Visible light-induced destabilization of endocytosed liposomes.
(33/2215)
The potential biomedical utility of the photoinduced destabilization of liposomes depends in part on the use of green to near infrared light with its inherent therapeutic advantages. The polymerization of bilayers can be sensitized to green light by associating selected amphiphilic cyanine dyes, i.e. the cationic 1,1'-dioctadecyl-3,3,3', 3'-tetramethylindocarbocyanine (DiI), or the corresponding anionic disulfonated DiI (DiI-DS), with the lipid bilayer. The DiI sensitization of the polymerization of 1, 2-dioleoyl-sn-glycero-3-phosphoethanolamine/1,2-bis[10-(2', 4'-hexadienoyloxy)-decanoyl]-sn-glycero-3-phosphocholine liposomes caused liposome destabilization with release of encapsulated aqueous markers. In separate experiments, similar photosensitive liposomes were endocytosed by cultured HeLa cells. Exposure of the cells and liposomes to 550 nm light caused a net movement of the liposome-encapsulated 8-hydroxypyrene-1,3,6-trisulfonic acid (HPTS) from low pH compartment(s) to higher pH compartment(s). This suggests that photolysis of DiI-labelled liposomes results in delivery of the contents of the endocytosed liposomes to the cytoplasm. The release of HPTS into the cytoplasm appears to require the photoactivated fusion of the labelled liposomes with the endosomal membrane. These studies aid in the design of visible light sensitive liposomes for the delivery of liposome-encapsulated reagents to the cytoplasm. (+info)
Splendours and miseries of the brain.
(34/2215)
In this speculative essay, I examine two evolutionary developments underlying the enormous success of the human brain: its capacity to acquire knowledge and its variability across individuals. A feature of an efficient knowledge-acquiring system is, I believe, its capacity to abstract and to formulate ideals. Both attributes carry with them a clash between experience of the particular and what the brain has developed from experience of the many. Both therefore can lead to much disappointment in our daily lives. This disappointment is heightened by the fact that both abstraction and ideals are subject to variability in time within an individual and between individuals. Variability, which is a cherished source for evolutionary selection, can also be an isolating and individualizing feature in society. Thus the very features of the human brain which underlie our enormous evolutionary success can also be a major source of our misery. (+info)
The structure of colour naming space.
(35/2215)
An experiment is described which replicates recent name mapping work, and delves further into the detailed structure of colour naming space. Observers freely named 1044 CRT-displayed colour-background combinations, sampled regularly along the (u',v') axes of the 1976 UCS, and along a luminance axis. Three response measures - response times, confidence ratings and consistencies - were obtained. These measures were collapsed by principal components analysis (PCA) into 'nameability', a single measure of ease of naming of colours. The structure of colour naming space and the use of different colour name types, were investigated. Data confirmed the uniqueness of basic colour terms as compared with the non-basic terms, agreeing with previous constrained naming studies. Colour naming space was found to exhibit regular structure, which appears to be linked to fundamental response categories, and to previous observations that colour naming space may be divided into five major regions. (+info)
Conscious and unconscious processing of nonverbal predictability in Wernicke's area.
(36/2215)
The association of nonverbal predictability and brain activation was examined using functional magnetic resonance imaging in humans. Participants regarded four squares displayed horizontally across a screen and counted the incidence of a particular color. A repeating spatial sequence with varying levels of predictability was embedded within a random color presentation. Both Wernicke's area and its right homolog displayed a negative correlation with temporal predictability, and this effect was independent of individuals' conscious awareness of the sequence. When individuals were made aware of the underlying sequential predictability, a widespread network of cortical regions displayed activity that correlated with the predictability. Conscious processing of predictability resulted in a positive correlation to activity in right prefrontal cortex but a negative correlation in posterior parietal cortex. These results suggest that conscious processing of predictability invokes a large-scale cortical network, but independently of awareness, Wernicke's area processes predictive events in time and may not be exclusively associated with language. (+info)
Genetic and biochemical characterization of the pathway in Pantoea citrea leading to pink disease of pineapple.
