Adenosine and Glutamate Modulate Each Other's Release from Rat Hippocampal Synaptosomes

Abstract: In rat hippocampal synaptosomes, adenosine decreased the K⁺ (15 mM) or the kainate (1 mM) evoked release of glutamate and aspartate. An even more pronounced effect was observed in the presence of the stable adenosine analogue, R-phenylisopropyladenosine. All these effects were reversed by the selective adenosine A₁ receptor antagonist 8-cyclo-pentyltheophylline. In the same synaptosomal preparation, K⁺ (30 mM) strongly stimulated the release of the preloaded [³H]adenosine in a partially Ca²⁺-dependent and tetrodotoxin (TTX)-sensitive manner. Moreover, in the same experimental conditions, both l -glutamate and l -aspartate enhanced the release of [³H]adenosine derivatives ([³H]ADD). The gluta-mate-evoked release was dose dependent and appeared to be Ca²⁺ independent and tetrodotoxin insensitive. This effect was not due to metabolism because even the nonmetabolizable isomers d -glutamate and d -aspartate were able to stimulate [³H]ADD release. In contrast, the specific glutamate agonists N-methyl-d -aspartate, kainate, and quisqualate failed to stimulate [³H]ADD release, suggesting that glutamate and aspartate effects were not mediated by known excitatory amino acid receptors. Moreover, NMDA was also ineffective in the absence of Mg²⁺ and l -glutamate-evoked release was not inhibited by adding the specific antagonists 2-amino-5-phosphonovaleric acid or 6–7-dinitroquinoxaline-2, 3-dione. The stimulatory effect did not appear specific for only excitatory amino acids, as γ-anunobutyric acid stimulated [³H]ADD release in a dose-related manner. These results suggest that, at least in synaptosomal preparations from rat hippocampus, adenosine and glutamate modulate each other's release. The exact mechanism of such interplay, although still, unknown, could help in the understanding of excitatory amino acid neurotoxicity.     

Ability of human sera to neutralise the activity of Vero cytotoxins VT1, VT2 and variant forms of VT2

Abstract Sera, from 17 patients with diarrhoea or haemolytic uraemic syndrome, and six healthy adults, were tested for neutralisation of Vero cytotoxins (VT). For all 17 patients there was evidence of infection with Escherichia coli O157. Sera from two controls but from none of the patients neutralised VT1, although two patients were infected by strains producing VT1 and VT2. Sera from all six controls and 14 patients neutralised VT2 derived from strains 933 and E32511, but not variant forms of VT2 derived from strains E32511, E57, B2F1 and H.1.8. This neutralising activity warrants further investigation, especially as many 0157 VTEC carry both VT2 and VT2 variant genes.     

Neurotrophic Factors Prevent Ceramide-Induced Apoptosis Downstream of c-Jun N-Terminal Kinase Activation in PC12 Cells

Abstract: Neurotrophic factors prevent apoptosis of PC12 cells in serum-free medium. The present study determines whether neurotrophic factors can prevent ceramide-induced apoptosis in PC12 cells and investigates the role that c-Jun N-terminal kinase (JNK) activation may play in this system. Ceramide-induced apoptosis was inhibited by nerve growth factor, basic fibroblast growth factor, pituitary adenylyl cyclase-activating peptide, 4-(8-chlorophenylthio)cyclic AMP, and the caspase inhibitor benzyloxycarbonyl-Val-Ala- dl -Asp fluoromethyl ketone (zVAD-FMK). It was surprising that inhibition of extracellular signal-regulated kinase and/or phosphatidylinositol 3-kinase did not markedly block the protective effects exerted by neurotrophic factors against ceramide-induced apoptosis, suggesting that neurotrophic factors can promote survival independently of these signaling pathways. Treatment of PC12 cells with ceramide resulted in a time-dependent increase in JNK activity. However, neither neurotrophic factors nor zVAD-FMK attenuated ceramide-stimulated JNK activation. Further experiments indicated that ceramide-induced apoptosis in PC12 cells requires new protein synthesis, and that nerve growth factor and zVAD-FMK can prevent apoptosis after JNK activity has been detected. These results indicate that ceramide-induced JNK activation is an early event and may be required for the expression of essential components of the apoptotic machinery. It is anticipated that neurotrophic factors inhibit ceramide-induced apoptosis by affecting signaling events downstream of JNK activation.     

