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Query: UNIPROT:P50583 (asymmetrical)
 12,197 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Neurons in the ventrolateral (VL) subdivision of rat trigeminal nucleus oralis (Vo) have most of their dendritic arbors confined within this region. This study examines the morphology and synaptic connections of a population of myelinated primary trigeminal axons that arborize within VL and are in a position to provide input directly to VL neurons. Primary axons were visualized for light and electron microscopic analysis by injecting 30% horseradish peroxidase (HRP) in 2% dimethylsulfoxide (DMSO) into the sensory root of the trigeminal nerve and allowing 24-36 hours for the anterograde transport of HRP into the terminal axonal arbors. This population is characterized by its cone-shaped terminal arbors, which generate many axonal endings (2-8 micron in diameter) along unmyelinated terminal strands. These arbors arise from collaterals emanating from thinly myelinated (2-5 micron in diameter) parent branches descending in the spinal V tract, which, on the basis of their size, are considered to be small myelinated (A sigma) primary trigeminal axons. HRP-labeled P endings belonging to this population of primary axons are scalloped, filled with spherical to ovoid (40-70 nm in diameter) synaptic vesicles, and lie centrally in glomeruli where they make asymmetrical axodendritic synapses on dendritic shafts and spine heads. It is at these synapses that this population of primary trigeminal axons is probably transferring its input directly to the dendritic arbors of VL neurons. The dendritic shafts and spine heads also receive symmetrical to intermediate axodendritic synapses from endings containing flattened (70 X 29 nm) synaptic vesicles. These terminals also establish axo-axonic synapses on the P ending. Other synaptic components found less often in the glomeruli include small terminals containing oval (14-23 nm) synaptic vesicles that establish symmetrical to intermediate synapses on the P ending, boutons containing pleomorphic (35-80 nm) synaptic vesicles that form symmetrical to intermediate synapses on the P ending as well as on dendritic shafts, and small peripheral endings containing round (20-40 nm) synaptic vesicles that establish asymmetrical synapses on dendritic shafts.
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PMID:Morphology and synaptic connections of myelinated primary axons in the ventrolateral region of rat trigeminal nucleus oralis. 395 93

The developmental sequence of nerve-epithelial cell contacts, leading up to the formation of the mature receptoneuronal synapse, has been studied in the basilar papilla of chick embryos with electron microscopy. The receptor epithelium before innervation, on embryonic days 3-4, consists of a homogeneous population of primitive cells; hair cells and supporting cells cannot be distinguished. During innervation of the epithelium (embryonic days 5-7), the invading peripheral fibers of cochlear ganglion cells penetrate the basal lamina and form nerve-epithelial attachments with the epithelial cell bases. Once within the epithelium some fibers turn and spread in the transverse dimension across the basilar papilla through channels formed between the basal epithelial processes. Subsequently, nerve-epithelial attachments are observed more superficially within the epithelium. Hair cells and supporting cells differentiate during early synaptogenesis (embryonic days 8-9). Receptoneural synapses, possibly derived from the nerve-epithelial attachments formed during the innervation stage, are first seen during this period. They are characterized by symmetrical or asymmetrical membrane densities, separated by a cleft containing a dense material. At many of these junctions synaptic bodies, as well as dense-cored and coated vesicles, gather in the hair cells. During mid-synaptogenesis (embryonic days 11-13) the hair cells proliferate synaptic bodies, many of which are not located at receptoneural junctions. The preterminal portions of the sensory endings form large swellings, containing flocculent material, endoplasmic reticulum and vesicles. Late in synaptogenesis (embryonic days 15-17) the swellings disappear, while synaptic endings are transformed to foot-shaped terminals. In the hair cells, synaptic bodies not associated with junctions disappear. Efferent synapses are first seen during this period. This sequence of ultrastructural changes, which the developing sensory nerve endings and their target cells undergo in parallel, can be correlated with observations of Golgi preparations from a companion study. These correlations suggest that the innervation of the cochlea involves the following developmental processes. Initially the peripheral fibers of the ganglion cells grow directly toward the otocyst in fascicles. Having reached the base of the primitive receptor epithelium, the axonal endings, including some with growth cones, encounter a barrier in the basal lamina. When they enter some of the fibers attach to the basal end-feet of the primitive epithelial cells.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:The growth of cochlear fibers and the formation of their synaptic endings in the avian inner ear: a study with the electron microscope. 397 82

