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

The commissural connections of the area dentata were investigated with the Fink-Heimer silver impregnation method and the commissural terminals in the hilus of the fascia dentata further studied by electron microscopy of anterograde degeneration. The commissural endings in the molecular layer were found to terminate as previously reported by others. In addition it was shown that the hilus also receives a significant commissural input. The commissural afferents to both the molecular layer and the hilus terminate along the full rostro-caudal extent of the area dentata, but with varying densities. The degeneration in the molecular layer is maximal dorso-rostrally and declines in the caudo-ventral direction, whereas the degeneration in the hilus varies inversely. The commissural terminals in the hilus make asymmetrical contacts with dendritic spines and to a lesser extent with dendritic stems. Dark, but otherwise apparently normal terminals with the features of mossy fiber boutons, were encountered in low numbers in both decommissurated and control animals. The commissural projection to the dentate area originates in the opposite hilus and possibly the adjacent part of CA3 (CA3c). Fibers from middle dorso-basal levels of the hilus to the opposite molecular layer are distributed more rostrally than ventrally relative to the level of the source of the fibers.
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PMID:Commissural connections of the dentate area in the rat. 90 20

A brief application of high K+ or excitatory amino acids (i.e. kainic acid) generated repetitive synchronized burst that persisted for the duration of the application, in the CA3 field. Once excitability has been enhanced, further stimulation of various inputs evoked burst instead the typical excitatory postsynaptic potential--inhibitory postsynaptic potential sequence evoked in control conditions. These long-lasting changes in synaptic efficacy involved the activation of glutamate receptors of N-methyl-D-aspartate (NMDA) subtype. A brief period of hyperactivity (i.e. kindling of limbic pathways or administration of kainic acid) also resulted in a more delayed synaptic remodeling, notably of hippocampal mossy fibers (i.e. the axons of granule cells that mostly contact the apical dendrites of CA3 pyramidal neurons). Thus mossy fibers sprouted and made multiple ectopic asymmetrical synapses with spines of both granule cells dendrites and basilar dendrites of CA3 pyramidal cells. Finally, sprouting of mossy fibers was associated with a significant rise in the density of kainic acid binding sites (fmol/mg tissue) in the aberrantly innervated zones: the inner third of molecular layer and the stratum oriens of CA3. Saturation studies revealed that this rise did not significantly affect the affinity (Kd values) but the Bmax. In conclusion, brief seizure episodes produced in the hippocampus remarkably long-lasting changes in synaptic efficacy; synaptic density and the mean density of excitatory amino acid receptors of non-NMDA subtype. The role that such plastic changes may play in the permanence of the epilepsy is finally discussed.
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PMID:Long-term potentiation and sprouting of mossy fibers produced by brief episodes of hyperactivity. 133 65

Calretinin-containing cells were visualized with immunocytochemistry in the rat dorsal hippocampal formation. Calretinin immunoreactivity was present exclusively in non-pyramidal cells in all layers of the dentate gyrus and the CA1-3 areas. Calretinin-positive neurons and processes were most abundant in the hilus of the dentate gyrus and in the stratum lucidum of the CA3 region. Several calretinin-immunoreactive cells were located within the hippocampal fissure. A distinct band of calretinin-immunoreactive fibres occupied the superficial part of the granule cell layer and the lowest part of the molecular layer. Closer examination of the calretinin-positive cells revealed that they formed two distinct cell groups. One group of cells, found exclusively in the stratum lucidum of the CA3 area and in the hilus of the dentate gyrus, was covered with numerous spines. Their somata and dendrites were restricted to stratum lucidum and to the hilus. Cells of the other group had smooth, often varicose, radially running dendrites, and were present in all areas and layers of the hippocampal formation. Two to three thick primary dendrites arose from the irregularly shaped cell body of spiny cells and emitted fine secondary branches only distally (70-100 microns) from the soma, where they formed a profuse network. The extensive dendritic tree of the cells spread horizontally within stratum lucidum and span a distance of 400-600 microns both in the septotemporal and in the transverse directions. The layer-specific location of these cells and their processes suggested that the majority of their input may derive from mossy fibres. This presumption has been confirmed by electron microscopic examination. A large number of asymmetrical synapses were found to cover the soma, the dendritic shafts and the spines (four to six synapses/spine) of the cells. A large proportion of the synapses were formed by boutons, which showed the distinctive features of mossy fibre terminals. Three to six primary dendrites arose from the multipolar, bipolar or pyramidal-shaped somata of spine-free cells, which were smaller than the somata of spiny cells. The smooth and frequently varicose dendrites branched proximally and ran primarily radially. Dendrites ascended or descended through several layers and received both asymmetrical and symmetrical synapses. In the CA1 subfield, the vertically running dendrites frequently contacted other calretinin-immunoreactive spine-free dendrites or cell bodies. Two or three calretinin-immunoreactive dendrites were often seen to be attached for over 100 or, occasionally, 200 microns and several puncta adherentia were observed between them using the electron microscope.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Calretinin is present in non-pyramidal cells of the rat hippocampus--I. A new type of neuron specifically associated with the mossy fibre system. 158 17

