Cartwheel neurons of the dorsal cochlear nucleus: a Golgi-electron microscopic study in rat

Cartwheel neurons in rat dorsal cochlear nucleus (DCN) were studied by Golgi impregnation-electron microscopy. Usually situated in layers 1-2, cartwheel neurons (10-14 micrometers in mean cell body diameter) have dendritic trees predominantly in layer 1. The dendrites branch at wide angles. Most primary dendrites are short, nontapering, and bear only a few sessile spines. Secondary and tertiary dendrites are short, curved, and spine-laden. The perikaryon forms symmetric synapses with at least two kinds of boutons containing pleomorphic vesicles. The euchromatic nucleus is indented and has an eccentric nucleolus. The cytoplasm shows several small Nissl bodies, a conspicuous Golgi apparatus, and numerous subsurface and cytoplasmic cisterns of endoplasmic reticulum with a narrow lumen, joined by mitochondria in single or multiple assemblies. In primary dendrites mitochondria are situated peripherally, while in distal branches they become ubiquitous and relatively more numerous. Dendritic shafts usually form symmetric synapses with boutons that contain pleomorphic vesicles. The majority of the dendritic spines are provided with a vesiculo-saccular spine apparatus. All dendritic spines have asymmetric synapses. Most of these are formed with varicosities of thin, unmyelinated fibers (presumably axons of granule cells) running parallel to the long axis of the DCN or radially. These varicosities contain round, clear synaptic vesicles. On the initial axon segment few symmetric synapses are present. The axon acquires a thin myelin sheath after a short trajectory. Cartwheel neurons outnumber all other neurons in layers 1-2 (with the exception of granule cells), and presumably correspond to type C cells with thinly myelinated axons described by Lorente de Nó. The axons of these neurons provide a dense plexus in the superficial layers without leaving the DCN. The possible functional role of cartwheel neurons is discussed.     

Structure of the piriform cortex of the opossum. I. Description of neuron types with golgi methods

The piriform cortex was studied in the adult opossum with rapid Golgi and Golgi-Cox techniques. Most pyramidal cells in the deep part of layer II and layer III resemble those in other parts of the cerebral cortex by virtue of a single apical dendritic trunk, multiple basal dendrites, a large number of small to medium dendritic spines, and a deeply directed axon. Pyramidal cells in the superficial part of layer II are similar with the exception that “secondary” apical dendrites often emerge directly from the cell body rather than from a single primary trunk. With conservative criteria for categorization, nine different types of nonpyramidal cells were distinguished, four of which have not been previously described. Layer I contains a small number of neurons with both smooth and spiny dendrites including distinctive fusiform cells with large somatic appendages. As in other species, the most common type of nonpyramidal neuron in layer II is the semilunar cell which has only apically directed dendrites. These cells have distinctive large spines confined to their distal dendritic segments. The mid to deep portion of layer III contains multipolar neurons with smooth dendrites that resemble the well-known large stellate cells in neocortex. In addition, layer III contains three non-pyramidal neuron types with spiny dendrites: (1) fusiform and multipolar cells with complex, branched dendritic appendages and somatic spines, (2) very large multipolar cells (up to 35 μm mean diameter) with large-diameter dendrites that give rise to abruptly tapering side branches and filiform spines, and (3) multipolar cells with profusely spiny dendrites. In all three layers, small neurons have been found with spherical cell bodies and “axoniform” dendrites that resemble the so called neurogliaform neurons described in a variety of brain areas. A striking feature of the organization of the piriform cortex is that, with the exception of the neurogliaform neurons, the different types of nonpyramidal cells tend to be segregated in individual layers or sublayers. Physiological implications of the results are discussed. Remarks are also made concerning the potential of the piriform cortex as a model cortical system.     