After a lesion in the sensorimotor and adjacent cortex in normal adult rats, degenerating terminals showing the dense reaction form asymmetrical contacts with spines, dendrites of various sizes, soma and other axonal terminals. Filamentous degeneration is also present. After neonatal deep cerebellar nuclear lesions involving the dentate nucleus and the adjacent interposed nucleus, the cerebrocorticorubral fibers form similar synaptic contacts with somatic, dendritic and axonal profiles. The incidence of axo-dendritic contacts on spine is reduced, while that of axo-dendritic contacts on small, medium-sized and large dendrites and axo-somatic contacts is increased.
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PMID:An electron microscopic study of the corticorubral fibers after neonatal deep cerebellar nuclear lesions in albino rats. 400 49

In order to investigate axolemmal development in a glial cell deficient environment, normal and irradiated dorsal funiculus in rat lumbosacral spinal cord was examined by freeze-fracture electron microscopy. At 3 days of age, normal fibres are all unmyelinated and of small (less than 0.5 micron) diameter. The unmyelinated axons have a moderate density (approximately 850 microns-2) of intramembranous particles (IMPs) on P-fracture faces and a low IMP density (approximately 300 microns-2) on E-faces. IMPs are homogeneously distributed along both fracture faces. By 19 days of age, the normal dorsal funiculus is well populated with myelinated axons and glial cells, as well as a sizable population of unmyelinated fibres. Nearly all of the myelinated fibres have a large (greater than 1.0 micron) diameter; whereas, most unmyelinated axons are of small (less than 0.5 micron) calibre. The axolemma of unmyelinated axons is relatively undifferentiated, with an asymmetrical distribution of IMPs (P-face: approximately 1100 microns-2; E-face: approximately 450 microns-2). Myelinated fibres show nodal and paranodal regions with P-face and E-face ultrastructure similar to previous descriptions. Internodal axolemma appears relatively homogeneous, with P-faces being highly particulate (approximately 2100 microns-2) and a low IMP density (approximately 200 microns-2) on E-faces. Following irradiation of the lumbosacral spinal cord at 3 days of age, there is a severe reduction in the number of glial cells and myelinated fibres in this region when the tissue is examined at 19 days of age. Despite the deficiency of glial cells in this tissue, axonal and axolemmal development continue. Numerous large (greater than 1.0 micron) diameter axons are present in this irradiated tissue. Large diameter axons show a high (approximately 2000 microns-2) density of IMPs on P-faces; E-face IMP density remains at approximately 440 micron-2. Small calibre axons also have an asymmetrical distribution of particles (P-face: approximately 1100 microns-2; E-face: 280 microns-2). The axolemmal E-faces of some glial cell deprived fibres exhibit regions with greater than normal (approximately 750 microns-2) density of IMPs. These results demonstrate that some aspects of axonal and axolemmal development continue in a glial cell deficient environment, and it is suggested that axolemmal ultrastructure is, at least in part, independent of glial cell association.
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PMID:Membrane ultrastructure of developing axons in glial cell deficient rat spinal cord. 400 13

The organization of projections from the principal sensory trigeminal nucleus (PSN) to the hypoglossal nucleus (XII) in the rat was investigated at the light and electron microscopic level with retrograde and anterograde axonal tracer techniques. Microiontophoretic injection of horseradish peroxidase (HRP) into XII resulted in retrograde labeling of neurons confined to the dorsal one-third of the PSN. Labeled neurons were found bilaterally, although a clear preponderance for ipsilateral distribution was evident. Most labeled neurons were found in the medial one-third and caudal two-thirds of the PSN. Labeled neurons were large (30-50 micron), round-to-pear shaped multipolar cells with dendrites oriented primarily in the mediolateral direction. At the electron microscopic level, HRP reaction product was found throughout the cytoplasm of soma and processes of PSN projection neurons. The ultrastructural characteristics of these cells included a round, centrally placed nucleus and invaginated nuclear envelope, sparse Nissl bodies, numerous free ribosomes, mitochondria, lysosomes and Golgi complexes. Three to four main stem dendrites gradually tapered from the cell body and numerous synaptic terminals impinged upon soma and dendrites of labeled PSN neurons. Microiontophoretic injection of tritiated amino acids or HRP into the dorsal one-third of the PSN resulted in moderately dense terminal labeling in XII bilaterally, although mainly ipsilaterally. Terminal labeling was found diffusely throughout all regions of XII. Fibers descended the brainstem in the dorsolateral reticular formation and entered XII ventrolaterally. At the electron microscopic level, boutons containing HRP reaction product were found to synapse on dendritic processes in XII. Labeled boutons were characterized by clear, spherical vesicles and an asymmetrical postsynaptic density. The significance of these results are discussed in relation to oro-lingual motor behavior.
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PMID:Organization of projections from the principal sensory trigeminal nucleus to the hypoglossal nucleus in the rat: an experimental light and electron microscopic study with axonal tracer techniques. 401 94

