Organization of the neurons in the anterior division of the anteroventral cochlear nucleus of the cat. Light-microscopic observations

The anterior division of the anteroventral cochlear nucleus of the cat was studied in the light microscope. Criteria were developed to distinguish neurons in the Nissl-stained anteroventral cochlear nucleus which could then be correlated with those types found in Golgi preparations. Based on the patterns of distribution of the neuronal types, their size and shape, and the number of primary dendrites, the bushy cells (Golgi) are shown to correspond to the spherical cells (Nissl), whereas the stellate and small cells (Golgi) correspond to the ovoid cells (Nissl).The present results provide a background for a detailed study of the synaptic organization of the different cell types of the anterior division with the electron microscope and electrophysiological methods.     

The neuronal architecture of the anteroventral cochlear nucleus of the cat in the region of the cochlear nerve root: Golgi and Nissl methods

This report characterizes the cells and fibers in one part of the cochlear nucleus, the posterior division of the anteroventral cochlear nucleus. This includes the region where the cochlear nerve root enters the brain and begins to form endings. Nissl stains reveal the somata of globular cells with dispersed Nissl substance and those of multipolar cells with coarse, clumped Nissl bodies. Both parts of the posterior division contain cells with each Nissl pattern, but in different relative numbers and locations. Golgi impregnations demonstrate two types of neurons: bushy cells, with short bush-like dendrites, and stellate and elongate cells, with long tapered dendrites. Several varieties of bushy cells, differing in the morphology of the cell body and in the size and extent of the dendritic field, can be distinguished. Comparison of the distributions of these cell types, as well as cellular morphology, suggest that the globular cells recognized in Nissl stains correspond to bushy neurons, while the multipolar cells correspond to stellate and elongate neurons. Golgi impregnations reveal large end-bulbs and smaller boutons from cochlear nerve fibers, as well as boutons from other, unidentified sources, ending in this region.The particular arrangements of the dendritic fields of the different cell types and the axonal endings associated with them indicate that these neurons must have different physiological properties, since they define different domains with respect to the cochlear and non-cochlear inputs.     

The neuronal architecture of the anteroventral cochlear nucleus of the cat in the region of the cochlear nerve root: Electron microscopy

We have studied the posterior division of the anteroventral cochlear nucleus, where the cochlear nerve root enters the brain, in the cat. In Nissl preparations, this region contains two types of neuronal cell bodies: globular and multipolar. The two types can be identified in the electron-microscope by comparing Nissl substance and rough endoplasmic reticulum. Globular cell bodies receive many synaptic terminals, which cover 85% of the surface. In contrast, multipolar cell bodies are almost entirely wrapped by thin glial sheets—synaptic terminals contact less than 15% of the surface and tend to cluster at the bases of dendrites. Synaptic terminals are of three kinds, types 1, 2, and 3, which contain large round, small round-to-oval, and small flattened synaptic vesicles, respectively. Terminals of all three kinds synapse on both types of cell bodies. However, only globular cell bodies receive the largest type 1 terminals, which correspond to end-bulbs, seen in Golgi impregnations to arise from cochlear nerve axons. Cochlear ablation leads to degeneration of type 1, but not type 2 or 3 terminals.We conclude that neurons with globular cell bodies receive heavy somatic input from the cochlear nerve, as well as from other sources. Neurons with multipolar cell bodies receive very little input to their perikarya—giving their dendrites a more important role in determining their response properties. We suggest a morphological basis for correlating individual kinds of neurons with certain electrophysiological response types.     

The neuronal architecture of the anteroventral cochlear nucleus of the cat in the region of the cochlear nerve root: horseradish peroxidase labelling of identified cell types

