摘要:

AbstractWhile neurofilaments have long been considered early markers of neuronal differentiation, they cannot be detected in most newly postmitotic neurons of the developing central nervous system (CNS). Here we show that these neurons already express the neuronal intermediate filament protein α‐internexin at high levels. α‐internexin is expressed by most, if not all, neurons as they begin differentiation and shows no overlap with vimentin, whose expression in the CNS is restricted to mitotic neuronal precursors. In the adult, α‐internexin is the only intermediate filament gene expressed by the cerebellar granule cells, the source of the thin‐caliber parallel fibers; conversely, neurofilament proteins are highly expressed in large neurons, which express α‐internexin at low levels. These data suggest that neuronal intermediate filaments may regulate axonal stability and/or diameter through changes not only in their number, but also in their subunit composition. © 1994 W

ISSN:0092-7317    

DOI:10.1002/cne.903420202

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractThe neurons which synthesize and release luteinizing hormone‐releasing hormone (LHRH), are hypothesized to originate in the epithelium of the medial olfactory pit and to migrate into the brain along a scaffolding made up of neural cell adhesion molecule (NCAM)‐immunoreactive branches of the terminal and vomeronasal nerves. These LHRH neurons, studied by immunocytochemical and autoradiographic procedures, were found to originate within a very short period of embryogenesis, specifically day 10, in mice, and to follow a remarkably ordered spatiotemporal course along the migration route into the brain.The purpose of the present experiments was to determine whether perturbation of the NCAM‐immunoreactive migration route, at a particular time in development, would arrest the migration of LHRH neurons into the brain. We found that a 1 μl injection of antiserum to NCAM into the area of the olfactory pit, on day 10 of embryogenesis, significantly reduced the number of LHRH‐immunoreactive neurons seen in the epithelium of the medial olfactory pit, with a concomitant significant reduction in the number of LHRH‐immunoreactive cells seen outside of the placode, on the migration route. These results confirm our initial hypothesis that LHRH neurons migrate from the epithelium of the olfactory pit to the brain and indicate that NCAM plays a causal role in this phenomenon. © 1994 Wile

ISSN:0092-7317    

DOI:10.1002/cne.903420203

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractThe peptide neurotransmitter vasoactive intestinal peptide (VIP) has neurotrophic properties and influences neurobehavioral development. To assess the role of VIP during neural ontogeny, the present work traces the development of VIP mRNA with in situ hybridization and VIP receptors with in vitro autoradiography in rat central nervous system (CNS) from embryonic day 14 (E14) to the adult.VIP mRNA was not evident in the CNS until birth. Postnatally, it was expressed in several distinct brain regions, but its distribution bore little relation to that of VIP receptors.VIP receptors were present and expressed changing patterns of distribution throughout CNS development. The changing patterns were the result of (1) the transient appearance of GTP‐insensitive VIP receptors in several regions undergoing mitosis or glial fasciculation and (2) the transient appearance of GTP‐sensitive VIP receptors homogeneously distributed throughout the CNS during the first 2 postnatal weeks, the period of the brain growth spurt. At E14‐16 VIP binding was dense throughout the brainstem and spinal cord, but limited in the rest of the brain. From E19 to postnatal day 14 (P14), while VIP binding was higher in germinal zones, it tended to be uniformly dense throughout the remainder of the brain. By P21 the adult pattern began to emerge; VIP binding was unevenly distributed and was related to specific cytoarchitectural sites.Since the expression of VIP in the CNS is limited to postnatal development but VIP receptors are abundant prenatally, we suggest that extraembryonic VIP may act upon prenatal VIP receptors to regulate ontogenic events in the brain. © 1994 Wiley‐L