The ultrastructural features and synaptic relationships of cholecystokinin (CCK)-immunoreactive cells of rat and cat hippocampus were studied using the unlabeled antibody immunoperoxidase technique and correlated light and electron microscopy. CCK-positive perikarya of variable shape and size were distributed in all layers and were particularly concentrated in stratum pyramidale and radiatum: the CCK-immunoreactive neurons were nonpyramidal in shape and the three most common types had the morphological features of tufted, bipolar, and multipolar cells. Electron microscopic examination revealed that all the CCK-positive boutons established symmetrical (Gray's type II) synaptic contacts with perikarya and dendrites of pyramidal and nonpyramidal neurons. The origin of some of the boutons was established by tracing fine collaterals that arose from the main axon of two CCK-immunostained cells and terminated in the stratum pyramidale; these collaterals were then examined in the electron microscope. The axon of one such neuron exhibited a course parallel to the pyramidal layer and formed pericellular nets of synaptic boutons upon the perikarya of pyramidal neurons. This pattern of axonal arborization is very similar to that of some of the basket cells, previously suggested to be the anatomical correlate for pyramidal cell inhibition. Typical dendrites of pyramidal cells also received symmetrical synaptic contacts from CCK-immunoreactive boutons, and some of these boutons could be shown to originate from a local neuron in stratum radiatum. Many CCK-immunoreactive cells received CCK-labeled boutons upon their soma and dendritic shafts. Synaptic relationship, established by multiple "en passant" boutons, was observed between CCK-positive interneurons of the stratum lacunosum-moleculare and radiatum. The soma and dendrites of the CCK-immunostained neurons also received symmetrical and asymmetrical synapses from nonimmunoreactive boutons. These results indicate that the CCK-immunoreactive neurons participate in complex local synaptic interactions in the hippocampus.
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PMID:Cholecystokinin-immunoreactive cells form symmetrical synaptic contacts with pyramidal and nonpyramidal neurons in the hippocampus. 404 96

The ultrastructure of the optic and trigeminal nerves of the rat, cryofixed by use of a liquid nitrogen-propane jet, was examined, paying special attention to the myelin sheath and the cytoskeleton of the axoplasm. The cytoskeleton of the axoplasm is formed by a meshwork of neurofilaments and microtubules connected both to each other and also to the cell organelles and axolemma. These cross-linkers are fixed to the longitudinal neurofilaments in a helical arrangement, which could be a morphological substrate for the diverse axonal transport phenomena. The myelin sheath is formed by concentrically apposed membrane pairs, which are not fused together. The corresponding major and intraperiod lines seen using classical electron microscopy are in fact fissures that are obscured by the pattern of the selective deposition of osmium at certain sites and cannot be interpreted as specific structures. The cryofixed myelin membranes have the appearance of predominantly globular subunits arranged in an asymmetrical bilayer. The globular particles are of diverse diameter and occupy varying positions within the membrane. The tight junctions or zonulae occludentes of the myelin are formed by arrays of isolated particles, and consequently the fibril formation seems to be a result of the chemical fixation.
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PMID:Ultrastructural aspects of cryofixed nerves. 405 70