Golgi impregnations of the posterior part of the cat's anteroventral cochlear nucleus have revealed two types of neurons, bushy cells with short bush-like dendrites and stellate cells with long, tapered processes; Nissl stains have revealed globular and multipolar cell bodies with dispersed and clumped ribosomal patterns, respectively. In the present study, we injected horseradish peroxidase into the trapezoid body. Ipsilaterally, retrograde, diffuse labelling of neurons, presumably through damaged fibers, yielded Golgi-like profiles of numerous bushy cells with typical dendrites and with thick axons projecting toward the trapezoid body. Stellate cells were almost never labelled in this way. Anterograde diffuse labelling of thick axons demonstrated calyx endings in the contralateral medial nucleus of the trapezoid body. In the electron-microscope, the perikarya of diffusely-filled bushy neurons were found to have the dispersed ribosomal pattern and the kinds of synaptic endings typical of globular cells, including large profiles of end-bulbs from cochlear nerve axons. After injections restricted to the medial trapezoid nucleus, granularly-labelled cells in the cochlear nucleus were almost completely confined to the contralateral side; Nissl counterstaining showed them to be globular cells in the posterior part of the anteroventral cochlear nucleus. After larger injections, involving surrounding regions of the superior olivary complex, granular labelling occurred throughout the ventral cochlear nucleus on both sides. There is also evidence that stellate cells in Golgi impregnations correspond to multipolar cell bodies in Nissl stains. We conclude that bushy cells typically correspond to globular cells, which receive end-bulbs from the cochlea and send thick axons to the contralateral medial trapezoid nucleus, where they form calyces on principal cells. Principal cells, in turn, are known to project to the lateral superior olive and to one of the nuclei of origin of the crossed olivo-cochlear bundle, which feeds back to the cochlea. In this circuit, correlations between synaptic patterns and particular physiological signal transfer characteristics can be suggested. These could be related to binaural intensity interactions in the lateral superior olive and to a regulatory loop involving the olivo-cochlear bundles.     

The fine structure of two types of stellate cells in the anterior division of the anteroventral cochlear nucleus of the cat

The stellate cells in the anterior division of the anteroventral cochlear nucleus of the cat were studied with the electron microscope. Although only one type of stellate cell has been identified at the light-microscopic level, two types can be recognized in electron micrographs. Both can be distinguished from the bushy cells that are also present in the anterior division, since they lack the nuclear cap of granular endoplasmic reticulum characteristic of the bushy cells. The somas of the type I stellate cells receive very few synaptic contacts, but the number of synaptic terminals increases markedly along the proximal dendrites. In contrast, both the soma and proximal dendrites of the type II stellate cells receive numerous synaptic contacts. Both neuronal types receive synaptic endings that contain large, spherical vesicles and that disappear after cochlear ablation. Both types of stellate cells are also contacted by synaptic terminals with small vesicles similar to those that contact bushy cells. In addition, the type II stellate cells receive a type of synaptic ending unlike those previously described. This is a relatively large terminal, containing large, flattened or disk-shaped vesicles, and forming slightly asymmetric synaptic complexes with the postsynaptic cell. These terminals as well as those with small synaptic vesicles survive cochlear ablation. The sources of the non-cochlear terminals are not known.The results indicate that the anterior division of the anteroventral cochlear nucleus of the cat contains at least three types of large neurons, each of which receives synaptic input from the cochlea as well as from other sources. The organization of the synaptic endings on the surface of each type is different. Since distinctive arrangements of cochlear and non-cochlear synaptic terminals could result in different response patterns to acoustic stimuli, each of these neuronal types may correspond to a different type of single unit, defined physiologically.     

Neuronal architecture in nucleus magnocellularis of the chicken auditory system with observations on nucleus laminaris: A light and electron microscope study

This report presents the major structural features of neurons and their afferent input in nucleus magnocellularis, the avian homologue of the mammalian anteroventral cochlear nucleus. Results of light-microscope observations, as seen in Golgi, Nissl, and normal fiber preparations, as well as ultrastructural morphology are reported. In addition, cells and axons in nucleus laminaris, the presumed homologue of the mammalian medial superior olivary nucleus, are also described.In Golgi-impregnated material, the mature principal cell in nucleus magnocellularis has an ovoid soma encrusted with somatic spines. A dendrite, when present, emerges from the cell soma, travels for a short distance and breaks into a tuft of stubby terminal branches. Foremost among the afferents to nucleus magnocellularis are auditory nerve axons that terminate in large, axosomatic endings, or endbulbs, covering a large portion of the somatic surface. Other afferents, which also end in relation to the perikaryon, are of undetermined and perhaps multiple origins. The neurons resemble the bushy cells of the mammalian anteroventral cochlear nucleus. Evidence is presented that individual axons from the nucleus magnocellularis bifurcate and send branches to the nucleus laminaris bilaterally, thus placing constraints on the binaural interactions possibly involved in lateralization functions.In electron micrographs, the end-bulbs appear as large, elongate structures which can cover a third of the cell soma. Multiple sites of synaptic specialization occur along these terminals. The synaptic membrane complexes may form directly on the cell body or on the sides or crests of somatic spines. These complexes are characterized by asymmetric membrane densities with a cluster of clear, spherical vesicles on the axonal side. Other small terminal profiles are also present on the somata receiving the end-bulbs. Dendritic profiles are scarce, in agreement with observations in Golgi impregnations.The structural findings indicate that the medial part of the nucleus magnocellularis is homologous to the anterior part of the mammalian anteroventral cochlear nucleus in that the neurons of nucleus magnocellularis are homologous to the bushy cells of the cat. On this basis, the cells in nucleus magnocellularis could faithfully preserve the acoustic response patterns generated in the auditory nerve. This should, in turn, allow a secure relay of bilateral latency differences essential for binaural interactions in the nucleus laminaris.     

