Is object search mediated by object-based or image-based representations?

Recent research suggests that visually specific memory representations for previously fixated objects are maintained during scene perception. Here we investigate the degree of visual specificity by asking whether the memory representations are image-based or object-based. To that end we measured the effects of object orientation on the time to search for a familiar object from amongst a set of 7 familiar distractors arranged in a circular array. Search times were found to depend on the relative orientations of the target object and the probe object for both familiar and novel objects. This effect was found to be partly an image matching effect but there was also an advantage shown for the object's canonical view for familiar objects. Orientation effects were maintained even when the target object was specified as having unique or similar shape properties relative to the distractors. Participants' eye movements were monitored during two of the experiments. Eye movement patterns revealed selection for object shape and object orientation during the search process. Our findings provide evidence for object representations during search that are detailed and share image-based characteristics with more high-level characteristics from object memory.     

Cardiovascular role of urotensin II: effect of chronic infusion in the rat

Urotensin II (UII) is a potent vaso-active peptide thought to have multiple roles in the regulation of cardiovascular physiology and pathophysiology. The actions of UII are complex and difficult to interpret given its systemic hemodynamic effects and variable action on different vascular beds and isolated vessels. Direct effects of UII on the myocardium, include myocyte hypertrophy, extracellular matrix deposition and contractility. These observations, together with elevated plasma levels found in disease, are common traits reported in other pathophysiologically implicated neurohormonal systems. In this review, we include original data obtained from chronic infusion of UII in rats. We report a reduction in first derivative of left ventricular pressure (+dP/dt), as well as an increase in the ratio of left ventricular collagen I:III, that may contribute to the reduced myocardial contractility observed in these animals.     

Presenilin expression during induced differentiation of the human neuroblastoma SH-SY5Y cell line

Human neuroblastoma SH-SY5Y cells stably transfected with both wild-type and exon-9 deleted (deltaE9) presenilin constructs were used to study the role of the presenilin proteins during differentiation. Cells transfected with either wild-type or deltaE9 PS1, of which the latter abolishes normal endoproteolytic cleavage of the protein, showed no obvious differences in their ability to differentiate to a neuronal-like phenotype upon treatment with retinoic acid (RA). A defined pattern of PS1 expression was observed during differentiation with both RA and the phorbol ester TPA. Full-length PS1 was shown to increase dramatically within 5-24 h of RA treatment. TPA gave an earlier and longer lasting increase in full-length PS1 levels. The intracellular distribution pattern of PS1 was markedly altered following RA treatment. Within 24h PS1 was highly up-regulated throughout the cell body around the nucleus. Between 2 and 4 weeks PS1 staining appeared punctate and also localised to the nucleus. Increases in PS1 expression upon treatment with RA and TPA were blocked by treatment with cycloheximide, indicating a role of de-novo protein synthesis in this effect. PS2 expression remained unchanged during differentiation. Levels of full-length PS1 were also seen to increase during neurogenesis and neuronal differentiation in the forebrain of first trimester human foetuses between 6.5 and 11 weeks. These combined observations support the idea that PS1 is involved in neuronal differentiation by a mechanism likely independent of endoproteolysis of the protein.     

Applications of proteomic methodologies to human pregnancy research: a growing gestation approaching delivery?

Maternal and perinatal morbidity and mortality rates are significantly higher in pregnancies complicated by preterm labor, pre-eclampsia and fetal growth restriction. Decades of research have not translated into a clear understanding of the underlying pathophysiologies or effective identification of women who are at high risk of developing these complications. Often the severity of these diseases does not correlate with the clinical symptoms, and current diagnostic methods are unable to accurately predict the conditions prior to clinical presentation. Though several potential markers have been proposed for each of these disorders, to date none have proven clinical utility. Emerging proteomic technology is only beginning to be employed in pregnancy research. A comprehensive analysis of gestational tissues can be expected to contribute to the elucidation of the complex molecular mechanisms of pregnancy and related complications. Comparison of the expression profiles of normal and pathogenic tissues and biofluids may also highlight novel candidate marker proteins that have so far remained undetected. More interestingly, rapidly evolving technologies using sophisticated bioinformatic tools are demonstrating their potential in disease diagnostics by using overall protein profiles to detect diseases. The clinical significance of these methodological advances is enormous. Early diagnosis together with improved understanding of underlying molecular mechanisms can enhance outcomes and increase effective management and therapeutic options.     

Natural variation in the sexually selected feather ornaments of crested auklets (Aethia cristatella) does not predict future survival

We evaluated whether sexually selected crest and auricular plumefeather ornaments of crested auklet (Aethia cristatella) adultscovaried with individual local survival over 11 years (1991–2001).Crested auklets (n = 364 total) were captured near breedingsites, marked with color rings, and local survival estimateswere based on color ring resightings at a breeding colony. Survivalestimates and relationships among local survival and crest length,auricular plume length, mass and tarsus were evaluated usingthe program MARK. The best models included four groups, definedby sex and ease of resighting, that differed in resighting rate(p) but not local survival rate (). This model structure effectivelyexplained sources of variation in local survival and resightabilityamong individuals. The best fitting model showed local survivalrate varying annually, while accounting for differences in resightabilityof marked individuals between the sexes and groups ([t], p[sex*easeof resighting]). Annual local survival varied from 0.940 ±0.029 (SE) in 1993–1994 to 0.767 ± 0.034 in 1997–1998and averaged 0.859 ± 0.019. We found no evidence thatcrested auklet local survival covaried with continuous variationin individuals' ornaments. Simulations indicated that our dataset was sufficient to detect a relationship between local survivaland a covariate that equaled or exceeded a range of 8%. Theimplications for competing sexual selection mechanisms of empiricallymeasured survival–ornament relationships are controversial,but our study emphasizes that survival estimates for such investigationsmust control for confounding factors such as resighting rateas well as have sufficient statistical power and time scaleto be biologically meaningful. Our results are most consistentwith the idea that the conspicuous variation in crested auklet'sshowy ornaments is arbitrary with respect to individual viabilityas quantified by their long-term survival.     

Cre-mediated germline mosaicism: a new transgenic mouse for the selective removal of residual markers from tri-lox conditional alleles

The binary Cre-lox conditional knockout system requires an essential part of the target gene to be flanked by loxP sites, enabling excision in vivo upon Cre expression. LoxP sites are introduced by homologous recombination, together with a selectable marker. However, this marker can disturb gene expression and should be removed. The marker is therefore often prepared with a third, flanking loxP site (tri-lox construct), facilitating its selective removal by partial Cre-lox recombination. We have shown that this excision can be achieved in vivo in the germline using EIIaCre transgenic mice, and have described the advantages of in vivo over in vitro removal. We show here that MeuCre40, a new transgenic mouse, more reliably and reproducibly generates an optimal partial mosaic Cre-lox recombination pattern in the early embryo. This mosaicism was transmitted to the germline and to many other tissues. Alleles with partial deletions, in particular floxed alleles from which the selectable marker was removed, were readily recovered in the next generation, after segregation from the transgene. Segregation via paternal or maternal transmission led to successful recovery of the alleles of interest. We also obtained total deletion of the floxed regions in the same experiment, making this transgene a polyvalent Cre-lox tool. We rigorously tested the ability of MeuCre40 to solve tri-lox problems, by using it for the in vivo removal of neo^R- and hprt-expression cassettes from three different tri-lox mutants.