The nucleus of the tractus solitarius is a site for termination of primary afferents originating from a variety of visceral receptors. The localization of bouton terminals of slowly adapting lung stretch (SAR) afferent fibers originating from the tracheobronchial tree have been described in the companion paper (Kalia and Richter, '85). The most conspicuous finding regarding the location of SAR terminals is that they are concentrated within specific subnuclear groups of the nucleus of the tractus solitarius (nTS) and are distributed widely in the rostrocaudal plane of the medulla oblongata. These light microscopic features have provided us with valuable information with regard to the organization of visceral afferents in the central nervous system. The synaptic profiles formed by the 476 bouton terminals of these HRP-labeled afferents have been described in this paper in serial thin sections. All of the bouton terminals examined under the electron microscope were found to contain round synaptic vesicles. Synaptic boutons (1.0-3.0 microns in diameter) were usually of the en passant variety and made contact with different structures depending upon the subnucleus which was examined. In the ventral (v) and the ventrolateral (vl) subnuclei of the nTS, asymmetrical (type I) synaptic contacts containing round, clear synaptic vesicles of 35-50 microns in diameter were found and these contacts were made with (1) the soma of cell bodies located in that subnucleus; (2) spiny dendrites in that nucleus; (3) vesicle-containing axon terminals that were presynaptic to the HRP-labeled bouton terminal; and (4) vesicle-containing dendrites in which the HRP profile was presynaptically located. The terminal axon remained myelinated till the last 1 micron before the bouton terminal was formed. There was no distinct, unmyelinated portion of the terminal axon. The synaptic bouton received axon-axonal synapses from unlabeled bouton terminals containing round, clear vesicles. This is the first report of the localization of these afferent fibers as well as of the regional variations in the ultrastructure of boutons of physiologically identified terminals. It appears likely that the lung stretch afferent fibers, by having axon-axonal as well as axon-somatic contact in the ventral, ventrolateral, and intermediate subnuclei of the nTS, can interact in a variety of different ways in this region. The significance of these features in relation to the precise influence of respiratory afferents on central respiratory mechanisms needs to be evaluated further.
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PMID:Morphology of physiologically identified slowly adapting lung stretch receptor afferents stained with intra-axonal horseradish peroxidase in the nucleus of the tractus solitarius of the cat. II. An ultrastructural analysis. 407 45

"Gap" junctions, the morphological correlate for low-resistance junctions, are demonstrated between some mossy fiber terminals and granule cell dendrites in some lower vertebrate cerebella (gymnotid and frog). Most of the gap junctions (GJs) seen in the gymnotid-fish cerebellum exhibit an asymmetrical configuration, the electron-opaque cytoplasmic material underlying the junction being more extensive in the dendritic than in the axonal side. In the frog cerebellum, the GJs have a symmetrical distribution of such electron-opaque material. In both species the GJs are encountered at the same synaptic interface as the conventional synaptic zone (CSZ), constituting "mixed synapses" in a morphological sense. The axonal surface covered by CSZs is larger than that covered by GJs. In mammalian cerebellum, GJs are observed only in the molecular layer, between perikarya, dendrites, or perikarya and dendrites of the inhibitory interneurons. These GJs are intermixed with attachment plates and intermediary junctions interpreted as simply adhesive. In the mammalian cerebellum, a new type of junction which resembles the septate junctions (SJs) of invertebrate epithelia is observed between axonal branches forming the tip of the brush of basket fibers around the initial segment of the Purkinje cell axon. It is suggested that such junctions may be modified forms of septate junctions. The physiological implications of the possible existence of high-resistance cross-bridges between basket cell terminals, which may compartmentalize the extracellular space and thus regulate extracellular current flow, must be considered.
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PMID:Specialized membrane junctions between neurons in the vertebrate cerebellar cortex. 453 7

Serotonergic axonal endings in layers I and II of the dorsal horn of the medulla were identified by autoradiography. In adult cats, pretreated with a monoamine oxidase inhibitor, tritiated serotonin ([3H]5-HT) was topically applied onto the surface of the caudal medulla. Light autoradiographs from 1 micrometer sections demonstrated silver grains in both layers I and II. In EM autoradiographs, two categories of axonal endings were labeled by [3H]5-HT uptake: dome-shaped endings which form a single synapse and scalloped endings which form multiple synapses. Each category was further divided into several types based on morphological criteria. The [3H]5-HT-labeled endings synapse primarily on small caliber dendritic shafts and spines, with the dome-shaped endings forming both symmetrical and asymmetrical synapses and the scalloped endings forming only asymmetrical synapses. Dome-shaped endings were most common and two types were found in layers I and II while a third type was found only in layer II. Layer I contained a single type of scalloped ending while layer II contained three types of scalloped endings. In a series of experiments designed to provide another approach to identifying serotonergic endings, 5,6-dihydroxytryptamine, a serotonin neurotoxin, was either topically applied onto the caudal medulla or injected into the fourth ventricle. Following treatment with the neurotoxin, blackened degenerating dome-shaped and scalloped endings similar to those labeled in the [3H]5-HT uptake experiments were found in layers I and II. The presence of serotonergic endings in layer I suggests that some of these endings synapse on the dendrites of layer I projection neurons where they may inhibit the output of the projection neuron directly. Serotonergic endings in layer II may modulate the activity of layer II interneurons by synapsing directly on these interneurons. The interneurons in layer II may function by mediating the transfer of inputs from primary endings in these layers to layer I projection neurons.
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PMID:Ultrastructural characterization of axonal endings in the substantia gelatinosa which take up [3H]serotonin. 615 52


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