摘要:

AbstractSynaptic transmission can be blocked very efficiently by inhibitory synapses on axon initial segments. Inhibitory chandelier cells forming synapses on the axon initial segment of pyramidal neurons have been found in the neocortex and hippocampus proper. Here we describe an axo‐axonic local circuit neuron in the rat fascia dentata that establishes synaptic contacts with axon inital segments of numerous dentate granule cells. Examination of a large number of Golgi‐impregnated nongranule cells in the fascia dentata of rats revealed a group of neurons with characteristics of chandelier cells. Thus these cells exhibited an extensive axonal plexus within the granular layer that characteristically formed vertical aggregations of axonal varicosities. The cell bodies of these neurons were located in the inner molecular layer or in the outer part of the granular layer. Their dendrites invaded the molecular layer, suggesting an afferent innervation similar to that of the granule cells. Well impregnated putative axo‐axonic cells were gold‐toned for an electron microscopic analysis. The cell bodies and dendrites of these neurons exhibited characteristic ultrastructural features of nongranule cells, i.e., large amounts of perinuclear cytoplasm, infoldings of the nuclear membrane, and a large number of synaptic contacts on the perikaryon and on the smooth dendritic shafts. The axon originating from the cell body or from a proximal dendrite gave rise to numerous vesicle‐filled varicosities that almost exclusively formed symmetric synaptic contacts with axon initial segments. A semiquantitative study of five axonal complexes demonstrated that 92.3% of identified postsynaptic elements were initial segments of granule cell axons. Immunostaining with antibodies against glutamate decarboxylase (GAD) and parvalbumin (PARV) revealed a subpopulation of neurons that very much resembled the Golgiimpregnated axo‐axonic cells with regard to cell body location, dendritic arborization, and fine structural characteristics of perikarya and dendrites. GAD and PARV were found to be coexistent in these cells. Moreover, we found GAD‐ and PARV‐immunoreactive terminals in symmetric synaptic contact with axon initial segments of granule cells. The present study has shown a hitherto unknown axo‐axonic cell in the rat fascia dentata. On the basis of our immunocytochemical findings, we hypothesize that this cell exerts a strong inhibitory effect on dentate granule cells. This way, signal transmission from the fascia dentata to the hippocampus proper within the “trisynaptic pathway” can efficiently be controlled by a group of highl

ISSN:0092-7317    

DOI:10.1002/cne.902930102

出版商:Wiley‐Liss, Inc.    

年代:1990

数据来源: WILEY

摘要:

AbstractBy using both light and electron microscopic immunocytochemical methods, Met5‐Enkephalin‐Arg6‐Gly7‐Leu8(MEAGL)‐like immunoreactive structures were detected in the pelvic ganglion of male rats. Denervation studies were carried out to determine the origin of these immunoreactive fibers and the projection of immunoreactive neurons within the pelvic ganglion. MEAGL‐like immunoreactivity was found in numerous axon boutons, some small, intensely fluorescent (SIF) cells, and a few principal ganglion neurons. Most of the immunoreactive nerve fibers formed pericellular plexuses surrounding the ganglion cells. In addition, there were a few scattered varicose fibers. These fiber plexuses could be classified into two types: type I (∼90% of fibers), which consisted of 80‐120 small boutons that synapsed on either the dendrites (80% of cases) or somata (20% of cases) of principal neurons; and type II (∼10% of fibers), which consisted of 20‐40 larger boutons that formed axodendritic synapses exclusively. After transection of the hypogastric and pelvic nerves, virtually all of the pericellular fiber remained. According to their ultrastructure, these remaining fibers were considered to arise from SIF cells. Following the injection of Fast Blue into the bladder wall, some of the MEAGL‐like immunoreactive principal neurons were retrogradely labeled. The results of this study indicate that there are two origins for the MEAGL‐like immunoreactive fibers detected in the pelvic ganglion: most arise from preganglionic neurons in the spinal cord, and a small proportion may originate from intraganglionic MEAGL‐like immunoreactive SIF cells or principal neurons. Some MEAGL‐like immunoreactive principal neurons may pro

ISSN:0092-7317    

DOI:10.1002/cne.902930103

出版商:Wiley‐Liss, Inc.    