Pyramidal neurones of the dorsal cochlear nucleus: A golgi and computer reconstruction study in cat

The main projection neurones of the dorsal cochlear nucleus, termed pyramidal, bipolar or fusiform cells, have an apical dendritic arbor approaching the ependymal surface of the nucleus and a basal arbor oppositely directed. In Golgi-Del Rio-Hortega material these neurones were studied, with the light microscope, in nonconventional planes of sectioning oriented across or parallel to the main axis of the elongated nucleus. The pyramidal neurones were seen to be flattened across this axis.The size, shape and orientation of 21 cells from six blocks were studied in detail with computer-aided graphic reconstructions including stereo views. Camera lucida drawings of each cell (usually from several sections) were digitized to obtain x and y coordinates while z coordinates (depths in the tissue) were read from the fine focus knob during microscopy and typed interactively during digitization. The z values were corrected for the effects of refractive index differences in the optical system.Since it was the aim of this study to focus on some fundamental principles of structure and arrangement of pyramidal cells in the dorsal cochlear nucleus rather than on topographic variations, only the middle, regularly built part of the nucleus was examined. Towards the ends of the nucleus the architecture is less regular and will require separate analysis.Measurements of arbor and total cell height and of dendritic length are given. The height of the apical and basal arbor in individual cells showed considerable reciprocity. The total dendritic length was up to 8300 μm (average 6536 μm). The basal arbors always proved to be conspicuously flattened; roughly, the width varied between about 300 and 700 μm (average 489 μm) and the thickness between 65 and 105 μm (average 80 μm). The apical arbors were also often flattened but much less and with a greater variability than the basal arbors (average width 319 μm, thickness 115 μm). The two arbors of individual cells were practically coplanar, the arbor planes showing only moderate angularity (bend) and/or torsion relative to each other (angularity maximum 10°, average 5°; torsion maximum 18°, average 6°). The mutual orientation of cells from the same block was examined. The planes through the basal arbors proved to be very parallel, the differences in orientation angles being between 10 and 0° with rare exceptions. Clearly flattened, apical arbors showed a somewhat greater spread.It may be fundamental for the tonotopic organization of the dorsal cochlear nucleus that a high degree of flatness and parallel orientation are found in the basal arbor which is a target of primary cochlear afferents. Our findings invite detailed charting of these fibers in relation to the arbor planes. Also in electrophysiological studies the planarity and regular orientation of the pyramidal cells should be taken into consideration.     

Desending and intrinsic inputs to dorsal cochlear nucleus of cats: A horseradish peroxidase study

Horseradish peroxidase was injected unilaterally into the dorsal cochlear nucleus of adult cats in efforts to find neurons innervating the dorsal cochlear nucleus from (1) higher auditory nuclei or (2) other subdivisions of the cochlear nucleus. Following horseradish peroxidase injections and short survival periods, reactive neurons were most common in the dorsal and ventral nuclei of the lateral lemniscus and in the superior olivary complex of both sides of the brain stem. In the superior olivary complex, most neurons of the medial segment and border cells of the lateral segment reacted as did periolivary cells of the ventrolateral, dorsomedial, and preolivary areas, but not in the medial nucleus of the trapezoid body. Hilus neurons of the lateral superior olive reacted contralateral to the injection site. Although inferior colliculus neurons contained lightly stained granules bilaterally, more reactive neurons (including unusually large tripolar neurons) contained heavily stained granules in the contralateral colliculus. Intrinsic reactive neurons mainly included ipsilateral octopus cells, multipolar neurons of the nerve root regions, and stellate cells of the more rostra] anteroventral cochlear nucleus. All findings were confirmed by comparison to control animals.Our findings of specific neuronal types projecting to the cat dorsal cochlear nucleus suggest a relatively greater input from the nuclei of the lateral lemnisci of both sides than previously believed. Also, our results showed an unusually heavy input from the nearby superior olivary complex to the dorsal cochlear nucleus as well as inputs from specific cell types of the ipsilateral antero- and postero-ventral cochlear nucleus. By correlating these findings with those of other types of studies, we concluded that (1) too much emphasis has been placed upon inputs to the dorsal cochlear nucleus from the inferior colliculus relative to the descending pontine inputs and that (2) a new circuit involving the ventral cochlear nucleus, the dorsal cochlear nucleus and the medial superior olive may provide binaural information to large dorsal cochlear nucleus cells that terminate in their own unique areas of higher auditory nuclei.     