Maturation of granule cell dendrites after mossy fiber arrival in hippocampal field CA3

Most granule neurons in the rat dentate gyrus are born over the course of the first 2 postnatal weeks. The resulting heterogeneity has made it difficult to define the relationship between dendritic and axonal maturation and to delineate a time course for the morphological development of the oldest granule neurons. By depositing crystals of the fluorescent label Dil in hippocampal field CA3, we retrogradely labeled granule neurons in fixed tissue slices from rats aged 2-9 days. The results showed that all labeled granule cells, regardless of the age of the animal, exhibited apical dendrites. On day 2, every labeled neuron had rudimentary apical dendrites, and a few dendrites on each cell displayed immature features such as growth cones, varicosities, and filopodia. Some cells displayed basal dendrites. By day 4, the most mature granule neurons had longer and more numerous apical branches, as well as various immature features. Most had basal dendrites. On days 5 and 6, the immature features and the basal dendrites had begun to regress on the oldest cells, and varying numbers of spines were present. On day 7, the first few adult-like neurons were seen: immature features and basal dendrites had disappeared, all dendrites reached the top of the molecular layer, and the entire dendritic tree was covered with spines. These data show that dendritic outgrowth occurs before, or concurrent with, axon arrival in the CA3 target region, and that adult-like granule neurons are present by the end of the first week.     

A study of neuronal types in Clarke's column in the adult cat

Three neuronal classes have been identified in Clarke's column in the adult cat. The smallest cells (class A) exhibit variable dendritic branching patterns. Medium-sized neurons (class B) can be subdivided into multipolar and fusiform cells. The majority of the multipolar cells have elongated perikarya and their dendrites project in a radial fashion, while the fusiform neurons often have their long axis perpendicularly oriented. The large Clarke cells (class C) and their dendrites project in the cranio-caudal direction. Their dendrites are generally smooth and often extend for over 1000 μ from the perikaryon, but three types of dendritic specializations have been noted: spines, branchlets and varicosities. These specializations are not strictly restricted to Clarke cells. Dendrites of all three cell types cross the nuclear boundaries. Some enter the dorsal columns via Rexed's lamina V and others enter laminae VI, VII and X. Neurons whose cell bodies lie within laminae V, VI, VII and X occasionally send dendrites into Clarke's column. Class A cells account for at least 60% of the total neuronal population of Clarke's column and outnumber the Clarke cells (class C) by approximately three to one. Class B neurons are the least common and form between 6 and 16% of the population.     

Two types of GABA-accumulating neurons in the superficial gray layer of the cat superior colliculus

Two types of neuron in the upper superficial gray layer of the cat superior colliculus accumulated exogenous ³H-gamma-aminobutyric acid intensely. The first type was a horizontal cell with a fusiform cell body, horizontal dendrites, a low synaptic density, but a high percentage of cortical synaptic contacts. This cell had presynaptic dendrites. The second type was a granule cell (type A) with a small round cell body, thin and obliquely oriented dendrites, a moderate synaptic density, and few cortical synaptic contacts. These two types differed in size, shape, dendritic morphology, and patterns of synaptic input. They likely participate in different inhibitory mechanisms. Four types of unlabeled neurons were also identified. Type B granule cells were found only within the upper subdivision of the superficial gray layer. They had moderate-sized cell bodies, a high synaptic density, and numerous somatic spines. A third type of granule cell (type C) was found only in the deep subdivision of the superficial gray. This type had a low synaptic density and spines that contained synaptic vesicles. Vertical fusiform and stellate forms were also found. We conclude that at least six types of neurons populate the upper superficial gray layer of the cat superior colliculus.     

The Differentiation of Dentate Granule Cells Following Transplantation

Immature cells transplanted into an adult host must adapt to their new environment. In the present study we have shown the dendritic development of dentate granule cells following transplantation. The adult host granule cells were lesioned by a fluid injection into the infragranular cleavage plane of the dentate gyrus. Few, if any, granule cells survived the lesion and the molecular layer (ML) shrank. When allogeneic neonatal granule cells were included in the fluid, the host granule cells were simultaneously killed and replaced. In order to visualize the dendrites, the granule cells were filled with Lucifer yellow (LY) in fixed sections and subsequently immunoreacted with an antibody to LY. The granule cell dendrites in the transplant were shorter in length, had a greater cross-sectional area, had more spines, and were more coiled and bent than control granule cell dendrites. The dendrites in the transplant formed functional synapses as indicated by cytochrome oxidase histochemistry and the transplant prevented xc03some of the ML shrinkage. Acetylcholin-esterase (ACHE) xkreaction product increased both in lesioned and in transplant groups. The laminar pattern of ACHE in the control ML was not seen after the lesion and did not return in animals with successful transplants. We conclude that (i) the dendrites of neurons in the transplant adapted to the adult host environment and a shrinking ML with remarkable structural plasticity; (ii) the transplant prevented some of the shrinkage of the ML; (iii) the transplant could not reverse some of the lesion-induced changes in host organization, such as the organization of ACHE inputs to the ML; and (iv) a phenotypically specific population of transplanted neurons can replace traumatically lesioned neurons of the same type even if the host conditions continue to change.     

