Mode of action of β-carboline convulsants on the insect nervous system and their potential as insecticides

Little information is available on the actions of β-carboline convulsants on insect GABA receptors or their potential as insecticides. Accordingly, two compounds (3-ethoxy-β-carboline, 3-EBC; dimethoxy-β-carboline-3-methyl ester, DMCM) were studied for their effects on Drosophila melanogaster larval neuron discharge and also in lethality bioassays on adult female D. melanogaster and adult male Blattella germanica. Recordings of nerve spiking in the isolated larval central nervous system showed that 3-EBC and DMCM inhibited nerve discharge, and this inhibitory effect was not additive with that of GABA, confirming that the inhibition was expressed through an action on the GABA receptor. Nerve blockage induced by β-carbolines could not be reversed by picrotoxinin, indicating that there may exist some overlap or negative allosteric coupling between the picrotoxinin and β-carboline binding sites. DMCM and 3-EBC effectively antagonized the effects of exogenously applied GABA in nerve preparations from insecticide-susceptible larvae. In contrast, preparations from the rdl strain of D. melanogaster, which possesses a GABA receptor that is highly resistant to cyclodienes and related convulsants, were less sensitive to the GABA antagonist effect of DMCM. Neither of the β-carbolines produced any appreciable mortality in insects, even when synergized with piperonyl butoxide or S,S,S-tributyl phosphorotrithioate, The toxicity of the β-carbolines is probably limited by their relatively weak effects on the GABA receptor and perhaps also by pharmacokinetic factors. These considerations, coupled with the cross-resistance observed in cyclodiene-resistant insects, suggest that the currently available β-carbolines are not viable as lead compounds for insecticide screening efforts. © 1997 SCI.     

成都郊区土壤芽孢杆菌的生防潜力

利用格网抽样技术和重点抽样相结合的混合随机抽样技术结合全球定位系统(GPS)采集了成都市郊区27个样点的耕作层土样,用常规方法对其芽孢杆菌进行分离、计数,分析了芽孢杆菌在拮抗病原菌方面的潜在能力及其空间分布情况。从27个土样中共分离出333个菌株,对立枯丝核菌、果腐刺盘孢菌和新月弯孢菌之一具有拮抗作用的菌株共85株,其中拮抗效果好的有26株,拮抗3种病原菌的效果依次为新月弯孢菌、果腐刺盘孢菌和立枯丝核菌。效果较好的拮抗菌株主要归属于B.licheniformis、B.subtilis和B.megaterium。拮抗菌数量空间分布以成都市郊区中部地区较高,四周较低,其低值区在西北方向即郫县-金牛区一带和东南龙泉驿局部地区,高值区分布于新津和新都的局部地区。     

蜡蚧轮枝菌拮抗菌——粪产碱杆菌生物学特性的初步研究

分离到了一种对蜡蚧轮枝菌具有明显抑制作用的细菌,采用生理生化反应方法对该细菌进行种类鉴定.结果表明,该细菌为粪产碱杆菌(Alcaligenes faecalis)菌株.在不同温度下对该细菌的生长速度和对不同抗生素的敏感性进行研究,发现在弱酸性条件下,该菌生长最快的温度为30-39℃,对卡那霉素、氯霉素、四环素、链霉素都敏感,对卡那霉素的完全抑制最低浓度为60μg.mL-1.     

Impact of preharvest application of biological control agents on postharvest diseases of fresh fruits and vegetables

During the storage of harvested commodities, environmental parameters are quite stable. For this and other reasons, it is generally believed that biological control by means of microbial antagonists may have a greater potential for success when applied postharvest. However, one of the major obstacles to the development of postharvest biocontrol agents is that they are unable to control previously established infections, such as latent and quiescent infections and incipient infections occurring through wounds resulting from harvesting operations. Field application of biocontrol agents may enable early colonisation of fruit surfaces, thus protecting from these infections. Moreover, preharvest applications can be an appropriate strategy for fruits and vegetables subject to damage in postharvest handling. To be successful in preharvest applications, putative biocontrol agents must be able to tolerate low-nutrient availability, UV radiation, high temperature and dry conditions. Some reports of postharvest biological control accomplished by preharvest applications, include apples, avocados, sweet cherries, grapes, and strawberries. This paper provides a brief overview on particular aspects of preharvest application of biocontrol agents to reduce postharvest decay. Research areas relevant for the development of this strategy are also indicated.     

