摘要:

AbstractThe human olfactory epithelium has been previously studied with scanning electron microscopy; however, most studies have been limited to examining the epithelial surface. In an attempt to examine structures below the surface, we scanned epithelial fractures that occurred during tissue preparation. This made it possible to obtain unique three‐dimensional images of cell profiles from the mucosal surface through the full depth of the epithelium. We examined supporting cells, olfactory neurons, basal cells, and a fourth cell type, the microvillar cell. Supporting cells had a microvillar surface and were in close contact with olfactory neurons and their processes. Olfactory neurons were primarily located in the middle and lower epithelial regions. Basal cells occurred alone or in clusters adjacent to the basal lamina. Microvillar cells were always observed in the upper epithelial region. They were flask‐ or pear‐shaped, had a tuft of microvilli that extended into the nasal cavity, and a thin axon‐like process that passed basally towards the lamina propria.This study represents the first comprehensive scanning electron microscopy examination of the human olfactory epithelium. Three‐dimensional images obtained for each epithelial cell type allowed us to examine cell processes and their close contacts, especially between supporting cells and olfactory neurons. These results also revealed the irregular and patchy distribution of olfactory receptors within the human nasal cavity. Further studies that examine the detailed morphology of the human olfactory epithelium should provide a better understanding of the physiological mechanism and clinical disorders that affect olfactory function

ISSN:0092-7317    

DOI:10.1002/cne.902970102

出版商:Wiley‐Liss, Inc.    

年代:1990

数据来源: WILEY

摘要:

AbstractThe cytoarchitecture, myeloarchitecture, and neocortical connectivity of the rat medial geniculate body (MGB) were comprehensively studied in adult and immature rats to define major anatomical divisions and nuclei. The MGB is a highly intricate structure composed of the ventral (MGv), dorsal (MGd), and medial (MGm) divisions and component nuclei, each having reciprocal connections with auditory neocortex. The MGv lies inferior to the midgeniculate bundle and extends to the rostral, but not caudal MGB tip. The MGv is composed of ventral and ovoid nuclei bounded by a marginal zone, each region containing dark staining small and medium sized, densely packed neurons shown to have tufted dendritic morphology; in contrast to the MGd, but similar to the dorsal lateral geniculate nucleus, only the perikarya of MGv neurons stain for Nissl in early postnatal material. Ventral nucleus cells align with afferent brachial axons, which penetrate the nucleus in a dorsoventral direction, whereas rostrocaudal cellular arrays are retrogradely labeled after injections of horseradish peroxidase (HRP) into auditory cortex. The ovoid nucleus is a double spiraled structure encircled and penetrated by afferent fibers that determine the orientation of constituent perikarya. Neurons in the transition zone align with a spray of axons emanating from the juncture of the ovoid and midgeniculate bundles. Marginal zone neurons are oriented in parallel to the free geniculate wall.The MGd resides within and superior to the midgeniculate bundle, and is composed of several nuclei that stain palely for myelin. In immature material, both dendritic processes and somata in the MGd stain for Nissl with our protocol; many of these cells show a stellate arborization pattern that distinguishes this region from the MGv, but is similar to the staining pattern of immature neurons of the lateral posterior nucleus. The adult dorsal nucleus has medium‐sized, loosely packed neurons. The deep dorsal nucleus is situated among the fibers of the midgeniculate bundle and contains loosely packed round and fusiform cells; the latter cell type constitutes a minor proportion of the adult neuronal population but the major cell type in immature animals. The caudodorsal nucleus, which occupies the caudal tip of the MGB and rostrally courses superior to the dorsal nucleus, contains small, dark staining multipolar cells; the ventrolateral nucleus courses inferior to the MGv. The suprageniculate and limitans nuclei are included in the auditory thalamus on the basis of connections with auditory neocortex; the former has medium to dark staining mixed‐sized cells, and the latter has densely packed cells which form a vertical column. HRP‐labeled cells of dorsal division nuclei typically show either stellate or tufted dendritic morphologies.The MGm is traversed by dense myelinated fiber bundles emanating from the brachium of the inferior colliculus and includes very large “magnocellular” neurons, which predominate caudally, as well as medium‐sized and small cells. “Magnocellular” neurons are elongate, triangular, or round, have loose, nonuniform packing, and tend to orient vertically; many of these cells have sparse, stellate d

ISSN:0092-7317    

DOI:10.1002/cne.902970103

出版商:Wiley‐Liss, Inc.    

