Lateral Cerebellar Nucleus Research Articles

Age-related and region-specific increase in number of concentric lamellar bodies in axon terminals and presynaptic axons in central nervous system of groggy mutant rat.

In some regions of the central nervous system (CNS) of the groggy rat, a mutant with a movement disorder, concentric lamellar bodies (CLBs) were formed in numerous axon terminals and presynaptic axons. These bodies were counted electron microscopically in the lateral cerebellar nuclei of Slc:Wistar and groggy mutant rats at 20 to 180 days of age. In the Slc:Wistar rat groups, the mean numbers of axonal CLBs were mostly under 1.0 per 100 microns2, except for the 30-day-old rat group which showed a value of 1.7. In the groggy rat groups, the numbers of axonal CLBs greatly increased from 40 days of age onward, reaching the maximum mean number of 23.7 per 100 microns2 in the 90-day-old rat group and subsequently decreasing; however, significant numbers were still present in the 180-day-old rat group. Since these bodies have been reported to contain an acid phosphatase (ACPase), the regional specificity of their appearance in the CNS was examined by light and electron microscopic ACPase histochemistry. In the 90- and 180-day-old groggy rats, numerous particulate deposits of ACPase reaction products were found in the neuropil of the lateral, interposed and medial cerebellar nuclei, the superior, lateral and spinal vestibular nuclei, and the spinal gracile nuclei. By electron microscopy, the particulate deposits in the cerebellar and vestibular nuclei were confirmed as the CLBs in axon terminals, while those in the gracile nuclei were revealed to be the dystrophic axons. Thus, it was suggested that the axon terminals and presynaptic axons, having a high capacity to form the CLBs in the groggy rats from 40 days of age onward, belong to the Purkinje cells.

Cellular localization of nerve growth factor-like immunoreactivity in adult rat brain: Quantitative and immunohistochemical study

To elucidate the role and the mechanism of action of nerve growth factor in the adult central nervous system, we investigated the localization of nerve growth factor-like immunoreactivity in adult rat brain, both quantitatively and immunohistochemically, using polyclonal anti-nerve growth factor immunoglobulin G. We raised rabbit polyclonal anti-mouse nerve growth factor antibody with an extremely high titer as 10 −9 determined by an enzyme immunoassay. The affinity-purified anti-nerve growth factor immunoglobulin G specifically recognized nerve growth factor with no cross-reaction to recombinant brain-derived neurotrophic factor and neurotrophin-3 evaluated by an enzyme immunoassay. We quantified nerve growth factor content in each layer of the adult rat cerebral cortex and in each small piece (0.225 mg wet weight tissue) of the diencephalon, brainstem and cerebellum with a highly sensitive two-site enzyme immunoassay. Nerve growth factor content was unevenly distributed in the cerebral cortex (dense in layers II/III and V/VI and sparse in layers I and IV). Moderate to high levels of nerve growth factor were registered in the habenular nuclei, zona incerta, ventral tegmental area, substantia nigra, locus coeruleus, ventral cochlear nucleus, trapezoid body, lateral vestibular nucleus, cerebellar nuclei and paraflocculus. Immunohistochemically, the nerve growth factor-like immunoreactivity was found in the cell bodies, dendrites and axons of adult rat central neurons, not only in the cerebral cortex, hippocampus and basal forebrain, but also in the diencephalon, brainstem and cerebellum. The population of neurons with nerve growth factor-like immunoreactivity was limited, but unexpectedly widespread, and the density of these cells correlated well with the content determined by an enzyme immunoassay in the present and a previous study [Nishio T. et al. (1992) Expl Neurol. 116, 76–84]. The monoamine neurons, including dopaminergic, noradrenergic and serotonergic neurons, showed intense nerve growth factor-like immunoreactivity, indicating that the central monoaminergic neuronal system may also be involved in the nerve growth factor trophic system. To visualize nerve growth factor transported in the axons and to enhance the immunostaining in the nerve growth factor-producing cells, we injected colchicine, a potent inhibitor of microtubule polymerization and a blocker of axoplasmic transport, into the lateral ventricle of adult Wistar rat brain. Colchicine treatment enhanced the intensities of nerve growth factor-like immunoreactivity in the axons and cell bodies, especially in the axon hillocks and the proximal axons of the nerve growth factor-producing neurons. This observation may suggest the existence of an orthograde axonal transport system for nerve growth factor in the central neurons. These results suggest that nerve growth factor may exist in widespread populations of adult central neurons, including the monoaminergic neurons, and may exert a trophic effect on these neurons through not only a retrograde manner but also an orthograde manner of transport.