Structural correlates of functionally distinct X-cells in the lateral geniculate nucleus of the cat

In the companion paper (Humphrey and Weller, '88), we demonstrated 2 physiologically different groups of X-cells (XL and XN) in the A-laminae of the cat lateral geniculate nucleus. In order to investigate their possible morphological correlates, we iontophoresed horseradish peroxidase intracellularly into physiologically identified XL- and XN-cells and examined their light microscopic appearance. The 11 HRP-labeled XL-cells constituted the smallest relay neurons in the A-laminae, and were similar morphologically. All had small somata (mean soma size = 236 micron2), very thin (less than 1.0 micron) axons, few primary dendrites, and narrow, sinuous distal dendrites, which usually formed trees that were oriented perpendicular to laminar borders. The dendrites could be smooth or display beadlike varicosities, hairlike appendages, and/or occasional complex stalked appendages, but their most consistent feature was numerous clusters of grapelike dendritic appendages located at or near dendritic branch points. The 14 labeled XN-cells were structurally more heterogeneous, and they included relay neurons and interneurons. Eight of 11 XN-relay cells differed markedly from the XL-cells. These XN-cells were multipolar neurons with medium to large somata (mean soma size = 365 micron2), small to medium-size axons (1.0-2.0 micron), numerous primary dendrites, and straight distal dendrites that formed radially symmetric trees. The dendrites of the cells were largely smooth, except for occasional spines and/or hairs, and they were devoid of grapelike and other complex appendages. The three other XN-relay neurons had morphologies either similar to XL-cells or intermediate between XL-cells and more simple, multipolar XN-relay cells, but two of these cells had larger somata and axons than most XL-cells. Finally, three XN-cells were intrageniculate interneurons, which possessed small somata (mean soma size = 174 micron2), fine sinuous dendrites covered with beadlike varicosities on stalked appendages, and no obvious axon. These results reveal that, despite minor overlap, there are marked structural differences between XL- and XN-cells. Among the relay cells, these differences relate to soma and axon diameter, dendritic orientation, and the presence or absence of grapelike dendritic appendages. Our finding that interneurons were strongly excited at short latencies by spot onset supports the hypothesis (Mastronarde, '87a; Humphrey and Weller, '88) that such interneurons provide the major inhibitory input to XL-cells, and that this input is important in generating the spot-induced early dips in XL-cell discharge.     

Synaptic organization in the dorsal cochlear nucleus of the cat: a light and electron microscopic study

This report describes some observations of the synaptic organization of one region of the cat dorsal cochlear nucleus (DCN). The large “fusiform cell” and its innervation from the cochlea are emphasized. The morphology of the mature fusiform cell and its postnatal development are described in rapid Golgi impregnations of perfusion-fixed littermate cats. The mature features are correlated with profiles of fusiform cell bodies, apical dendrites, and basal dendritic trunks in electron micrographs from adult cat brains. Small neurons and granule cells are also identified in electron micrographs. In Golgi impregnations, axons of small cells and granule cells may terminate upon fusiform cells. Six classes of axons can be distinguished in rapid Golgi impregnations of the DCN. Two classes are of cochlear origin. One axonal class arises from small cells. The sources of the remaining axonal classes have not been identified in this study. Primary afferents can terminate as large, mossy endings in the DCN neuropil. They can also participate in axonal nests along with axons and dendrites of small cells. In electron micrographs, four synaptic endings can be distinguished. Primary cochlear fibers end in large terminals with asymmetrical synaptic complexes and round, clear vesicles. Primary axons can end in glomeruli, resembling those of the cerebellum, or in synaptic nests which are conglomerates of neuronal processes including other types of endings. The origins of the other synaptic types are not yet known. According to this study, primary afferent input could influence fusiform cells directly or indirectly, via small cells and granule cells.     