年代:1990

数据来源: WILEY

摘要:

AbstractThe medial geniculate body (MGB) of the rat was studied with Golgi methods to determine the distribution of neurons identified by dendritic morphology. These findings were compared with major divisions and constituent nuclei established by somatic and fiber architectonics, and by connections with temporal neocortex (Clerici et al.:Society of Neuroscience Abstracts12:1272, 1986; 13:325, 1987;Anatomical Record218:23, 1987; Winer and Larue:Journal of Comparative Neurology257:282–315, 1987; Clerici and Coleman:Journal of Comparative Neurology297:14–31, 1990). It was found that an elaboration of the prototypical scheme proposed by Morest (Journal of Anatomy98:611–630, 1964) for partitioning the mammalian MGB is valid for characterizing the rat MGB.Two predominant categories of principal neuron dendritic patterning were identified: a bushy cell having tufted dendritic fields and a stellate cell with a radiate dendritic domain. Tufted neurons have large caliber dendritic trunks that divide profusely into daughter branches close to the soma with intertwining higher order branches that maintain a relatively restricted dendritic field. Stellate neurons typically emit primary dendrites in all directions that then divide dichotomously at wide angles at subsequent orders of branching to produce a somewhat spheroidal dendritic field.In the present study, the rat MGB is found to be a tripartite structure composed of ventral (MGv), dorsal (MGd), and medial (MGm) divisions, each uniquely characterized by constituent dendritic morphology. The paramount neuronal class of the MGv is the tufted principal cell. In the ventral and ovoid nuclei of the MGv the neuronal orientation of highly oriented bitufted cells is in register with afferent brachial axons. In the ventral nucleus, this arrangement approximates vertical with a dorsomedial tilt most prominent rostrally; in the ovoid nucleus, tufted cells adhere to the double spiraled course of afferent axons. The transition zone between ventral and ovoid nuclei contains tufted neurons that align with radially oriented fibers issuing from the junction of the ovoid and midgeniculate bundles. Bitufted neurons of the marginal zone parallel fibers at the lateral margin of the geniculate.Within the MGd the dorsal and caudodorsal nuclei are characterized by stellate cells with extensive dendritic arbors and bushy neurons with dendritic branches less tufted than those observed in the MGv. The deep dorsal nucleus contains bitufted neurons that polarize with the long axis of the midgeniculate bundle and intermingle with stellate neurons. The suprageniculate nucleus includes neurons with large somata and long, sparsely branched and dorsoventrally oriented dendrites orthagonal to corticothalamic axons, as well as smaller neurons and classical stellate cells. Neurons of the limitans nucleus have elongated dendritic fields directed along the medial border of the auditory thalamus.Among the variety of cell types of the MGm are ones with the largest somata in the MGB, the prominent “magnocellular” neurons. These cells emit only a few gradually tapering dendrites, which are encrusted with appendages; dendrites branch at irregular intervals and lie oblique to incoming axons from the brachium of the inferior colliculus. The MGm also contains smaller neurons, both tufted and radiate in typology, along with more classical stellate cells.The distribution of cells characterized by morphological features of dendrites corresponds to anatomical regions of the MGB identified by cytoarchitecture, myeloarchitecture, and necortical connectivity. The structural of the rat MGB are mostly typical of mammalian forms, which suggests the rat provides a use for the auditory

ISSN:0092-7317    

DOI:10.1002/cne.902970104

出版商:Wiley‐Liss, Inc.    

年代:1990

数据来源: WILEY

摘要:

AbstractThe neuroblasts forming nucleus magnocellularis, the avian homologue of the mammalian ventral cochlear nucleus, migrate by growth and elongation of their leading processes and by perikaryal translocation through these processes from the matrix zone of the rhombic lip to the acoustico‐vestibular anlage. Golgi methods were used on staged chick embryos to reconstruct the morphogenetic phases of migration and early differentiation in situ. Fluorescence labeling of the living cells in vitro elucidated the role of axonal growth in the migratory process.In situ, branching cochlear nerve fibers, tipped with growth cones, enter the acoustico‐vestibular anlage at E4.5–5.5before migrationof the magnocellularis neuroblasts at E.5.5–6.5. The premigratory neuroblasts in the matrix zone of the rhombic lip resemble primitive epithelial cells, which extend branched, curving processes into a characteristic formation, the rhombic whorl. The leading process of the migrating magnocellularis neuroblasts gives rise to a bifurcating axon at the interface between the matrix and mantle zones. The lateral branch becomes the recurrent ipsilateral collateral; the medial branch crosses the midline, heading toward the contralateral target site in the region of the presumptive nucleus laminaris. The cell bodies of the migratory neuroblasts appear in intermediate locations along the migration route as they translocate radially through their leading processes past the axonal bifurcation and then tangentially and obliquely into the mantle zone. Neuroblasts destined for nucleus laminaris migrate coincidentally with magnocellularis neuroblasts. Nucleus angularis neuroblasts migrate later in development, after E6.5.In vitro, injections of a nontoxic fluorescent dye (diI) were made into explants of the medulla in the region of the contralateral target area at the time of neuroblast migration. DiI retrogradely labeled the cell bodies of premigratory magnocellularis neuroblasts in the matrix zone and of migratory neuroblasts in the mantle zone through their medial, crossing axonal branches. The morphology of the living neuroblasts in the explants resembled that in the Golgi impregnations at the corresponding stages of migration. Anterograde axonal transport also occurred.These results demonstrate migration by perikaryal translocation and early axon extension of a specific group of neuroblasts in the central nervous system. The morphology of the migrating neuroblasts is such that a simple radial arrangement of cellular guides, glial or otherwise, would not account for their configurations. The available evidence supports the proposition that cellular elongation and perikaryal translocation constitute the general mode of neuronal migration in the central nervous system. The early extension of axons into their target sites may play a critical role in migration and early development of specific types of

ISSN:0092-7317    

DOI:10.1002/cne.902970105

出版商:Wiley‐Liss, Inc.    

年代:1990

数据来源: WILEY

摘要:

AbstractThe time and place of initial contacts between afferent axons and their target cells are not known for most regions of the mammalian CNS. To address this issue, we have selectively visualized afferent climbing fiber axons together with their synaptic targets, Purkinje cells, in postnatal mouse cerebellum. Climbing fibers were orthogradely labeled by injection of rhodamine isothiocyanate into their brainstem source, the inferior olivary nucleus. Purkinje cells were localized with an antibody to a calcium‐binding protein, calbindin D‐28k(CaBP), in the same section or in adjacent sections.A novel view of the olivocerebellar projection and the morphology of climbing fiber arbors prior to the well‐known “nest” stage has emerged from this analysis. At birth, climbing fibers project into the zone of Purkinje cells, before these cells have aligned into a monolayer. During this phase, climbing fibers have simple morphologies consisting of relatively unbranched terminal arbors and small tapered growing tips. Purkinje cells are arranged 3–6 cells deep and have tufted dendrites and relatively smooth somata.By postnatal days 3–4, climbing fibers branch over several adjacent Purkinje cell perikarya, which are still organized in a band several cells thick. From postnatal days 5–7, when climbing fibers subsequently make focused nests on individual cells, Purkinje somata are smoother and form a more distinct monolayer. Up to this time, however, climbing fibers continue to associate with Purkinje perikarya, even though Purkinje cell dendrites have emerged and branched extensively. By postnatal days 8–10, climbing fiber terminals climb onto the trunk of the relatively mature Purkinje dendritic tree.At birth, mossy fibers originating from the pontine nuclei resemble immature climbing fibers in that they also have a simple unbranched morphology and growing tips, but project only so far as the internal granule cell layer. Occasional individual fibers reach into the Purkinje zone both at postnatal day 0 and postnatal day 4, confirming that the fibers formerly described as “combination fibers” (Mason and Gregory, '84,J. Neurosci.4:1715–1735) can be mossy in origin.These data demonstrate that climbing fibers project among Purkinje cells earlier than suspected, before these afferents begin to arborize and form pericellular nests. Our observations are not in accord with the view derived from autoradiographic tracing studies that, as in other cortical areas, climbing afferents wait in the vicinity of Purkinje cells in the early neonatal period, then advance onto these cells in synchrony with Purkinje cell alignment into a monolayer and dendritic maturation. Instead, climbing afferents associate with Purkinje perikarya for an extended period during target cell positioning and initial dendritic growth, lagging behind in their translocation up relatively ma

ISSN:0092-7317    

DOI:10.1002/cne.902970106

出版商:Wiley‐Liss, Inc.    