The origin of serotoninergic afferents to the cat's cerebellar nuclei

In the cat, serotoninergic (5HT) axons and terminals form a dense plexus that is present throughout the granule cell and Purkinje cell layers of the cerebellar cortex and all of the cerebellar nuclei. The intent of the present study was to identify the source of 5HT fibers in the cerebellar nuclei. The medial, interposed, and lateral cerebellar nuclei were selectively injected with either rhodamine or fluorescein-labeled latex microspheres that were retrogradely transported to brainstem neurons. Transverse sections of the brainstem were processed with a primary antibody to 5HT and secondary antibody tagged with either rhodamine or fluorescein. The location of neurons containing both serotonin-like immunoreactivity and retrogradely transported microspheres was plotted. All three of the cerebellar nuclei receive 5HT afferents from the nucleus locus coeruleus, the dorsal raphe nucleus, and the dorsal tegmental nucleus. In addition, the medial nucleus receives projections from the superior central nucleus, the nucleus raphe obscurus, the nucleus raphe magnus, and the periolivary reticular formation. The interposed nuclei receive additional projections from the nucleus raphe magnus, whereas the lateral nucleus receives additional projections from the superior central nucleus. In conclusion, the 5HT projections to the cerebellar nuclei do not appear to be collaterals of those projecting to the cortex (Kerr and Bishop, J Comp Neurol 304:502-515, 1991). These findings suggest that, although the cortex and nuclei are anatomically and physiologically related, they do not process all information in parallel.

Non-N-methyl-D-aspartate receptors mediate neocerebellar excitation at accessory oculomotor nuclei synapses of the rat.

The nature of the receptor which mediates cerebellar-evoked monosynaptic excitations recorded from the accessory oculomotor nuclei (AON), i.e. the nucleus of posterior commissure, the nucleus of Darkschewitsch and the interstitial nucleus of Cajal, was studied in adult rats. Effects of exogenously applied excitatory amino acid (EAA) agonists N-methyl-D-aspartate (NMDA) and quisqualate (QUIS) and of selective NMDA receptor antagonist 2-amino-5-phosphonovaleric acid (2APV) and non-NMDA receptor antagonist 6,7-dinitroquinoxaline-2,3-dione (DNQX) were examined on both amino acid induced and synaptic excitation. Microiontophoretic application of NMDA and QUIS in the AON of the rat increases the neuronal discharge in a dose-dependent manner. These findings suggest that in the rat cells belonging to AON bear both NMDA and non-NMDA receptors. This result was confirmed by the fact that applications of 2APV selectively antagonized NMDA-induced responses without affecting those to QUIS, while DNQX blocked specifically the excitatory responses to QUIS and did not affect NMDA-mediated excitations. We did not observe any difference, between rats anesthetized with urethane and those anesthetized with halothane, with respect to capability of EAA agonists NMDA and QUIS to increase the AON cells activity and of EAA receptor antagonists 2APV and DNQX to abolish the NMDA-induced and the QUIS-induced effects, respectively. In addition, monosynaptic excitations induced by the stimulation of cerebellar lateral nucleus were abolished by microiontophoretic application of DNQX, but not of 2APV. This finding indicates that neocerebellar inputs activate specifically non-NMDA receptors of AON neurons.

Cerebellar influences on accessory oculomotor nuclei of the rat: A neuroanatomical, immunohistochemical, and electrophysiological study

With the aim to evaluate a possible neocerebellar control on eye movements, the projections from the cerebellar lateral nucleus (LN) to the accessory oculomotor nuclei (i.e., the nucleus of posterior commissure, the nucleus of Darkschewitsch, and the interstitial nucleus of Cajal), the putative neurotransmitters subserving this pathway, and the nature of the synaptic influences exerted by these projections were studied in adult rats. We used the orthograde transport of horseradish peroxidase conjugated with wheat germ agglutinin (WGA-HRP) to identify the mesencephalic areas where cerebellofugal fibers terminate, and retrograde labeling with the fluorescent dye fluoro-gold to estimate the incidence of cerebellar neurons projecting to the accessory oculomotor nuclei. Orthograde labeling showed that only a small contingent of cerebellofugal fibers reaches the contralateral accessory oculomotor nuclei. The retrogradely labeled cells were located primarily in the small-celled part of LN. By immunohistochemistry, we observed that all the cells retrogradely labeled from the accessory oculomotor area were also stained by using glutamate or aspartate antisera, but none of them were double-stained with a GABA antiserum. Electrical stimulation of the contralateral LN elicited changes in firing rate of a significant fraction of cells belonging to the accessory oculomotor nuclei (36.4% in the nucleus of posterior commissure, 47.1% in the nucleus of Darkschewitsch, and 44.6% in the interstitial nucleus of Cajal). In 57.8% of the cases, the responses were excitations, most of which had latencies and response characteristics compatible with a monosynaptic linkage. The remaining 42.2% of the cases were inhibitions with latencies ranging between 5 and 22 ms. Extracellular field potential recordings within the contralateral accessory oculomotor nuclei were interpreted as arising from impulses propagating along excitatory axons projecting in a bundle from the cerebellum. Stimulation of LN area in rats following intranuclear injection of kainic acid was not capable of evoking short latency excitations, so these responses can be considered to depend on the activation of LN efferents. The LN projection on accessory oculomotor nuclei could be part of the final precise control exerted by the neocerebellum on those brain structures concerned with movements of the eyes.