Scrapie infection diminishes spines and increases varicosities of dendrites in hamsters: a quantitative Golgi analysis

An altered morphology of neuronal dendrites has been shown to be associated with many degenerative diseases of the central nervous system (CNS). Scrapie is a CNS degenerative disorder caused by a novel infectious particle or prion. Golgi impregnation studies showed that neurons in the scrapie-infected brains of hamsters contained varicose swellings and diminished numbers of dendritic spines. In order to ascertain whether or not these differences were statistically significant, quantitative methods were applied to brain samples from scrapie-infected hamsters and compared to uninfected controls. Golgi impregnated layer III pyramidal neurons from both motor and visual cortex exhibited two types of changes in infected animals. First, loss of dendritic spines on the apical shaft of both motor and visual neurons were found from 50 to 200 microns from the cell body (p less than 0.001). Second, spherical varicosities on dendritic stalks ranging from 7 to 25 microns in diameter were found. The average number of varicosities per cell was 18.1 in infected animals with varicosities on dendrites of controls numbering less than 3 per cell. Less than 2% of the control cells exhibited these varicosities, while greater than 80% of the scrapie dendrites exhibited varicosities. These changes in scrapie are similar to those reported in Creutzfeldt-Jakob and Alzheimer's disease in human patients.     

The posterior lateral line lobe of certain gymnotoid fish: Quantitative light microscopy

The posterior lateral line lobe of the wave species of gymnotoid fish was investigated with the Golgi technique. The posterior lobe has a laminar structure and contains II cell types differentially distributed in the various laminae (fig. 13). The major laminae, from ventral to dorsal are the deep fiber layer, containing multipolar neurons; the deep neuropil layer, containing ovoid neurons and a sub-lamina of spherical cells; the granule cell lamina, containing two types of granule cell; the plexiform laminae; the polymorphic cell lamina, containing basilar pyramids, non-basilar pyramids, giant fusiform cells, and polymorphic cells; the stratum fibrosum; the molecular lamina, containing neurons of the ventral molecule layer and stellate cells. The spherical cells are regularly distributed in their sub-lamina and appear to receive one type of primary afferent input. Another type of primary afferent input ends in the deep neuropil and granule layers, in proximity to the basilar dendrites of the granule cells and of the basilar pyramids. The basilar pyramidal cell spatially alternates with the non-basilar pyramidal cell, so that the basilar dendritic trees of nearest-neighbour basilar pyramids show almost no overlap. Descending input to the posterior lobe ends in the molecular layer, in proximity to apical dendrites of both pyramidal cells, giant fusiform cells, polymorphic cells, and one type of granule cell. There are three afferent fiber systems in the molecular layer, one running transversely, one longitudinally, and one vertically. Local circuitry in the posterior lobe is precisely organized and involves projections of granule cells onto overlying pyramidal cells. The polymorphic cell may also be involved in the intrinsic circuits of the posterior lobe.     

Synaptic connections of neuropeptide Y (NPY) immunoreactive neurons in the hilar area of the rat hippocampus

Synaptic connections and fine structural characteristics of neuropeptide Y-immunoreactive (NPY-i) neurons in the fascia dentata were studied using an antiserum against NPY. Normal and colchicine pretreated rats were examined to study the synaptic connections of NPY-i neurons in the normal fascia dentata. The perforant pathway and fimbria fornix were transected to label afferent fibers to NPY-positive cells. Horseradish peroxidase conjugated with wheat germ agglutinin (HRP-WGA) was injected into the contralateral hippocampus to study commissural projections of hippocampal NPY-i neurons, and to search for NPY-i synaptic contacts on immunonegative commissural cells. Since earlier reports have shown that at least half of the NPY-i neurons also contain somatostatin (SS), the distribution of NPY-i neurons in the hilar area was determined and compared with that of SS-i neurons. Four types of dentate NPY-i neurons were distinguished: Type 1: large multipolar cells in the deep hilus (9%). Type 2: medium-sized multipolar and fusiform hilar neurons with dendrites occasionally reaching the outer molecular layer (64%). Type 3: pyramidal shaped cells in the granule cell layer with long apical dendrites reaching the outer molecular layer (20%). Type 4: small multipolar NPY-i cells located in the molecular layer (7%). Our results indicate two overlapping but not identical cell populations of NPY-i and SS-i neurons. Light and electron microscopic analysis of the normal fascia dentata demonstrated that the majority of NPY-i terminals are located in the outer molecular layer of the dentate gyrus, where they establish symmetric synaptic contacts on dendritic shafts and occasionally on spines of granule cells. A moderate number of NPY-i synapses were also found on dendrites in the inner molecular layer and on the cell body of granule cells. Numerous symmetric NPY-i synapses were found on dendrites and somata of neurons in the hilar area. Some NPY-i dendrites in the hilar area received mossy axon collateral input. After transection of the perforant pathway degenerated axon terminals could be found in synaptic contact with NPY-i dendrites in the outer molecular layer. Commissurotomy revealed direct commissural input to NPY-i dendrites in the inner molecular layer and in the hilus. After injection of HRP-WGA into the contralateral hippocampus 2% of hilar NPY-i neurons were retrogradely labeled and symmetric NPY-i synapses were found on the cell bodies and dendrites of unstained HRP-WGA labeled neurons.(ABSTRACT TRUNCATED AT 400 WORDS)     

