Altitude-Dependent Distribution of Ambient Gamma Dose Rates in a Mountainous Area of Japan Caused by the Fukushima Nuclear Accident

Large amounts of airborne radionuclides were deposited over a wide area in eastern Japan, including mountainous regions, during the devastating Fukushima Dai-ichi nuclear power plant accident. Altitudinal distributions of ambient gamma dose rate in air were measured in a mountainous area at the northern rim of the Kanto Plain, Japan, using a portable instrument carried along the mountain trails. In the Nikko Mountain area, located 120 km north of Tokyo, the altitudinal distribution exhibited a maxima at ∼900–2 000 m above sea level (ASL). This area was not affected by precipitation until 2300 Japan Standard Time (JST) on March 15, 2011. By that time, a substantial amount of radionuclides had been transported from the damaged reactor, according to the numerical simulations using transport models. Meteorological sounding data indicated that the corresponding altitudes were within the cloud layer. A visual-range monitor deployed in an unmanned weather station at 1 292 m ASL also recorded low visibility on the afternoon of March 15. From these findings, it was deduced that the altitude-dependent radioactive contamination was caused by the cloud/fog deposition process of the radionuclides contained in aerosols acting as cloud condensation nuclei

Kinetic Evaluation of Photosensitivity in Bi-Stable Variants of Chimeric Channelrhodopsins

<div><p>Channelrhodopsin-1 and 2 (ChR1 and ChR2) form cation channels that are gated by light through an unknown mechanism. We tested the DC-gate hypothesis that C167 and D195 are involved in the stabilization of the cation-permeable state of ChRWR/C1C2 which consists of TM1-5 of ChR1 and TM6-7 of ChR2 and ChRFR which consists of TM1-2 of ChR1 and TM3-7 of ChR2. The cation permeable state of each ChRWR and ChRFR was markedly prolonged in the order of several tens of seconds when either C167 or D195 position was mutated to alanine (A). Therefore, the DC-gate function was conserved among these chimeric ChRs. We next investigated the kinetic properties of the ON/OFF response of these bi-stable ChR mutants as they are important in designing the photostimulation protocols for the optogenetic manipulation of neuronal activities. The turning-on rate constant of each photocurrent followed a linear relationship to 0–0.12 mWmm⁻² of blue LED light or to 0–0.33 mWmm⁻² of cyan LED light. Each photocurrent of bi-stable ChR was shut off to the non-conducting state by yellow or orange LED light in a manner dependent on the irradiance. As the magnitude of the photocurrent was mostly determined by the turning-on rate constant and the irradiation time, the minimal irradiance that effectively evoked an action potential (threshold irradiance) was decreased with time only if the neuron, which expresses bi-stable ChRs, has a certain large membrane time constant (eg. τ_m > 20 ms). On the other hand, in another group of neurons, the threshold irradiance was not dependent on the irradiation time. Based on these quantitative data, we would propose that these bi-stable ChRs would be most suitable for enhancing the intrinsic activity of excitatory pyramidal neurons at a minimal magnitude of irradiance.</p></div

Summary of the effects of C128A/C167A or D156A/D195A mutation on the photocurrents of ChR2, ChRWR and ChRFR.

<p><b>A,</b> Comparison of τ_OFF. <b>B,</b> Comparison of peak amplitude.</p

OFF response kinetics.

<p><b>A–C,</b> Sample photocurrent records of ChR2-C128A (<b>A</b>), ChRWR-C167A (<b>B</b>) and ChRFR-C167A (<b>C</b>) opened by blue LED light (0.12 mWmm⁻²) and closed by yellow LED light (0.058–0.32 mWmm⁻²). <b>D-F,</b> Photocurrents of each bi-stable ChR opened by cyan LED light (0.33 mWmm⁻²) and closed by orange LED light (0.10–1.4 mWmm⁻²). <b>G,</b> Shutting-off rate constant (τ_OFF⁻¹) of ChR2-C128A as a function of irradiance by yellow LED light (yellow circles) and orange LED light (orange diamonds). Each line was fitted for the least-squares protocol; <i>y</i> = 16<i>x</i>+0.073 (yellow) and <i>y</i> = 4.4<i>x</i>+0.058 (orange). <b>H,</b> Similar relationships in ChRWR-C167A; <i>y</i> = 47<i>x</i>+0.23 (yellow) and <i>y</i> = 9.0<i>x</i>+0.12 (orange). <b>I,</b> Similar relationships in ChRFR-C167A; <i>y</i> = 25<i>x</i>+0.08 (yellow) and <i>y</i> = 5.8<i>x</i>+0.070 (orange).</p

Differential sensitivity to irradiance and duration among neurons.

