Improvement to the air-injection technique to estimate xylem vulnerability to cavitation

Several techniques have been developed to quantify the degree of embolism of the xylem using hydraulic conductance. Although there have been several improvements to these techniques, their reliability is still questionable and many technical pitfalls persist. We are proposing here a manometric approach to improve the accuracy of xylem cavitation measurement by the original air-injection technique which uses twigs exposed to pressurized air to cause cavitation. The measured parameter is air bubble production (P _b) caused by xylem cavitation in birch (Betula pendula Roth) twigs from which the percent increase in bubble production is calculated to quantify xylem cavitation. Data produced by three different methods (bench-drying, air-injection, and manometric approach) are compared. Xylem vulnerability curves (VCs) constructed by the reference and reliable bench-drying technique and the manometric approach show similar sigmoid “S” shape, but a small anomaly appeared in the VC constructed by the original air-injection technique. The xylem pressure inducing 50% of embolism (P ₅₀) was the same with the three techniques. Furthermore, there was a strong positive correlation between the estimators of xylem cavitation measured by the three different methods. For its reliability, precision and ease we recommend the manometric technique as an improved version of the original hydraulic air-injection method.     

Hair to document exposure to glibenclamide

Among the drugs that are used to incapacitate victims such as kids or elderly for sedation or for criminal gain such as sexual offences or robberies, glibenclamide, an antidiabetic was never mentioned. To document the interest of hair testing in such forensic situations, we have developed an original method to test for glibenclamide. A 30-year-old man was admitted to the Emergency Unit for coma and seizures after a party with some members of his family. Blood glucose was 0.40 g/l. A hair specimen was collected several weeks after the event and divided into two segments of 2 cm. Twenty milligrams of each segment cut into small pieces were incubated overnight in a phosphate buffer (pH 5.5), in presence of gliclazide used as internal standard (IS). A liquid/liquid extraction was realized with a mixture of diethyl ether/methylene chloride, and hair extract was separated on a XTerra MS C18 column using a gradient of acetonitrile and formate buffer. Detection of glibenclamide was achieved using two transitions: m/z 493.9 to 168.9 and 493.9 to 368.8. Linearity was observed from 5 to 1000 pg/mg (r2 = 0.956) with a limit of quantification at 5 pg/mg and a clean-up recovery of about 61%. Within-batch precision and bias were 9.0 and 9.5%, respectively. Ion suppression tested on drug-free hair was about 50%. Glibenclamide tested positive in the two consecutive segments (root to 2 cm: 23 pg/mg and 2-4 cm: 31 pg/mg). These findings were in accordance with a repetitive exposure to the drug. The concentrations were compared with those obtained after a single and a daily dose administration. In the hair of a subject receiving a single 5mg dose and collected 4 weeks later, glibenclamide was detected in the proximal segment at 5 pg/mg. After a 20 mg/day dose, the hair concentration of a subject under glibenclamide therapy was 650 pg/mg.     

Admissions to Hospital due to Drugs

In a survey of adverse drug reactions in wards of two Belfast hospitals for 52 weeks in 1965–6, 2·9% of 1,268 patients seen were admitted to hospital because of adverse reactions to drugs taken for therapeutic reasons and 2·1% were admitted because of self-poisoning. Patients admitted because of adverse drug reactions were older than those admitted because of self-poisoning and stayed in hospital longer. Among the drugs which caused the adverse reactions were digitalis preparations, antibiotics, corticosteroids, anticoagulants, analgesics, and tranquillizers. Hypersensitivity and side-effect types of reactions were the most common. Barbiturates were the most frequently used drugs in suicidal attempts.     

Telomeres and cancer: from crisis to stability to crisis to stability

Telomere attrition unleashes genomic instability, promoting cancer development. Once established, however, the malignant clone often re-establishes genomic stability through overexpression of telomerase. In two papers, one in this issue of Cell and one in the subsequent issue, DePinho and colleagues explore the consequences of telomerase re-expression and its validity as a therapeutic target in mouse models of cancer.     

From sequence to structure to networks

A report on the 7th European Conference on Computational Biology (ECCB), Cagliari, Italy, 22-26 September 2008.     

Failure of CD4 T-cells to respond to liver-derived antigen and to provide help to CD8 T-cells