Structural characterization of marginal (lamina I) spinal cord neurons in the cat: a Golgi study.

The neuronal population of the spinal cord lamina I (marginal zone) was structurally characterized, in the cat, by the use of the Golgi method complemented by multivariate analysis of morphometric data. Four cell types were identified, two of them including two subtypes. Fusiform cells accounted for 43% of impregnated cells and presented flame-shaped rostrocaudally elongated perikarya and bipolar, either strictly longitudinal (fusiform A; 37%) or longitudinal and ventral (fusiform B; 6%) dendritic arbors with numerous short-pedicled spines. Fusiform cells preferentially occupied the lateral one-third of lamina I. Multipolar cells (22%) had ovoid perikarya with bulging surfaces and numerous primary dendritic trunks. Two subtypes could be distinguished: multipolar A cells (12%) with highly ramified dendrites covered with variably shaped spines and multipolar B cells (10%) with looser and less spiny dendritic arbors expanded for longer distances. Multipolar cells were more commonly found in the medial half of lamina I. Flattened cells (16%) possessed discoid perikarya flattened across the dorsoventral axis and aspiny, scarcely ramified dendritic arbors distributed horizontally within lamina I. They predominated in the intermediate one-third of the lamina. Pyramidal cells had triangular prismatic perikarya partially encased in the white matter overlying lamina I. They represented 19% of the impregnated neurons and were located along the entire lateromedial extent of the lamina. Each neuronal type included a few cells with perikarya and dendritic arbors three times larger than the rest. These so-called giant cells amounted to 6% of the entire lamina I neuronal population. According to the present data, the neuronal population of the spinal cord lamina I of the cat strongly resembles that of the rat (Lima and Coimbra, J. Comp. Neurol. 244:53-71, 1986), which strengthens the functional relevance of this structural classification.     

Golgi analyses of dendritic organization among denervated olfactory bulb granule cells

In the vertebrate olfactory bulb, the primary projection neurons, mitral and tufted cells, have reciprocal dendrodendritic synapses with respective subpopulations of anaxonic interneurons called granule cells. In the neurological murine mutant Purkinje Cell Degeneration (PCD), all mitral cells are lost during early adulthood. As a consequence, a subpopulation of granule cells is deprived of both afferent input and efferent targets. The effect of this event on the morphology and sublaminar distribution of granule cells was studied with light microscopic Golgi procedures in affected homozygous recessive PCD mutants and normal heterozygous littermate controls. In the control mice, a minimum of three subpopulations were identified predominantly on the basis of the topology of apical dendrites and their spinous processes within the external plexiform layer (EPL) of the olfactory bulb: type I had dendrites extending across the full width of the EPL and a homogeneous distribution of spines; type II had dendritic arbors confined to the deeper EPL; type III had apical dendrites that arborized extensively within the superficial EPL with no arbors or spines present in the deeper EPL. Prior studies suggest that type II cells form connections with mitral cells; type III cells form connections with tufted cells; and type I cells may integrate information from both populations of projection neurons. In the mutant PCD mice, the classification of subpopulations of granule cells proved difficult due to a compression of dendritic arbors within the EPL. Dendritic processes followed a more horizontal tangent relative to the radial orientation seen in control mice. The length of dendritic branches was reduced by approximately 20% with a corresponding decrease in the number of spines. The density of spines (#/1 micron of dendrite) was constant in both controls and mutants at approximately 0.21. Truncation of the dendrites in the PCD mutants appeared to occur at terminal portions because the number of dendritic bifurcations was equal in both groups of mice. The data are discussed in terms of subpopulations of granule cells in the mouse olfactory bulb, the sublaminar organization of olfactory bulb circuits, and the capacity for survival and plasticity in the reciprocal dendrodendritic circuits mediated by the granule cell spines.     

