Visual unpatterned input determines the occurrence of reward-contingent positive variation

Résumé Des chats porteurs d'électrodes corticales Ag-AgCl non polarisables et de lentilles de contact translucides, ont été entraînés, dans obscurité, à presser un levier pour obtenir 0,8 ml de lait. Ils montrent des périodes d'activité lente de haut voltage, c'est-à-dire un phénomène ECoG connu comme synchronisation de post-reinforcement sur le cortex pariéto-occipital. Quand cette synchronisation associée à la variation positive de contingent est supprimée dans l'obscurité, ces phénomènes dépendent de l'influx de la lumière diffuse et non de la perception visuelle.

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Supported by PHS grant No. NB 06385 to T.J.M., and by the training grants No. GM 81 to J.L.Y., J.T.H. and No. MH 8396 to J.H.R.     

Scaling metabolism from organisms to ecosystems

Understanding energy and material fluxes through ecosystems is central to many questions in global change biology and ecology. Ecosystem respiration is a critical component of the carbon cycle and might be important in regulating biosphere response to global climate change. Here we derive a general model of ecosystem respiration based on the kinetics of metabolic reactions and the scaling of resource use by individual organisms. The model predicts that fluxes of CO2 and energy are invariant of ecosystem biomass, but are strongly influenced by temperature, variation in cellular metabolism and rates of supply of limiting resources (water and/or nutrients). Variation in ecosystem respiration within sites, as calculated from a network of CO2 flux towers, provides robust support for the model's predictions. However, data indicate that variation in annual flux between sites is not strongly dependent on average site temperature or latitude. This presents an interesting paradox with regard to the expected temperature dependence. Nevertheless, our model provides a basis for quantitatively understanding energy and material flux between the atmosphere and biosphere.     

A 20-km-diameter multi-ringed impact structure in the North Sea

Most craters found on Earth are highly eroded, poorly preserved and only exposed on land. Here we describe a multi-ringed impact structure discovered in the North Sea from the analysis of three-dimensional seismic reflection data. The structure is 20 km in diameter, and has at least ten distinctive concentric rings located between 2 and 10 km from the crater centre. The structure affects Cretaceous chalk and Jurassic shales, and is well preserved below several hundred metres of post-impact Tertiary strata, which constrains its age to be 60-65 Myr old. The formation of concentric ringed impact structures at this relatively small scale had not previously been thought possible, especially on the terrestrial planets. We have mapped the ring structures at a resolution of tens of metres both laterally and in depth, and show that the rings are fault-bounded graben structures, similar to fault arrays formed in low-strain-rate detachment tectonic settings. Strata deeper than 500 m palaeodepth appear unfaulted, and we infer that the concentric ring structures may have accommodated post-impact extension towards the excavated crater, through detachment on weak layers within the chalk.     

Involvement of DARPP-32 phosphorylation in the stimulant action of caffeine

Caffeine has been imbibed since ancient times in tea and coffee, and more recently in colas. Caffeine owes its psychostimulant action to a blockade of adenosine A(2A) receptors, but little is known about its intracellular mechanism of action. Here we show that the stimulatory effect of caffeine on motor activity in mice was greatly reduced following genetic deletion of DARPP-32 (dopamine- and cyclic AMP-regulated phosphoprotein of relative molecular mass 32,000). Results virtually identical to those seen with caffeine were obtained with the selective A(2A) antagonist SCH 58261. The depressant effect of the A(2A) receptor agonist, CGS 21680, on motor activity was also greatly attenuated in DARPP-32 knockout mice. In support of a role for DARPP-32 in the action of caffeine, we found that, in striata of intact mice, caffeine increased the state of phosphorylation of DARPP-32 at Thr 75. Caffeine increased Thr 75 phosphorylation through inhibition of PP-2A-catalysed dephosphorylation, rather than through stimulation of cyclin-dependent kinase 5 (Cdk5)-catalysed phosphorylation, of this residue. Together, these studies demonstrate the involvement of DARPP-32 and its phosphorylation/dephosphorylation in the stimulant action of caffeine.     

Development of anisotropic structure in the Earth's lower mantle by solid-state convection

Seismological observations reveal highly anisotropic patches at the bottom of the Earth's lower mantle, whereas the bulk of the mantle has been observed to be largely isotropic. These patches have been interpreted to correspond to areas where subduction has taken place in the past or to areas where mantle plumes are upwelling, but the underlying cause for the anisotropy is unknown-both shape-preferred orientation of elastically heterogeneous materials and lattice-preferred orientation of a homogeneous material have been proposed. Both of these mechanisms imply that large-strain deformation occurs within the anisotropic regions, but the geodynamic implications of the mechanisms differ. Shape-preferred orientation would imply the presence of large elastic (and hence chemical) heterogeneity whereas lattice-preferred orientation requires deformation at high stresses. Here we show, on the basis of numerical modelling incorporating mineral physics of elasticity and development of lattice-preferred orientation, that slab deformation in the deep lower mantle can account for the presence of strong anisotropy in the circum-Pacific region. In this model-where development of the mineral fabric (the alignment of mineral grains) is caused solely by solid-state deformation of chemically homogeneous mantle material-anisotropy is caused by large-strain deformation at high stresses, due to the collision of subducted slabs with the core-mantle boundary.     

