The neural basis of task-switching in working memory: Effects of performance and aging

We studied the performance of young and senior subjects on a well known working memory task, the Operation Span. This is a dual-task in which subjects perform a memory task while simultaneously verifying simple equations. Positron-emission tomography scans were taken during performance. Both young and senior subjects demonstrated a cost in accuracy and latency in the Operation Span compared with performing each component task alone (math verification or memory only). Senior subjects were disproportionately impaired relative to young subjects on the dual-task. When brain activation was examined for senior subjects, we found regions in prefrontal cortex that were active in the dual-task, but not in the component tasks. Similar results were obtained for young subjects who performed relatively poorly on the dual-task; however, for young subjects who performed relatively well in the dual-task, we found no prefrontal regions that were active only in the dual-task. Results are discussed as they relate to the executive component of task switching.

Light-Induced Changes in Hydrogen, Calcium, Potassium, and Chloride Ion Fluxes and Concentrations from the Mesophyll and Epidermal Tissues of Bean Leaves. Understanding the Ionic Basis of Light-Induced Bioelectrogenesis1

Noninvasive, ion-selective vibrating microelectrodes were used to measure the kinetics of H+, Ca2+, K+, and Cl− fluxes and the changes in their concentrations caused by illumination near the mesophyll and attached epidermis of bean (Vicia faba L.). These flux measurements were related to light-induced changes in the plasma membrane potential. The influx of Ca2+ was the main depolarizing agent in electrical responses to light in the mesophyll. Changes in the net fluxes of H+, K+, and Cl− occurred only after a significant delay of about 2 min, whereas light-stimulated influx of Ca2+ began within the time resolution of our measurements (5 s). In the absence of H+ flux, light caused an initial quick rise of external pH near the mesophyll and epidermal tissues. In the mesophyll this fast alkalinization was followed by slower, oscillatory pH changes (5–15 min); in the epidermis the external pH increased steadily and reached a plateau 3 min later. We explain the initial alkalinization of the medium as a result of CO2 uptake by photosynthesizing tissue, whereas activation of the plasma membrane H+ pump occurred 1.5 to 2 min later. The epidermal layer seems to be a substantial barrier for ion fluxes but not for CO2 diffusion into the leaf.

Cerebral energetics and the glycogen shunt: Neurochemical basis of functional imaging

Positron-emission tomography and functional MRS imaging signals can be analyzed to derive neurophysiological values of cerebral blood flow or volume and cerebral metabolic consumption rates of glucose (CMRGlc) or oxygen (CMRO2). Under basal physiological conditions in the adult mammalian brain, glucose oxidation is nearly complete so that the oxygen-to-glucose index (OGI), given by the ratio of CMRO2/CMRGlc, is close to the stoichiometric value of 6. However, a survey of functional imaging data suggests that the OGI is activity dependent, moving further below the oxidative value of 6 as activity is increased. Brain lactate concentrations also increase with stimulation. These results had led to the concept that brain activation is supported by anaerobic glucose metabolism, which was inconsistent with basal glucose oxidation. These differences are resolved here by a proposed model of glucose energetics, in which a fraction of glucose is cycled through the cerebral glycogen pool, a fraction that increases with degree of brain activation. The “glycogen shunt,” although energetically less efficient than glycolysis, is followed because of its ability to supply glial energy in milliseconds for rapid neurotransmitter clearance, as a consequence of which OGI is lowered and lactate is increased. The value of OGI observed is consistent with passive lactate efflux, driven by the observed lactate concentration, for the few experiments with complete data. Although the OGI changes during activation, the energies required per neurotransmitter release (neuronal) and clearance (glial) are constant over a wide range of brain activity.

The genetic basis of epidermolysis bullosa simplex with mottled pigmentation.

Epidermolysis bullosa simplex (EBS) is a group of autosomal dominant skin diseases characterized by blistering, due to mechanical stress-induced degeneration of basal epidermal cells. It is now well-established that the three major subtypes of EBS are genetic disorders of the basal epidermal keratins, keratin 5 (K5) and keratin 14 (K14). Here we show that a rare subtype, referred to as EBS with mottled pigmentation (MP), is also a disorder of these keratins. Affected members of two seemingly unrelated families with EBS-MP had a C to T point mutation in the second base position of codon 24 of one of two K5 alleles, leading to a Pro: Leu mutation. This mutation was not present in unaffected members nor in 100 alleles from normal individuals. Linkage analyses mapped the defect to this type II keratin gene (peak logarithm of odds score at phi = 0 of 3.9), which is located on chromosome 12q11-q13. This provides strong evidence that this mutation is responsible for the EBS-MP phenotype. Only conserved between K5 and K6, and not among any of the other type II keratins, Pro-24 is in the nonhelical head domain of K5, and only mildly perturbs the length of 10-nm keratin filaments assembled in vitro. However, this part of the K5 head domain is likely to protrude on the filament surface, perhaps leading to additional aberrations in intermediate filament architecture and/or in melanosome distribution that are seen ultrastructurally in patients with the mutation.

The solution structure of the Raf-1 cysteine-rich domain: a novel ras and phospholipid binding site.

