zone by activity elicited in spino-olivocerebellar paths through percutaneous stimulation of fore- and hindlimbs; a small (15–30 nl) injection of WGA-HRP was then made into the zone. The distributions in the deep cerebellar nuclei were determined (with light microscopy) both for terminal labelling due to anterograde axonal transport by Purkinje cells and for cell bodies labelled due to retrograde transport in N–C axons. The extent to which injection sites were confined to the C₁ zone was assessed both by comparing injection site and zone widths and by determining the distributions of retrogradely labelled neurones within the contralateral inferior olive. The C–N projection from the part of the zone in PML pa (a forelimb part) terminates almost exclusively (perhaps exclusively) in nucleus interpositus anterior (NIA), primarily in caudal and dorsal parts, where it overlaps heavily with the C–N projections from the lobule V parts (also forelimb parts) of the C₁ and C₃ zones as previously defined. The C–N projection from the part of the zone in PML pc (a hindlimb part) also terminates virtually exclusively in NIA but primarily in almost all parts of the medial third of the nucleus. There is, nevertheless, sufficient overlap between the PML pa and PML pc projections that approximately one third of the termination territory of each projection overlaps that of the other. The PML pc part of the zone is almost entirely lacking in a N–C projection, as previously found for the lobule V part of the C₁ zone (and C₃ zone). However, the PML pa part of the zone receives N–C projections that arise, in descending order of size, from nucleus interpositus posterior (NIP), from NIA, from the NIA/nucleus lateralis (NL) fusion area and (perhaps) NL. The projection from NIP is similar in size to that provided by the nucleus to the C₂ zone in lobule V of the anterior lobe. The findings are discussed, with particular emphasis on their implications for the hypothesis that the cerebellum is divisible into a number of olivo-cortico-nuclear complexes or compartments. Received: 3 April 1997 / Acccepted: 22 July 1997     

Identification and distribution of the spinal and hypophyseal projection neurons in the paraventricular nucleus of the rat. A light and electron microscopic study with the horseradish peroxidase method

Summary The distribution of labeled neurons in the paraventricular nucleus of the hypothalamus (PVN) was studied following injections of horseradish peroxidase (HRP) into the spinal cord (C8 to T1) or the hypophysis in the rat. Injections were also made in the spinal cord in another group of animals, which were subjected to water deprivation for a period of 3 days, and the PVN of these animals was examined with the electron microscope.Spinal projection neurons (paraventriculospinal tract, PVST, neurons) formed two groups; the dorsal and the ventral groups. They were located within the parvocellular part of the PVN and fused into one at the caudal level. The neurons of the dorsal group were well assembled whereas those of the ventral group were intermingled with paraventriculohypophyseal tract (PVHT) neurons, which were concentrated in the magnocellular part. Electron microscopic observations revealed that HRP-labeled neurons after spinal injections did not contain neurosecretory granules and that they were not affected by water deprivation. On the other hand, neurons containing a number of neurosecretory granules displayed a significant degree of dilatation of the endoplasmic reticulum as the result of water deprivation. These neurons contained no HRP granules.The present findings suggest that the PVST neurons are distinct from the PVHT neurons and that the neuronal groups of both systems form different cell columns within the nucleus.Abbreviations C caudal - D dorsal - Mgc magnocellular part - NH neurohypophysis - PVHT paraventriculohypophyseal tract - PVN paraventricular nucleus - PVST paraventriculospinal tract - R rostral - SC spinal cord - V ventral - III third ventricle     

Connections of Purkinje cell axons of lobule X with vestibulospinal neurons projecting to the cervical cord in the rat

Connections of Purkinje cell axons of lobule X (nodulus vermis) with vestibulospinal neurons have been demonstrated in the rat, by anterograde labeling of axons with biotinylated dextran (BD) injected into sublobule Xa and by retrograde labeling of neurons with cholera toxin subunit B (CTB) injected into cervical segments. Labeled terminals of Purkinje cell axons were numerous in the superior vestibular nucleus, the parvocellular (MVpc) and the caudal part (MVc) of the medial vestibular nucleus (MV), and group y. A limited number of labeled terminals were seen in the caudal part of the descending vestibular nucleus (DV). Occasional labeled terminals were seen in the lateral part of the lateral vestibular nucleus (LV) whereas few labeled terminals were seen in the magnocellular part of the MV (MVmc). Vestibulospinal neurons labeled from the C2 and C3 segments were seen bilaterally in the MVmc, MVpc, MVc, and DV, and ipsilaterally in the LV. CTB-labeled vestibulospinal neurons in contact with BD-labeled terminals of Purkinje cell axons were identified in the lateral part of the MVpc, near the border between the MVpc and MVmc, or close to the dorsal acoustic stria, and in the middle part of the MVc at its rostral level. The present study suggests that Purkinje cells of lobule X regulate the output of cervical-projecting vestibulospinal neurons in the MVpc and MVc.     

