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Active Zones (active + zone)
Kinds of Active Zones Selected AbstractsHigh-frequency stimuli preferentially release large dense-core vesicles located in the proximity of nonspecialized zones of the presynaptic membrane in sympathetic gangliaDEVELOPMENTAL NEUROBIOLOGY, Issue 4 2008F. Cifuentes Abstract We characterized the effect of a brief high-frequency stimulus on the number, distribution, and optical density of large dense-core vesicles (LDCVs) in the nerve terminals of the rat superior cervical ganglia. From 4.21 ± 0.37 LDCVs/bouton detected in control nerve terminals, a stimulus of 40 Hz for 1 min released 41% of LDCVs, decreasing their number to 2.48 ± 0.14 LDCVs/bouton (p = 0.0009). In control ganglia, most dense vesicles were located close to the plasma membrane (at ,100 nm); in contrast, in stimulated ganglia they were broadly distributed with respect to the active zone. The mean distance of LDCVs to membrane and active zones was 95 ± 8 nm and 473 ± 15 nm, respectively. The analysis of the core density showed that both groups had a similar asymmetric distribution with the same average. Stimulation preferentially released those vesicles located ,100 nm from the plasma membrane that had no apparent relationship with the active zone. After the stimulus, the average distances of LDCVs to the plasma membrane and active zone did not change, suggesting that the stimulus also caused the relocation of inner LDCVs. Interestingly, optical density analysis showed that the released vesicles had low range densities, and suggested that LDCVs release their entire content. We conclude that LDCV exocytosis mainly involves those vesicles located ,100 nm from the plasma membrane and occurs in regions of synaptic boutons presumed to be nonspecialized. These results agree with the characteristics of the classical model that proposes full content release. © 2008 Wiley Periodicals, Inc. Develop Neurobiol, 2008. [source] Contribution of Chloroflexus respiration to oxygen cycling in a hypersaline microbial mat from Lake Chiprana, SpainENVIRONMENTAL MICROBIOLOGY, Issue 8 2007Lubos Polerecky Summary In dense stratified systems such as microbial mats, photosynthesis and respiration are coupled due to a tight spatial overlap between oxygen-producing and -consuming microorganisms. We combined microsensors and a membrane inlet mass spectrometer with two independent light sources emitting in the visible (VIS) and near infrared (NIR) regions to study this coupling in more detail. Using this novel approach, we separately quantified the activity of the major players in the oxygen cycle in a hypersaline microbial mat: gross photosynthesis of cyanobacteria, NIR light-dependent respiration of Chloroflexus -like bacteria (CLB) and respiration of aerobic heterotrophs. Illumination by VIS light induced oxygen production in the top ,1 mm of the mat. In this zone CLB were found responsible for all respiration, while the contribution of the aerobic heterotrophs was negligible. Additional illumination of the mat with saturating NIR light completely switched off CLB respiration, resulting in zero respiration in the photosynthetically active zone. We demonstrate that microsensor-based quantification of gross and net photosyntheses in dense stratified systems should carefully consider the NIR light-dependent behaviour of CLB and other anoxygenic phototrophic groups. [source] High level of mGluR7 in the presynaptic active zones of select populations of GABAergic terminals innervating interneurons in the rat hippocampusEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 12 2003Peter Somogyi Abstract The release of neurotransmitters is modulated by presynaptic metabotropic glutamate receptors (mGluRs), which show a highly selective expression and subcellular location in glutamatergic terminals in the hippocampus. Using immunocytochemistry, we investigated whether one of the receptors, mGluR7, whose level of expression is governed by the postsynaptic target, was present in GABAergic terminals and whether such terminals targeted particular cells. A total of 165 interneuron dendritic profiles receiving 466 synapses (82% mGluR7a-positive) were analysed. The presynaptic active zones of most GAD-(77%) or GABA-positive (94%) synaptic boutons on interneurons innervated by mGluR7a-enriched glutamatergic terminals (mGluR7a-decorated) were immunopositive for mGluR7a. GABAergic terminals on pyramidal cells and most other interneurons in str. oriens were mGluR7a-immunonegative. The mGluR7a-decorated cells were mostly somatostatin- and mGluR1,-immunopositive neurons in str. oriens and the alveus. Their GABAergic input mainly originated from VIP-positive terminals, 