年代:1990

数据来源: WILEY

摘要:

AbstractCone photoreceptor pedicles from midperipheral regions of the human retina (6 mm from the foveal center) have been studied by light and electron microscopy. Three areas of cone pedicle mosaic were serially thin‐sectioned, in the tangential plane, from the inner border of the outer plexiform layer to the emergence of the cone axons from the cone pedicles. Semithin sections were then collected from the cone axon level through the cone cell bodies to the cone inner segment level. Two hundred twenty‐one cone pedicles were followed by this means to their respective inner segments. Eight percent of the cone pedicles were from cones with inner segment characteristics of the blue cones. All 221 cone pedicles were reconstructed by tracing images from electron micrographs. The cone pedicle locations, surface areas, telodendrial projections, and synaptic ribbons could then be measured by morphometry and analyzed by statistical methods. Some selected cone pedicles were reconstructed by computer graphics methods.The cone pedicles identified as belonging to the blue cone type could be distinguished from the surrounding longer wavelength types on the following morphological criteria: 1) they were smaller (50% the area of the surrounding pedicles), 2) they contained shorter synaptic ribbons, 3) they exhibited essentially no telodendrial contact to neighboring cone pedicles, 4) they were positioned slightly more vitread in the outer plexiform layer than neighboring pedicles, and 5) their irregular occurrence in the cone mosaic coincided with the distribution criteria established in our previous paper (Ahnelt et al:J. Comp. Neurol.255:18‐34, 87) for putative blue sensitive cones in midperipheral human r

ISSN:0092-7317    

DOI:10.1002/cne.902930104

出版商:Wiley‐Liss, Inc.    

年代:1990

数据来源: WILEY

摘要:

AbstractTwo subpopulations of retinopetal neurons in the nucleus olfactoretinalis (NOR) were revealed by means of general histological, tract tracing, and immunohistochemical methods in a marine teleost, the whitespotted greenling (Hexagrammos stelleri). Two types of cells in the NOR (M cell, L cell) were morphologically distinguishable from one another. The cell bodies of M cells were medium‐size and fusiform, while those of L cells were large and ellipsoidal or irregular. M cells were located at the ventralmost region of the junction between the olfactory bulb and telencephalon, while L cells were scattered more rostrally along the ventromedial surface of the olfactory bulb. Following applications of HRP or Fluoro‐Gold to the optic nerve, almost all M cells and about half of the L cells were labeled in the contralateral NOR. L cells showed strong immunoreactivities to gonadotropin releasing hormone (GnRH) and Phe‐Met‐Arg‐Phe‐NH2(FMRFamide), whereas M cells showed only weak GnRH‐immunoreactivity and no FMRFamide‐immunoreactivity. Axons of L cells were detected in the optic nerve by means of GnRH‐ and FMRFamide‐immunohistochemistry. The axons were concentrated in the myelinated edge (the oldest area) of the “ribbon” optic nerve. GnRH‐ and FMRFamideimmunoreactive fibers constituted a plexus at the junction between the inner nuclear layer and inner plexiform layer. The existence of two structurally separate classes of NOR cells suggests two functionally separate channels f

ISSN:0092-7317    

DOI:10.1002/cne.902930105

出版商:Wiley‐Liss, Inc.    

年代:1990

数据来源: WILEY

摘要:

AbstractOur goal was to devise methods of implanting defined populations of the cellular constituents of peripheral nerve into regions of spinal cord injury. This objective derived from the knowledge that the cellular environment of peripheral nerve is known to be supportive of axon regeneration from both central and peripheral neurons. Two of the constituents of the peripheral nerve environment known to influence axonal growth are the Schwann cell and extracellular matrix (particularly basal lamina), both of which can be obtained in culture. We describe here large‐scale methods of establishing purified populations of rat sensory neurons to which purified populations of Schwann cells were added. These essentially monolayer preparations were then scrolled and cut into lengths of proper shape and size to provide implants for sites of spinal cord injury in newborn rats. We also describe methods enabling the addition of leptomeningeal components to the implants; this addition contributes a proliferating population of vascular endothelial cells (identified by immunostaining) to the otherwise vasculature‐free neuron/Schwann cell implant. Light and electron microscopic observations were made to characterize the implants. When the implant was ready for use, it contained Schwann cells that were differentiated, i. e., had begun to ensheathe axons and form basal lamina. The use of a medium containing human plasma to foster endothelial cell growth led to increased neurite fasciculation and Schwann cell migratory activity in the outgrowth, particularly when the neurons and Schwann cells were cultured on leptomeninges. The second paper in this series reports the deportment of these implants and their influence on corticospinal tract growth after placement into regions of dorsal column injury in neonatal rats (Kuhlengel et al.,J. Comp. Neurol293:74‐91,

ISSN:0092-7317    

DOI:10.1002/cne.902930106

出版商:Wiley‐Liss, Inc.    

