BackgroundNeural progenitor is a generic term used for undifferentiated cell populations of neural stem, neuronal progenitor and glial progenitor cells with abilities for proliferation and differentiation. We have shown functional expression of ionotropic N-methyl-D-aspartate (NMDA) and gamma-aminobutyrate type-A receptors endowed to positively and negatively regulate subsequent neuronal differentiation in undifferentiated neural progenitors, respectively. In this study, we attempted to evaluate the possible functional expression of nicotinic acetylcholine receptor (nAChR) by undifferentiated neural progenitors prepared from neocortex of embryonic rodent brains.Methodology/Principal FindingsReverse transcription polymerase chain reaction analysis revealed mRNA expression of particular nAChR subunits in undifferentiated rat and mouse progenitors prepared before and after the culture with epidermal growth factor under floating conditions. Sustained exposure to nicotine significantly inhibited the formation of neurospheres composed of clustered proliferating cells and 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide reduction activity at a concentration range of 1 µM to 1 mM without affecting cell survival. In these rodent progenitors previously exposed to nicotine, marked promotion was invariably seen for subsequent differentiation into cells immunoreactive for a neuronal marker protein following the culture of dispersed cells under adherent conditions. Both effects of nicotine were significantly prevented by the heteromeric α4β2 nAChR subtype antagonists dihydro-β-erythroidine and 4-(5-ethoxy-3-pyridinyl)-N-methyl-(3E)-3-buten-1-amine, but not by the homomeric α7 nAChR subtype antagonist methyllycaconitine, in murine progenitors. Sustained exposure to nicotine preferentially increased the expression of Math1 among different basic helix-loop-helix proneural genes examined. In undifferentiated progenitors from embryonic mice defective of NMDA receptor subunit-1, nicotine was still effective in significantly inhibiting the proliferation.Conclusions/SignificanceFunctional α4β2 nAChR subtype would be constitutively expressed to play a role in the mechanism underlying the determination of proliferation and subsequent differentiation fate into a neuronal lineage in association with preferential promotion of Math1 expression in undifferentiated neural progenitors of developing rodent neocortex independently of NMDA receptor activation.

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This paper reports the dynamic post-discharge phenomena of laser-triggered discharge-produced plasmas (LTDPP) for extreme ultraviolet lithography (EUVL) sources. A pulsed laser was focused on the high-voltage tin cathode surface to form tin vapor jet across a 5 mm long anodecathode gap, which leads to the electrical breakdown. The post-discharge phenomena were observed using both of the Schlieren method and high-speed camera. Schlieren images show the dynamic evolution of the discharge plasma and the development of tin droplets. Visible emission from the plasma lasted for more than 1 µs after the current stopped. The droplets emerged from the cathode approximately 100 µs after discharge and spread throughout the electrodes gap. Various sizes of droplets stagnate in the gap for milliseconds. The subsequent laser pulse and voltage application show an interaction between the droplets and the subsequent discharge. The subsequent laser pulse evaporates not only the cathode surface but also the droplets, which influence the tin vapor distribution in the gap. This uncertain vapor distribution affects the formation process of microplasmas that emit EUV.

Extreme ultraviolet (EUY) source remains a key issue for industrial application of EUY lithography. Currently, lasertriggered discharge (LTD) tin plasma is the most promising discharge produced plasma EUY source. High frequency discharge of up to tens of kHz is required to achieve sufficient average radiation power. However, the choice of discharge frequency is restricted by the recovery time of the tin fuel plasma. Although much experimental and theoretical work has been performed to investigate discharge plasma dynamics and its corresponding EUY radiation process during main discharge, study regarding post-discharge stage after main discharge is scant. This paper presents a study of plasma decay and tin fuel residual recovery following a laser triggered discharge for high repetition rate EUY source. First, the insulation strength recovery of tin fuel residual between electrodes after main discharge was measured by time lapse electrical breakdown voltage test. A breakdown voltage measurement system was designed composed mainly of a second high voltage pulse circuit and its isolation and protection circuits with the main discharge. The electrical recovery curve was measured. The tin vapor decay process was also characterized by means of time-resolved Mach-Zender interferometer. Additionally, the influence of tin fuel plasma recovery process on highly repetitive EUY source performance is discussed. In the nonfull electrical recovery region, secondary self-discharge was observed and its affect on plasma dynamics and EUY emission was studied. After full electrical recovery, the following laser-triggered discharge was investigated using the second pulsed laser to confirm the reproducibility of plasma dynamics and EUY pulse stability relative to the proceeding main discharge for different discharge time intervals.