Library

Notes: Abstract: Certain modifications of the neuronal cytoskeleton that are associated with development also occur during regeneration of adult mammalian peripheral nerve. The aim of the present study was to examine one such modification, the tyrosination of a-tubulin. Adult rats were anaesthetized and the left or right sciatic nerve randomly selected and crushed to induce regeneration. In certain instances nerves were crushed then ligatured about the crush, to prevent regeneration. Five days later the rats were killed and the regenerating (or ligatured) and the contralateral (control) nerves were removed. Quantitative immunoblotting of nerve homogenates with antibodies that recognize tyrosinated a-tubulin and total a-tubulin revealed a significant increase (p 〈 0.01) in the proportion of a-tubulin that was tyrosinated in nerve pieces distal (peripheral) to a nerve crush compared with nerve pieces proximal (central) to a nerve crush and to uncrushed nerve. No such difference occurred in ligatured (crushed but nonregenerating) nerve, implying that the increase was related to the presence of regenerating fibres; nor was there any gradient in tyrosination of α-tubulin in control nerves. This effect was confirmed by cytofluorimetric scanning and fluorescence confocal laser scanning microscopy of fixed sections of control and regenerating nerve, stained with antibodies directed against tyrosinated a-tubulin. When nerves were separated into fractions containing assembled and nonassembled tubulin, a significant (p 〈 0.01) increase was found in the proportion of tyrosinated α-tubulin in the nonassembled tubulin fraction in nerve pieces containing regenerating fibres. This occurred in the absence of a change in the proportion of assembled and nonassembled tubulin. Measurements of tubulin:tyrosine ligase activity, by incorporation of [3H] tyrosine into endogenous nerve tubulin in vitro, indicated a decrease in tyrosine incorporation into tubulin from nerve pieces distal, compared with those proximal to a nerve crush. There was no such difference in ligatured nerves. It is proposed that the increased amount of tyrosinated a-tubulin is related to an alteration in assembly rate of microtubules required for neurite outgrowth and that the apparent decrease in the tubulin:tyrosine ligase activity in vitro reflects the increased tyrosination in vivo.

Notes: The apparent channel mobility of a metal/SiO2/Si field-effect transistor as determined from the current-voltage measurement may yield a significantly underestimated value if proper care is not taken to restrict the applied source-drain voltage. Unlike the well-known velocity saturation effect, the effect to be discussed is due to the nonuniform distribution of carriers along the channel, and therefore is independent of the channel length, but is a function of the ratio of the source-drain voltage to the thermal voltage kT/e. It is more pronounced for devices with thinner gate oxide in the low carrier-concentration regime.

Notes: The roughness at the metal/gate oxide interface of metal-oxide-semiconductor field-effect transistor (MOSFET) has been modeled. The mobility of electrons inside the channel of the MOSFET, limited by the scattering resulting from this roughness, has been calculated. The magnitude of this scattering mechanism is a strong function of the oxide thickness. For a MOSFET with very thin gate oxide (〈100 A(ring)), this limiting mobility may become comparable to the total mobility, and the scattering of electrons by the remote interface roughness can no longer be ignored.

Notes: Abstract Fossil fuels account for about 80% of energy consumption in Asia. Because of its abundance and easy recoverability, especially in India and China, coal will remain the fuel of choice in the foreseeable future. If current trends continue, sulfur dioxide emissions from Asia may soon equal the emissions from North America and Europe combined. These trends portend a variety of local, regional, and global environmental impacts. Acid rain damages human health, ecosystems, and built surfaces. Many ecosystems will be unable to absorb these increased acidic depositions, leading to irreversible ecosystem damage with far-reaching implications for health, forestry, agriculture, fisheries, and tourism. RAINS-ASIA is a scenario-generating tool used to estimate the extent of damages caused by acid rain and to review the costs and impacts of alternatives to provide a look into the future. Its use extends from national-, regional-, and city-scale evaluation and inputs for cost-effective options analyses, to international negotiations on transboundary pollution.

