摘要:

AbstractThe cytoarchitectonic organization of the medial geniculate body and adjoining thalamic nuclei was analyzed in the mustached bat (Pteronotus parnellii). These subdivisions provide a reference for structural, physiological, conncetional, and nurochemical work. Most nuclei recognized in other mammals exist in the mustached bat, although the relative volume of the three divisions was species specific. The ventral division contains medium‐sized neurons and a few smaller cells and is well developed. Neurons in the lateral part lie in regularly aligned rows corresponding to the laminae in Golgi material; in the medial part, these laminae are obscured by fibers. The dorsal dividion has at least four nuclei, each with a unique cytoarchitecture and myeloarchitectonic organization. The suprageniculate nucleus is prominent and has many large radiate neurons. Cells in the superficial dorsal nucleus have weakly laminated dendrites, while dorsal nucleus neurons have spherical dendritic fields. There is a wide range of neuropil patterns within the dorsal division. The suprageniculate nucleus has thick myelinated axons, while the fibers in the superficial and dorsal nuclei are much thinner. The rostral pole nucleus becomes prominent in the anterior one‐half of the auditory thalamus; its architectonic affiliation is equivocal, and connectional and immunocytochemical studies suggest that it may belong to the dorsal division. The medial division is one nucleus with many types of neurons, and it has coarse axons without laminar orientation. It is the smallest of the divisions and is present throughout the medial geniculate complex, except at the caudal tip and at the rostral pole.Many features of medial geniculate body organization evident in other mammals are recognized in the mustached bat. These include a prominent ventral division, some of whose neurons have a laminar organization, and a comparatively small medial division that is devoid of fibrodendritic laminae. Other features, such as the presence of a large rostral pole nucleus, whose homologue in other species is uncertain, or the sparse number or small cells that may participate in local circuits, set it apart from carnivores and primates and suggest that there are species specific patterns of medial geniculate body organization. © 1994 Wiley‐Lis

ISSN:0092-7317    

DOI:10.1002/cne.903460202

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

年代:1994

数据来源: WILEY

摘要:

AbstractThe neurons in the medial geniculate body were studied in Golgi preparations from adult mustached bats (Pteronotus parnellii). Their somatic and dendritic configurations were compared with those of cells in other, nonecholocating mammals. A second goal was to use the thalamic nuclear subdivisions derived from Golgi material to integrate the findings in parallel studies of cytoarchitecture, immunocytochemistry, and tectothalamic connections.Three primary divisions are defined. The ventral division is large and has a stereotyped neuronal organization. Medium‐sized perikarya (about 10 μm in diameter) represent tufted neurons; the fibrodendritic plexus forms laminae in the lateral part along which midbrain axons terminate. A smaller, possibly intrinsic, neuron with thin, sparse dendrites is rarely impregnated. Neurons in the larger, medial part, which represents frequencies of 60 kHz and higher, have more spherical dendritic fields; their branching pattern remains tufted, and the laminar organization was less evident. The dorsal division is about equal in size, and it has many nuclei and a corresponding neuronal diversity. These neurons are medium‐sized except in the suprageniculate nucleus, where many cells are larger. Four dorsal division nuclei are recognized. Each has neurons with radiate or weakly tufted dendritic arbors. Superficial dorsal nucleus neurons are oriented from medial to lateral, imparting a slightly laminated appearance to the neuropil. A few smaller, stellate neurons with modest dendritic domains are present. Suprageniculate nucleus neurons have radiating dendritic fields that project spherically; they have fewer branches than dorsal nucleus neurons. The posterior limitans nucleus is dorsomedial to the suprageniculate nucleus; it has small neurons with long, sparsely branched dendrites. The rostral pole nucleus, included in the dorsal division on cytoarchitectonic grounds, had too few neurons impregnated to reveal its neuronal architecture. The medial division, the smallest of the main parts, is one nucleus with at least six types of cells, including the magnocellular, bushy tufted, disc‐shaped, medium‐sized multipolar, elongated, and small stellate neurons. There is no laminar arrangement.Many of the neurons resemble those in rodent, marsupial, carnivore, and primate auditory thalamic nuclei. Despite such morphological correspondences, functional differences, such as the evolution of combination sensitivity, suggest that structurally comparable auditory thalamic neurons may subserve diverse physiological representations. © 1994 Wiley

ISSN:0092-7317    

DOI:10.1002/cne.903460203

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

年代:1994

数据来源: WILEY

摘要:

AbstractThis study examined the output of the central nucleus of the inferior colliculus to the medial geniculate body and other parts of the nervous system in the mustached bat (Pteronotus parnellii). Small deposits of anterograde tracers (horseradish peroxidase, [3H]leucine,Phaseolus vulgarisleucoagglutinin, wheat germ agglutinin conjugated to horseradish peroxidase, or biocytin) were made at physiologically defined sites in the central nucleus representing major components of the bat's echolocation signal. The topography, frequency specificity, and axonal morphology of these outputs were studied.The medial geniculate body was a major target of inferior collicular neurons, with three distinct input patterns. The projection to the ventral division was tonotopically organized, but had a relatively sparse contribution from neurons representing frequency modulated components of the biosonar pulse. The second input was to the rostral medial geniculate body, in which projections from inferior collicular neurons representing constant frequency sonar components were separated from those representing frequency modulated components. A third input was to the suprageniculate nucleus, which received strong, topographically arranged projections. Inputs to the dorsal nucleus and medial division were also observed.Extrathalamic regions receiving input included the pontine gray, external nucleus of the inferior colliculus, pericollicular tegmentum, nucleus of the brachium of the inferior colliculus, and pretectum. These central nucleus projections differed in organization and the structure of axon terminals, suggesting different physiological influences on their target nuclei. These results demonstrate that the central nucleus has divergent projections to various sensory and premotor nuclei, besides its well‐established projection to the medial geniculate body. © 1994 Wiley‐Liss,

ISSN:0092-7317    

DOI:10.1002/cne.903460204

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

年代:1994

数据来源: WILEY

摘要:

AbstractWe combined transganglionic tracing methods with postembedding electron microscopic immunocytochemistry to determine whether identified primary afferent fibers terminating in spinal laminae I‐IV may use glutamate and aspartate as neurotransmitters. Sciatic injections of wheat‐germ agglutinin conjugated to horseradish peroxidase labeled fine afferent fibers with terminals in laminae I‐II of the lumbar spinal cord, whereas injections of the B subunit of cholera toxin conjugated to horseradish peroxidase labeled primary afferent terminals in deeper laminae. Many labeled primary afferent terminals in superficial laminae were involved in glomerular synaptic arrangements; others established nonglomerular contacts. Most glomerular arrangements were clearly immunopositive for glutamate, compared with dendrites, astrocytes, or terminals immunopositive for γ‐aminobutyic acid (GABA). The degree of enrichment varied in labeled terminals of different morphological types. Aspartate was enriched, though to a lesser degree than glutamate, in labeled central terminals of glomeruli in superficial laminae. Labeled primary afferent terminals in laminae III‐IV were immunopositive for glutamate, though at lower levels than glomerular terminals in superficial laminae. Aspartate was not enriched in these terminals compared with dendrites, glia, and GABA‐positive terminals. These results support a neurotransmitter role for glutamate in primary afferents to the dorsal horn. Quantitative differences in the content of glutamate in identified primary afferent terminals may be related to functional differences. Enrichment of aspartate in terminals in superficial but not deep laminae is compatible with a role for this amino acid in sustained, NMDA‐mediated phenomena characteristic of activity in fine caliber afferents. © 1994

ISSN:0092-7317    

DOI:10.1002/cne.903460205

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

年代:1994

数据来源: WILEY

摘要:

AbstractOcular regression in subterranean species has been shown to be associated with a number of alterations in the retina and in retinal pathways. In order to examine the consequences of eye reduction, the visual system was studied in two species of the murine genus,Ellobius, a specialized fossorial rodent. The axial length of the eye is only 2.2 mm inE.lutescensand 2.9 mm in E.talpinus. The mean soma size of ganglion cells in Nissl‐stained flatmounts is approximately 10 μm inE.lutescensand 12 μm inE.talpinus. The soma size distribution in both species appears unimodal and falls within a range‐of 6–17 μm in diameter. The topographic distribution of ganglion cells shows a weak centroperipheral gradient, and an area centralis cannot be distinguished. The total number of neurons in the ganglion cell layer in Nissl‐stained flat mounts is 12,000 inE.lutescensand 28,500 inE.talpinusand, following injection of retrograde tracers in the superior colliculus, is, respectively, 3,600 and 20,000. Based on the axial length and maximum ganglion cell density, the calculated retinal magnification factor (20–26 μm/degree) and spatial resolution (0.4–0.9 cycles/degree) of these minute eyes are extremely reduced. Retinofugal projections, demonstrated by autoradiography and horseradish peroxidase histochemistry, are similar to those in other rodents. The superior colliculus is well developed and receives a predominantly contralateral projection. Ganglion cells projecting to the contralateral colliculus are distributed over the entire retina, while cells that project ipsilaterally are restricted to the ventrotemporal region. The dorsal lateral geniculate nucleus has clearly defined binocular and monocular segments, including a partial segregation of regions receiving ipsilateral or contralateral retinal innervation. In addition, a localized region of label is observed medial to the geniculate nucleus. The retina also sends a bilateral projection to the suprachiasmatic nucleus; the intergeniculate leaflet; the pretectum; and the medial, lateral, and dorsal terminal nuclei of the accessory optic system. Sparse retinal projections were also seen in the bed nucleus of the stria terminalis, the anterior thalamus, and the inferior colliculus. A substantial retinal projection is observed in the basal telencephalon, including the cortical amygdaloid region, the diagonal band of Broca, the olfactory tubercle, and the piriform cortex. The results suggest that the morphological constraints of reduced eye size are reflected in the retina by a generally homogeneous organization but that central visual projections are not substantially modified as in some more specialized, strictly subterranean rodents. © 1994