Serotonin (5-HT) immunocytochemistry was used at the electron microscopic level to examine 5-HT neurons reinnervating and hyperinnervating the hippocampus of adult rat, three to four months after a total 5-HT denervation and subsequent graft of embryonic raphe cells. The study focused on immunostained nerve cell bodies, dendrites and axon terminals (varicosities) in the core of grafts, and on a large single section sampling of axon terminals from a CA3 and a dentate gyrus sector of the outgrowth, which were systematically compared to the endogenous 5-HT innervation of the same regions described in a companion paper. The shape, size and synaptic investment of the grafted 5-HT somata and their dendrites resembled those of in situ 5-HT neurons. Clusters of small, clear vesicles were sometimes seen along these 5-HT dendrites. 5-HT axonal varicosities were fairly numerous in the core. A few were directly apposed to, or made asymmetrical synaptic contact with the immunostained dendrites and perikarya, but the vast majority showed no indication of junctional specialization (synaptic incidence of 19%, as stereologically extrapolated for whole varicosities). Occasional myelinated 5-HT axons were also present in the core of grafts. In the two outgrowth sectors, the graft-borne 5-HT varicosities were similar in size, content, frequency of synaptic contact and identity of junctional and appositional elements, irrespective of their laminar location. Moreover, none of these parameters were significantly different from those of the endogenous innervation. Notably, in spite of their excessive number, the synaptic incidence of the outgrowth 5-HT varicosities remained inferior to 20%. The similarity between the respective microenvironments of the supernumerary, graft-borne 5-HT terminals and of their normal counterparts could only be explained by a random intratissular distribution of these varicosities in both the normal and the grafted hippocampus. Thus, in spite of their transplantation and growth into an abnormal milieu, and the fact that they hyperinnervated the host tissue, the grafted embryonic 5-HT neurons appeared committed to express a particular set of intrinsic and relational morphological features corresponding to their normal adult characteristics.
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PMID:Ultrastructural features of serotonin neurons grafted to adult rat hippocampus: an immunocytochemical analysis of their cell bodies and axon terminals. 195 16

Non-pyramidal cells in the rat hippocampus were examined with a combined Golgi-electron microscopic method. The somata of non-pyramidal cells were ovoid, about 15 X 30 micron, and several smooth and/or varicose dendrites extended from them. With electron microscopy, Golgi-impregnated gold-toned non-pyramidal cells showed distinctive fine structural features. The somata displayed large nuclei and an extensive perikaryal cytoplasm. The nuclei showed extensive cytoplasmic invaginations, little heterochromatin, conspicuous nucleoli, and intranuclear rods composed of filamentous bundles. The perikaryal cytoplasm was rich in cell organelles such as well-developed cisternae of rough endoplasmic reticulum and Golgi apparatus, and numerous clusters of free ribosomes and mitochondria. Many synaptic boutons, most of which formed asymmetrical synapses, impinged upon the somata and dendrites. Gap junctions were seen on varicose dendrites of Golgi-impregnated non-pyramidal cells. These gap junctions were patch-like, about 0.1-0.6 micron in diameter, and situated in the stratum radiatum or stratum oriens of the CA1 and CA3 regions 70-230 micron from the soma. They displayed a characteristic cytoplasmic semidense material undercoating the junctional membranes. The gap junctions were usually formed between impregnated and unimpregnated varicose dendrites. Thirteen of a total of 22 gap junctions involving the impregnated dendrites were situated singly, whereas the remaining nine were on four impregnated dendrites in clusters of two or three side by side. In the latter cases, two pairs of junctions were formed between pairs of dendrites running parallel to each other, and each of the other two pairs was formed among three dendrites, appearing to make a dendritic network bridged by gap junctions. One gap junction was seen between two impregnated dendrites originating from two identified Golgi-impregnated non-pyramidal cells. These observations revealed unequivocally that non-pyramidal cells in the hippocampus form gap junctions with one another on their dendrites.
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PMID:Gap junctions between non-pyramidal cell dendrites in the rat hippocampus (CA1 and CA3 regions): a combined Golgi-electron microscopy study. 396 32