Connections of Purkinje cell axons of lobule X with vestibulocerebellar neurons projecting to lobule X or IX in the rat

Connections of Purkinje cell axons of lobule X (nodulus) with vestibulocerebellar neurons projecting to lobule X or IX (uvula) were revealed in the rat. Purkinje cell axons were anterogradely labeled with biotinylated dextran (BD) injected into sublobule Xa while vestibular neurons were retrogradely labeled with cholera toxin subunit B (CTB) injected into sublobule Xa or IXc. Labeled terminals of Purkinje cell axons of lobule X were numerous in the superior vestibular nucleus (SV), medial parts of the parvocellular (MVpc) and the caudal part (MVc) of the medial vestibular nucleus (MV), and group y. These subdivisions of the vestibular nuclei contained many neurons projecting to lobule X or IX. Lobule-X-projecting and lobule-IX-projecting neurons were in contact with terminals of Purkinje cell axons of lobule X in the MVpc and MVc. They were distributed dorsally to medially in medial parts of the MVpc and MVc. The present study suggests that Purkinje cells in lobule X regulate the output of a population of lobule-X-projecting or lobule-IX-projecting neurons of the MVpc and MVc.     

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

Summary Details of cerebellar afferent projections from the vestibular nuclei were investigated by the method of retrograde axonal transport of horseradish peroxidase (HRP) in the cat. The distribution of labeled cells in the vestibular nuclei following HRP injections in various parts of the cerebellum indicates that vestibular neurons in the medial and descending nuclei and cell groups f and x project bilaterally to the entire cerebellar vermis, the flocculus, the fastigial nucleus and the anterior and posterior interpositus nuclei. In addition, labeled cells (giant, medium and small) were consistently found bilaterally in the superior and lateral vestibular nuclei following HRP injections in the nodulus, flocculus, fastigial nucleus, and following large injections in the vermis. No labeled cells were observed in cases of HRP injections in crus I and II, the paramedian lobule, paraflocculus and lateral cerebellar nuclei. The present findings indicate that secondary vestibulocerebellar fibers project to larger areas in the cerebellum and originate from more subdivisions and cell groups of the vestibular nuclear complex than previously known.List of Abbreviations B.c. superior cerebellar peduncle (brachium conjunctivum) - D descending (inferior) vestibular nucleus - f cell group f in descending vestibular nucleus - g group rich in glia cells, caudal to the medial vestibular nucleus - HIX hemispheral lobule IX - HVIIA cr. Ia, p; cr. IIa, p anterior and posterior folia of crus I and II of the ansiform lobule - HVIIB, HVIIIA, B sublobules A and B of hemispheral lobules VII and VIII - i.c. nucleus intercalatus (Staderini) - L lateral vestibular nucleus (Deiters) - l small-celled lateral group of lateral vestibular nucleus - M medial (triangular or dorsal) vestibular nucleus - N. cu. e. accessory cuneate nucleus - N. f. c. cuneate nucleus - N. mes. V mesencephalic nucleus of trigeminal nerve - N.tr. s. nucleus of solitary tract - N. VII facial nerve - pfl. d. dorsal paraflocculus - pfl. v. ventral paraflocculus - S superior vestibular nucleus (Bechterew) - Sv. cell group probably representing the nucleus supravestibularis - Tr. s. solitary tract - x small-celled group x, lateral to the descending vestibular nucleus - y small-celled groupy, lateral to the lateral vestibular nucleus (Deiters) - z cell group dorsal to the caudal part of the descending vestibular nucleus - I–VI vermian lobules I–VI - V, VI, XII cranial motor nerve nuclei - VIIA, B; VIIIA, B anterior and posterior sublobules of lobules VII and VIII - IX uvula - X nodulus; dorsal motor nucleus of vagus nerve On leave from the Laboratory of Neurobiology and Department of Anatomy, Faculty of Science, Mahidol University, Bangkok, Thailand, under the Felllowship Program of the Norwegian Agency for International Development (NORAD)