Cerebellar nuclear projections from the basilar pontine nuclei and nucleus reticularis tegmenti pontis as demonstrated with PHA-L tracing in the rat.

Small iontophoretic placements of the orthogradely transported axonal tracer Phaseolus vulgaris leucoagglutinin (PHA-L) were made in portions of the basilar pontine nuclei (BPN) or nucleus reticularis tegmenti pontis (NRTP) to determine if these cell groups provide projections to the cerebellar nuclei (CN) in the rat and if so, to visualize the morphology of the axons and terminals and illustrate any topographical organization in this system. Axons that originated from BPN or NRTP neurons and contained PHA-L were visualized by an immunohistochemical procedure that involved sequential incubation of tissue sections with goat anti-PHA-L antibody, biotinylated rabbit anti-goat immunoglobulin, and a biotin-avidin-peroxidase conjugate. Following injections of PHA-L restricted to ventral and medial portions of the BPN, labeled fibers were observed in the brachium pontis, the white matter dorsal to the CN, and to a lesser extent, in the white matter of the parafloccular stalk. Labeled preterminal axons entered the CN and gave rise to beaded axons that arborized primarily within dorsal portions of the lateral, interposed, and medial cerebellar nuclei. Injections of PHA-L restricted to either lateral portions of the BPN or ventrolateral regions of NRTP produced labeled fibers in the cerebellum that most frequently involved the parafloccular stalk and ventral portions of the CN. In contrast, dorsomedial NRTP injections resulted in the presence of labeled fibers both in the dorsal cerebellar white matter and the parafloccular stalk as well as dorsal and ventral portions of the CN. With the exception of the rostral and medial territory of interpositus anterior which received very sparse input, all portions of each CN subdivision seemed to exhibit some degree of terminal labeling. The density of labeled axon terminals in the CN appeared to be somewhat greater in the NRTP-injected cases compared to BPN-injected animals. These observations indicate that in the rat, both the BPN and NRTP contain neurons whose axons distribute to the CN. It is likely that most of the axons which project to the CN are collaterals of fibers that continue into the cerebellar cortex as mossy fibers but confirmation of this point must await further investigation. In light of the extensive projections from the cerebral cortex to the BPN and NRTP, this axonal system provides the cerebral cortex with a relatively direct route of access to the CN via one synapse in the BPN or NRTP.

Functional organization of the ventral lateral geniculate complex of the tree shrew (Tupaia belangeri): II. Connections with the cortex, thalamus, and brainstem.

Connections of the ventral lateral geniculate complex (GLv) in the tree shrew were traced by anterograde and retrograde transport of WGA-HRP. The results buttress earlier findings that GLv in this species is composed of two main divisions, lateral and medial, each of which differs in its connections with the brainstem and cerebral cortex. The connections of the lateral division (GLv) suggest that it participates in visuosensory functions: it receives input from the retina, striate cortex, pretectum, and retino-recipient layers of the superior colliculus. These connections help clarify the identification of the internal and external subdivisions of GLv inasmuch as projections from both the superior colliculus and pretectum terminate in the external subdivision and each, in turn, receives a projection from the internal subdivision. Connections of the medial division suggest that this part of the nucleus is involved with visuomotor functions. Thus, the medio-caudal subdivision projects to the pontine nuclei, the prerubral field and the central lateral nucleus. The medio-caudal subdivision also receives projections from the lateral cerebellar nucleus, so that the GLv-ponto-cerebello-GLv loop involves mainly one subdivision of GLv. The medio-rostral subdivision receives projections from the pretectum and parietal cortex. Its output is directed primarily at the intermediate and deep layers of the superior colliculus. All of these targets of GLv, the pons, prerubral field, and deep layers of the superior colliculus, are known to play a role in the coordination of head and eye movements. Additional connections of GLv with the vestibular nuclei, intralaminar nuclei, hypothalamus, and facial motor nucleus are also described.

Anatomy of the turtle cerebellorubral circuit studied in vitro using neurobiotin and biocytin

We have combined the rapid anterograde and retrograde transport of neurobiotin and biocytin with the extended viability of the isolated turtle brainstem-cerebellum to conduct in vitro studies of the chelonian cerebellorubral circuit. Tracers were pressure injected in 15–25 nl quantities and the optimal transport time was 16 h. Tissue sections were incubated with avidin-biotin-HRP complex and reacted with DAB. Retrogradely labeled soma, dendrites and axons, and anterogradely labeled axons and to a lesser extent terminals were visible with both tracers. Red nucleus injections resulted in dense retrograde label in the contralateral lateral cerebellar nucleus and a heavily labeled contralateral rubrospinal tract. Cerebellar nucleus injections revealed light retrograde and dense terminal label in the contralateral red nucleus, together with retrograde label in a cell cluster in the ipsilateral ventrolateral medullary reticular formation, an area we identify as the lateral reticular nucleus. Injections into this medullary region resulted in heavy mossy fiber input to the ipsilateral cerebellum and moderate retrograde label in the contralateral red nucleus. These results identify prominent recurrent projections between the lateral cerebellar nucleus, red nucleus and lateral reticular nucleus, in addition to revealing other features of the cerebellorubral circuit.

Neurons with strongly negative-charged surface-coats in adult rat brain as detected by staining with cationic iron colloid.

Light microscopy of tissue sections stained either with cationic iron colloid (pH 1.0-2.0) and nuclear fast red or with this colloid and thionin showed that the adult rat brain contains a considerable number of neurons which are strongly negative-charged by being coated with sulfated proteoglycans such as chondroitin sulfates. These neurons are distributed mainly in the cerebral cortex, hippocampus, zona incerta, medial and lateral cerebellar nuclei, ventral pontine nuclei and certain other areas. In the hippocampal formation, the strongly negative-charged cells seem identical with the GABAergic inhibitory interneurons reactive to the lectin Vicia villosa agglutinin. Neurons, including the GABAergic Purkinje's cells, of the cerebellar cortex showed no reaction to our cationic iron colloid at pH values of 1.0-2.0. Many non-GABAergic pyramidal cells in the lamina ganglionalis of cerebral cortex and many non-GABAergic large neurons of the ventral pontine nuclei were highly reactive to our colloid at pH values of 1.0-2.0. This suggests that our cationic iron colloid at pH values of 1.0-2.0 mainly stains certain subtypes of GABAergic neurons as well as some non-GABAergic neurons projecting long associational or commissural fibers.

Topographic organization of the corticonuclear projections from the paraflocculus in the albino rat: an autoradiographic orthograde tracing study.

The topographic organization of corticonuclear projections from the paraflocculus was studied in rats by an autoradiographic orthograde tracing method. The corticonuclear fibers from the paraflocculus terminated primarily in the caudoventral part of the lateral cerebellar nucleus and in the lateral part of the posterior interpositus nucleus. The rostrolateral part of the ventral paraflocculus projected only to the lateral nucleus, and the caudomedial part projected only to the posterior interpositus nucleus. Although differential projections from the dorsal and ventral paraflocculi were not clearly observed, the dorsal paraflocculus appeared to project to slightly more dorsal parts of the lateral and posterior interpositus nuclei than did the ventral paraflocculus. The lateral, medial, rostral, and caudal parts of each sublobule tended to project to the ventral, dorsal, rostral, and caudal regions within the caudoventral part of the lateral nucleus, respectively, despite massive overlap in the individual terminal fields. The corticonuclear projection from the dorsal and ventral paraflocculi to the posterior interpositus nucleus were organized in different directions; those from the dorsal paraflocculus were organized rostrocaudally, while those from the ventral paraflocculus were organized mediolaterally. These results suggest that in rats the corticonuclear projections from the paraflocculus are topographically organized in the mediolateral and rostrocaudal directions as well as in the dorsoventral direction.