ISSN:0092-7317    

DOI:10.1002/cne.903420204

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractMicroinjections of biocytin have been made in the granular layer of the rat cerebellar cortex in order to label the axonal projections of a localised population of granule cells. Light microscopic techniques were used to determine the lengths of the parallel fibres and to measure the spacing and size of the fibre varicosities. Fibres were longest in the superficial one‐third of the molecular layer, where mean overall length was 4.7 mm, and mean length decreased to 4.2 mm in the lower one‐third of the molecular layer. We found no very short fibres but a small population deep in the molecular layer had a branch length of about one‐half the average. Mean intervaricosity interval and varicosity size varied with distance from proximal to distal along the fibres. Mean intervaricosity interval was 3.7 μm within 250 μm of the fibre bifurcation points and progressively increased towards the distal ends, where the mean interval was 7.4 μm. Mean varicosity size was 0.82 μm2in this proximal region and decreased to 0.47 μm2about 1.2 mm distally. Mean intervaricosity interval on the ascending axons of the granule cells was 4.0 μm. Electron microscopy revealed that a high proportion (89%) of the parallel fibre varicosities formed synaptic junctions. The majority of the synapses (91%) were formed on Purkinje cell dendritic spines. Some varicosities also formed simultaneous synaptic contacts or double synapses with two spines. These double synapses occurred more frequently in the proximal region of the fibres (11%) than on the distal ends (2%). The length of the postsynaptic density also differed according to the location of the varicosities and the mean length at the proximal parallel fibre synapses was 0.59 μm compared with 0.38 μm at the distal synapses. It is concluded that a beam or bundle of parallel fibres originating from cells in a focal region of the granular layer will exert a graded synaptic influence on its target Purkinje cells, with the most powerful influence occurring on cells located around the proximal region of the fibres where they bifurcate and the weakest action being exerted on cells located at the distal end of the fibres. © 1994 W

ISSN:0092-7317    

DOI:10.1002/cne.903420205

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractConsiderable progress has been made in recent years in identifying molecules with restricted expression in mammalian spinal cord at early developmental stages. However, the significance of the different expression patterns for most of these molecules is nuclear because so little is known about the development of various classes of spinal interneurons. Recently, we have characterized the development of rat spinal cord interneurons with an axon that crosses in the ventral commissure (Silos‐Santiago and Snider, J. Comp. Neurol., 325:514, 1992). In the current study, we describe the morphological development of ipsilaterally projecting spinal interneurons in laminae V–VIII of the thoracic spinal cord. These neurons were labelled by retrograde lateral diffusion of DiI after crystals were placed in various locations in the embryonic thoracic cord.By E14, approximately 48 hours after the first interneurons are generated, eight different groups of ipsilateral interneurons are present in the spinal cord. By E15, these groups of ipsilateral interneurons have reached distinct locations within the gray matter. Even at this early stage, different groups of cells have elaborated characteristic dendritic arborizations. By E19, at least 17 different types of ipsilateral interneurons can be identified on the basis of location and dendritic morphology. In general, ipsilateral interneurons are located more dorsally and laterally than commissural interneurons at all stages of embryonic development. Furthermore, in comparison with commissural neurons, fewer ipsilateral interneurons have dendritic arbors with a mediolateral orientation in the transverse plane.This work demonstrates that rat embryonic spinal cord contains a large number of morphologically distinct classes of interneurons that extend axons into the ipsilateral lateral funiculus. These neurons can be distinguished from commissural neurons on the basis of location and morphology. These results, taken together with those from our previous study, provide a framework for the localization of gene expression to different classes of spinal interneurons at early developmental stages. © 1994 Wiley‐Lis

ISSN:0092-7317    

DOI:10.1002/cne.903420206

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractResearch on the implication of the amygdala in classical fear conditioning suggests that the central amygdaloid nucleus is the output station of the amygdala for conditioned fear responses, while the lateral nucleus acts as the input nucleus, at least for auditory conditioned stimuli. However, the nature and locus of the plastic changes taking place between these two nuclei are unknown partly because the neurotransmitter(s) used by intra‐amygdaloid projections of the lateral nucleus has not been identified. To address this issue in cats, anterograde tracing withPhaseolus vulgaris‐leucoagglutinin (PHA‐L) was combined with postembedding immunocytochemistry for gamma‐aminobutyric acid (GABA) and glutamate.Two sectors can be recognized in the lateral nucleus of the cat: a shell located laterally along the external capsule, and a core. Iontophoretic injections of PHA‐L in these two sectors revealed that they have nonoverlapping intra‐amygdaloid targets with the exception of a common projection to the central lateral nucleus. The core projects mainly to itself and to the basomedial nucleus, whereas the shell contributes a massive projection to the basolateral nucleus. No projection of the lateral nucleus to the central medial nucleus was found. Electron microscopically, PHA‐L‐labeled axon terminals in the lateral, basomedial, basolateral, and central lateral nuclei as well as in the perirhinal and insular cortices formed asymmetric synapses (100%; n = 289) with dendritic spines (77–100%). Moreover, postembedding immunocytochemistry revealed that PHA‐L‐labeled axon terminals are immunoreactive for glutamate but not GABA.Since most amygdaloid projections to the brainstem originate in the central medial nucleus, these results suggest that intra‐amygdaloid targets of the lateral nucleus are involved in the transmission of auditory conditioned stimuli to the central medial nucleus. Moreover, these findings imply that intra‐amygdaloid projections of the lateral nucleus use glutamate but not GABA as a neurotransmitte