(37/2215)
Pink disease of pineapple, caused by Pantoea citrea, is characterized by a dark coloration on fruit slices after autoclaving. This coloration is initiated by the oxidation of glucose to gluconate, which is followed by further oxidation of gluconate to as yet unknown chromogenic compounds. To elucidate the biochemical pathway leading to pink disease, we generated six coloration-defective mutants of P. citrea that were still able to oxidize glucose into gluconate. Three mutants were found to be affected in genes involved in the biogenesis of c-type cytochromes, which are known for their role as specific electron acceptors linked to dehydrogenase activities. Three additional mutants were affected in different genes within an operon that probably encodes a 2-ketogluconate dehydrogenase protein. These six mutants were found to be unable to oxidize gluconate or 2-ketogluconate, resulting in an inability to produce the compound 2,5-diketogluconate (2,5-DKG). Thus, the production of 2,5-DKG by P. citrea appears to be responsible for the dark color characteristic of the pink disease of pineapple. (+info)
The role of colour in signalling and male choice in the agamid lizard Ctenophorus ornatus.
(38/2215)
Bright coloration and complex visual displays are frequent and well described in many lizard families. Reflectance spectrometry which extends into the ultraviolet (UV) allows measurement of such coloration independent of our visual system. We examined the role of colour in signalling and mate choice in the agamid lizard Ctenophorus ornatus. We found that throat reflectance strongly contrasted against the granite background of the lizards' habitat. The throat may act as a signal via the head-bobbing and push-up displays of C. ornatus. Dorsal coloration provided camouflage against the granite background, particularly in females. C. ornatus was sexually dichromatic for all traits examined including throat UV reflectance which is beyond human visual perception. Female throats were highly variable in spectral reflectance and males preferred females with higher throat chroma between 370 and 400 nm. However, female throat UV chroma is strongly correlated to both throat brightness and chest UV chroma and males may choose females on a combination of these colour variables. There was no evidence that female throat or chest coloration was an indicator of female quality. However, female brightness significantly predicted a female's laying date and, thus, may signal receptivity. One function of visual display in this species appears to be intersexual signalling, resulting in male choice of females. (+info)
Field trial of a haemoglobin colour scale: an effective tool to detect anaemia in preschool children.
(39/2215)
The objective of this study was to evaluate the performance of the Haemoglobin Colour Scale, developed by Stott and Lewis, to diagnose anaemia in a primary health care setting where anaemia was prevalent and severe. Three measures of anaemia were compared in 535 preschool children: haemoglobin based on the Haemoglobin Colour Scale, clinical assessment in three sites (conjunctiva, palm and nail bed) and haemoglobin based on a digital haemoglobinometer (HemoCue method) taken as gold standard. A statistically significant correlation (r = 0.80, coefficient = 0.77 and Y intercept = 2.33) was obtained between the results of the Haemoglobin Colour Scale and the HemoCue. In more than 80% of cases, the difference between the colour scale readings and the results of the HemoCue was within 1 g/dl. Of 415 anaemic children (Hb < 11 g/dl by HemoCue), 85.2% were so identified by the Haemoglobin Colour Scale and 19.7% were classified anaemic by clinical pallor. Of 19 severely anaemic children (Hb < 7 g/dl by HemoCue), 73.6% were identified as severely anaemic and 100% were classified as anaemic by the colour scale, 61.1% were classified as anaemic using clinical pallor. We found the Haemoglobin Colour Scale to be a useful tool in identifying anaemic and severely anaemic children. Efficiencies in term of cost, accuracy and time make it an important resource in primary health care settings in developing countries. Further testing with other staff in other settings is recommended to determine the usefulness of large-scale distribution. (+info)
Vision: can colour contribute to motion?
(40/2215)
Whether colour patterns that have no luminance variation can evoke the perception of visual motion has long been a controversial issue. Recent studies using new and old techniques have now provided compelling evidence that colour can indeed contribute to motion perception. (+info)