90% of which expressed high levels of mGluR7a in the presynaptic active zone. Parvalbumin-positive synaptic terminals were rare on mGluR7a-decorated cells, but on these neurons 73% of them were mGluR7a-immunopositive. Some type II synapses innervating interneurons were immunopositive for mGluR7b, as were some type I synapses. Because not all target cells of VIP-positive neurons are known it has not been possible to determine whether mGluR7 is expressed in a target-cell-specific manner in the terminals of single GABAergic cells. The activation of mGluR7 may decrease GABA release to mGluR7-decorated cells at times of high pyramidal cell activity, which elevates extracellular glutamate levels. Alternatively, the presynaptic receptor may be activated by as yet unidentified endogenous ligands released by the GABAergic terminals or the postsynaptic dendrites. [source] The life history of Salicaceae living in the active zone of floodplainsFRESHWATER BIOLOGY, Issue 4 2002S. KARRENBERG 1.,Exposed riverine sediments are difficult substrata for seedling establishment because of extremes in the microclimate, poor soil conditions and frequent habitat turnover. Various species of willows and poplars (Salicaceae) appear to be particularly successful in colonising such sediments and are often dominant in floodplain habitats throughout the northern temperate zone. 2.,In many Salicaceae regeneration seems to be adapted to regular disturbance by flooding. Efficient seed dispersal is achieved by the production of abundant seed in spring and early summer, which are dispersed by air and water. Seeds are short-lived and germinate immediately on moist surfaces. Seedling establishment is only possible if these surfaces stay moist and undisturbed for a sufficient period of time. 3.,Larger plants of Salicaceae have exceptional mechanical properties, such as high bending stability, which enable them to withstand moderate floods. If uprooted, washed away or fragmented by more powerful floods these plants re-sprout vigorously. 4.,While these life characteristics can be interpreted as adaptations to the floodplain environment, they may also cause a high genetic variability in populations of Salicaceae and predispose Salicaceae to hybridization. Thus, a feed back between adaptive life history characteristics and the evolutionary process is proposed. [source] CAST2: identification and characterization of a protein structurally related to the presynaptic cytomatrix protein CASTGENES TO CELLS, Issue 1 2004Maki Deguchi-Tawarada The cytomatrix at the active zone (CAZ) is thought to define the site of Ca2+ -dependent exocytosis of neurotransmitters. We have recently identified a novel CAZ protein from rat brain which we have named CAST (CAZ-associated structural protein). CAST forms a large molecular complex with other CAZ proteins such as Bassoon, RIM1 and Munc13-1, at least through direct binding to RIM1. Here, we have identified a rat protein that is structurally related to CAST and named it CAST2. Subcellular fractionation analysis of rat brain shows that CAST2 is also tightly associated with the postsynaptic density fraction. Like CAST, CAST2 directly binds RIM1 and forms a hetero-oligomer with CAST. In primary cultured rat hippocampal neurones, CAST2 co-localizes with Bassoon at synapses. Furthermore, immunoelectron microscopy reveals that CAST2 localizes to the vicinity of the presynaptic membrane of synapses in mouse brain. Sequence analysis reveals that CAST2 is a rat orthologue of the human protein ELKS. ELKS has also recently been identified as Rab6IP2 and ERC1. Accordingly, the original CAST is tentatively re-named CAST1. These results indicate that CAST2 is a new component of the CAZ and, together with CAST1, may be involved in the formation of the CAZ structure. [source] A numerically scalable domain decomposition method for the solution of frictionless contact problemsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 12 2001D. Dureisseix Abstract We present a domain decomposition method with Lagrange multipliers for solving iteratively frictionless contact problems. This method, which is based on the FETI method and therefore is named here the FETI-C method, incorporates a coarse contact system that guides the iterative prediction of the active zone of contact. We demonstrate numerically that this method is numerically scalable with respect to both the problem size and the number of subdomains. Copyright © 2001 John Wiley & Sons, Ltd. [source] Synaptic localization of neuroligin 2 in the rodent retina: Comparative study with the dystroglycan-containing complexJOURNAL OF NEUROSCIENCE RESEARCH, Issue 4 2010Leona Lui Abstract Several recent studies have shown that neuroligin 2 (NL2), a component of the cell adhesion neurexins,neuroligins complex, is localized postsynaptically at hippocampal and other inhibitory synapses throughout the brain. Other studies have shown that components of the dystroglycan complex are also localized at a subset of inhibitory synapses and are coexpressed with NL2 in brain. These data prompted us to undertake a comparative study between the localization of NL2 and the dystroglycan complex in the rodent retina. First, we determined that NL2 mRNA is expressed both in the inner and in the outer nuclear layers. Second, we found that NL2 is localized both in the inner and in the outer synaptic plexiform layers. In the latter, the horseshoe-shaped pattern of NL2 and its extensive colocalization with RIM2, a component of the presynaptic active zone at ribbon synapses, argue that NL2 is localized presynaptically at photoreceptor terminals. Third, comparison of NL2 and the dystroglycan complex distribution patterns reveals that, despite their coexpression in the outer plexiform layer, they are spatially segregated within distinct domains of the photoreceptor terminals, where NL2 is selectively associated with the active zone and the dystroglycan complex is distally distributed in the lateral regions. Finally, we report that the dystroglycan deficiency in the mdx3cv mouse does not alter NL2 localization in the outer plexiform layer. These data show that the NL2- and dystroglycan-containing complexes are differentially localized in the presynaptic photoreceptor terminals and suggest that they may serve distinct functions in retina. © 2009 Wiley-Liss, Inc. [source] An improved method for determination of Holocene coastline changes around two ancient settlements in southern Anatolia: a geoarchaeological approach to historical land degradation studiesLAND DEGRADATION AND DEVELOPMENT, Issue 4 2003Y. Bal Abstract Two well-known ancient sites in southern Anatolia were selected to investigate and quantify the impact of historical land degradation on the Mediterranean coast of Turkey. These sites are the Luwian settlements of Kelenderis (modern Ayd,nc,k) and nearby Nagidos (Bozyaz,), both in Mersin Province and both occupied since around 4000,BP. Changes in local climatic conditions over this period have produced variations in the rates of fluvial transport of sediment/soil from the hinterland into the relevant deltaic regions, thus influencing rates of coastal progradation and aggradation. In addition, both eustatic and neotectonic movements have contributed to deltaic subsidence and/or hinterland uplift, with consequential impact on coastal evolution (positive or negative). The novel geoarchaeological methodology adopted in this study involves the creation of a graphical archive from detailed and standardised measurements taken from rectified mono- and stereoscopic aerial photographs. These archival data were then integrated with data from several types of historical map and field measurements in order to develop a geographical information system (GIS) database that could be interrogated, enabling graphical models of past coastal change to be constructed and calculations then made of the coastal configurations at successive historical periods. These calculations reveal that over the past 6000 years there has been only limited erosion/degradation in the karstic hinterland supplying the sediment to these two study sites (contrary to some previous statements concerning the high degradation risk of Mediterranean karst terrains). Furthermore, rates of progradation in each delta appear to have become diminished or even reversed in the past several decades as a result of both natural and anthropogenic factors. The precise contribution of neotectonic movements in this seismically active zone remains unquantified and is a topic requiring further interdisciplinary study. Copyright © 2003 John Wiley & Sons, Ltd. [source] Light emitting diodes on silicon substrates: preliminary resultsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 10 2009Alexandre Bondi Abstract III-V quantum wells (QW) superlattices have been grown by molecular beam epitaxy on GaP substrates for photonics applications on silicon. We first present room temperature photoluminescence (PL) results for GaAsP/GaP QWs. A detailed analysis of low temperature PL experiments is then performed. QW contribution is pointed out, and the structuration of the QW emission is attributed to LA phonon replica. A comparison with electronic bandstructure is performed, and a discussion is proposed on the nature of the observed transition (direct or indirect). Finally, it is shown that these QWs can be used as active zone in light emitters on silicon. Growth of good quality GaP epilayers on silicon is also presented. The crystalline quality of the deposited GaP near the GaP/Si interface is studied by Raman spectroscopy. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Impaired development of hippocampal mossy fibre synapses in mouse mutants for the presynaptic scaffold protein BassoonTHE JOURNAL OF PHYSIOLOGY, Issue 12 2010Frederic Lanore Bassoon, a protein highly concentrated at the synaptic active zone, is thought to participate in the organization of the cytomatrix at the site of neurotransmitter release. Bassoon is amongst the first proteins to accumulate at newly formed synaptic junctions, raising the question of the functional role of this protein in the early stages of synaptic development. Here we show that the course of synaptic maturation of hippocampal mossy fibre (MF) synapses (glutamatergic synapses with multiple release sites) is markedly altered during the first 2 weeks of postnatal development in mutant mice lacking the central region of Bassoon (Bsn,/, mice). At postnatal day 7 (P7), Bsn,/, mice display large amplitude MF-EPSCs with decreased paired pulse ratios, an abnormality which may be linked to deficits in the organization of the presynaptic active zone. Surprisingly, 1 week later, decreased MF-EPSCs amplitude is observed in Bsn,/, mice, consistent with the inactivation of a subset of synaptic release sites. Finally, at more mature states a decreased posttetanic potentiation is observed at MF-synapses. These results support the notion that Bassoon is important for organizing the presynaptic active zone during the postnatal maturation of glutamatergic synapses. [source] High-frequency stimuli preferentially release large dense-core vesicles located in the proximity of nonspecialized zones of the presynaptic membrane in sympathetic gangliaDEVELOPMENTAL NEUROBIOLOGY, Issue 4 2008F. Cifuentes Abstract We characterized the effect of a brief high-frequency stimulus on the number, distribution, and optical density of large dense-core vesicles (LDCVs) in the nerve terminals of the rat superior cervical ganglia. From 4.21 ± 0.37 LDCVs/bouton detected in control nerve terminals, a stimulus of 40 Hz for 1 min released 41% of LDCVs, decreasing their number to 2.48 ± 0.14 LDCVs/bouton (p = 0.0009). In control ganglia, most dense vesicles were located close to the plasma membrane (at ,100 nm); in contrast, in stimulated ganglia they were broadly distributed with respect to the active zone. The mean distance of LDCVs to membrane and active zones was 95 ± 8 nm and 473 ± 15 nm, respectively. The analysis of the core density showed that both groups had a similar asymmetric distribution with the same average. Stimulation preferentially released those vesicles located ,100 nm from the plasma membrane that had no apparent relationship with the active zone. After the stimulus, the average distances of LDCVs to the plasma membrane and active zone did not change, suggesting that the stimulus also caused the relocation of inner LDCVs. Interestingly, optical density analysis showed that the released vesicles had low range densities, and suggested that LDCVs release their entire content. We conclude that LDCV exocytosis mainly involves those vesicles located ,100 nm from the plasma membrane and occurs in regions of synaptic boutons presumed to be nonspecialized. These results agree with the characteristics of the classical model that proposes full content release. © 2008 Wiley Periodicals, Inc. Develop Neurobiol, 2008. [source] High level of mGluR7 in the presynaptic active zones of select populations of GABAergic terminals innervating interneurons in the rat hippocampusEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 12 2003Peter Somogyi Abstract The release of neurotransmitters is modulated by presynaptic metabotropic glutamate receptors (mGluRs), which show a highly selective expression and subcellular location in glutamatergic terminals in the hippocampus. Using immunocytochemistry, we investigated whether one of the receptors, mGluR7, whose level of expression is governed by the postsynaptic target, was present in GABAergic terminals and whether such terminals targeted particular cells. A total of 165 interneuron dendritic profiles receiving 466 synapses (82% mGluR7a-positive) were analysed. The presynaptic active zones of most GAD-(77%) or GABA-positive (94%) synaptic boutons on interneurons innervated by mGluR7a-enriched glutamatergic terminals (mGluR7a-decorated) were immunopositive for mGluR7a. GABAergic terminals on pyramidal cells and most other interneurons in str. oriens were mGluR7a-immunonegative. The mGluR7a-decorated cells were mostly somatostatin- and mGluR1,-immunopositive neurons in str. oriens and the alveus. Their GABAergic input mainly originated from VIP-positive terminals, 90% of which expressed high levels of mGluR7a in the presynaptic active zone. Parvalbumin-positive synaptic terminals were rare on mGluR7a-decorated cells, but on these neurons 73% of them were mGluR7a-immunopositive. Some type II synapses innervating interneurons were immunopositive for mGluR7b, as were some type I synapses. Because not all target cells of VIP-positive neurons are known it has not been possible to determine whether mGluR7 is expressed in a target-cell-specific manner in the terminals of single GABAergic cells. The activation of mGluR7 may decrease GABA release to mGluR7-decorated cells at times of high pyramidal cell activity, which elevates extracellular glutamate levels. Alternatively, the presynaptic receptor may be activated by as yet unidentified endogenous ligands released by the GABAergic terminals or the postsynaptic dendrites. [source] Selective GABAergic innervation of thalamic nuclei from zona incertaEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 6 2002P. Barthó Abstract Thalamocortical circuits that govern cortical rhythms and ultimately effect sensory transmission consist of three major interconnected elements: excitatory thalamocortical and corticothalamic neurons and GABAergic cells in the reticular thalamic nucleus. Based on the present results, a fourth component has to be added to this scheme. GABAergic fibres from an extrareticular diencephalic source were found to selectively innervate relay cells located mainly in higher-order thalamic nuclei. The origin of this pathway was localized to zona incerta (ZI), known to receive collaterals from corticothalamic fibres. First-order nuclei were innervated only in zones showing a high density of calbindin-positive neurons. The large GABA-immunoreactive incertal terminals established multiple contacts preferentially on the proximal dendrites of relay cells via symmetrical synapses with multiple release sites. The distribution, ultrastructural characteristics and postsynaptic target selection of extrareticular terminals were similar to type II muscarinic acetylcholine receptor-positive boutons, which constituted up to 49% of all GABAergic terminals in the posterior nucleus. This suggests that a significant proportion of the GABAergic input into certain thalamic territories involved in higher-order functions may have extrareticular origin. Unlike the reticular nucleus, ZI receives peripheral and layer V cortical input but no thalamic feedback; it projects to brainstem centres and has extensive intranuclear recurrent collaterals. This indicates that ZI exerts a conceptually new type of inhibitory control over the thalamus. The proximally situated, multiple active zones of ZI terminals indicate a powerful influence on the firing properties of thalamic neurons, which is conveyed to multiple cortical areas via relay cells which have widespread projections to neocortex. [source] Contact-dependent aggregation of functional Ca2+ channels, synaptic vesicles and postsynaptic receptors in active zones of a neuromuscular junctionEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 3 2001David A. DiGregorio Abstract To examine whether Ca2+ channels aggregate in a contact-dependent manner, we characterized the distribution of synaptic vesicles and postsynaptic receptors, and compared it to the location of Ca2+ entry sites, in a Xenopus laevis nerve-muscle coculture preparation using a localized Ca2+ detection method. The majority (75%) of Ca2+ entry sites at spontaneously formed nerve,muscle contacts were associated with enhanced immunofluorescence to the synaptic vesicle protein, SV2. In contrast, only 11% of recorded sites without Ca2+ transients exhibited significant SV2 immunofluorescence. When comparing the spatial distribution of synaptic markers with that of Ca2+ entry sites, we found that the majority of Ca2+ entry sites (61%) were associated with both enhanced SV2 immunofluorescence and R-BTX fluorescence, thereby identifying putative neurotransmitter release sites where Ca2+ channels, synaptic vesicles and postsynaptic receptors are colocalized. Using polystyrene beads coated with a heparin binding protein known to mediate in vitro postsynaptic receptor clustering, we show that the location of Ca2+ domains was associated with enhanced SV2 immunofluorescence at neurite-to-bead contacts. We conclude that the localization of functional Ca2+ channels to putative active zones follows a contact-dependent signalling mechanism similar to that known to mediate vesicle aggregation and AChR clustering. [source] Ischemia-induced modifications in hippocampal CA1 stratum radiatum excitatory synapsesHIPPOCAMPUS, Issue 10 2006Tatiana Kovalenko Abstract Relatively mild ischemic episode can initiate a chain of events resulting in delayed cell death and significant lesions in the affected brain regions. We studied early synaptic modifications after brief ischemia modeled in rats by transient vessels' occlusion in vivo or oxygen,glucose deprivation in vitro and resulting in delayed death of hippocampal CA1 pyramidal cells. Electron microscopic analysis of excitatory spine synapses in CA1 stratum radiatum revealed a rapid increase of the postsynaptic density (PSD) thickness and length, as well as formation of concave synapses with perforated PSD during the first 24 h after ischemic episode, followed at the long term by degeneration of 80% of synaptic contacts. In presynaptic terminals, ischemia induced a depletion of synaptic vesicles and changes in their spatial arrangement: they became more distant from active zones and had larger intervesicle spacing compared to controls. These rapid structural synaptic changes could be implicated in the mechanisms of cell death or adaptive plasticity. Comparison of the in vivo and in vitro model systems used in the study demonstrated a general similarity of these early morphological changes, confirming the validity of the in vitro model for studying synaptic structural plasticity. © 2006 Wiley-Liss, Inc. [source] Ultrastructural correlates of synapse withdrawal at axotomized neuromuscular junctions in mutant and transgenic mice expressing the Wld geneJOURNAL OF ANATOMY, Issue 3 2003Thomas H. Gillingwater Abstract We carried out an ultrastructural analysis of axotomized synaptic terminals in Wlds and Ube4b/Nmnat (Wld) transgenic mice, in which severed distal axons are protected from Wallerian degeneration. Previous studies have suggested that axotomy in juvenile (< 2 months) Wld mice induced a progressive nerve terminal withdrawal from motor endplates. In this study we confirm that axotomy-induced terminal withdrawal occurs in the absence of all major ultrastructural characteristics of Wallerian degeneration. Pre- and post-synaptic membranes showed no signs of disruption or fragmentation, synaptic vesicle densities remained at pre-axotomy levels, the numbers of synaptic vesicles clustered towards presynaptic active zones did not diminish, and mitochondria retained their membranes and cristae. However, motor nerve terminal ultrastructure was measurably different following axotomy in Wld transgenic 4836 line mice, which strongly express Wld protein: axotomized presynaptic terminals were retained, but many were significantly depleted of synaptic vesicles. These findings suggest that the Wld gene interacts with the mechanisms regulating transmitter release and vesicle recycling. [source] Seeking long-term relationship: axon and target communicate to organize synaptic differentiationJOURNAL OF NEUROCHEMISTRY, Issue 5 2006Michael A. Fox Abstract Synapses form after growing axons recognize their appropriate targets. The subsequent assembly of aligned pre and postsynaptic specializations is critical for synaptic function. This highly precise apposition of presynaptic elements (i.e. active zones) to postsynaptic specializations (i.e. neurotransmitter receptor clusters) strongly suggests that communication between the axon and target is required for synaptic differentiation. What trans-synaptic factors drive such differentiation at vertebrate synapses? First insights into the answers to this question came from studies at the neuromuscular junction (NMJ), where axon-derived agrin and muscle-derived laminin ,2 induce post and presynaptic differentiation, respectively. Recent work has suggested that axon- and target-derived factors similarly drive synaptic differentiation at central synapses. Specifically, WNT-7a, neuroligin, synaptic cell adhesion molecule (SynCAM) and fibroblast growth factor-22 (FGF-22) have all been identified as target-derived presynaptic organizers, whereas axon-derived neuronal activity regulated pentraxin (Narp), ephrinB and neurexin reciprocally co-ordinate postsynaptic differentiation. In addition to these axon- and target-derived inducers of synaptic differentiation, factors released from glial cells have also been implicated in regulating synapse assembly. Together, these recent findings have profoundly advanced our understanding of how precise appositions are established during vertebrate nervous system development. [source] The synapsin cycle: A view from the synaptic endocytic zoneJOURNAL OF NEUROSCIENCE RESEARCH, Issue 12 2007E. Evergren Abstract Although the synapsin phosphoproteins were discovered more than 30 years ago and are known to play important roles in neurotransmitter release and synaptogenesis, a complete picture of their functions