ISSN:0092-7317    

DOI:10.1002/cne.903420207

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractRecent neurophysiological and magnetic resonance imaging studies of clinically “complete” human spinal cord injuries indicate that some patients have considerable subclinical function and substantial morphological integrity of descending spinal tracts. In contrast, extensive histopathological changes, including cell death, have been described in central nervous system nuclei projecting to the cord following experimental transection or hemisection of the spinal cord in animal models. We have used a rodent model of severe compression cord injury that more closely resembles the clinical pathophysiology to investigate the extent of the persistence of the rubrospinal projection. Counts of red nucleus neurons retrogradely labelled with Fluorogold demonstrate that in contrast to the results obtained with transection models, compression injuries of the spinal cord donotresult in massive loss of rubrospinal projections, at least up to 8 weeks postinjury. The results also suggest that many of the axons persist distal to the lesion site and that they are functionally intact with respect to retrograde transport capabilities. © 1994 Wiley‐Lis

ISSN:0092-7317    

DOI:10.1002/cne.903420208

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractA basic principle of organization in auditory centers is the topographic‐tonotopic order. Whether this applies to the dorsal nucleus of the lateral lemniscus (DNLL), however, is still debated. To clarify this problem, we have utilized the neuroanatomical tracers horseradish peroxidase (HRP) and biotinylated dextran (BD) injected into different regions of the central nucleus of the inferior colliculus (CNIC) in the rat.After large injections of HRP that included most of the CNIC, retrogradely labelled neurons were found all across the ipsi‐ and contralateral DNLL, showing that all parts of this nucleus innervate the CNIC bilaterally. More neurons were seen consistently on the side contralateral to the injection site. Labelled fibers, however, were abundant ipsilaterally, but scarce in the contralateral DNLL.Single, small injections of HRP or BDinto the CNIC resulted in labelling in restricted areas of the ipsi‐ and contralateral DNLL. In coronal sections, the neurons and fibers labelled in the ipsilateral DNLL formed a well‐defined, ring‐shaped structure made of dendrites and axons oriented parallel to each other, which we termed “annular band.” The observation of serial sections revealed that the annular band seen in any individual section represents a slice through a more or less complete three‐dimensional, hollow, ovoid structure oriented rostrocau‐dally. The position and diameter of the annular band changed as the injection site was shifted along the tonotopic axis of the CNIC. Single injections placed in the ventromedial, high‐frequency region of the CNIC produced a large annular band along the periphery of the DNLL. After injections placed in progressively more dorsolateral, lower‐frequency regions of the CNIC, the annular band became smaller in diameter and occupied a successively more central position in the DNLL. Double injections along the tonotopic axis of the CNIC resulted in two roughly concentric annular bands. The labelled neurons and fibers in the contralateral DNLL systematically occupied a position symmetric to the annular band seen ipsilaterally.These findings indicate that the rat DNLL is primarily composed of neurons with flattened dendritic arbors and flattened fields of terminal fibers. These two elements intermingle, forming concentric layers around the geometric center of the nucleus. The axons of neurons within corresponding layers on the two sides converge onto the CNIC of both sides in a strict topographic fashion: the peripheral layers project to the ventromedial, high‐frequency region of the CNIC, and the central layers project to the dorsolateral, low‐frequency region. These results suggest that the concentric arrangement of the DNLL is the substrate of its tonotopic organizatio