ISSN:0092-7317    

DOI:10.1002/cne.903460206

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

年代:1994

数据来源: WILEY

摘要:

AbstractAstrocytes in the central nervous system (CNS) respond to injury and disease by proliferating and extending processes. The intermediate filament protein of astrocytes, glial fibrillary acidic protein (GFAP) also increases in astrocytes. These cells are called “reactive astrocytes” and are thought to play a role in CNS repair. We have previously demonstrated rapid increases (<6 hours) in GFAP‐immunoreactive and silver‐impregnated glial processes in the chick cochlear nucleus, nucleus magnocellularis (NM), following cochlea removal or activity blockade of the eighth nerve. It was not known whether these changes were the result of glial proliferation, glial hypertrophy, or both. The present study examined the time course of astrocyte proliferation in NM following cochlea removal.Postnatal chicks received unilateral cochlea removal and survived for 6, 12, 18, 24, 36, 48, and 72 hours. Bromodeoxyuridine was used to label proliferating cells. The volume and number of labeled cells in NM was calculated for both the experimental and control sides of the brains for experimental animals was well as for unoperated control animals.A subset of astrocytes continuously divide in the normal posthatch chick brainstem. The percentage of labeled nuclei increases within NM 36 hours following cochlea removal and is robust by 48 hours. This increase is due to astrocyte proliferation within, rather than migration to, NM. These resulis indicate that rapid increases in GFAP following reduced activity are independent of cell proliferation. The time course of astrocyte proliferation suggests that cellular degeneration within the nucleus may play a role in upregulating astrocyte proliferation. © 1994 Wiley

ISSN:0092-7317    

DOI:10.1002/cne.903460207

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

年代:1994

数据来源: WILEY

摘要:

AbstractThe objective of the present study was, by using the Mongolian gerbil (Meriones unguiculatus) as an animal model, to provide data on the growth dynamics of central auditory and visual nuclei and to relate the growth of these structures to the growth of the entire brain. So far, no such systematic study has been performed in any mammalian species. The knowledge of the rates of development of central nervous sensory structures might be useful for understanding the contribution of the central nervous system to maturation of sensory processing.Increases in volumes of nuclei and changes in their shape were analyzed for animals at the day of birth (P0); at postnatal days P7, P15, P22, P28; and in the third month (P90). The auditory nuclei investigated were the cochlear nucleus, the superior olivary complex, the nuclei of the lateral lemniscus, the inferior colliculus, and the medial geniculate body. From the visual system, the superior colliculus and the lateral geniculate body were studied.At P15 (shortly after the onset of central auditory responsiveness), the volumes of all auditory nuclei examined reached only 60–70% of their adult sizes; i.e., they showed considerable growth afterwards. At the same time (shortly before the animals open their eyes), the visual nuclei had almost reached their adult sizes (superior colliculus, 91%; lateral geniculate nucleus, 97%).These data demonstrate that different sensory nuclei contribute in highly different fashions to brain growth. There are system‐specific differences in growth dynamics between central auditory and visual nuclei. However, the absolute growth of nuclei in both sensory systems relates to the brain regions. The data do not support the idea of a peripheral‐to‐central gradient in the growth of central auditory nuclei. © 1994 Wiley

ISSN:0092-7317    

DOI:10.1002/cne.903460208

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

年代:1994

数据来源: WILEY

摘要:

AbstractThe morphology of projection neurons of the isthmic nucleus was studied inRana esculenta, R. nigromaculata, Bufo marinus, B. bufo gargarizans, andXenopus laevisfrom a comparative anatomical point of view. The main point of this work was to provide an anatomical basis for electrophysiological studies. Neurons projecting to the ipsilateral optic tectum were labeled by retrograde transport of horseradish peroxidase and cobaltous lysine complex injected into the optic tectum. Contralaterally projecting cells were filled by injecting the tracer substances into the crossed isthmotectal tract.Cells of the anterior nonrim cortex and the rostral part of the medulla project to the ipsilateral tectum. A band of cells in the middle of the medulla, a few cells in the caudal part of the medulla, and most of the neurons in the rim cortex project to the contralateral tectum.Five types of neurons were distinguished in the rim cortex ofR. esculenta. Most of them have piriform perikarya and their dendrites arborize in the rim neuropil. In the medulla of the isthmic nucleus ofR. escalenta, seven types of neurons were distinguished. Most of these neurons also exist in the other species. Medullary cells are piriform, fusiform, or multipolar, and are variable in size and in dendritic arborization. The isthmic neurons of the twoRanaeandBufospecies are similar. The dominant cell types inXenopusare multipolar with extensive dendritic arborization, which occupies more space in the nucleus than in the other species.Neurons with narrow dendritic trees may represent a system of fine resolution, and those neurons with extensive dendritic arborization may belong to a coarser system. © 1994 Wiley‐Liss, I

ISSN:0092-7317    

DOI:10.1002/cne.903460209

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

年代:1994

数据来源: WILEY

ISSN:0092-7317    

DOI:10.1002/cne.903460201

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

年代:1994

数据来源: WILEY