The Raf-1 protein kinase is the best-characterized downstream effector of activated Ras. Interaction with Ras leads to Raf-1 activation and results in transduction of cell growth and differentiation signals. The details of Raf-1 activation are unclear, but our characterization of a second Ras-binding site in the cysteine-rich domain (CRD) and the involvement of both Ras-binding sites in effective Raf-1-mediated transformation provides insight into the molecular aspects and consequences of Ras-Raf interactions. The Raf-1 CRD is a member of an emerging family of domains, many of which are found within signal transducing proteins. Several contain binding sites for diacylglycerol (or phorbol esters) and phosphatidylserine and are believed to play a role in membrane translocation and enzyme activation. The CRD from Raf-1 does not bind diacylglycerol but interacts with Ras and phosphatidylserine. To investigate the ligand-binding specificities associated with CRDs, we have determined the solution structure of the Raf-1 CRD using heteronuclear multidimensional NMR. We show that there are differences between this structure and the structures of two related domains from protein kinase C (PKC). The differences are confined to regions of the CRDs involved in binding phorbol ester in the PKC domains. Since phosphatidylserine is a common ligand, we expect its binding site to be located in regions where the structures of the Raf-1 and PKC domains are similar. The structure of the Raf-1 CRD represents an example of this family of domains that does not bind diacylglycerol and provides a framework for investigating its interactions with other molecules.

The molecular basis of Sanfilippo syndrome type B.

The Sanfilippo syndrome type B is a lysosomal storage disorder caused by deficiency of alpha-N-acetylglucosaminidase; it is characterized by profound mental deterioration in childhood and death in the second decade. For understanding the molecular genetics of the disease and for future development of DNA-based therapy, we have cloned the cDNA and gene encoding alpha-N-acetylglucosaminidase. Cloning started with purification of the bovine enzyme and use of a conserved oligonucleotide sequence to probe a human cDNA library. The cDNA sequence was found to encode a protein of 743 amino acids, with a 20- to 23-aa signal peptide immediately preceding the amino terminus of the tissue enzyme and with six potential N-glycosylation sites. The 8.5-kb gene (NAGLU), interrupted by 5 introns, was localized to the 5'-flanking sequence of a known gene, EDH17B, on chromosome 17q21. Five mutations were identified in cells of patients with Sanfilippo syndrome type B: 503del10, R297X, R626X, R643H, and R674H. The occurrence of a frameshift and a nonsense mutation in homozygous form confirms the identity of the NAGLU gene.

A Schistosoma mansoni fatty acid-binding protein, Sm14, is the potential basis of a dual-purpose anti-helminth vaccine.

Molecular cloning of components of protective antigenic preparations has suggested that related parasite fatty acid-binding proteins could form the basis of the protective immune crossreactivity between the parasitic trematode worms Fasciola hepatica and Schistosoma mansoni. Molecular models of the two parasite proteins showed that both molecules adopt the same basic three-dimensional structure, consisting of a barrel-shaped molecule formed by 10 antiparallel beta-pleated strands joined by short loops, and revealed the likely presence of crossreactive, discontinuous epitopes principally derived from amino acids in the C-terminal portions of the molecules. A recombinant form of the S. mansoni antigen, rSm14, protected outbred Swiss mice by up to 67% against challenge with S. mansoni cercariae in the absence of adjuvant and without provoking any observable autoimmune response. The same antigen also provided complete protection against challenge with F. hepatica metacercariae in the same animal model. The results suggest that it may be possible to produce a single vaccine that would be effective against at least two parasites, F. hepatica and S. mansoni, of veterinary and human importance, respectively.

The Study of the Public Space

Except for the "practical exercises" section, this work is registered under the following ISBN numbers: 978-84-15768-61-6 and 978-84-15768-62-3

Optimisation of analytical methods for the characterisation of oranges, clementines and citrus hybrids cultivated in Spain on the basis of their composition in ascorbic acid, citric acid and major sugars

Three HPLC methods were optimised for the determination of citric acid, succinic acid and ascorbic acid using a photodiode array detector and fructose, glucose and sucrose using a refractive index in twenty eight citrus juices. The analysis was completed in <16 min. Two different harvests were taken into account for this study. For the season 2011, ascorbic acid content was comprised between 19.4 and 59 mg vitamin C/100 mL; meanwhile for the season 2012, the content was slightly higher for most of the samples ranging from 33.5 to 85.3 mg vitamin C/100 mL. Moreover, the citric acid content in orange juices ranged between 9.7 and 15.1 g L−1, while for clementines the content was clearly lower (i.e. from 3.5 to 8.4 g L−1). However, clementines showed the highest sucrose content with values near to 6 g/100 mL. Finally, a cluster analysis was applied to establish a classification of the citrus species.

The Economic Basis of Attitudes towards the European Community: Familiarity Breeds Content. Institute for Advanced Studies Political Science Series, 12 April 1994

The purpose of this paper is to analyse the economic basis of mass support for, and opposition to the European Community. In other words the main question is: to what extent, and in what ways, is popular support or opposition to the EC dependent upon economic circumstances and considerations? Behind this research question lies the matter of the legitimacy of the EC in the eyes of citizens across Europe. In some respects the results of this study are frustrating and inconclusive. In other respects, however, the results suggest some clear generalizations and conclusions. First, we have found rather little evidence that the EC or European unification are evaluated in primarily economic terms. Secondly, support seems to be associated more strongly with social and attitudinal variables of a non-economic kind. Thirdly, the figures suggest that diffuse and somewhat idealistic reasons for supporting unification and EC membership tend to outweigh more specific reasons. Fourthly, a solid foundation of inertia, custom, and national tradition seem to maintain support and make it grow.