Calretinin immunoreactive structures in the human hippocampal formation

The calcium-binding protein calretinin is present in an intrinsic GABAergic and an extrinsic non-GABAergic system in the rat and monkey hippocampal formation. Important species differences have been noted in hippocampal cell types immunostained for calretinin and the termination pattern of calretinin containing hypothalamic afferents in the hippocampus. In the present study, calretinin-containing neurons were visualized using immunocytochemistry in the human hippocampal formation of individuals which showed no significant neuropathological alterations. Calretinin-immunoreactivity was present exclusively in non-granule cells of the dentate gyrus and in non-pyramidal cells of Ammon's horn. Calretinin-positive neurons were found most frequently in the hilus of the fascia dentata and in strate radiatum and lacunosum-moleculare of CA1, whereas neurons in CA2 and CA3 were rarely immunostained. The majority of calretinin-immunoreactive neurons were small, bipolar or fusiform neurons. The dendritic trees of the calretinin-positive neurons were, for the most part, parallel to the dendrites of the principal cells. In the hilus, however, we observed cells with dendrites restricted to the hilar area. These dendrites were parallel to the granule cell layer. In the stratum lacunosum-moleculare, neurons with dendrites oriented parallel to the hippocampal fissure were frequently detected. In general, dendrites were smooth or sparsely spiny, displaying small conventional spines. The axons usually emerged from the proximal dendrite and could be followed over long distances. Axons were thin, had small varicosities and displayed only few collaterals which branched relatively far away from the cell body. Distinct bands of darkly stained calretinin-positive fibers occupied the innermost portion of the dentate molecular layer and the pyramidal cell layer of CA2. This distribution of calretinin-immunoreactive structures in the human hippocampus is similar to that observed in other primates but differs from that described in lower mammals, i.e., the rat. Our findings suggest that primates may share a common hippocampal calrtinin-containing system, presumably both the intrinsic GABAergic and the extrinsic hypothalamic non-GABAergic components. © 1995 Wiley-Liss, Inc.     

Anatomy of cultured mouse cerebellum. I. Golgi and electron microscopic demonstrations of granule cells, their afferent and efferent synapses

The development of granule cells and their connections was reinvestigated in organotypic cultures of cerebellum. Modified Golgi-Cox preparations showed numerous maturing granule cells, some with fully mature claw-shaped dendritic endings, within presumptive cortex. Large cortical neurons often had dendrites richly encrusted with synaptic spines. Sometimes bundles of thin parallel processes were oriented orthogonally to the spiny dendrites. Semithin sections and electron micrographs showed granule cell somas distributed in closely packed clusters, with directly apposed cell membranes. Several types of glio-glial membrane apposition were observed, including extensive desmosome-like junctions. The neuropil contained closely packed bundles of thin parallel processes and numerous synaptic complexes, often within the parallel bundles. The postsynaptic elements, when identifiable, often proved to be dendritic spines; axodendritic and axosomatic synapses were less common than axospinous. A few synaptic complexes resembled glomeruli, with linked granule cell dendrites surrounding a presynaptic element. The concurrence of several lines of evidence proves the identity of granule cells in presumptive cortex, but the existence of basket and Golgi Type II neurons and the source of presynaptic element in the glomerulus cannot be demonstrated. The criteria and importance of rigorous cell identification in cultures are discussed.     

