Type IIa RPTPs and Glycans: Roles in Axon Regeneration and Synaptogenesis

Type IIa receptor tyrosine phosphatases (RPTPs) play pivotal roles in neuronal network formation. It is emerging that the interactions of RPTPs with glycans, i.e., chondroitin sulfate (CS) and heparan sulfate (HS), are critical for their functions. We highlight here the significance of these interactions in axon regeneration and synaptogenesis. For example, PTPσ, a member of type IIa RPTPs, on axon terminals is monomerized and activated by the extracellular CS deposited in neural injuries, dephosphorylates cortactin, disrupts autophagy flux, and consequently inhibits axon regeneration. In contrast, HS induces PTPσ oligomerization, suppresses PTPσ phosphatase activity, and promotes axon regeneration. PTPσ also serves as an organizer of excitatory synapses. PTPσ and neurexin bind one another on presynapses and further bind to postsynaptic leucine-rich repeat transmembrane protein 4 (LRRTM4). Neurexin is now known as a heparan sulfate proteoglycan (HSPG), and its HS is essential for the binding between these three molecules. Another HSPG, glypican 4, binds to presynaptic PTPσ and postsynaptic LRRTM4 in an HS-dependent manner. Type IIa RPTPs are also involved in the formation of excitatory and inhibitory synapses by heterophilic binding to a variety of postsynaptic partners. We also discuss the important issue of possible mechanisms coordinating axon extension and synapse formation.     

Commercialized fast reactor cycle systems and reactor core performance of the promising fast reactors

The Feasibility Study on Commercialized Fast Reactor (FR) Cycle Systems is under progress in order to propose prominent FR cycle systems that will respond to the diverse needs of society in the future. The design studies on various FR system concepts have been achieved and then the evaluations of potential to achieve the development targets have been also carried out. Crucial development issues have been found out for each FR system concept and their development plans for the key technologies are summarized as the roadmap. As a result, it has been confirmed that the sodium-cooled FR concept is highly suited to the development targets and R&D issues are related enhancing the economy with certain perspectives for realization. A flexible and robust development program for the FR cycle system will be proposed taking account of the characteristics for each FR concept until the end of the Phase II study.     

Daily variation in an intensity of kaolin-induced writhing reaction in mice

The daily variation in an intensity of kaolin-induced writhing reaction was examined in mice kept under conditions of light; 07:00 - 19:00 and dark; 19:00 - 07:00. The number of writhes was counted for 30 minutes after a single intraperitoneal injection of kaolin at 00:00, 02:00, 04:00, 06:00, 08:00, 10:00, 12:00, 14:00, 16:00, 18:00, 20:00 and 22:00. The number of writhes showed a daily variation with a peak at 18:00 and a trough at 06:00. The intensity of writhing reaction was significantly reduced by pretreatment with the bradykinin B1 (Des-Arg9-[Leu8]-BK) and B2 (icatibant) receptor antagonists. Significant daily variation in this parameter was still observed in the group with the B1 antagonist, but disappeared in the B2 antagonist-treated group. These results suggest that the kaolin-induced writhing reaction shows the daily variation with a peak at the end of the resting period and a trough at the end of the active period. The B2 receptor mediated stimuli appears to be involved in this phenomenon.     

Long Crack R-Curve of Aligned Porous Silicon Nitride

Long crack R -curve of a porous Si₃N₄ with aligned fibrous grains was investigated, using a chevron-notched beam technique. A crack was constrained to propagate normal to the grain alignment. The crack growth resistance of aligned porous Si₃N₄ was much larger compared with that of dense Si₃N₄ ceramics. Microstructure observations showed that pullouts of fibrous grains in aligned porous Si₃N₄ markedly increased during crack propagation relative to those of dense Si₃N₄, due to the existence of pores. The efficient grain pullouts in porous Si₃N₄ increased the bridging stress at the crack wake.     

Current measurement system utilizing cryogenic techniques for theabsolute measurement of the magnetic flux quantum

A series of systems composed of cryogenic devices such as a Josephson potentiometer and a cryogenic current comparator, developed to precisely measure a current with any value up to 1 A, is proposed. These systems will be used to measure the injected electrical energy with an uncertainty of the order of 0.01 p.p.m. or less in the absolute measurement of the magnetic flux quantum by superconducting magnetic levitation. Some preliminary experiments are described     

Novel π-conjugated organoboron polymers: Poly (ethynylene-phenylene-ethynylene-borane)s

Summary Novel poly(ethynylene-phenylene-ethynylene-borane)s were prepared by polycondensation between bifunctional lithium acetylide and aryldimethoxyborane. The polymers obtained are expected as a novel type of organoboron π-conjugated polymers via vacant p-orbital of boron atom. The polymerization between dilithium 2,5-didodecyloxybenzene- 1,4-diethynilide and tripyldimethoxyborane [tripyl=2,4,6-triisopropylphenyl] gave the corresponding polymer in 67% yield. From gel permeation chromatographic analysis (THF, PSt standards), the number-average molecular weight of the polymer was found to be 2700. In the UV-vis spectrum of the polymer (in chloroform at room temperature), an absorption maximum was observed at 397 nm. The fluorescence emission spectrum (in chloroform, room temperature, excitation wavelength at 400 nm) showed its λ_max at 456 nm in the visible blue region. The polymers obtained were very soluble in common organic solvents such as THF, chloroform and benzene. Received: 11 April 2000/Accepted: 22 April 2000     

Alternating boration copolymerization between diyne and bisallene

Summary Alternating boration copolymerization between 1,4-diallenylbenzene (2) and 2,7-diethynylfluorene (3) was examined using diphenylbromoborane (1) to give the corresponding copolymer (4). The organoboron copolymer obtained was characterized by ¹H-, ¹¹B-NMR, IR, and UV-vis absorption spectra. Received: 5 August 1999/Accepted: 31 August 1999     

Incorporation of a well-defined polyether side-chain into segmented poly(ether-urethane urea) and examination for blood-compatibility

A new method of introducing a hydrophilic polyether side chain into segmented polyurethane using a polypropylene oxide macromer with 1,3-diol at one chain-end, which behaves as chain extender, is described. In this procedure, a molecular-designed side-chain is incorporated quantitatively and directly into polyurethane biomedical elastomer. The design is also of interest to biomaterials in artificial organs.