within the nerve terminal is lacking. It has been shown that these proteins play an important role in the clustering of synaptic vesicles (SVs) at active zones and function as modulators of synaptic strength by acting at both pre- and postdocking levels. Recent studies have demonstrated that synapsins migrate to the endocytic zone of central synapses during neurotransmitter release, which suggests that there are additional functions for these proteins in SV recycling. © 2007 Wiley-Liss, Inc. [source] LANDSCAPE ATTRIBUTES AS CONTROLS ON GROITHD WATER NITRATE REMOVAL CAPACITY OF RIPARIAN ZONES,JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION, Issue 6 2001Arthur J. Gold ABSTRACT: Inherent site factors can generate substantial variation in the ground water nitrate removal capacity of riparian zones. This paper examines research in the glaciated Northeast to relate variability in ground water nitrate removal to site attributes depicted in readily available spatial databases, such as SSUIRGO. Linking site-specific studies of riparian ground water nitrate removal to spatial data can help target high-value riparian locations for restoration or protection and improve the modeling of watershed nitrogen flux. Site attributes, such as hydric soil status (soil wetness) and geomorphology, affect the interaction of nitrate-enriched ground water with portions of the soil ecosystem possessing elevated biogeochemical transformation rates (i.e., biologically active zones). At our riparian sites, high ground water nitrate-N removal rates were restricted to hydric soils. Geomorphology provided insights into ground water flowpaths. Riparian sites located on outwash and organic/alluvial deposits have high potential for nitrate-enriched ground water to interact with biologically active zones. In till deposits, ground water nitrate removal capacity may be limited by the high occurrence of surface seeps that markedly reduce the time available for biological transformations to occur within the riparian zone. To fully realize the value of riparian zones for nitrate retention, landscape controls of riparian nitrate removal in different climatic and physiographic regions must be determined and translated into available spatial databases. [source] ZnCdO/ZnO , a new heterosystem for green-wavelength semiconductor lasingLASER & PHOTONICS REVIEWS, Issue 3 2009S. Kalusniak Abstract We report on our efforts to cultivate the ternary compound ZnCdO as a semiconductor laser material. Molecular beam epitaxy far from thermal equilibrium allows us to overcome the standard solubility limit and to fabricate alloys with band gaps ranging from 3.4 down to 2.1 eV. Optimized structures containing well-defined quantum wells as active zones are capable of low-threshold lasing under optical pumping up to room temperature. The longest lasing wavelength achieved so far is 510 nm. [source] Regenerated synapses in lamprey spinal cord are sparse and small even after functional recovery from injuryTHE JOURNAL OF COMPARATIVE NEUROLOGY, Issue 14 2010Paul A. Oliphint Abstract Despite the potential importance that synapse regeneration plays in restoring neuronal function after spinal cord injury (SCI), even the most basic questions about the morphology of regenerated synapses remain unanswered. Therefore, we set out to gain a better understanding of central synapse regeneration by examining the number, distribution, molecular composition, and ultrastructure of regenerated synapses under conditions in which behavioral recovery from SCI was robust. To do so, we used the giant reticulospinal (RS) neurons of lamprey spinal cord because they readily regenerate, are easily identifiable, and contain large synapses that serve as a classic model for vertebrate excitatory neurotransmission. Using a combination of light and electron microscopy, we found that regenerated giant RS synapses regained the basic structures and presynaptic organization observed at control giant RS synapses at a time when behavioral recovery was nearly complete. However, several obvious differences remained. Most strikingly, regenerated giant RS axons produced very few synapses. In addition, presynaptic sites within regenerated axons were less complex, had fewer vesicles, and had smaller active zones than normal. In contrast, the densities of presynapses and docked vesicles were nearly restored to control values. Thus, robust functional recovery from SCI can occur even when the structures of regenerated synapses are sparse and small, suggesting that functional recovery is due to a more complex set of compensatory changes throughout the spinal network. J. Comp. Neurol. 518:2854,2872, 2010. © 2010 Wiley-Liss, Inc. [source] | ||||||||||||||||||||||||||||