Genome sequence of the human malaria parasite Plasmodium falciparum

The parasite Plasmodium falciparum is responsible for hundreds of millions of cases of malaria, and kills more than one million African children annually. Here we report an analysis of the genome sequence of P. falciparum clone 3D7. The 23-megabase nuclear genome consists of 14 chromosomes, encodes about 5,300 genes, and is the most (A + T)-rich genome sequenced to date. Genes involved in antigenic variation are concentrated in the subtelomeric regions of the chromosomes. Compared to the genomes of free-living eukaryotic microbes, the genome of this intracellular parasite encodes fewer enzymes and transporters, but a large proportion of genes are devoted to immune evasion and host-parasite interactions. Many nuclear-encoded proteins are targeted to the apicoplast, an organelle involved in fatty-acid and isoprenoid metabolism. The genome sequence provides the foundation for future studies of this organism, and is being exploited in the search for new drugs and vaccines to fight malaria.     

Changes with hypertension and maturation in the response of stomach fundus to acetylcholine

The purpose of these experiments was to compare the contractile response to ACh of stomach fundal strips from hypertensive (SHR) and normotensive (WKY) rats during the development of hypertension. The results indicate that the reactivity to ACh is the same in fundal strips from young SHR and WKY rats; however, with maturation strips from WKY rats undergo a reduction in responsiveness which does not occur in the SHR. Therefore, strips from older SHR rats are more reactive to ACh than are those from age matched WKY rats.     

Calcium transients in aequorin-injected frog cardiac muscle.

The Ca2+ -sensitive bioluminescent protein aequorin was microinjected into cells of frog atrial trabeculae to study intracellular calcium transients associated with excitation-contraction coupling. The amplitude of the aequorin signal increased with extracellular Ca2+ concentration and stimulus frequency, but decreased with stretch. Isoprenaline and acetylstrophanthidin both increased the amplitude, but had strikingly different effects on the time course of the signal.     

Cooperation,power, and the impact of information systems

Imagination suggests that the computer as a communication tool is potentially a significant factor in enhancing cooperative work, especially where the participants are located over a physical or temporal distance. Implementation of innovative information technology offers enhancement of operational efficiency to an enterprise in a turbulent business environment. Communications and decision making are inseparable. Industrial democracy (ID) is a particular arrangement of decisionmaking power where decision makers have to be informed and decisions have to be communicated. Cooperation implies a redistribution of power and the weakening of the traditional management organizational heirarchy. Cogently, this effect is mirrored by the potential of management information systems to redistribute information and, hence, power within an enterprise. The response of traditional management personnel to the threat of information technology (IT) to established positions of authority, is one of defense. Conventional systems analysis is unsuited for the design task of ID information systems. The methods employed by systems analysis preserve or reproduce the formal hierarchical structure of managerial organization. Soft systems methodology is explored as a means of confronting the sociopolitical factors present in the specification of information systems for an ID.     

Capture of hydroxymethylene and its fast disappearance through tunnelling

Singlet carbenes exhibit a divalent carbon atom whose valence shell contains only six electrons, four involved in bonding to two other atoms and the remaining two forming a non-bonding electron pair. These features render singlet carbenes so reactive that they were long considered too short-lived for isolation and direct characterization. This view changed when it was found that attaching the divalent carbon atom to substituents that are bulky and/or able to donate electrons produces carbenes that can be isolated and stored. N-heterocyclic carbenes are such compounds now in wide use, for example as ligands in metathesis catalysis. In contrast, oxygen-donor-substituted carbenes are inherently less stable and have been less studied. The pre-eminent case is hydroxymethylene, H-C-OH; although it is the key intermediate in the high-energy chemistry of its tautomer formaldehyde, has been implicated since 1921 in the photocatalytic formation of carbohydrates, and is the parent of alkoxycarbenes that lie at the heart of transition-metal carbene chemistry, all attempts to observe this species or other alkoxycarbenes have failed. However, theoretical considerations indicate that hydroxymethylene should be isolatable. Here we report the synthesis of hydroxymethylene and its capture by matrix isolation. We unexpectedly find that H-C-OH rearranges to formaldehyde with a half-life of only 2 h at 11 K by pure hydrogen tunnelling through a large energy barrier in excess of 30 kcal mol(-1).