A cell-based reporter assay for screening for EcR agonist/antagonist activity of natural ecdysteroids in Lepidoptera (Bm5) and Diptera (S2) cell cultures,followed by modeling of ecdysteroid-EcR interactions and normal mode analysis

Ecdysteroid signal transduction is a key process in insect development and therefore an important target for insecticide development. We employed an in vitro cell-based reporter bioassay for the screening of potential ecdysone receptor (EcR) agonistic and antagonistic compounds. Natural ecdysteroids were assayed with ecdysteroid-responsive cell line cultures that were transiently transfected with the reporter plasmid ERE-b.act.luc. We used the dipteran Schneider S2 cells of Drosophila melanogaster and the lepidopteran Bm5 cells of Bombyx mori, representing important pest insects in medicine and agriculture. Measurements showed an EcR agonistic activity only for cyasterone both in S2 (EC₅₀ = 3.3 μM) and Bm5 cells (EC₅₀ = 5.3 μM), which was low compared to that of the commercial dibenzoylhydrazine-based insecticide tebufenozide (EC₅₀ = 0.71 μM and 0.00089 μM, respectively). Interestingly, a strong antagonistic activity was found for castasterone in S2 cells with an IC₅₀ of 0.039 μM; in Bm5 cells this effect only became visible at much higher concentrations (IC₅₀ = 18 μM). To gain more insight in the EcR interaction, three-dimensional modeling of dipteran and lepidopteran EcR-LBD was performed. In conclusion, we showed that the EcR cell-based reporter bioassay tested here is a useful and practical tool for the screening of candidate EcR agonists and antagonists. The docking experiments as well as the normal mode analysis provided evidence that the antagonist activity of castasterone may be through direct binding with the receptor with specific changes in protein flexibility. The search for new ecdysteroid-like compounds may be particularly relevant for dipterans because the activity of dibenzoylhydrazines appears to be correlated with an extension of the EcR-LBD binding pocket that is prominent in lepidopteran receptors but less so in the modeled dipteran structure.     

促黄体素释放激素和多巴胺拮抗物对鲇促性腺激素释放的作用

以珠江流域鲇为研究对象，分别在性腺发育早期、性腺发育晚期、性腺发育成熟与产卵前期、性腺退化期注射促黄体素释放激素类似物和多巴胺D2受体拮抗物，处理后6h、12h、24h测定血液中的促性腺激素水平变化。结果表明，在性腺发育的各个时期，促黄体素释放激素类似物和多巴胺D2受体拮抗物联合注射能显著剂激鲇促性腺激素分泌；鲇脑垂体促性腺激素的分泌受下丘脑释放的促性腺素释放激素和多巴胺的双重调节，多巴胺只能抑制促性腺素释放激素诱导的促性腺激素分泌。在建立鲇人工繁殖技术时，可采用促黄体素释放激素类似物和多巴胺D2受体拮抗物联合注射方法。     

水稻稻瘟病拮抗链霉菌的诱变选育

以稻瘟病拮抗链霉菌St-10为出发菌株,进行紫外线(UV)和60Co-γ射线的诱变选育,初步明确了该菌株紫外线20 cm照射距离下的最佳照射时间为40 s,60Co-γ射线最佳处理剂量为6万伦琴。经初筛和复筛后,获得了一株遗传稳定性好的突变菌株C-18,其相对抑菌率由出发菌株的52.4%提高到73.5%,是出发菌株的1.4倍。     

白细胞介素1受体拮抗药对小鼠中枢神经系统的影响

利用重组人白细胞介素1受体拮抗药(IL 1ra),一次性给小鼠雾化吸入IL 1ra1.0、3.0、10.0mg·kg-1和等容量的磷酸缓冲液(PBS),研究其对小鼠中枢神经系统的药理作用。结果表明:IL 1ra(3.0mg·kg-1)在给药后20min内可引起小鼠自主活动次数的明显增多;并且IL 1ra呈剂量依赖性地对抗戊巴比妥钠的中枢抑制作用,使小鼠睡眠潜伏期延长、持续时间缩短,与PBS对照组相比差异显著或极显著,说明IL 1ra对小鼠中枢神经系统可产生兴奋作用。