Yusuke Sakurai

Trophic Effects of PACAP on Pancreatic Islets: A Mini-Review

Progressive beta-cell insufficiency in the pancreas is a hallmark of both types I and II diabetes, and agents that protect against beta-cell dysfunction are potential drug targets for diabetes mellitus. Pituitary adenylate cyclase-activating polypeptide (PACAP) is a strong secretagogue of insulin from pancreatic islets and is suggested to be involved in physiological blood glucose homeostasis and the pathology of diabetes. Recent studies in genetically engineered animal models have shown that PACAP stimulates pancreatic functions, especially in cooperation with other regulatory factors including glucose. Furthermore, chronic activation of PACAP signaling regulates pancreatic islet mass in a context-dependent manner. Accumulating in vivo and in vitro evidence suggest that PACAP has trophic effects and regulates both proliferation and cell viability of beta-cells and thereby contributes to protection against diabetes. This review focuses on such trophic actions of PACAP on pancreatic beta-cells and discusses the pathophysiological significance of pancreatic PACAP, with the aim to provide information for future development of treatment for diabetes.

Methods to improve radiation sensitivity of chemically amplified resists by using chain reactions of acid generation

The approach toward the enhancement of the resist sensitivity was investigated by introducing the radical chain reactions into the acid generation processes. The acid yields of various ionic and nonionic acid generators in some solvents and films were examined to search the most efficient system of the radical chain acid proliferation reactions. The acid proliferation was discussed using Gibbs free energy change of the electron transfer reactions in the chain reactions. The most efficient system to realize the chain reactions was the combination of iodonium salt acid generator and secondary alcohol acid amplifiers. In acrylic polymer resists containing the iodonium salt and the alcohol compounds, resist sensitivity was enhanced in electron beam lithography.

Rapid Recrystallization of Amorphous Silicon Utilizing Very-High-Frequency Microplasma Jet at Atmospheric Pressure

The rapid recrystallization of amorphous silicon (a-Si) utilizing a very-high-frequency (VHF) plasma jet of argon (Ar) at atmospheric pressure is investigated. A highly crystallized polycrystalline Si film is synthesized by optimizing the translating velocity of the substrate stage and the flow rate of argon. The temperature of the plasma exposure area reaches 1350±300 °C and the recrystallization of a-Si proceeded with time constants of 30–50 ms. The effects of the translating velocity of the substrate stage and the flow rate of argon on the rapid recrystallization of a-Si are demonstrated along with its mechanism.

RF Microplasma Jet at Atmospheric Pressure: Application to Rapid Recrystallization of Amorphous Silicon

A novel rapid recrystallization technique for amorphous silicon (a-Si) utilizing an rf microplasma jet of argon at atmospheric pressure is presented. A highly crystallized polycrystalline silicon film (poly-Si) was synthesized uniformly by the rapid plasma annealing of a-Si films deposited on glass and aluminum plates by translating the substrate stage at 0.05–250 mm/s. X-ray diffraction analysis, Raman scattering and I–V measurements demonstrated that 0.3–3-µm-thick a-Si samples could be fully crystallized below several milliseconds. Film crystallinity is discussed in terms of the traveling velocity of the substrate stage, the flow rate of argon, and the thickness of as-deposited a-Si films.

Negative Resist Material Based on Polysilanes for Electron Beam and X-Ray Lithographies

In the present paper, we describe the mechanisms of photo- and radiation-induced reactions in silicon based resist materials, polysilanes with Si-branchings and Si–H bondings, candidates for future resist materials. Polysilanes have been previously confirmed to show positive-type resist properties for ultra violet (UV) light, electron beams (EB), and X-rays under all conditions. However, the cross-linking reaction of the polymer became dominant in the polysilane with Si-branchings, upon irradiation with UV light, EB, and ion beams. The efficiency of the cross-linking reaction strongly depended on the ratio of Si-branching producing polymer gels in the polysilane with a higher amount of Si-branching than 5%, even with γ-ray irradiation. Polyhydrosilanes containing vinyl groups were revealed to cause efficient cross-linking reactions in the presence of catalysts for hydrosilylation upon exposure to deep UV or X-rays, leading to high-sensitive negative resist materials for extreme UV lithography.

PACAP Inhibits β-cell Mass Expansion in a Mouse Model of Type II Diabetes: Persistent Suppressive Effects on Islet Density

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a potent insulinotropic G-protein-coupled receptor ligand, for which morphoregulative roles in pancreatic islets have recently been suggested. Here, we evaluated the effects of pancreatic overexpression of PACAP on morphometric changes of islets in a severe type II diabetes model. Following cross-breeding of obese-diabetic model KKAy mice with mice overexpressing PACAP in their pancreatic β-cells, the resulting KKAy mice with or without PACAP transgene (PACAP/+:Ay/+ or Ay/+ mice) were fed with a high-fat diet up to the age of 11 months. Pancreatic sections from 5- to 11-month-old littermates were examined. Histomorphometric analyses revealed significant suppression of islet mass expansion in PACAP/+:Ay/+ mice compared with Ay/+ mice at 11 months, but no significant difference between PACAP/+ and +/+ (wild-type) mice, as previously reported. The suppressed islet mass in PACAP/+:Ay/+ mice was due to a decrease in islet density but not islet size. In addition, the density of tiny islets (<0.001 mm2) and of insulin-positive clusters in ductal structures were markedly decreased in PACAP/+:Ay/+ mice compared with Ay/+ mice at 5 months of age. In contrast, PACAP overexpression caused no significant effects on the level of aldehyde-fuchsin reagent staining (a measure of β-cell granulation) or the volume and localization of glucagon-positive cells in the pancreas. These results support previously reported inhibitory effects of PACAP on pancreatic islet mass expansion, and suggest it has persistent suppressive effects on pancreatic islet density which may be related with ductal cell-associated islet neogenesis in type II diabetes.

Reaction mechanisms in silicon-based resist materials: polysilanes for deep-UV, EUV, and x-ray lithography

The present paper describes mechanisms of photo- and radiation induced reactions in silicon based resist materials: polysilanes with Si-branchings and Si-H bondings, as a candidate for EUV and X-ray resist materials. Polysilanes have been previously confirmed to show positive-type resist properties for UV light, electron beams (EB), X-rays, etc. at any conditions. However the cross-linking reaction of the polymer became dominant in the polysilane with Si-branchings upon irradiation to UV light, EB, and ion beams. The efficiency of the cross-linking reaction strongly depended on the ratio of Si-branching giving polymer gels in the polysilane with higher amount of Si-branching than 5% even for (gamma) -ray irradiation. Polyhydrosilanes containing vinyl groups revealed to cause efficient cross-linking reactions with the presence of catalysts for hydrosilylation upon exposure to deep UV or X-rays, leading to high-sensitive negative resist materials for EUV lithography.