Anticipation and Choice Heuristics in the Dynamic Consumption of Pain Relief

Humans frequently need to allocate resources across multiple time-steps. Economic theory proposes that subjects do so according to a stable set of intertemporal preferences, but the computational demands of such decisions encourage the use of formally less competent heuristics. Few empirical studies have examined dynamic resource allocation decisions systematically. Here we conducted an experiment involving the dynamic consumption over approximately 15 minutes of a limited budget of relief from moderately painful stimuli. We had previously elicited the participants’ time preferences for the same painful stimuli in one-off choices, allowing us to assess self-consistency. Participants exhibited three characteristic behaviors: saving relief until the end, spreading relief across time, and early spending, of which the last was markedly less prominent. The likelihood that behavior was heuristic rather than normative is suggested by the weak correspondence between one-off and dynamic choices. We show that the consumption choices are consistent with a combination of simple heuristics involving early-spending, spreading or saving of relief until the end, with subjects predominantly exhibiting the last two.     

The case against (-)-catechin involvement in allelopathy of Centaurea stoebe (spotted knapweed)

Proving allelopathic chemical interference is a daunting endeavor, in that production and movement of a phytotoxin from a donor plant to a receiving plant must be demonstrated in the substrate in which the plants grow, which is usually a complex soil matrix. The soil levels or soil flux levels of the compound generated by the donor must be proven to be sufficient to adversely affect the receiving plant. Reports of (-)-catechin to be the novel weapon used by Centaurea stoebe (spotted knapweed) to invade new territories are not supported by the paper featured in this Addendum, nor by papers produced by two other laboratories. These papers find that (-)-catechin levels in soil in which C. stoebe grows are orders of magnitude below levels that cause only minor growth effects on reported sensitive species. Furthermore, the claim that (-)-catechin acts as a phytotoxin through causing oxidative damage is refuted by the fact that the molecule is a strong antioxidant and is quickly degraded by extracellular root enzymes.Key words: allelochemical, allelopathy, catechin, chemical interference, phytotoxin, spotted knapweed     

Ab initio prediction of metabolic networks using Fourier transform mass spectrometry data

Fourier transform mass spectrometry has recently been introduced into the field of metabolomics as a technique that enables the mass separation of complex mixtures at very high resolution and with ultra high mass accuracy. Here we show that this enhanced mass accuracy can be exploited to predict large metabolic networks ab initio, based only on the observed metabolites without recourse to predictions based on the literature. The resulting networks are highly information-rich and clearly non-random. They can be used to infer the chemical identity of metabolites and to obtain a global picture of the structure of cellular metabolic networks. This represents the first reconstruction of metabolic networks based on unbiased metabolomic data and offers a breakthrough in the systems-wide analysis of cellular metabolism.     

IL-1 beta-deficient mice are resistant to induction of experimental SLE

IL-1 is one of the most pleiotropic pro-inflammatory and immunostimulatory cytokines. Overproduction of IL-1 has been shown to be involved in the pathogenicity of various autoimmune inflammatory diseases, including systemic lupus erythematosus (SLE). However, the different contributions that the IL-1 agonistic molecules make in their in vivo native milieu, IL-1beta which is mainly secreted against IL-1alpha which is mainly cell-associated, have not been established. Experimental SLE can be induced in mice by injection with monoclonal anti-DNA antibodies bearing a major idiotype designated, 16/6Id. In the present study, experimental SLE was induced in mice deficient in specific IL-1 molecules, i.e. IL-1alpha(-/-), IL-1beta(-/-), IL-1alpha/beta(-/-) (double KO) and in control BALB/c mice. Mice deficient in IL-1beta , i.e. IL-1beta(-/-) and IL-1alpha/beta(-/-) mice, developed lower levels of anti-dsDNA antibodies after immunization with 16/6Id, as compared to IL-1alpha(-/-) or control BALB/c mice. Disease manifestations were milder in mice deficient in IL-1beta expression. The representative cytokine cascade that is characteristic of overt experimental SLE was also shown to be reduced in groups of mice that lacked IL-1beta as compared to mice deficient in IL-1alpha, which is mainly cell-associated. Altogether, our results point to the importance of secretable IL-1beta, rather than cell-associated IL-1alpha, in the immunostimulatory and inflammatory phenomena that mediate the pathogenesis of experimental SLE.     

Differential behavioural and hormonal responses of voles and spiny mice to owl calls

Rodents usually respond to the presence of owls by reducing overall activity, in particular foraging. In this study, a playback of recorded tawny owl, Strix aluco, calls was sufficient to induce a marked effect in the social (Gunther's) vole, Microtus socialis. Some of the voles exposed to owl calls reduced their activity ('freeze' pattern) unlike control voles exposed to a human voice. Other voles, however, dashed around the cage ('flee' pattern). Owl calls also increased corticosterone levels in the voles, showing that the calls induced stress. We suggest that the behavioural dichotomy to freeze or flee in voles is a result of differences in individual normal behaviour and/or in stimulus interpretation. In the common spiny mouse, Acomys cahirinus, no behavioural changes were detected after exposure to owl calls, despite increased cortisol levels which are indicative of stress. Differences in the habitats of voles and spiny mice may explain the apparent lack of behavioural response in the latter. They are rock-dwelling rodents preferentially foraging between boulders and in rock crevices, where they are relatively protected from aerial predation, whereas voles forage in relatively open spaces. Copyright 1999 The Association for the Study of Animal Behaviour.     

Podophyllum peltatum possesses a beta-glucosidase with high substrate specificity for the aryltetralin lignan podophyllotoxin

A beta-glucosidase with high specificity for podophyllotoxin-4-O-beta-D-glucopyranoside was purified from the leaves of Podophyllum peltatum. The 65-kDa polypeptide had optimum activity at pH 5.0 and was essentially inactive at pH 6.5 or above. Maximum catalytic activity of this glucosidase was obtained at 45 degrees C, but the enzyme was not heat stable. This beta-glucosidase displayed higher substrate specificity for podophyllotoxin-4-O-beta-D-glucopyranoside than for the other lignans tested, and for the (1-->3) linkage of laminaribiose than for other glucosidic linkages.     

Glutathione-dependent oxidative modification of protoporphyrin and other dicarboxylic porphyrins by mammalian and plant peroxidases.

Protoporphyrin, an intermediate in heme and chlorophyll biosynthesis, can accumulate in human and plant tissues under certain pathological conditions and is a photosensitizer used in cancer phototherapy. We previously showed that protoporphyrin and the related non-natural dicarboxylic porphyrin deuteroporphyrin are rapidly oxidized by horseradish peroxidase in the presence of some thiols, especially glutathione. This study reports that bovine lactoperoxidase, but not leucocyte myeloperoxidase, can also catalyze this reaction and that Tween and ascorbic acid are inhibitors. Exogenous hydrogen peroxide is not required and cannot replace glutathione. Deuteroporphyrin was oxidized to a unique green chlorin product with two oxygen functions added directly to the characteristic reduced pyrrole ring of the chlorin. Spectroscopic and chromatographic results suggest that protoporphyrin was oxidized not to a green chlorin, but to a much more polar red porphyrin modified by oxidative addition to the two vinyl side chains. Two related nonnatural dicarboxylic porphyrins, with ethyl or hydroxyethyl instead of vinyl side chains, are not substrates or products for this enzymatic conversion.