Central transport and distribution of labelled glutamic and aspartic acids to the cochlear nucleus in cats: an autoradiographic study.

Tritiatedl-glutamic acid orl-aspartic acid were injected unilaterally into the cochleas of adult cats, and 4 h-7 days later the localization of label was studied by light-microscopic autoradiography in sections of the brain stem. All experiments with [³H]glutamate and most with [³H]aspartate produced visibly denser grains and quantitatively higher grain counts in the cochlear nucleus of the injected side than in the cochlear nucleus of the noninjected side. In general, [³H]glutamate produced dense label ipsilaterally in all major subdivisions of the cochlear nucleus except the molecular layer of the dorsal division and the granular cell cap of the ventral division, in patterns like those after injections of [³H]leucine. The most heavily labelled areas were those that received the densest inputs of primary cochlear fibers. By contrast, [³H]aspartate produced dense grains in the ventral, but not in the dorsal, cochlear nucleus. The results with [³H]glutamate closely resembled those after [³H]leucine or [¹⁴C]leucine injections, but the results with [³H]aspartate showed consistent differences from those after [³H]leucine. After [³H]aspartate, label was densely located around cell bodies and basal dendrites, but not around primary dendrites of octopus cells, in contrast to the dense perisomatic and peridendritic label after [³H]glutamate. Also, relatively low grain counts occurred in the nerve root entry zone and in the deep dorsal cochlear nucleus after [³H]aspartate, although high counts occurred in those same zones after either [³H]glutamate or [³H]leucine injections.Consistent differences in labelling after glutamate and after aspartate suggest differences in their uptake, metabolic conversion and/or transport to the cochlear nucleus by cochlear fibers. The morphological differences shown here agree with the distribution of those two amino acids in the cat cochlear nucleus as shown by microchemical analyses.     

Non-N-methyl-D-aspartate receptors mediating synaptic transmission in the avian cochlear nucleus: effects of kynurenic acid, dipicolinic acid and streptomycin

We have examined the effects of a number of excitatory amino acid antagonists on transmission at the cochlear nerve-nucleus magnocellularis synapse in the chicken. Using an in vitro preparation and bath application of drugs, we studied the effects of kynurenic acid and several related substances, streptomycin and a selective N-methyl-D-aspartate receptor antagonist, DL-alpha-aminosuberate. The last compound had no effect on evoked transmission. Of the various kynurenic acid-related compounds tested, only kynurenic and dipicolinic acid selectively altered responses in nucleus magnocellularis. Quinolinic acid, a kynurenic acid analogue that is structurally akin to dipicolinic acid but which acts selectively at N-methyl-D-aspartate receptors, was without effect. The effect of kynurenic acid was solely inhibitory, completely blocking postsynaptic responses with a potency dependent on the frequency of nerve stimulation. No such frequency dependence was seen with dipicolinic acid although this compound also completely suppressed evoked responses. In addition dipicolinic acid potentiated postsynaptic responses at concentrations only slightly lower than those causing inhibition. Streptomycin inhibited responses in nucleus magnocellularis but this effect seems to result partially from the ability of the drug to inhibit presynaptic calcium influx. Our finding that selective antagonists of N-methyl-D-aspartate receptors were ineffective while antagonists of both receptor types, such as kynurenic and dipicolinic acids, inhibited evoked responses reinforces the conclusion that postsynaptic receptors mediating transmission at this synapse are of the non-N-methyl-D-aspartate type [Nemeth et al. (1983) Neurosci. Lett. 40, 39-44].(ABSTRACT TRUNCATED AT 250 WORDS)     

Descending projections from the inferior colliculus to the dorsal cochlear nucleus in the cat: An autoradiographic study