年代:1990

数据来源: WILEY

摘要:

AbstractThe effects of prenatal exposure to ethanol on the structure and function of corticospinal neurons was investigated. The subjects were the 3–4‐month‐old offspring of hooded rats fed a nutritionally balanced liquid diet containing 6.7% (v/v) ethanol (Et), pair‐fed a nutritionally matched isocaloric diet (Ct), or fed chow and water (Ch). Corticospinal neurons in primary somatosensory cortex were examined by intracellularly recording and filling cells that were driven by antidromic stimulation of the pyramidal decussation.In the control rats, corticospinal neurons comprised a homogeneous morphophysiological population. Morphologically, all of the antidromically driven cells examined were pyramidal neurons with cell bodies in layer Vb. The dendrites of these neurons were spinous and branched within layers I, IV, and V. Their axons arborized within layers IV, V, and VI and some collaterals extended laterally for distances up to 2.6 mm from the cell body. The mean conduction latency was 3.6 and 3.4 msec for Ch‐ and Ct‐treated rats, respectively.In Et‐treated rats, corticospinal neurons constituted a heterogeneous population. The laminar distribution of the corticospinal neurons in Et‐treated rats was broad; the cell bodies of labeled neurons were in layers II, IV, V, and VI. The dendrites of layer Vb neurons were spinous; however, many of the spines appeared dysmorphic and the density of spines was significantly greater (32%) in Et‐treated rats than in Ct‐treated rats. Although the dendritic branching pattern for layer Vb neurons was similar to that described for the controls, a Sholl analysis showed that the complexity and extent of their dendritic trees were significantly greater in Et‐treated rats. The axons of all layer Vb neurons in Et‐treated rats had long horizontal processes that arborized in layers IV–VI, and some neurons also had an array of collaterals that ascended to layer I. The mean conduction latency for layer Vb neurons was 3.9 msec. The structure and function of ectopic neurons (those in layers II, IV, Va, Vc, and VI) in Et‐treated rats differed markedly from those of the layer Vb neurons. Morphologically, the dendritic and axonal fields of these neurons were narrower than for the layer Vb neurons, and the ectopic neurons had a mean conduction latency of 7.1 msec.The heterogeneity of the population of corticospinal neurons in Et‐treated rats may result from the effects of ethanol on early events in neuronal development such as neur

ISSN:0092-7317    

DOI:10.1002/cne.902970107

出版商:Wiley‐Liss, Inc.    

年代:1990

数据来源: WILEY

摘要:

AbstractThe role of acetylcholine (ACh) in cerebral cortical activity has recently been reevaluated. It now seems clear that this neurotransmitter increases the magnitude of cortical responses. Although substantial information has been gathered regarding the role of ACh in sensory information processing, little is known about the participation of ACh in the organization of maps in the cerebral cortex. To address this issue, we used 2 methods to manipulate the supply of ACh in the somatosensory cortex of cats: (1) unilateral neurotoxic lesions of the basal forebrain and (2) unilateral topical applications of the cholinergic antagonist, atropine. For each experimental condition, the animal received an injection of 2‐deoxyglucose (2DG) while identical somatic stimuli were delivered to the right and left forepaws. In the somatosensory cortex, the 2DG uptake most often occurred in the form of patches that extended from layer II to IV. When the patches were reconstructed into 2‐dimensional maps of activity throughout the somatosensory cortex, they formed strips that ran in the rostrocaudal direction. The reconstructed maps revealed that the 2DG patterns in ACh‐depleted and the normal cortex were similar in their overall topographic distribution. Depletion or antagonism of ACh, however, caused the stimulus‐evoked metabolic label to be reduced in dimension and density. Measurements of background activity levels were obtained by using (1) cytochrome oxidase histochemistry or (2) metabolic activity values in regions of somatosensory cortex that were not specifically stimulated. This analysis indicated that background values in the ACh‐depleted hemispheres were not different from those in the normal hemispheres. The absence of ACh therefore appears to reduce the cortical response to stimulation, while background activity values do not change. These observations indicate that ACh plays a significant role in the processing of sensory information and the organization of somatosensory cort

ISSN:0092-7317    

DOI:10.1002/cne.902970108

出版商:Wiley‐Liss, Inc.    