<p><b>A,</b> The threshold irradiance to evoke an action potential was related to the membrane time constant (τ_m) for the blue LED pulse of either 0.1 s (closed diamonds) or 1 s (open circles). <b>B,</b> Reduction of threshold irradiance of the type-1 neurons with prolongation of the pulse duration. <b>C,</b> The latency to evoke an action potential was related to τ_m. <b>D,</b> The delayed firing of type-1 neurons with prolongation of the pulse duration. Statistical significance was evaluated with Mann-Whitney <i>U</i> test; *, P < 0.05 and **, P < 0.005.</p

ON response kinetics.

<p><b>A–C,</b> Sample photocurrent records of ChR2-C128A (<b>A</b>), ChRWR-C167A (<b>B</b>) and ChRFR-C167A (<b>C</b>) opened by blue LED light (0.0021–0.12 mWmm⁻²) and closed by yellow LED light (0.32 mWmm⁻²). <b>D-F,</b> Photocurrents of each bi-stable ChR opened by cyan LED light (0.014–0.33 mWmm⁻²) and closed by orange LED light (1.4 mWmm⁻²). <b>G,</b> Turning-on rate constant (τ_ON⁻¹) of ChR2-C128A as a function of irradiance by blue LED light (blue circles) and cyan LED light (cyan diamonds). Each line was fitted for the least-squares protocol; <i>y</i> = 640<i>x</i>+2.0 (blue) and <i>y</i> = 190<i>x</i>+0.76 (cyan). <b>H,</b> Similar relationships in ChRWR-C167A; <i>y</i> = 530<i>x</i>+1.1 (blue) and <i>y</i> = 390<i>x</i>+1.9 (cyan). <b>I,</b> Similar relationships in ChRFR-C167A; <i>y</i> = 480<i>x</i>+0.35 (blue) and <i>y</i> = 240<i>x</i>+1.1 (cyan).</p

Photocurrent time course of chimeric ChRs and their DC gate mutants.

<p>Each trace is a typical photocurrent evoked by blue LED light (0.12 mWmm⁻²) for the time indicated by a blue line (10 s). <b>A,</b> ChR2. <b>B,</b> ChRWR/C1C2. <b>C,</b> ChRFR. <b>D,</b> ChR2-C128A. <b>E,</b> ChRWR-C167A. <b>F,</b> ChRFR-C167A. <b>G,</b> ChR2-D156A. <b>H,</b> ChRWR-D195A. <b>I,</b> ChRFR-D195A.</p

Photostimulation of a neuron as a function of time and irradiance.

<p><b>A,</b> A series of recordings from a typical type-1 neuron. Depolarization by blue LED irradiation for 0.1 s (blue traces) and repolarization by yellow LED light for 5 s (brown line; 0.32 mWmm⁻²). The threshold irradiance was 0.095 mWmm⁻². <b>B,</b> Another series of recordings from the same neuron with blue LED irradiation for 1 s with a threshold irradiance of 0.037 mWmm⁻². <b>C,</b> The maximal depolarization amplitude as function of irradiance; closed diamond, 0.1-s pulse and open circle, 1-s pulse). <b>D,</b> Responses of a typical type-2 neuron to blue LED irradiation for 0.1 s (blue traces) with a threshold irradiance of 0.0066 mWmm⁻². <b>E,</b> Responses to blue LED irradiation for 1 s (blue traces) with the same threshold irradiance. <b>F,</b> The maximal depolarization amplitude as a function of irradiance. Scale bars, 0.2 s (time), 0.2 mWmm⁻² (blue traces: irradiance) and 20 mV (black traces: membrane potential) for A, B, D and E.</p