Descending auditory projections from different subdivisions of the inferior colliculus to the dorsal cochlear nucleus were investigated in experiments using the autoradiographic technique. Tritiated leucine injections confined to the pericentral nucleus of the inferior colliculus resulted in the appearance of dense grain clusters distributed over the outer fusiform cell and molecular layers of the ipsilateral dorsal cochlear nucleus. The pattern and distribution of dense grain clusters strongly resembled the central terminals of glomeruli described previously in the dorsal cochlear nucleus. Injections into the dorsal region of the central nucleus of the inferior colliculus led to a more diffuse distribution of grains over the middle and outer fusiform cell layer and over the innermost molecular layer of the dorsal cochlear nucleus on both sides. Dense grain clusters were also evident after these injections but they appeared to result from the concomitant injection into the overlying pericentral nucleus. Finally, injections of tritiated leucine into the ventral region of the central nucleus of the inferior colliculus (which included some cells of the dorsal nucleus of the lateral lemniscus) resulted in the heaviest labelling of the dorsal cochlear nucleus. Grains were distributed perisomatically and peridendritically around fusiform cells of the fusiform cell layer and giant cells of the deep dorsal cochlear nucleus on both sides.The results indicate that the pericentral nucleus and the more dorsal region of the central nucleus of the inferior colliculus establish overlapping connections with the outermost fusiform cell and molecular layers of the dorsal cochlear nucleus. Both sets of connections seem to be made principally with interneurons through glomerular and other inputs to scattered small cells which exist in these laminae. Since cortical and thalamic descending fibers directly innervate only the most dorsal regions of the inferior colliculus, it may be that this region of the tectum selectively mediates activity from these higher auditory centers. Such centers may indirectly influence fusiform cell response properties through collicular inputs to small cells of the dorsal cochlear nucleus that contact fusiform cells. A more substantial and direct projection was shown to arise from the ventral region of the inferior colliculus to innervate both the fusiform and giant cells. As such, the descending connections from the ventral inferior colliculus may be more likely to influence directly the output of both the fusiform and giant cells and, therefore, the projection of auditory information from the dorsal cochlear nucleus to higher levels.     

Dendritic arrangements in the cat medial superior olive

Examination of material prepared for electron microscopy and with Golgi and reduced silver methods for light microscopy, reveals the existence of both rostro-caudal and dorso-ventral components of the dendritic arrangement within the cell plate of the medial superior olivary nucleus. Cell types in addition to the central bipolar and marginal cells classically associated with the medial superior olive were found. They include multipolar cells, cells which are rostro-caudally elongated and those whose dendritic treees are restricted to one half of the nucleus. Many cells that appear bipolar in transverse section also have rostro-caudal dendritic shafts that can be seen in sagittal sections to form an overlapping mesh. The dendritic terminal arbors curve and intertwine at all medio-lateral levels across the nucleus. Beyond the glial sheets that cover the cell surface and its single layer of synaptic terminals are fascicles of myelinated axons running either perpendicularly to the cell plate or rostro-caudally. This pattern of soma, terminal, glia and axons is interrupted by occasional sites of direct contact between dendrites that are often characterized by attachment plaques.Multiple cell types, varying dendritic arrangements and the presence of dendro-dendritic appositions provide an anatomical substrate for a greater complexity of connections and interactions than previously associated with the medial superior olive.     

Subsurface and cytoplasmic cisterns associated with mitochondria in pyramidal neurons of the rat dorsal cochlear nucleus

Pyramidal cells, the principal neurons of the dorsal cochlear nucleus in the rat, have a system of hypolemmal cisterns as prominent as that of cerebellar Purkinje cells. In their perikarya nearly all the subsurface cisterns are closely apposed to mitochondria as in Purkinje cells. This feature emphasizes a similarity between the two types of neuron which both have dendrites residing in the molecular layer. In addition, cochlear pyramidal neurons contain a distinct cytoplasmic cysternal core which includes cisternae with narrow lumina. These occasionally form simple and multiple assemblies with mitochondria.     

Pyramidal input to the intracerebellar nuclei of the cat

In unanesthetized cats it has been found that pyramidal volleys elicited upon medullary pyramidal tract stimulation were capable of modifying the discharge of 41% of intracerebellar nuclear cells, via pontocerebellar systems impinging predominantly on the lateral cerebellar cortex. The incidence of responsive cells was 80% in the dentate nucleus compared with 10% in the fastigial nucleus, 11% in the anterior and 12% in the posterior division of the interpositus nucleus. The response was in 59% of the cases excitation followed by inhibition, in 30% of the cases a pure excitation and in 11% of the cases a pure inhibition. Excitation, pure or followed by inhibition, had a mean latency of 5.78 ms and a mean duration of 12.21 ms, while inhibition displayed a mean latency of 9.03 ms and a mean duration of 34.64 ms. The possible functional significance of the pyramidal input to the lateral cerebellum is briefly discussed in relation to a possible convergence of pyramidal and associative impulses in single cerebellar neurons.     

Organization of the disynaptic pathway from the anteroventral cochlear nucleus to the lateral superior olivary nucleus in the ferret

 The medial nucleus of the trapezoid body (MNTB) is one of three major nuclei of the superior olivary complex and provides an important inhibitory input from the contralateral ear to the lateral superior olivary nucleus (LSO) in the initial binaural pathway for coding interaural intensity differences. The major input to the MNTB from the contralateral anteroventral cochlear nucleus (AVCN) involves giant, calyx-like endings that have a one-to-one relationship with cells in the MNTB as confirmed in the ferret in this study. The main objective of the present study was to define the subsequent organization of projections from cells receiving these calyx-like endings. Several anatomical tracers (Phaseolus vulgaris leucoagglutinin, dextran-biotin, and biocytin) were used that are transported both anterogradely and retrogradely within neuronal projections in order to define the organization of MNTB connections with the LSO in the adult ferret. Analysis focused on determining the topography in both the transverse and longitudinal planes of the projections. Focal tracer injections in the LSO resulted in retrograde labeling of a long, narrow column of cells in the MNTB. The orientation and location of labeled cells was dependent on the medial-lateral position of the injection site. In the rostral-caudal dimension of MNTB, there was no such topographic relation between the injection site and the position of labeled cells. Labeled cells in the MNTB were distributed more or less evenly in a longitudinal column regardless of whether the injection site was restricted to the rostral, middle or caudal part of the LSO. In keeping with this pattern, tracer injections in the MNTB resulted in bands of labeled axons that distributed endings throughout the rostral-caudal axis of the LSO. These bands or sheets varied in medial-lateral position relative to the location of the injection site, but lacked any such rostral-caudal gradient. Thus, overall the MNTB-LSO projections have a convergent-divergent pattern of organization. While MNTB cells receive singular calyx-like endings from the AVCN, LSO cells receive projections from a long column of cells in the MNTB. Implications for processing interaural intensity differences are discussed. Accepted: 23 July 1998     

Ultrastructural distribution of glycinergic and GABAergic neurons and axon terminals in the rat dorsal cochlear nucleus,with emphasis on granule cell areas

A knowledge of neurotransmitters in the neurons of the rat cochlear nuclear complex is of importance in understanding the function of auditory circuits. Using post-embedding ultrastructural immunogold labelling, the distribution of glycinergic and GABAergic neurons and axonal terminals has been studied in the molecular, fusiform and polymorphic layers of the rat dorsal cochlear nucleus (DCN). This technique is not limited by the penetration of antibodies into the nervous tissue as in pre-embedding methods, and allows a fine neurochemical mapping of the nervous tissue. Numerous glycinergic and GABAergic axon terminals contain pleomorphic and flat synaptic vesicles, and are present in all layers (1, 2, 3) of the dorsal cochlear nucleus. Glycine and GABA-negative large terminals (mossy fibres) are mainly seen in granule cell areas of layer 2 (fusiform layer). Mossy fibres contact the dendrites of GABA- and glycine-negative granule cells and of the few unipolar brush cells (excitatory neurons). The least common cells in the granule cell areas are GABAergic and glycinergic Golgi-stellate neurons. In unipolar brush cells, aggregations of vesicles seem to be the origin of their characteristic ringlet-bodies. Golgi-stellate cells send their inhibitory terminals to the dendrites of granule and unipolar brush cells, occasionally directly to mossy fibres. Small or (less frequently) large GABAergic terminals contact the soma or the main dendrite of unipolar brush cells. The circuit of a hypothetical functional unit of neurons in the DCN is proposed. The inputs from auditory tonotopic or non-auditory non-tonotopic mossy fibres eventually reach pyramidal cells through axons from the granule cells or unipolar brush cells. Pyramidal cells convey an excitatory signal from the DCN to higher mesencephalic nuclei for further elaboration of the acoustic signal.     

Somatotopical organization of the projection from the nucleus interpositus anterior of the cerebellum to the red nucleus. An experimental study in the cat with silver impregnation methods

Summary Small lesions were done in various areas of the nucleus interpositus anterior (NIA) of the cerebellum, and the distribution of terminal degeneration was studied in the red nucleus with the methods of Nauta and Glees. The NIA projects to the contralateral red nucleus. Two principles of organization can be demonstrated in the projection: a caudorostral arrangement in the red nucleus corresponds to a mediolateral organization in the NIA and a mediolateral arrangement in the red nucleus corresponds to a caudorostral organization of the NIA. The latter distribution coincides with the somatotopical areas of the red nucleus defined by Pompeiano and Brodal (1957). Special attention has been paid to the questions of the subdivision of the cerebellar nuclei and of the course of the fibres issuing from the nuclei in the cerebellar hilus. The present findings on the projection of the NIA to the red nucleus have been correlated with recent anatomical and physiological data on the cerebellum and the red nucleus.Abbreviations BC brachium conjunctivum - c caudal - d dorsal - Ext extensor effects - Flex flexor effects - forel forelimb area - HB hook-bundle - Hb. P habenulo-peduncular tract - hindl hindlimb area - I lateral - m medial - NF nucleus fastigii or medialis - NIA nucleus interpositus anterior - NIP nucleus interpositus posterior - NL nucleus lateralis - r rostral - v ventral - III root fibres of the third nerve - IV fourth ventricle Fellow of the Canadian Medical Research Council.     

Projections from the central nucleus of the amygdala to the nucleus pontis oralis in the rat: An anterograde labeling study

The present study was designed to elucidate the neuronal projections from the amygdala to the nucleus pontis oralis (NPO). We propose that glutamatergic cells in the central nucleus of the amygdala (CNA) activate neurons in the NPO, which is the critical brainstem site that is responsible for the generation and maintenance of active (REM) sleep. Phaseolus vulgaris-leucoagglutinin (PHA-L), an anterograde transported neuronal tracer, was iontophoresed into the CNA of adult male Sprague-Dawley rats. After a survival time of 7-8 days, the animals were perfused with a fixative and brain tissue was prepared for histological analysis. Sections of the NPO and CNA, which were immunostained with an antibody against PHA-L, were examined with light microscopy. In addition, in order to identify the phenotype of PHA-L-labeled fibers and terminals in the NPO, a double immunohistochemical technique was employed with antibodies against PHA-L and the vesicular glutamate transporter type 2 (VGluT2). Numerous PHA-L-labeled axons and terminals were found in the NPO ipsilateral to the injection site in the CNA. Within the NPO, the majority of labeled fibers were located in the dorsolateral portion of the caudal part of the nucleus. Double-labeling immunostaining studies revealed that PHA-L-labeled axons and terminals in the NPO were glutamatergic. The present demonstration of direct, excitatory (glutamatergic) projections from the CNA to the NPO provide an anatomical basis for the amygdalar control of active sleep.     

Projections of the pulvinar-lateral posterior complex to visual cortical areas in the cat

The projections of the pulvinar-lateral posterior complex of the cat were studied using the autoradiographic tracing method and related to 15 previously defined cortical areas. The results indicate that each of three separate zones within the pulvinar-lateral posterior complex has a different pattern of projection. The most lateral zone, the pulvinar, sends fibers to at least seven cortical areas, most of which are known to have input from other visual areas within the brain: the splenial visual area, the cingulate gyrus, and areas 5, 7, 19, 20a and 21a. A zone located just medial to the pulvinar, the lateral division of the lateral posterior complex, projects to at least eight visual areas in the cortex: areas 17, 18, 19, 20a, 21a, 21b, the posteromedial lateral suprasylvian area and the ventral lateral suprasylvian area. The most medial zone, the intermediate division of the lateral posterior complex, projects to at least four cortical areas: 20a, the posterior suprasylvian area, the posterolateral lateral suprasylvian area and the dorsal lateral suprasylvian area. Of the 15 cortical areas that receive fibers from the pulvinar-lateral posterior complex, only three (areas 19, 20a and 21a) receive projections from more than one of these thalamic zones, and only one of the cortical areas (20a) receives fibers from all three zones.Thus, the data support the division of the pulvinar lateral posterior complex into three zones on the basis of their unique and largely non-overlapping projections to the visual cortex.