年代:1990

数据来源: WILEY

摘要:

AbstractThe purpose of this study was to test the effectiveness of implants derived from peripheral neural tissue to serve as bridges following interruption of the developing corticospinal tract (CST). Implants prepared from purified populations of cultured dorsal root ganglion neurons (DRGNs) and Schwann cells (SCs) (Kuhlengel et al.,J. Comp Neurol.293:63‐73, 1990) were placed into thoracolumbar regions of neonatal rat spinal cord from which a 2‐mm length of dorsal columns had been removed by suction. These cords were examined by a number of techniques 10 days to 6 months later.The implants, recognizable by their DRGN content, filled the vacated dorsal columns and survived the longest periods examined. The most effective method to maintain implant position was dorsal placement of collagen‐coated Nitex filter. Implants were inserted either at the time of lesioning of 5 days later. The implant survival rate was better (72% vs. 50%) and meningeal scarring was less with immediate implantation, but delayed implantation resulted in better implant‐cord fusion and the implant better filled the lesion cavity. DRGN/SC implants became well vascularized without leptomeningeal cells; this may explain why implant survival was not improved with leptomeningeal cell addition. Particularly well‐differentiated implants (full extracellular matrix production and myelination) did not fuse as well with cord as did those less well differentiated. The addition of nerve growth factor to the Nitex filter collagen coating led to improved survival of DRGNs in implants. Electron microscopy showed that astrocytes populated the implant‐cord junction region and migrated into implants. Typical SCs related to nonmyelinated and myelinated axons were present in implants. Close proximity of astrocytes and central myelin to SCs and peripheral myelin demonstrated good implant integration with cord. Clusters of SCs, astrocytes, and axons, all enclosed within a common basal lamina, were observed in implants. Immunostaining for GFAP and laminin confirmed our microscopy findings that SCs did not migrate from implant into host but that astrocytes left host tissue to enter implants.Neuroanatomical tracing of CST neurons with HRP‐WGA showed that labeled fibers were not present in the implant but were fasciculated just beneath in gray matter. These fibers remained clustered in gray matter under‐neath the ventral dorsal columns caudal to the lesion. In lesioned but not implanted rats, labeled fibers were only diffusely distributed in gray matter. Delayed implantation led to more variation in fasciculation compared with immediate implantation. In conclusion. DRGN/SC implants did not serve as tissue bridges but appeared to influence adjacent cord parenchyma to permit CST fiber fasciculation that persisted bey

ISSN:0092-7317    

DOI:10.1002/cne.902930107

出版商:Wiley‐Liss, Inc.    

年代:1990

数据来源: WILEY

摘要:

AbstractStereological methods were used to examine the consequences of prenatal exposure to ethanol on the structure of area 3, primary somatosensory cortex, of the mature hooded rat. Pregnant rats were fed a liquid diet containing 6.7% (v/v) ethanol (Et), pairfed an isocaloric liquid control diet (Ct), or fed a diet of chow and water (Ch). Cresyl violet‐stained sections of 3‐month‐old pups were examined. The corrected mean size of the cell bodies of neurons in layers other than layer V was significantly smaller in the Ettreated rats; conversely, the mean somatic size of glia in each layer was significantly larger in the Ettreated rats. The laminar cell packing density for neurons and glia, however, was similar in rats from both treatment groups. The overall volume of area 3 and the volume of individual layers were about 33% smaller in Et‐treated rats than in the pair‐fed controls. Thus, the estimated total number of neurons in Et‐treated rats (1.79*106) was significantly fewer than in Chtreated rats (2.77*106) and in Ct‐treated rats (2.66*106). The total number of glia also was about 30% fewer in Et‐treated rats than in the controls. Not all layers were affected equivalently. The space occupied by the neuropil was significantly greater in Et‐treated rats, but only in layers II/III, IV, and VI; hence, the cell body/neuropil ratio in these layers was less in Et‐treated rats than in the controls. Therefore, microcephaly caused by prenatal exposure to ethanol results not only from a miniaturization of the brain, but also from a permanent abnormal organization

ISSN:0092-7317    

DOI:10.1002/cne.902930108

出版商:Wiley‐Liss, Inc.    

年代:1990

数据来源: WILEY

摘要:

AbstractA detailed analysis of the cortical projections of the medial septum‐diagonal band (MS/DB) complex was carried out by means of anterograde transport of Phaseolus vulgaris leucoagglutinin (PHA‐L). The tracer was injected iontophoretically into cell groups of the medial septum (MS) and the vertical and horizontal limbs of the diagonal band of Broca (VDB and HDB), and sections were processed immunohistochemically for the intra‐axonally transported PHA‐L. The labeled efferents showed remarkable differences in regional distribution in the cortical mantle dependent on the position of the injection site in the MS/DB complex, revealing a topographic organization of the MS/DB‐cortical projection. In brief, the lateral and intermediate aspects of the HDB, also referred to as the magnocellular preoptic area, predominantly project to the olfactory nuclei and the lateral entorhinal cortex. The medial part of the HDB and adjacent caudal (angular) part of the VDB are characterized by widespread, abundant projections to medial mesolimbic, occipital, and lateral entorhinal cortices, olfactory bulb, and dorsal aspects of the subicular and hippocampal areas. Projections from the rostromedial part of the VDB and from the MS are preponderantly aimed at the entire hippocampal and retrohippocampal regions and to a lesser degree at the medial mesolimbic cortex. Furthermore, the MS projections are subject to a clear mediolateral topographic arrangement, such that the lateral MS predominantly projects to the ventral/temporal aspects of the subicular complex and hippocampus and to the medial portion of the entorhinal cortex, whereas more medially located cells in the MS innervate more septal/dorsal parts of the hippocampal and subicular areas and more lateral parts of the entorhinal cortex. PHA‐L filled axons have been observed to course through a number of pathways, i. e., the fimbria‐fornix system, supracallosal stria, olfactory peduncle, and lateral piriform route (the latter two mainly by the HDB and caudal VDB). Generally, labeled projections were distributed throughout all cortical layers, although clear patterns of lamination were present in several target areas. The richly branching fibers were abundantly provided with both “boutons en passant” and terminal boutons. Both distribution and morphology of the labeled basal forebrain efferents in the prefrontal, cingulate, and occipital cortices closely resemble the distribution and morphology of the cholinergic innervation as revealed by immunohistochemical demonstration of choline acetyltransferase. In contrast, the labeled projections to the olfactory, hippocampal, subicular, and entorhinal areas showed a heterogeneous morphology. Here, the distribution of only the thin varicose projections resembled the distribution of c

ISSN:0092-7317    

DOI:10.1002/cne.902930109

出版商:Wiley‐Liss, Inc.    

年代:1990

数据来源: WILEY

摘要:

AbstractThese studies investigated the response of olfactory bulb juxtaglomerular dopamine neurons to the loss of mitral cells in 6–7–month‐old Purkinje cell degeneration (PCD) mice. Previous studies in normal mice, with tyrosine hydroxylase (TH) enzyme as a marker, demonstrated that following peripheral olfactory afferent denervation in TH activity and immunoreactivity. These intrinsic dopamine neurons also receive afferent input via dendrodendritic contacts with mitral cells. In contrast to the deficits produced by peripheral denervation, following mitral cell degeneration in homozygous recessive PCD mice, TH activity and immunoreactivity were unaltered as compared to normal heterozygous littermates. Moreover, TH activity in the substantia nigra also was unchanged, thus suggesting that the dopamine phenotype is resistant to the influences of thepcdgene. Despite the absence of a well‐defined effect of thepcdgene on neurons earing the TH phenotype, the expression of this mutation within the olfactory system is not limited to mitral cell degeneration. The current studies also demonstrate the absence of the anterior commissure, especially pars anterior, in homozygous recessive PCD mice at 6–7 months postnatal. Whether or not the loss of the anterior commissure is a primary effect or one that is secondary to mitral cell degeneration, this structural alteration provides evidence that thepcdgene exerts more widespread effects within the olfactory system than previously appreciated. The neuronal specificity of those effects remains apparent as indicated by the lack of change in TH e

ISSN:0092-7317    

DOI:10.1002/cne.902930110

出版商:Wiley‐Liss, Inc.    

年代:1990

数据来源: WILEY

摘要:

AbstractPeptides have been found in the retinas of all mammalian species studied to date, but little is known about their localization and function in the cat. Using two mouse monoclonal antibodies directed to somatostatin 14, we have observed two sparse groups of somatostatin‐immunoreactive neurons in the cat, both distributed preferentially in the inferior retina. The more numerous cell type is characterized by a small‐ to medium‐sized soma (mean diameter = 16.3 =9.0 μm; n = 186) with sparsely branching, far‐reaching varicose processes that ramify mainly in the inner plexiform layer. The majority of these cells are located in the ganglion cell layer, with the remainder in the proximal inner nuclear layer and the inner plexiform layer. They are in especially high density at the retinal margin. In morphology and soma size, these cells resemble wide‐field amacrine cells. The second cell type has a large, granular‐staining soma (mean diameter = 29.7 ± 14.8 μm; n = 145) with poorly stained primary processes and is found only in the ganglion cell layer. Cells of this type are most similar in their size and morphology to alpha ganglion cells.In contrast to the location of somatostatin‐immunoreactive somata, a dense meshwork of immunoreactive processes was observed at all eccentricities within the inner plexiform layer, adjacent to the inner nuclear layer and to the ganglion cell layer. Labeled processes arising from the inner plexiform layer were also occasionally detected in the outer plexiform layer and the nerve fiber layer. Additional processes of unknown origin were observed in the nerve fiber layer and the optic nerve head. The extensive distribution of immunoreactive processes suggests that somatcstatin‐immunoreactive somata located preferentially in the inferior half of the retina have a widespread influence

ISSN:0092-7317    

DOI:10.1002/cne.902930111

出版商:Wiley‐Liss, Inc.    

年代:1990

数据来源: WILEY