年代:1990

数据来源: WILEY

摘要:

AbstractNaturally occurring mutations are valuable tools for the study of neural development, especially when used in conjunction with the techniques of chimeric mouse production. In this study we examine the response of Purkinje cell dendrites to the altered developmental environment found in thelurcher↔ wild‐type chimera.Lurcher(+/Lc) is an autosomal dominant gene that causes the cell‐autonomous degeneration of all Purkinje cells of +/Lcgenotype. Thus, in +/Lc→ +/+ chimeras, only wild‐type Purkinje cells survive to maturity. The number of these survivors can vary from less than 10,000 to greater than 100,000, Previous work has shown that the final ratio of presynaptic granule cells to postsynaptic Purkinje cells is increased inlurcherchimeras. On average, therefore, one might expect that each remaining Purkinje cell would experience an increased supply of afferents, and our hypothesis was that dendritic growth and/or sprouting might occur as a result. This proved incorrect and, indeed, the Purkinje cells in thelurcherchimeras show changes of a predominantly atrophic nature. Unusual morphologies are found, including variable branching density, failure of the distal dendrite to reach the pial surface, loss of isoplanarity, and the frequent appearance of large caliber, primary or secondary dendritic branches ending abruptly in “stub ends.” Quantitative analysis of Golgi‐Cox impregnated material reveals that inlurcherchimeras the Purkinje cell dendritic arbor is reduced by more than 60% compared to wild‐type animals. We present possible explanations for this finding and consider several poten

ISSN:0092-7317    

DOI:10.1002/cne.902970109

出版商:Wiley‐Liss, Inc.    

年代:1990

数据来源: WILEY

摘要:

AbstractTo accumulate phylogenetic information on the central histaminergic system, we investigated the histaminergic system in the brain of the Reeves turtle,Chinemys reevesii, using the indirect immunofluorescent method with antiserum against histamine. Histaminergic neuronal cell bodies were found exclusively in the posterior part of the ventral hypothalamus. Histaminergic varicose fibers innervated almost all parts of the turtle brain, but tended to be concentrated in several areas. Very dense innervation was observed in the medial part of the telencephalon, ventrolateral part of the hypothalamus, nucleus habenularis lateralis, and ventromedial part of the tegmentum. Medium density of innervation was seen in the olfactory bulb, nucleus medialis amygdalae, and tectum. Only a few fibers were detected in the lateral part of the telencephalon, dorsal part of the hypothalamus, thalamus, rhombencephalon, and spinal cord. The main ascending fibers were observed in the lateral part of the hypothalamus, sending dense fiber bundles to the cortices dorsomedialis and medialis and nucleus habenularis lateralis. Descending fibers appeared to run in the ventral tegmental area, passing through the dorsal and ventral parts of the midline of the brain stem to the spinal cord. These findings indicate that the general morphological features of the histaminergic system in the turtle brain are similar to those in the mammalian and frog brains.

ISSN:0092-7317    

DOI:10.1002/cne.902970110

出版商:Wiley‐Liss, Inc.    

年代:1990

数据来源: WILEY

摘要:

AbstractThe retinal vasculature of the fovea of squirrel monkeys was studied in retinal whole mounts and in sections of the same retinas. At the center of the fovea there is an approximately circular avascular zone surrounded by a set of terminal capillaries in the inner nuclear layer. Within the foveal depression, four capillary planes that bear a precise relationship to the neuronal organization appear in a specific sequence with increasing eccentricity. The first plane to be established is the dominant, most voluminous one, located closest to the photoreceptors at the deep (sclerad) border of the inner nuclear layer. A second major plane appears next at the sclerad border of the ganglion cell layer.The two remaining, less voluminous planes occur at a slightly greater eccentricity. One of these, located at the shallow (vitread) border of the inner nuclear layer, often drains into the ganglion cell plane. The fourth plane is initially situated at the vitread border of the ganglion cell layer; with increasing eccentricity it moves into the nerve fiber layer. These capillaries are oriented like the nerve fibers with which they travel. Both the shallow inner nuclear and nerve fiber planes of capillaries show marked regional variations.The capillary planes are within or adjacent to regions of high cytochrome oxidase activity.The retinal vascular network is an unrecognized contributor to the optical filtering properties of the eye. In much of the central retina, a photon has a 40–50% chance of encountering one or more capillaries before it reaches a photorecepto

ISSN:0092-7317    

DOI:10.1002/cne.902970111

出版商:Wiley‐Liss, Inc.    

年代:1990

数据来源: WILEY