Notes: Amphiphysin and synaptojanin are two nerve terminal proteins with a putative role in synaptic vesicle endocytosis and recycling. We have investigated the intraneuronal dynamics and distribution of these two proteins, using nerve crush techniques in combination with immunofluorescence, cytofluorimetric scanning (CFS), confocal laser scanning microscopy and immuno-electron microscopy (EM). Accumulations of amphiphysin and synaptojanin immunoreactivities at the crush site were detected as short as 1 h after the lesion, indicating that a pool of these two partially cytosolic proteins moves along the axon by fast axoplasmic transport. The amount of proximal accumulation increased linearly between 1 and 8 h. CFS analysis demonstrated that only 30% of fast anterogradely transported amphiphysin and synaptojanin was returned by fast retrograde transport, in contrast to the 70% value observed for synaptophysin, a transmembrane protein. This indicates that the majority of amphiphysin and synaptojanin is degraded/metabolized in the nerve terminals. Immuno-EM showed that both amphiphysin and synaptojanin are primarily associated with heterogeneous membrane profiles in the crushed sciatic nerve and the immunoperoxidase reaction product is concentrated in the nerve terminal cytomatrix of the spinal cord. Both proteins were differentially distributed in subsets of nerve terminals, indicating heterogeneous expression in neurons.

Notes: The chromogranin family comprises chromogranin A and B, and secretogranin II. The present study has focused on the axonal transport of chromogranins/secretogranin II and their detailed distribution in peripheral nerves and the spinal cord. With radioimmunoassay (RIA) and column chromatography, we first studied the processing of chromogranin B and secretogranin II during axonal transport. No larger precursors of these peptides were detected in the sciatic nerves, indicating that they are already processed to a high degree early during axonal transport. We also analysed nerve segments above and below a crush, using RIA, in order to compare these accumulation data with those obtained by the cytofluorimetric-scanning (CFS) technique. For the latter technique, the amounts of accumulation distal to the crush (presumably representing recycling and retrogradely transported peptides) were 30–40% of the amounts in the proximal accumulation for chromogranin A and secretoneurin, in contrast to chromogranin B, which showed 15% recycling. With the RIA, the corresponding values for secretoneurin and PE-11 (antibody against chromogranin B) were 42% and 14%, respectively. Therefore, the data obtained by CFS were in excellent agreement with those obtained by RIA. In crushed sciatic nerves, chromogranin A was present in large axons as well as in small- and medium-sized axons. Chromogranin B was mainly restricted to large axons, while secretoneurin was localized to bundles of small axons. This differential distribution was also found in the spinal roots and in the peripheral terminals. Chromogranin A was present in both ventral and dorsal roots, and chromogranin B was detected in ventral roots and in large sensory axons in the dorsal roots. Secretoneurin was dominant in the dorsal root. Double-labelling studies with antibodies against choline acetyltransferase/vesicular acetylcholine transporter, or against tyrosine hydroxylase, confirmed that chromogranin A was distributed in cholinergic, sensory, as well as adrenergic neurons. Chromogranin B was mainly present in cholinergic motor neurons and large sensory neurons, and secretoneurin was restricted to adrenergic and sensory neurons. The present study demonstrates that chromogranins A and B, and secretoneurin are transported with fast axonal transport in the peripheral nerves, with different amounts of recycling, and that they are differentially distributed in different types of neurons in the peripheral nervous system and the spinal cord, suggesting that each of them may play a special role in subsets of neurons.

Notes: Synucleins are abundant nerve terminal proteins of hitherto unknown function. In diseases with Lewy bodies, human α-synuclein concentrates in these lesions in the cell body and mutations in α-synuclein lead to heritable Parkinson’s disease with Lewy bodies. This indicates that changes in the normal metabolism and axonal transport of α-synuclein is perturbed in these diseases. To investigate the normal axonal transport of synucleins we studied the rat visual system by nerve crush operations and metabolic labelling of the retinal ganglion cells followed by immunoprecipitation of nerve segments. We found by immunofluorescence microscopy of the crush-operated nerves that synucleins are transported by fast antero- and retrograde transport and colocalize with synaptophysin and SNAP-25 around the lesion. The metabolic labelling studies demonstrated that synucleins were moved through the nerve with all the rate components, the fast component and the slow components a and b, with component b predominating. Two-dimensional gel electrophoresis revealed that both α- and β-synuclein migrate through the nerve by slow component b in a ratio of 2 : 1.