The axon initial segments (ISs) of pyramidal cells in the rat hippocampus (CA3 region) were studied by means of light microscopy of Golgi-impregnated material and electron microscopy of random and serial thin sections. The ISs display three distinguishing characteristics; fascicles of microtubules, membrane undercoating and clusters of ribosomes. The ISs contain cisternal organelles which are often associated with synapses and are in continuity with smooth and rough endoplasmic reticulum. Small spines are recognized on the ISs both in the light and electron microscope. There are 10-25 on each IS and they are usually concentrated on the proximal 30 micrometers of the IS. Axonic spines contain spine apparatuses, clusters of ribosomes, multivesicular bodies and other organelles. Several collaterals are also recognized to originate from the axon proximal to the start of a myelin sheath. The IS receives many synapses both on its shaft and spines. Almost all of them are of the symmetrical type with flattened vesicles but a few asymmetrical synapses with spherical vesicles occur. Pyramidal cell ISs are very rarely presynaptic at asymmetrical synapses with spherical vesicles. Based on serial sectioning studies, the number of synapses on one IS is estimated at 100-200. These abundant synaptic contacts on the IS suggest that it is an important synaptic site. The possibility that there are two different inhibitory systems controlling the output of the pyramidal cell is discussed.
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PMID:The axon initial segment as a synaptic site: ultrastructure and synaptology of the initial segment of the pyramidal cell in the rat hippocampus (CA3 region). 720 37

The foetal hippocampal tissue (transplant) at 17th day of embryonic age was implanted into the ventral hippocampus of adult rats (host). The catecholaminergic fibre projections in the hippocampal transplants 90 days after operation were studied by immunohistochemical technique. It was observed that in the host hippocampus there was a large population of TH- immunoreactive slender fibres of only 0.5-1 microns in diameter. These fibres were distributed more densely in the hippocampal hilus and CA3 transparent layers than in molecular layers, but sparsely in pyramidal or granular layers. In the molecular and cellular layers of transplanted hippocampus some thicker (> 1 micron) TH-positive fibers were ended in a relatively dense branching. The immunoelectron-microscopic observations showed that many TH-positive boutons made synaptic contacts with immunonegative dendrites and dendritic spines in the hippocampal transplants, the majority of which were asymmetrical synapses with a 30 nm synaptic cleft and conspicuously thickened postsynaptic membranes. It is concluded that catecholaminergic fibres extend from the host brain into the hippocampal transplant to establish synapses with the target neurons.
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PMID:[Synaptic connections between the neurons and catecholaminegic fibres in the hippocampal transplant of rat]. 757 Jan 15

The mossy fiber synaptogenesis has been studied in hippocampal slice cultures. In vivo mossy fiber terminals contact the thorny excrescences of CA3 pyramidal neurons over a restricted portion, i.e. the proximal part of the apical dendrite. In organotypic cultures mossy fibers expand their terminal field and invade the infrapyramidal area of the CA3 region and the supragranular layer of the dentate gyrus. Newly formed mossy fiber synapses in CA3 region were examined, through electron microscopy, in cultures taken at various time intervals. The main events of the formation of newly formed mossy fiber synapses can be summarized as follows. During the first week following explantation mossy fiber axons contact the dendritic shaft of the pyramidal dendrite and establish both symmetrical and asymmetrical contacts. Subsequent modifications occur in the postsynaptic portion facing the mossy fiber bouton: (i) a massive accumulation of polyribosomes and coated vesicles in the subsynaptic cytoplasm; (ii) undulations of the plasma membrane; (iii) disappearance of neurotubules at postsynaptic sites and appearance of a fine network of filamentous material. Later on in culture, complex giant spines invaginate within the synaptic bouton. In conclusion this study shows that CA3 pyramidal neurons following deafferentation retain the capacity to form thorny excrescences, when contacted by mossy fibers. Moreover these results suggest a crucial role for mossy fibers to induce the formation of thorny excrescences in an heterotopic localization, i.e. over the basilar dendrites of CA3 pyramidal neurons.
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PMID:Development of mossy fiber synapses in hippocampal slice culture. 795 49