Viral control of bacterial biodiversity – evidence from a nutrient-enriched marine mesocosm experiment

We demonstrate here results showing that bottom-up and top-down control mechanisms can operate simultaneously and in concert in marine microbial food webs, controlling prokaryote diversity by a combination of viral lysis and substrate limitation. Models in microbial ecology predict that a shift in the type of bacterial growth rate limitation is expected to have a major effect on species composition within the community of bacterial hosts, with a subsequent shift in the composition of the viral community. Only moderate effects would, however, be expected in the absolute number of coexisting virus–host pairs. We investigated these relationships in nutrient-manipulated systems, under simulated in situ conditions. There was a strong correlation in the clustering of the viral and bacterial community data supporting the existence of an important link between the bacterial and viral communities. As predicted, the total number of viral populations was the same in all treatments, while the composition of the viral community varied. Our results support the theoretical prediction that there is one control mechanism for the number of niches for coexisting virus–host pairs (top-down control), and another mechanism that controls which virus–host pairs occupy these niches (bottom-up control).     

Disruption of the reproductive behaviour of Scaphoideus titanus by playback of vibrational signals

Scaphoideus titanus Ball (Hemiptera: Cicadellidae: Deltocephalinae) is the vector of the grapevine disease Flavescence dorée. In S. titanus the male–female duet (MFD), based on species-specific vibrational signals, is essential for successful copulation. The female reply within a duet is a single pulse that is coupled with the male pulse with constant latency. It has been shown that a rival male can interrupt an existing duet by emitting disruptive noise signals. We tested whether the reproductive behaviour of S. titanus can be disrupted by the playback of intra-specific and synthesized vibrational signals. Tested males responded to the playback of an MFD with typical rivalry behaviour. Such behaviour includes silent search for a duetting female (satellite behaviour) and/or emission of disruptive signals. These signals were emitted either after exchange of male–female pulses or after two male pulses coupled by latency corresponding to the female response window. The onset of male disruptive signals overlapped with a female pulse. We suggest that the intruder's disruptive signals can mask the female reply and confuse courting males. Playback of disruptive vibrational signals reduced the level of male calling and interrupted an established MFD that consequently resulted in a significantly reduced number of copulations. These results indicate that the vibrational communication channel is open to interference either from abiotic environmental noise or from signals produced by sexual competitors or heterospecifics. The present study also suggests that a detailed understanding of leafhopper behaviour is essential for trying new approaches in the development of more environmentally friendly control practices.     

Heterogeneity of Multimedia Exposures to Neurotoxic Elements (Al,As, Cd,Pb, Mn,and Hg) in Breastfed Infants from Porto Velho,Brazil