Morphology and physiology of cells in slice preparations of the dorsal cochlear nucleus of mice

Horseradish peroxidase (HRP) was injected into cells from which intracellular recordings were made in slices of the dorsal cochlear nucleus (DCN) in order to correlate physiology with morphology. In general, the morphology of cells labeled intracellularly with HRP corresponded to those made with Golgi impregnations in mice and other mammals. The following cells were labeled: one granule cell, four cartwheel cells, eight fusiform cells, two other cells in the fusiform cell layer, and two tuberculoventral association cells in the deep layers of the DCN. The axon of the granule cell runs parallel to isofrequency laminae with collaterals branching perpendicularly and running along the tonotopic axis. The cartwheel cells have dendrites in the molecular layer that are densely covered with spines. The axon of one cell terminates just dorsally to the cell body. Fusiform cells have the characteristic spiny, apical and smooth, basal dendrites. The basal dendrites are conspicuously oriented parallel to isofrequency laminae. Axons of the fusiform cells exit through the dorsal acoustic stria without branching. The two tuberculoventral association cells in the deep DCN have axons that terminate both in the deep DCN, within the same isofrequency lamina that contains the cell body, and in the ventral cochlear nucleus (VCN). Intracellular recordings from 11 of these cells show that they cannot be distinguished on the basis of their responses to intracellularly injected current. All cell types fired large action potentials that were followed by a fast and a slower undershoot, distinguishing them from cells of the VCN but not from one another. Most cells responded to shocks of the auditory nerve root with early EPSPs and later IPSPs. The latencies of EPSPs show that some were monosynaptic and others polysynaptic. That there was no systematic relationship between the latencies of EPSPs and the cell types from which they were recorded shows that shocks to the nerve root may have activated more than just the large, myelinated, auditory nerve fibers.     

Glutamate-immunoreactivity in the retina and optic tectum of goldfish

Glutamate was immunohistochemically localized in the goldfish retina and tectum at the light and electron microscopic (E.M.) levels using double affinity purified antisera against glutaraldehyde conjugated L-glutamate. In retina, glutamate-immunoreactivity (Glu+) was observed in cone inner segments, cone pedicles, bipolar cells, a small number of amacrine cells and the majority of cells in the ganglion cell layer. The latter were shown to be ganglion cells by simultaneous retrograde labeling. Centrally, Glu+ was observed in axons in the optic nerve and tract, and in stratum opticum and stratum fibrosum et griseum superficialis (SFGS) of the tectum. The Glu+ in the optic pathway disappeared four days after optic denervation and was restored by regeneration without affecting the Glu+ of intrinsic tectal neurons. In tectum, Glu+ was also observed in torus longitudinalis granule cells, toral terminals in stratum marginale, some pyramidal neurons in the SFGS, multipolar and fusiform neurons in stratum griseum centrale, large multipolar and pyriform projection neurons in stratum album centrale, and many periventricular neurons. Glu+ was also localized within unidentified puncta throughout the tectum and within radially oriented dendrites of periventricular neurons. At the E.M. level, a variety of Glu+ terminals were observed. Glu+ toral terminals formed axospinous synapses with dendritic spines of pyramidal neurons. Ultrastructurally identifiable Glu+ putative optic terminals formed synapses with either Glu+ or Glu- dendritic profiles, and with Glu- vesicle-containing profiles, presumed to be GABAergic. These findings are consistent with the hypothesis that a number of intrinsic and projection neurons in the goldfish retinotectal system, including most ganglion cells, may use glutamate as a neurotransmitter.     

Dementia of frontal lobe type and motor neuron disease. A Golgi study of the frontal cortex.

Neuropathological findings in a 38 year old patient with dementia of frontal lobe type and motor neuron disease included pyramidal tracts, myelin pallor and neuron loss, gliosis and chromatolysis in the hypoglossal nucleus, together with frontal atrophy, neuron loss, gliosis and spongiosis in the upper cortical layers of the frontal (and temporal) lobes. Most remaining pyramidal and non-pyramidal neurons (multipolar, bitufted and bipolar cells) in the upper layers (layers II and III) of the frontal cortex (area B) had reduced dendritic arbors, proximal dendritic varicosities and amputation of dendrites as revealed in optimally stained rapid Golgi sections. Pyramidal cells in these layers also showed depletion of dendritic spines. Neurons in the inner layers were preserved. Loss of receptive surfaces in neurons of the upper cortical layers in the frontal cortex are indicative of neuronal disconnection, and are "hidden" contributory morphological substrates for the development of dementia.