The complete axon arborization of a single CA3 pyramidal cell has been reconstructed from 32 (60 microns thick) sections from the rat hippocampus following in vivo intracellular injection of neurobiotin. The same sections were double-immunostained for parvalbumin--a calcium-binding protein selectively present in two types of GABAergic interneurons, the basket and chandelier cells--in order to map boutons of the pyramidal cell in contact with dendrites and somata of these specific subsets of interneurons visualized in a Golgi-like manner. The axon of the pyramidal cell formed 15,295 boutons, 63.8% of which were in stratum oriens, 15.4% in stratum pyramidale and 20.8% in stratum radiatum. Only 2.1% of the axon terminals contacted parvalbumin-positive neurons. Most of these were single contacts (84.7%), but double or triple contacts (15.3%) were also found. The majority of the boutons terminated on dendrites (84.1%) of parvalbumin-positive cells, less frequently on cell bodies (15.9%). In order to estimate the proportion of contacts representing synapses, 16 light microscopically identified contacts between boutons of the filled pyramidal cell axon and the parvalbumin-positive targets were examined by correlated electron microscopy. Thirteen of them were found to be asymmetrical synapses, and in the remaining three cases synapses between the labelled profiles could not be confirmed. We conclude that the physiologically effective excitatory connections between single pyramidal cells and postsynaptic inhibitory neurons are mediated by a small number of contacts, mostly by a single synapse. This results in a high degree of convergence and divergence in hippocampal networks.
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PMID:Complete axon arborization of a single CA3 pyramidal cell in the rat hippocampus, and its relationship with postsynaptic parvalbumin-containing interneurons. 812 22

The cellular and subcellular localization of the GluRA, GluRB/C and GluRD subunits of the alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) type glutamate receptor was determined in the rat hippocampus using polyclonal antipeptide antibodies in immunoperoxidase and immunogold procedures. For the localization of the GluRD subunit a new polyclonal antiserum was developed using the C-terminal sequence of the protein (residues 869-881), conjugated to carrier protein and absorbed to colloidal gold for immunization. The purified antibodies immunoprecipitated about 25% of 3[H]AMPA binding activity from the hippocampus, cerebellum or whole brain, but very little from neocortex. These antibodies did not precipitate a significant amount of 3[H]kainate binding activity. The antibodies also recognize the GluRD subunit, but not the other AMPA receptor subunits, when expressed in transfected COS-7 cells and only when permeabilized with detergent, indicating an intracellular epitope. All subunits were enriched in the neuropil of the dendritic layers of the hippocampus and in the molecular layer of the dentate gyrus. The cellular distribution of the GluRD subunit was studied more extensively. The strata radiatum, oriens and the dentate molecular layer were more strongly immunoreactive than the stratum lacunosum moleculare, the stratum lucidum and the hilus. However, in the stratum lucidum of the CA3 area and in the hilus the weakly reacting dendrites were surrounded by immunopositive rosettes, shown in subsequent electron microscopic studies to correspond to complex dendritic spines. In the stratum radiatum, the weakly reacting apical dendrites contrasted with the surrounding intensely stained neuropil. The cell bodies of pyramidal and granule cells were moderately reactive. Some non-principal cells and their dendrites in the pyramidal cell layer and in the alveus also reacted very strongly for the GluRD subunit. At the subcellular level, silver intensified immunogold particles for the GluRA, GluRB/C and GluRD subunits were present at type 1 synaptic membrane specializations on dendritic spines of pyramidal cells throughout all layers of the CA1 and CA3 areas. The most densely labelled synapses tended to be on the largest spines and many smaller spines remained unlabelled. Immunoparticle density at type 1 synapses on dendritic shafts of some non-principal cells was consistently higher than at labelled synapses of dendritic spines of pyramidal cells. Synapses established between dendritic spines and mossy fibre terminals, were immunoreactive for all studied subunits in stratum lucidum of the CA3 area. The postembedding immunogold method revealed that the AMPA type receptors are concentrated within the main body of the anatomically defined type 1 (asymmetrical) synaptic junction. Often only a part of the membrane specialization showed clustered immunoparticles. There was a sharp decrease in immunoreactive receptor density at the edge of the synaptic specialization. Immunolabelling was consistently demonstrated at extrasynaptic sites on dendrites, dendritic spines and somata. The results demonstrate that the GluRA, B/C and D subunits of the AMPA type glutamate receptor are present in many of the glutamatergic synapses formed by the entorhinal, CA3 pyramidal and mossy fibre terminals. Some interneurons have a higher density of AMPA type receptors in their asymmetrical afferent synapses than pyramidal cells. This may contribute to a lower activation threshold of interneurons as compared to principal cells by the same afferents in the hippocampal formation.
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PMID:High-resolution immunogold localization of AMPA type glutamate receptor subunits at synaptic and non-synaptic sites in rat hippocampus. 884 93


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