Cerebellar stimulation modulates thalamic noxious-evoked responses

Parafascicular (PF) neurons responding to noxious stimuli and focal electrical stimulation of midbrain, diencephalon, and hypothalamic nuclei, which send projections to PF, modulates the PF spontaneous and noxious-evoked responses. Some cerebellar efferents ascend to PF. This investigation attempted to study the effect of cerebellar stimulation on spontaneous and noxious-evoked PF neuronal activity in rats. It was observed that 26% (73/280) of PF neurons responded to a noxious stimulus. The PF neuronal population exhibits two cell types according to their response pattern following the noxious stimulus. One type of PF neurons were excited (n = 53) and were classified as nociceptive-on cells. The second type of PF neurons responded to noxious stimulus by a decrease in the ongoing firing rate (n = 20) and were classified as nociceptive-off cells. The responses of these two types of nociceptively identified cells were tested following cerebellar lateral nucleus stimulation (Lat.N.S.) utilizing several current intensities. Lat.N.S. with lower intensities (0.1-0.2 mA) elicited suppression of both spontaneous and nociceptive-evoked discharges of the nociceptive-on neurons, although higher intensities (0.4-0.6 mA) elicited excitation on both discharges of this type of neuron. In contrast, Lat.N.S. induced a monophasic intensity-dependent suppression of both the spontaneous and the nociceptive-evoked discharges of the nociceptive-off neurons. The results indicate that Lat.N.S. modulates the nociceptive-evoked responses of PF neurons. The possible role and related pathways of cerebellum in modulating noxious input were discussed.

Dopaminergic and non-dopaminergic neurons in the ventral tegmental area of the rat project, respectively, to the cerebellar cortex and deep cerebellar nuclei

It has been suggested recently that dopamine in the cerebellum not only acts as a precursor for noradrenaline in afferent fibers supplied by locus coeruleus neurons, but also subserves an independent transmitter role in a separate neural system. The present study was initiated to investigate the possible sources for dopaminergic innervation of the cerebellum. Employing anterograde and retrograde axonal tracing with cholera toxin and a combination of fluorescent retrograde axonal tracing with Fluoro-Gold and tyrosine hydroxylase immunofluorescence histochemistry, we found in the rat that the ventral tegmental area, containing the A10 dopaminergic cell group, sends projection fibers to the cerebellum bilaterally with a slight contralateral predominance. The projections from the ventral tegmental area to the cerebellum were segregated into the dopaminergic one to the cerebellar cortex and the non-dopaminergic one to the deep cerebellar nuclei. Dopaminergic fibers projecting from the ventral tegmental area to the cerebellar cortex terminated mainly in the granular layer, additionally in the Purkinje cell layer, but not at all in the molecular layer. They were distributed predominantly in the crus I ansiform lobule and paraflocculus, and to a lesser extent in the crus II ansiform lobule. On the other hand, non-dopaminergic fibers projecting from the ventral tegmental area to the deep cerebellar nuclei were seen to terminate mainly in the lateral nucleus, to a lesser extent in the interpositus nucleus, but not at all in the medial nucleus. The ventral tegmental area was also observed to receive projection fibers from the lateral and interpositus cerebellar nuclei bilaterally with a contralateral predominance. The projections from the ventral tegmental area to the cerebellum revealed in the present study might exert limbic influences upon the cerebro-cerebellar loops subserving the execution and co-ordination of voluntary movements.

Comparison of gene expression for two distinct bombesin receptor subtypes in postnatal rat central nervous system

The two mammalian bombesin-like peptides, gastrin-releasing peptide (GRP) and neuromedin B (NMB), are structurally related neuropeptides reported to elicit a variety of responses in different cell types, including modulation of neuronal activity and growth. Two distinct bombesin receptor subtypes have recently been characterized: a mouse GRP-preferring receptor (GRP-R) derived from Swiss 3T3 fibroblasts and a rat esophagus NMB-preferring bombesin receptor (NMB-R). In this study, we report the cloning and structural characterization of the rat GRP-R cDNA. The rat GRP-R and NMB-R cDNAs were used to map the regional distribution of these two bombesin receptor subtypes in rat CNS using in situ hybridization. Throughout postnatal development, cells expressing either receptor mRNA were found within the forebrain, brain stem, and spinal cord. The most distinct expression patterns were observed in the forebrain, where GRP-R mRNA was prominent in the hypothalamic region but NMB-R mRNA expression was strongest in olfactory and thalamic regions. In other brain regions, including dentate gyrus and nucleus ambiguus, both receptor mRNAs were detected. In the majority of brain regions, the adult pattern of expression was seen at birth. However, in several CNS regions, GRP-R and NMB-R mRNA showed striking changes during postnatal development (PN1, PN9, and PN16). In the dentate gyrus, GRP-R and NMB-R mRNA expression increased, while in the caudate-putamen and lateral cerebellar nucleus, expression decreased. These regional changes in receptor expression during postnatal life may be significant for both normal brain growth and development.

Sulforhodamine labeling of neural circuits engaged in motor pattern generation in the in vitro turtle brainstem-cerebellum

A fluorescent molecular probe was used in combination with a novel in vitro preparation to study spatial patterns of neural activity associated with motor pattern generation. The in vitro brainstem-cerebellum preparation takes advantage of the turtle's unusual resistance to anoxia to preserve the entire neural network that connects the cerebellum, red nucleus, and reticular formation. This preparation was bathed in a 0.01% solution of sulforhodamine while it was activated unilaterally by electrical stimulation of the dorsal quadrant of the spinal cord for 1 hr. Sulforhodamine is a small, sulfonated, highly charged fluorescent molecule that is taken up by endocytosis. To examine its distribution in the cerebellum and brainstem, coronal sections were prepared and viewed under epifluorescence illumination. Distinctive spatial patterns of labeling were associated with unilateral electrical stimulation of the in vitro network, suggesting that dye uptake was activity dependent. Blockade of uptake with altered magnesium and calcium concentrations indicated that single spike discharge evoked ortho- or antidromically was insufficient to induce dye uptake. Instead, sulforhodamine staining correlated with the presence of burst discharge that was recorded extracellularly from the red nucleus. Blockade of burst discharge with excitatory amino acid receptor antagonists prevented dye uptake in the red nucleus, the lateral cerebellar nucleus, and other structures that are known to be interconnected by recurrent anatomical pathways. These results suggest that sulforhodamine is internalized by intensely active neurons. The spatial distributions of label support the hypothesis that burst discharges in the turtle red nucleus are mediated by excitatory amino acid neurotransmitters and sustained by recurrent excitation in cerebellorubral synaptic pathways. Positive feedback in these recurrent pathways may provide an important driving force for the generation of motor programs that control limb movements.

Efferent projections from the flocculus in the albino rat as revealed by an autoradiographic orthograde tracing method

The terminal sites of floccular efferent fibers were investigated in the albino rat by an autoradiographic orthograde method. The corticonuclear fibers terminated in the caudoventral part of the lateral cerebellar nucleus and in the caudoventral region of the lateral part of the posterior interpositus nucleus. A few fibers from the rostral flocculus terminated in the granular cell layer of the basolateral part of the nodulus and uvula as mossy fiber type terminals. The projection to the nodulus and uvula was confirmed, by an additional retrograde HRP study, to originate from scattered spindle-shaped cells in the floccular stalk. The corticovestibular fibers terminated massively in the subnucleus y. The fibers passing through the subnucleus y divided into two bundles; one bundle coursed rostrally to terminate in the lateral and ventral parts of the superior vestibular nucleus, while the other bundle passed through the lateral and then ventral parts of the lateral vestibular nucleus, supplying a few terminals to these regions, to terminate sparsely in the rostral to intermediate part of the medial vestibular nucleus and the rostroventral part of the spinal vestibular nucleus. Some fibers passing through the lateral vestibular nucleus coursed rostrally to terminate in the medial part of the superior vestibular nucleus. Sparse terminals derived from the rostral flocculus were found in the prepositus hypoglossal nucleus. No definitive differential efferent projections were demonstrated in the rat flocculus.

The cerebellopontine system: an electrophysiological study in the rat

We examined the effects of electric stimulation of the cerebellar lateral nucleus (LN) in the rat on the activity of single pontocerebellar neurons in the basilar pontine nuclei (BPN) and the reticulotegmental nucleus (RtTg). We found that about half of the cells of these nuclei that were influenced by LN stimulation were inhibited. A significant fraction of both excitatory and inhibitory responses had latencies of less than 4 ms and were able to follow high frequency stimulation, compatible with a monosynaptic linkage. Extracellular field potential recordings within the BPN and RtTg were interpreted as arising from impulses propagating along inhibitory axons projecting in a bundle from the cerebellum to these pontine structures. Microionophoretic administration of GABA antagonists bicuculline or picrotoxin abolished or attenuated most inhibitory effects. Therefore, we conclude that LN-induced inhibition is most likely mediated by cerebellopontine GABAergic fibers. The functional significance of this cerebellopontine inhibitory circuit is discussed.

The neurons of origin of non-cortical afferent connections to the oculomotor nucleus. A retrograde labeling study in the rabbit.

The cellular origin of the brainstem projections to the oculomotor nucleus in the rabbit has been investigated by using free (HRP) and lectin-conjugated horseradish peroxidase (WGA-HRP). Following injections of these tracers into the somatic oculomotor nucleus (OMC), retrogradely labeled cells have been observed in numerous brainstem structures. In particular, bilateral labeling has been found in the four main subdivisions of the vestibular complex, predominantly in the superior and medial vestibular nuclei and the interstitial nucleus of Cajal, while ipsilateral labeling was found in the rostral interstitial nucleus of the medial longitudinal fascicle (Ri-MLF), the Darkschewitsch and the praepositus nuclei. Neurons labeled only contralaterally have been identified in the following structures: mesencephalic reticular formation dorsolateral to the red nucleus, abducens internuclear neurons, group Y, several areas of the lateral and medial regions of the pontine and medullary reticular formation, ventral region of the lateral cerebellar nucleus and caudal anterior interpositus nucleus. This study provides also information regarding differential projections of some centers to rostral and caudal portions of the OMC. Thus, the rostral one-third appears to receive predominant afferents from the superior and medial vestibular nuclei, while the caudal two-thirds receive afferents from all the four vestibular nuclei. Finally, the group Y sends afferents to the middle and caudal, but not to the rostral OMC.

The GABAergic cerebello-olivary projection in the rat

Immunocytochemical detection of glutamate decarboxylase (GAD), the predominant biosynthetic enzyme of gamma-aminobutyric acid (GABA), reveals the presence of a dense GABAergic innervation in all parts of the inferior olive. One brain center that provides a substantial projection to the inferior olive is the cerebellar nuclei, which contain many small GABAergic neurons. These neurons were tested as a source of GABAergic olivary afferents by combining retrograde tract tracing with GAD immunocytochemistry. As expected from previous studies, injections of wheat germ agglutinin-conjugated horseradish peroxidase (WGA-HRP) into the inferior olive retrogradely label many small neurons in the interposed and lateral cerebellar nuclei and the dorsal part of the lateral vestibular nucleus, and fewer neurons in the ventro-lateral region of the medial cerebellar nucleus. These projections are predominantly crossed and are topographically arranged. The vast majority, if not all, of these projection neurons are also GAD-positive. The relative contribution of this projection to the GABAergic innervation of the inferior olive was tested by lesion of the cerebellar nuclei, or the superior cerebellar peduncle. Within 10 days the lesion eliminates most GAD-immunoreactive boutons in the principal olive, the rostral lamella of the medial accessory olive, the ventrolateral outgrowth, and the lateral part of the dorsal accessory olive ventral fold. Thus, the effectiveness of this depletion demonstrates that the cerebellar nuclei provide most of the GABAergic innervation to regions of the inferior olive known to receive a cerebellar projection. Moreover, when the lateral vestibular nucleus is damaged, the dorsal fold of the dorsal accessory olive is depleted of GABAergic boutons. The synaptic relations that boutons of the GABAergic cerebello-olivary projection share with olivary neurons were investigated at the electron microscopic level by GAD-immunocytochemistry, anterograde degeneration of the cerebellar axons or anterograde transport of WGA-HRP. All of these methods confirm that GABAergic, cerebello-olivary axon terminals contain pleomorphic vesicles, and synapse on various portions of olivary neurons, and especially on dendritic spines within glomeruli, often in very close proximity to the gap junctions that characteristically couple the dendritic profiles. These results demonstrate four major points: that virtually all of the GABAergic, and presumably inhibitory, neurons of the cerebellar and dorsal lateral vestibular nuclei are projection neurons; that a large portion of the inferior olive receives GABAergic afferents from the cerebellar nuclei; that a portion of the dorsal accessory olive receives GABAergic afferents from the dorsal lateral vestibular nucleus; and that cerebello-olivary fibers often synapse near gap junctions, and therefore could influence electrical coupling of olivary neurons.

