Morphine 6 glucuronide stimulates nitric oxide release in mussel neural tissues: evidence for a morphine 6 glucuronide opiate receptor subtype

We have previously demonstrated that Mytilus edulis pedal ganglia contain opiate alkaloids, i.e., morphine and morphine 6 glucuronide (M6G), as well as mu opiate receptor subtype fragments exhibiting high sequence similarity to those found in mammals. Now we demonstrate that M6G stimulates pedal ganglia constitutive nitric oxide (NO) synthase (cNOS)-derived NO release at identical concentrations and to similar peak levels as morphine. However, the classic opiate antagonist, naloxone, only blocked the ability of morphine to stimulate cNOS-derived NO release and not that of M6G. CTOP, a mu-specific antagonist, blocked the ability of M6G to induce cNOS-derived NO release as well as that of morphine, suggesting that a novel mu opiate receptor was present and selective toward M6G. In examining a receptor displacement analysis, both opiate alkaloids displaced [³H]-dihydromorphine binding to the mu opiate receptor subtype. However, morphine exhibited a twofold higher affinity, again suggesting that a novel mu opiate receptor may be present. Received 1 November 2001; received after revision 1 February 2002; accepted 1 February 2002     

Microbial cycling of volatile organic sulfur compounds

Microbial cycling of volatile organic sulfur compounds (VOSCs), especially dimethyl sulfide (DMS) and methanethiol (MT), is intensively studied because these compounds play an important role in the processes of global warming, acid precipitation, and the global sulfur cycle. VOSC concentrations in freshwater sediments are low due to the balance between the formation and degradation of these compounds. These reactions occur for the greater part at the oxic/anoxic interphase of sediment and water column. In contrast to marine ecosystems, where dimethylsulfoniopropionate is the main precursor of MT and DMS, in freshwater ecosystems, VOSCs are formed mainly by methylation of sulfide and to a lesser extent from the degradation of S-containing amino acids. One of the major routes for DMS and MT formation through sulfide methylation is anaerobic O-demethylation of methoxylated aromatic compounds. Inhibition studies have revealed that the major part of the endogenously produced MT and DMS is degraded anaerobically by methanogens. The major bacterial groups involved in formation and consumption of VOSCs are described.     

Multiple ionization of atom clusters by intense soft X-rays from a free-electron laser

Intense radiation from lasers has opened up many new areas of research in physics and chemistry, and has revolutionized optical technology. So far, most work in the field of nonlinear processes has been restricted to infrared, visible and ultraviolet light, although progress in the development of X-ray lasers has been made recently. With the advent of a free-electron laser in the soft-X-ray regime below 100 nm wavelength, a new light source is now available for experiments with intense, short-wavelength radiation that could be used to obtain deeper insights into the structure of matter. Other free-electron sources with even shorter wavelengths are planned for the future. Here we present initial results from a study of the interaction of soft X-ray radiation, generated by a free-electron laser, with Xe atoms and clusters. We find that, whereas Xe atoms become only singly ionized by the absorption of single photons, absorption in clusters is strongly enhanced. On average, each atom in large clusters absorbs up to 400 eV, corresponding to 30 photons. We suggest that the clusters are heated up and electrons are emitted after acquiring sufficient energy. The clusters finally disintegrate completely by Coulomb explosion.     

The role of parasites in sympatric and allopatric host diversification

Exploiters (parasites and predators) are thought to play a significant role in diversification, and ultimately speciation, of their hosts or prey. Exploiters may drive sympatric (within-population) diversification if there are a variety of exploiter-resistance strategies or fitness costs associated with exploiter resistance. Exploiters may also drive allopatric (between-population) diversification by creating different selection pressures and increasing the rate of random divergence. We examined the effect of a virulent viral parasite (phage) on the diversification of the bacterium Pseudomonas fluorescens in spatially structured microcosms. Here we show that in the absence of phages, bacteria rapidly diversified into spatial niche specialists with similar patterns of diversity across replicate populations. In the presence of phages, sympatric diversity was greatly reduced, as a result of phage-imposed reductions in host density decreasing competition for resources. In contrast, allopatric diversity was greatly increased as a result of phage-imposed selection for resistance, which caused populations to follow divergent evolutionary trajectories. These results show that exploiters can drive diversification between populations, but may inhibit diversification within populations by opposing diversifying selection that arises from resource competition.     

Directionally selective calcium signals in dendrites of starburst amacrine cells

The detection of image motion is fundamental to vision. In many species, unique classes of retinal ganglion cells selectively respond to visual stimuli that move in specific directions. It is not known which retinal cell first performs the neural computations that give rise to directional selectivity in the ganglion cell. A prominent candidate has been an interneuron called the 'starburst amacrine cell'. Using two-photon optical recordings of intracellular calcium concentration, here we find that individual dendritic branches of starburst cells act as independent computation modules. Dendritic calcium signals, but not somatic membrane voltage, are directionally selective for stimuli that move centrifugally from the cell soma. This demonstrates that direction selectivity is computed locally in dendritic branches at a stage before ganglion cells.     

脉冲激光照射下生物质材料的传热特性

采用快速瞬态温度检测系统测定高能脉冲激光作用下生物质材料的温度动态变化,研究生物质材料瞬态传热特性以及激光脉冲宽度、功率密度、材料厚度与初始含湿量对温度变化规律的影响.根据实验现象,尝试提出脉冲激光作用下生物质材料传热的数学模型,数值模拟分析表明,计算与实验结果基本吻合,能较好地反应脉冲激光作用下生物质材料的传热特性,为进一步深入研究和理论分析积累了有价值的实验资料,提供了可供参考的经验.     

Palaeolake and palaeoenvironment between 42 and 18 kaBP in tengger desert, NW China

Comprehensive field investigations and laboratory analyses show that palaeolakes, including fresh- mesohaline water Megalake Tengger and other semi-con- nected, isolated water bodies, during late Pleistocene covered an area of more than 20000 km², which is more than half of the Tengger Desert in NW China. Stratigraphic correlation and chronological evidence indicate that before ca. 42000 aBP the area was more arid. The palaeolakes started to develop around 40000 uncal. ¹⁴C aBP but until 37000 ¹⁴C aBP their scope was limited. High water levels established from 35000 ¹⁴C aBP lasted until 22000 ¹⁴CaBP. Lake levels regressed between 22000 and 20000 ¹⁴C aBP but transgressed from 20000 to 18600 ¹⁴C aBP. Subsequently, water level declined further and the Megalake Tengger finally desiccated at around 18000 ¹⁴C aBP. Megalake Tengger possessed a fresh-mesohaline water property, implying that the regional precipitation increased significantly. During the period of Megalake Tengger, the climate was warmer-humid than present. The annual rainfall was 250 to 350 mm more than that of today and the temperature was 1.5 to 3.0℃ higher.     

Superoxide activates mitochondrial uncoupling proteins.

Uncoupling protein 1 (UCP1) diverts energy from ATP synthesis to thermogenesis in the mitochondria of brown adipose tissue by catalysing a regulated leak of protons across the inner membrane. The functions of its homologues, UCP2 and UCP3, in other tissues are debated. UCP2 and UCP3 are present at much lower abundance than UCP1, and the uncoupling with which they are associated is not significantly thermogenic. Mild uncoupling would, however, decrease the mitochondrial production of reactive oxygen species, which are important mediators of oxidative damage. Here we show that superoxide increases mitochondrial proton conductance through effects on UCP1, UCP2 and UCP3. Superoxide-induced uncoupling requires fatty acids and is inhibited by purine nucleotides. It correlates with the tissue expression of UCPs, appears in mitochondria from yeast expressing UCP1, and is absent in skeletal muscle mitochondria from UCP3 knockout mice. Our findings indicate that the interaction of superoxide with UCPs may be a mechanism for decreasing the concentrations of reactive oxygen species inside mitochondria.