Infant exposure to neurotoxic elements is a public health issue that needs monitoring with regard to breast milk composition. We studied six neurotoxic elements in breast milk samples at different stages of lactation in mothers from Porto Velho, Brazil. We used a flow-injection mercury system (FIMS) to determine total Hg concentrations and an inductively coupled plasma optical emission spectrometer (ICP-OES) to determine the concentrations of Al, As, Cd, Pb, and Mn in 106 donors of a human milk bank. Association rules analyses were applied to determine the pattern of binary and ternary mixtures of the measured exposants. The metal concentration was mostly below the limit of detection (LOD) for Cd (99%), Pb (84%), and Hg (72%), and it was above the LOD for As (53%), Mn (60%), and Al (82%), respectively. Median concentrations (dry weight) of Al, As, Hg, Mn, and Pb were 1.81 μg/g, 13.8 ng/g, 7.1 ng/g, 51.1 ng/g, and 0.43 μg/g, respectively. Al is singly the most frequent element to which infants are exposed. Occurring binary combination (> LOD) was 56% for Al-Mn, 41% for Al-As, 22% for Al-Hg, and 13% for Al-Pb. In 100% of neonates, exposure to Al-ethylmercury (EtHg) occurred through immunization with thimerosal-containing vaccines (TCV). Association rules analysis revealed that Al was present in all of the multilevel combinations and hierarchical levels and that it showed a strong link with other neurotoxic elements (especially with Mn, As, and Hg). (a) Nursing infants are exposed to combinations of neurotoxicants by different routes, dosages, and at different stages of development; (b) In breastfed infants, the binary exposures to Al and total Hg can occur through breast milk and additionally through TCV (EtHg and Al); (c) The measured neurotoxic elements were found at low frequencies in breast milk and at concentrations that pose no public health concerns for milk banking.     

Pretreatment Antibiotic Resistance in Helicobacter pylori Infection: Results of Three Randomized Controlled Studies

Background. Although combinations of antibiotics and antisecretory drugs are useful for treatment of Helicobacter pylori infection, treatment failure is common. The aim of this study was to evaluate the relation between pretreatment antibiotic resistance and outcome by using six different treatment regimens for H. pylori infection. Patients and Methods. Three hundred sixty-nine consecutive H. pylori–infected patients with dyspeptic symptoms were enrolled in three consecutive randomized, controlled, single-center clinical trials: trial A, 128 patients; trial B, 125 patients; trial C, 116 patients. Treatments consisted of (A) a 15-day course of dual therapy (omeprazole, 20 mg bid, and amoxicillin, 1 gm bid, or clarithromycin, 500 mg tid) (OA vs OC); (B) a 7-day triple therapy of omeprazole, 20 mg bid, plus metronidazole, 500 mg bid, and amoxicillin, 1,000 mg bid, or clarithromycin, 500 mg tid (OMA vs OMC); or (C) omeprazole, 20 mg bid, plus metronidazole, 500 mg bid, plus tetracycline, 500 mg qid, or doxycycline, 100 mg tid (OMT vs OMD). Diagnostic endoscopy was made in all patients before and 5 to 6 weeks after therapy. Six biopsies were taken from each patient for histology, rapid urease test, and H. pylori culture; antibiotic susceptibility testing was performed using the E-test method. Results. Overall cure rates were poor for both dual therapies OA and OC (38% and 37%, respectively) and for triple therapies OMA, OMC, and OMD (57%, 55%, and 58%, respectively). The OMT combination was successful in 91% (95% confidence interval [CI], 80.4%–97%). Metronidazole resistance was present in 29.7% (95% CI, 24%–35%), amoxicillin resistance was present in 26% (95% CI, 21%–32%), clarithromycin resistance was present in 23.1% (95% CI, 18%–29%), tetracycline resistance was present in 14% (95% CI, 10%–20%), and doxycycline resistance was present in 33.3% (95% CI, 21%–47%). Antibiotic resistance markedly reduced the cure rates and accounted for most of the poor results with the triple therapies: 89% versus 23%; 77% versus 26%; 100% versus 60%; and 67% versus 23% for OMC, OMA, OMT, and OMD, respectively. OMT appeared to be the best because of the high success rate with metronidazole-resistant H. pylori (71%) and in low-level tetracycline resistance. Conclusions. Pretreatment antibiotic-resistant H. pylori can, in part, explain the low cure rate of the infection and the variability in outcome in reported trials.     

Typing Tuber melanosporum and Chinese black truffle species by molecular markers

Morphologically similar species such as Chinese black truffles and Tuber melanosporum were typed by restriction length polymorphism of internal transcribed spacers. This analysis together with sequence comparison revealed the presence of high genetic variability among fruit bodies collected in China. Selection of primer pairs allowed the internal transcribed spacer region of both Chinese truffles and T. melanosporum to be specifically amplified.