Stratum Corneum Function: A Structural Study with Dynamic Synchrotron X-ray Diffraction Experiments.

Studies on the effectiveness of substances such as drugs and cosmetics that act on the skin require structural evidence at the molecular level in the stratum corneum to clarify their interaction with intercellular lipid and soft keratin. For this purpose, when applying the substances to the stratum corneum X-ray diffraction experiment is one of the powerful tools. To detect minute structural changes in a stratum corneum sample, using a "solution cell", dynamic synchrotron X-ray diffraction measurements were performed when applying aqueous solution of the substances to the stratum corneum: (1) It was found that a surfactant, sodium dodecyl sulfate, significantly disrupted the long-period lamellar structure. (2) To study the effects of water, structural modifications of the short-period lamellar structure and the soft keratin in corneocytes were measured as a function of time. At the initial water content of 15 wt%, the spacings of the short-period lamellar structure and the soft keratin increased toward those at the water content of 25 wt%, that is a key water content in the stratum corneum. (3) Nanoparticles composed of assembly of amphiphilic molecules are one of the leading pharmaceutical formulations. When the nanoparticles were applied, a new assembly of amphiphilic molecules originated from the nanoparticle appeared. This phenomenon suggests that the formation of the new assembly at the surface of skin is concerned with the release of the drug from the nanoparticles. (4) When ethanol was applied to the stratum corneum, only the liquid state in the intercellular lipid matrix was dissolved. After the removal of ethanol from this stratum corneum, the ordered hydrocarbon-chain packing structures appeared. From this fact we would propose that the liquid state region is the main pathway for hydrophobic drugs with a small molecular weight in connection with the so-called 500 Da rule. Here, not only the technique but also the background to these studies and the characteristic results obtained from these studies are explained.

Attentional capture by the onset and offset of motion signals outside the spatial focus of attention.

The present study examined whether participants were able to ignore a task-irrelevant commencement or cessation of optic flow while they were engaging in a letter-identification task, as claimed by adherents of the view that attentional set determines deployment of attention, or whether irrelevant events would capture attention regardless of observers' attentional set, as claimed by adherents of a broad range of views emphasizing the behavioral urgency of stimulus motion. Observers identified a green letter in a central rapid stream of heterogeneously colored nontargets. A completely task-irrelevant optic flow occurred in the periphery. If attentional deployment were governed by a top-down attentional set, the letter identification would be unaffected by the temporal change in the optic flow. The results reflected attentional capture by commencement or cessation of optic flow, which is inconsistent with the top-down view. When the peripheral dots expanded at various speeds before onset of the target, identification was impaired relative to when no motion occurred. Mere commencement or cessation of motion was sufficient to produce the capture effect. Qualitative (commencement or cessation) rather than quantitative changes (acceleration or deceleration) of the motion display were critical for the occurrence of attentional capture. We conclude that salient discontinuities in optic flow induce attentional capture when observers search for a feature in a different stimulus domain, an idea implying a unique role for of expanding global motion in the deployment of visual attention.

[Comparative study of five trialkyltin compounds: their metabolites in rat organs 24 hours after single oral treatment].

OBJECTIVE: The objective of this study is to provide basic information on the metabolic fate of five trialkyltins, namely, trimethyltin, triethyltin, tripropyltin, tributyltin, and trioctyltin, in rats. METHODS: The levels of trialkyltin and its metabolites in the liver, kidneys, brain, and blood of rats and mice were determined 24h after single oral treatment with trimethyltin, triethyltin, tripropyltin, tributyltin, and trioctyltin by gas chromatography. The doses (as tin) of the trialkyltin compounds were 2.98 mg/kg for trimethyltin and triethyltin, 18.23 mg/kg for tripropyltin and tributyltin and 24.09 mg/kg for trioctyltin. RESULTS: For the trimethyltin and triethyltin treatments, no metabolites of either trialkyltin accumulated in the organs, except for the kidney in the triethyltin treatment. The levels of trimethyltin and triethyltin in the blood of the rats were markedly higher than those of the mice. For the tripropyltin and tributyltin treatments, the predominant metabolites in the liver and kidneys were found to be dialkyltins. Furthermore, despite the higher dose, the level of total tin in the organs 24 h after treatment with trioctyltin were markedly lower than those of the other trialkyltins tested. CONCLUSION: There are clear differences in the metabolic fates of the tin metabolites of the five trialkyItins studied. These results should be considered when carrying out toxicological research on trialkyltins.