ISSN:0092-7317    

DOI:10.1002/cne.903420209

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractVestibular nerve afferents innervating the bullfrog utriculus differ in their response dynamics and sensitivity to natural stimulation. They also supply hair cells that differ markedly in hair bundle morphology. To examine the peripheral innervation patterns of individual utricular afferents more closely, afferent fibers were labeled by the extracellular injection of horseradish peroxidase (HRP) into the vestibular nerve after sectioning the vestibular nerve medial to Scarpa's ganglion to allow the degeneration of sympathetic and efferent fibers. The peripheral arborizations of individual afferents were then correlated with the diameters of their parent axons, the regions of the macula they innervate, and the number and type of hair cells they supply.The utriculus is divided by the striola, a narrow zone of distinctive morphology, into medial and lateral parts. Utricular afferents were classified as striolar or extrastriolar according to the epithelial entrance of their parent axons and the location of their terminal fields. In general, striolar afferents had thicker parent axons, fewer subepithelial bifurcations, larger terminal fields, and more synaptic endings than afferents in extrastriolar regions. Afferents in a juxtastriolar zone, immediately adjacent to the medial striola, had innervation patterns transitional between those in the striola and more peripheral parts of the medial extrastriola. Most afferents innervated only a single macular zone. The terminal fields of striolar afferents, with the notable exception of a few afferents with thin parent axons, were generally confined to one side of the striola.Hair cells in the bullfrog utriculus have previously been classified into four types based on hair bundle morphology (Lewis and Li: Brain Res.83:35–50, 1975). Afferents in the extrastriolar and juxtastriolar zones largely or exclusively innervated Type B hair cells, the predominant hair cell type in the utricular macula. Striolar afferents supplied a mixture of four hair cell types, but largely contacted Type B and Type C hair cells, particularly on the outer rows of the medial striola. Afferents supplying more central striolar regions innervated fewer Type B and larger numbers of Type E and Type F hair cells. Striolar afferents with thin parent axons largely supplied Type E hair cells with bulbed kinocilia in the innermost striolar rows. © 1994 Wiley‐Liss,

ISSN:0092-7317    

DOI:10.1002/cne.903420210

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractThe lateral preoptic and lateral hypothalamic regions contain the majority of the cell groups embedded in the fibre trajectories of the medial forebrain bundle on its course through the hypothalamus. Recent studies have extended considerably the parcellation of the lateral hypothalamic region, and, therefore, the need to emphasize new insights into the anatomical organisation of projections from the neurons of the lateral hypothalamic region. In the present study we describe the anatomical organisation of efferent projections from the lateral preoptic and lateral hypothalamic regions to the hypothalamic paraventricular nucleus (PVN) on the basis of retrograde‐ and anterograde‐tracing techniques. Iontophoretic injections of the retrograde tracer, cholera toxin subunit B, into the PVN revealed that most hypothalamic nuclei project to the PVN. Within the lateral hypothalamic region, retrogradely labelled cells were concentrated in the intermediate hypothalamic area, the lateral hypothalamic area, and the perifornical nucleus, whereas fewer retrogradely labelled cells were found in the lateral preoptic area.To determine the distribution of terminating fibres in subnuclei of the heterogeneous PVN, iontophoretic injections of the anterograde tracerPhaseolus vulgaris‐leucoagglutinin were delivered into distinct areas of the lateral hypothalamic region. Neurons of the intermediate hypothalamic area projected mainly to the PVN subnuclei, which contained parvicellular neuroendocrine cells. In contrast, neurons of the rostral and tuberal parts of the lateral hypothalamic area and the perifornical nucleus projected to the PVN subnuclei, which contained parvicellular neurons that send descending projections to preganglionic cell groups in the medulla and spinal cord. The perifornical nucleus was the only area within the lateral hypothalamic region that consistently innervated magnocellular perikarya of the PVN. Finally, all areas of the lateral hypothalamic region contributed substantially to fibres terminating in the perinuclear shell of the PVN. These results demonstrate that anatomically distinct areas of the lateral hypothalamic region have distinct projections to subnuclei of the PVN and further substantiate the view that the lateral hypothalamic region as well as the PVN constitute anatomically and functionally heterogeneous structures. © 1994 Wiley‐L

ISSN:0092-7317    

DOI:10.1002/cne.903420211

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY