白细胞介素－2中枢镇痛作用途径的探讨

抗ＩＬ－２受体α亚基的单克隆抗体不能阻断ＩＬ－２的中枢镇痛作用,以及丧失与ＩＬ－２受体β亚基结合能力的ＩＬ－２突变体仍具有提高大鼠痛阈的能力,这表明ＩＬ－２的中枢镇痛作用并不是通过ＩＬ－２受体所介导,亦表示ＩＬ－２的免疫和镇痛作用是通过不同的受体途径实现的。加之内源性阿片肽与ＩＬ－２分子有着共同的抗原决定基和结构相似性,提示ＩＬ－２可以与阿片受体直接结合产生中枢镇痛效应。从放射免疫法测定的ＩＬ－２侧脑室注射后不同时间大鼠脑内不同核团的内源性阿片肽含量,推测ＩＬ－２的中枢镇痛作用可能还与弓状核、室旁核、蓝斑等核团的β－ＥＰ和ＬＥＫ有关。     

Investigation of the effect of combined variations in temperature, pH, and NaCl concentration on nisin inhibition of Listeria monocytogenes and Staphylococcus aureus.

Gradient plates were used to investigate the effects of varying temperature, pH, and sodium chloride (NaCl) concentration on nisin inhibition of Staphylococcus aureus and Listeria monocytogenes, Nisin was incorporated into the plates of 0, 50, 100, 250, and 500 IU ml -1. Gradients of pH (3.7 to 7.92) at right angles to NaCl concentration (2.1 to 7% [wt/vol]) were used for the plates, which were incubated at 20, 25, 30 and 35 degrees C. Growth on the plates were recorded by eye and by image analysis. The presence of viable but nongrowing cells was revealed by transfer to nongradient plates. Lower temperatures and greater NaCl concentrations increased the nisin inhibition of S. aureus synergistically. Increasing the NaCl concentration potentiated the nisin action against L. monocytogenes; the effect of temperature difference was not so apparent. Between pH 7.92 and ca. pH 5, a fall pH appeared to increase nisin's effectiveness against both organisms. At more acid pH values (ca. pH 4.5 to 5), the organisms showed resistance to both nisin and NaCl at 20 and 25 degrees C. Similar results were obtained with one-dimensional liquid cultures.     

Ecological determinants of biofilm formation

Biofilm formation is discussed in terms of the ecological processes involved in their formation. It is emphasised that any cell responds to its environment i.e. to the composition of a liquid layer a few microns thick adjacent to the cell surface. The concept of multidimensional habitat domains defining the growth limits to every species is introduced, and put into the context of competition between different organisms. Activity domains of organisms are discussed and a definition for the niche of an organism introduced. The development of a biofilm on a clean surface is described. The constant depth film fermenter is introduced as an appropriate tool for investigating spatial and temporal sequence in biofilm formation. Finally, nutrient concentration is considered and the effects of diffusion limitation on film structure explored with the aid of a cellular automaton model.     

Monitoring the persistence of Laccaria bicolor as an ectomycorrhizal symbiont of nursery-grown Douglas fir by PCR of the rDNA intergenic spacer

The large-scale inoculation of selected beneficial ectomycorrhizal fungi in forest nurseries has generated renewed interest in the ecology of these symbiotic fungi. However, information on the dissemination and persistence of introduced symbionts is scarce due to the limitation of the current identification methods. To identify ectomycorrhizal fungi on single root tips, we investigated the polymorphism of the PCR-amplified ribosomal DNA intergenic spacer (IGS) from a wide range of ectomycorrhizal fungi. To investigate the reliability of this molecular approach in large-scale surveys, the dissemination and persistence on Douglas fir seedlings of the introduced Laccaria bicolor S238N were assessed in a forest nursery in the Massif Central (France). Several hundred ectomycorrhizas and fruiting bodies were sampled from plots where control and L. bicolor inoculated-Douglas fir seedlings were grown for 1.5 years. PCR typing of mycorrhizas indicated that trees inoculated with L. bicolor S238N remained exclusively colonized by that isolate (or sexually derived isolates) for the entire test period. In contrast, control seedlings were infected by indigenous isolates of Laccaria laccata and Thelephora terrestris. The molecular evidence for the persistence of the introduced mycobiont despite the competition from indigenous isolates of the same species provides further illustration of the potential of exotic species for large-scale microbial application.