CD4 T-cell help is required for the induction of efficient CD8 T-cells responses and the generation of memory cells. Lack of CD4 T-cell help may contribute to an exhausted CD8 phenotype and viral persistence. Little is known about priming of CD4 T-cells by liver-derived antigen. We used TF-OVA mice expressing ovalbumin in hepatocytes to investigate CD4 T-cell priming by liver-derived antigen and the impact of CD4 T-cell help on CD8 T-cell function. Naïve and effector CD4 T-cells specific for ovalbumin were transferred into TF-OVA mice alone or together with naïve ovalbumin-specific CD8 T-cells. T-cell activation and function were analyzed. CD4 T-cells ignored antigen presented by liver antigen-presenting cells (APCs) in vitro and in vivo but were primed in the liver-draining lymph node and the spleen. No priming occurred in the absence of bone-marrow derived APCs capable of presenting ovalbumin in vivo. CD4 T-cells primed in TF-OVA mice displayed defective Th1-effector function and caused no liver damage. CD4 T-cells were not required for the induction of hepatitis by CD8 T-cells. Th1-effector but not naïve CD4 T-cells augmented the severity of liver injury caused by CD8 T-cells. Our data demonstrate that CD4 T-cells fail to respond to liver-derived antigen presented by liver APCs and develop defective effector function after priming in lymph nodes and spleen. The lack of CD4 T-cell help may be responsible for insufficient CD8 T-cell function against hepatic antigens.     

Readiness to attend to visual foreground cues

Nonhuman primate genera are differentially inclined to attend to stimuli of the immediate foreground. When great apes were trained to a criterion on each of a series of two-choice visual discrimination problems and then given critical test trials with irrelevant visual cues ($\text{1}\text{2}$ in wire mesh) positioned immediately in front of each problem's objects, accuracy of performance was significantly more disrupted in orang-utans (Pongo) than in chimpanzees (Pan) and gorillas (Gorilla). Two groups of chimpanzees known to differ profoundly in complex-learning skills did not differ in their readiness to attend to irrelevant foreground cues; hence, it is concluded that the observed differences among the three genera of great apes must be species related and associated with how arboreal/terrestial they are in their natural habitats.     

Cortical potentials evoked to response to a signal to make a memory-guided saccade

The difference in parameters of visually guided and memory-guided saccades was shown. Increase in the memory-guided saccade latency as compared to that of the visually guided saccades may indicate the deceleration of saccadic programming on the basis of information extraction from the memory. The comparison of parameters and topography of evoked components N1 and P1 of the evoked potential on the signal to make a memory- or visually guided saccade suggests that the early stage of the saccade programming associated with the space information processing is performed predominantly with top-down attention mechanism before the memory-guided saccade and bottom-up mechanism before the visually guided saccade. The findings show that the increase in the latency of the memory-guided saccades is connected with decision making at the central stage of the saccade programming. We proposed that wave N2, which develops in the middle of the latent period of the memory-guided saccades, is correlated with this process. Topography and spatial dynamics of components N1, P1 and N2 testify that the memory-guided saccade programming is controlled by the frontal mediothalamic system of selective attention and left-hemispheric brain mechanisms of motor attention.     

Attending to remember and remembering to attend

Attention and memory are intimately linked. Two functional imaging studies in this issue of Neuron provide novel evidence for this powerful, reciprocal relationship. Turk-Browne and colleagues report that attention simultaneously facilitates the formation of both implicit and explicit memories, while Summerfield and colleagues demonstrate that memory for the past can guide the allocation of attention in the present. Together, these elegant studies reveal bidirectional interactions between attention and memory.     

Commentary Polyamines to Target Drugs to Dna

In neutral solutions polyamines are fully protonated, and hence are really polyammonium cations (PAC). Spermine, for example, carries four positive charges in a linear system, H₃N⁺(CH₂)₃N⁺H₂(CH₂)₄N⁺H₂ (CH₂)₃N⁺H₃. There is a very powerful coulombic interaction between aqueous DNA and such cations, thus the cations are attracted to the DNA over large distances, and once close to the DNA normally remain there for long periods. A key issue is; are the cations mobile, or do they remain at one preferred site for significant periods? The latter is the currently preferred concept, but NMR and EPR evidence will be presented in favour of the former. If the former is correct, then PACs may be able to act as good drug delivery systems. In its simple form the concept is that any drug that acts directly on DNA can be chemically bound to a PAC. Once in the cell, this PAC-drug complex (PAC-D) will be carried to DNA and will move very rapidly along the exposed strands until it recognises the site of action. This may be some special base sequence region, a damaged site, or the PAC-D unit may simply be present prior to potential damage, so that this can be repaired very rapidly. Some of our current studies on these systems are described.     

My perpetual cycle: from student to researcher to teacher to student ..

This contribution stems from the personal experience of the author regarding how he became acquainted with embryology and how he finally entered the field of developmental biology. It reports his feelings as a student of the Histology and Embryology course as it was taught in the late 1970s, and his present efforts in teaching developmental biology to university students. In the Developmental Biology course at Pisa University today, students are taught the tissue, molecular and genetic mechanisms that regulate development of several model systems. Drosophila is introduced at the beginning, because of the great knowledge that it has brought to the unraveling of the molecular aspects of development and because it allows several basic concepts to be introduced, and vertebrate systems follow. Other topics include the classic experiments on amphibian systems, which are explained in the light of recent molecular advances, as well as the genetically more versatile vertebrate systems such as the mouse.     

Reply to Letter to the Editor

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