Organization of the cerebellum in the pigeon (Columba livia): II. Projections of the cerebellar nuclei

The projections of the deep cerebellar nuclei in the pigeon have been delineated using autoradiographic and histochemical (WGA-HRP) tracing techniques. A medial (CbM) and lateral (CbL) cerebellar nucleus are recognized and CbM may be further partitioned into internal, intermediate, and intercalate divisions. As in mammals, most extracerebellar projections of CbM travel in the fasciculus uncinatus (FU); the rest travel with those of CbL in the brachium conjunctivum (BC). In the pigeon, both of these pathways are bilaterally but primarily contralaterally projecting systems. FU is a predominantly descending tract, with terminations within (1) the vestibular complex, (2) a column of contiguous medial reticular nuclei from pontine to caudal medullary levels; (3) the plexus of Horsley portion of the parvicellular reticular formation, continuing through the nucleus centralis medullae oblongatae, pars dorsalis, into intermediate layer VII of the cervical spinal cord, down to cervical segment 8-9; (4) the lateral reticular nucleus and the paragigantocellular reticular nucleus; (5) the dorsal lamella of the inferior olive. Rostrally FU terminals are found in the locus ceruleus and dorsal subcerulean nucleus. Minimal FU projections are also seen to the motor trigeminal nucleus and the subnucleus oralis of the descending trigeminal system. A small projection from the intercalate division of CbM travels in BC and projects upon the midbrain central grey, the intercollicular nucleus, the lateral tectal periventricular grey, the stratum cellulare externum and, sparsely, upon the dorsolateral thalamus. The bulk of BC originates from the lateral cerebellar nucleus and consists of a massive ascending and a small descending branch. The ascending system projects upon the red nucleus and the dorsally adjacent interstitial nucleus of Cajal and midbrain central grey, the prerubral fields continuing into the stratum cellulare externum, the nucleus intercalatus thalami, the ventrolateral thalamic nucleus, the medial spiriform nucleus, the nucleus principalis precommissuralis, the nucleus of the basal optic root, the nucleus geniculatus lateralis pars ventralis, the dorsolateral thalamus, including the dorsal intermediate posterior, and the dorsolateral intermediate and anterior nuclei. BC also contains axons from the infracerebellar nucleus, which projects upon the trochlear and the oculomotor nuclei. The descending branch of BC distributes to the papilioform nucleus, the medial pontine nucleus, the gigantocellular and paramedian reticular nuclei, and, minimally, the rostral portions of the medial column and ventral lamella of the inferior olive. Taken in conjunction with data on amphibia and reptiles the present findings suggest that the fundamental ground plan of vertebrate cerebellar organization involves a medial and lateral cerebellar nucleus.(ABSTRACT TRUNCATED AT 400 WORDS)

Trigeminal primary afferent projections to “non‐trigeminal” areas of the rat central nervous system

The central projections of rat trigeminal primary afferent neurons to various "non-trigeminal" areas of the central nervous system were examined by labeling the fibers with wheat germ agglutinin-horseradish peroxidase (WGA-HRP) transported anterogradely from the trigeminal ganglion. This technique produced a clear and comprehensive picture of trigeminal primary afferent connectivity that was in many ways superior to that which may be obtained by using degeneration, autoradiography, cobalt labeling, or HRP transganglionic transport techniques. Strong terminal labeling was observed in all four rostrocaudal subdivisions of the trigeminal brainstem nuclear complex, as well as in the dorsal horn of the cervical spinal cord bilaterally, numerous brainstem nuclei, and in the cerebellum. Labeling in the ipsilateral dorsal horn of the cervical spinal cord was very dense at C1, moderately dense at C2 and C3, and sparse at C4-C7. Numerous fibers crossed the midline in the medulla and upper cervical spinal cord and terminated in the contralateral pars caudalis and dorsal horn of the spinal cord from C1-C5. The latter axons terminated most heavily in the mandibular and ophthalmic regions of the contralateral side. Extremely dense terminal labeling was observed in the ipsilateral paratrigeminal nucleus and the nucleus of the solitary tract, moderate labeling was seen in the supratrigeminal nucleus and in the dorsal reticular formation, and small numbers of fibers were observed in the cuneate, trigeminal motor, lateral and superior vestibular nuclei, and in the cerebellum. The latter fibers entered the cerebellum in the superior cerebellar peduncle and projected to the posterior and anterior lobes as well as to the interposed and lateral deep cerebellar nuclei. Most projections in this study originated from fibers in the dorsal part of the spinal tract of V, suggesting a predominantly mandibular origin for these fibers. Projections from the ophthalmic and maxillary divisions, in contrast, were directed mainly to the cervical spinal cord bilaterally, to contralateral pars caudalis, and to certain areas of the reticular formation. In conclusion, this study has demonstrated that somatosensory information from the head and face may be transmitted directly to widespread and functionally heterogeneous areas of the rat central nervous system, including the spinal cord dorsal horn, numerous brainstem nuclei, and the cerebellum.(ABSTRACT TRUNCATED AT 400 WORDS)